custom-made hot stamping plate, its production method and hot stamped member

专利摘要:
Patent Specification: "Custom-made hot-stamping plate, hot-stamped limb, and methods for producing them". A custom-made hot-stamping plate includes a welded portion formed by joint welding of the first aluminum-coated steel plate and the second aluminum-coated steel plate, an average concentration of al of a weld metal in the welded portion is. In a range of 0.3 wt.% to 1.5 wt.%, an ac3 point of the weld metal is 1250 ° c or lower, and additionally an aluminum layer formed during joint welding is present at a surface of the welded portion.
公开号:BR112014023783B1
申请号:R112014023783
申请日:2013-03-28
公开日:2019-09-10
发明作者:Kawasaki Kaoru；Yoshinaga Takahiro；Naito Yasuaki；Miyazaki Yasunobu
申请人:Nippon Steel & Sumitomo Metal Corp；Nippon Steel Corp；
IPC主号:

专利说明:

Descriptive Report of the Invention Patent for MADE-TO-MEASURE PLATE FOR HOT STAMPING, ITS PRODUCTION METHOD AND HOT STAMPED MEMBER. Technical Field of the Invention [001] The present invention relates to a plate made to measure for hot stamping that is obtained by multiple welding of steel sheets, and is offered for hot stamping (also called hot pressing or tempering of matrix, however, here referred to as hot stamping), and a method for producing it. In addition, the present invention relates to a hot stamped member obtained by performing hot stamping on the plate made to measure for hot stamping, and a method for producing it.
[002] Priority is claimed to Japanese Patent Application No. 2012-074222, filed on March 28, 2012, and Japanese Patent Application No. 2012-093812, filed on April 17, 2012, the contents of which are here incorporated by reference.
Related Technique [003] In recent years, there has been an increased demand to reduce the weight of an automobile structure for the proposal to decrease the amount of CO2 gas emission from the point of view of global environmental protection, and, consequently, there are active studies related to the application of a high-strength steel plate to the members of the automobile. Additionally, a required strength of steel is also gradually increasing.
[004] However, the high strength of a steel sheet leads to an increase in the pressing force required for pressing, and an increase in the size of a facility is accompanied by an increase in the facility's costs. Additionally, it is pointed out that, in a case where a higher resistance is provided to a
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2/56 steel plate, the difficulty of formation resulting from the high strengthening of the steel plate can cause problems with the costs for changing a die, costs for reducing matrix wear, and degradation of productivity due to rebalancing for improvement shape-fixing property, which leads to an increase in costs.
[005] Hot stamping draws attention as one of the methods to solve the problems described above. Hot stamping refers to a technique in which a steel sheet is heated to a high temperature, and is pressed in a high temperature range. Particularly, hot stamping is a technique in which a steel plate is pressed in a temperature range of Ponto Ar3 or higher, the steel plate is quickly cooled through heat transfer using a matrix (pressing matrix), and phase transformation, such as transformation of martensite or transformation of bainite, is caused in the structure of the steel sheet under the application of a pressing pressure, so that a pressed product, having a high strength and an excellent shape fixing property , can be produced.
[006] On the other hand, to optimize the yield and productivity of a pressed product, a custom-made sheet is used as a material for pressing for automobile members and the like.
[007] The custom-made sheet refers to a material for pressing obtained by joining the edge surfaces of multiple steel sheets by laser welding, or similar, according to the intended use. The use of made-to-measure sheet enables unrestricted change in sheet thickness, or resistance in a single product. As a result, the product's functionality improves, and the number of members can be reduced.
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3/56 [008] However, for most members that require corrosion resistance, such as automobile members, a zinc-coated steel plate is used. However, in a case where a piece of metal to be stamped or stamped (material for pressing) is hot stamped, the piece of metal to be stamped or stamped is heated to a temperature in the range of 700 ° C to 1000 ° Ç. This temperature is close to the boiling point of zinc, or is higher than the boiling point of zinc. Therefore, when hot stamping is carried out on the zinc-coated steel plate, there is a case where a portion of the layer coated on the surface is melted or evaporated during heating for hot stamping. Therefore, as a piece of metal to be stamped or coined for hot stamping, it is desirable to use a steel plate covered with an Al-based plate having a higher boiling point than the zinc-based plate, ie , a so-called steel sheet coated with aluminum from the point of view of suppressing the melting or evaporation of the coated layer.
[009] However, in Patent Document 1, it is pointed out that, in a case where the joint welding is carried out on an aluminum plate, the aluminum, which is a coated layer, moves on the weld metal, segregates, forms an intermetallic region, serves as a fracture starting point, and degrades the deformability of a joined portion.
[0010] Patent Document 1 also reveals that welding is carried out after removing the coated layer in a portion to be welded, in order to solve the problem described above.
Prior Art Document
Patent Document
Patent Document 1 Japanese Translation Published No. 2009534529 of the PCT International Publication
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Description of the Invention
Problems to be Solved by the Invention [0011] According to the method disclosed by Patent Document 1, it is possible to suppress the movement and concentration of aluminum in the weld metal from the coated layer, and it is possible to suppress adverse effects caused by the movement and aluminum concentration. However, a steel sheet obtained using the method disclosed by Patent Document 1 does not have a coated layer on a portion to be welded, and therefore there is a problem with the occurrence of decarburization or oxidation of the weld metal during hot stamping. , or a problem of a member obtained by hot stamping having poor corrosion resistance. In addition, a new step of removing the coated layer in a portion to be welded is required, and therefore, degradation in productivity, or an increase in costs, is caused.
[0012] The invention was produced in consideration of the techniques described above of the related technique, and an objective of the invention is to provide a tailor-made sheet for hot stamping that enables ensuring sufficient joint strength for hot stamping, and a method for production of the same. In addition, another objective of the invention is to provide a hot stamped member obtained using the custom-made hot stamping plate, and a method for producing it.
Means to Solve the Problem [0013] The present inventors conducted studies to omit the process for removing the coated layer in a portion to be welded, which is proposed in Patent Document 1. That is, intensive studies were conducted to put into practice the use of a custom-made sheet for hot stamping obtained by carrying out joint welding on the coated layer in a portion to be welded
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5/56 on an aluminum-coated steel plate, without removing the coated layer, which is difficult to achieve in Patent Document 1.
[0014] As a result, the inventors recently found that when the movement and concentration of aluminum in the weld metal from the coated layer is accelerated, instead of preventing the movement and concentration of aluminum in the weld metal from the layer coated, as proposed in Patent Document 1, it is possible to form an aluminum layer on the surface of the weld metal. In addition, it was recently verified that when the aluminum layer is formed on the surface of the weld metal by accelerating the movement and concentration of aluminum in the weld metal, it is possible to solve the problem of the occurrence of decarburization or oxidation of the weld metal during hot stamping, or the limb problem obtained through hot stamping having poor corrosion resistance.
[0015] On the other hand, a new problem has also been found that, when the movement and concentration of aluminum in the weld metal from the coated layer are excessively accelerated, it is difficult to ensure sufficient joint resistance in the aluminum-coated steel plate hot stamped.
[0016] The fact described above was verified to result not from the formation of the intermetallic region, as described in Patent Document 1, but from the fact that the movement and concentration of aluminum in the weld metal from the coated layer during welding increases the Ac ₃ point of the weld metal at a high temperature, and thus it becomes difficult to increase the resistance by hardening the weld metal in a hot stamping process, or the fact that, in some cases, resistance is weakened due to tempering.
[0017] Consequently, the inventors conducted studies to
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6/56 ensure sufficient joint strength in a hot stamped member after hot stamping even when the weld metal is not sufficiently tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process . As a result, the inventors came up with a new idea of increasing the strength of the weld metal in advance before the hot stamping process to achieve high strength of the weld metal by tempering in the hot stamping process.
[0018] In addition, the inventors have found that when the movement and concentration of aluminum in the weld metal from the coated layer is controlled within an appropriate range, and the Ac ₃ point of the weld metal is adjusted to a predetermined temperature , or lower, it is possible to quench the weld metal during a cooling process in a joint welding process which is a process before hot stamping, and in this way it becomes possible to increase the strength of the weld metal . That is, it has been found that, even when the weld metal is not tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process, it is possible to ensure sufficient joint strength in a stamped member a hot after hot stamping.
[0019] Additionally, the inventors found that the increase in the durability of the weld metal enables the acceleration of tempering during the cooling process in the joint welding process, which is a process before hot stamping, adjusting the Ac point of the weld metal. welding at a predetermined or lower temperature, capable of using tempering in the hot stamping process, and adjusting the minimum thickness of the weld metal to a predetermined or greater value, which enables it to ensure resistance to
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7I5Q highest joint after hot stamping.
[0020] In addition, the inventors found that specifying the shape of the weld metal enables a safer contact between the vicinity of a welded portion on a plate made to measure for hot stamping and a die, and thus it is possible to more safely temper the vicinity of the welded portion on the sheet made to measure for hot stamping through the heat transfer of the die.
[0021] Additionally, the inventors have found that by increasing the oxygen content in the weld metal, it is possible to improve the hardness of the weld metal.
[0022] The present invention was produced based on the new findings described above, and the essences of these are as described below.
[0023] (1) That is, according to a first aspect of the present invention, a custom-made sheet for hot stamping is provided, including a welded portion formed by top weld of a first aluminum coated steel sheet, and a second aluminum-coated steel plate, where an average concentration of Al of a weld metal in the welded portion is 0.3% by mass to 1.5% by mass, in the following formula (1), a point Ac3 of the weld metal defined in ° C unit is 1250 ° C or lower, and, in addition, an aluminum layer formed during butt welding is present on a surface of the welded portion.
Expression 1
Ac ₃ = 9 1 0 - 2 3 0 XC ” ^S -1 5. 2XN1 + 44. 7XSI + 104
XV +3 1. 5XMo + 13. lXW-3 0XMn-UXCr-2 0XCu + 700XP + 400XAl + 120XAs + 400XTi - * - Formula (1) [0024] Here, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti in the formula represent quantities of individual elements in the weld metal in mass%, and elements not contained are considered to have
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8/56 an amount of zero in computing.
[0025] (2) on the plate made to measure for hot stamping, according to the above described (1), additionally, in the following formula (2), Δϊμ defined in unit second can be 0.5 second or longer.
Expression 2
SiA-S '<Al Mn Cu Ni Mo Crx (l-0.16xTc>). _o ]
Atpj = cxp ·! 10.6 C + -------- + - + - 4 4 + ---- 1 ----------- '+ ΔΗ - 4.81
II 24 6 15 12 6 8. II • · · Formula (2) [0026] Here, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in the formula represent the quantities of individual elements in the weld metal in mass%, elements not contained are considered to have a quantity of zero in the computation, and ΔΗ in the formula represents a numerical value defined as described below according to the quantity of B in mass%, and fN when the fN is adjusted to (0.02N) / 0.02 using the amount of N in the weld metal in mass%. When B <0.0001, ΔΗ = 0,
When 0.0001 <B <0.0002, ΔΗ = 0.03χίΝ,
When 0.0002 <B <0.0003, ΔΗ = 0.06χίΝ, and
When 0.0003 <B, ΔΗ = 0.09χίΝ.
[0027] (3) In the plate made to measure for hot stamping, according to the above described (1) or (2), additionally, an Aci point of the weld metal defined in ° C unit in the following formula (3) it can be 860 ° C or higher.
Expression 3
Aci = exp (6.5792 - 0.038058 x C + 0.052317 x Si + 0.011872 x Ni 0.045575 x V + 1.18057 x Al + 0.011442 x W-0.013403 x Cu + 5 , 5207 x B + 0.91209 x S - 1.1002 x D + 0.060014 x Mn x C - 0.96628Cr x C + 0.550625 x Cr x Si + 0.39802 x Mo x C - 0.3482 x Mo x Mn + 0.40986 x Mo x Si - 0.12959 x Mo x Cr - 0.048128 x Ni x C - 0.01090 x Mn ² 0.03550 x Si ² + 0.010207 x Cr ² + 0 , 36074 x Mo ² - 0.0030705 x
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Ni ² } ... Formula 3 [0028] Here, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in the formula represent quantities, in mass%, of individual elements in the weld metal, and elements not contained are considered to have a zero content in computation.
[0029] (4) In the plate made to measure for hot stamping, according to any of the above described (1) to (3), when a thickness of a thinner portion of the weld metal is represented by t in mm unit , the plate thickness of the first aluminum-coated steel plate is represented by t1 in mm unit, and the plate thickness of the second aluminum-coated steel plate is represented by t2 in mm unit, in a case where t1 is equal to t2, up to 80% or more of t1; and in a case where t1 is different from t2, t can be 80% or more of the smallest of t1 and t2.
[0030] (5) In the plate made to measure for hot stamping, according to any of the above described (1) to (4), in a case where t1 which is the plate thickness of the first coated steel plate of aluminum is equal to t2 which is the plate thickness of the second aluminum coated steel plate, a maximum height of the weld metal can be 300 pm, or shorter of an extended line of a surface of the first coated steel plate. aluminum; and in a case where t1 is different from t2, a maximum height of the weld metal can be 300 pm or shorter from an extended line of a thicker surface of the first aluminum-coated steel plate and the second aluminum plate. aluminum coated steel.
[0031] (6) In the plate made to measure for hot stamping, according to any of the above described (1) to (5), an oxygen content in the weld metal can be 50 ppm or higher than a content of medium oxygen in a first steel sheet which is a base material for coating the first aluminum coated steel sheet
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10/56 and the second steel sheet which is a base material for coating the second aluminum coated steel sheet.
[0032] (7) According to a second aspect of the present invention, there is provided a method for producing a custom-made sheet for hot stamping in which joint welding is carried out using a first aluminum-coated steel sheet and a second aluminum-coated steel plate, including determination of welding conditions so that an average concentration of Al of a weld metal in a welded portion falls within a range of 0.3% by mass to 1.5% by mass, and an Ac3 point (° C) of the weld metal defined by the following formula (1) is 1250 ° C or lower; and forming an aluminum layer derived from the aluminum-coated layers of the first aluminum-coated steel plate and the second aluminum-coated steel plate on a weld metal surface in the welded portion by performing welding under the welding conditions.
Expression 4
Ac3 = 910 - 230 x C ⁰ ' ⁵ - 15.2 x Ni + 44.7 x Si + 104 x V + 31.5 x Mo +
13.1 x W - 30 x Mn - 11 x Cr - 20 x Cu + 700 x P + 400 x Al + 120 x As + 400 x Ti ... Formula (1) [0033] Here, C, Ni, Si , V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti in the formula represent quantities of individual elements in the weld metal in mass%. In addition, elements not contained are considered to have an amount of zero in the computation.
[0034] (8) In the method for producing a custom-made sheet for hot stamping, as described above (7), when determining the welding conditions, in addition, the welding conditions can be determined so that Aím defined by the following formula (2) in second units is 0.5 seconds, or longer.
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Expression 5
Si + 5xAl Μη Cu Ni Mo Crx (l-0.16xTc>) _{Λ rr} j. "1
Atpj = expl 10.6 C + ------- + - + - 4 4 + 1 ----------- '+ ΔΗ - 4.81
II 24 6 15 12 6 8. II • · · Formula (2) [0035] Here, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in the formula represent quantities of individual elements in the weld metal in mass%, and elements not contained are considered to have a zero amount in computing. In addition, ΔΗ in the formula represents a numerical value defined as described below according to the amount of B in mass%, and fN when the fN is adjusted to (0.02-N) / 0.02 using the amount of N in the weld metal in mass%.
When B <0.0001, ΔΗ = 0,
When 0.0001 <B <0.0002, AH = 0.03xfN,
When 0.0002 <B <0.0003, AH = 0.06xfN, and
When 0.0003 <B, AH = 0.09xfN.
[0036] (9) In the method for producing a custom-made sheet for hot stamping, as described above (7) or (8), additionally, when determining the welding conditions, the welding conditions can be determined so that an Aci point defined by the following formula (3) in unit ° C is 860 ° C, or lower.
Expression 6
Aci = exp (6.5792 - 0.038058 x C + 0.052317 x Si + 0.011872 x Ni 0.045575 x V + 1.18057 x Al + 0.011442 x W - 0.013403 x Cu + 5 , 5207 x B + 0.91209 x S - 1.1002 x D + 0.060014 x Mn x C - 0.96628Cr x C + 0.550625 x Cr x Si + 0.39802 x Mo x C - 0.3482 x Mo x Mn + 0.40986 x Mo x Si - 0.12959 x Mo x Cr - 0.048128 x Ni x C - 0.01090 x Mn ² 0.03550 x Si ² + 0.010207 x Cr ² + 0 , 36074 x Mo ² - 0.0030705 x Ni ² } ... Formula 3) [0037] Here, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in the formula
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12/56 represent the quantities, in mass%, of individual elements in the weld metal, and elements not contained are considered to have a content of zero in the computation.
[0038] (10) In the method for producing a custom-made sheet for hot stamping, in accordance with any of the above (7) to (9), additionally, when determining the welding conditions, the welding conditions can be determined so that when a thickness of a thinner portion of the weld metal is represented by t in unit mm, a sheet thickness of the first aluminum-coated steel sheet is represented by t1 in unit mm, and a thickness of the second aluminum-coated steel plate is represented by t2 in mm unit, in a case where t1 is equal to t2, at is 80% or more of t1; and in a case where t1 is different from t2, t is 80% or more less than t1 and t2.
(11) In the method for producing a custom-made sheet for hot stamping, according to any of the above (7) to (10), additionally, when determining the welding conditions, the welding conditions can be determined so that in a case where t1 which is the plate thickness of the first aluminum coated steel plate is equal to t2 which is the plate thickness of the second aluminum coated steel plate, a maximum height of the metal of weld is 300 pm or shorter from an extended line of a surface of the first aluminum-coated steel plate; and in a case where t1 is different from t2, a maximum height of the weld metal is 300 pm or shorter from an extended line of a thicker surface of the first aluminum-coated steel sheet and the second steel sheet aluminum coated.
[0040] (12) In the method for producing a plate made under
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13/56 measure for hot stamping, according to any of the above (7) to (11), when determining the welding conditions, the welding conditions can be determined so that an oxygen content in the weld metal it is 50 ppm or higher than an average oxygen content in a steel sheet which is a base material for coating the first aluminum coated steel sheet and the second aluminum coated steel sheet.
[0041] (13) In the method for producing a custom-made sheet for hot stamping, according to any of the above (7) to (12), the joint weld can be any one of laser welding, welding electron beam, and plasma welding. [0042] (14) In the method for producing a custom-made sheet for hot stamping, according to any of the above (7) to (13), the joint welding can be laser welding performed while providing a filler wire.
[0043] (15) In accordance with a third aspect of the present invention, there is provided a hot stamped member obtained by performing hot stamping on the custom-made hot stamping plate, according to any of the above (1) to (6), in which a product of a hardness of the weld metal and a thickness of a thinner portion of the weld metal is greater than both a product of a hardness of the first aluminum-coated steel sheet and the thickness of sheet of the first aluminum-coated steel sheet, and a product of a hardness of the second aluminum-coated steel sheet and a sheet thickness of the second aluminum-coated steel sheet.
[0044] (16) In accordance with a fourth aspect of the present invention, there is provided a method for producing a hot-stamped member including performing hot stamping on the custom-made hot stamping sheet, according to
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14/56 any of the above (1) to (6), where, after hot stamping, a product of a hardness of the weld metal and a thickness of a thinner portion of the weld metal are adjusted to be larger than both a product of a hardness of the first aluminum-coated steel sheet and a sheet thickness of the first aluminum-coated steel sheet, and a product of a hardness of the second aluminum coated steel sheet and a thickness of the second aluminum-coated steel plate.
Effects of the Invention [0045] According to the present invention, it is possible to provide a custom-made sheet for hot stamping having a high joint strength after hot stamping even when an aluminum-coated steel sheet is welded by joint without removal of a coated layer in a portion to be welded.
[0046] In addition, according to the present invention, it is possible to provide a hot stamped member having a high joint strength after hot stamping even when a plate made to measure for hot stamping obtained by carrying out joint welding in a steel sheet coated with aluminum without removing a coated layer in a portion to be welded, is used.
Additionally, since the surfaces of the weld beads of the custom-made sheet described above for hot stamping and hot stamped members are covered with aluminum, it is possible to solve the problem of the occurrence of decarburization or oxidation of the weld metal during hot stamping. , or the problem of poor corrosion resistance after hot stamping.
Brief Description of the Drawing [0047] FIG. 1 is a photograph showing an example of a cross section of a welded portion formed by making
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[0048] FIG. 2 is a flowchart showing an example of a method for producing a custom-made sheet according to the present embodiment.
[0049] FIG. 3 is a flow chart showing an example of a method for producing a hot stamped member, according to the embodiment.
Embodiments of the Invention [0050] Hereinafter, a plate made to measure for hot stamping, according to an embodiment of the present invention (hereinafter, in some cases, referred to as the plate made to measure, according to the embodiment ), a method for producing the same, a hot stamped member, according to an embodiment of the present invention (hereinafter, in some cases, referred to as the hot stamped member, according to the embodiment), and a method for producing it, will be described.
1. Custom-made sheet for hot stamping [0051] (The average concentration of Al of a weld metal: 0.3% by mass to 1.5% by mass) [0052] The custom-made sheet, according to with the embodiment, it is obtained by joining multiple aluminum-coated steel sheets through joint welding, and a welded portion containing a weld metal is present in a welded joint portion.
[0053] In the custom-made sheet, according to the embodiment, it is important to control the movement of aluminum in the weld metal of a coated layer within an appropriate range, as described below, to ensure the bond strength after hot stamping by suppression of decarburization or oxidation
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16/56 of the weld metal during hot stamping, and additionally ensure corrosion resistance after hot stamping. To control the movement of aluminum in the weld metal from the coated layer, it is important to adjust the average concentration of Al in the weld metal in a range of 0.3% by mass to 1.5%.
[0054] The inventors found that, in a plate made to measure for hot stamping obtained by butt welding of a steel plate coated with aluminum without removing a coated layer in a portion to be welded, when the average concentration of Al in the weld metal it is adjusted to a certain value or more, by movement and concentration of aluminum in the weld metal of a coated layer, it is possible to form an aluminum layer on the weld metal surface. That is, it has been found that the surface of the weld metal (weld bead) is covered with an aluminum layer formed during joint welding, as shown in FIG. 1. In addition, it was recently verified that, since the surface of the weld metal is covered with the aluminum layer, it is possible to solve the problem of the occurrence of decarburization or oxidation of the weld metal during hot stamping, or the problem of a member obtained by hot stamping (hot stamped member) having poor corrosion resistance. The reason for the fact described above is not clear, but it is considered that, during joint welding, a coating metal (aluminum) molten in a heat-affected zone, is removed in the flux in the weld bead melting pool, and the coating metal having a lower melting point than steel diffuses to the surface of the weld bead even after the melt puddle solidifies, thereby covering the weld bead.
[0055] When the average concentration of Al in the weld metal is less than 0.3% by mass, the movement and concentration of
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17/56 aluminum in the weld metal from the coated layer is not enough, and it is not possible to sufficiently form an aluminum layer on the weld metal surface. Therefore, it is not possible to solve the problem of the occurrence of decarburization or oxidation of the weld metal during hot stamping, or the problem of a member obtained through hot stamping having poor resistance to corrosion. Therefore, in the embodiment, the average concentration of Al in the weld metal is adjusted to 0.3% by weight, or more. [0056] On the other hand, in the plate made to measure for hot stamping obtained by top welding of a steel plate coated with aluminum, without removing a coated layer in a portion to be welded, when the movement and concentration of aluminum in the weld metal from the coated layer are properly controlled, it is possible to temper the weld metal during a cooling process in a joint welding process which is a process before hot stamping. In this case, it becomes possible to increase the resistance of the weld metal in advance before a hot stamping process. That is, even when the weld metal is not tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process, it is possible to ensure sufficient joint strength after hot stamping (on a stamped member) the hot). On the other hand, in a case where the aluminum moves excessively and is concentrated in the weld metal from the coated layer, the average concentration of Al in the weld metal becomes very high. Since Al is a ferrite first, when the average concentration of Al in the weld metal becomes very high, austenite is not generated during the cooling process in the joint welding process, which is a process before hot stamping, and the weld metal is not sufficiently tempered during the cooling process in the
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18/56 welding process. Therefore, it is not possible to effect the high strength of the weld metal, and it is impossible to ensure sufficient joint strength after hot stamping. When the movement and concentration of aluminum in the weld metal from the coated layer is properly suppressed, it is possible to ensure sufficient joint strength after hot stamping.
[0057] When the average concentration of Al in the weld metal exceeds 1.5% by mass, it is not possible to ensure sufficient joint strength after hot stamping for the reason described above. Therefore, the average concentration of Al in the weld metal is adjusted to 1.5% by weight, or less. When the average concentration of Al in the weld metal is adjusted to 1.5% by mass or less, it is possible to obtain a hardened structure, such as a martensite structure, or a martensite and bainite structure, by tempering the weld metal. during the cooling process in the joint welding process, which is a process before hot stamping.
(The Ac ₃ point of the weld metal: 1250 ° C or lower) [0058] The inventors found that even when the average concentration of Al in the weld metal is 1.5% by weight or less, in the chemical composition of the welding material, in a case where the C or Mn content is small, and the Si content is large, it becomes difficult to increase the resistance of the weld metal in tempering advance during the cooling process in the welding process that is a process before hot stamping, that is, it is difficult to ensure sufficient joint strength after hot stamping. With respect to the fact described above, the inventors conducted intensive studies. As a result, it was confirmed that when the Ac ₃ point (° C) defined by the following formula (1) is adjusted to 1250 ° C or lower, it becomes possible to increase the
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19/56 resistance of the weld metal in advance by tempering the weld metal during the cooling process in the joint welding process, which is a process before hot stamping. That is, it has been experimentally confirmed that, when the point Ac3 is set to 1250 ° C or lower, sufficient joint strength can be ensured after hot stamping even when the weld metal is not tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process.
[0059] In a case where the weld metal Ac3 point defined by formula (1) is higher than 1250 ° C, it becomes difficult to temper the weld metal during the cooling process in the joint welding process , which is a process before hot stamping, and therefore it is difficult to ensure sufficient joint strength after hot stamping. Therefore, the weld metal Ac3 point, defined by formula (1), is adjusted to 1250 ° C or lower.
Expression 7
Ac3 = 910 - 230 x C ⁰ ' ⁵ - 15.2 x Ni + 44.7 x Si + 104 x V + 31.5 x Mo +
13.1 x W - 30 x Mn - 11 x Cr - 20 x Cu + 700 x D + 400 x Al + 120 x As + 400 x Ti ... Formula (1) [0060] Here, the element symbols in the formula (C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti) represent the quantities (mass%) of individual elements in the weld metal. In addition, elements not contained are considered to have an amount of zero in the computation.
[0061] The formula in point Ac3 is a formula well known by a document (The Physical metallurgy of Steels, authored by Leslie. W. C, translated and edited by Kouda Shigeyasu, published by Maruzen Company, Limited (1985), p . 273).
[0062] Since a lower Ac3 point is more advantageous for the
Petition 870190039032, of 25/04/2019, p. 22/71
20/56 tempering during the cooling process in the joint welding process, which is a process before hot stamping, the lower limit of point Ac3 is not particularly specified. (Aim of the weld metal: 0.5 second or longer) [0063] As described above, to ensure sufficient joint strength after hot stamping, it is important to increase the strength of the weld metal in tempering feed during cooling process in the joint welding process, which is a process before hot stamping. To increase the resistance of the weld metal in tempering advance, it is preferable to increase the durability of the weld metal in addition to the control of the Ac3 point.
[0064] Aim defined by the following formula (2) is the durability index that indicates a limit cooling time (seconds) in which the weld metal structure becomes completely martensite due to cooling. A higher value of Aím indicates easier tempering. Formula (2) is described in, for example, a document (Kasuya and Hashiba, Nippon Steel Technical Report No. 385, p. 48 to 55 (2006)).
[0065] When Aím defined by the following formula (2) is set to 0.5 seconds or longer, it is possible to increase the resistance of the weld metal in tempering advance during the cooling process in the joint welding process which is a process before hot stamping. In addition, an increase in weld metal strength facilitates ensuring sufficient joint strength after hot stamping. Therefore, in the custom-made sheet, according to the embodiment, Aim of the weld metal defined by formula (2) is preferably adjusted to 0.5 second or longer. It is most preferably set to 1.0 seconds or longer. Since a longer Aím leads to a
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21/56 higher durability, it is not necessary to particularly limit the upper limit of Aím.
Expression 8 λχ LL Si + 5xAl Mn Cu Ni Mo Crx (l-0.16x4Cr) _Λ „1
Atu = cxp ·! 10.6 C + -------- + - + - 4 4--4 ----- * ----------- ^l + Mí - 4.81
II 24 615 12 6 8. } I • · · Formula (2) [0066] Here, the respective element symbols (C, Si, Al, Mn, Cu, Ni, Mo, and Cr) represent the contents (mass%) of the elements in the metal weld, and non-contained elements are considered to have a zero content in computation. In addition, ΔΗ in the formula represents a numerical value defined as described below according to the amount of B in mass% when the fN is adjusted to (0.02N) / 0.02 using the amount of N in the weld metal in % in large scale. When B <0.0001, ΔΗ = 0,
When 0.0001 <B <0.0002, AH = 0.03xfN,
When 0.0002 <B << 0.0003, AH = 0.06xfN, and
When 0.0003 <B, AH = 0.09xfN.
[0067] (The weld metal's Aci point: 860 ° C, or lower) [0068] As described above, when the movement and concentration of aluminum in the weld metal from the coated layer is accelerated, the Ac ₃ point of the weld metal reaches a high temperature, and therefore it becomes difficult to adjust the point Ac ₃ of the weld metal to the heating temperature, or lower, during the hot stamping process. However, it is possible to adjust the Aci point of the weld metal to the heating temperature, or lower, during the hot stamping process. When the Aci point is adjusted to the heating temperature, or lower, during the hot stamping process, it becomes possible to achieve high strengthening of the weld metal by tempering in the hot stamping process. Therefore, it becomes possible to ensure a stronger joint resistance after hot stamping. Therefore, the
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22/56 Aci point of the weld metal defined by the following formula (3) is preferably 860 ° C or lower.
Expression 9
Aci = exp (6.5792 - 0.038058 x C + 0.052317 x Si + 0.011872 x Ni 0.045575 x V + 1.18057 x Al + 0.011442 x W - 0.013403 x Cu + 5 , 5207 x B + 0.91209 x S - 1.1002 x D + 0.060014 x Mn x C - 0.96628Cr x C + 0.550625 x Cr x Si + 0.39802 x Mo x C - 0.3482 x Mo x Mn + 0.40986 x Mo x Si - 0.12959 x Mo x Cr - 0.048128 x Ni x C - 0.01090 x Mn ² 0.03550 x Si ² + 0.010207 x Cr ² + 0 , 36074 x Mo ² - 0.0030705 x Ni ² } ... Formula 3) [0069] Here, the respective element symbols (C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo) represent the quantities (% by mass) of the elements in the weld metal, and elements not contained are considered to have a quantity of zero in the computation.
[0070] Since a lower point Ac1 is more advantageous for tempering in the hot stamping process, the lower limit of point Ac1 is not particularly specified.
(Shape of the weld metal) [0071] In the butt weld carried out with the edge surfaces cut by shearing steel sheets (steel sheet coated with aluminum) brought face to face with each other, it is normal to weld the edge surface with a weld bead having a concave (locally narrowed) surface with respect to the steel sheet surface in consideration of the cutting precision of the edge surface. In this case, the thickness of the thinner portion of the weld metal of the custom-made sheet, according to the embodiment, is preferably adjusted to be 80% or more of the sheet thickness of the coated steel sheet welded by joining with aluminum. . Then, it is possible to increase the strength of a welded joint section (the thinner plate thickness in a case where the
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23/56 plate thicknesses are different). The thickness of the thinner portion of the weld metal is more preferably set to be 90% or more of the plate thickness (the thinner plate thickness in a case where the plate thicknesses are different) than the coated steel plate welded by joining with aluminum. The thickness of the thinner portion of the weld metal in the embodiment refers to the thickness of the thinner portion of the portions that are completely produced from the weld metal in the direction of the plate thickness on the steel plate.
[0072] To increase the thickness of the weld metal, for example, the locally narrowed portion can be filled using a filler metal, such as a filler wire. However, in a case where the thickness of the weld metal is increased by carrying out joint welding on the edge surface of the steel sheet using a filler metal, such as a filler wire for the purpose of improving the joint strength , the maximum height of the weld metal surface is preferably adjusted to 300 pm or shorter from an extended line of the surface (the thickest surface in a case where the plate thicknesses are different) of the welded coated steel sheet by joining with aluminum. Then, it is possible to bring the vicinity of the welded portion more securely to the plate made to measure for hot stamping and a matrix in contact with each other during hot stamping. Therefore, it is possible to more safely carry out the tempering of the vicinity of the welded portion on the sheet made to measure for hot stamping through heat transfer from the die.
(The oxygen content of the weld metal) [0073] The oxygen content in the weld metal for the custom-made sheet, according to the embodiment, is preferably adjusted to 50 ppm or higher than the content of medium oxygen in the steel plate
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24/56 which is a base material for coating coated steel sheet welded by joining with aluminum. Then, while the detailed mechanism is unclear, the martensite block size in the weld metal becomes small, and the weld metal hardness is improved. To increase the oxygen content of the weld metal, it is possible, for example, to use a metal core bead when welding. In a case where the metal core cord is used, the oxygen content varies depending on the amount of metal core cord supply, and therefore the metal core cord can be supplied in an amount according to the desired oxygen content. The upper limit of the difference between the oxygen content in the weld metal and the average oxygen content of the steel sheet, which is the base material for coating the coated steel sheet welded by joining with aluminum, is not particularly limited, but it is preferably adjusted to 300 ppm or less, from the point of view of suppressing the formation of a coarse oxide.
(Aluminum-coated steel plate) [0074] The aluminum-coated steel plate used in the custom-made plate, according to the embodiment, is not particularly limited. For example, as the aluminum-coated steel sheet offered for joint welding to obtain the custom-made sheet, according to the embodiment, steel sheets of the same type can be used, but steel sheets having different characteristics, such as as resistance, they can be used for the proposal to provide different characteristics to the individual portions.
[0075] In a case where the aluminum coated steel sheet is applied to a portion where the improvement of the mechanical characteristics by the hot stamping temper is required, an aluminum coated steel sheet, including as the base material, for example, a steel sheet having a chemical composition
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25/56 containing by mass% C: 0.15% to 0.25%, Si: 0.1% to 0.35%, Mn: 0.8% to 1.8%, Cr: 0.01% 0.5%, B: 0.1% or less (including 0%) with a remainder of Fe and impurities, or a steel plate having a chemical composition additionally containing one or more of Ti, Nb, and Mo, in the basis of the chemical composition described above, can be used. [0076] It is not necessary to specify in particular the strength of the aluminum-coated steel sheet to be welded by joining, which is used in the custom-made sheet, according to the embodiment, from the point of view of the strength after hot stamping . However, when operability, such as suppression before joint welding, is taken into account, the tensile strength before hot stamping is preferably in the range of 270 MPa to 590 MPa.
[0077] The sheet thickness range of the aluminum-coated steel sheet to be welded by joining, which is used in the custom-made sheet, according to the embodiment, is, for example, 0.8 mm to 4.0 mm, and is preferably 0.8 mm to 2.0 mm.
[0078] The aluminum-coated layer on the aluminum-coated steel sheet prevents corrosion of the steel sheet, and prevents the generation of a scale (an iron oxide) generated by the oxidation of the surface of the steel sheet heated to a high temperature during the hot stamping of the steel sheet. Since the aluminum-coated layer has a higher and similar boiling point than a layer coated with an organic material, or layers coated with other metallic materials (for example, Zn-based material), when formed using a hot stamping, it becomes possible to process the aluminum-coated layer at a high temperature. Therefore, the feature described above is advantageous from the point of view of tempering the welding material in the hot stamping process. From the above point of view
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26/56 described, it is preferable to form the aluminum-coated layer on both surfaces of the steel sheet.
[0079] The aluminum-coated layer can be formed on the surface of the steel sheet using, for example, a hot-dip coating method. Any coated layers can be used, considering that the coated layer contains a major component of Al. There is no particular limitation related to components other than Al. For example, the coated layer can contain 3 wt% to 15 wt% of Si. When the Si content is adjusted to 3% by mass or more, it is possible to control an alloy layer generated during the coating of a hot-dip metal. On the other hand, when the Si content is adjusted to 15% or less, it is possible to ensure favorable operability and corrosion resistance in the coated layer.
2. Method for producing a custom-made hot stamping plate (The method for adjusting the chemical composition of the weld metal) [0080] As described above, on the custom-made hot stamping plate obtained by butt welding of an aluminum-coated steel plate, without removing the coated layer in a portion to be welded, an Ac3 spot of the weld metal becomes high due to the movement and concentration of aluminum in the weld metal from the coated layer during welding junction. As a result, there is a case where it becomes difficult to increase the resistance by tempering the weld metal in the hot stamping process, or the resistance is decreased due to tempering.
[0081] Therefore, in the method for producing a custom-made plate, according to the embodiment, welding is carried out after the conditions are adjusted so that the average concentration of Al of the weld metal is in a range of 0.3 mass% to 1.5% in
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27/56 mass, and the AC3 point (° C) of the weld metal defined by the formula described above (1) is 1250 ° C or lower (welding condition determination process: S1). In this case, since it becomes possible to increase the resistance of the weld metal in advance by tempering during the cooling process in the joint welding process which is a process before hot stamping, it is possible to ensure sufficient resistance to the joint after hot stamping, even when the weld metal is not tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process.
[0082] Additionally, in the method for producing a custom-made plate, according to the embodiment, an aluminum layer derived from the aluminum-coated layer on the aluminum-coated steel plate to be welded is formed on the metal surface welding (welding process: S2).
[0083] Here, the average Al concentration of the weld metal can be computed by computing the Al content incorporated in the weld metal from the coated layer using the widths of the weld beads, and the thickness of the coated layers on the front and the back of the aluminum-coated layer, the groove intervals, and the like, estimating the content of Al incorporated from the steel sheet, which is a base material for coating, or the content of Al incorporated of a filler metal in a case where the filler metal is used, and using the values described above and the weld metal cross-sectional area. That is, the average concentration of Al can be estimated from the chemical composition of the aluminum-coated steel sheet, the coating weight, the sheet thickness, the groove intervals, the chemical composition of the filler metal, and the like. Therefore, it is possible to control the average Al concentration of the weld metal by determining the welding conditions in
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28/56 consideration of the facts described above.
[0084] For example, to adjust the average Al concentration of the weld metal to 1.5% by weight or less, without using a filler metal, it is possible to use a steel plate having a plate thickness in a range of 0.8 mm to 2.0 mm in a case where a double-sided aluminum-coated steel sheet having a coating weight of 40/40 g / m ² is welded by joining with 0.2 mm groove intervals or 0.4 mm. In addition, it is possible to use a steel plate having a plate thickness in the range of 1.4 mm to 4.0 mm in a case where a double-sided aluminum-coated steel plate having a coating weight of 80 / 80 g / m ² is welded by joining with groove intervals of 0.2 mm or 0.4 mm. It is preferable to adjust the sheet thickness of the aluminum-coated steel sheet to 3.0 mm or less in a case where a double-sided aluminum-coated steel sheet having a coating weight of 80/80 g / m ² is junction welded with groove intervals of 0.2 mm or 0.4 mm.
[0085] In a case where the coating weight of the plate is large, depending on the plate thickness of the steel plate as well, there is a case in which it is difficult to adjust the average Al concentration of the weld metal to 1.5% in bulk, or less. In such a case, it is preferable to form gaps in the top portion of the steel sheet, and dilute Al by filling the gaps with the weld metal using a filler metal, such as a filler wire during welding. Then, the amount of the weld metal increases, and it is possible to adjust the Al concentration of the weld metal to 1.5% by weight, or less. A powdered filler metal, or a corded filler metal, can be used; however, from the point of view of performance, it is appropriate to supply the filler metal to the fillet metal in the form of a cord, i.e. a filler wire.
Petition 870190039032, of 25/04/2019, p. 31/71
29/56 [0086] The point AC3 (° C) of the weld metal defined by the formula described above (1), AtM (seconds) defined by the formula described above (2), and the point Ac1 (° C) of the weld metal weld defined by the formula described above (3), can also be estimated using the same method as the control of the average concentration of Al. When welding is carried out under welding conditions in which the chemical composition of the aluminum-coated steel sheet, the weight coating, sheet thickness, groove intervals, chemical composition of the filler metal, and the like, are adjusted based on the above estimate, it is possible to easily adjust the Ac3 point (° C) to 1250 ° C, or more low, AtM (seconds) at 0.5 seconds, or longer, and the point Ac (° C) at 860 ° C, or lower.
[0087] Specifically, it is preferable to estimate the filler metal components and the filler metal supply quantity in the following order, and to experimentally confirm the filler metal components and the filler metal supply quantity using the estimated components and the estimated supply quantity.
[0088] (i) First, the shape of the weld bead is estimated from the plate thickness, groove intervals, and the amount of heat input from the welded steel sheet to be welded. The melting widths of the coated layer are obtained from the estimated widths of the weld beads on the front and rear portion of the steel sheet, and the Al content penetrated by weld from the layer coated on the weld metal that forms the bead. weld is estimated based on the melting width and the thickness of the plate. In addition, a quantity content of the weld metal is obtained from the estimated shape of the weld bead, and the components of the weld metal are estimated from the components (chemical components) of the aluminum-coated steel plate to be welded. composition
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30/56 of the filler wire to be used, and the Al content penetrated by welding into the weld metal.
[0089] (ii) Then, the estimated components of the weld metal are investigated, and whether or not the components are suitable for the conditions described above (the average concentration of Al, the point Ac3, and the like), are determined. In a case where the components are not suitable, the composition of the filler thread is changed, and then whether or not the components are suitable for the conditions described above, is determined.
[0090] (iii) In a case where the components become suitable to the conditions described above by changing the composition of the filler wire, the filler wire is changed to a cord having the new components. In a case where the components are not suitable for the conditions described above even after changing the composition of the filler wire, the quantity content of the weld metal is increased by changing the groove intervals. In addition, the components of the weld metal after changing the groove intervals are estimated in the order of (i) described above, and whether or not the weld metal is suitable for the conditions described above is determined.
[0091] So far, a case in which the components or supply quantity of the filler wire are adjusted with attention paid to the components of the weld metal has been described, but the components or supply quantity of the filler wire can be adjusted by, with respect to the relationship between the hardness of the base metal of the steel sheet and the hardness of the weld metal as well, estimating whether or not the relationship between the hardness of the base metal of the steel sheet and the hardness of the weld metal satisfies the conditions described below using a method to estimate the Hv hardness (BM) of the steel plate and the Hv hardness (WM) of the weld metal after stamping
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31/56 hot.
[0092] As described above, the use of the filler metal makes it possible to adjust the point Ac3 (° C), ÁtM (seconds), and the point Ac1 (° C), not only by diluting Al, but also by adjusting chemical composition, quantity of supply, or the like. In addition, the use of filler metal also makes it possible to improve the joint strength by increasing the thickness of the weld metal, or by controlling the shape. As described above, the thickness of the thinner portion of the weld metal of the custom-made sheet, according to the embodiment, is preferably adjusted to be 80% or more of the sheet thickness (the thinner sheet thickness in a case where that sheet thicknesses are different) from coated steel sheet welded by joining with aluminum. Therefore, an increase in the thickness of the weld metal using the filler metal is preferable from the point of view of improving the joint strength. However, the maximum height of the weld metal surface is preferably adjusted to 300 pm or shorter from an extended line of the surface (the thickest surface in a case where the sheet thicknesses are different) of the coated steel sheet welded by junction with aluminum, since the vicinity of the welded portion on the sheet made to measure for hot stamping is more assuredly tempered.
[0093] From the point of view of increasing the durability of the weld metal, it is advantageous to supply carbon (C), or an element that increases the durability from the filler metal to the weld metal. However, a solid cord having a high C content, or an alloying element, is difficult to produce, and therefore a nucleated cord having an outer layer of steel filled with carbon powder or metal powder (also called a cord metal core, since it does not contain a flux) is preferably used as the
Petition 870190039032, of 25/04/2019, p. 34/71
32/56 filling for ease of use. Since the metal core cord is filled with carbon powder or metal powder, the use of the metal core cord facilitates the supply of C and similar to the weld metal. When welding is carried out using the nucleated bead containing carbon powder, and the C content in the weld metal is made to be greater than the C content of the base metal, it is possible to make the hardness of the weld metal higher than than the hardness of the base metal. A hot stamped member including the weld metal described above is preferable since, even when the hot stamped member is significantly deformed due to an impact or the like, the junction portion does not preferentially fracture, and therefore the greatest resistance to sufficient joint can be ensured.
[0094] In metal core cord, metal powder having a large specific surface area, such as iron powder, is used. Since oxygen is adsorbed on the surface of the metal powder, it is possible to increase the oxygen content in the weld metal by carrying out welding using the metal core bead. As described above, the oxygen content in the weld metal is preferably adjusted to 50 ppm or higher than the average oxygen content in the steel sheet which is a base material for coating the coated steel sheet welded by joining with aluminum. The detailed mechanism is not clear, but an increase in the oxygen content in the weld metal decreases the martensite block size in the weld metal, and the hardness of the weld metal improves. Since the oxygen content varies, depending on the amount of supply from the metal core bead, it is possible to adjust the oxygen content in the weld metal to 50 ppm or higher than the average oxygen content in the steel plate that is a base material for coating coated steel sheet welded by joining with aluminum by adjusting the amount of supply of the metal core cord, according to the desired oxygen content.
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33/56 (Welding method) [0095] As described above, on the plate made to measure for hot stamping obtained by butt welding a steel plate coated with aluminum without removing a coated layer in a portion to be welded, the point Ac3 of the weld metal is made to reach a high temperature by movement and concentration of aluminum in the weld metal from the coated layer during welding, and it is difficult to increase the resistance by tempering the weld metal in the hot stamping process. However, when the strength of the weld metal is increased in advance by tempering during the cooling process in the joint welding process which is a process before hot stamping, it is possible to ensure sufficient joint strength after hot stamping even when the weld metal is not tempered in the hot stamping process, or the weld metal is tempered in the hot stamping process. Therefore, the welding method being used is preferably a welding method in which the weld penetration width of the steel sheet is small, and the cooling rate after welding is rapid. Examples of welding methods capable of the welding described above include welding methods in which the energy density is high, and a heat source capable of intensively heating a narrow region is used, such as laser welding, plasma welding, and electron beam welding. Among the welding methods described above, the laser welding method is more suitable. In the laser welding method, there is no particular limitation regarding the type and the like of a laser oscillator, and welding can be carried out with a laser output, according to the sheet thickness of a steel plate being used. At the same time, it is also possible to supply the filler wire and perform welding as described above.
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34/56 [0096] FIG. 2 illustrates an example of the method for producing the custom-made sheet described above for hot stamping.
3. Hot stamped member (The hardness of the weld metal after hot stamping) [0097] A hot stamped member, according to the embodiment, can be obtained by carrying out the hot stamping on the custom-made plate for stamping a hot, according to the embodiment. In a case where the hot-stamped member is mounted on an automobile as a structural member, the hot-stamped member is required not to maintain fracture in the weld bead even when significantly deformed by an impact, and to exhibit favorable deformability, characteristics energy-absorbing, and stress-proof.
[0098] To satisfy the requirements described above, the strength of the welded portion on the hot stamped member is required to be higher than the strength of any portions on the well-stamped aluminum top coated steel plate.
[0099] That is, to satisfy what was described above, in the hot stamped member, the product of the Hv hardness (WM) of the weld metal after hot stamping, and the thickness t (WM) of the thinner portion of the metal weld, are required to be greater than any of the product of hardness Hv1 (BM) and the thickness of plate t1 (BM) of a coated steel plate welded by joining with aluminum after hot stamping, and the product of hardness Hv2 (BM) and the plate thickness t2 (BM) of the other coated steel plate welded by joining with aluminum after hot stamping, that is, they are required to satisfy
Hv (WM) xt (WM)> min {Hv1 (BM) xt1 (BM), Hv2 (BM) xt2 (BM)}.
[00100] Here, the hardness of the weld metal is the average of three measured values of Vickers hardness obtained by removing the maximum value and the
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35/56 minimum value of values measured at five points in the droplet cross section of the central portion in the direction of the plate thickness, and the hardness of the steel plate is the average of Vickers hardness values measured at three points in the cross section in the same way. In addition, the min {} described above represents a function that returns to the minimum value outside of increases.
[00101] When the point Ac3 of the weld metal is increased due to the movement and concentration of aluminum in the weld metal from the coated layer, there is a case where the weld metal does not become austenite during heating in hot stamping , and is tempered and softened. In such a case too, it is possible to satisfy Hv (WM) xt (WM)> min {Hv1 (BM) xt1 (BM), Hv2 (BM) xt2 (BM)} by selecting the combination of a steel plate to be welded, welding conditions, and the like. Then, the hot-stamped member exhibits sufficient functions as a structural member of an automobile.
[00102] The production conditions for producing the custom-made hot stamping plate, in which a hot stamped member meets the conditions described above, can be obtained, can be experimentally obtained by performing hot stamping on a plate made tailored for hot stamping produced for test proposal, and repeating the verification of the hot stamped member obtained. In addition, it is also possible to estimate whether or not the custom-made sheet meets the conditions described above by estimating the Hv hardness (BM) of the hot-stamped steel sheet and the Hv hardness (WM) of the weld metal.
[00103] For example, first, the C content of the weld metal is estimated from a variety of conditions, such as the chemical composition, plate thickness, and welding conditions of a steel plate to be welded by joining, and the chemical composition of a wire
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36/56 filling in a case where the filling thread is used. Then, the hardness Hv (M) when the weld metal is martensite is calculated from the following formula (4) using the estimated C content. Then, the calculated hardness is subtracted by 100. Then, the lower limit of the weld metal hardness can be estimated.
Expression 10
Hv (M) = 884 x C x (1 - 0.3 x C ² ) + 294 ... Formula (4) [00104] Here, 100 is an experimentally obtained numerical value. Aluminum is incorporated into the weld metal from the layer coated on the aluminum-coated steel plate, and thus the point Ac1 and point Ac3 of the weld metal increase. Therefore, depending on the heating conditions or the average concentration of Al in the weld metal during the hot stamping process, the weld metal does not completely transform into austenite, and instead becomes a two-stage region in the stamping process a hot, or does not turn into austenite at all, and is simply tempered. Here, the weld metal is softened as much as possible in a case where the weld metal does not turn into austenite, and is simply tempered, but it has been experimentally confirmed that the hardness (degree of softness) is at most approximately Hv ( M) -100. Therefore, the lower limit of the weld metal hardness can be obtained using Hv (M) -100.
[00105] In addition, with respect to the hot-stamped steel plate, a hot-stamped steel plate lower than the value of Hv (M) calculated from formula (2) and the value calculated from {1650x (C + f (B)) + 10xSi + 80x (Mn + Cr + V + 2xMo + 2xNb + Cu / 2 + Ni / 4) + Ni / 4} using the element contents (mass%) of the steel plate are employed as the estimated value of Hv (BM).
[00106] Here, f (B) is a value determined by content B, and, in the case of B content> 0.0004% by mass, f (B) = 0.03, and, in the case of
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37/56 B content <0.0004% by mass, f (B) = 0.
[00107] It is possible to estimate the possibility of mounting a steel plate that configures the plate made to measure by determining whether or not the conditions described above are satisfied based on the estimated value of the hardness obtained in the manner described above, on the plate thickness of the steel plate to be welded by joining, and in the minimum weld metal thickness.
4. Method for producing a hot stamped member [00108] A method for producing a hot stamped member, according to the embodiment, includes a hot stamping process (S3) for carrying out hot stamping on the plate made according to the measure described above, according to the embodiment, and, after the hot stamping process, the hardness product of the weld metal and the thinner portion of the weld metal is adjusted to be greater than the hardness product and the plate thickness of any aluminum-coated steel plate to be welded. Hot stamping conditions can follow an ordinary method. That is, in a case where tempering is carried out in the hot stamping process, it is normal to heat an aluminum-coated steel sheet, which is the target, at a temperature of the point Ac3 or higher (for example, approximately 900 ° C), and then perform hot stamping. In a case where the tempered structure is produced in a complex structure, the heating temperature can be adjusted in a range from point Ac to point Ac3.
[00109] From the point of view of safely carrying out the tempering of the sheet made to measure for hot stamping, it is preferable to use a direct water cooling matrix in which the steel sheet is cooled by spraying cooling water from of the die as a die for hot stamping.
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38/56 [00110] FIG. 3 shows an example of the method described above for producing a hot stamped member.
Example 1 [00111] To obtain a custom-made sheet having different resistances in some parts after hot stamping, a steel sheet 1 (HS Steel Type) having a tensile strength that reached 1470 MPa or mott after hot stamping, and steel plates 2 (Steel Types 270, 440, and 590) having tensile strength before hot stamping of 270 MPa, 440 MPa, and 590 Mpa, were prepared. The plate thickness of the steel plates was adjusted in a range of 1.0 mm to 1.8 mm.
[00112] To individually prepare the average aluminum concentrations in the weld metal, a steel plate having an aluminum plate coated on only one surface in an amount of 20 gr / m ² , and steel plates having aluminum plates coated in both surfaces in an amount of 20 gr / m ² per surface, 40 gr / m ² per surface, and 80 gr / m ² per surface, were produced for testing purposes by coating aluminum plates to the external surfaces of the plates. steel without aluminum plate.
[00113] The steel sheets were brought face to face as shear cut, and were welded using fiber laser. The diameter of the laser light collection site was adjusted to 0.6 mm. The shielding during welding was performed using a shielding nozzle (with an internal diameter of 6 mm) having the same axis as the laser beam with the deadlock (the distance between the tip of the nozzle and the surface of the steel plate) adjusted at 10 mm under a condition of the air gas flow rate of 20 liters / min. The welding rate was maintained at 4 m / min, and the laser output was adjusted in a range from 2 kW to 4 kW according to the plate thickness.
[00114] The average concentration of aluminum (Al) in the weld metal was
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39/56 analyzed and obtained using the weld metal sampled after a concentrated layer of Al on the surface is polished and removed after laser welding. In addition, the cross-sectional observation of the welded portion and the measurement of the drop thickness were carried out to verify the qualities of the welded portion after laser welding. [00115] Subsequent to laser welding, hot stamping was performed on the custom-made sheet obtained (material from a piece of metal to be stamped or stamped). Hot stamping was performed by heating the metal piece material to be stamped or minted to 900 ° C through furnace heating, and inserting the metal piece material to be stamped or minted in a matrix, and a planar plate was prepared.
[00116] In order to verify the tempered state by the hot stamping, the hardness of the base metal portion after the hot stamping, and the hardness of the weld bead portion, were measured. In addition, observation of the oxidation state of the weld bead surfaces during hot stamping, and a stress test in which a load was applied orthogonally to the weld bead, were carried out as assessments of the performance of the stamped members in which the resistance was individually provided in some parts. The stress test was carried out according to JIS 2241: 2011.
[00117] As a result of the stress test, it has been determined that sufficient joint strength is obtained in a case where the hot-stamped member was not fractured in the weld metal, but fractured in the base metal. However, in a case where the hot-stamped member fractures the base metal portion at a significantly lower strength than the original strength of the base metal, it has been determined that sufficient joint strength cannot be achieved.
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40/56 [00118] The steel plates used and the results of a variety of measurements made after welding and hot stamping are described in Tables 1 and 2.
[00119] The results of the tests carried out in Nos. 1 to 15 can be evaluated as described below.
[00120] In a case where a steel plate for hot stamping not including plate, and steel plate of Steel Type 270 not including plate, were welded by joining, and then hot stamped, the concentration average aluminum in the weld metal was low, the aluminum layer on the surface of the weld bead was not observed, and thick oxide film was formed on the weld bead. The oxide film was partially removed when touched. Therefore, it was not possible to obtain the adhesiveness of a layer, even when coating was carried out in the state described above (No. 1). In addition, the same test was performed on the steel plate having a plate coated on only one surface in an amount of 20 g / m ² . As a result, as expected, the average aluminum concentration in the weld metal was low, the aluminum layer on the surface of the weld bead was not clear, and a thick oxide film was formed on the surface of the weld bead in the process hot stamping (No. 2).
[00121] Therefore, as a result of selecting a variety of plate coating weight or sheet thickness of steel sheets, and conducting tests in which the average aluminum concentrations in the weld metal are individually prepared, it has been confirmed that , when the average aluminum concentration in the weld metal was 0.3% by mass or more, in the hot stamping process, it was possible to avoid the formation of a thick oxide film (Nos. 3 to 5, 9, 11, 12, and 14). In the steel sheets described above, layers concentrated with Al were formed in order to cover the
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41/56 surfaces of the weld bead due to the aluminum on the plates. The layers concentrated with Al are considered to form a dense oxide film on the surface of the weld bead during hot stamping in synchronization with the selective oxidation of molten aluminum in the weld metal, and suppress the formation of a thick oxide film.
[00122] On the other hand, when the average aluminum concentration in the weld metal becomes very high, the durability of the weld metal has been lost, and the hot-stamped fracture in the weld metal in the stress test after stamping hot (No. 7). When the coating weight of the plate becomes large, or the thickness of the steel plate becomes thin, and thus the average concentration of Al in the weld metal becomes high, at the heating temperature in the process of hot stamping, the metallographic structure cannot be completely transformed into austenite, and the weld metal has not been sufficiently tempered. In addition, it can be confirmed that when the point Ac3 defined by the formula described above (1) was higher than 1250 ° C, austenite was not generated during the cooling process after laser welding, and the weld metal has not been tempered. Therefore, the product of the hardness of the weld metal and the thickness of the thinner portion in the weld metal become smaller than the product of the hardness of the base metal on the low strength side and the plate thickness, the hot stamped member. fracture in the weld metal in the stress test after hot stamping (Nos. 6, 7, and 13).
[00123] In addition, when the thickness of the weld metal becomes very small compared to the plate thickness of the base metal sheet, the strength of the welded joint portion has been decreased, and the hot-stamped fractured member in the weld metal in the stress test after hot stamping (No. 13).
[00124] In addition, Nos. 9 and 10 are examples where the thickness
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42/56 of the weld metal was adjusted by supplying a solid bead (YGW12) having a diameter of 0.9 mm during welding to ensure the thickness of the weld metal. Feed speeds have been adjusted to two types, that is, the same as the welding rate and double the welding rate. At the feed speed, which was the same as the welding rate, fracture occurred in the base metal, and a favorable joint can be obtained (No. 9); however, when the feed speed was adjusted to double the weld rate, the drop becomes high, the base metal in the vicinity of the weld bead was not tempered, fracture occurred at a low strength compared to the strength of the base metal ( No. 10).
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Table 1
No. Steel sheet 1 Steel sheet 2 Reason forfilling feed speed Average Al concentration of weld metal (% by mass) Weld metal Ac3 (° C) Drop surface oxidation during hot stamping Aluminum layer on the drop surface Steel type Thickness ofplate (mm) Plate thickness (gr / m ² / gr / m ² ) Steel type Plate thickness (mm) Plate thickness (gr / m ² / gr / m ² ) 1 HS 1.6 0/0 270 1.6 0/0 - 0.04 836 Yes No 2 1.6 20/0 1.6 20/0 - 0.19 899 Yes No, sure 3 1.6 20/20 1.6 20/20 - 0.35 963 No Yes 4 1.8 40/40 1.8 40/40 - 0.60 1062 No Yes 5 1.0 40/40 1.0 40/40 - 1.05 1243 No Yes 6 1.4 80/80 1.4 80/80 - 1.49 1417 No Yes 7 1.2 80/80 1.2 80/80 - 1.73 1514 No Yes 9 1.8 40/40 1.8 40/40 a 0.44 995 No Yes 10 1.8 40/40 1.8 40/40 Two 0.35 956 No Yes 11 HS 1.8 40/40 440 1.8 40/40 - 0.59 1038 No Yes 12 1.0 40/40 1.0 40/40 - 1.05 1218 No Yes 13 1.8 80/80 1.8 80/80 - 1.16 1263 No Yes 14 HS 1.8 40/40 590 1.8 40/40 - 0.60 1040 No Yes
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Table 2
No. After hot stamping (hot stamped member) Hardness ofsource material on the side ofresistance (Hv) Plate thickness x hardness of source material of resistance side Weld drop hardness (Hv) Weld drop thickness (mm) Weld drop thickness ratio (%) Plate thickness x weld drop hardness Tension test 1 195 312 324 1.5 94 486 Fractured in source material 2 193 309 320 1.45 91 464 Fractured in source material 3 196 314 310 1.55 97 481 Fractured in source material 4 192 346 243 1.7 94 413 Fractured in source material 5 199 199 240 0.9 90 216 Fractured in source material 6 195 273 199 1.3 93 259 Fractured in weld metal 7 192 230 202 1.1 92 222 Fractured in weld metal 9 191 344 260 0.25 / 0.28 * 129 606 Fractured in source material 10 160 288 201 0.45 / 0.65 * 161 468 Low resistance fracture 11 277 499 366 1.65 92 604 Fractured in source material 12 280 280 339 0.95 95 322 Fractured in source material 13 275 495 284 1.35 75 383 Fractured in weld metal 14 370 666 390 1.75 97 683 Fractured in source material tura d and swelling front side / AH swelling structure to the rear side
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Example 2 [00125] To obtain a custom-made sheet having different resistances in some parts after hot stamping, a steel sheet (HS Steel Type) having a tensile strength that reached 1470 MPa or more by hot stamping, and a steel plate (Steel Type 590) having a tensile strength before hot stamping of 590 MPa, were joined by laser welding or plasma welding. The sheet thicknesses of the used steel sheets were adjusted in a range of 1.0 mm to 1.8 mm.
[00126] At this time, to individually prepare the average aluminum concentrations in the weld metal, in addition to a steel plate having no aluminum plate, the steel plates having aluminum plates coated on both surfaces in an amount of 40 g / m ² per surface and 80 g / m ² per surface, were produced.
[00127] The steel sheets were brought face to face as shear cut, the groove intervals between the steel sheets were adjusted, and then the steel sheets were welded using fiber laser, while a filler metal during welding.
[00128] A laser beam having a focal length of 300 mm and an optical light collecting system having a diameter of 0.6 mm light collecting location were used, and the defocusing distance was adjusted to 18 mm. The shielding during welding was carried out using a shielding nozzle (with an internal diameter of 6 mm) having the same axis as the laser beam with the deadlock (the distance between the tip of the nozzle and the surface of the steel plate) adjusted to 10 mm under a condition of the air gas flow rate of 30 liters / min. The welding rate and processing point output were maintained at 4 m / min and 4.5 kW, and the fill metal supply rate was adjusted accordingly.
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46/56 according to the plate thickness and the groove intervals in order to be approximately the same according to the plate thickness. [00129] During the joint welding, the groove intervals between the plates were changed from 0.1 mm to 0.4 mm, a bead having a diameter of 1.2 mm was supplied as the filler metal, the welding was performed, and the weld metal components were adjusted.
[00130] Like the filler metal, four filler wires, that is, an SX-1LD metal core bead manufactured by Nippon Steel & Sumikin Welding Co., Ltd., a YGW12 solid bead, a A-Fill solid bead (C: 0.45%, Si: 0.8%, Mn: 1.5%, P: 0.015%, and S: 0.011%) that was produced at that time for test proposal, and a metal core cord B-fill (C: 0.6%, Si: 0.8%, Mn: 6.0%, P: 0.01%, and S: 0.009%) produced for the test proposal, were used.
[00131] After laser welding, the layer concentrated with Al on the surface was ground and removed, and the average aluminum concentration in the weld metal was analyzed and obtained using the sampled weld metal. In addition, to check the qualities of the welded portion after laser welding, cross-sectional observation of the welded portion and measurement of the drop thickness were performed.
[00132] After welding, the custom-made sheet obtained (material from a piece of metal to be stamped or minted) was hot stamped. Hot stamping was performed by heating the metal piece material to be stamped or minted to 900 ° C through furnace heating, and inserting the metal piece material to be stamped or minted in a matrix, and a planar plate was prepared. After hot stamping, to check the tempering state of the hot stamping, the hardness of the low strength side base metal portion after hot stamping,
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47/56 and the hardness of the weld bead portion were measured. In addition, a stress test in which a load was applied orthogonally to the weld bead was performed like the performance evaluations of the hot-stamped members in which the resistance was individually provided in some parts, and a Charpy impact test was performed to investigate the hardness of the welded portion. In the impact test, the notch location in a notch test specimen was adjusted in the center of the weld metal. The stress test was carried out according to JIS 2241: 2011, and the Charpy impact test was carried out according to JIS Z2242: 2005.
[00133] The steel sheets used and the results of a variety of measurements made after welding and hot stamping are described in Tables 3 and 4.
[00134] The results of the tests carried out in Nos. 101 to 121 can be evaluated as described below.
[00135] When the coating weight of the plate was large, or the plate thickness of the steel plate was thin, the average aluminum concentration in the weld metal becomes very high. In a case where the average aluminum concentration in the weld metal reached 1.5 mass% or more, the durability of the weld metal was lost, and the hot-stamped fracture in the weld metal in the stress test (No 101).
[00136] Even in a case where the average aluminum concentration was suppressed to less than 1.5% by mass, when the groove intervals were narrow, an increase in the C content in the weld metal by a nucleated bead of flow was small, and there is a case where the point Ac3 becomes high. Therefore, at the heating temperature in the hot stamping process, the metallographic structure cannot be completely transformed into austenite, and there is a case where the weld metal was not sufficiently
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Tempered 48/56. It becomes clear that when the AC3 spot becomes higher, the weld metal has not been tempered in laser welding either. According to the tests, when the AC3 point defined by the formula described above (1) was higher than 1250 ° C, the weld metal does not become austenite even during the cooling process after laser welding, and the weld metal has not been tempered. Therefore, it has been confirmed that the hardness of the weld metal becomes low compared to the hardness of the base metal, and the hot-stamped member fractures the weld metal in the stress test after hot stamping. In addition, it was also confirmed in the impact test that fractures propagated in the weld metal and the hot stamped fracture in the weld metal (Nos. 102, 112, 115, and 118).
[00137] Therefore, the groove intervals between the steel plate were adjusted to be large, and the welding was performed by supplying a nucleated bead of flux SX-1LD having a high content of C and a high content of Mn. As a result, it was possible to increase the C content in the weld metal, and increase the average concentration of Al, and therefore the weld metal was tempered, the hardness of the weld metal becomes high compared to the hardness of the base metal, and it can be confirmed that the hot-stamped member fractures the low-strength side metal in the stress test after hot stamping. In addition, since the weld metal hardness was also sufficient in the impact test, the fractures propagated through the base metal, and the hot-stamped fracture in the base metal (Nos. 103 to 106, 109, 113, 114, 116, 117, and 120).
[00138] However, when the thickness of the weld metal was very thin compared to the plate thickness of the base metal sheet, the strength of the welded joint portion decreased, and the hot-stamped fracture in the weld metal after hot stamping (No. 107). When the supply quantity
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49/56 SX-1LD has been excessively increased to prevent fracture in the weld metal, the thickness of the weld metal becomes too thick, the contact between the steel sheet and the matrix in the vicinity of the welded portion becomes poor during hot stamping, the low strength side base metal was not tempered, and the joint fractured at a lower strength than the base metal strength (No. 108). [00139] Then, the effects of the solid YGW12 bead, the Filler-A solid bead produced for the test proposal, in which the C content and the Mn content were increased, and the B-fill metal core cord produced for the test proposal in which the C content and the Mn content were increased to be greater than those of SX-1LD, were investigated.
[00140] As a result of carrying out welding by supplying YGW 12, the value of Aím becomes shorter than 0.5 seconds, and the weld metal was not sufficiently tempered during hot stamping. Therefore, the hardness of the weld metal becomes low compared to the hardness of the base metal, and the hot-stamped member fractured in the weld metal in the stress test after hot stamping (No. 110).
[00141] As a result of carrying out the welding, while supplying the solid Fill-A bead produced for the test proposal, it was possible to increase the C content in the weld metal, and to decrease the average concentration of Al. weld metal has been tempered, and the hardness of the weld metal becomes high compared to the hardness of the base metal. As a result, the hot stamped member fractured in the low strength side base metal in the stress test after hot stamping. However, in the solid bead, the oxygen content in the weld metal is approximately 40 ppm more than the average value of the base metal, and the hardness of the weld metal becomes low, and therefore in the impact test, the fractures propagated in the metal
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50/56 weld, and the hot-stamped member fractured in the weld metal (No. 111).
[00142] As a result of carrying out welding using the B-fill metal core cord produced for testing purposes, despite the conditions under which a large Al content was incorporated into the weld metal (the groove intervals of the plate steel were small, the plate thickness of the steel plate was thin, and the plate thickness was also thick), the weld metal was tempered, and the hardness of the weld metal became high compared to the hardness of the metal base. As a result, it can be confirmed that the hot stamped member fractures the low strength side base in the stress test after hot stamping. In addition, since the metal core strand was used as the filler metal, oxygen was incorporated into the weld metal, the hardness of the weld metal becomes sufficient, and fractures propagated through the base metal, and the stamped member hot fracture in the base metal in the impact test (No. 119).
[00143] As a result of performing welding by supplying SX-1LD using plasma welding instead of laser welding as the welding method, the width of the weld bead becomes as wide as 2 mm or more, and therefore, a large content of Al was supplied from the coated layer of the steel plate to the weld metal, and the estimated value of the point Ac3 was above 1250 ° C, regardless of sufficient groove intervals. As a result, the metallographic structure does not become austenite during the cooling process after laser welding, and the weld metal has not been tempered. Therefore, the hardness of the weld metal becomes small compared to the hardness of the base metal, and it was confirmed that the hot-stamped member fractures the weld metal in the stress test after hot stamping (No. 112). However, as long as the same
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51/56 plasma welding also decreased the average aluminum concentration of the weld metal, as a result of carrying out welding by adjusting the sheet thickness of the steel sheet to be as thick as 1.8 mm, adjusting the weight of coating of the plate at 40 gr / m ² , and supply of SX-1LD, the estimated value of the point Ac3 was below 1250 ° C, and the weld metal was tempered during the cooling process after laser welding. In addition, since it was possible to adjust the thickness of the weld metal in the direction of the plate thickness to be equal to or greater than the plate thickness of the base metal using the bead, the value of the plate thickness * hardness of the metal weld certainly becomes equal to or greater than the plate thickness * hardness of the base metal, and it has been confirmed that the hot stamped fracture in the base metal after hot stamping in the stress test. Additionally, it has been confirmed that, since the metal core cord was used, in the impact test as well, the fractures propagate through the base metal, and the hot-stamped fracture in the base metal (No. 121).
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Table 3
No. Steel sheet 1 Steel sheet 2 Breaks Welding method in Filling Average Al concentration of weld metal (% by mass) Weld metal Ac3 (° C) Atm Amount of oxygen increase of the source metal Ac1 (° C) Steel type Plate thickness (mm) Plate thickness (gr / m ² / gr / m ² ) Steel type Plate thickness (mm) Plate thickness (gr / m ² / gr / m ² ) 101 HS 1.0 80/80 590 1.0 80/80 0.1 Laser SX-1LD 1.51 1387 3.6 120 940 102 1.2 80/80 1.2 80/80 0.1 Laser SX-1LD 1.20 1261 4.3 150 891 103 1.2 80/80 1.2 80/80 0.4 Laser SX-1LD 0.84 1103 12.7 80 840 104 1.2 80/80 1.2 80/80 0.3 Laser SX-1LD 0.97 1160 8.6 80 858 105 1.4 80/80 1.4 80/80 0.4 Laser SX-1LD 0.78 1083 10.4 170 830 106 1.8 80/80 1.8 80/80 0.4 Laser SX-1LD 0.60 1008 11.5 200 803 107 1.2 80/80 1.2 80/80 0.3 Laser SX-1LD 0.97 1160 8.6 150 858 108 1.2 40/40 1.2 80/80 0.4 Laser SX-1LD 0.84 1103 12.7 120 840 109 1.2 40/40 1.2 40/40 0.4 Laser SX-1LD 0.43 937 14 150 780 110 1.2 40/40 1.2 40/40 0.2 Laser YGW12 0.57 1037 0.48 150 788 111 1.2 40/40 1.2 40/40 0.4 Laser Filling-A 0.44 948 4.67 40 781 112 1.2 80/80 1.2 80/80 0.4 Plasma SX-1LD 1.20 1261 4.3 220 891 113 1.0 80/80 1.0 80/80 0.4 Laser SX-1LD 0.92 1132 15.4 120 853 114 1.8 80/80 1.0 80/80 0.4 Laser SX-1LD 0.89 1129 7.3 120 846 115 1.8 80/80 1.0 80/80 0.2 Laser SX-1LD 1.18 1255 2.8 120 886 116 1.6 40/40 1.6 40/40 0.4 Laser SX-1LD 0.34 905 11.5 150 768 117 1.4 40/40 1.4 40/40 0.4 Laser SX-1LD 0.41 935 10.4 120 777 118 1.0 80/80 1.0 80/80 0.2 Laser SX-1LD 1.23 1267 7.1 150 898 119 1.0 80/80 1.0 80/80 0.2 Laser Filling-B 1.23 1204 235 100 847 120 1.0 40/40 1.0 40/40 0.2 Laser SX-1LD 0.64 1031 7.1 100 807 121 1.8 40/40 1.8 40/40 0.4 Plasma SX-1LD 0.38 924 7.1 250 769
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Table 4
No. After hot stamping (hot stamped member) Hardness ofmaterial oflow side originresistance (Hv) Plate thickness x low side source material hardnessresistance Weld drop hardness (Hv) Thickness ofweld drop (mm) Weld drop thickness ratio (%) Plate thickness x drop hardnessweld Tension test Charpy impact test 101 383 383 329 1.1 110 362 Fractured in weld metal Propagated through weld metal 102 384 461 339 1.3 111 451 Fractured in weld metal Propagated through weld metal 103 380 456 395 1.3 108 514 Fractured in source material Propagated through source material 104 382 458 385 1.4 117 539 Fractured in source material Propagated through source material 105 377 528 381 1.5 107 572 Fractured in source material Propagated through source material 106 380 684 385 2.0 111 770 Fractured in source material Propagated through source material 107 382 458 372 0.9 78 346 Fractured in weld metal Propagated through weld metal 108 160 192 390 1.9 158 741 Low fracturedresistance Propagated through source material 109 378 454 395 1.4 117 553 Fractured in source material Propagated through source material
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No. After hot stamping (hot stamped member) Hardness ofmaterial oflow side originresistance (Hv) Plate thickness x low side source material hardnessresistance Weld drop hardness (Hv) Thickness ofweld drop (mm) Weld drop thickness ratio (%) Plate thickness x drop hardnessweld Tension test Charpy impact test 110 381 457 241 1.3 129 313 Fractured in weld metal Propagated through weld metal 111 380 456 403 1.4 129 564 Fractured in source material Propagated through weld metal 112 382 458 339 1.3 108 441 Fractured in weld metal Propagated through weld metal 113 385 385 399 1.2 120 479 Fractured in source material Propagated through source material 114 384 384 373 1.2 120 448 Fractured in source material Propagated through source material 115 385 385 329 1.1 110 362 Fractured in weld metal Propagated through weld metal 116 384 614 387 1.8 113 697 Fractured in source material Propagated through source material 117 379 531 381 1.6 114 610 Fractured in source material Propagated through source material 118 386 386 360 1.1 105 378 Fractured in weld metal Propagated through weld metal 119 384 384 421 1.2 120 505 Fractured in source material Propagated through source material
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No. After hot stamping (hot stamped member) Hardness ofmaterial oflow side originresistance (Hv) Plate thickness x low side source material hardnessresistance Weld drop hardness (Hv) Thickness ofweld drop (mm) Weld drop thickness ratio (%) Plate thickness x drop hardnessweld Tension test Charpy impact test 120 378 378 382 1.2 120 458 Fractured in source material Propagated through source material 121 379 682 385 2.1 117 809 Fractured in source material Propagated through source material
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Industrial Applicability [00144] According to the present invention, it is possible to provide a custom-made sheet for hot stamping having a high joint strength after hot stamping even when an aluminum-coated steel sheet is welded by joining without removing a coated layer in a portion to be welded.
[00145] In addition, according to the present invention, it is possible to provide a hot stamped member having a high joint strength after hot stamping even when a plate made to measure for hot stamping obtained by carrying out the joint welding in an aluminum-coated steel plate without removing a coated layer in a portion to be welded is used. Additionally, since the surfaces of the weld beads after welding are covered with aluminum, it is possible to solve the problem of the occurrence of decarburization or oxidation of the weld metal during hot stamping, or the problem of a member obtained by hot stamping having poor corrosion resistance after hot stamping.

权利要求:
Claims (15)
[1]
1. Plate made to measure for hot stamping, characterized by the fact that it comprises:
a welded portion formed by butt weld of a first aluminum coated steel plate and a second aluminum coated steel plate, in which an average concentration of Al of a weld metal in the welded portion is 0.3% by weight at 1.5% by mass, in the following formula (1), an Ac3 point of the weld metal defined in ° C unit is 1250 ° C or lower, and in addition, an aluminum layer formed during butt welding is present on a surface of the welded portion,
Expression 1
A c ₃ = 9 1 0 - 2 3 0 XC ^{0 5} —1 5. 2XN1 + 44. 7XSÍ + 104
XV + 31. SXMo + 13. lXW-3 0XMn-l lXCr-2 0XCu + 700XP + 400XA! + 120XAs + 400XTÍ '' 'Formula (1) where, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti in the formula represent quantities of individual elements in the weld metal in mass%.
[2]
2. Plate made to measure for hot stamping, according to claim 1, characterized by the fact that, in addition, in the following formula (2), Aím defined in second unit is 0.5 seconds or longer,
Expression 2 ,, ί, _Λ Α Si + 5xÀl Mn Cu Ni Mo Cr x (l-0.16x _Λ J
A _tM = exp | 10 ^ C ₊ ^ _i - ₊ _ ₊ _ ₊ _ ₊ _ ₊ —1— ---- J ₊ AH | -4. ₈ j • '' Formula (2) where, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in the formula represent quantities of individual elements in the weld metal in mass%, and ΔΗ in the formula represents a value numeric value defined as described below according to the amount of B in% in
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2/7 mass, and fN when fN is adjusted to (0.02-N) / 0.02 using the amount of N in the weld metal in% by mass, when B <0.0001, ΔΗ = 0, when 0.0001 <B <0.0002, AH = 0.03xfN, when 0.0002 <B <0.0003, AH = 0.06xfN, and when 0.0003 <B, AH = 0.09xfN.
[3]
3. Plate made to measure for hot stamping according to claim 1 or 2, characterized by the fact that, in addition, an Aci point of the weld metal defined in ° C unit in the following formula (3) is 860 ° C or lower,
Expression 3
Ac _x = exp (6.5792- 0.038058 x C + 0.052317 Χ0Ϊ + 0.011872 x Ni
- 0.045575 x V + 0.18057 x Al + 0.011442 x W -0.013403 x Cu 4- 5.5207 x B + 0.91209 x 5 -1.1002 x P + 0.060014 x Mn x C - 0.096628Cr x C + 0.050625 x Cr x Si + 0.39802 x Mo x C - 0.34782 xMoxMn + 0.40986 x Mo x Si
-0.12959 xMoxCr-0.048128xNixC-0.01090xMn ² -0.03550xSi ² + 0.010207 x Cr ² + 0.36074 x Mo ² - 0.0030705 x Ni ² ) • * · Formula (3) where, C, Si, Ni, V, Al, W , Cu, B, S, P, Mn, Cr, and Mo in the formula represent quantities, in weight%, of individual elements in the weld metal.
[4]
4. Plate made to measure for hot stamping according to any one of claims 1 to 3, characterized in that, when a thickness of a thinner portion of the weld metal is represented by t in unit mm, a thickness of sheet of the first aluminum-coated steel sheet is represented portl in mm unit, and a sheet thickness of the second aluminum-coated steel sheet is represented by t2 in mm unit, in a case where t1 is equal to t2, at is 80% or more of t1, and in a case where t1 is different from t2, at is 80% or more of less than t1 and t2.
Petition 870190039032, of 25/04/2019, p. 61/71
3/7
[5]
5. Plate made to measure for hot stamping according to any one of claims 1 to 4, characterized by the fact that, in a case where the t1 which is the plate thickness of the first aluminum coated steel plate is equal to t2 which is the plate thickness of the second aluminum coated steel plate, a maximum height of the weld metal is 300 pm or shorter from an extended line of a surface of the first aluminum coated steel plate; and in a case where t1 is different from t2, a maximum height of the weld metal is 300 pm or shorter from an extended line of a thicker surface of the first aluminum coated steel sheet and the second steel sheet aluminum coated.
[6]
6. Plate made for hot stamping according to any one of claims 1 to 5, characterized by the fact that an oxygen content in the weld metal is 50 ppm or higher than an average oxygen content in a first steel plate which is a base material for coating the first aluminum coated steel plate, and a second steel plate which is a base material for coating the second aluminum coated steel plate.
[7]
7. Method for producing a custom-made sheet for hot stamping, as defined in any one of claims 1 to 6, in which joint welding is performed using a first aluminum-coated steel sheet and a second coated steel sheet aluminum, the method being characterized by the fact of understanding:
determine the welding conditions so that an average concentration of Al of a weld metal in a welded portion falls in a range of 0.3 mass% to 1.5 mass%, and a point Ac3 (° C) of weld metal defined by the following formula (1) is 1250 ° C or lower; and
Petition 870190039032, of 25/04/2019, p. 62/71
4/7 form an aluminum layer derived from aluminum-coated layers of the first aluminum-coated steel sheet and the second aluminum-coated steel sheet on a weld metal surface in the welded portion by performing welding under the welding conditions ,
Expression 4
Ac 3 = 9 1 0 - 2 3 0 XC ° ⁵ - 1 5. 2XN1 + 44. 7XSI + 104
XV + 31. SXMo + 13. 1XW-3 0XMI1-1 lXCr-2 0XCu + 700XP + 400XAl + 12QXAs + 40ÜXTÍ - * - Formula (1) where, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P , Al, As, and Ti in the formula represent quantities of individual elements in the weld metal in mass%.
[8]
8. Method for producing a custom-made sheet for hot stamping, according to claim 7, characterized by the fact that, when determining the welding conditions, in addition, the welding conditions are determined so that Δϊμ defined by the following formula (2) in unit seconds is 0.5 seconds or longer,
Expression 5., Irt / r. Si + 5xAl Mn Cu Ni Mo CrA - $ AC * 4Cr , _Λ J
A _tM = exp | 10 ^ C ₊ ^ _i - ₊ _ ₊ _ ₊ _ ₊ _ ₊ —----> ₊ ΛΗ | -4. ₈ | • '' Formula (2) where, C, Si, Al, Mn, Cu, Ni, Mo, and Cr in the formula represent quantities of individual elements in the weld metal in mass%, and ΔΗ in the formula represents a defined numerical value as described below according to the amount of B in mass%, and fN when the fN is adjusted to (0.02-N) / 0.02 using the amount of N in the weld metal in mass%, when B <0.0001, ΔΗ = 0, when 0.0001 <B <0.0002, ΔΗ = 0.03χίΝ, when 0.0002 <B <0.0003, ΔΗ = 0.06χίΝ, and
Petition 870190039032, of 25/04/2019, p. 63/71
5/7 when 0.0003 <B, AH = 0.09xfN.
[9]
9. Method for producing a plate made to measure for hot stamping, according to claim 7 or 8, characterized by the fact that, in addition, when determining the welding conditions, the welding conditions are determined so that an Aci point defined by the following formula (3) in ° C unit is 860 ° C or lower,
Expression 6
Ac, = exp (6.5792 - 0.038058 x C + 0.052317 x Si + 0.011872 x Ni
- 0.045575 x V + 0.18057 x Al + 0.011442 x W -0.013403 x Cu + 5.5207 x B + 0.91209 x 5 -1.1002 x P + 0.060014 x Mn x C - 0.0966280 x C + 0.050625 x Cr x Si + 0.39802 x Mo x C - 0.34782 xMoxMn + 0.40986 xMox Si
- 0.12959 xMoxCr- 0.048128 x Ni * C -0.01090 x Mn ² - 0.03550 x Si ² + 0.010207 x Cr ² + 0.36074 x Mo ² - 0.0030705 x Ni ² )
- - - Formula (3) where, C, Si, Ni, V, Al, W, Cu, B, S, P, Mn, Cr, and Mo in the formula represent quantities, in mass%, of individual elements in the metal soldering.
[10]
10. Method for producing a plate made to measure for hot stamping, according to any one of claims 7 to 9, characterized in that, additionally, when determining the welding conditions, the welding conditions are determined according to so that when a thickness of a thinner portion of the weld metal is represented by t in unit mm, a plate thickness of the first aluminum-clad steel sheet is represented by t1 in unit mm, and a plate thickness of the second aluminum-coated steel plate is represented by port2 in mm unit, in a case where t1 is equal to t2, at is 80% or more of t1; and in a case where t1 is different from t2, t is 80% or more less than t1 and t2.
Petition 870190039032, of 25/04/2019, p. 64/71
6/7
[11]
11. Method for producing a custom-made sheet for hot stamping, according to any of claims 7 to 10, in addition, when determining the welding conditions, characterized by the fact that the welding conditions are determined so that in a case where t1 which is the plate thickness of the first aluminum coated steel plate is equal to t2 which is the plate thickness of the second aluminum coated steel plate, a maximum height of the weld metal is 300 pm or shorter from an extended line of a surface of the first aluminum-coated steel plate; and in a case where t1 is different from t2, a maximum height of the weld metal is 300 pm or shorter from an extended line of a thicker surface of the first aluminum-coated steel sheet and the second steel sheet aluminum coated.
[12]
12. Method for producing a custom-made sheet for hot stamping, according to any of claims 7 to 11, characterized in that, when determining the welding conditions, the welding conditions are determined so that an oxygen content in the weld metal is 50 ppm or higher than an average oxygen content in a steel sheet which is a base material for coating the first aluminum coated steel sheet and the second aluminum coated steel sheet .
[13]
13. Method for producing a custom-made sheet for hot stamping, according to any one of claims 7 to 12, characterized by the fact that the junction welding is any one of laser welding, electron beam welding, and plasma welding.
[14]
14. Method for producing a plate made to measure for hot stamping, according to any of the
Petition 870190039032, of 25/04/2019, p. 65/71
7/7 claims 7 to 13, characterized by the fact that joint welding is laser welding performed while providing a filler wire.
[15]
15. Hot stamped member obtained by carrying out hot stamping on the plate made to measure for hot stamping, according to any one of claims 1 to 6, characterized by the fact that a product of a weld metal hardness and a thickness of a thinner portion of the weld metal is greater than a product of a hardness of the first aluminum-coated steel sheet, and a sheet thickness of the first aluminum-coated steel sheet and a product of a hardness of the second sheet aluminum coated steel and a plate thickness of the second aluminum coated steel plate.

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同族专利:

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公开号 | 公开日

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US20180126437A1|2018-05-10|

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KR101636639B1|2016-07-05|

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KR20140131557A|2014-11-13|

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RU2594766C2|2016-08-20|

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CN104204257B|2016-07-27|

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EP2832887A4|2016-05-04|

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ZA201406690B|2016-02-24|

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RU2014139827A|2016-05-20|

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IN2014DN07785A|2015-05-15|

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TWI527655B|2016-04-01|

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US10807138B2|2020-10-20|

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CA2866466A1|2013-10-03|

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CA2866466C|2016-10-25|

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US20150043962A1|2015-02-12|

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US9901969B2|2018-02-27|

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EP2832887A1|2015-02-04|

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CN104204257A|2014-12-10|

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MX2014011514A|2015-01-16|

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TW201343313A|2013-11-01|

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WO2013147035A1|2013-10-03|

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RU2594766C9|2016-12-20|

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法律状态:
2018-11-06| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|

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2019-03-26| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application according art. 36 industrial patent law|

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2019-07-02| B09A| Decision: intention to grant|

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2019-08-20| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |

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2019-09-10| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/03/2013, OBSERVADAS AS CONDICOES LEGAIS. (CO) 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/03/2013, OBSERVADAS AS CONDICOES LEGAIS |

优先权:

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申请号 | 申请日 | 专利标题

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JP2012074222A|JP5316664B2|2012-03-28|2012-03-28|Tailored blank for hot stamping|

---

JP2012093812A|JP5316670B1|2012-04-17|2012-04-17|Tailored blank for hot stamping and its manufacturing method|

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PCT/JP2013/059287|WO2013147035A1|2012-03-28|2013-03-28|Tailored blank for hot stamping, hot-stamped member, and processes for producing same|

---