METHODS FOR CHASSI HOT PRINTING AND CHASSI HOT PRINTING

专利摘要:
Methods for Production of Hot Stamped Chassis and Hot Stamped Chassis The present invention relates to a method for producing a hot stamped chassis, the method including: a hot rolling step; a winding step; a cold rolling step; a continuous annealing step; and a hot stamping step, wherein the continuous annealing step includes a step of heating the cold rolled steel sheet to a temperature range of equal to or greater than ac1 ° c and less than ac3 ° c; a step of cooling the cold-rolled steel plate heated from the highest heating temperature to 660 ° c at a cooling rate equal to or less than 10 ° c / s; and a step of holding the cooled cold rolled steel sheet over a temperature range of 550 ° C to 660 ° C for one minute to 10 minutes.
公开号:BR112013009520B1
申请号:R112013009520-2
申请日:2011-10-21
公开日:2019-05-07
发明作者:Kunio Hayashi；Toshimitsu Aso；Toshimasa Tomokiyo；Hitoshi Tanino；Ryozo Wada
申请人:Nippon Steel & Sumitomo Metal Corporation；Toyota Jidosha Kabushiki Kaisha；Aisin Takaoka Co., Ltd.；
IPC主号:

专利说明:

Descriptive Report of the Invention Patent for METHODS FOR THE PRODUCTION OF HOT PRINTED CHASSIS AND HOT PRINTED CHASSIS.
Technical Field [001] The present invention relates to a hot stamped chassis having an unheated portion with little variation in hardness, and to a method of producing the hot stamped chassis.
[002] Priority is claimed over Japanesa Patent Application No. 2010-237249, registered on October 22, 2010, and over Japanesa Patent Application No. 2010-289527, registered on December 27, 2010, the contents of which are incorporated here for reference.
Background of the Technique [003] In order to obtain high strength components of a grade of 1180 MPa or more used for automobile or similar components with excellent dimensional accuracy, in recent years a technology (hereinafter referred to as die forming) has been developed to perform resistance of a product conformed by heating a steel sheet to an austenite strip, pressing in a soft and high ductility state, and then cooling quickly (tempering) in a pressing mold to perform the martensitic transformation.
[004] In general, a steel plate used for hot stamping contains a large amount of component C to guarantee the strength of the product after hot stamping and contains austenite stabilizing elements such as Mn and B to ensure the ability to hardening when cooling a mold. However, although strength and hardening capacity are necessary properties for a hot stamped product, when producing a steel sheet that is its material, these properties
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2/70 are disadvantageous in many cases. As a representative disadvantage, with a material having a high hardening capacity, a hot rolled steel sheet after the hot rolling step tends to have an irregular microstructure in some places on the hot rolled coil. Consequently, as a means to resolve the microstructure irregularities generated in a hot rolling step, it can be considered to perform the quenching by a batch annealing step after a hot rolling step or a cold rolling step, meanwhile the step annealing in batches usually takes 3 to 4 days and thus is not preferable from the point of view of productivity. In recent years, on normal steel other than a hardening material used for special purposes, from the point of view of productivity, it has become common to perform heat treatment by a continuous annealing step, different from the batch annealing step.
[005] However, in the case of a continuous annealing step, since the annealing time is short, it is difficult to perform the carbide spheroidization to perform the softening and the regularity of a steel sheet by the long-term heat treatment such as a batch annealing. The spheroidization of the carbide and a treatment to soften and regularize the steel sheet by retaining it in the vicinity of the transformation point Ac1 for about several tens of hours. On the other hand, in the case of a short-term heat treatment such as a continuous annealing step, it is difficult to guarantee the annealing time required for spheroidization. That is, in a continuous annealing installation, about 10 minutes is the upper limit of time for holding at a temperature in the vicinity of the point Ac1, due to the restriction of the length of the installation. In such a short time, once the carbide is cooled before being subjected to spheroidization, the
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3/70 steel has an irregular microstructure in a hardened state. Such partial variation of the microstructure becomes a reason for variation in the hardness of a hot stamping material.
[006] Currently, in a widely used hot stamping, it is common to perform hardening at the same time as the pressing work after heating the steel sheet that is the material by heating in the oven, and by heating in an oven heating to an austenite single phase temperature. It is possible to resolve the variation in strength of the material described above. However, a method of heating a hot stamping material by the heating furnace has poor productivity since heating takes a long time. Consequently, a technology for improving the productivity of the hot stamping material by a short-term heating method by an electric heating method is described. Using the electric heating method, it is possible to control the temperature distribution of the plate material in a conductive state by modifying the density of the current flowing into the same plate material (for example, Patent Document 1).
[007] If the temperature variation exists in the steel plate for hot stamping by partial heating of the steel plate, the microstructure of the steel plate does not change significantly from the microstructure of the base material in an unheated portion. Consequently, the hardness of the base material before heating directly becomes the hardness of the component. However, as mentioned above, the material that is subjected to cold rolling after hot rolling and continuous annealing has a variation in strength as shown in FIG <1, and thus the unheated portion has a large variation in hardness. Consequently, there is a problem that a conformed component has a variation in
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4/70 collision performance and the like and thus it is difficult to control the accuracy of component quality.
[008] In addition, to resolve the variation in hardness, when it is heated to a temperature equal to or greater than the point Ac3 in order to be a single austenite phase in an annealing step, a hardened phase such as martensite or bainite is generated in a final step of the annealing step due to the high hardening capacity due to the effect of Mn or B described above, and the material hardness increases significantly. As for the hot stamping material, this not only becomes the reason for the abrasion of the mold on a disc before stamping, but it also significantly decreases the ability to fix the shape of the unheated portion. Consequently, considering not only the desired hardness after quenching the hot stamping, the forming capacity or the ability to fix the shape of the unheated portion, a preferable material before the hot stamping is a material that is soft and has small variation in hardness, and a material that has an adequate amount of C and a hardening capacity to obtain the desired hardness after the hot stamping quench. However, considering production costs as a priority and assuming steel sheet production in a continuous annealing facility, it is difficult to perform the control described above by a relative technique annealing technology.
[009] Consequently, if a shaped chassis is obtained by hot stamping a steel sheet that is heated so as to make the heated portion and the unheated portion exist on the steel plate, there is the problem that the chassis shaped one by one include a variation in hardness in the unheated portion.
List of Citations
Patent Document 1 Patent Application does not examinePetition 870190000733, of 04/01/2019, p. 13/96
5/70 from Japanesa, First Publication No. 2009-274122
Non-Patent Documents 1 Iron and Steel Materials, The Japan Institute of Metals, Maruzen Publishing Co., Ltd. pg. 21
Non-Patent Documents 2 Steel Standardization Group, A Review of the Steel Standardization Group's Method for the Determination of Critical Points of Steel, Metal Progress, Vol. 49, 1946, pg. 1169
Non-Patent Document 3 Yakiiresei (Hardening of steels) - Motomekata to katsuyou (How to obtain and its use) -, (author: OWAKU Shigeo, publisher: Nikkan Kogyo Shimbun Summary of the Invention Technical Problem [0010] An objective of this invention is to solve the aforementioned problems and provide a method for producing a hot stamped chassis that can suppress the variation in hardness in an un-hardened portion even if the steel plate, which is heated to make the portion heated and to unheated portion exists there, is hot stamped, and the hot stamped chassis that has a small variation in hardness in the unhardened portion Solution to the Problem [0011] An outline of the present invention made to solve the aforementioned problems is as follows .
(1) In accordance with a first aspect of the present invention, a method is provided for producing a hot stamped chassis including the steps of hot rolling a plate containing chemical components that include, by weight%, 0.18% at 0.35% C, 1.0% to 3.0% Mn, 0.01% to 1.0% Si, 0.001% to 0.02% P, 0.0005% to 0.01% of S, 0.001% to 0.01% of N, 0.01% to 1.0% of Al, 0.005% to 0.2% of Ti, 0.0002% to 0.005% of B, and 0.002% to 2 , 0% Cr, and the balance of Fe and the inevitable impurities, to obtain a plate
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6/70 hot-rolled steel; winding the hot rolled steel sheet that is subjected to hot rolling; cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; continuously annealing the cold rolled steel sheet which is subjected to cold rolling to obtain a hot stamping steel sheet; and perform hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that the heated portion in which the highest heating temperature is equal to or greater than Ac3 ° C, and an unheated portion in which the highest heating temperature is equal to or less than Ac1 ° C are existing, where continuous annealing includes heating the cold rolled steel layer to a temperature range equal to or greater than Ac1 ° C and less than Ac3 ° C ; cooling the cold rolled steel sheet heated from the highest heating temperature to 660 ° C at a cooling rate of 10 ° C / s or less; and retain the cooled cold-rolled steel sheet in a temperature range of 550 ° C to 660 ° C for one minute to 10 minutes.
(2) In the method for producing a stamped chassis according to item (1), the chemical components may also include one or more elements between 0.002% to 2.0% Mo, 0.002% to 2.0% Nb, 0.002 % to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% of Ca , 0.0005% to 0.0050% Mg, and 0.0005% to 0.0050% REM.
(3) In the method for producing a hot stamped chassis as per item (1), any one between a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a coating process alloy cast aluminum, and an electroplating process, can be performed after the continuous annealing step.
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7/70 (4) In the method for producing a hot stamped chassis as per item (2), any one between a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a process bonded cast aluminum coating, and an electroplating process, can be performed after the continuous annealing step.
(5) In accordance with a second aspect of the present invention, a method is provided for producing a hot stamped chassis including the steps of: hot laminating a plate containing chemical components that include, by weight%, 0.18% at 0.35% C, 1.0% at 3.0% Mn, 0.01% at 1.0% Si, 0.001% at 0.02% P, 0.0005% at 0.01 % S, 0.001% to 0.01% N, 0.01% to 1.0% Al, 0.005% to 0.2% Ti, 0.0002% to 0.005% B, and 0.002% to 2.0% Cr, and the balance of Fe and the inevitable impurities, to obtain a hot-rolled steel plate that is subjected to hot rolling; winding the hot rolled steel sheet that is subjected to hot rolling; cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet; continuously annealing the cold rolled steel sheet which is subjected to cold rolling to obtain a hot stamping steel sheet; and perform hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that the heated portion in which the highest heating temperature is equal to or greater than Ac3 ° C, and an unheated portion in the which the highest heating temperature is equal to or less than Ac1 ° C are present, where in hot rolling, finishing hot rolling configured with a machine with 5 or more consecutive rolling chairs, lamination is performed by adjusting it if the finishing hot rolling temperature FiT in a final Fi laminator in a temperature range of (Ac3 - 80) ° C to (Ac3 + 40) ° C,
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8/70 by adjusting the time from the beginning of the lamination in a laminator Fi3 that is the machine before the final laminator Fi until the end of the lamination in the final laminator Fi to be equal to or greater than 2.5 seconds, and adjusting it if the hot rolling temperature Fi-3T in the F-3 laminator to be equal to or less than FiT + 100 ° C, and after retaining in a temperature range of 600 ° C to Ar3 ° C for 3 seconds to 40 seconds , winding is performed, continuous annealing includes: heating the cold rolled steel sheet to a temperature range equal to or greater than (Aci - 40) ° C and less than Ac3 ° C; cooling the cold rolled steel sheet heated from the highest heating temperature to 660 ° C at a cooling rate equal to or less than 10 ° C / s; and retain the cold-rolled steel sheet cooled over a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes.
(6) In the method for producing a hot stamped chassis according to item (5), the chemical components may also include one or more elements between 0.002% to 2.0% Mo, 0.002% to 2.0% Nb , 0.002% to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% Ca, 0.0005% to 0.0050% Mg, and 0.0005% to 0.0050% REM.
(7) In the method for producing a hot stamped chassis as per item (5), any one between a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a coating process alloy cast aluminum, and an electroplating process, can be performed after the continuous annealing step.
(8) In the method for producing a hot stamped chassis according to item (6), any one between a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a coating process alloy cast aluminum, and an electroplating process,
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9/70 can be performed after the continuous annealing step.
(9) In accordance with a third aspect of the present invention, a hot stamped chassis is provided which is formed using the method for producing a hot stamped chassis according to any of items (1) to (8) , where, when the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%, AHv is equal to or less than 25 and Hv_Ave is equal to or less than 200, when amount of C in the steel plate is equal to or greater than 0.25% and less than 0.30%, AHv is equal to or less than 32 and Hv_Ave is equal to or less than 220; and when the amount of C in the steel plate is equal to or greater than 0.30% and less than 0.35%, AHv is equal to or less than 38 and Hv_Ave is equal to or less than 240, where AHv represents the variation in Vickers hardness of the unheated portion, and Hv_Ave represents the average Vickers hardness of the unheated portion.
Advantageous Effects of the Invention [0012] According to the methods according to items (1) to (8) described above, since steel sheet is used in which the physical properties after annealing are smooth and regular, even when hot stamping a steel sheet that is heated so that a heated portion and an unheated portion are present on the steel sheet, it is possible to stabilize the hardness of the unheated portion of the hot stamped product.
[0013] In addition, a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a cast aluminum alloy coating process, and an electroplating process, after the continuous annealing, it is advantageous since it is possible to avoid the generation of scale on a surface, it is unnecessary to increase the temperature in a non-oxidizing atmosphere to avoid the generation of
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10/70 scale when the temperature of the hot stamping is increased, or the peeling process after the hot stamping is unnecessary, and also the rust prevention of the hot stamped product is presented.
[0014] In addition, by using such methods, it is possible to obtain a hot stamped chassis in which, when the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%, AHv is equal to or less than 25 and Hv_Ave is equal to or less than 200, when the amount of C in the steel plate is equal to or greater than 0.25% and less than 0.30%, AHv is equal to or less than 32 and Hv_Ave is equal to or less than 220, and when the amount of C in the steel plate is equal to or greater than 0.30% and less than 0.35%, AHv is equal to or less than 38 and Hv_Ave is equal to or less than 240, where AHv represents the variation in the Vickers hardness of the unheated portion, and Hv_Ave represents the average Vickers hardness of the unheated portion.
Brief Description of the Drawings [0015] FIG. 1 is a view showing the variation in the hardness of a steel sheet for hot stamping after continuous annealing of the relative technique.
[0016] FIG. 2 is a view showing the temperature history model in a continuous annealing step of the present invention.
[0017] FIG. 3A is a view showing the variation in the hardness of a steel sheet for hot stamping after continuous annealing in which the winding temperature is set to 680 ° C.
[0018] FIG. 3B is a view showing the variation in the hardness of a steel sheet for hot stamping after continuous annealing in which the winding temperature is set to 750 ° C.
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11/70 [0019] FIG. 3C is a view showing the variation in the hardness of a steel sheet for hot stamping after continuous annealing in which the winding temperature is set to 500 ° C.
[0020] FIG. 4 is a view showing an example of a hot stamped product of the present invention.
[0021] FIG. 5 is a view showing example hot stamping steps of the present invention.
[0022] FIG. 6 is a view showing the variation in the curing ability when hot stamping by Cre / CrM and Mne / MnM in the present invention.
[0023] FIG. 7A is the result of a segmented pearlite observed by an SM at 2000x magnification.
[0024] FIG. 7B is the result of segmented pearlite observed by a SEM with 5000x magnification.
[0025] FIG. 8A is the result of non-segmented perlite observed by SEM with 2000x magnification.
[0026] FIG. 8B is the result of non-segmented perlite observed by SEM with 5000x magnification.
Description of Configurations [0027] Hereafter preferred configurations of the present invention will be described.
[0028] Initially, a method for calculating Ac3 that is important in the present invention will be described. In the present invention, since it is important to obtain an accurate value of Ac3, it is desirable to measure the value experimentally, instead of calculating it from a calculation equation. In addition, it is also possible to measure Ac1 from the same test. As an example of a measurement method as described in Non-Patent Documents 1 and 2, a method of obtaining from changing the length of a steel sheet is common.
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12/70 when it heats and cools. At the time of heating, the temperature at which austenite begins to appear is AC1; and the temperature at which the single austenite phase appears is Ac3, and it is possible to read each temperature from the change in extent. In an experimental measurement case, it is common to use a method of heating the steel sheet after cold rolling to a heating rate when it actually heats up in a continuous annealing step, and to measure Ac3 on the expansion curve. . The heating rate here is an average heating rate in a temperature range of 500 ° C to 650 ° C which is a temperature equal to or less Ac1, and heating is performed at a constant rate using the heating rate .
[0029] In the present invention, the measured result is used when the rate of temperature increase is adjusted by 5 ° C / s.
[0030] However, the temperature at which the transformation from a single austenite phase to a low temperature transformation phase such as ferrite or bainite begins, is Ar3 layer, however in relation to the transformation in a hot rolling stage, Ar3 changes depending on hot rolling conditions or the cooling rate after rolling. Consequently, Ar3 was calculated with a calculation model described in ISIJ International, Vol. 32 (1992), No. 3, and the Ar3 retention time at 600 ° C was determined by the correlation with an actual temperature.
[0031] Hereinafter, a steel sheet for hot stamping according to the present invention used in a method for producing a hot stamped chassis.
(Hot Stamping Steel Plate Quenching Index) [0032] Since the hot stamping material is expected to obtain high hardness after quenching, the hot stamping material is generally designed to have a high component carbon and a component having high hardening capacity
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13/70 ment. Here, high hardening capacity means that the Dlinch value which is the quenching index is equal to or greater than 3. It is possible to calculate the DIinch value based on ASTM A255-67. A detailed calculation method is shown in Non-Patent Document 3. Several methods of calculating the DIinch value have been proposed, in relation to a fB equation for calculation using an additive method and by calculating the effect of B, it is possible to use if an equation of fB = 1 + 2.7 (0.85% by weight of C) described in Non-Patent Document 3. In addition, it is necessary to designate the austenite grain size number according to the added amount of C , however, in practice, since the austenite grain size n ° changes depending on hot rolling conditions, the calculation can be performed by standardizing the grain size n as n ° 6.
[0033] The DIinch value is an index showing the hardening capacity, and it is not always connected to the hardness of a steel plate. That is, the hardness of the martensite is determined by the amounts of C and other elements in the solid solution. Consequently, the problems of this specification do not occur in all steel materials having a large amount of C added. Even in a case where a large amount of C is included, the phase transformation of a steel plate happens relatively more quickly at as long as the DIinch value is a low value, and thus the phase transformation is almost completed before winding in the ROT cooling. In addition, also in an annealing step, since the transformation of ferrite takes place easily on cooling from the highest heating temperature, it is easy to produce a soft hot stamping material. However, the problems of this specification are clearly shown in a steel material that has a high DIinch value and a large amount of added C. Consequently, significant effects of the present invention
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14/70 are obtained in a case where a steel material contains 0.18% to 0.35% C and the DIinch value is equal to or greater than 3. However, when the DIinch value is extremely high, since the transformation of ferrite in continuous annealing does not happen, a value of about 10 is preferable as an upper limit of the DIinch value.
(Chemical Components of the Hot Stamping Steel Plate) [0034] In the method for producing a hot stamped chassis according to the present invention, a hot stamping steel plate produced from a steel part including components is used chemicals that include C, Mn, Si, P, S, N, Al, Ti, B, and Cr and the balance of Fe and the inevitable impurities. In addition, as optional elements, one or more elements between Mo, Nb, V, Ni, Cu, Sn, Ca, Mg, and REM can be contained. A preferred range of the contents of each element will now be described. % indicating p content means% by mass. In the hot stamping steel plate, unavoidable impurities other than the elements described above can be contained as long as their content is in a degree that does not significantly disturb the effects of the present invention, however as small an amount as possible is preferable.
(C: 0.18% to 0.35%) [0035] When the C content is less than 018%, the hardened strength after stamping becomes low, and the increase in hardness in a component becomes small. However, when the C content exceeds 0.35%, the forming capacity of the unheated portion that is heated to the point Ac1 or less is significantly decreased.
Consequently, the lower limit value of C is 0.18, preferably 0.20 and more preferably 0.22%. The upper limit of C is 0.35%, preferably 0.33%, and more preferably 0.30%.
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15/70 (Mn: 1,, 0% to 3.0%) [0037] When the Mn content is less than 1.0%, it is difficult to guarantee hardening capacity when hot stamping. However, when the Mn content exceeds 3.0%, Mn segregation occurs easily at the time of hot rolling.
Consequently, the value of the lower limit of Mn is 1.0%, preferably 1.2%, and more preferably 1.5%. The upper limit value of Mn is 3.0%, preferably 2.8%, and more preferably 2.5%.
(Si: 0.01% to 1.0%) [0039] Si has an effect of slightly improving the hardening capacity, however the effect is light. As Si has a large amount of hardening of the solid solution compared to other elements that are contained, it is possible to reduce the amount of C to obtain the desired hardness after quenching. Consequently, it is possible to contribute to the improvement of the welding capacity, which is a disadvantage of steel that has a large amount of C. Consequently, its effect is great when the added amount is large, however when its added amount exceeds 1.0 %, due to the generation of oxides on the surface of the steel plate, the chemical conversion coating to transmit corrosion resistance is significantly degraded, or the galvanizing wetting capacity is disturbed. In addition, its lower limit is not particularly provided, however about 0.01% which is the amount of Si used at a normal level of deoxidation is a practical lower limit.
[0040] Consequently, the lower limit value of Si is 0.01%. The upper limit value of Si is 1.0%, and preferably 0.8%.
(P: 0.001% to 0.02%) [0041] P is an element that has a high endure property
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16/70 cement of the solid solution, however when its content exceeds 0.02%, the chemical conversion coating is degraded in the same way as the Si case. In addition, its lower limit is not particularly provided, however it is difficult to have the content of less than 0.001% since the cost increases significantly.
(S: 0.0005% to 0.01%) [0042] Since S generates inclusions such as MnS that degrade toughness or workability, it is desired that its added amount is small. Consequently, their amount is preferably equal to or less than 0.01%. In addition, its lower limit is not particularly provided, however it is difficult to have a content of less than 0.0005% since the cost increases significantly.
(N: 0.001% to 0.01%) [0043] Since N degrades the effect of improving the hardening capacity when performing the addition of B, it is preferable to have an extremely small amount added. From this point of view, its upper limit is adjusted to 0.01%. In addition, the lower limit is not particularly provided, however it is difficult to have a content of less than 0.001% as the cost increases significantly.
(Al: 0.01% to 1.0%) [0044] Since Al has the hardening property of the solid solution in the same way as Si, it can be added to reduce the added amount of C. Once that Al degrades the chemical conversion coating or the galvanizing wetting capacity in the same way as Si, its upper limit is 1.0%, and the lower limit is not particularly provided, however 0.01% which is the amount of Al mixed at the deoxidation level is a practical lower limit.
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17/70 (Ti: 0.005% to 0.2%) [0045] Ti is advantageous for detoxifying N which degrades the effect of adding B. That is, when the N content is large, B is bound to N and BN is formed. Since the effect of improving the hardening capacity of B is exhibited at the time of a solid solution state of B, although B is added in a state of large amount of N, the effect of improving the hardening capacity is not obtained . Consequently, by adding Ti, it is possible to fix N as TiN and for B to remain in a solid solution state. In general, the amount of Ti needed to obtain this effect can be obtained by adding the amount that is approximately four times the amount of N from the atomic weight ratio. Consequently, when considering the N content inevitably mixed, a content equal to or greater than 0.005%, which is the lower limit, is necessary. In addition, Ti is bonded with C, and TiC is formed. Since the effect of improving the delayed fracture property after hot stamping can be obtained, when the delayed fracture property actively improves, it is preferable to add equal to or more than 0.05% Ti. However, if the amount added exceeds 0.2%, crude TiC is formed on an austenite or similar grain edge, and fractures are generated in hot rolling, so that 0.2% is adjusted as an upper limit.
(B: 0.0002% to 0.005%) [0046] B is one of the most efficient elements as an element to improve the hardening capacity with low cost. As described above, when adding B, since it needs to be in a solid solution state, it is necessary to add Ti, if necessary. In addition, since its effect is not obtained when its amount is less than 0.0002%, 0.0002% is adjusted as a lower limit. However, once its effect becomes healthy
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18/70 turbid when its quantity exceeds 0.005%, it is preferable to adjust 0.005% as an upper limit.
(Cr: 0.002% to 2.0%) [0047] Cr improves the hardening capacity and toughness with a content equal to or greater than 0.002%. The improvement in toughness is achieved by an effect of improving the delayed fracture property by the carbide alloy conformation or a grain refining effect of the austenite grain size. However, when the Cr content exceeds 2.0%, its effects become saturated.
(Mo: 0.002% to 2.0%) (Nb: 0.002% to 2.0%) (V: 0.002% to 2.0%) [0048] Mo, Nb, and V improve the hardening capacity and toughness with a content equal to or greater than 0.002%, respectively. The effect of improving toughness can be obtained by improving the delayed fracture property by forming carbide alloy, or by refining the austenite grain size. However, when the content of each element exceeds 2.0%, its effects become saturated. Consequently, the amounts contained in Mo, Nb, and V can be in the range of 0.002% to 2.0%, respectively.
(Ni: 0.002% to 2.0%) (Cu: 0.002% to 2.0%) (Sn: 0.002% to 2.0%) [0049] In addition, Ni, Cu, and Sn improve toughness with a content equal to or greater than 0.002%, respectively. However, when the content of each element exceeds 2.0%, its effects become saturated. Consequently, the amounts contained in Ni, Cu, and Sn can be in the range of 0.002% to 2.0%, respectively.
(Ca: 0.0005% to 0.0050%)
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19/70 (Mg: 0.0005% to 0.0050%) (REM: 0.0005% to 0.0050%) [0050] Ca, Mg, and REM have effects of grain refining of inclusions with content equal to or greater than 0.0005% and its suppression. However, when the amount of each element exceeds 0.0050%, its effects become saturated. Consequently, the amounts contained in Ca, Mg, and REM can be in the range of 0.0005% to 0.0050%, respectively.
(Microstructure of the Steel Plate for Hot Stamping) [0051] The microstructure of the steel plate for hot stamping will be described below.
[0052] FIG. 2 shows the temperature history model in the continuous annealing step. In FIG. 2, Ac1 means a temperature at which the reverse transformation to austenite begins to occur at the time of the temperature increase, and Ac3 means the temperature at which the metal composition of the steel sheet becomes completely austenite at the time of the temperature increase. The steel sheet subjected to the cold rolling step is in a state in which the microstructure of the hot rolled sheet is crushed by cold rolling and, in that state, the steel sheet is in a hardened state with extremely high displacement density. . In general, the microstructure of the hot-rolled steel sheet of the tempering material is a mixed structure of ferrite and perlite. However, the microstructure can be controlled for a structure formed mainly if bainite or formed mainly of martensite, by a coiling temperature of the hot-rolled sheet. As will be described later, when the steel sheet for hot stamping is produced, heating the steel sheet to a temperature equal to or greater than Ac1 ° C in a heating step, the volume fraction of non-ferrite recrystallized is adjusted to be equal to or me
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20/70 nor 30%. In addition, by adjusting the highest heating temperature to be less than Ac3 ° C in the heating step and cooling from the highest heating temperature to 660 ° C at a cooling rate equal to or less than 10 ° C / s in the cooling stage, the transformation of ferrite takes place on cooling, and the steel plate is softened. When, in the cooling step, the transformation of ferrite is promoted and the steel plate is softened, it is preferable that the ferrite remains slightly in the heating step, and consequently, it is preferable to adjust the highest heating temperature to be (Aci + 20) ° C to (Ac3 - 10) ° C. Heating up to this temperature range, in addition to which the hardened non-recrystallized ferrite is softened by recovery and recrystallization due to the displacement movement at annealing, it is possible to austenitize the hardened non-recrystallized ferrite. In the heating step, the non-recrystallized ferrite remains lightly, in a subsequent cooling step at a cooling rate equal to or less than 10 ° C / s and the retaining step retains in a temperature range of 550 ° C to 660 ° C for 1 minute to 10 minutes, the ferrite grows by nucleating the non-recrystallized ferrite, and precipitation of cementite is promoted by the concentration of C in the untransformed austenite. Consequently, the main microstructure after the steel sheet annealing step for hot stamping as the configuration is configured of ferrite, cementite, and perlite, and contains a part of the remaining austenite, martensite and bainite. The range of the highest heating temperature in the heating step can be expanded by adjusting the rolling conditions in the hot rolling stage and the cooling conditions in ROT. That is, the problem factor originates in the variation of the microstructure of the hot-rolled sheet, and if the microstructure of the hot-rolled sheet is adjusted so that the hot-rolled sheet is
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21/70 homogenized and the recrystallization of the ferrite after cold rolling takes place regularly and quickly. although the lower limit of the highest heating temperature in the heating step is expanded to (Aci - 40) ° C, it is possible to suppress the remaining non-crystallized ferrite and expand the conditions in the retention step (as will be described later, in a range from 450 ° C to 660 ° C for 20 seconds to 10 minutes).
[0053] In greater detail, the steel sheet for hot stamping includes a metallic structure in which a volume fraction of ferrite obtained by the combination of recrystallized ferrite and transformed ferrite is equal to or less than 50%, and the volume fraction of the fraction of non-recrystallized ferrite is equal to or less than 30%. When the ferrite fraction is less than 50%, the strength of the steel plate after the continuous annealing step becomes hard. In addition, when the fraction of non-recrystallized ferrite exceeds 30%, the hardness of the steel sheet after the continuous annealing step becomes hard.
[0054] The ratio of non-recrystallized ferrite can be measured by analyzing an Electron Back Scattering diffraction Pattern (EBSP). The discrimination of the non-recrystallized ferrite and the other ferrite, that is, the recrystallized ferrite and the transformed ferrite can be performed by analyzing the crystal orientation measurement data of the EBSP using the Average Kernel Disorientation method (KAM method). The displacement is recovered in the non-recrystallized ferrite grains, however, there is a continuous change in the orientation of the crystal generated due to plastic deformation at the time of cold rolling. However, the change in crystal orientation in ferrite grains except for non-recrystallized ferrite is extremely small. This is because, although the crystal orientation of adjacent crystal grains is greatly different due to recrystallization and transformation, the crystal orientation in a crystal grain is not changed. Full name
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22/70
KAM, since it is possible to quantitatively show the difference in the crystal orientation of adjacent pixels (measuring points), in the present invention, when defining the grain edge between a pixel in which a difference in the average crystal orientation with the point adjacent measurement is within 1 ° (degree) and a pixel in which the difference in average crystal orientation with the adjacent measurement point is equal to or greater than 2 ° (degrees), the grain having a crystal grain size equal to or greater than 3 qm is defined as ferrite other than non-recrystallized ferrite, that is, recrystallized ferrite and transformed ferrite.
[0055] In addition, on the steel sheet for hot stamping, (A) a value of the Cre / CrM ratio of the Cr Cr concentration submitted to the solid iron carbide solution and the CrM Cr Cr concentration submitted to the solid solution in a base material is equal to or less than 2, or (B) the value of the Mne / MnM ratio of the Mne concentration of Mn submitted to the solid solution in iron carbide and the MnM concentration of Mn submitted to the solid solution in a base material is equal a or less than 10, [0056] Cementite which is a representative of iron carbide is dissolved in austenite at the time of heating the hot stamping. And the concentration of C in austenite is increased. At the time of heating in a hot stamping step, when it is heated to a low temperature for a short period of time by rapid heating or similar, cementite dissolution is not sufficient and the hardening capacity or hardness after tempering is not it is enough. The dissolution rate of cementite can be improved by reducing the amount of distribution in the cementite of Cr or Mn which are elements easily distributed in the cementite. When the Cre / CrM value exceeds 2 and the Mne / MnM value exceeds 10, the dissolution of cementite in austenite at the time of heating
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23/70 for a short time is insufficient. It is preferable that the Cre / CrM value is equal to or less than 1.5 and the Mne / MnM value is equal to or less than 7.
[0057] Cre / CrM and Mne / MnM can be reduced by the method for producing a steel sheet. As will be described in detail, it is necessary to suppress the diffusion of substitute elements in the iron carbide, and it is necessary to control the diffusion in the hot rolling step, and in the continuous annealing step after cold rolling. Substitute elements such as Cr or Mn are different from interstitial elements such as C or N, and diffuse into iron carbide because they are kept at a high temperature of 600 ° C or longer for a long time. To avoid this, there are two main methods. One is a method of dissolving all austenite by heating the iron carbide generated in the hot rolling to Ac1 to Ac3 in continuous annealing and performing slow cooling from the highest heating temperature to a temperature rate equal to or less than 10 ° C / s and retention at 550 ° C at 660 ° C to generate the transformation of ferrite and iron carbide. Since the iron carbide generated by continuous annealing is generated in a short time, it is difficult for the substitute elements to diffuse.
[0058] In the other one, in the cooling stage after the hot rolling stage, by the end of the transformation of ferrite and pearlite, it is possible to achieve a smooth and regular state in which the amount of diffusion of the substitute elements in the iron carbide in the perlite is small. The reason for limiting hot rolling conditions will be described later. Consequently, in the state of the hot-rolled sheet after hot rolling, it is possible to adjust the Cre / CrM and Mne / MnM values as low values. Thus, in the continuous annealing step after cold rolling, even with annealing in a temperature range of (Aci - 40) ° C in which it occurs
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24/70 only the recrystallization of the ferrite, if it is possible to complete the transformation in the ROT cooling after the hot rolling, it is possible to adjust Cre / CrM and Mne / MnM to be low.
[0059] As shown in FIG. 6, the lower limit values were determined from an expansion curve when C-1 is retained in which the Cre / CrM and Mne / MnM values are low and C-4 in which the Cre / CrM and Mne / values MnM are high, for 10 seconds after heating to 850 ° C to 150 ° C / s, and then cool to 5 ° C / s. That is, while the transformation begins from the vicinity of 650 ° C in cooling, in a material in which the Cre / CrM and Mne / MnM values are high, a clear phase transformation is not observed at a temperature equal to or less than 400 ° C, in the material in which the Cre / CrM and Mne / MnM values are high. That is, by adjusting the Cre / CrM and Mne / MnM values to be low, it is possible to improve the hardening capacity after rapid heating.
[0060] A method of measuring the analysis of Cr and Mn components in iron carbide is not particularly limited, however, for example, the analysis can be performed with an energy diffusion spectrometer (EDS) connected to a TEM, by production of replica materials extracted from arbitrary locations on the steel plate and observed using the electronic transmission microscope (TEM) with a magnification of 1000x or more. In addition, for analysis of CR and Mn components in a source phase, EDS analysis can be performed on ferrite grains sufficiently separated from iron carbide, by producing a commonly used thin film.
[0061] In addition, in the steel sheet for hot stamping, the fraction of non-segmented perlite can be equal to or greater than 10%. The non-segmented perlite shows that the perlite that is austenitized once in the annealing step is transformed into a perlite again in the cooling step, the non-segmented perlite shows that the
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25/70 Cre / CrM and Μπθ / Μπμ values are lower.
[0062] If the fraction of non-segmented pearlite is equal to or greater than 10%, the hardening capacity of the steel plate is improved.
[0063] When the microstructure of the hot-rolled steel sheet is formed from ferrite and perlite, if the ferrite is recrystallized after cold rolling the hot-rolled steel sheet to about 50%, usually the location that indicates the non-segmented perlite is in a state in which the perlite is finely segmented, as shown in the result observed by the SEM of FIGURES 7A and 7B. On the other hand, when heated in continuous annealing to be equal to or greater than Ac1, after the pearlite is austenitized once, by the subsequent cooling and retention stage, the transformation of ferrite and the transformation of perlite occur. Since the perlite is formed by transformation for a short time, the perlite is in a state in which it does not contain the substitute elements in the iron carbide and has the non-segmented shape as shown in FIGURES 8A and 8B.
[0064] The area ratio of the non-segmented perlite can be obtained by observing a specimen cut and polished with an optical microscope, and measuring the ratio using a method of counting points.
(First Configuration) [0065] A method for producing a hot-stamped steel plate according to the first configuration of the present invention will now be described.
[0066] The method for producing a hot stamped steel sheet according to the configuration includes at least one hot rolling step, a coiling step, a cold rolling step, a continuous annealing step, and a sPetition 870190000733, of 04/01/2019, p. 34/96
26/70 hot capping. Each step will now be described in detail.
(Hot Rolling Step) [0067] In the hot rolling step, a piece of steel having the chemical components described above is heated (reheated) to a temperature equal to or greater than 1100 ° C, and the hot rolling is performed. The steel part can be a plate obtained immediately after being produced by a continuous casting plant, or it can be produced using an electric oven. By heating the steel part to a temperature equal to or greater than 1100 ° C, carbide and carbon forming elements can be sufficiently subjected to decomposition-dissolution in the steel material. In addition, by heating the steel part to a temperature equal to or greater than 1200 ° C, precipitated carbonitrides in the steel part can be dissolved sufficiently. However, it is not preferable to heat the steel part to a temperature above 1280 ° C, from the point of view of production cost.
[0068] When the finishing temperature of the hot rolling mill is less than Ar3 ° C, the transformation of ferrite occurs in the rolling by contacting the surface layer of the steel sheet and a rolling mill, and the resistance to deformation of the rolling mill can be significantly high. The upper limit of the finishing temperature is not particularly provided, however the upper limit can be adjusted to around 1050 ° C.
(Cooling step) [0069] It is preferable that the winding temperature in the winding step after the hot rolling step is in a temperature range of 700 ° C to 900 ° C (ferrite transformation and perlite transformation range ) or in a temperature range of 25 ° C to 500 ° C (martensite or bainite transformation range). In general, since the coil after winding is
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27/70 cooled from the edge portion, the cooling history becomes irregular, and as a result, the microstructure irregularity occurs easily, however, by winding the hot rolled coil in the temperature range described above, it is possible to suppress the occurrence of irregularity in the microstructure in the hot rolling stage. However, even with a winding temperature beyond the preferred range, it is possible to significantly reduce its variation compared to the relative technique by controlling the microstructure in continuous annealing.
(Cold Rolling Stage) [0070] In the cold rolling stage, the coiled hot rolled steel sheet is cold rolled after pickling, and cold rolled steel sheet is produced.
(Continuous annealing step) [0071] In the continuous annealing step, the cold-rolled steel sheet is subjected to continuous annealing. The continuous annealing step includes a step of heating the cold rolled steel sheet in a temperature range equal to or greater than AcUC and less than Ac3 ° C, and the cooling step of subsequently cooling the cold rolled steel sheet up to 660 ° C from the highest heating temperature by adjusting the cooling rate to 10 ° C / s or less, and a retention step to subsequently retain the cold rolled steel sheet over a temperature range of 550 ° C at 660 ° C for 1 minute to 10 minutes.
(Hot stamping step) [0072] In the hot stamping step, hot stamping is performed for the steel plate that is heated so as to have a heated portion and an unheated portion. The heated portion (hardening portion) is heated to the temperature of Ac3 or more. Common conditions can be employed for your rate
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28/70 heating or for the subsequent cooling rate. However, since production efficiency is extremely low at a heating rate of less than 3 ° C / s, the heating rate can be adjusted to be equal to or greater than 3 ° C / s. In addition, since the heated portion may not be sufficiently tempered or heat may transfer to the unheated portion, in particular at a cooling rate of less than 3 ° C / a, the cooling rate may be adjusted to be equal to or greater than 3 ° C / s.
[0073] The heating method for making the steel plate have the heated portion and the unheated portion is not particularly regulated and, for example, a method of performing electrical heating, a method of providing a mere thermal insulator in the portion that does not must be heated, a method of heating a particular portion of the steel sheet by infrared radiation, or the like can be employed. The upper limit of the highest heating temperature can be adjusted to 1000 ° C in order to prevent the unheated portion from being heated due to heat transfer. In addition, retention at the highest heating temperature may not be performed since it is not necessary to provide a particular retention time since the reverse transformation to the austenite single phase is obtained.
[0074] The heated portion means a portion in which the highest heating temperature at the time of heating the steel sheet in the stamping process reaches Ac3 or higher. The unheated portion means a portion where the highest heating temperature at the time of heating the steel sheet in the hot stamping process is in the temperature range equal to or less than Ac1. The unheated portion includes a portion that it is unheated, and a portion that is heated to Ac1 or less.
[0075] According to the method for producing a chassis es
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29/70 hot plug described above, since the steel plate is used for hot pressing in which the hardness is regular and which is soft, even in a case of hot stamping the steel plate in a state of including a unheated portion, it is possible to reduce the variation in hardness of the unheated portion of the stamped chassis. In detail, it is possible to perform the following AHv which represents a variation in the Vickers hardness of the unheated portion, and Hv_Ave which represents the average Vickers hardness of the unheated portion.
[0076] If the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%, AHv is equal to or less than 25 and Hv_Ave is equal to or less than 200.
[0077] If the amount of C in the steel plate is equal to or greater than 0.25% and less than 0.30%, AHv is equal to or less than 32 and Hv_Ave is equal to or less than 220.
[0078] If the amount of C in the steel plate is equal to or greater than 0.30% and less than 0.35%, AHv is equal to or less than 38 and Hv_Ave is equal to or less than 240.
[0079] The steel sheet for stamping contains enough component C to guarantee resistance in the quench after hot stamping and contains Mn and B, and in such a steel component having a high hardening capacity and a high concentration of C. the microstructure of the hot rolled sheet after the hot rolling step tends to easily become uneven. However, according to the method for producing cold rolled steel sheet for hot stamping according to the configuration, in the continuous annealing step subsequent to the last stage of the cold rolling step, the cold rolled steel sheet is heated in a temperature range equal to or greater than Ac1 ° C and less than Ac3 ° C, and then cooled from the highest temperature to 660 ° C at a cooling rate equal to or less than 10 ° C / s, and then kept in
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30/70 a temperature range of 550 ° C to 660 ° C for 1 minute to 10 minutes, and so the microstructure can be obtained to be regular.
[0080] In the continuous annealing line, a hot dip galvanizing process, a galvanizing process, a cast aluminum coating process, a bonded cast aluminum coating process, and an electroplating process can also be performed. The effects of the present invention are not lost even when the coating process is carried out after the annealing step.
[0081] As shown in the schematic view of FIG. 2, the microstructure of the steel sheet subjected to the cold rolling stage is a non-recrystallized ferrite. In the method for producing a steel layer according to the configuration, in the continuous annealing step, heating up to a heating range equal to or greater than Ac1 ° C and less than Ac3 ° C, which is the highest temperature range that At point Ac1, heating is carried out until there is a double-phase coexistence with the austenite phase in which the non-crystallized ferrite remains slightly. After that, in the cooling step at a cooling rate equal to or less than 10 ° C / s, the transformed ferrite grows which is nucleated with the non-crystallized ferrite that remains at the highest heating temperature. Then, in the step of retaining the steel sheet at a temperature range of 550 ° C to 660 ° C for 1 minute to 10 minutes, the thickening of C in the untransformed austenite occurs at the same time as the transformation of ferrite, and the precipitation of cementite or transformation of perlite is promoted by retention in the same temperature range.
[0082] The steel sheet for hot stamping contains enough component C to ensure hardening of the quench after hot stamping and contains Mn and B, and B generally has the effect of suppressing the generation of ferrite nucleation at the time of cooling
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31/70 from the single austenite phase, and when cooling is performed after heating to the single austenite phase equal to or greater than Ac3, it is difficult for ferrite transformation to occur. However, keeping = the heating temperature in the continuous annealing step in a temperature range equal to or greater than Ac1 ° C and less than Ac3 ° C which is immediately below Ac3, the ferrite remains slightly in a state where non-recrystallized ferrite almost hardened is transformed inversely into austenite, and in the subsequent cooling step at a cooling rate equal to or less than 10 ° C / s and in the retention step at a temperature range of 550 ° C to 660 ° C for 1 minute to 10 minutes, softening is accomplished by the growth of ferrite by nucleation of the remaining ferrite. In addition, if the heating temperature in the continuous annealing step is greater than Ac3 ° C, since the single austenite phase occurs mainly, and then the transformation of ferrite on cooling is insufficient and the hardening is carried out, the temperature described above is set as the upper limit, and if the heating temperature is less than Ac1, once the volume fraction of the non-recrystallized ferrite becomes high and the hardening is carried out, the temperature described above is adjusted as the lower limit.
[0083] In addition, in the retention step of retaining cold rolled steel sheet in a temperature range of 550 ° C to 660 ° C for 1 minute to 10 minutes, precipitation of cementite or transformation of perlite can be promoted in untransformed austenite in which the C is thickened after the transformation of ferrite. Thus, according to the method for producing a steel sheet according to the configuration, even in a case of heating a material having a high hardening capacity to a temperature immediately below the point Ac3 by continuous annealing, most parts of the mill
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32/70 steel sheet structure can be adjusted as ferrite and cementite. According to the processing state of the transformation, bainite, martensite, and remaining austenite exist slightly after cooling in some cases.
[0084] In addition, if the temperature in the holding step exceeds 660 ° C, the ferrite transformation procedure is delayed and the annealing takes a long time. On the other hand, when the temperature is below 550 ° C, the very ferrite that is generated by the transformation is hardened, it is difficult for cementite precipitation or the transformation of the perlite to happen, or there is bainite or martensite that are transformation products at lower temperatures. In addition, when the retention time exceeds 10 minutes, the continuous annealing installation subsequently becomes longer and requires a high cost and, on the other hand, when the retention time is less than 1 minute, the transformation of ferrite, the precipitation of cementite, or the transformation of perlite is insufficient, the structure is formed mainly of bainite and martensite in which most parts of the microstructure after cooling are hardened phases, and the steel sheet is hardened.
[0085] According to the production method described above, winding the hot rolled coil submitted to the hot rolling step in a temperature range of 700 ° C to 900 ° C (ferrite and perlite range), or winding in a temperature range of 25 ° C to 550 ° C, which is a temperature range of transformation at low temperature, it is possible to suppress the irregularity of the microstructure of the hot-rolled coil after winding. That is, the 600 ° C neighborhood in which normal steel is generally wound is a temperature range in which the transformation of ferrite and the transformation of perlite occurs, however, when winding a type of steel having a high hardening capacity in the same track has
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33/70 durations after adjusting the conditions of the finishing of the hot lamination performed normally, since there is almost no transformation in a section of the cooling equipment that is called the Exit Table (hereinafter called ROT) since the finishing lamination of the hot rolling stage until winding, the transformation from austenite phase occurs after winding. Consequently, when considering the direction of the coil width, the cooling rates in the edge portion exposed to the outside air and in the central protected portion of the outside air are different from each other. In addition, also in the case of considering the longitudinal direction of the coil, in the same way as described above, the cooling stories at an anterior end or at a posterior end of the coil that may be in contact with the external air and in the intermediate portion protected from outside air are different from each other. Consequently, in the component that has high hardening capacity, when winding in a temperature range in the same way as in the case of normal steel, the microstructure or strength of the hot-rolled sheet varies significantly in a coil due to the difference in the history of cooling. When annealing is carried out by the continuous annealing installation after cold rolling using hot rolled sheet, in the ferrite recrystallization temperature range equal to or less than Ac1, a significant change in resistance is generated as shown in FIG. 1 for the variation in the rate of recrystallization of the ferrite caused by the variation of the microstructure of the hot-rolled sheet. However, when heating to a temperature range equal to or greater than Ac1 and cooling in the state, not only an amount of non-recrystallized ferrite remains, but the austenite that is partially inversely transformed to the bainite or martensite that it is a hardened phase, and it becomes a hard material with variation
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34/70 significant. When heated to a temperature equal to or greater than AC3 to completely remove the non-crystallized ferrite, a significant hardening is performed after cooling with an effect of elements to improve the hardening capacity such as Mn and B. Consequently, it is disadvantageous to perform winding in the range described above for regularity of the microstructure of the hot-rolled sheet. That is, winding is carried out in the temperature range of 700 ° C to 900 ° C, since cooling is sufficiently carried out from the state and high temperature after winding, it is possible to form the entire coil with the structure ferrite / perlite. However, laminating in the temperature range of 25 ° C to 550 ° C, it is possible to form the entire coil in bainite or martensite which are hard.
[0086] FIGURES 3A to 3C show the variation in the strength of the steel sheet for hot stamping after continuous annealing with different winding temperatures for the hot rolled coil. FIG. 3A shows a case of performing continuous annealing by setting the winding temperature to 680 ° C, FIG. 3B shows a case of execution of continuous annealing by adjusting the winding temperature to 750 ° C, that is, in the temperature range of 700 ° C to 900 ° C (ferrite transformation and perlite transformation range), and FIG . 3C shows a case of continuous annealing execution and the adjustment of the winding temperature in 500 ° C, that is, in the temperature range of 25 ° C to 500 ° C (range of transformation of bainite and transformation of martensite). In FIGURES 3A to 3C, ATS indicates the variation of the steel plate (maximum value of the tensile strength of the steel plate - its minimum value). As shown clearly in FIGURES 3A to 3C, by performing continuous annealing with suitable conditions, it is possible to obtain regular strength and soft hardness of the steel sheet after annealing.
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35/70 [0087] Using steel that has regular resistance, in the hot stamping step, even in the case of using an electric heating method that inevitably generates an irregularity in the temperature of the steel sheet after heating, it is it is possible to stabilize the resistance of a component of the shaped product after hot stamping. For example, for an electrode retaining portion or the like in which the temperature does not increase by electrical heating and in which the strength of the steel sheet material itself affects the strength of the product, regularly controlling the strength of the sheet material steel itself, it is possible to improve the precision control of the quality of the shaped product after hot stamping.
(Second Configuration) [0088] A method for producing a hot-stamped steel sheet according to a second configuration of the present invention will now be described.
[0089] The method for producing a hot stamped steel sheet according to the configuration includes at least one hot rolling step, a coiling step, a cold rolling step, a continuous annealing step and a stamping step the hot. Each step will now be described in detail. (Hot Rolling Step) [0090] In the hot rolling step, a piece of steel having the chemical components described above is heated (reheated) to a temperature equal to or greater than 1100 ° C, and the hot rolling is performed. The steel part can be a plate obtained immediately after being produced by a continuous casting plant, or it can be produced using an electric oven. By heating the steel part to a temperature equal to or greater than 1100 ° C, carbide and carbon forming elements can be sufficiently
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36/70 subjected to decomposition-dissolution in the steel material. In addition, by heating the steel sheet to a temperature equal to or greater than 1200 ° C, precipitated carbonitrides on the steel sheet can be sufficiently dissolved. However, it is not preferable to heat the steel part to a temperature greater than 1280 ° C, from the point of view of production cost.
[0091] In the hot lamination step of the configuration, in the finishing hot lamination configured with a machine with 5 or more consecutive lamination chairs, the lamination is performed by (A) adjusting the temperature of the FiT finishing hot lamination in a final laminator Fi in a temperature range of (Ac3 80) ° C to (Ac3 + 40) ° C, by (B) adjusting the time from the beginning of the lamination in a final laminator Fi-3 which is a laminator prior to final laminator Fi until the end of the lamination in the final laminator Fi to be equal to or greater than 2.5 seconds, and for (C) adjust the hot rolling temperature Fi-3T in the Fi-3 laminator to be equal to or less than (FiT + 100) ° C, and then retention is performed in a temperature range of 600 ° C to Ar3 ° C for 3 seconds to 40 seconds, and winding is performed in the winding step.
[0092] Performing such a hot lamination, it is possible to perform the stabilization and transformation from austenite to ferrite, perlite or bainite which is the low temperature transformation phase in the ROT (exit table) which is the cooling bed in the hot rolling and it is possible to reduce the variation in the hardness of the steel sheet accompanied by a deviation of the cooling temperature generated after the coil winding. To complete the transformation in the ROT, refining the austenite grain size and holding it at a temperature equal to or less than Ar3 ° C in the ROT for a long time are important conditions.
[0093] When the FiT is less than (Ac3 - 80) ° C, the possibility of
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37/70 ferrite transformation in hot rolling becomes high and the resistance to deformation in hot rolling is not stabilized. On the other hand, when FiT is greater than (AC3 + 40) ° C, the austenite grain size immediately before cooling after finishing hot rolling becomes crude, and the transformation of the ferrite is delayed. It is preferable that FiT be adjusted over a temperature range from (AC3 - 70) ° C to (AC3 + 20) ° C. By adjusting the heating conditions as described above, it is possible to refine the grain size of the austenite after the finishing lamination, and it is possible to promote the transformation of ferrite on cooling in the ROT. Consequently, once the transformation takes place in the ROT, it is possible to greatly reduce the variation of the microstructure in the longitudinal and coil width directions caused by the variation in the coil cooling after winding.
[0094] For example, in the case of a hot rolling line including seven final laminators, the transit time from laminator F4 corresponding to the third laminator from laminator F7 which is the final chair of laminator F7 is set to 2 , 5 seconds or more. When the transit time is less than 2.5 seconds, since the austenite is not recrystallized between the chairs, the B segregated to the edge of the austenite grain significantly delays the transformation of the ferrite and it is difficult to happen the phase transformation in the ROT. The transit time is preferably equal to or greater than 4 seconds. It is not particularly limited, however, when the transition time is equal to or greater than 20 seconds, the temperature of the steel sheet between the chairs decreases greatly and it is impossible to perform hot rolling.
[0095] In order to recrystallize so that austenite is refined and B does not exist at the edge of the austenite grain, it is necessary to complete the lamination at an extremely low temperature equal to or
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38/70 greater than Ar3, and recrystallize austenite in the same temperature range. Consequently, the temperature on the lamination output side of laminator F4 is adjusted to be equal to or less than (FiT + 100) ° C. This is because it is necessary to lower the rolling temperature of the F4 laminator to obtain an effect of refining the grain size of the austenite in the last stage of the finishing lamination. The lower limit of Fi-3T is not particularly provided, however, since the temperature on the outlet side of the final laminator F7 is FiT, this is set as its lower limit.
[0096] Adjusting the retention time in the temperature range from 600 ° C to Ar3 ° C to be a long time, the transformation of the ferrite occurs. Since Ar3 is the starting temperature of the ferrite transformation, it is set as the upper limit, and 600 ° C at which the softened ferrite is generated is set as the lower limit. Its preferred temperature range is 600 ° C to 700 ° C in which ferrite transformation generally takes place more quickly.
(Coiling Step) [0097] Maintaining the coiling temperature in the coiling step after the hot rolling step at 600 ° C to Ar3 ° C for 3 seconds or more in the cooling step, the steel sheet is laminated to in which the ferrite transformation took place is wound in the state. Substantially, although it is altered by the length of the installation's ROT, the steel sheet is wound in the temperature range from 500 ° C to 650 ° C. By executing the hot rolling described above, the microstructure of the hot rolled sheet after cooling the coil has a structure including mainly ferrite and perlite, and it is possible to suppress the irregularity of the microstructure generated in the hot rolling step.
(Cold Rolling Stage) [0098] In the cold rolling stage, the cold rolled steel sheet
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Hot coiled 39/70 is cold rolled after pickling, and cold rolled steel sheet is produced.
(Continuous Annealing Stage) [0099] In the continuous annealing stage, the cold-rolled steel sheet is subjected to continuous annealing. The continuous annealing step includes a heating step of heating the cold rolled steel sheet in a temperature range equal to or greater than (Aci - 40) ° C and less than Ac3 ° C, and a cooling step of subsequently cool the cold rolled steel sheet to 660 ° C from the highest rolling temperature by setting the cooling rate to 10 ° C / s or less, and the retention step of subsequently retaining the cold rolled steel sheet to cold in a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes. (Hot Stamping Stage) [00100] In the hot stamping stage, the hot stamping is performed for the steel plate that is heated so as to have a heated portion and an unheated portion. The heated portion (hardened portion) is heated to the temperature of Ac3 or more. General conditions can be used for your heating rate or the subsequent cooling rate. However, since production efficiency is extremely low at a heating rate of less than 3 ° C / s, the heating rate can be adjusted to be equal to or greater than 3 ° C / s. In addition, since the heated portion may not be sufficiently tempered or heat may transfer to the unheated portion, in particular, at a cooling rate of less than 3 ° C / s, the cooling rate may be adjusted to be equal to or greater than 3 ° C / s.
[00101] The heating method for making the steel plate have the heated portion and the unheated portion is not particularly regulated and, for example, an electric heating execution method,
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40/70 a method of providing a heat insulating member in the portion that is not to be heated, a method of heating a particular portion of the steel sheet by infrared ray radiation, or the like may be employed.
[00102] The upper limit of the highest heating temperature can be adjusted to 1000 ° C in order to prevent the unheated portion from being heated due to heat transfer. In addition, retention at the highest heating temperature may not be performed since it is not necessary to provide a particular retention time since the reverse transformation to the single austenite phase is achieved.
[00103] The heated portion means a portion in which the highest heating temperature at the time of heating the steel sheet in the hot stamping process reaches Ac3 or more. The unheated portion means a portion where the highest heating temperature at the time of heating the steel sheet in the stamping process is within the temperature range of equal to or less than Ac1. The unheated portion includes a portion that is not heated, and a portion that is heated to Ac1 or less.
[00104] According to the method for producing a hot stamped chassis described above, since a steel plate is used for hot pressing in which the hardness is regular and which is soft, even in a case of stamping a steel sheet in a state of including an unheated portion, it is possible to reduce the variation in hardness of the unheated portion of the hot stamped chassis. In detail, it is possible to perform the following AHv which represents the variation in the Vickers hardness of the unheated portion, and Hv_Ave which represents the average Vickers hardness of the unheated portion. If the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%, AHv is equal to or less than 25 and Hv_Ave is equal to
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41/70 or less than 200.
[00105] If the amount of C in the steel plate is equal to or greater than 0.25% and less than 0.30%, AHv is equal to or less than 32 and Hv_Ave is equal to or less than 220.
[00106] If the amount of C in the steel plate is equal to or greater than 0.30% and less than 0.35%, AHv is equal to or less than 38 and Hv_Ave is equal to or less than 240.
[00107] Since the steel sheet is wound on a coil after the transformation from austenite to ferrite or perlite in the ROT by the hot rolling step of the second configuration described above, the variation in the strength of the steel sheet accompanied by the deviation the cooling temperature generated after winding is reduced. Consequently, in the continuous annealing stage subsequent to the last stage of the cold rolling stage, the cold rolled steel sheet is heated in the temperature range equal to or greater than (Ac1 - 40) ° C to less than Ac3 ° C, subsequently cooling from the highest temperature to 660 ° C at a cooling rate of 10 ° C / s or less, and subsequently keeping in a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes, it is possible to carry out the regularity of the microstructure in the same way as in the improved way for the production method of a steel sheet described in the first configuration.
[00108] In the continuous annealing line, a hot dip galvanizing process, a cast aluminum coating process, a cast aluminum alloy coating process, and an electroplating process can also be performed. The effects of the present invention are not lost even when the coating process is carried out after the annealing step.
[00109] As shown in the schematic view of FIG. 2, the microstructure of the steel sheet submitted to the cold rolling stage is
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42/70 a non-recrystallized ferrite. In the method for producing a steel sheet for hot stamping according to the second configuration, in addition to the first configuration in which, in the continuous annealing step, by heating to a heating range equal to or greater than (Aci - 40) ° C and lower than Ac3 ° C, heating is carried out until it has a double-phase coexistence with the austenite phase in which the non-recrystallized ferrite remains slightly, it is possible to decrease the heating temperature to proceed with the recovery and recrystallization of the ferrite in the coil, even with the heating temperature from Aci ° C to (Aci - 40) ° C in which the reverse transformation of austenite does not occur. In addition, using the hot-rolled sheet showing the regular structure, after heating to a temperature equal to or greater than Aci ° C and less than Ac3 ° C, it is possible to decrease the temperature and shorten the retention time after cooling at a cooling rate equal to or less than 10 ° C / s, compared to the first configuration. This shows that the transformation of the ferrite occurs more quickly in the cooling step from austenite by obtaining the regular microstructure, and it is possible to sufficiently achieve regularity and softening of the structure, even with conditions of lower temperature retention and short time. That is, in the steel plate retention stage in the temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes, the thickening of C in the untransformed austenite occurs at the same time as transformation of ferrite, and the precipitation of cementite or the transformation of perlite occurs rapidly by retention in the same temperature range.
[00110] From these points of view, when the temperature is lower than (Aci - 40) ° C, since the recovery and recrystallization of the ferrite is insufficient, it is adjusted as a lower limit and, however, when the temperature is equal to or greater than Ac3 ° C, since the transformation
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43/70 ferrite mass does not occur sufficiently and the resistance after annealing increases significantly, due to the delay in the generation of ferrite nucleation by the effect of adding B, it is adjusted as the upper limit. In addition, in the subsequent cooling step at a cooling rate equal to or less than 10 ° C / s and the retention step at a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes, softening is performed by the growth of the ferrite by the nucleation of the remaining ferrite.
[00111] Here, in the plate retention stage in a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes, precipitation of cementite or transformation of perlite can be promoted in the untransformed austenite in which the C is thickened after the transformation of ferrite. Thus, according to the method for producing a steel sheet according to the configuration, even in the case of heating a material having a high hardening capacity to a temperature immediately below the point Ac3 by continuous annealing, most parts of the microstructure of the sheet steel can be adjusted as ferrite and cementite. According to the state of transformation, bainite, martensite, and remaining austenite exist slightly after cooling, in some cases. [00112] In addition, if the temperature in the holding step exceeds 660 ° C, the ferrite transformation event is delayed and the annealing takes a long time. On the other hand, when the temperature is below 450 ° C, the ferrite that is generated by the transformation is hardened, it is difficult for the cementite precipitation or the transformation of the perlite to happen, or the bainite or martensite that is the product occurs low temperature processing. In addition, when the holding time exceeds 10 minutes, the continuous annealing installation subsequently becomes longer and a high cost is required, on the other hand. When the retention time is less than
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44/70 seconds, the transformation of ferrite, the precipitation of cementite, or the transformation of perlite is insufficient, the structure is formed mainly of bainite or martensite in which the most important parts of the microstructure after cooling are hardened phases, and the plate steel is hardened.
[00113] FIGURES 3A to 3C show the variation in the strength of the steel sheet for hot stamping after continuous annealing with different winding temperatures for the hot rolled coil. FIG. 3A shows a case of performing continuous annealing by setting the winding temperature to 680 ° C, FIG. 3B shows a case of carrying out continuous annealing by adjusting the winding temperature to 750 ° C, that is, in the temperature range 700 ° C to 900 ° C (ferrite transformation range and perlite transformation range), and FIG. 3C shows a case of continuous annealing execution, adjusting the winding temperature to 500 ° C, that is, in the temperature range of 25 ° C to 500 ° C (bainite transformation and martensite transformation range). In FIGURES 3A to 3C,. TS indicates the variation of the steel plate (maximum value of tensile strength of the steel plate - its minimum value). As shown clearly in FIGURES 3A to 3C, by performing continuous annealing with suitable conditions, it is possible to obtain regular strength and soft hardness of the steel sheet after annealing.
[00114] Using a steel having regular resistance, in the hot stamping step, even in the case of using an electric heating method that inevitably generates an irregularity in the temperature of the steel sheet after heating, it is possible to stabilize the strength of a product component formed after hot stamping. For example, for an electrode retaining portion or similar where the temperature does not rise due to heating
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45/70 electrical equipment and in which the resistance of the material of the steel plate itself affects the resistance of the product, by regular control of the resistance of the material of the steel plate itself, it is possible to improve the precision control of the quality of the formed product after hot stamping.
[00115] Above, the present invention has been described based on the first configuration and the second configuration, however the present invention is not limited only to the configurations described above, and several modifications within the scope of the claims can be performed. For example, even in the hot rolling stage of the first configuration, it is possible to employ the conditions of the second configuration.
Examples [00116] The following will describe examples of the present invention.
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Table 1
Steel type Ç Mn Si P s N Al You B Cr Ac1 Ac3 DIinch (% in large scale) (° C) (° C) - THE 0.22 1.35 0.15 0.009 0.004 0.003 0.010 0.020 0.0012 0.22 735 850 4.8 B 0.22 1.65 0.03 0.009 0.004 0.004 0.010 0.010 0.0013 0.02 725 840 3.5 Ç 0.22 1.95 0.03 0.008 0.003 0.003 0.010 0.012 0.0013 0.15 725 830 4.2 D 0.23 2.13 0.05 0.010 0.005 0.004 0.020 0.015 0.0015 0.10 720 825 5.2 AND 0.28 1.85 0.10 0.008 0.004 0.003 0.015 0.080 0.0013 0.01 725 825 3.8 F 0.24 1.63 0.85 0.009 0.004 0.003 0.032 0.020 0.0014 0.01 740 860 5.4 G 0.21 2.62 0.12 0.008 0.003 0.003 0.022 0.015 0.0012 0.10 725 820 8.0 H 0.16 1.54 0.30 0.008 0.003 0.003 0.020 0.012 0.0010 0.03 735 850 3.4 I 0.40 1.64 0.20 0.009 0.004 0.004 0.010 0.020 0.0012 0.01 730 810 4.1 J 0.21 0.82 0.13 0.007 0.003 0.003 0.021 0.020 0.0011 0.01 735 865 1.8 K 0.28 3.82 0.13 0.008 0.003 0.004 0.020 0.010 0.0012 0.13 710 770 7.1 L 0.26 1.85 1.32 0.008 0.004 0.003 0.020 0.012 0.0015 0.01 755 880 9.2 M 0.29 1.50 0.30 0.008 0.003 0.004 1,300 0.020 0.0018 0.01 735 1055 4.6 N 0.24 1.30 0.03 0.008 0.004 0.003 0.020 0.310 0.0012 0.20 730 850 4.1 O 0.22 1.80 0.04 0.009 0.005 0.003 0.010 0.020 0.0001 0.10 725 830 2.2 P 0.23 1.60 0.03 0.009 0.005 0.003 0.012 0.003 0.0010 0.01 725 840 1.3 Q 0.21 1.76 0.13 0.009 0.004 0.003 0.021 0.020 0.0013 0.20 730 835 7.5 R 0.28 1.65 0.05 0.008 0.003 0.004 0.025 0.015 0.0025 0.21 725 825 7.9 s 0.23 2.06 0.01 0.008 0.003 0.003 0.015 0.015 0.0022 0.42 715 815 8.4 T 0.22 1.60 0.15 0.008 0.004 0.003 0.022 0.015 0.0021 2.35 710 810 16.1
02/917
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Table 2
Steel type Mo Nb V Ni Ass Sn Here Mg REM (% in large scale) THE 0.05 0.003 BÇD0.04 0.010.0080.003 ANDF0.060.04 0.02 0.003 G 0.20.005 0.003H 0.002IJK 0.05 L 0.002 MN 0.15 O 0.10.005 PQ 0.11 R 0.15 0.08 0.0020.003sT
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Table 3
Kind ofsteel Condition No. Hot rolling conditions for winding Conditions of continuous annealing F4T F7T (AC3-80) (AC3 + 40) Time between step 4 and step 7 Retention time at 600 ° C to Ara CT Higher heating temperature Rate ofcooling Holding temperature Time toretention [° C] [° C] [° C] [° C] [s] [s] [° C] [° C] [° C / s] [° C] [s] THE 1 955 905 770 890 2.7 2.1 680 830 3.5 585 320 2 945 900 770 890 2.9 1.3 500 825 4.2 580 330 3 945 900 770 890 2.2 0.3 800 830 4.1 585 320 4 940 900 770 890 2.8 2.5 680 700 4.3 570 330 5 945 905 770 890 2.9 3.1 675 870 4.5 580 300 6 955 910 770 890 2.5 3.2 685 820 13.5 560 290 7 950 905 770 890 2.6 2.9 680 825 5.2 530 300 8 945 905 770 890 2.2 4.6 685 810 4.6 575 45 9 880 820 770 890 4.6 8.2 580 810 4.2 560 310 10 875 810 770 890 4.5 7.9 610 710 4.3 470 35 B 1 960 890 760 880 2.2 4.0 650 820 3.5 580 290 2 950 895 760 880 2.8 1.0 500 815 5 560 300 3 945 895 760 880 2.6 3.0 670 860 4.5 560 320 4 945 900 760 880 2.9 3.0 670 810 5 500 310
02/81
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Kind ofsteel Condition No. Hot rolling conditions for winding Conditions of continuous annealing F4T F7T (AC3-80) (AC3 + 40) Time between step 4 and step 7 Retention time at 600 ° C to Ara CT Higher heating temperature Rate ofcooling Holding temperature Time toretention [° C] [° C] [° C] [° C] [s] [s] [° C] [° C] [° C / s] [° C] [s] 5 890 830 760 880 4.8 7.2 600 805 3.9 570 50 6 900 845 760 880 5.1 7.6 590 705 4.5 460 45 Ç 1 970 905 750 870 2.2 4.0 650 820 5.6 570 300 2 960 910 750 870 2.8 4.0 680 815 5.5 570 290 3 965 915 750 870 2.3 4.0 680 810 5.2 510 280 4 960 910 750 870 3.0 3.0 680 700 4.3 560 300 5 880 800 750 870 5.2 7.5 610 695 4.5 475 28 6 895 820 750 870 4.5 6.5 590 790 3.1 560 32 7 980 930 750 870 2.5 2.6 720 690 2.5 480 35 8 980 820 750 870 6.2 7.0 590 780 3.6 570 25 9 890 810 750 870 4.4 6.3 600 655 2.3 595 30 10 900 830 750 870 4.5 6.5 580 755 3.5 470 5
02/617
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Table 4
Kind ofsteel Condition No. Hot rolling conditions for coiling Conditions of continuous annealing F4T F7T (AC3-80) (AC3 + 40) Time between step 4 and step 7 Retention time at 600 ° C to Ara CT Higher heating temperature Rate ofcooling Holding temperature Time toretention [° C] [° C] [° C] [° C] [s] [s] [° C] [° C] [° C / s] [° C] [s] D 1 950 910 745 865 3.2 4.0 680 700 2.1 500 324 2 960 910 745 865 2.1 4.0 680 810 4.3 580 320 3 965 920 745 865 2.0 4.0 680 775 1.6 580 405 4 960 915 745 865 3.3 3.0 680 775 2.9 540 270 5 965 910 745 865 2.3 4.0 680 800 2.2 540 405 6 975 930 745 865 2.9 4.0 680 800 4.3 500 270 7 960 910 745 865 2.1 1.0 500 700 2.1 680 324 8 950 920 745 865 2.1 2.0 500 775 1.6 580 405 9 950 910 745 865 2.2 0.0 750 700 2.1 550 324 10 955 915 745 865 2.3 0.0 750 775 1.6 580 405 AND 1 950 900 745 865 2.5 3.0 680 800 2.3 575 325 2 960 890 745 865 2.5 1.0 500 805 2.5 580 320 3 965 895 745 865 2.9 1.0 750 795 2.8 580 328 4 955 890 745 865 3.1 3.0 680 840 2.5 580 315 5 955 890 745 865 2.2 3.0 680 800 13.5 580 300
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Kind ofsteel Condition No. Hot rolling conditions for coiling Conditions of continuous annealing F4T F7T (AC3-80) (AC3 + 40) Time between step 4 and step 7 Retention time at 600 ° C to Ara CT Higher heating temperature Rate ofcooling Holding temperature Time toretention [° C] [° C] [° C] [° C] [s] [s] [° C] [° C] [° C / s] [° C] [s] 6 945 895 745 865 2.2 1.0 680 800 4.2 520 350 7 950 895 745 865 2.3 1.0 680 795 3.5 575 45 8 900 830 745 865 5.3 7.2 595 785 4.2 610 55 9 910 810 745 865 6.4 8.1 600 700 3.9 460 22 F 1 960 910 780 900 2.2 2.2 675 840 4.6 560 325 2 950 900 780 900 2.1 2.3 675 830 4.3 585 520 3 950 920 780 900 2.1 3.0 450 835 3.5 580 320 4 960 900 780 900 1.8 1.0 775 825 3.5 575 350 5 950 905 780 900 1.9 1.5 685 730 3.6 580 305
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Table 5
Steel Type Condition No. Hot rolling conditions for coiling Conditions of continuous annealing F4T F7T (AC3-80) (Aca + 40) Time between step 4 and step 7 Retention time at 600 ° C to Ara CT Higher heating temperature Cooling rate Holding temperature Retention time [° C] [° C] [° C] [° C] [s] [s] [° C] [° C] [° C / s] [° C] [s] G 1 960 905 740 860 2.2 2.5 680 800 3.8 555 320 2 970 910 740 860 2.5 2.6 680 805 4.2 585 545 3 950 910 740 860 2.6 2.4 400 800 4.1 575 320 4 950 915 740 860 2.3 2.2 800 790 3.5 580 315 5 955 920 740 860 2.5 2.3 680 710 3.5 580 295 H 1 960 915 770 890 2.4 2.1 685 830 4.2 580 305 2 955 920 770 890 2.5 2.5 680 760 4.1 550 310 I 1 950 905 730 850 2.6 2.1 675 800 3.2 580 290 2 955 900 730 850 2.7 2.5 670 790 2.8 540 285 J 1 945 905 785 905 2.8 2.1 680 840 3.5 580 300 2 950 910 785 905 2.6 2.1 685 750 3.8 530 310 K 1 - - 690 810 2.9 - - - - - - L 1 960 920 800 920 2.3 2.5 680 850 5.2 560 300 M 1 960 910 975 1095 2.5 4.0 680 860 4.5 580 305 N 1 - - 770 890 - - - - - - - O 1 960 910 750 870 2.9 2.1 670 810 3.5 580 305 2 965 905 750 870 2.5 2.1 680 750 4.2 520 310 P 1 970 930 760 880 2.9 2.3 680 820 4.5 580 300 Q 1 960 910 755 875 2.1 2.5 680 810 5 575 310 R 1 940 905 745 865 2.2 2.1 610 785 4.2 575 305 s 1 945 910 735 855 2.4 2.2 605 795 3.2 585 295 T 1 - - 730 850 - - - - - - -
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Table 6
Steel Type Condition No. Material Microstructure Cre / CrM Mne / MnM ATS TS_Ave Ferrite fraction Ferrite fractionrecrystallized no- Non-perlite fractionsegmented [MPa] [MPa] [vol.%] [vol.%] [vol.%] - -1 60 620 65 10 25 1.3 8.22 40 590 75 5 20 1.5 8.13 35 580 65 5 30 1.4 7.54 150 750 45 55 0 3.2 14.3 THE 5 55 760 20 0 0 1.5 7.5 6 60 720 35 5 0 1.2 8.77 90 710 45 5 5 1.3 7.38 55 720 40 10 5 1.5 7.89 30 580 75 5 20 1.3 7.910 55 640 85 5 10 1.5 7.51 60 600 70 5 15 1.4 8.92 30 590 65 10 15 1.2 8.4 B 3 85 700 35 0 0 1.5 8.8 4 95 690 45 10 5 1.3 8.25 35 585 70 10 15 1.5 8.26 45 635 80 5 10 1.6 8.51 60 610 65 10 15 1.2 7.82 65 605 70 15 15 1.4 8.23 105 705 45 10 5 1.4 8.84 150 685 40 60 0 3.3 12.8 Ç 5 40 645 80 10 10 2.2 9.4 6 35 620 70 5 25 1.2 8.17 95 730 40 60 0 3.5 11.98 115 725 35 10 10 1.4 8.29 85 820 5 95 0 2.2 9.610 45 735 60 15 5 1.2 7.5
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Table 7
Steel Type Condition No. Material Microstructure Cre / CrM Mne / MnM ATS TS_Ave Ferrite fraction Ferrite fractionrecrystallized no- Non-perlite fractionsegmented [MPa] [MPa] [vol.%] [vol.%] [vol.%] - -1 166 690 40 55 5 3.5 13.22 62 610 70 10 20 1.2 7.63 70 620 65 20 15 1.5 8.14 73 690 45 15 5 1.2 7.9 D 5 58 680 40 10 5 1.4 8.2 6 120 720 40 10 0 1.1 7.4 7 100 700 40 60 0 3.2 12.28 28 630 65 15 15 1.5 9.49 115 700 40 60 0 2.9 11.510 46 620 65 10 10 1.2 8.51 80 685 75 10 15 1.5 8.62 60 680 70 20 10 1.2 7.83 55 675 65 25 10 1.1 8.24 80 810 40 0 0 1.5 9.1 AND 5 80 760 30 20 0 1.3 8.86 90 840 45 20 5 1.4 8.57 80 950 45 15 5 1.2 7.58 40 630 65 10 15 1.3 8.89 35 610 70 30 0 2.2 9.61 70 640 65 10 15 1.5 7.6 F 2 50 610 60 10 20 1.2 7.83 45 600 70 5 15 1.3 8.2
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Steel Type Condition No. Material Microstructure Cre / CrM Mne / MnM ATS TS_Ave Ferrite fraction Ferrite fractionrecrystallized no- Perlite fractionsegmented no- [MPa] [MPa] [vol.%] [vol.%] [vol.%] - -4 40 605 75 10 15 1.5 7.55 135 680 45 55 0 2.5 13.5
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Table 8
Steel Type Condition No. Material Microstructure Cre / CrM Mne / MnM ATS TS_Ave Ferrite fraction Ferrite fractionrecrystallized no- Non-perlite fractionsegmented [MPa] [MPa] [vol.%] [vol.%] [vol.%] - -1 70 635 60 30 10 1.3 9.22 55 605 65 20 15 1.4 8.9 G 3 40 620 65 20 15 1.4 8.54 40 610 60 20 20 1.6 8.85 165 695 40 60 0 2.2 13.2 H 1 70 620 80 10 10 1.8 9.3 2 105 680 80 20 0 2.5 13.3 I 1 130 830 65 15 20 1.2 7.52 150 850 45 10 15 1.5 8.2 J 1 50 580 75 15 10 1.3 8.5 2 60 585 45 40 15 1.6 11.9 K 1 - - - - - - - L 1 70 650 65 25 10 1.6 9.2 M 1 140 760 70 10 20 1.7 8.5 N 1 - - - - - - - O 1 30 610 70 20 10 1.5 6.8 2 55 600 75 10 15 1.6 7.5 P 1 30 600 75 15 10 1.3 8.5 Q 1 30 595 65 20 15 1.3 8.9 R 1 65 705 60 10 30 1.8 9.2 s 1 35 605 75 10 15 1.5 9.3 T 1 - - - - - - -
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Table 9
Steel type Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv THE 1 Plating byhot dipping 18 190 462 Good2 galvanizingzation 12 181 468 Good3 Plating byhot dipping 11 178 465 Good4 - 46 230 462 Good Non-recrystallized ferrite remains 5 - 17 233 456 Good Insufficient ferrite transformation and cementite precipitation 6 - 18 220 459 Good Insufficient ferrite transformation 7 - 28 217 471 Good Insufficient ferrite transformation and cementite precipitation 8 - 17 220 468 Good Insufficient ferrite transformation and cementite precipitation 9 - 21 179 465 Good10 - 19 196 458 GoodB 1 Plating byhot dipping 18 184 468 Good2 Coating bycast aluminum 9 181 468 Good3 - 26 214 471 Good Ferrite transformation and cementite precipitation
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Steel type Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv insufficient 4 - 29 211 468 Good Insufficient ferrite transformation and cementite precipitation 5 Plating byhot dipping 21 180 478 Good6 - 23 195 475 GoodÇ 1 Plating byhot dipping 18 187 474 Good2 Plating byhot dipping 20 185 478 Good3 - 32 216 481 Good Insufficient ferrite transformation and cementite precipitation 4 - 46 210 474 Good Non-recrystallized ferrite remains 5 electroplating 12 197 466 Good6 - 15 187 468 Good7 Plating byhot dipping 53 224 461 Good Insufficient ferrite transformation and cementite precipitation 8 - 42 223 475 Good Insufficient ferrite transformation and cementite precipitation 9 - 43 250 485 Good Insufficient ferrite recrystallization 10 - 48 220 495 Good Insufficient cementite precipitation
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Table 10
Kind ofsteel Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv D 1 - 51 211 468 Good Non-recrystallized ferrite remains 2 - 19 187 474 Good3 Hot dip galvanizingGalvanizing hot dip galvanizing 21 190 478 Good4 - 22 211 474 Good Insufficient ferrite transformation and cementite precipitation 5 - 18 208 478 Good Insufficient ferrite transformation and cementite precipitation 6 - 37 220 481 Good Insufficient ferrite transformation and cementite precipitation 7 - 31 214 479 Good Insufficient ferrite transformation 8 electroplating 9 193 474 Good9 - 35 214 481 Good Ferrite transformation and precipitation of
59/70
Petition 870190000733, of 04/01/2019, p. 68/96
Kind ofsteel Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv insufficient lying 10 - 14 190 478 GoodAND 1 - 24 210 539 Good2 Hot dip galvanizing 18 208 542 Good3 Hot dip galvanizing 17 207 539 Good4 - 24 248 545 Good Insufficient ferrite transformation and cementite precipitation 5 - 24 233 539 Good Insufficient ferrite transformation 6 - 28 257 536 Good Insufficient ferrite transformation and cementite precipitation 7 - 24 291 539 Good Insufficient ferrite transformation and cementite precipitation 8 - 13 191 521 Good9 - 15 185 533 GoodF 1 Coating with 21 196 478 Good
60/70
Petition 870190000733, of 04/01/2019, p. 69/96
Kind ofsteel Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv alloy cast aluminum2 - 15 187 481 Good3 Hot dip galvanizing 14 184 481 Good4 Hot dip galvanizing 12 185 484 Good5 - 40 202 484 Good Non-recrystallized ferrite remains
61/70
Petition 870190000733, of 04/01/2019, p. 70/96
Table 11
Kind ofsteel Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv G 1 - 21 194 465 Good2 electroplating 17 185 468 Good3 - 12 190 465 Good4 Hot dip galvanizing 12 187 456 Good5 - 47 208 456 Good Non-recrystallized ferrite remains H 1 - 21 190 349 Good Strength after hot stamping is less than 1180 MPa 2 - 32 208 346 Good I 1 - 40 254 - Good End portion fractures are generated when forming by hot stamping 2 - 46 260 - Good J 1 - 15 178 383 Good Hv is in the range even with the relative technique method for low capacity 2 - 18 179 386 Good
62/70
Petition 870190000733, of 04/01/2019, p. 71/96
Kind ofsteel Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Notehardening city. AHv Hv_Ave Hv K 1 - - - - Good Hot rolling is difficult L 1 - 21 199 484 Poor Poor chemical conversion coating M 1 - 43 233 545 Poor Poor chemical conversion coating N 1 - - - - Good Hot rolling is difficult O 1 - 9 187 383 Good AHv is in the range even with the relative technique method for low hardening capacity. 2 - 17 184 380 Good P 1 - 9 184 386 Good AHv is in the range even with the relative technique method for low hardening capacity. Q 1 Hot dip galvanizing 9 182 468 GoodR 1 - 19 216 513 Good
63/70
Petition 870190000733, of 04/01/2019, p. 72/96
Steel type in Condition No. Type of coating Variation of hardness in the non-hardened portion Hardness of the non-hardened portion Chemical conversion coating Note AHv Hv_Ave Hv s 1 - 12 186 466 GoodT 1 - - - - - Hot rolling is difficult
0Z / 1 9
Petition 870190000733, of 04/01/2019, p. 73/96
65/70 [00117] A steel having components of the steel material shown in Table 1 and Table 2 was melted and prepared, heated to 1200 ° C, laminated, and wound to a CT winding temperature shown in Tables 3 to 5, a steel strip having a thickness of 3.2 mm being produced. The rolling was carried out using a hot rolling line including seven finishing laminators. Tables 3 to 5 show the type of steel, condition No., hot rolling conditions for winding, and the condition of continuous annealing. Ac1 and Ac3 were measured experimentally using a steel plate having a thickness of 1.6 mm which was obtained by rolling with a cold rolling rate of 50%. For the measurement of Ac1 and Ac3, the measurement was performed from the expansion and contraction curve by formats, and values measured at a heating rate of 5 ° C / s are described in Table 1. Continuous annealing was performed for the steel strip at a heating rate of 5 ° C / s with conditions shown in Tables 3 to 5. In addition, in Tables 6 to 8, the resistance variation (ATS), the average resistance value (TS_Ave) are shown , the microstructure of the steel strip, Cre / CrM, and Mne / MnM acquired based on the tensile strength measured in 10 portions of the steel strip after continuous annealing. The fraction of the microstructure shown in Tables 6 to 8 was obtained by observing the cut and polished specimen with the optical microscope and measuring the ratio using a point counting method. After that, as shown in FIG. 5, an electrical heating was performed using an electrode 2 in relation to the steel plate 1 for hot pressing, thus heating the steel plate for hot pressing so that a heated portion 1-a and an unheated portion 1- b exist on the steel plate. Then, hot stamping was performed. The heated portion 1-a is heated at a heating rate of 30 ° C / s until the temperature reaches Ac3 + 50 ° C,
Petition 870190000733, of 04/01/2019, p. 74/96
66/70 and then, without performing temperature retention after heating, the mold was cooled to a cooling rate of not less than 20 ° C / s. The hardness of the unheated portion 1-b as shown in FIG. 5 was measured by obtaining the average value of five points using the Vickers hardness tester with a load of 5 kgf, in the cross section of 0.4 mm deep from the surface. Regarding the hot rolled coil, 30 parts are selected at random and the difference between the maximum hardness and the minimum hardness was obtained as ΔΗν, and its average was obtained as Hv_Ave. The minimum value of ΔΗν is significantly affected by the amount of C in the steel material, so the present invention employs the following criteria for the minimum value.
[00118] If the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%,. Hv <25 and Hv_Ave <200.
[00119] If the amount of C in the steel plate is equal to or greater than 0.25% and less than 0.3%,. Hv <32 and Hv_Ave <220.
[00120] If the amount of C in the steel plate is equal to or greater than 0.3% and less than 0.35%,. Hv <38 and Hv_Ave <240.
[00121] In the tensile test, samples of steel plates were extracted from the portions in 20 m from the initial location and the final location of the steel strip, and the tensile strength was acquired by performing tensile tests in the rolling direction. to obtain tensile strength values in the respective 5 portions in the width direction as measured portions.
[00122] As for the hardening capacity, if the chemical components are outside the range of the present invention, the hardening capacity is low and thus the variation in hardness or the increase in hardness in the production of the steel sheet as described in the opening of that specification does not occur. Consequently, when the hardness of the unheated portion of the component is measured
Petition 870190000733, of 04/01/2019, p. 75/96
67/70 after hot stamping, low hardness and low variation of hardness can be obtained stably even if the present invention is not employed. Therefore, this is considered to be outside the invention. More specifically, a product produced by employing a condition that is outside the range of the present invention but which satisfies the minimum AHv value mentioned above is considered to be outside of the present invention.
[00123] Then, using a pressing mold and a piece of steel plate that was cut from the produced steel plate and heated electrically with electrodes shown schematically in FIG. 5, the hot stamping was performed, thus producing a hot stamped component with a shape as illustrated in FIG., 4, In the hot stamping, the heating rate of the central portion was adjusted to be 50 ° C / s and the plate steel was heated to the highest heating temperature of 870 ° C. The final portion of the steel plate was an unheated portion since the electrode temperature was approximately room temperature. To easily generate the temperature variation in the steel plate depending on the areas of the steel plate, as shown in FIG. 4, the electrically heated steel plate with an electrode electric heating unit through which the cooling medium passes has been pressed. The mold used in the pressing was a hat-shaped mold, and R with a type of punch and mold was set to 5R. In addition, the heights of the vertical hat wall were 50 mm and the disc holding pressure was adjusted to 10 t.
[00124] Furthermore, since it is a precedent condition for using a hot stamping material in the present invention, a case where the maximum hardness in the hardened portion after hot stamping becomes less than Hv 400 is considered to be out of the invention. The maximum hardness of the hardened portion was measured
Petition 870190000733, of 04/01/2019, p. 76/96
68/70 in HARDNESS MEASUREMENT AREA FOR HARDENED PORTION as shown in FIG. 5 where the steel plate is heated to AC3 or more and is in direct contact with the mold. The measurement of the hardness was conducted by 30 components to obtain the average value as similar to the measurement of the hardness of the unheated portion as mentioned above.
[00125] For the chemical conversion coating, a phosphate crystal state was observed with five visual fields using a scanning electron microscope with a magnification of 10000x using = if an immersion agglutination liquid that is normally used, and it was determined as a pass if there was no clearance in the crystal state (Pass = or: good, Failed: poor).
[00126] Test examples A-1, A-2, A-3, B-1, B-2, B-5, B-6, C-1, C-2, C-5, C-6 , D-2, D-3, D-8, D-10, E-1, E-2, E-3, E-8, E-9, F-1, F-2, F3, F-4 , G-1, G-2, G-3, G-4, Q-1, R-1, and S-1 were determined to be good since they were in the range of conditions. In test examples A-4, C-4, D-1, D-9, F-5, and G-5, since the highest heating temperature was less than the range of the present invention, ferrite does not -recrystallized remained and AHv became high. In test examples A-5, B-3, and E-4, since the highest heating temperature at continuous annealing was greater than the range of the present invention, the austenite single phase structure was obtained at the highest temperature of heating, and the transformation of ferrite and the precipitation of cementite in the subsequent cooling and retention did not happen, the hard phase fraction after annealing became high, and Hv_Ave became high. In test examples A-6 and E-5, since the cooling rate from the highest heating temperature on continuous annealing was higher than the range of the present invention, the ferrite transformation did not occur sufficiently, and Hv_Ave has become high. In test examples A-7, D-4, D-5, DPetition 870190000733, of 04/01/2019, p. 77/96
69/70
6, and E-6, since the retention temperature at continuous annealing was less than the range of the present invention, the transformation of ferrite and precipitation of cementite were insufficient, and Hv_Ave became high. In test example D-7, since the retention temperature at continuous annealing was higher than the range of the present invention, the transformation of ferrite did not happen sufficiently, and Hv_Ave became high. In test examples A-8 and E-7, since the retention time on continuous annealing was shorter than the range of the present invention, the transformation of ferrite and precipitation of cementite were insufficient, and, Hv_Ave became tall. When comparing test examples B-1, C-2, and D-2 and test examples B-4, C-3, and D-6 which have similar production conditions in the type of steel that has almost same C concentration of the steel material and having different DIinch values of 3.5, 4.2 and 5.2, it was found that, when the DIinch value was large, the improvement of AHv and Hv_Ave was significant. Since type H steel had a C content of 0.16%, the hardness after quenching in the hot stamping became less, and was not suitable as a hot stamping component. Since steel type I has a large amount of 0.40% C. The forming capacity of the unheated portion was generated at the time of hot stamping. A type of steel J had a small amount of Mn of 0.82%, and the hardening capacity was low. Since type K and N steels respectively had a large amount of Mn of 3m82% and Ti of 0.310%, it was difficult to perform hot rolling, which is part of the production step of a stamped component. Since type L and M steels had respectively a large amount of Si of 1.32% and Al of 1.300%, the chemical conversion coating of the stamped component was degraded. Since type O steel had a small amount of B added and type P steel disintegrated
Petition 870190000733, of 04/01/2019, p. 78/96
70/70 insufficient use of N due to the addition of Ti, the hardening capacity was low.
[00127] In addition, as found in Tables 3 to 11, although the surface treatment due to the coating or the like has been carried out, the effects of the present invention have not been disturbed.
Industrial Applicability [00128] In accordance with the present invention, it is possible to provide a method for producing a hot stamped chassis that can suppress the variation in hardness in an un-hardened portion even if the steel sheet that is heated so as to having a heated portion and an unheated portion is hot-stamped, and a hot-stamped chassis that has a small variation in hardness in the un-hardened portion.

权利要求:
Claims (9)
[1]
1. Method for producing a hot stamped chassis, characterized by the fact that it comprises:
hot-laminate a plate containing chemical components that include, by weight%, 0.18% to 0.35% C, 1.0% to 3.0% Mn, 0.01% to 1.0% Si, 0.001% to 0.02% P, 0.0005% to 0.01% S, 0.001% to 0.01% N, 0.01% to 1.0% Al, 0.005% to 0 , 2% Ti, 0.0002% to 0.005% B, and 0.002% to 2.0% Cr, and the balance being Fe and the inevitable impurities, to obtain a hot-rolled steel sheet, wind the sheet hot-rolled steel that is subjected to hot rolling;
cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet;
continuously annealing the cold rolled steel sheet which is subjected to cold rolling to obtain a hot stamping steel sheet; and perform hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that there is the heated portion in which the highest heating temperature is equal to or greater than Ac3 ° C, and the unheated portion where the highest heating temperature is equal to or less than Ac1 ° C, where continuous annealing includes:
heat the cold-rolled steel sheet to a temperature range equal to or greater than Ac1 ° C and less than Ac3 ° C;
cooling the cold rolled steel sheet heated from the highest heating temperature to 660 ° C at a cooling rate equal to or less than 10 ° C / s; and keep the cold rolled steel sheet cooled in a
Petition 870190000733, of 04/01/2019, p. 80/96
[2]
2/5 temperature range from 550 ° C to 660 ° C for one minute to 10 minutes.
2. Method for the production of a chassis, according to claim 1, characterized by the fact that the chemical components also include one or more elements between 0.002% to 2.0% Mo, 0.002% to 2.0% Nb , 0.002% to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% Ca, 0.0005% to 0.0050% Mg, and 0.0005% to 0.0050% REM.
[3]
3. Method for producing a hot stamped chassis, according to claim 1, characterized by the fact that it also comprises executing any one between a hot dip galvanizing process, a galvanizing process, an aluminum coating process molten, a coating process with cast aluminum alloy and an electroplating process after continuous annealing.
[4]
4. Method for producing a hot stamped chassis, according to claim 2, characterized by the fact that it also comprises executing any one between a hot dip galvanizing process, a galvanizing process, an aluminum coating process molten, a coating process with cast aluminum alloy and an electroplating process after continuous annealing.
[5]
5. Method for producing a hot stamped chassis, characterized by the fact that it comprises:
hot-laminate the plate containing chemical components that include, in mass%, 0.18% to 0.35% of C, 1.0% to 3.0% of Mn, 0.01% to 1.0% of Si, 0.001% to 0.02% P, 0.0005% to 0.01% S, 0.001% to 0.01% N, 0.01% to 1.0% Al, 0.005% to 0 , 2% Ti, 0.0002% to 0.005% B, and 0.002% to 2.0% Cr, the balance being Fe and the inevitable impurities to obtain a hot-rolled steel plate;
Petition 870190000733, of 04/01/2019, p. 81/96
3/5 winding the hot rolled steel sheet which is subjected to hot rolling;
cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet;
continuously annealing the cold rolled steel sheet which is subjected to cold rolling to obtain a hot stamping steel sheet; and perform hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that there is the heated portion in which the highest heating temperature is equal to or greater than Ac3 ° C, and the unheated portion where the highest heating temperature is equal to or less than Ac1 ° C, where in hot rolling, in finishing hot rolling configured with a machine with 5 or more consecutive rolling chairs, lamination is performed by adjusting if the finishing hot rolling temperature FiT in a final laminator Fi in a temperature range of (Ac3 - 80) ° C to (Ac3 + 40) ° C, adjusting the time between the start of rolling in a laminator Fi-3 which is a machine prior to the final laminator Fi until the end of the lamination on the final laminator Fi to be equal to or greater than 2.5 seconds, and by adjusting the hot rolling temperature Fi-3T on the Fi- laminator 3 to be equal to or less than FiT + 100 ° C, and after retention in a temperature range of 600 ° C to Ar3 ° C for 3 seconds to 40 seconds, winding is performed, and continuous casting includes:
heat the cold rolled steel sheet to a temperature range equal to or greater than (Aci - 40) ° C and less than Ac3 ° C;
cool the cold rolled steel sheet heated from the highest heating temperature to 660 ° at a rate equal to or
Petition 870190000733, of 04/01/2019, p. 82/96
4/5 less than 10 ° C / s; and retain the cold-rolled steel sheet cooled over a temperature range of 450 ° C to 660 ° C for 20 seconds to 10 minutes.
[6]
6. Method for producing a hot stamped chassis, according to claim 5, characterized by the fact that the chemical components also include one or more elements between 0.002% to 2.0% Mo, 0.002% to 2.0 % Nb, 0.002% to 2.0% V, 0.002% to 2.0% Ni, 0.002% to 2.0% Cu, 0.002% to 2.0% Sn, 0.0005% to 0 .0050% Ca, 0.0005% to 0.0050% Mg, and 0.0005% to 0.0050% REM.
[7]
7. Method for producing a hot stamped chassis, according to claim 5, characterized by the fact that it also comprises executing any one between a hot dip galvanizing process, a galvanizing process, an aluminum coating process molten, a coating process with cast aluminum alloy and an electroplating process after continuous annealing.
[8]
8. Method for producing a hot stamped chassis, according to claim 6, characterized by the fact that it also comprises executing any one between a hot dip galvanizing process, a galvanizing process, an aluminum coating process molten, a coating process with cast aluminum alloy and an electroplating process after continuous annealing.
[9]
9. Hot stamped chassis, characterized by the fact that it is formed using the method for producing a hot stamped chassis, as defined in any one of claims 1 to 8, in which:
when the amount of C in the steel plate is equal to or greater than 0.18% and less than 0.25%, AHv is equal to or less than 25
Petition 870190000733, of 04/01/2019, p. 83/96
5/5 and Hv_Ave is equal to or less than 200;
when the amount of C in the steel plate is equal to or greater than 0.25% and less than 0.30%, AHv is equal to or less than 32 and Hv_Ave is equal to or less than 220; and when the amount of C in the steel plate is equal to or greater than 0.30% and less than 0.35%, AHv is equal to or less than 38 and Hv_Ave is equal to or less than 240, where AHv represents the variation in Vickers hardness of the unheated portion, and Hv_Ave represents an average Vickers hardness of the unheated portion.

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法律状态:
2018-10-09| B07A| Technical examination (opinion): publication of technical examination (opinion)|

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2019-02-26| B09A| Decision: intention to grant|

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2019-05-07| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 21/10/2011, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 21/10/2011, OBSERVADAS AS CONDICOES LEGAIS |

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2019-11-26| B25D| Requested change of name of applicant approved|Owner name: TOYOTA JIDOSHA KABUSHIKI KAISHA (JP) ; AISIN TAKAO |

优先权:

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申请号 | 申请日 | 专利标题

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JP2010-237249|2010-10-22|

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JP2010237249|2010-10-22|

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JP2010289527A|JP5752409B2|2010-12-27|2010-12-27|Manufacturing method of hot stamping molded product with small hardness variation and molded product thereof|

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JP2010-289527|2010-12-27|

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PCT/JP2011/074297|WO2012053636A1|2010-10-22|2011-10-21|Process for producing hot stamp molded article, and hot stamp molded article|

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