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    • 专利摘要:
    Patent Specification: "Hot-stamping element steel plate and method for producing it". The present invention relates to a steel plate for a hot stamping member containing, as a chemical composition, 0.10 mass% to 0.35 mass% of c; 0.01 mass% to 1.0 mass% of itself; 0.3 mass% to 2.3 mass% of mn; 0.01 mass% to 0.5 mass% of al; limited to 0.03% by weight or less of p; limited to 0.02 mass% or less of s; limited to 0.1% by weight or less than n; and a balance consisting of fe and the inevitable impurities, in which a standard deviation of the diameters of iron carbides that are contained in a region from a surface to a position 1/4 of the thickness of the steel plate is less than or equal to 0.8 µm.
    公开号:BR112013027213B1
    申请号:R112013027213-9
    申请日:2012-04-26
    公开日:2019-04-02
    发明作者:Hiroyuki Tanahashi；Jun Maki
    申请人:Nippon Steel & Sumitomo Metal Corporation；
    IPC主号:
    专利说明:

    Descriptive Report of the Invention Patent for STEEL SHEET FOR HOT STAMPING ELEMENT AND METHOD FOR THE PRODUCTION OF THE SAME.
    TECHNICAL FIELD [001] The present invention relates to a steel plate for a hot stamping element capable of desirably being used for hot stamping which is a forming method to obtain a high strength element, and a method of production.
    [002] Priority is claimed over Japanese Patent Application No. 2011-100019, filed on April 27, 2011, and the content of which is incorporated herein by reference.
    BACKGROUND OF THE TECHNIQUE [003] In the field of automobiles, construction machinery, and the like, there has been intense research on how to reduce mass using a high strength material. For example, in the automobile field, the number of high-strength steel plates used has constantly increased in order to suppress an increase in the mass of a vehicle, which is required to ensure safety in the event of a collision and to perform high and improve fuel efficiency to reduce carbon dioxide emissions.
    [004] In such an increase in the quantity of high-strength steel plates used, the most significant problem is a phenomenon called "deterioration in the capacity of fixing the shape" that is inevitably caused when the strength of a steel plate increases. The "deterioration in the capacity of fixing the shape" refers to the general term for a phenomenon in which the amount of spring effect after forming increases along with an increase in strength; and so, the desired shape is difficult to obtain. To solve a problem caused by such a phenomenon, a process (for example,
    Petition 870180144845, of 10/26/2018, p. 5/67
    2/54 recompression) that is unnecessary for a low strength material (a material having a superior fixing capacity or having no problem in fixing the shape) can be added, or the shape of the product can be changed.
    [005] As a method to solve this problem, a hot forming method called hot stamping attracted attention. In this hot forming method, a steel sheet (workpiece) is heated to a predetermined temperature (usually a temperature at which the steel sheet is in the austenite phase) to reduce strength (ie, promote forming) and then it is formed with a mold at a lower temperature (for example, room temperature) than that of the workpiece. With such a forming method, a workpiece can be easily shaped and a rapid cooling treatment (quenching) can be carried out using the temperature difference between the workpiece and the mold. Therefore, the strength of a shaped product can be guaranteed.
    [006] In relation to a steel plate suitable for this hot stamping and a method of forming it, several techniques are reported.
    [007] Patent Document 1 describes a steel sheet from which a member having superior impact properties and delayed fracture resistance can be obtained after hot forming (corresponding to hot stamping) by controlling the quantity of elements contained and of the relationships between the quantities of the elements to be in predetermined ranges.
    [008] Patent Document 2 describes a method for obtaining a high strength component by controlling the quantities of the elements contained and the relationships between the quantities of the elements and the relationships between the quantities of the elements to be
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    3/54 in predetermined ranges as described above; and heating the steel sheet in a nitriding atmosphere before forming. [009] Patent Document 3 describes means for obtaining a hot-pressed product at high productivity by specifying chemical components and a microstructure and limiting heating and forming conditions.
    [0010] Recently, the utility of hot stamping has been widely recognized, and the application of hot stamping has also been discussed for several elements. Such elements include, for example, a long component such as a vehicle's central pillar.
    [0011] The present inventors found that a small but certain amount of deflection occurred in such a long component, unlike a short component in which the deflection was negligible.
    [0012] The present inventors assume that the reason that deflection occurs is as follows: the cooling conditions during hot stamping are deviated from the ideal uniform conditions by an increase in the size of a component and, as a result, non-uniform stresses are introduced into the component.
    [0013] As a result of detailed investigations in relation to the reason for such unevenness, the present inventors had a feeling that the unevenness of stresses may be related to the variation in the carbon concentration of a steel sheet immediately before the hot stamping ( immediately before forming using a mold).
    [0014] As a result of the studies, it was discovered that in a heating process immediately before forming, dissolving behavior of iron carbides in a steel plate is the key to suppress the unevenness.
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    4/54 [0015] In general, a steel sheet for hot stamping includes the ferrite phase as the primary phase, pearlite and the like as the secondary phase, and a microstructure composed of iron carbides. In such a steel plate, the carbon produced from the iron carbides in the heating process before forming takes a solid solution in the austenite phase, this austenite phase is tempered to be transformed into a martensite phase and, as a result, a high resistance can be obtained. The resistance of the produced martensite phase depends strongly on the cooling conditions and the concentration of carbon that undergoes a solid solution in the austenite phase. Therefore, it can easily be assumed that a method of uniformly dissolving iron carbides in the heating process has a strong effect on the mechanical properties of a shaped product obtained in the subsequent process.
    [0016] In addition, as a result of detailed studies, the present inventors found that the uniformity of carbon concentration in the austenite phase was strongly affected not by the size (average size) of the iron carbides before heating, but by their size distribution . However, there are no examples of investigating a hot stamping steel plate from this point of view.
    [0017] Patent Documents 1 to 3 have no description regarding the carbide size distribution., [0018] Patent Documents 1 and 2 do not discuss under which conditions a cold-rolled steel sheet is annealed or investigate the control of carbides on a steel plate.
    [0019] Patent Document 3 does not even have a description regarding the history of heating, which is more important to control a carbide state during the annealing of a cold rolled steel sheet, nor does it investigate the carbide control.
    Petition 870180144845, of 10/26/2018, p. 8/67
    5/54 [0020] Patent Document 4 describes a technique in which the spheroidization ratio and the average particle diameter of the carbides are controlled to be in predetermined ranges, thus obtaining a steel sheet having superior local ductility and hardening capacity . However, Patent Document 4 has no description regarding the carbide size distribution.
    [0021] In addition, to obtain a predetermined metallographic structure, extremely special annealing is required, and production on a common type of continuous annealing equipment or continuous hot dip coating equipment is not considered. Therefore, in Patent Document 4, the annealing conditions are not regulated to control the carbide size distribution.
    [0022] Patent Document 5 describes a technique in which the average particle diameter of the iron carbides is controlled to be in a predetermined range, thereby obtaining a steel plate having greater stress stability under the conditions of heat treatment and resistance greater than delayed fracture. However, Patent Document 5 has no description regarding the carbide size distribution.
    [0023] Patent Document 5 neither describes the history of heating up to the maximum heating temperature nor does it describe in relation to the control of carbide size distribution.
    [0024] Patent Document 6 describes a technique in which the average ferrite particle diameter and the ratio of spheroidal carbides having a predetermined size for all spheroidal carbides are controlled to obtain a superior high carbon steel sheet in resistance to wear. However, Patent Document 6 has no description regarding the size distribution
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    6/54 of the carbides.
    [0025] In addition, in order to obtain a predetermined steel sheet, it is necessary that the hot-rolled steel sheet and the cold-rolled steel sheet be annealed many times over a long time. In addition, production on a common type of continuous annealing equipment or continuous hot dip coating equipment is not considered. Therefore, in Patent Document 6, the annealing conditions are not regulated to control the carbide size distribution.
    [0026] Patent Document 7 describes a technique in which the average diameter of the particular ferrite and the average particle diameter of the carbides are controlled to obtain a high-strength steel plate of medium or high carbon that has superior grouping quality . However, Patent Document 7 has no description regarding the carbide size distribution.
    [0027] In addition, Patent Document 7 describes a cold rolled steel sheet in the state as cold rolled, and a cold rolled steel sheet that is annealed under low temperature annealing conditions of 350 ° C at 700 ° C and a long time of 10 hours to 40 hours. In addition, production and a common type of continuous annealing equipment or continuous hot dip coating equipment is not considered. Therefore, in Patent Document 7, the conditions of continuous annealing are not regulated to control the carbide size distribution.
    [0028] As a result of the study, the present inventors found that the size distribution of the iron carbides had a close relationship with the change in the rate of increase in the temperature of the steel sheet during the heating of a cold rolled steel sheet. However, there are no examples of research on a method of producing a hot stamped steel sheet
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    7/54 from that point of view.
    PREVIOUS TECHNICAL DOCUMENTS
    PATENT DOCUMENT [0029] [Patent Document 1] Unexamined Japanese Patent Application, First Publication No. 2005-139485 [0030] [Patent Document 2] Unexamined Japanese Patent Application, First Publication No. 2005-200670 [ 0031] [Patent Document 3] Unexamined Japanese Patent Application, First Publication No. 2005-205477 [0032] [Patent Document 4] Unexamined Japanese Patent Application, First Publication No. H11-80884 [0033] [Document Patent 5] Unexamined Japanese Patent Application, First Publication No. 2003-268489 [0034] [Patent Document 6] Unexamined Japanese Patent Application, First Publication No. 2006-274348 [0035] [Patent Document 7] Unexamined Japanese Patent Application, First Publication No. 2006-291236
    DESCRIPTION OF THE INVENTION
    PROBLEM THAT THE INVENTION SHOULD SOLVE [0036] In view of the circumstances described above, the present invention should provide a steel plate for a stamping member in which the size distribution of iron carbides in the steel plate is controlled in order to reduce the deflection that occurs easily when a long component is produced by hot stamping; and a method of producing it.
    MEANS TO SOLVE THE PROBLEMS [0037] To solve the problems described above, the present inventors studied deeply. As a result, it was discovered that when the distribution of iron carbide diameters that were contained in a region from the surface to a position
    Petition 870180144845, of 10/26/2018, p. 11/67
    8/54 at 1/4 of the thickness of a steel sheet was in a predetermined range, the deflection of a shaped component can be significantly effectively suppressed regardless of the variation in cooling conditions during forming. In addition, it has been found that such a steel sheet can be obtained by controlling the conditions when a cold rolled steel sheet has been annealed for recrystallization, thus completing the present invention after trial and error.
    THE SUMMARY OF THE SAME IS AS FOLLOWS.
    [0038] (1) In accordance with one aspect of the invention, a steel sheet is provided for a hot stamping member, the steel sheet including, as a chemical composition, 0.10% by weight at 0.35% by weight mass of C; 0.01 mass% to 1.0 mass% of Si; 0.3 mass% to 2.3 mass% of Mn; 0.01 wt% to 0.5 wt% Al; limited to 0.03 wt% or less of P, limited to 0.02 wt% or less of S; limited to 0.1% by weight or less of N; and a balance consisting of Fe and the inevitable impurities, in which the standard deviation of the diameters of iron carbides that are contained in a region from the surface to a position 1/4 of the thickness of the steel sheet is less than or equal to 0.8 mm.
    [0039] (2) In the steel plate for a hot stamped member according to item (1), the chemical composition may also contain one or more elements selected from the group consisting of 0.01% by weight at 2.0 % by mass of Cr; 0.001% by mass to 0.5% by weight of Ti; 0.001% by mass to 0.5% by weight of Nb; 0.0005 mass% to 0.01 mass% of B; 0.01 wt% to 1.0 wt% Mo; 0.01 mass% to 0.5 mass% W; 0.01 mass% to 0.5 mass% of V; 0.01 wt% to 1.0 wt% Cu; and 0.01 wt% to 5.0 wt% of Ni.
    [0040] (3) On steel plate for a stamping member to
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    9/54 hot according to item (1) or (2), a coating layer of Al having a coating thickness of 50 mm or less can be formed on the surface.
    [0041] (4) In the steel plate for a hot stamping member according to item (1) or (2), a coating layer of Zn having a coating thickness of 30 mm or less can be formed on the surface.
    [0042] (5) In the steel plate for a hot stamping member according to item (1) or (2), a layer of Zn-Fe alloy having a coating thickness of 45 mm or less can be formed on the surface .
    [0043] (6) According to another aspect of the invention, a method of producing a steel sheet for a hot stamping member is provided, the method including performing a recrystallization annealing process in which a laminated steel sheet cold is heated so that the change d / dt (DT / Dt; ° C / s 2 ) at a rate of increase in the temperature of the steel plate from 300 ° C to a maximum temperature S satisfies the expression 1 below and so that the maximum temperature S is 720 ° C to 820 ° C, where T represents the temperature of the steel plate (° C), t represents the time (seconds), and DT / Dt represents the rate of increase (° C / s) of the temperature of the steel sheet for a time Dt (seconds) during the heating of the recrystallization annealing process, and where the cold rolled steel sheet contains, as a chemical composition, during the heating of the recrystallization annealing process , and where the cold rolled steel sheet contains, as a composition mica, 0.10 mass% to 0.35 mass% of C; 0.01 mass% to 1.0 mass% of Si; 0.3 mass% to 2.3 mass% of Mn; 0.01 wt% to 0.5 wt% Al; limited to 0.03% by weight or less than P; limited to 0.02% by weight or less of S; limited to 0.1% by mass or mePetition 870180144845, of 10/26/2018, p. 13/67
    10/54 in N; and a balance consisting of Fe and the inevitable impurities.
    -0.20 <d / dt (DT / Dt) <0 (Expression 1) [0044] (7) In the method of producing a steel plate for hot stamping members according to item (6), the chemical composition it may also contain one or more elements selected from the group consisting of 0.01 wt% to 2.0 wt% Cr; 0.001% by mass to 0.5% by weight of Ti; 0.001% by mass to 0.5% by weight of Nb; 0.0005 mass% to 0.01 mass% of B; 0.01 wt% to 1.0 wt% Mo; 0.01 mass% to 0.5 mass% W; 0.01 mass% to 0.5 mass% of V; 0.01 wt% to 1.0 wt% Cu; and 0.01 wt% to 5.0 wt% of Ni.
    [0045] (8) In the method of producing a steel plate for a hot stamping member according to item (6) or (7), the change d / dt (DT / Dt) can be twice a coefficient of one second degree variable when the temperature is read at a time interval of 10 seconds or less from the temperature history during the heating of the recrystallization annealing process and then a polynomial approximation curve of the second degree is determined so that the coefficient of determination R 2 is greater than or equal to 0.99.
    [0046] (9) The method of producing a steel plate for a hot stamping member according to any of items (6) to (8), after the recrystallization annealing process, may also include dipping the plate. cold rolled steel in an Al bath to form a layer of Al coating on a cold rolled steel sheet surface.
    [0047] (10) The method of producing a steel plate for a hot stamping member according to any of items (6) to (8), after the recrystallization annealing process, can also
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    11/54 also include dipping the cold rolled steel sheet in a Zn bath to form a layer of Zn coating on a surface of the cold rolled steel sheet.
    [0048] (11) The method of producing a steel plate for a hot stamping member according to any of items (6) to (8), after the recrystallization annealing process, may also include dipping the plate. cold rolled steel in a Zn bath to form a Zn coating layer on a cold rolled steel sheet surface; and heating the cold rolled steel sheet to 600 ° C or less to form a layer of Zn-Fe alloy on a surface of the cold rolled steel sheet.
    ADVANTAGE OF THE INVENTION [0049] With the steel sheet for a hot-stamping member depending on the aspect, the deflection of a long shaped product that is shaped into a widely known type of hot stamping equipment is extremely small. Therefore, when this shaped product is connected with another component, there is a low possibility of defects. For the reason described above, the steel sheet for a hot stamping member according to the aspect has an effect of increasing the hot stamping application (component) range.
    [0050] In addition, with the steel plate for a hot stamping member according to item (3) to (5), the Zn coating layer, and the Zn-Fe alloy layer that had small defects such as such as exfoliation, desquamation and fractures after hot stamping can be achieved. Therefore, in that case, the corrosion resistance and surface quality of the steel sheet for a hot stamping member can also be improved.
    [0051] In addition, in the method of producing a steel plate for a hot-stamping member according to the aspect, an equipment
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    12/54 existing steelmaking equipment can be used. In addition, even when a long shaped product is produced by hot stamping, a steel sheet can be provided for a hot stamping member capable of significantly reducing deflection.
    [0052] In addition, in the method of producing a steel plate for a hot stamping member according to item (9) to (11), the corrosion resistance and surface quality of the steel plate for a stamping member hot can also be improved.
    BRIEF DESCRIPTION OF THE DRAWINGS [0053] FIG. 1A is a perspective view showing a die (steel sheet) before being formed using hot stamping.
    [0054] FIG. 1B is a perspective view showing a steel shape after forming using hot stamping.
    [0055] FIG. 2 is a side view illustrating a method of measuring the deflection of a long component.
    [0056] FIG. 3 is a perspective view illustrating a method of stamping a die (steel sheet) onto a sheet using hot stamping.
    [0057] FIG. 4 is a graph illustrating the relationship between the standard deviation of iron carbide sizes and deflection when the heating conditions before hot stamping are a temperature of 900 ° C and a time of 1 minute in Example 1.
    [0058] FIG. 5 is a graph illustrating the relationship between standard deviation of iron carbide sizes and deflection when the heating conditions prior to hot stamping are a temperature of 900 ° C and a time of 10 minutes in Example 1.
    [0059] FIG. 6 is a graph illustrating the relationship between d / dt (DT / Dt)
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    13/54 and the standard deviation of iron carbide sizes in Example
    1.
    [0060] FIG. 7 is a diagram illustrating the temperature history of a steel sheet from the start of heating to the maximum temperature in Examples 3, 4 and 5.
    MODALITIES OF THE INVENTION [0061] The present inventors prepared a hot stamping member using a steel sheet containing C: 0.22% by mass, Si: 0.3% by mass, and Mn: 1.2% by mass, and carried out studies to evaluate their properties. The present inventors have investigated the actual conditions of deflection in detail particularly in consideration of the application to a long component. During the investigation, it was discovered that, even when steel sheets having substantially the same chemical components and the same tensile strength were hot stamped under the same conditions, there was a difference between the deflection sizes of the shaped products. Therefore, as a result of the detailed investigation regarding the reason why there was a difference in the deflection size between the steel sheets, the present inventors found that (i) there was a difference between the variations in the hardness of the portions close to the surface of the products conformed in comparison with the steel sheets between them; (ii) this difference was caused by an iron carbide size distribution in a portion close to the surface of a steel plate before hot stamping; and (iii) to obtain the desired size distribution of iron carbides, it was preferable that the conditions of the recrystallization annealing of a cold rolled steel sheet are controlled in a predetermined range.
    [0062] Although their details are described in the Examples, the present inventors have experimentally discovered a distribution
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    14/54 of suitable sizes of the iron carbides and suitable annealing conditions based on the results of these experiments, thus completing the invention.
    [0063] Hereinafter, a steel sheet for a hot stamping member (steel sheet) will be described according to an embodiment of the invention.
    [0064] Initially, the chemical components of the steel plate will be described. Henceforth, "%" of each chemical component represents "% by mass".
    <C: 0.10% to 0.35%>
    [0065] C is the most important element from the point of view of increasing the strength of the steel sheet using hot stamping. To obtain the strength of at least approximately 1200 MPa after hot stamping, the C content in the steel is controlled to be greater than or equal to 0.10%. On the other hand, when the C content in the steel plate is greater than 0.35%, there is a concern about the deterioration of toughness. Therefore, the upper limit of the C content is adjusted to 0.35%. To also improve toughness, the C content is preferably less than or equal to 0.32% and more preferably less than or equal to 0.30%.
    Si: 0.01% to 1.0%>
    [0066] Si is a solute reinforcing element, and 0.01% Si can be effectively used as a solute reinforcing element. However, when the Si content in steel is greater than 1.0%, there is a concern that defects may be caused during chemical conversion coating or coating after hot stamping. Therefore, the upper limit of the Si content is adjusted to 1.0%. The lower limit of Si content is not particularly limited, and the effect of controlling iron carbides can be obtained independently of the lower limit. However, when the content is reduced more than necessary, the
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    15/54 steel production load increases. Therefore, the Si content is controlled to be greater than or equal to 0.01%. The lower limit of the Si content is a reference value of Si that is contained in the steel due to deoxidation. To perform a more stable surface treatment, the Si content is preferably less than or equal to 0.9% and more preferably less than or equal to 0.8%.
    <Mn: 0.3% to 2.3%>
    [0067] Like Si, Mn works as a solute reinforcing element and is also an effective element to increase the hardening capacity of the steel sheet. In order to reliably obtain the effects of improving strength and hardening capacity, the Mn content in steel is controlled to be greater than or equal to 0.3%. However, when the Mn content in steel is greater than 2.3%, the effects are saturated. Therefore, the upper limit of the Mn content is adjusted to 2.3%. To also increase the strength, the Mn content is preferably greater than or equal to 0.5% and more preferably greater than or equal to 1.0%.
    <P: 0.03% or less>, <S: 0.02% or less>
    [0068] Both elements are impurities and have an adverse effect on the ability to work hot. Therefore, P is limited to be less than or equal to 0.03%, and S is limited to be less than or equal to 0.02%.
    <Al: 0.01% to 0.5%>
    [0069] Since Al is preferable as a deoxidation element, the Al content in steel can be greater than or equal to 0.01%. However, when a large amount of Al is contained in the steel, crude oxides are formed and thus the mechanical properties of the steel plates deteriorate. Therefore, the upper limit of the Al content is adjusted to 0.5%.
    <N: 0.1% or less>
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    16/54 [0070] Since N is easily linked with Ti and B, and the N content is controlled to be less than or equal to 0.1 so that the desired effects of Ti and B are reduced. To increase toughness, it is preferable that the N content is small, for example, preferably less than or equal to 0.01%. When the N content is reduced more than necessary, a huge load is applied to the steelmaking process. Therefore, the reference value of the lower limit of the N content can be adjusted to 0.0010%.
    [0071] The chemical elements described above are basic components (basic elements) of steel according to the modality. A chemical composition in which the basic elements are controlled (contained or limited), and its balance is iron and the inevitable impurities, is a basic composition depending on the modality. However, in addition to these basic components (instead of a part of the balance Fe), steel according to the modality may optionally also contain the following chemical elements (optional elements) are inevitably incorporated (for example, the content of each optional element) less than the lower limit) in steel, the effects of the modality do not deteriorate.
    [0072] That is, optionally, steel according to the modality may also contain one or more optional elements selected from the group consisting of Cr, Ti, Nb, B, Mo, W, V, Cu, and Ni. To reduce the cost of the connection, it is not necessary that these optional elements are intentionally added to the steel, and all the lower limits of the contents of Cr, Ti, Nb, B, Mo, W, V, Cu, and Ni are 0%.
    <Cr: 0.01% to 2.0%>
    [0073] Cr is an element that has the effect of increasing the hardening capacity and is thus used properly. To obtain the effect safely, the Cr content is controlled to be greater than or equal to 0.01%. On the other hand, even when Cr having a content of 2.0
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    17/54 or more is added to the steel, the effect is saturated. Therefore, the upper limit of the Cr content is adjusted to 2.0%.
    <Ti: 0.001% to 0.5%>
    [0074] Ti serves to stably bring about an effect of B (described below) through the formation of nitrides, and thus is a useful element. To obtain this effect safely, the Ti content is preferably greater than or equal to 0.001%. On the other hand, when Ti foot is excessively added to steel, nitrides are formed excessively and the toughness and trimming properties of the surface deteriorate. Therefore, the upper limit of the Ti content is adjusted to 0.5%.
    <Nb: 0.001% to 0.5%>
    [0075] Nb forms carbonitrides, increases the strength of the steel, thus making it a useful element. To obtain the effect of increasing strength safely, the Nb content in steel is preferably greater than or equal to 0.001%. However, when Nb having a content greater than 0.5% is contained in the steel, there is a concern that the hot rolling control capacity may deteriorate. Therefore, the upper limit of the Nb content is adjusted to 0.5%.
    <B: 0.0005% to 0.01%>
    [0076] B is an element that increases the hardening capacity. When the B content in steel is greater than or equal to 0.0005%, the effect of increasing the hardening capacity can be obtained safely. On the other hand, the excessive addition of B leads to the deterioration of the hot working capacity and the deterioration of ductility. Therefore, the upper limit of the B content is adjusted to 0.01%.
    <Mo: 0.01% to 1.0%>, <W: 0.01% to 0.5%>, <V: 0.01% s 0.5%>
    [0077] These elements are elements that have the effect of increasing the hardening capacity and thus can be used properly. To obtain the effect with confidence, the content of each element is controlled to be greater than or equal to 0.01%. For another
    Petition 870180144845, of 10/26/2018, p. 21/67
    On the other hand, since Mo, W and V are expensive elements, it is preferable that the concentration at which the effect is saturated is adjusted as an upper limit. It is preferable that the upper limit of the Mo content is 1.0; and the upper limit of the W and V content is 0.5%.
    Cu: 0.01% to 1.0%>
    [0078] Cu has the effect of increasing the strength of the steel sheet by adding Cu having a content of 0.01% or more to steel. On the other hand, since the excessive addition of Cu leads to deterioration in the surface quality of a hot-rolled steel sheet, the upper limit of the Cu content is adjusted to 1.0%. Therefore, the Cu content can be 0.01% to 1.0%.
    <Ni: 0.01% to 5.0%>
    [0079] Ni has an effect of increasing the hardening capacity and thus is a useful element. When the Ni content is greater than or equal to 0.01%, the effect is achieved safely. On the other hand, since Ni is an expensive element, the upper limit of the Ni content is adjusted to 5.0% at which the effect is saturated. Therefore, the Ni content can be 0.01% to 5.0%. In addition, since Ni serves to suppress the deterioration in the surface quality of a hot rolled steel plate caused by Cu, it is preferable that Ni is contained together with Cu.
    [0080] In the modality, a component different from the components described above is Fe. Inevitable impurities that are incorporated from a dissolved raw material such as scrap, a refractory and the like are allowed as another component different from the components described above.
    [0081] As described above, the steel plate according to the modality has the chemical composition that contains the basic elements described above and the balance consisting of Fe and the inevitable impurities, or the chemical composition that contains the basic elements above.
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    19/54 ma described, at least one element selected from the group consisting of the optional elements described above, and the balance consisting of Fe and the inevitable impurities.
    c Standard Deviation of Iron Carbide Diameters Included in the Region from the Surface to the position at 1/4 of the Thickness: 0.8 mm or less>
    [0082] The distribution of iron carbide sizes is the most important factor in the modality.
    [0083] According to the study of the present inventors, it was discovered that the size of the deflection, which is observed in a long shaped component using hot stamping, strongly depended on the variation in the hardness of a portion close to the surface of the plate. steel, and the variation in carbon concentration before hot stamping. In addition, it was discovered that when the sizes of the iron carbides were more uniform, the variation in the carbon concentration can be reduced.
    [0084] The greater the degree of uniformity of the sizes of iron carbides, the greater the degree of uniformity of the dissolution behaviors of iron carbides in the heating process before hot stamping. Therefore, the carbon concentration in the austenite phase is more easily made uniform. As a result, the variation in hardness is reduced, and the deflection of a member is also supposed to be reduced.
    [0085] The ratio between the size of the deflection and the variation in hardness is not entirely clear. However, presumably, this relationship is considered to have a relationship with the following mechanism. That is, among the control factors (degree of carbon supersaturation, displacement density, degree of refinement of an organization unit (for example, a slat or block), and a state of reprecipitated iron carbides) of the hardness of the produced martensite phase
    Petition 870180144845, of 10/26/2018, p. 23/67
    20/54 per quench, particularly when there is a variation in the displacement density of a portion close to the surface of a component, an uneven uniform stress is easily induced in the component. In this case, when it is attempted that an uneven uniform stress is released after the component is released from a stamping mold, deflection occurs.
    [0086] The deflection of a shaped product that is shaped using hot stamping is defined as follows.
    That is, with a method illustrated schematically in Figures 1A and 1B, a matrix 11 is formed into a steel plate 12, and the steel shape 12 is released from the mold. Then, as illustrated in FIG. 2, the steel shape 12 is set upright on the surface of the plate 21, When this steel shape 12 is seen in the width direction (in a side view), the distance d (mm) from a line connecting both the sides of the steel form 12 in the longitudinal direction towards the center of the steel form 12 in the longitudinal direction is defined as a deflection of the steel sheet 12.
    [0088] In this case, in relation to the size of the steel plate (die) 11 before hot stamping, the width W is 170 mm and the length L is 1000 mm. From the steel plate 11, the shape of the equilateral steel 12 with a base having a size of approximately 70 mm is obtained. When the deflection d is less than or equal to 5 mm, it is assessed that the deflection is suppressed.
    [0089] The shaped product described above (steel shape 12) is merely an example of shaped product that is prepared to evaluate the deflection d when the steel sheet according to the modality is shaped. The steel sheet according to the modality can be applied to various forms of products formed under various conditions of hot stamping.
    [0090] The deflection of a shaped product is reduced when the
    Petition 870180144845, of 10/26/2018, p. 24/67
    21/54 length of the shaped product is shorter than 1000 mm or when the width of the shaped product is greater than 170 mm. When the steel sheet according to the modality is applied to such a shaped product the modality is applied to such a shaped product, an effect of also suppressing the deflection d of the shaped product can be obtained.
    [0091] In the modality, the standard deviation of the diameters of iron carbides, which are contained in a region from the surface to a position 1/4 of the thickness (position that is distant from the surface of the steel sheet by 1 / 4 of the thickness in the direction through the thickness) of the steel plate, is controlled to be less than or equal to 0.8 mm. When this standard deviation is greater than 0.8 mm, the deflection d of a shaped product is greater than 5 mm, and it is determined that the deflection is not tolerable.
    [0092] The size distribution of iron carbides is measured as follows.
    [0093] That is, initially a section parallel to the rolling direction of the steel plate (section that includes the direction through the thickness) is polished and is properly treated with a strong acid used to etch “etchant” that emerges from the carbide (for example, a Picric acid in ethanol “etchant picral”). Then, using a scanning electron microscope, the section range from the surface to a position 1/4 of the thickness of the steel plate is observed continuously at a magnification of 5000 times. The microscopic field is enlarged until the number of iron carbides measured is at least 600. As the size (diameter) of an iron carbide, the average size of the longest and shortest side of the iron carbide is used. Based on the size data obtained from the iron carbides, the standard deviation is calculated. To calculate the standard deviation, commercially available statistical software can be used.
    Petition 870180144845, of 10/26/2018, p. 25/67
    22/54
    With such a measurement method, iron carbides having a size of approximately 0.1 mm or larger are measured. Consequently, the average size of iron carbides can be greater than or equal to 0.5 mm or greater than or equal to 1 mm. When the standard deviation of iron carbide diameters is less than or equal to 0.8 mm, the average size of iron carbides is not particularly limited, but can be, for example, less than or equal to 5 mm or less than or equal to 3 mm.
    [0094] The thickness (coating thickness) of an Al coating layer, and of a Zn-Fe alloy layer has no effect on the deflection of a component after hot stamping. However, when these thicknesses are excessively large, there is a concern that they may have an effect on the forming capacity. As described below in the Examples, when the thickness of an Al coating layer is greater than 50 mm, skinning occurs; when the thickness of a Zn coating layer is greater than 30 mm, Zn often adheres to the mold and when the thickness of the Zn alloy layer is greater than 45 mm, fractures are observed in many portions of the alloy layer. Thus, when the thickness of each layer is excessively large, productivity deteriorates. Therefore, in relation to the thickness of these layers, the thickness of an Al coating layer can be limited to less than or equal to 50 mm, the thickness of a Zn alloy layer can be limited to less than or equal to 30 mm, and the thickness of a layer of Zn-Fe alloy can be limited to less than or equal to 45 mm.
    [0095] When these layers are thin, there are no problems regarding the conformability. Meantime. From the point of view of corrosion resistance, which is the purpose of the formation of these layers, the lower limit of the thickness of each layer can be adjusted.
    Petition 870180144845, of 10/26/2018, p. 26/67
    23/54 as follows. That is, the thickness of an Al coating layer is preferably greater than or equal to 10 mm. In addition, the thickness of the Zn coating layer is preferably greater than or equal to 5 mm and more preferably greater than or equal to 10 mm. The thickness of a layer of Zn-Fe alloy is preferably greater than or equal to 10 mm and more preferably greater than or equal to 15 mm.
    [0096] In the steel sheet having a surface on which an Al coating layer, a Zn coating layer and a Zn-Fe alloy coating layer is formed, "surface" is defined as follows.
    [0097] Initially, a layer of Al coating of the steel plate according to the modality includes two layers of an external layer containing Al as the main component and an internal layer (lateral layer of the steel plate) that is considered to be formed by the reaction de Al and Fe. The boundary between this inner layer and the steel plate (coated steel plate) is defined as the surface of the steel plate.
    [0098] Next, a coating layer of Zn of the steel plate according to the modality includes two layers of an external layer containing Zn as the main component and an internal layer (lateral layer of the steel plate) that is formed by the reaction of Fe and a small amount of Al added to the Zn bath. The boundary between this inner layer and the steel sheet (coated steel sheet) is defined as the surface of the steel sheet.
    [0099] In addition, a layer of Zn-Fe alloy of the steel plate according to the modality includes multiple layers of alloy containing Zn and Fe. The boundary between the innermost side layer (lateral layer of the steel plate) between these multiple alloy layers and the steel plate (coated steel plate) is defined as the surface of the plate
    Petition 870180144845, of 10/26/2018, p. 27/67
    24/54 steel.
    [00100] Finally, a method of producing a steel sheet for a hot stamping member will be described in accordance with an embodiment of the present invention.
    [00101] In the method of production of the steel plate according to the modality, the production of the steel, the casting, the hot rolling, and the cold rolling are carried out with a common method, thus obtaining a cold rolled steel plate. In the steel production process, chemical components of the steel are controlled in order to satisfy the chemical composition according to the modality described above, and the steel obtained is used as a plate for continuous casting. The hot lamination of the obtained plate (steel) starts, for example, at a heating temperature of 1300 ° C or less (for example, 1000 ° C to 1300 ° C) and ends at around 900 ° C (for example , 850 ° C to 950 ° C). The winding temperature can be adjusted to around 600 ° C (for example, 450 ° C to 800 ° C). The reduction of hot rolling can be adjusted to 60% to 90%. The hot-rolled steel sheet (steel) obtained after winding is cold-rolled through a pickling process. The reduction of cold rolling can be adjusted to 30% to 90%. The annealing for recrystallization of the cold rolled steel sheet produced as above is extremely important. Using continuous annealing equipment, the plate temperature (plate temperature) from 300 ° C to a maximum temperature S (° C) satisfies Expression (1) below and so that the maximum temperature S is 730 ° C to 820 ° C.
    0.2 <d / dt (DT / Dt) <0 (Expression 1) [00102] In this Expression, T represents the temperature of the steel plate (° C), t represents the time (seconds), DT / Dt represents the change (° C) in the temperature of the steel plate for a time Dt (seconds) during the heating of the recrystallization annealing process,
    Petition 870180144845, of 10/26/2018, p. 28/67
    25/54 ed / dt (ΔΤ / Dt) represents the change (° C / s 2 ) in the rate of increase in the temperature of the steel sheet from 500 ° C to the maximum temperature S. A criterion based on which t is 0 ( zero) is not particularly limited and, for example, can be a time when a time to start heating the recrystallization annealing process or a time when the temperature reaches 300Ό due to heating the recrystallization annealing process.
    [00103] These conditions are determined based on the results of the experiments described below in the Examples.
    [00104] The temperature of the steel plate during annealing is measured using a radiation thermometer provided in an annealing equipment previously or a thermocouple provided in the steel plate. The temperature history of a steel plate obtained as above and expressed by a quadratic function of time, and a second differential coefficient of that quadratic function is determined as d / dt (ΔΤ / Dt). The quadratic function is obtained with a method in which the temperature of the steel plate is read in a short time (10 seconds or less, or preferably 5 seconds or less) from the temperature history described above to prepare a temperature adjustment. data (t, T); a graph of these data adjustments is generated using (again) commercially available spreadsheet software; and this graph is approximated by a polynomial of the second degree ..
    [00105] When the cold rolled steel sheet is annealed for recrystallization under these conditions, a steel sheet is obtained in which the standard deviation of the diameters of the iron carbides that are contained in a region from the surface to a position a 1/4 of the thickness of the steel sheet is less than or equal to 0.8 mm. However, the reason for this is not clear. For example, in an annealing process in which the rate of increase in the temperature of a plate
    Petition 870180144845, of 10/26/2018, p. 29/67
    26/54 of steel is gradually reduced, the progress of recrystallization and the dissolution of the initial iron carbides are supposed to be well balanced, and thus the uniformity of a distribution of iron carbides in the annealed steel sheet is increased.
    [00106] Heating conditions from room temperature to 300 ° C are not particularly limited.
    [00107] After the temperature of the steel plate reaches the temperature S, the steel plate can be kept at temperature S for a short period of time or can proceed to the cooling process immediately. When the steel sheet is maintained at a temperature S, the retention time is preferably less than or equal to 180 seconds, and more preferably mentor than or equal to 120 seconds from the point of view of suppressing the hardening of the grains.
    [00108] The rate of cooling from temperature S is not particularly limited, but it is preferable that rapid cooling in which the average rate of cooling is greater than or equal to 30 ° C / s is avoided. Most steel sheets for hot stamping are supplied for hot stamping after being trimmed to a predetermined shape. Therefore, when rapid cooling is performed after annealing, the trimming load increases and so there is a concern that production efficiency may decrease.
    [00109] The steel sheet can be cooled to room temperature after annealing, or it can be dipped in a bath of molten Al while being cooled to form a layer of Al coating on the surface of the steel sheet.
    [00110] The molten Al bath can contain 0.1% to 20% Si.
    [00111] The Si contained in the Al coating layer has an effect on the reaction of Al and Fe that is caused before hot stamping and during heating. An excessive reaction can harm
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    27/54 characterize the forming capacity by pressing the coating layer. On the other hand, an excessive suppression of the reaction can lead to Al's adherence in the press mold. To avoid such problems, the Si content in the Al coating layer is preferably 1% to 15%, and more preferably 3% to 12%.
    [00112] In addition, during cooling and after annealing, the steel sheet can be dipped in a bath of molten Zn to form a layer of Zn coating on the surface of the steel sheet.
    [00113] In addition, the steel sheet can be dipped and a molten Zn bath to form a Zn coating layer on the surface of the steel sheet, and the steel sheet on which the Zn coating layer is formed can be heated to 600 ° C or less to form a layer of Zn-Fe alloy on the surface of the steel sheet. The lower limit of the connection temperature is not particularly limited, and can be, for example, 450 ° C.
    [00114] The molten Zn bath may contain 0.01% to 3% Al.
    [00115] Al in the molten Zn bath has a strong effect on a Zn and Fe reaction. When the Zn coating layer is formed, the interdiffusion between Zn and Fe can be suppressed due to interference from a Fe reaction layer and Al. On the other hand, when a layer of Zn-Fe alloy is formed, Al can be used to control the desired layer to be a main layer between multiple layers having different properties such as workability and adhesion with steel.
    [00116] These effects can be developed when the molten Zn bath contains 0.01% to 3% Al. The concentration of Al can be selected by the producer according to the capacity of the production equipment and the purpose.
    [00117] As in the modality described above, in this modality the
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    Thicknesses (coating thicknesses) of an Al coating layer, a Zn layer, and a Zn-Fe alloy layer can be controlled to be less than or equal to a predetermined thickness. That is, it is preferable that the coating thickness of an Al coating layer is less than or equal to 50 mm; the coating thickness of a Zn coating layer is less than or equal to 30 mm; and the coating thickness of a layer of Zn-Fe alloy is less than or equal to 45 mm.
    [00118] The steel sheet for a hot stamping member according to the invention has the effects of the invention regardless of the thickness of the sheet and the strength after hot stamping. However, it is preferable that the steel sheet is handled like a steel strip from the point of view of ensuring high productivity in the respective processes, from hot rolling, cold rolling, annealing and coating (forming a coating layer) . Consequently, the preferred sheet thickness of the desired steel sheet is approximately 0.5 mm to 3.5 mm. In addition, to also reduce the weight of a member through high reinforcement, the preferable strength of the desired steel sheet after stamping is approximately 1200 MPa to 2000 MPa in terms of tensile strength.
    [00119] The effects of the invention will now be described on the basis of examples.
    EXAMPLE 1 [00120] Steel parts (steels) having chemical components as shown in Table 1 were obtained through steel production and casting. These steels were subjected to hot rolling, in which heating was carried out at 1250 ° C and the finishing temperature was 910 ° C, and were wound at a coil temperature
    Petition 870180144845, of 10/26/2018, p. 32/67
    29/54 operation of 620 ° C. As a result, hot rolled steel sheets having a thickness of 3.2 mm were obtained. These hot-rolled steel sheets were stripped and hot-rolled. These hot-rolled steel sheets were stripped and cold-rolled. As a result, cold rolled steel sheets having a thickness of 1.6 mm were obtained.
    [00121] The cold-rolled steel sheets described above were annealed for recrystallization under the conditions shown in Table 2 to obtain steel sheets for hot stamping.
    [00122] Under condition x, a cold-rolled steel sheet was heated from 300 ° C to 60 ° C at a constant heating rate of 10 ° C / s and then heated to 800 ° C at a constant heating rate 10 ° C / s and then heated to 800 ° C at a constant heating rate of 2 ° C / s. In this case, in both the 300 ° C to 600 ° C and 600 to 800 ° C temperature ranges, the d / dt (DT / Dt) changes in the rate of temperature rise of a steel plate were 0 ( zero), respectively. Under the other conditions, in a range of 300 ° C to temperature S, the cold-rolled steel sheet was heated so that the change d / dt (DT / Dt) in the rate of increase in the temperature of the steel sheet was constant. One method of obtaining this d / dt (DT / Dt) will be described in detail in Example 3.
    [00123] A sample was collected from the steel sheet for hot stamping, a section parallel to the rolling direction of the sample was polished, and the microstructure of the section was made to emerge using a "etchant picral". Then, using a scanning electron microscope, the region from the surface of the cold-rolled steel sheet (sample) to a position 0.4 mm away from the surface of the steel sheet in the direction of thickness (position at 1 / 4 of the thickness of the steel plate) was observed at a magnification of 5000 times to measure the sizes of the iron carbide. This observation was carried out until the
    Petition 870180144845, of 10/26/2018, p. 33/67
    30/54 the number of iron carbides measured is greater than or equal to 600. Then the measured data were processed to obtain the standard deviation.
    [00124] Meanwhile, a die having a size of 170 mm x1000 mm was prepared from the steel sheet described above. This die was formed by hot stamping in the form of equilateral steel on a base having a size of approximately 70 mm. The deflection d (mm) of the sample was measured with the method illustrated in FIG. 2.
    [00125] The heating conditions before the hot stamping were a temperature of 900 ° C and retention times of 1 minute and 10 minutes.
    [00126] In addition, a matrix 32 having a size of 210 mm x300 mm was prepared from the cold rolled steel sheet described above. Using an upper mold 31a and a lower mold 31b of a stamping plate illustrated in FIG. 3, the die 32 was hot stamped under the same forming conditions (except the shape) as those of the steel shape 12 to obtain a material for measuring the tensile strength. From this material, two JIS 5 tensile specimens were collected. To collect the specimens, machining by electric discharge was performed. A tensile test was performed on the specimens obtained to obtain the tensile strength sb (average value of the two pieces).
    [00127] In table 3, steel symbols, annealing conditions are shown. The change d / dt (DT / Dt) in the rate of increase of the temperature of a steel plate of 300 ° C until a maximum temperature S (° C), the average value and the standard deviation of the sizes of the iron carbides sb (average value of the two by), and the deflection d.
    [00128] In the steel sheets (n 1 to 8, 10, 11, 13, and 15 to 25) obtained by annealing under annealing conditions of i, iii, iv, vi, viii, ix and
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    31/54 that satisfy the conditions of the invention, a tensile strength of approximately 1200 MPa to 1500 MPa was obtained, and a small deflection having a size of 5 mm or less was observed. On the other hand, in the steel sheets (Nos 9, 12, 14, 26, and 27) obtained by annealing under conditions of annealing that did not satisfy the conditions of the invention, a deflection having a more than 5 mm size was observed ..
    [00129] As illustrated in FIG. 4 (heating conditions before hot stamping 900 ° C and a retention time of 1 minute) and FIG. 5 (heating conditions before hot stamping at 900 ° C and a retention time of 10 minutes), it was obvious that the results above depended heavily on the standard deviation of the sizes of the iron carbides that were contained in a region from the surface to a position 1/4 of the thickness of a steel plate before hot stamping; and when the standard deviation of the sizes of the iron carbides that were contained in a region from a surface to a position 1/4 of the thickness of the steel sheet before hot stamping was less than or equal to 8 mm (n the 1 to 8, 10, 11, 13, and 15 to 25 (indicated by open circles), a long hot-stamped member having a lower deflection can be obtained.
    [00130] On the other hand, it was obvious that, when the standard deviation was larger than 8 mm (Nos 9, 12, 14, 26, and 27, indicated by solid circles and solid triangles) the deflection d was greater than 8 mm that was intolerable.
    [00131] In addition, it was obvious that to obtain a steel plate in which the standard deviation of the sizes of the iron carbides that were contained in a region from the surface to a position 1/4 of the thickness of a steel plate steel before hot stamping was less than or equal to 0.8 mm, the annealing recrystallizes
    Petition 870180144845, of 10/26/2018, p. 35/67
    32/54 tion was preferably performed under conditions in which the change d / dt (DT / Dt) at a rate of increase in the temperature of the steel sheet from 300 ° C to a maximum temperature S (° C) satisfied made an expression of -0.2 <d / dt (DT / Dt) <0; and the maximum temperature S was 72 ° C to 820 ° C, as indicated by open circles in FIG. 6. When d / dt (DT / Dt) was less than -0.2, or greater than or equal to 0, or when S is less than 720 ° C or greater than 820 ° C, as indicated by solid circles and by the solid triangles in the same design, and the standard deviation of the sizes of the iron carbides was greater than 0.8 mm.
    TABLE 1
    Steel symbol Chemical components (% by mass) Ç Si Mn P s Al N Others The 0.25 0.3 1.3 0.02 0.002 0.03 0.004 Ti: 0.03, B: 0.003 B 0.22 0.3 1.2 0.02 0.002 0.03 0.003ç 0.21 0.3 1.4 0.02 0.002 0.03 0.002 B: 0.004 d 0.20 0.2 1.2 0.02 0.002 0.03 0.004 Cr: 0.2, Ti: 0.02, B: 0.002 and 0.18 0.2 1.3 0.02 0.002 0.03 0.003 Cr: 1.4, Ti: 0.02, B: 0.002 f 0.15 0.3 1.1 0.02 0.002 0.03 0.003 Cr: 0.1, B: 0.004 g 0.12 0.2 1.3 0.02 0.002 0.03 0.003 Ti: 0.03, Nb: 0.01, B: 0.003 H 0.10 0.1 1.0 0.02 0.002 0.03 0.003 Cr: 0.2, Ti: 0.02, B: 0.003 i 0.23 0.1 0.6 0.02 0.002 0.03 0.003 Cr: 0.2, Ti: 0.02, B: 0.002 j 0.26 0.1 0.3 0.02 0.002 0.03 0.003 Cr: 0.2, Ti: 0.02, B: 0.002
    TABLE 2
    Condition No. d / dt (DT / Dt) (° C / s 2 ) Temperature S (° C) Cooling conditionsi -0.05 800 Not withheld. Cooling to 670 ° C at an average cooling rate of 6 ° C / s, Example
    Petition 870180144845, of 10/26/2018, p. 36/67
    33/54
    Condition No. d / dt (DT / Dt) (° C / s 2 ) Temperature S (° C) Cooling conditions Held at 670 ° C for 10 seconds, air-cooled to room temperatureii -0.05 710 Same as above Comparative example iii -0.05 720 Same as above Example iv -0.1 820 Same as above Example v -0.1 830 Same as above Comparative example saw -0.2 800 Same as above Example vii -0.21 800 Same as above Comparative example viii -0.005 800 Same as above Example ix -0.02 800 Held at 800 ° C for 10 seconds, air-cooled to room temperature Example x 0 800 Same as above Comparative example xi 0.1 725 Held at 725 ° C for 10 seconds, air-cooled to room temperature Comparative example
    [00132] Underlined items represent items outside the range of the invention.
    [00133] In condition number x, the heating rate of 300 ° C s
    600 ° C is constant at 10 ° C / s, and the heating rate from 600 ° C to 800 ° C was constant at 2 ° C / s.
    Petition 870180144845, of 10/26/2018, p. 37/67
    TABLE
    No. Steel symbol Annealing conditions d / dt (DT / Dt) (° C / s 2 ) Average value (gm) of iron carbide sizes Standard deviation (gm) of iron carbide sizes Heating conditions before hot stampingMaintained at 900 ° C for 1 minute Maintained at 900 ° C for 10 minutes SB(MPa) d (mm) SB(MPa) d (mm) 1 The i -0.05 1.3 0.51 1506 2.4 1508 2.2 Example 2 B i -0.05 1.2 0.44 1500 2.0 1505 2.0 Example 3 ç i -0.05 1.2 0.63 1493 2.7 1497 2.8 Example 4 d i -0.05 1.2 0.57 1491 2.6 1493 2.5 Example 5 and i -0.05 1.4 0.50 1502 2.7 1505 2.2 Example 6 f i -0.05 1.1 0.49 1419 2.3 1425 2.0 Example 7 g i -0.05 1.0 0.46 1306 1.6 1310 1.8 Example 8 H i -0.05 1.5 0.79 1200 3.8 1203 3.4 Example 9 The ii -0.05 1.9 0.92 1476 9.1 1502 9.9 Example 10 The iii -0.05 1.3 0.52 1505 2.8 1505 2.6 Example 11 The iv -0.1 1.2 0.53 1496 3.6 1499 3.8 Example 12 The v -0.1 1.8 1.01 1501 13.1 1504 12.2.0 Comparative example 13 The saw -0.2 1.4 0.40 1504 3.8 1508 4.0 Example 14 The vii -0.21 1.7 0.89 1499 9.0 1504 8.8 Comparative example 15 The viii -0.005 1.6 0.60 1502 3.3 1510 3.2 Example 16 The ix -0.02 1.6 0.58 1509 2.6 1516 2.6 Example
    34/54
    Petition 870180144845, of 10/26/2018, p. 38/67
    No. Steel symbol Annealing conditions d / dt (DT / Dt) (° C / s 2 ) Average value (gm) of iron carbide sizes Standard deviation (gm) of iron carbide sizes Heating conditions before hot stampingMaintained at 900 ° C for 1 minute Maintained at 900 ° C for 10 minutes OB(MPa) d (mm) SB(MPa) d (mm) 17 B ix -0.02 1.5 0.60 1508 4.5 1512 4.4 Example 18 ç ix -0.02 1.2 0.39 1502 3.0 1509 3.6 Example 19 d ix -0.02 1.3 0.33 1504 3.9 1506 3.6 Example 20 and ix -0.02 1.2 0.29 1499 3.3 1500 3.0 Example 21 f ix -0.02 1.7 0.52 1491 4.1 1496 4.2 Example 22 g ix -0.02 1.6 0.42 1290 1.7 1292 1.2 Example 23 H ix -0.02 1.5 0.37 1209 1.4 1209 1.0 Example 24 i i -0.05 1.3 0.41 1500 3.0 1501 3.1 Example 25 j i -0.05 1.3 0.39 1508 2.7 1511 2.9 Example 26 The x 0 1.4 0.85 1489 9.8 1503 9.0 Comparative example 27 The xi 01 2.0 0.90 1490 10.8 1496 10.0.2 Comparative example
    35/54
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    36/54 [00134] Underlined items represent items outside the range of the invention.
    EXAMPLE 2 [00135] Steel parts (steels) having chemical components as shown in Table 4 were obtained through production and casting. These steels were treated under the same conditions as those of Example 1 to obtain hot-rolled steel sheets having a thickness of 3.0 mm. These hot-rolled steel sheets were stripped and cold-rolled. As a result, cold rolled steel sheets having a thickness of 1.2 mm were obtained.
    [00136] These cold-rolled steel sheets were annealed for recrystallization under conditions i, vii, and ix shown in Table 2 to obtain steel sheets for hot stamping.
    [00137] The sizes of the iron carbides that were contained in a region from the surface of the cold-rolled steel sheet obtained to a position that was 0.3 mm away from the surface of the steel sheet in the direction of thickness (a position at 1/4 of the thickness of the steel plate) were measured, and the standard deviation of the sizes of iron carbides was obtained. In addition, the cold-rolled steel sheets thus obtained were hot stamped under both heating conditions to be held at 900 ° C for 1 minute and for 5 minutes to obtain steel shapes. In addition, by measuring the deflection d of each steel form with the same method as in Example 1, tensile test pieces were collected from the steel form to obtain the tensile strength sb.
    [00138] Their results are shown in Table 5.
    [00139] In steel sheets for hot stamping obtained by annealing recrystallization under annealing conditions I and ix that have met the conditions of the invention, even when a plate
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    37/54 pa of steel contains more chemical components such as Mo, W, V, Cu, and Ni, the standard deviation of the sizes of iron carbides from the surface to a position 1/4 of the thickness of the steel plate was less than or equal to 0.8 mm. In addition, in this case, it was obvious that the deflection of a long component (steel form) was less than or equal to 5 mm regardless of the heating conditions (holding time at 900 ° C) before hot stamping, and a upper hot stamping member was obtained.
    [00140] On the other hand, in steel sheets obtained by annealing recrystallization under the conditions of annealing vii that did not satisfy the conditions of the invention, the standard deviation of the sizes of iron carbides from the surface to a position at 1/4 the thickness of the steel plate was greater than 0.8 mm. In this case, it was obvious that the deflection of a hot stamping member was greater than 5 mm regardless of the heating conditions (holding time at 900C) before hot stamping, and such steel sheet had low forming capacity in the stamping the hot.
    TABLE 4
    Steel symbol Chemical components (% by mass) Ç Si Mn P s Al N Others 2a 0.35 0.4 1.0 0.02 0.004 0.03 0.004 Cr: 0.2, Ti: 0.01, B: 0.002, Cu: 0.1,Ni: 0.1 2b 0.31 0.5 1.3 0.02 0.004 0.03 0.004 Cr: 0.5, Ti: 0.02, B: 0.004, Nb: 0.02, Mo: 0.2 2c 0.28 0.9 1.7 0.02 0.004 0.03 0.004 W: 0.2, Ni: 2.0 2d 0.25 0.8 1.8 0.02 0.004 0.03 0.004 Ti: 0.03, B: 0.003, Mo: 0.2, Ni: 1.0 2e 0.22 0.6 1.6 0.02 0.004 0.03 0.003 Mo: 0.1, W: 0.5, V: 0.5 2f 0.21 0.4 1.4 0.02 0.004 0.03 0.002 B: 0.005, Mo: 0.1, V: 0.5 2g 0.20 0.3 1.3 0.02 0.004 0.03 0.004 Cr: 0.2, Tr: 0.02,
    Petition 870180144845, of 10/26/2018, p. 41/67
    38/54
    Steel symbol Chemical components (% by mass) Ç Si Mn P s Al N Others Mo: 0.2, W: 0.4 2 am 0.18 0.3 1.3 0.02 0.004 0.03 0.003 Cr: 1.4, Ti: 0.02, B: 0.0022, Mo: 0.1, V: 0.2
    Petition 870180144845, of 10/26/2018, p. 42/67
    TABLE 5
    No. Steel symbol Annealing conditions Average value (pm) of iron carbide sizes Standard deviation (pm) of iron carbide sizes Finishing conditions before hot stampingRetained at 900 ° C for 1 minute Retained at 900 ° C for 5 minutes oB (MPa) d (mm) oB (MPa) d (mm) 28 2a i 1.8 0.38 1794 3.4 1795 3.3 Example 29 2a vii 2.2 0.84 1785 9.9 1792 9.6 Comparative example 30 2a ix 1.9 0.49 1794 2.8 1800 2.9 Example 31 2b i 1.7 0.26 1698 4.8 1703 4.8 Example 32 2b vii 2.4 1.07 1691 9.3 1697 9.0 Example 33 2b ix 1.7 0.27 1708 3.5 1710 3.4 Example 34 2c i 1.9 0.45 1596 4.5 1598 4.7 Example 35 2c vii 2.5 1.03 1580 10.3 1592 10.1 Comparative example 36 2c ix 2.0 0.62 1590 4.2 1590 4.1 Example 37 2d i 1.6 0.29 1490 2.1 1493 1.8 Example 38 2d vii 2.4 1.26 1492 9.6 1504 9.7 Comparative example 39 2d ix 1.9 0.50 1496 4.5 1497 4.4 Example 40 2e i 2.2 0.79 1492 3.6 1492 3.5 Example 41 2e vii 2.3 0.93 1491 12.2 1502 12.0 Comparative example 42 2e ix 1.8 0.30 1510 4.3 1516 4.6 Example
    39/54
    Petition 870180144845, of 10/26/2018, p. 43/67
    No. Steel symbol Annealing conditions Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes Finishing conditions before hot stampingRetained at 900 ° C for 1 minute Retained at 900 ° C for 5 minutes oB (MPa) d(mm) oB (MPa) d(mm) 43 2f i 1.8 0.22 1503 3.3 1507 3.2 Example 44 2f vii 2.6 1.16 1506 9.5 1515 9.5 Comparative example 45 2f ix 2.2 0.19 1520 4.4 1521 4.6 Example 46 2g i 1.8 0.74 1490 4.2 1496 4.6 Example 47 2g vii 2.4 1.03 1493 14.2 1508 14.0 Comparative example 48 2g ix 1.7 0.53 1528 4.1 1528 4.1 Example 49 2 am i 1.6 0.44 1503 2.9 1508 3.0 Example 50 2 am vii 2.0 0.83 1513 7.2 1514 7.4 Example 51 2 am ix 1.8 0.65 1520 4.2 1524 4.2 Comparative example
    40/54
    Petition 870180144845, of 10/26/2018, p. 44/67
    41/54 [00141] Underlined items represent items outside the range of the invention.
    EXAMPLE 3 [00142] Steel parts (steels) having chemical components as shown in Table 6 were obtained through the production of steel and casting. These steels were treated under the same conditions as those of Example 1 to obtain hot-rolled steel sheets having a thickness of 2.5 mm. These hot-rolled steel sheets were stripped and cold-rolled. As a result, cold rolled steel sheets having a thickness of 1.2 mm were obtained.
    [00143] These cold rolled steel sheets were heated up to 800 ° C according to the temperature history illustrated in FIG. 7, were cooled immediately to a cooling rate of 6.5 ° C / s, and were dipped in a bath of molten Al (containing 10% Si and the inevitable impurities) at 670 ° C. Then, the cold rolled steel sheets were removed from the molten Al bath after 5 seconds. The deposit amount of the coating layer was adjusted using a gas cleaner, followed by air cooling to room temperature.
    [00144] When the temperature of the steel plate and the time after the beginning of the annealing (time elapsed after the beginning of the heating) are represented by T (° C) and t (seconds), respectively, data in relation to T and t can be read from the temperature history of FIG. 7 as shown below in Table 7. From this reading data, a graph was generated using Excel spreadsheet software (produced by Microsoft Corporation), and that graph was approximated by a second degree polynomial. As a result, an approximation expression illustrated in FIG. 7 (T = 0.0374 * t 2 + 10.302xt + 79.949). Rounding off each coefficient of this
    Petition 870180144845, of 10/26/2018, p. 45/67
    42/54 approximation expression, the relationship between T and t can be defined as T = -0.037t 2 + 10.3t + 80. Therefore, d / dt (DT / Dt) was -0.074.
    [00145] In addition, as illustrated in FIG. 7, the coefficient of determination R 2 of the approximation expression obtained was 0.999. Like this example, d / dt (DT / Dt) used in the invention can be a value that is twice the coefficient of t 2 (coefficient of a second degree variable) when the temperature is read at a time interval (where greater than 0 seconds) of 10 seconds or less or 5 seconds or less from a temperature history during the heating of the recrystallization annealing process and then an approximation curve (second degree polynomial approximation curve) is determined so that the coefficient of determination R 2 is greater than or equal to 0.99.
    [00146] In the steel sheet obtained, sizes of iron carbides that were contained in, a region from a boundary between an inner layer (reaction layer of Al and Fe) of a layer of Al coating and the plate of steel to a position that is 0.3 mm away from the border in the direction through the thickness was measured, and the standard deviation of the sizes of the iron carbides was obtained. During the measurement of iron carbides, the thickness (total thickness of two layers) of the Al coating layer was measured. In addition, with the same method as in Example 1, the steel sheet was hot stamped into a steel form and a sheet to measure the deflection d and tensile strength sb. In this case, the heating conditions before hot stamping were maintained at 900 ° C for 1 minute.
    [00147] The results are shown in Table 8.
    [00148] In all examples (52 to N 71), a heat embossing member was obtained having a deflection of 5 mm or less size. However, the examples Nos 56, 61, 66, and 71 in which s
    Petition 870180144845, of 10/26/2018, p. 46/67
    43/54 thickness of the Al coating layer was greater than 50 mm, skinning was highly frequently observed in a steel-shaped region from a corner portion to the final portion. In examples in which the Al coating layer thickness was less than or equal to 50 mm, skinning was not observed. Consequently, when the Al coating layer is formed on the surface of the steel sheet, the upper limit of the Al coating layer thickness is preferably less than or equal to 50 mm from the coating quality point of view. In Table 8, regarding the quality of the Al coating layer, examples in which skinning was not observed in the Al coating layer were evaluated as “A”, and examples in which skinning was observed in the Al coating layer were rated “B”.
    TABLE 6
    Steel symbol With chemical components (% by mass) Ç Si Mn P s Al N Others 3rd 0.34 0.09 1.8 0.02 0.004 0.04 0.002 Cr: 0.2, Mo: 0.2, Cu: 0.1, Ni: 0.05 3b 0.26 0.18 1.4 0.02 0.004 0.04 0.002 Cr: 0.002, Ti: 0.02, B: 0.003, Mo: 0.2, W: 0.1,V: 0.1 3c 0.23 0.12 1.3 0.01 0.008 0.03 0.003 Cr: 0.13, Ti: 0.03, Nb: 0.02, B: 0.002 3d 0.13 0.33 1.0 0.01 0.008 0.03 0.003 B: 0.0005
    TABLE 7
    t (s) T (° C) 0.32 42.99 4.68 98.13 8.76 138.17 12.11 174.93 15.46 208.73
    Petition 870180144845, of 10/26/2018, p. 47/67
    44/54
    t (s) T (° C) 18.16 236.3 21.19 266.82 24.58 297.67 28.94 340.66 32.32 371.18 35.68 402.03 40.04 429.6 44.43 463.41 49.15 500.16 53.87 530.69 58.56 558.25 63.64 589.1 69.01 616.67 74.74 644.24 79.46 662.62 86.52 690.19 92.9 711.85 100.32 730.23 106.05 742.37 111.42 757.79 116.14 769.94 121.55 782.41 127.6 797.51
    TABLE 8
    No. Steel symbol Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes OB(MPa) d(mm) Al coating layer thickness (mm) Quality of Al coating layer52 3rd 2.0 0.51 1784 3.3 16.1 THE Example 53 3rd 2.0 0.48 1789 3.5 32.2 THE Example
    Petition 870180144845, of 10/26/2018, p. 48/67
    45/54
    No. Steel symbol Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes OB(MPa) d(mm) Al coating layer thickness (mm) Quality of Al coating layer54 3rd 2.0 0.42 1801 3.2 33.9 THE Example 55 3rd 2.1 0.66 1792 4.0 48.8 THE Example 56 3rd 2.0 0.52 1790 3.8 51.0 B Example 57 3b 2.0 0.47 1516 3.5 15.0 THE Example 58 3b 1.9 0.39 1520 2.9 19.7 THE Example 59 3b 2.0 0.63 1524 4.1 34.9 THE Example 60 3b 2.1 0.68 1522 4.1 49.5 THE Example 61 3b 2.0 0.42 1534 3.4 54.8 B Example 62 3c 1.8 0.35 1502 2.9 14.9 THE Example 63 3c 1.8 0.32 1509 3.7 20.2 THE Example 64 3c 1.9 0.74 1513 4.8 34.5 THE Example 65 3c 1.9 0.76 1519 4.9 49.0 THE Example 66 3c 1.9 0.69 1524 4.4 55.9 B Example 67 3d 1.7 0.55 1318 4.1 17.0 THE Example 68 3d 1.8 0.67 1326 4.2 20.2 THE Example 69 3d 1.7 0.52 1320 4.0 30.2 THE Example 70 3d 1.7 0.50 1314 3.9 42.2 THE Example 71 3d 1.7 0.44 1310 3.7 53.1 B Example
    EXAMPLE 4 [00149] Steel sheets (steels) having chemical components as shown in Table 6 were obtained through steel production and casting. These steels were treated under the same conditions as those of Example 1 to obtain hot-rolled steel sheets having a thickness of 2.5 mm. These hot-rolled steel sheets were stripped and cold rolled. As a result, cold rolled steel sheets having a thickness of 1.2 mm were obtained.
    [00150] These cold rolled steel sheets were heated up to 800 ° C according to the same temperature history as in example 3, they were immediately cooled to an average rate of cooling
    Petition 870180144845, of 10/26/2018, p. 49/67
    46/54 at 6.5 ° C / s, and were immersed in a bath of molten Zn (containing 0.15% Al and the inevitable impurities) at 460 ° C. Then, the cold rolled steel sheets were removed from the molten Zn bath after 3 seconds. The deposit amount of the coating layer was adjusted using a gas scrubber, followed by air cooling to room temperature.
    [00151] In the obtained steel sheet, the sizes of the iron carbides that were contained in a region from the border between an inner layer (Al and Fe reaction layer) of a Zn coating layer and the steel sheet up to a position 0.3 mm away from the border in the direction through the thickness were measured, and the standard deviation of the sizes of iron carbides were obtained. During the measurement of iron carbides, the thickness (total thickness of the two layers) of the Zn coating layer was measured. In addition, with the same method as in Example 1, the steel sheet was hot stamped into a steel form and a sheet to measure the deflection d and tensile strength sb. In this case, the heating conditions before the hot stamping were two conditions of <1> heating the steel sheet to 880 ° C and holding at that temperature for 5 seconds, followed by air cooling to 700 ° C, and <2 > keep the temperature at 900 ° C for 1 minute.
    [00152] Their results are shown in Table 9.
    [00153] In all instances (n 72 to 91) obtained was a member of hot stamping having a deflection of 5 mm or less in size regardless of heating conditions prior to hot stamping. However, in Examples Nos 76, 81, 86, and 91 in which the thickness of the Zn coating layer was greater than 30 mm, Zn adhesion was observed highly frequently in a mold. In the examples in which the thickness of the Zn coating layer was less than or equal to 30 mm, adhesion was not observed
    Petition 870180144845, of 10/26/2018, p. 50/67
    47/54 vada. Consequently, when a coating layer of Zn is formed on the surface of the steel sheet, the upper limit of the thickness of the coating layer of Zn is preferably less than or equal to 30 mm from the point of view of coating quality. In Table 9, for the quality of the Zn coating layer, examples in which Zn did not adhere to the mold were rated as “A”, and examples in which Zn adhered to the mold were assessed as
    Petition 870180144845, of 10/26/2018, p. 51/67
    TABLE 9
    No. Steel symbol Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes Heating conditions before hot stamping Zn coating layer thickness (mm) Quality of Zn coating layer<1> <2> sb(MPa) d(mm) Sb(MPa) d(mm) 72 3rd 2.0 0.62 1784 3.9 1788 3.6 6.0 THE Example 73 3rd 2.0 0.39 1788 2.9 1795 3.1 12.6 THE Example 74 3rd 2.0 0.44 1803 4.1 1809 4.0 23.9 THE Example 75 3rd 2.1 0.51 1795 4.2 1796 4.2 28.7 THE Example 76 3rd 2.0 0.66 1793 4.4 1799 4.1 31.1 B Example 77 3b 2.0 0.55 1516 3.3 1520 3.6 11.0 THE Example 78 3b 1.9 0.39 1523 3.7 1533 3.6 19.6 THE Example 79 3b 2.0 0.77 1534 2.6 1535 2.9 24.8 THE Example 80 3b 2.1 0.46 1532 4.3 1536 3.9 29.2 THE Example 81 3b 2.0 0.37 1548 3.6 1555 3.8 32.7 B Example 82 3c 1.8 0.51 1518 3.7 1527 3.5 11.3 THE Example 83 3c 1.8 0.66 1537 5.0 1540 4.2 17.4 THE Example 84 3c 1.9 0.58 1524 4.2 1524 4.4 19.8 THE Example 85 3c 1.9 0.57 1539 4.7 1547 4.3 29.3 THE Example 86 3c 1.9 0.77 1548 3.9 1549 3.8 32.5 B Example 87 3d 1.7 0.46 1336 3.7 1345 3.2 11.0 THE Example
    Petition 870180144845, of 10/26/2018, p. 52/67
    No. Steel symbol Average value (gm) of iron carbide sizes Standard deviation (gm) of iron carbide sizes Heating conditions before hot stamping Zn coating layer thickness (gm) Quality of Zn coating layer<1> <2> Ob(MPa) d(mm) Ob(MPa) d(mm) 88 3d 1.8 0.42 1342 4.4 1344 4.1 17.0 THE Example 89 3d 1.7 0.32 1319 4.9 1322 4.3 20.4 THE Example 90 3d 1.7 0.69 1320 4.2 1320 4.2 28.9 THE Example 91 3d 1.7 0.70 1341 3.5 1349 3.4 33.0 B Example
    <1> Heat the steel sheet to 880 ° C and hold at that temperature for 5 seconds, followed by air cooling to 700 ° C <2> Maintain the temperature at 900 ° C for 1 minute
    Petition 870180144845, of 10/26/2018, p. 53/67
    50/54
    EXAMPLE 5 [00154] Steel parts (steels) having chemical components as shown in Table 6 were obtained through steel production and casting. These steels were treated under the same conditions as those of Example 1 to obtain hot-rolled steel sheets having a thickness of 2.5 mm. These hot-rolled steel sheets were stripped and cold-rolled. As a result, cold rolled steel sheets having a thickness of 1.2 mm were obtained.
    [00155] These cold-rolled steel sheets were heated to 800 ° C according to the same temperature history as Example 3, were immediately cooled to an average cooling rate of 6.5 ° C / s, and were dipped in a molten Zn bath (containing 0.13% Al, 0.03% Fe and the inevitable impurities) at 460 ° C. Then the cold rolled steel sheets were removed from the molten Zn bath after 3 seconds. The deposit amount of a coating layer was adjusted using a gas scrubber. Then the cold-rolled steel sheets were heated to 480 ° to form a layer of Zn-Fe alloy followed by air cooling to room temperature.
    [00156] In the obtained steel plate, sizes of iron carbides that were contained in a region from the border between the innermost layer (reaction layer between Zn and Fe) of a layer of Zn-Fe alloy and the plate of steel to an apposition 0.3 mm away from the border in the direction through the thickness were measured, and the standard deviation of the sizes of the iron carbides was obtained. During the measurement of iron carbides, the total thickness of the Zn-Fe alloy layer (including 4 layers) was measured. In addition, using the same method as Example 1, the steel sheet was hot stamped into a steel form and a sheet to measure the deflection of strength and
    Petition 870180144845, of 10/26/2018, p. 54/67
    51/54 traction sb. In that case, the heating conditions before the hot stamping were two conditions of <1> heating the steel sheet to 880 ° C and maintaining the temperature for 5 seconds, followed by air cooling to 700 ° C; and <2> keep the temperature at 900 ° C for 1 minute.
    [00157] The results thereof are shown in Table 10. [00158] In all Examples (n 92 to 111), there was obtained a hot embossing member having a deflection of 5 mm or less in size regardless of the conditions heating before hot stamping. However, in Examples Nos 96, 101, 106, and 111 in which the thickness of the Zn-Fe alloy layer is greater than 45 mm, small fractures were generated in the alloy layer after hot stamping. In the examples in which the thickness of the Zn-Fe alloy layer was less than or equal to 45 mm, no small fracture was generated. Consequently, when the ZnFe alloy layer is formed on the surface of the steel sheet, the upper limit of the thickness of the Zn-Fe alloy layer is preferably less than or equal to 45 mm from the point of view of coating quality. In Table 10, regarding the quality of the Zn-Fe alloy layer, examples in which no small fracture was generated in the ZnFe alloy layer were evaluated as "A"; and examples in which small fractures were generated in the Zn-Fe alloy layer were assessed as “B”.
    Petition 870180144845, of 10/26/2018, p. 55/67
    TABLE 10
    No. Steel symbol Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes Heating conditions before hot stamping Thickness (mm) of Zn-Fe coating layer Quality of the ZnFe coating layer<1> <2> Ob(MPa) d(mm) Ob(MPa) d(mm) 92 2a 2.0 0.42 1772 4.2 1777 4.2 15.0 THE Example 92 2a 2.0 0.44 1777 4.4 1778 4.6 20.2 THE Example 94 2a 2.0 0.29 1802 2.2 1815 2.0 21.1 THE Example 95 2a 2.1 0.72 1786 2.4 1788 2.0 29.9 THE Example 96 2a 2.0 0.79 1772 2.9 1775 2.5 46.0 B Example 97 2b 2.0 0.66 1505 2.9 1506 4.1 15.6 THE Example 98 2b 1.9 0.41 1519 4.1 1522 4.0 21.7 THE Example 99 2b 2.0 0.22 1512 2.2 1517 2.6 29.2 THE Example 100 2b 2.1 0.68 1502 4.8 1502 4.2 44.7 THE Example 101 2b 2.0 0.47 1518 4.6 1529 4.4 49.8 B Example 102 2c 1.8 0.45 1506 2.7 1509 2.9 14.4.5 THE Example 102 2c 1.8 0.52 1502 4.2 1512 4.0 20.7 THE Example 104 2c 1.9 0.55 1500 4.8 1507 4.0 24.7 THE Example 105 2c 1.9 0.59 1506 5.0 1508 4.2 42.2 THE Example 106 2c 1.9 0.67 1510 4.2 1522 4.2 45.2 B Example 107 2d 1.7 0.60 1207 2.2 1209 2.9 15.1 THE Example
    52/54
    Petition 870180144845, of 10/26/2018, p. 56/67
    No. Steel symbol Average value (mm) of iron carbide sizes Standard deviation (mm) of iron carbide sizes Heating conditions before hot stamping Thickness (mm) of Zn-Fe coating layer Quality of the ZnFe coating layer<1> <2> Ob(MPa) d(mm) Ob(MPa) d(mm) 108 3d 1.8 0.50 1313 3.6 1320 3.8 18.0 THE Example 109 3d 1.7 0.44 1320 3.8 1329 3.4 30.1 THE Example 110 3d 1.7 0.70 1314 4.4 1314 4.4 42.8 THE Example 111 3d 1.7 0.73 1310 4.8 1313 4.7 46.6 B Example
    <1> Heat the steel plate to 880 ° C and maintain the temperature for 5 seconds, followed by air cooling to 700 ° C <2> Maintain the temperature at 900 ° C for 1 minute
    Petition 870180144845, of 10/26/2018, p. 57/67
    54/54
    INDUSTRIAL APPLICABILITY [00159] A steel plate is provided for a hot stamping member capable of reducing the deflection that occurs easily when a long component is produced by hot stamping, and a method of producing it.
    DESCRIPTION OF REFERENCE NUMBERS AND SIGNS
    11: MATRIX (STEEL SHEET)
    12: STEEL SHAPE
    21: PLATE SURFACE
    31a: TOP MOLD
    31b: LOWER TEMPLATE
    32: MATRIX (STEEL SHEET)
    L: LENGTH
    W: WIDTH d: DEFLECTION
    权利要求:
    Claims (10)
    [1]
    1. Steel plate for a hot stamping member, the steel plate characterized by the fact that it consists of, as a chemical composition,
    0.10% by weight to 0.35% by weight of C;
    0.01 mass% to 1.0 mass% of Si;
    0.3 mass% to 2.3 mass% of Mn;
    0.01 wt% to 0.5 wt% Al;
    limited to 0.03% by weight or less than P;
    limited to 0.02% by weight or less of S;
    limited to 0.1% by weight or less of N;
    optionally one or more elements selected from the group consisting of
    0.01 wt% to 2.0 wt% Cr;
    0.001% by mass to 0.5% by weight of Ti;
    0.001% by mass to 0.5% by weight of Nb;
    0.0005 mass% to 0.01 mass% of B;
    0.01 wt% to 1.0 wt% Mo;
    0.01 mass% to 0.5 mass% W;
    0.01 mass% to 0.5 mass% of V;
    0.01 wt% to 1.0 wt% Cu; and
    0.01 mass% to 5.0 mass% of Ni; and the balance consisting of Fe and the inevitable impurities, in which the standard deviation of the diameters of the iron carbides that are contained in a region from a surface to a position 1/4 of the thickness of the steel plate is less than or equal to 0.8 mm.
    [2]
    2. Steel plate for a hot stamping member according to claim 1, characterized by the fact that a coating layerPetition 870180144845, of 10/26/2018, p. 59/67
    2/4 to Al having a coating thickness of 50 mm or less is formed on the surface.
    [3]
    Steel plate for a hot stamping member according to claim 1, characterized in that a coating layer of Zn having a coating thickness of 30 mm or less is formed on the surface.
    [4]
    Steel plate for a hot stamping member according to claim 1, characterized in that a layer of Zn-Fe alloy having a coating thickness of 45 mm or less is formed on the surface.
    [5]
    5. Method of producing a steel sheet for a hot stamping member, as defined in any one of claims 1 to 4, the method characterized by the fact that it comprises:
    perform a recrystallization annealing process in which the cold rolled steel sheet is heated so that the d / dt change (DT / Dt; ° C / s 2 ) at a rate of increase in the temperature of the steel sheet since 300 ° C to a maximum temperature S meets the expression 1 below and so that the maximum temperature S is 720 ° C to 820 ° C, where:
    T represents the temperature of the steel plate (° C), t represents the time (seconds) and DT / Dt represents the rate of increase (° C / s) of the temperature of the steel plate for a time Dt (seconds) during the heating the recrystallization annealing process, and the cold rolled steel sheet contains as a chemical composition,
    0.10% by weight to 0.35% by weight of C;
    0.01 mass% to 1.0 mass% of Si;
    Petition 870180144845, of 10/26/2018, p. 60/67
    3/4
    0.3 mass% to 2.3 mass% of Mn;
    0.01 wt% to 0.5 wt% Al;
    limited to 0.03% by weight or less than P;
    limited to 0.02% by weight or less of S;
    limited to 0.1% by weight or less of N; and the balance consisting of Fe and the inevitable impurities
    -0.20 <d / dt (DT / Dt) <0 (Expression 1).
    [6]
    6. Method of producing a steel plate for a hot stamping member according to claim 5, characterized by the fact that the chemical composition additionally contains one or more elements selected from the group consisting of
    0.01 wt% to 2.0 wt% Cr;
    0.001% by mass to 0.5% by weight of Ti;
    0.001% by mass to 0.5% by weight of Nb;
    0.0005 mass% to 0.01 mass% of B;
    0.01 wt% to 1.0 wt% Mo;
    0.01 mass% to 0.5 mass% W;
    0.01 mass% to 0.5 mass% of V;
    0.01 wt% to 1.0 wt% Cu; and
    0.01 mass% to 5.0 mass% of Ni.
    [7]
    7. Method of producing a steel sheet for a hot stamping member according to claim 5 or 6, characterized by the fact that the change d / dt (DT / Dt) is twice the coefficient of a variable of second degree when a temperature is read at a time interval of 10 seconds or less from the temperature history during the heating of the recrystallization annealing process and then a second degree polynomial approximation curve is determined so that
    Petition 870180144845, of 10/26/2018, p. 61/67
    4/4 a coefficient of determination R 2 is greater than or equal to 0.99,
    [8]
    8. Method of producing a steel sheet for a hot stamping member according to claim 5 or 6, characterized by the fact that, after the recrystallization annealing process, it further comprises:
    dipping the cold-rolled steel sheet in an Al bath to form a layer of Al-coating having a coating thickness of 50 mm or less on a surface of the cold-rolled steel sheet.
    [9]
    9. Method of producing a steel sheet for a hot stamping member according to claim 5 or 6, characterized by the fact that, after the recrystallization annealing process, it additionally comprises:
    dip the cold-rolled steel sheet into a Zn bath to form a layer of Zn coating having a coating thickness of 30 mm or less on a surface of the cold-rolled steel sheet
    [10]
    10. Method of producing a steel sheet for a hot stamping member according to claim 5 or 6, characterized by the fact that, after the recrystallization annealing process, it further comprises:
    dip the cold rolled steel sheet in a Zn bath to form a layer of Zn coating on a surface of the cold rolled steel sheet, and heat the cold rolled steel sheet to 600 ° C or less to form a Zn-Fe alloy layer having a coating thickness of 45 mm or less on a cold rolled steel sheet surface.
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    BR102012019118A2|2014-12-02|COLD LAMINATED STEEL SHEET AND HIGH RESISTANCE ELECTRODEPOSED STEEL SHEET, HAVING EXCELLENT FIRE HARDENING AND PLASTICITY, AND MANUFACTURING PROCESS OF THE SAME
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    同族专利:
    公开号 | 公开日
    JP5472531B2|2014-04-16|
    US9617624B2|2017-04-11|
    WO2012147863A1|2012-11-01|
    US20140044987A1|2014-02-13|
    EP2703511A1|2014-03-05|
    CA2832894C|2017-07-11|
    MX2013012422A|2013-12-06|
    EP2703511B1|2018-05-30|
    KR101617505B1|2016-05-02|
    MX351086B|2017-09-29|
    RU2552817C1|2015-06-10|
    TW201300550A|2013-01-01|
    TWI454584B|2014-10-01|
    PL2703511T3|2018-10-31|
    ZA201307763B|2014-06-25|
    CN103492600A|2014-01-01|
    EP2703511A4|2015-09-30|
    KR20130136565A|2013-12-12|
    CN103492600B|2015-12-02|
    CA2832894A1|2012-11-01|
    JPWO2012147863A1|2014-07-28|
    ES2683843T3|2018-09-28|
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    法律状态:
    2018-07-31| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|
    2019-02-05| B09A| Decision: intention to grant|
    2019-04-02| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 26/04/2012, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 26/04/2012, OBSERVADAS AS CONDICOES LEGAIS |
    2019-11-12| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2011100019|2011-04-27|
    JP2011-100019|2011-04-27|
    PCT/JP2012/061238|WO2012147863A1|2011-04-27|2012-04-26|Steel sheet for hot stamping members and method for producing same|
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