WO2024253077A1 - ブランク、構造部材の製造方法、及び構造部材 - Google Patents

ブランク、構造部材の製造方法、及び構造部材 Download PDF

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Publication number
WO2024253077A1
WO2024253077A1 PCT/JP2024/020325 JP2024020325W WO2024253077A1 WO 2024253077 A1 WO2024253077 A1 WO 2024253077A1 JP 2024020325 W JP2024020325 W JP 2024020325W WO 2024253077 A1 WO2024253077 A1 WO 2024253077A1
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Prior art keywords
blank
steel plate
steel
structural member
coefficient
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PCT/JP2024/020325
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English (en)
French (fr)
Japanese (ja)
Inventor
野樹 木本
雅寛 久保
敬之助 井口
秀昭 入川
宗士 藤田
優貴 鈴木
博司 吉田
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日本製鉄株式会社
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Priority to JP2024576646A priority Critical patent/JP7684626B2/ja
Publication of WO2024253077A1 publication Critical patent/WO2024253077A1/ja

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/20—Deep-drawing
    • B21D22/26—Deep-drawing for making peculiarly, e.g. irregularly, shaped articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D53/00—Making other particular articles
    • B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/02—Side panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/04—Door pillars ; windshield pillars
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/20—Floors or bottom sub-units
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • This disclosure relates to a blank for hot stamping. This disclosure also relates to a method for manufacturing a structural member using the blank, and to the structural member.
  • Structures such as the body of an automobile are made up of multiple structural members.
  • Structural members are manufactured, for example, by press-forming a blank.
  • structural members are sometimes manufactured using a press-forming method known as hot stamping.
  • Hot stamping is a technique in which a blank, which is a steel plate, is heated to a temperature in the austenite range, and then the blank is press-formed using a die, and the blank is held in the die and quenched by removing heat (rapid cooling).
  • Patent Document 1 discloses a method for manufacturing an automobile body side structural frame from multiple blanks. In this method, multiple blanks are joined to form a composite blank, and the composite blank is press-formed to manufacture the body side structural frame. Patent Document 1 also describes hot forming (hot stamping) the composite blank.
  • Patent Document 2 discloses a method for manufacturing a side structure for an automobile.
  • the side structure includes an inner frame and an outer frame.
  • Patent Document 2 describes that each of the inner frame and the outer frame is manufactured by hot stamping a tailored blank (composite blank) formed by welding multiple blanks.
  • Patent Document 1 discloses that a composite blank having an annular shape (single ring shape) in a plan view is subjected to hot stamping to form an annular body side structural frame in which pillars, rockers, etc. are integrated.
  • Patent Document 2 discloses that a composite blank having an annular shape (double ring shape) in a plan view is subjected to hot stamping to form an annular inner frame and an outer frame in which pillars, rockers, etc. are integrated.
  • a composite blank contains multiple steel plates with different thicknesses, the performance of the structural member may be reduced.
  • the blank in hot stamping, the blank is heated, for example, in a heating furnace until its microstructure is austenitized, and then formed into a structural member by a die.
  • a steel plate with a small thickness is more easily cooled than a steel plate with a large thickness
  • cooling proceeds by the time the blank is removed from the heating furnace and forming begins, causing diffusion transformation, which may make it difficult to harden. This makes it easier for uneven hardness to occur in the structural components.
  • thin steel plates are difficult to harden and tend to retain stress, which can cause twisting in the annular structural components and reduce the dimensional accuracy of the structural components. Uneven hardness and reduced dimensional accuracy can reduce the impact absorption performance (crash resistance) of the annular structural components. The reduction in impact absorption performance becomes more pronounced the larger the structural components become.
  • the objective of this disclosure is to provide a hot stamping blank that can improve the performance of annular structural components, particularly large and annular structural components, that include steel plates that have a smaller plate thickness compared to other steel plates.
  • a blank for hot stamping according to the present disclosure includes a plurality of steel plates.
  • the plurality of steel plates are arranged and joined to have an annular shape in a plan view of the blank.
  • the plurality of steel plates include a first steel plate and a second steel plate.
  • the first steel plate has a minimum plate thickness among the plurality of steel plates.
  • the second steel plate has a plate thickness greater than that of the first steel plate.
  • the value of coefficient A calculated by the following formula (1) using the chemical composition of the first steel plate is greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the second steel plate.
  • A 1.48 ⁇ (2.7 ⁇ C+0.4 ⁇ Si+Mn+0.45 ⁇ Ni+0.8 ⁇ Cr+2 ⁇ Mo) 3.42 (1)
  • the element symbols are substituted with the contents (mass %) of the corresponding elements.
  • the hot stamping blank disclosed herein can improve the performance of annular structural components, particularly large annular structural components, that include steel plates having a smaller plate thickness compared to other steel plates.
  • FIG. 1 is a plan view of a structural member according to a first embodiment.
  • FIG. 2 is a cross-sectional view taken along line II-II of FIG.
  • FIG. 3A is a schematic diagram for explaining the method for manufacturing a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3B is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3C is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3A is a schematic diagram for explaining the method for manufacturing a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3B is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3D is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment, and is a diagram showing a blank according to the first embodiment.
  • FIG. 3E is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment.
  • FIG. 3F is a schematic diagram for explaining the manufacturing method of the structural member according to the first embodiment.
  • FIG. 3G is a schematic diagram for explaining the manufacturing method of a structural member according to the first embodiment.
  • FIG. 4 is a cross-sectional view of a blank according to the second embodiment.
  • FIG. 5 is a cross-sectional view of a blank according to the third embodiment.
  • FIG. 6A is a cross-sectional view of a blank according to a modification of each embodiment.
  • FIG. 6B is another cross-sectional view of a blank according to a modification of each embodiment.
  • FIG. 6C is another cross-sectional view of a blank according to a modification of each embodiment.
  • FIG. 7 is a plan view of a structural member according to a modified example of each embodiment.
  • FIG. 8A is a diagram showing a division pattern of a structural member in the first embodiment.
  • FIG. 8B is a diagram showing another division pattern of the structural member in the first embodiment.
  • FIG. 8C is a diagram showing still another division pattern of the structural member in the first embodiment.
  • FIG. 8D is a diagram showing still another division pattern of the structural member in the first embodiment.
  • FIG. 8E is a diagram showing still another division pattern of the structural member in the first embodiment.
  • FIG. 8A is a diagram showing a division pattern of a structural member in the first embodiment.
  • FIG. 8B is a diagram showing another division pattern of the structural member in the first embodiment.
  • FIG. 8C is a diagram showing
  • FIG. 8F is a diagram showing yet another division pattern of the structural member in the first embodiment.
  • FIG. 8G is a diagram showing yet another division pattern of the structural member in the first embodiment.
  • FIG. 9A is a diagram showing a division pattern of a structural member in the second embodiment.
  • FIG. 9B is a diagram showing another division pattern of the structural member in the second embodiment.
  • FIG. 9C is a diagram showing yet another division pattern of the structural member in the second embodiment.
  • FIG. 9D is a diagram showing yet another division pattern of the structural member in the second embodiment.
  • the critical cooling rate V c90 has been used as an index of hardenability of steel materials.
  • ⁇ is calculated by 2.7 ⁇ C + 0.4 ⁇ Si + Mn + 0.45 ⁇ Ni + 0.8 ⁇ Cr + 2 ⁇ Mo.
  • ⁇ represents the degree of influence of each element on hardenability based on the amount of Mn. The larger ⁇ is, the smaller the critical cooling rate V c90 is, and the better the hardenability of the steel material is.
  • the coefficient A corresponds to the transformation start time when only the influence of the elements is considered, and the larger the coefficient A, the better the hardenability of the steel material.
  • the inventors further used the coefficient A to consider the appropriate arrangement of the steel material in the blank. As a result, the inventors completed a blank according to the embodiment.
  • a blank for hot stamping includes a plurality of steel plates.
  • the plurality of steel plates are arranged and joined to have an annular shape in a plan view of the blank.
  • the plurality of steel plates include a first steel plate and a second steel plate.
  • the first steel plate has a minimum plate thickness among the plurality of steel plates.
  • the second steel plate has a plate thickness greater than that of the first steel plate.
  • the value of coefficient A calculated by the following formula (1) using the chemical composition of the first steel plate is greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the second steel plate (first configuration).
  • A 1.48 ⁇ (2.7 ⁇ C+0.4 ⁇ Si+Mn+0.45 ⁇ Ni+0.8 ⁇ Cr+2 ⁇ Mo) 3.42 (1)
  • the element symbols are substituted with the contents (mass %) of the corresponding elements.
  • the thin first steel plate will begin a phase transformation (diffusion transformation) from austenite to ferrite earlier than the thick second steel plate after the blank is heated for hot stamping.
  • the coefficient A calculated based on the chemical composition of the first steel plate is greater than the coefficient A calculated based on the chemical composition of the second steel plate. That is, the first steel plate is made of a material that has a higher hardenability than the second steel plate, in other words, a material that starts diffusion transformation during cooling late.
  • the start of diffusion transformation in the first steel plate is delayed, and the difference in transformation start time between the first steel plate and the second steel plate can be reduced.
  • the blank is hot stamped, not only the relatively thick second steel plate but also the first steel plate having a minimum thickness can be well hardened, and the hardness of the structural member formed from the blank is easily uniformed.
  • the first steel plate is well quenched, stress is offset by transformation plasticity and residual stress is reduced, which makes it possible to suppress the occurrence of twisting in annular structural components due to the concentration of residual stress, thereby reducing the deterioration of dimensional accuracy.
  • the annular blank contains a first steel plate that is thinner than the second steel plate, the hardness of the structural component formed by hot stamping from the blank can be made uniform, and deterioration of dimensional accuracy can be suppressed. This makes it possible to improve the impact absorption performance (crash resistance performance) of annular structural components, particularly large and annular structural components.
  • the manufacturing method for a structural member according to the embodiment includes a step of preparing a blank according to the first or second configuration, a step of heating the multiple steel plates contained in the blank to an austenite transformation completion temperature or higher, and a step of using a die to form the heated blank into a structural member that is annular in plan view and quenching it (third configuration).
  • a structural member includes a member body.
  • the member body has an annular shape in a plan view.
  • the member body is formed by a plurality of steel plates joined to each other.
  • the plurality of steel plates include a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than the plate thickness of the first steel plate.
  • the value of coefficient A calculated by the following formula (1) using the chemical composition of the first steel plate is greater than the value of coefficient A calculated by the following formula (1) using the chemical composition of the second steel plate (fourth configuration).
  • A 1.48 ⁇ (2.7 ⁇ C+0.4 ⁇ Si+Mn+0.45 ⁇ Ni+0.8 ⁇ Cr+2 ⁇ Mo) 3.42 (1)
  • the element symbols are substituted with the contents (mass %) of the corresponding elements.
  • the structural member according to the fourth configuration may be a door ring part of an automobile.
  • the member body may include a front pillar, a center pillar, and a rocker connecting the front pillar and the center pillar (fifth configuration).
  • First Embodiment [Structural Members] 1 is a diagram (plan view) of a structural member 10 according to the present embodiment, viewed from above in a state in which the structural member 10 is placed on a horizontal surface.
  • the structural member 10 is used, for example, in the body of an automobile.
  • the structural member 10 is typically a door ring part of an automobile. In the present embodiment, an example in which the structural member 10 is a door ring part will be described.
  • the structural member 10 is a hot stamped member. That is, the structural member 10 is formed by hot stamping (hot press processing) a blank made of multiple steel plates.
  • the structural member 10 includes a member body 11.
  • the member body 11 has an annular shape in a plan view of the structural member 10.
  • the member body 11 includes a front pillar 111, a center pillar 112, and a rocker 113.
  • the center pillar 112 is disposed behind the front pillar 111.
  • the center pillar 112 extends generally in the vertical direction of the vehicle body.
  • the front pillar 111 extends toward the center pillar 112.
  • the rocker 113 is disposed below the front pillar 111 and the center pillar 112.
  • the rocker 113 connects the front pillar 111 and the center pillar 112.
  • the member body 11 is formed from a plurality of steel plates 21, 22, and 23 joined together.
  • the front pillar 111 is mainly composed of the steel plates 21 and 22.
  • the center pillar 112 is mainly composed of the steel plate 23.
  • the rocker 113 is composed of the steel plates 21 and 23.
  • FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.
  • FIG. 2 shows a cross-section of the structural member 10 cut along the thickness direction at the position of the steel plate 21.
  • the steel plate 21 has an open cross-section.
  • the steel plate 21 has, for example, a roughly hat-shaped shape in the cross-sectional view of the structural member 10. More specifically, the steel plate 21 includes a top plate 211, vertical walls 212 and 213, and flanges 214 and 215.
  • the vertical wall 212 is disposed on the opposite side of the vertical wall 213 with respect to the top plate 211. In the cross-sectional view of the structural member 10, one end of the vertical walls 212 and 213 is connected by the top plate 211.
  • the other end of the vertical walls 212 and 213 is connected to the flanges 214 and 215, respectively.
  • the flanges 214 and 215 protrude from the vertical walls 212 and 213 to the outside of the structural member 10.
  • the width W of the steel plate 21 at the position shown in FIG. 2, i.e., the width W of the lower part of the front pillar 111 (FIG. 1), may be 30 mm or more and 750 mm or less.
  • the height H of the lower part of the front pillar 111 may be 25 mm or more and 150 mm or less.
  • the width W is the distance from the R end of the corner part between the top plate 211 and the vertical wall 212 on the vertical wall 212 side to the R end of the corner part between the top plate 211 and the vertical wall 213 on the vertical wall 213 side in the cross section of the structural member 10.
  • the height H is the distance from the top plate 211 to the flanges 214, 215 along the plate thickness direction of the top plate 211.
  • the width W of the part of the steel plate 21 that corresponds to the locker 113 is, for example, 30 mm or more and 300 mm or less.
  • the height of the part of the steel plate 21 that corresponds to the locker 113 may be 25 mm or more and 150 mm or less.
  • the other steel plates 22, 23 (FIG. 1) also have an open cross section like the steel plate 21.
  • the steel plates 22, 23 can also have, for example, a roughly hat shape in a cross section of the structural member 10.
  • the width of the portion of the steel plate 22 that corresponds to the upper part of the front pillar 111 may be 15 mm or more and 300 mm or less.
  • the height of the portion of the steel plate 22 that corresponds to the upper part of the front pillar 111 may be 10 mm or more and 150 mm or less.
  • the width of the portion of the steel plate 23 that corresponds to the center pillar 112 may be 15 mm or more and 300 mm or less.
  • the height of the portion of the steel plate 23 that corresponds to the center pillar 112 may be 10 mm or more and 150 mm or less.
  • the size of the structural member 10, which is annular in plan view, is, for example, 1.0 m or more.
  • the size of the structural member 10 may be, for example, 4.0 m or less.
  • the size of the structural member 10 is the length of the line segment connecting any two points on the outer periphery of the structural member 10 that are farthest apart when the structural member 10 is placed on a horizontal surface and viewed vertically.
  • the method for manufacturing the structural member 10 includes the steps of preparing a blank 20, heating the blank 20, and forming the heated blank 20 into the structural member 10.
  • a blank 20 having a shape obtained by developing the structural member 10 is prepared.
  • the blank 20 includes a plurality of steel plates 21, 22, and 23.
  • the steel plates 21, 22, and 23 are arranged and joined to have an annular shape in a plan view of the blank 20.
  • FIGS. 3B, 3C, and 3D are cross-sectional views of the blank 20 showing the joints of the steel plates 21, 22, and 23.
  • FIGS. 3B, 3C, and 3D are cross-sectional views taken along lines IIIB-IIIB, IIIC-IIIC, and IIID-IIID in FIG. 3A, respectively.
  • the steel plate 21 is butt-joined to each of the steel plates 22 and 23. That is, the end faces of the steel plate 21 are joined in a state where the end face of the steel plate 21 abuts against the end face of the steel plate 22, and the other end face of the steel plate 21 is joined in a state where the end face of the steel plate 21 abuts against the end face of the steel plate 23.
  • the steel plate 22 is butt-joined to the steel plate 23 in addition to the steel plate 21.
  • the end face of the steel plate 22 is joined to the end face of the steel plate 23 in a state where the end face of the steel plate 22 abuts against the end face of the steel plate 23.
  • the steel plates 21, 22, and 23 are joined by, for example, laser welding.
  • the blank 20 is a so-called tailor weld blank.
  • the steel plate 21 has a plate thickness t1 .
  • the steel plate 22 has a plate thickness t2 .
  • the steel plate 23 has a plate thickness t3 .
  • the plate thicknesses t2 and t3 of the steel plates 22 and 23 are greater than the plate thickness t1 of the steel plate 21. That is, the plate thickness t1 of the steel plate 21 is the minimum plate thickness tmin of the steel plates 21, 22, and 23.
  • the plate thickness t2 of the steel plate 22 is greater than the plate thickness t3 of the steel plate 23. Therefore, the plate thickness t2 of the steel plate 22 is the maximum plate thickness tmax of the steel plates 21, 22, and 23.
  • the steel plate 22 does not necessarily have to have the maximum plate thickness tmax of the steel plates 21, 22, and 23.
  • the plate thickness t2 of the steel plate 22 may be equal to or less than the plate thickness t3 of the other steel plates 23.
  • the minimum plate thickness t min and the maximum plate thickness t max of the steel plates 21, 22, and 23 satisfy, for example, t max - t min ⁇ 0.2 (mm).
  • the plate thicknesses t min and t max may also satisfy t max - t min ⁇ 3.2 (mm).
  • the plate thickness t min of the steel plate 21 is, for example, less than 1.4 mm.
  • the plate thickness t min may be 0.8 mm or more.
  • the maximum plate thickness t max is, for example, less than 4.0 mm.
  • the plate thickness t max may be 1.4 mm or more.
  • Steel sheets 21, 22, and 23 may have a known chemical composition as a steel sheet for hot stamping.
  • the chemical composition of steel sheets 21, 22, and 23 contains, in mass%, C: 0.05-0.50%, Si: 0.020-1.000%, Mn: 0.20-2.50%, Ni: 0-0.50%, Cr: 0-0.50%, Mo: 0-0.5%, and B: 0.0005-0.0050%.
  • each of the steel plates 21, 22, and 23 may further contain, in mass%, one or more elements selected from the group consisting of Cu: 0.005-3.000%, Co: 0.005-0.500%, Sn: 0.005-0.500%, Ca: 0.0005-0.0050%, Mg: 0.0005-0.0050%, REM: 0.0005-0.0050%, and Sb: 0.0005-0.0200%.
  • the chemical composition of the steel plate 21 having the minimum plate thickness t min is different from the chemical compositions of the thicker steel plates 22 and 23.
  • the value of coefficient A calculated by the following formula (1) using the chemical composition of the steel plate 21 is different from the coefficient A calculated by formula (1) for each of the steel plates 22 and 23 using their chemical compositions.
  • A 1.48 ⁇ (2.7 ⁇ C+0.4 ⁇ Si+Mn+0.45 ⁇ Ni+0.8 ⁇ Cr+2 ⁇ Mo) 3.42 (1)
  • the content (mass%) of the corresponding element is substituted for the element symbol in formula (1). That is, the coefficient A of the steel plate 21 is calculated by substituting the content (mass%) of each element in the chemical composition of the steel plate 21 for the corresponding element symbol in formula (1). Similarly, the coefficient A of the steel plate 22 is calculated by substituting the content (mass%) of each element in the chemical composition of the steel plate 22 for the corresponding element symbol in formula (1).
  • the value of the coefficient A calculated by formula (1) using the chemical composition of the steel plate 21 is larger than the coefficient A calculated by formula (1) using the chemical composition of the steel plate 22.
  • the coefficient A of the steel plate 22 is the smallest among the coefficients A calculated by formula (1) for the steel plates 22 and 23 other than the steel plate 21.
  • a 1 -A 2 is preferably 0.10 or more, more preferably 0.20 or more.
  • a 1 ⁇ A 2 may be, for example, less than or equal to 11.50.
  • the coefficient A of the steel plate 23 is calculated by substituting the content (mass%) of each element in the chemical composition of the steel plate 23 into the corresponding element symbol in formula (1).
  • the value of the coefficient A calculated by formula (1) using the chemical composition of the steel plate 23 is equal to or greater than the value of the coefficient A calculated by formula (1) using the chemical composition of the steel plate 22.
  • the value of the coefficient A of the steel plate 23 is preferably smaller than the value of the coefficient A of the steel plate 21 having the minimum plate thickness t min . That is, among the multiple steel plates 21, 22, and 23 included in the blank 20, it is preferable that the coefficient A of the steel plate 21 having the minimum plate thickness t min is the largest.
  • a 1 -A 3 is preferably 0.10 or more, more preferably 0.20 or more. Although not particularly limited, A 1 -A 3 may be 11.50 or less. However, the coefficient A3 of the steel plate 23 may be equal to or greater than the coefficient A1 of the steel plate 21 ( A1 - A3 ⁇ 0).
  • the chemical composition of the steel plates 21, 22, and 23 contained in the blank 20 may be measured by a general analytical method.
  • analytical test pieces may be taken from each of the steel plates 21, 22, and 23, and the test pieces may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) to obtain the chemical composition of the steel plates 21, 22, and 23.
  • ICP-AES Inductively Coupled Plasma-Atomic Emission Spectrometry
  • C may be measured using the combustion-infrared absorption method.
  • the prepared blank 20 is formed into the structural member 10 (FIGS. 1 and 2) by hot stamping. During the hot stamping, the blank 20 is subjected to a heating step. Referring to FIG. 3E, in the heating step, the blank 20 is heated, for example, by a heating furnace 30.
  • the multiple steel plates 21, 22, and 23 included in the blank 20 are heated to an austenite transformation completion temperature (A c3 point) or higher.
  • the steel plates 21, 22, and 23 are heated, for example, to 900° C. or higher.
  • the microstructures of the steel plates 21, 22, and 23 are transformed, for example, entirely or almost entirely into the austenite phase.
  • the heated blank 20 is formed into an annular structural member 10 (Figs. 1 and 2) in a plan view using a die 40 and quenched.
  • the blank 20 heated in the heating process is removed from the heating furnace 30 (Fig. 3E) and transported to the die 40.
  • the die 40 is attached to a known press device.
  • the die 40 includes, for example, a punch 41 and a die 42.
  • the blank 20 is disposed between the punch 41 and the die 42.
  • the die 42 approaches relatively to the punch 41.
  • the blank 20 is clamped (pressed) by the punch 41 and the die 42 and formed into a shape that conforms to the forming surfaces of the punch 41 and the die 42.
  • the blank 20 remains clamped between the punch 41 and the die 42.
  • the blank 20 is cooled (quenched) by the die 40 and its microstructure is transformed into martensite. This allows the structural member 10 to be manufactured from the blank 20.
  • the value of the coefficient A calculated by the above formula (1) using the chemical composition of the steel sheet 21 having the minimum sheet thickness t min is larger than the coefficient A calculated by the formula (1) using the chemical composition of the steel sheet 22.
  • the value of the coefficient A calculated by the formula (1) using the chemical composition of the steel sheet 21 is preferably larger than the coefficient A calculated by the formula (1) using the chemical composition of the steel sheet 23.
  • the value of the coefficient A calculated by the formula (1) using the chemical composition of the steel sheet 21 may be equal to or smaller than the coefficient A calculated by the formula (1) using the chemical composition of the steel sheet 23.
  • the chemical composition of the steel sheets 21, 22, and 23 in the structural member 10 after hot stamping can be obtained by the same analytical method as that for the chemical composition of the steel sheets 21, 22, and 23 at the blank 20 stage.
  • the variation in martensite fraction is, for example, 20% or less.
  • the variation in martensite fraction is preferably 15% or less, and more preferably 10% or less.
  • the variation in martensite fraction can be measured as follows. That is, in the cross section of the structural member 10 at the position of the steel plate 21 having the minimum plate thickness t min , 10 or more analysis samples (e.g., long side is about 10 mm in size) are cut out from positions 20 mm or more away from the end and 10 mm or more away from each other, and then each is mirror-polished and etched with LePeller's reagent so that the plate thickness direction becomes the observation surface.
  • the image analysis method involves obtaining the maximum brightness value Lmax and the minimum brightness value Lmin from the image, determining the portion having pixels with brightness from Lmax-0.3 (Lmax-Lmin) to Lmax as a white region, and calculating the ratio of the number of pixels in the white region to the total number of pixels to measure the martensite fraction.
  • This image analysis is performed on a total of 30 observation fields of each analysis sample to determine the martensite fraction, and the average value is taken as the martensite fraction of each analysis sample.
  • the difference between the maximum and minimum values of the martensite fraction in 10 or more analysis samples is defined as the variation in the martensite fraction in the cross section of the structural member 10 at the position of the steel plate 21 having the minimum plate thickness t min .
  • the area fraction of martensite obtained by image analysis i.e., the area fraction of the white area
  • the area fraction of the white area may contain a few percent of the area fraction of retained austenite.
  • the variation in the martensite fraction is calculated as a difference, the impact is minor.
  • steel plate 21 can have a tensile strength of, for example, 0.5 GPa or more, and preferably has a tensile strength of 1.0 GPa or more.
  • steel plates 22 and 23 (FIG. 1) can have a tensile strength of, for example, 0.5 GPa or more, and preferably has a tensile strength of 1.0 GPa or more.
  • At least one of steel plates 21, 22, and 23 may have a tensile strength of 1.5 GPa or more after the forming process.
  • the tensile strength of each of steel plates 21, 22, and 23 may be the same as or different from the tensile strength of the other steel plates.
  • the coefficient A 1 of the steel plate 21 having the minimum plate thickness t min is greater than the coefficient A 2 of the thicker steel plate 22.
  • the coefficients A 1 and A 2 correspond to the time (transformation start time) until the steel plates 21 and 22 start diffusion transformation, respectively, after the heating of the blank 20 for hot stamping from the heating furnace 30 is completed.
  • the coefficients A 1 and A 2 are values corresponding to the transformation start time when only the influence of the elements is considered for each of the steel plates 21 and 22, without considering the influence of the plate thickness.
  • the coefficient A1 is larger than the coefficient A2 , it means that the steel plate 21 is made of a material having a higher hardenability than the steel plate 22, in other words, a material in which the start of diffusion transformation during cooling is delayed.
  • the coefficient A1 > the coefficient A2 as in this embodiment, the start of diffusion transformation in the steel plate 21 having the minimum plate thickness tmin can be delayed, and the difference in the transformation start time between the steel plates 21 and 22 can be reduced compared to when the coefficient A1 is equal to or smaller than the coefficient A2 .
  • the steel plate 21 having the minimum plate thickness tmin can be well hardened, and the hardness of the structural member formed from the blank 20 is easily made uniform.
  • the steel plate 21 is well hardened, stress is offset by transformation plasticity and the residual stress is reduced, so that the occurrence of twisting due to the concentration of residual stress in the annular structural member 10 can be suppressed. As a result, the deterioration of the dimensional accuracy of the structural member 10 can be reduced.
  • the annular blank 20 contains a steel plate 21 that is thinner than the steel plate 22, the hardness of the structural member 10 formed by hot stamping from the blank 20 can be made uniform, and deterioration of dimensional accuracy can be suppressed. Therefore, the impact absorption performance (crash resistance performance) of the annular structural member 10, particularly a large and annular structural member 10, can be improved.
  • the hardenability of the relatively thin steel plate 21 is improved, so that the hardness of the structural member 10 formed from the blank 20 can be made uniform. More specifically, even the steel plate 21 having the minimum plate thickness t min is well hardened, so that the variation in the martensite fraction in the steel plate 21 can be made 20% or less. As a result, for example, when a collision load is input to the structural member 10, deformation concentration is unlikely to occur, and the structural member 10 is more likely to exhibit high impact absorption performance. Therefore, even when an annular structural member 10 including a steel plate 21 having a small plate thickness, particularly a large and annular structural member 10, is formed from the blank 20, it is possible to reduce strength defects of the structural member 10 and improve the impact absorption performance of the structural member 10.
  • hardenability-deficient parts i.e., hardness-deficient parts
  • Second Embodiment Fig. 4 is a cross-sectional view of a blank 20A according to the second embodiment.
  • Fig. 4 shows a joint between a steel plate 21 having a minimum plate thickness t min and a steel plate 22 having a larger plate thickness t 2.
  • the blank 20A according to this embodiment has a configuration generally similar to that of the blank 20 according to the first embodiment, but differs from the blank 20 according to the first embodiment in that a coating 24 is provided on the steel plate 21.
  • the steel plate 21 having the minimum plate thickness t min has one surface covered with the coating 24.
  • the coating 24 is a substantially black coating.
  • the coating 24 may be a carbon-based surface treatment coating (a coating containing carbon (C)).
  • the coating 24 may contain, for example, carbon black.
  • the coating 24 may further contain a metal oxide.
  • the metal oxide may be, for example, one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide.
  • the coating 24 may also contain silica.
  • the coating 24 may be, for example, a surface treatment coating described in WO 2022/215229. That is, the coating 24 may contain graphite or soot instead of or in addition to carbon black. Alternatively, the coating 24 may contain, for example, an acicular compound having a hexagonal crystal structure with an aspect ratio of 4 to 50.
  • the compound having a hexagonal crystal structure is typically graphite (C), but may also be lanthanum silicate, magnesium diboride, beryllium oxide (beryllia), zinc oxide, ⁇ -quartz, goethite (NiS), wurtzite (ZnS), or the like.
  • the blank 20A according to this embodiment is formed into an annular structural member 10 (FIGS. 1 and 2) by the same manufacturing method as in the first embodiment.
  • the emissivity of the surface of the steel sheet 21 is increased by a substantially black coating 24 applied to the surface of the steel sheet 21.
  • the surface of the steel sheet 21 covered with the coating 24 has an emissivity of 60% or more at a measurement temperature of 25° C. and a wavelength of 8.0 ⁇ m, for example.
  • the steel sheet 21 can be quickly heated to a temperature in the austenite range to ensure a long high-temperature holding time of the steel sheet 21.
  • the austenite crystal grains in the microstructure of the steel sheet 21 become coarse, and the diffusion transformation of the steel sheet 21 after the heating process is completed can be further delayed. Therefore, the steel sheet 21 can be quenched more satisfactorily.
  • At least a portion of the coating 24 can remain on the surface of the steel sheet 21 after hot stamping.
  • one surface of the steel plate 21 is coated with the coating 24.
  • both surfaces of the steel plate 21 may be coated with the coating 24, which is substantially black.
  • the coating 24 may or may not be provided on one or both surfaces of the other steel plates 22, 23.
  • FIG. 5 is a cross-sectional view of a blank 20B according to a third embodiment.
  • Fig. 5 shows a joint between a steel sheet 21 having a minimum sheet thickness tmin and a steel sheet 22 having a larger sheet thickness t2 .
  • the blank 20B according to this embodiment has a configuration generally similar to that of the blank 20 according to the first embodiment, but differs from the blank 20 according to the first embodiment in that the steel sheets 21 and 22 are plated steel sheets.
  • the steel plate 21 has a base steel plate 21a and an aluminum-based plating layer 21b.
  • the aluminum-based plating layer 21b covers both surfaces of the base steel plate 21a.
  • the aluminum-based plating layer 21b is provided over the entire or almost the entire surfaces of both surfaces of the base steel plate 21a.
  • the steel plate 22 has a base steel plate 22a and an aluminum-based plating layer 22b.
  • the aluminum-based plating layer 22b covers both surfaces of the base steel plate 22a.
  • the aluminum-based plating layer 22b is provided over the entire or almost the entire surfaces of both surfaces of the base steel plate 22a.
  • the sheet thickness t min of the steel plate 21 is the sheet thickness including the base steel plate 21a and the aluminum-based plating layer 21b.
  • the sheet thickness t 2 of the steel plate 22 is the sheet thickness including the base steel plate 22a and the aluminum-based plating layer 22b.
  • the chemical composition of the aluminum-based plating layers 21b, 22b is not particularly limited.
  • a known aluminum-based plating layer (a plating layer whose main component is aluminum) can be used as the aluminum-based plating layers 21b, 22b.
  • the aluminum-based plating layers 21b, 22b are, for example, Al-Si-based plating layers.
  • the chemical compositions of the aluminum-based plating layers 21b, 22b may be the same or different.
  • the adhesion weights W1, W2 may each be 20 g/m2 or more and 120 g/m2 or less .
  • the adhesion weight W1 of the aluminum-based plating layer 21b is the average adhesion weight on both surfaces of the base steel sheet 21a.
  • the adhesion weight W2 of the aluminum-based plating layer 22b is the average adhesion weight on both surfaces of the base steel sheet 22a.
  • Each of the coating weights W1 and W2 is preferably 30 g/m 2 or more, and more preferably 35 g/m 2 or more.
  • Each of the coating weights W1 and W2 is preferably 115 g/m 2 or less, and more preferably 100 g/m 2 or less.
  • the coating weight W1 of the aluminum-based plating layer 21b in the steel sheet 21 having the minimum sheet thickness t min is less than the coating weight W2 of the aluminum-based plating layer 22b in the steel sheet 22 having the greater sheet thickness t 2.
  • the difference between the coating weights W1 and W2: W2-W1, is, for example, 10 (g/m 2 ) or more.
  • W2-W1 is preferably 20 (g/m 2 ) or more, and more preferably 30 (g/m 2 ) or more. W2-W1 may be 80 (g/m 2 ) or less. W2-W1 is preferably 70 (g/ m2 ) or less, and more preferably 60 (g/ m2 ) or less.
  • the adhesion amounts W1 and W2 satisfy the relationship W2/W1>1.0.
  • the adhesion amounts W1 and W2 preferably satisfy the relationship W2/W1 ⁇ 1.2, and more preferably W2/W1 ⁇ 1.5.
  • the coefficients A1 and A2 are calculated using the chemical compositions of the base steel sheets 21a and 22a. That is, the coefficient A1 of the steel sheet 21 is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel sheet 21a into the above-mentioned formula (1). Similarly, the coefficient A2 of the steel sheet 22 is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel sheet 22a into the formula (1). In this embodiment, as in the first embodiment, the coefficient A1 of the steel sheet 21 is larger than the coefficient A2 of the steel sheet 22. The coefficient A2 of the steel sheet 22 is the smallest coefficient A among the coefficients A calculated by the formula (1) for each of the multiple steel sheets included in the blank 20B.
  • the blank 20B according to this embodiment is formed into an annular structural member 10 (FIGS. 1 and 2) by the same manufacturing method as in the first embodiment.
  • the adhesion weight W1 of the aluminum-based plating layer 21b of the steel sheet 21 having the minimum sheet thickness t min is smaller than the adhesion weight W2 of the aluminum-based plating layer 22b of the steel sheet 22 having the larger sheet thickness t 2.
  • the temperature rise rate of the steel sheet 21 is significantly higher than that of the steel sheet 22.
  • the aluminum-based plating layer 21b on the surface of the steel sheet 21 is relatively thin, when the blank 20B is heated, alloying of the aluminum-based plating layer 21b with the iron contained in the base steel sheet 21a progresses quickly to the surface of the steel sheet 21, and both surfaces of the steel sheet 21 change to black or a color close to black. That is, the emissivity of both surfaces of the steel sheet 21 increases during the heating process. Therefore, the steel sheet 21 can be quickly heated to the austenite temperature range, and the high-temperature holding time of the steel sheet 21 can be secured for a long time. As a result, the austenite grains in the microstructure of the steel sheet 21 become coarse, and the diffusion transformation of the steel sheet 21 after the heating process is completed can be further delayed. Therefore, the steel sheet 21 can be more satisfactorily quenched.
  • the plating thickness K1 of the steel sheet 21 is smaller than the plating thickness K2 of the steel sheet 22.
  • the difference between the plating thicknesses K1 and K2: K2-K1 is, for example, 7 ( ⁇ m) or more.
  • K2-K1 may be 33 ( ⁇ m) or less.
  • the plating thicknesses K1 and K2 can satisfy the relationship K2/K1>1.0.
  • K2/K1 is preferably 1.2 or more, more preferably 1.5 or more.
  • the steel sheet 23 may be a plated steel sheet having a base steel sheet and a plating layer like the steel sheets 21 and 22, or may be a steel sheet (bare material) without a plating layer on the surface.
  • the plating layer may be an aluminum-based plating layer or a metal plating layer other than aluminum.
  • the adhesion amount and thickness of the plating layer on the base steel sheet are not particularly limited.
  • the coefficient A3 of the steel sheet 23 is calculated by substituting the content (mass%) of each element in the chemical composition of the base steel sheet into the above-mentioned formula (1).
  • the chemical compositions of the steel sheets 21, 22, and 23 can be measured by the general analysis method described in the first embodiment. The analysis of the chemical composition of the steel sheets 21, 22, and 23 may be performed after removing the plating layer on the surface by mechanical grinding.
  • the configuration of the blank 20B according to this embodiment can also be combined with the blanks 20 and 20A according to the first and second embodiments, respectively. That is, in each of the blanks 20 and 20A, the steel sheet 21 is a plated steel sheet having a base steel sheet 21a and an aluminum-based plating layer 21b, and the steel sheet 22 is a plated steel sheet having a base steel sheet 22a and an aluminum-based plating layer 22b, and the adhesion amount W1 of the aluminum-based plating layer 21b on the steel sheet 21 may be less than the adhesion amount W2 of the aluminum-based plating layer 22b on the steel sheet 22.
  • the adhesion weight W1 of the aluminum-based plating layer 21b on the steel sheet 21 may be equal to or greater than the adhesion weight W2 of the aluminum-based plating layer 22b on the steel sheet 22.
  • the plating layers of the steel sheets 21 and 22 may be metal plating layers other than aluminum, or the steel sheets 21 and 22 may be steel sheets (bare materials) that do not have a plating layer on their surface.
  • each of the blanks 20, 20A, and 20B includes three steel plates 21, 22, and 23.
  • the number of steel plates included in the blanks 20, 20A, and 20B is not limited to this.
  • the blanks 20, 20A, and 20B may be composed of two steel plates 21 and 22, or may include four or more steel plates.
  • the blanks 20, 20A, and 20B may include at least the steel plate 21 having the minimum plate thickness t min and the steel plate 22 having the plate thickness t 2 larger than the plate thickness t min .
  • the blanks 20, 20A, 20B which are annular in plan view, may typically include three or more steel plates.
  • the steel plate 21 is directly or indirectly joined to the steel plate 22.
  • the arrangement of the multiple steel plates including the steel plates 21 and 22 is not particularly limited.
  • the coefficient A1 of all the steel plates 21 is greater than the coefficient A2 of the steel plate 22.
  • the coefficient A of the steel plates other than the steel plates 21, 22 is equal to or greater than the coefficient A2 of the steel plate 22.
  • the steel plate 21 is butt-joined to each of the steel plates 22 and 23.
  • the steel plate 22 is butt-joined to the steel plate 23.
  • the steel plate 21 may be overlap-joined to at least one of the steel plates 22 and 23. That is, as shown in FIG. 6A, the end of the steel plate 21 may be overlapped on the end of the steel plate 22 and joined to the end of the steel plate 22 by, for example, spot welding or laser welding, so that the steel plates 21 and 22 form an overlap portion 25.
  • spot welding or laser welding so that the steel plates 21 and 22 form an overlap portion 25.
  • the end of the steel plate 21 may be overlapped on the end of the steel plate 23 and joined to the end of the steel plate 23 by, for example, spot welding or laser welding, so that the steel plates 21 and 23 form an overlap portion 25.
  • the end of steel plate 22 may be joined to the end of steel plate 23 by, for example, spot welding or laser welding while overlapping the end of steel plate 23, so that steel plates 22 and 23 form an overlap portion 25.
  • the joining method for adjacent steel plates may be butt joining or lap joining.
  • each of the blanks 20, 20A, and 20B may each be a single layer or multiple layers.
  • each of the multiple steel plates may be a single steel plate, or a plate material formed by overlapping multiple steel plates.
  • the die 40 used for hot stamping the blanks 20, 20A, and 20B includes a punch 41 and a die 42.
  • the configuration of the die 40 is not limited to the example described in the above embodiment.
  • the die 40 may further include, for example, a pad and a blank holder.
  • the main body 11 of the structural member 10 includes a front pillar 111, a center pillar 112, and a rocker 113.
  • the member main body 11 can further include other components.
  • the member main body 11 can further include a rear pillar 114.
  • the structural member 10 according to the above embodiment is a door ring part having a single ring shape (single door ring part).
  • the structural member shown in FIG. 7 is a door ring part having a double ring shape (double door ring part).
  • the blank that serves as the material also has a double ring shape.
  • Table 1 shows the types of steel sheets (materials) used in this analysis. For each material, Table 1 shows the content (mass%) of each element in the base material, the type of plating, and the coefficient A calculated using the above-mentioned formula (1).
  • Figures 8A to 8G show the division pattern of the structural members.
  • Figures 8A to 8G show the number of steel plates (materials) contained in the structural member, which is a single door ring part, and the positions of the joints between the steel plates in the structural member.
  • each steel plate is given a number in parentheses.
  • Example 1 the coefficient A value is maximum in the material (3) having the smallest plate thickness t min : 1.2 mm among the materials (1) to (3).
  • the coefficient A 1 of the thinnest material (3) is significantly larger than the smallest coefficient A 2 in the other materials (1) and (2).
  • the coefficient A 1 of the material (1) having the smallest plate thickness t min : 1.2 mm among the materials (1) to (3) is also significantly larger than the smallest coefficient A 2 in the other materials (2) and (3).
  • the coefficient A value is maximum in the material (2) having the smallest plate thickness t min : 1.2 mm among the materials (1) to (3).
  • the coefficient A 1 of the thinnest material (2) is also significantly larger than the smallest coefficient A 2 in the other materials (1) and (3).
  • the coefficient A1 of the thinnest material is equal to or lower than the coefficients A of the other materials.
  • the coefficient A corresponds to the transformation start time for each material when only the influence of the elements is considered, but the actual transformation start time for each material is also affected by the plate thickness, and becomes shorter as the plate thickness becomes smaller.
  • the "phase transformation start time” in Table 2 is the shortest time until the phase transformation to ferrite starts after the blank is heated at a furnace temperature of 920°C for 5 minutes and 30 seconds and removed from the heating furnace (the time until the thinnest material starts phase transformation). As shown in Table 2, the phase transformation start time was longer in Examples 1 to 3 than in Comparative Examples 1 and 2.
  • Example 3 and Comparative Example 2 which are the same conditions except for the material of the thinnest material (2), it can be seen that the phase transformation start time in Example 3 is slower than that in Comparative Example 2.
  • the coefficient A 1 of the thinnest material (2) is larger than the smallest coefficient A 2 among the other materials (1) and (3), and the hardenability of the thinnest material is higher than the hardenability of the other materials.
  • the coefficient A1 of the thinnest material (2) is equal to or less than the smallest coefficient A2 among the other materials (1) and (3), and the hardenability of the thinnest material is equal to or less than the hardenability of the other materials.
  • Example 3 the hardenability of the thinnest material is made higher than that of the other materials, so that the phase transformation start time of the thinnest material is extended compared to Comparative Example 2, and the phase transformation start time of the thinnest material and the phase transformation start time of the relatively thick other materials are uniformed. Therefore, in Example 3, after the heating of the blank is completed, it becomes easier to start forming before the phase transformation to ferrite starts in the thinnest material, and it becomes easier to uniformly harden the structural member.
  • the coefficient A1 of the material with the smallest plate thickness t min among the materials (1) to (4) is larger than the smallest coefficient A2 among the other relatively thick materials.
  • the coefficient A1 of the material with the smallest plate thickness t min among the materials (1) to (4) is equal to or smaller than the smallest coefficient A2 among the other relatively thick materials.
  • Example 6 When each Example is compared with the corresponding Comparative Example, it can be seen that the phase transformation start time is extended. For example, when Example 6 and Comparative Example 5, which are the same except for the material of the thinnest material (4), are compared, the phase transformation start time of Example 6 is delayed compared to Comparative Example 5.
  • the coefficient A1 of the thinnest material (4) is larger than the smallest coefficient A2 among the other materials (1) to (3), and the hardenability of the thinnest material is higher than the hardenability of one or more other materials.
  • Example 6 the coefficient A1 of the thinnest material (4) is equal to or smaller than the smallest coefficient A2 among the other materials (1) to ( 3 ), and the hardenability of the thinnest material is equal to or smaller than the hardenability of the other materials.
  • the hardenability of the thinnest material is made higher than the hardenability of the other materials, so that the phase transformation start time of the thinnest material is extended compared to Comparative Example 5, and the phase transformation start time of the thinnest material and the phase transformation start time of the relatively thick other materials are uniformed. Therefore, in Example 6, after the heating of the blank was completed, forming was likely to begin before the phase transformation to ferrite began in the thinnest material, making it easier for the structural member to be quenched uniformly.
  • Table 4 shows the analysis conditions and results for division patterns 5 to 7 shown in Figures 8E to 8G.
  • the structural members are formed from five pieces of material (1) to (5).
  • the coefficient A1 of the material having the smallest plate thickness tmin among the materials (1) to (5) is larger than the smallest coefficient A2 among the other relatively thick materials.
  • the coefficient A1 of the material having the smallest plate thickness tmin among the materials (1) to (5) is equal to or smaller than the smallest coefficient A2 among the other relatively thick materials.
  • Example 12 When each Example is compared with the corresponding Comparative Example, it can be seen that the phase transformation start time is extended. For example, when Example 12 and Comparative Example 8, which are the same except for the materials of the thinnest materials (1) and (4), are compared, the phase transformation start time of Example 12 is delayed compared to Comparative Example 8.
  • the coefficient A1 of the thinnest materials (1) and (4) is larger than the smallest coefficient A2 among the other materials (2), (3), and (5), and the hardenability of the thinnest material is higher than the hardenability of one or more other materials.
  • the coefficient A1 of the thinnest materials (1) and (4) is larger than all the coefficients A of the other materials (2), (3), and (5).
  • Example 12 the coefficient A1 of the thinnest materials (1) and (4) is equal to or smaller than the smallest coefficient A2 among the other materials (2), (3), and (5), and the hardenability of the thinnest material is equal to or smaller than the hardenability of the other materials.
  • the hardenability of the thinnest material was made higher than that of the other materials, so that the phase transformation start time of the thinnest material was extended compared to Comparative Example 8, and the phase transformation start time of the thinnest material and the phase transformation start time of the other relatively thick materials were made uniform. Therefore, in Example 12, after heating of the blank was completed, it became easier to start forming before the phase transformation to ferrite started in the thinnest material, and it became easier to uniformly harden the structural member.
  • Example 13 Comparative Example 9 which are the same except for the materials of the thinnest materials (1), (3), and (5)
  • the phase transformation start time is delayed in Example 13 compared to Comparative Example 9.
  • the smallest coefficient A1 among the thinnest materials (1), (3), and (5) is larger than the smallest coefficient A2 among the other materials (2) and (4), and the hardenability of the thinnest material is higher than the hardenability of one or more other materials.
  • all of the coefficients A of the thinnest materials (1), (3), and (5) are larger than the coefficients A of the other materials (2) and (4).
  • Example 13 the smallest coefficient A1 among the thinnest materials (1), (3), and (5) is equal to or smaller than the smallest coefficient A2 among the other materials (2) and (4), and the hardenability of the thinnest material is equal to or smaller than the hardenability of the other materials.
  • the hardenability of the thinnest material was made higher than that of the other materials, so that the phase transformation start time of the thinnest material was extended compared to Comparative Example 9, and the phase transformation start time of the thinnest material and the phase transformation start time of the other relatively thick materials were made uniform. Therefore, in Example 13, after heating of the blank was completed, it became easier to start forming before the phase transformation to ferrite started in the thinnest material, and it became easier to harden the structural member uniformly.
  • Example 18 and Comparative Example 12 material (2) and material (5), material (3) and material (4), and material (4) and material (5) each form an overlap at their joints.
  • material (2) and material (5), and material (3) and material (4) each form an overlap at their joints.
  • the coefficient A1 of the material with the smallest thickness tmin among the materials (1) to (5) is larger than the smallest coefficient A2 among the other relatively thick materials.
  • the coefficient A1 of the material with the smallest thickness tmin among the materials ( 1 ) to (5) is equal to or smaller than the smallest coefficient A2 among the other relatively thick materials.
  • phase transformation start times of Examples 18 and 19 are slower than those of Comparative Examples 12 and 13. Therefore, it was confirmed that even when an overlapping portion exists in a blank, the phase transformation start times of each material in the blank can be made uniform by making the coefficient A1 of the thinnest material larger than the smallest coefficient A2 among the other materials.
  • the steel plates used as materials were selected from those shown in Table 1.
  • the division pattern of the structural members is as shown in Figures 9A to 9D.
  • Figures 9A to 9D show the number of steel plates (materials) contained in the structural members that are double door ring parts, and the positions of the joints between the steel plates in the structural members.
  • each steel plate used as material is given a number in parentheses.
  • Table 6 shows the analysis conditions and results for division patterns 8 and 9 shown in Figures 9A and 9B.
  • the structural member is formed from six pieces of material (1) to (6).
  • the coefficient A1 of the minimum thickness tmin among the materials (1) to (6) is larger than the minimum coefficient A2 among the other relatively thick materials.
  • the coefficient A1 of the minimum thickness tmin among the materials (1) to (6) is equal to or smaller than the minimum coefficient A2 among the other relatively thick materials.
  • the minimum coefficient A1 among the materials (1) to (7) having the minimum plate thickness t min is larger than the minimum coefficient A2 among the other relatively thick materials.
  • the minimum coefficient A1 among the materials ( 1 ) to (7) having the minimum plate thickness t min is equal to or smaller than the minimum coefficient A2 among the other relatively thick materials.
  • Examples 14 and 16 in Table 8 are examples with the same conditions as Examples 14 and 16 shown in Table 4.
  • Example 15A has the same division pattern and material combination as Example 15 shown in Table 4, but some of the materials form overlapping portions at the joints.
  • Comparative Example 10A has the same division pattern and material combination as Comparative Example 10 shown in Table 4, but some of the materials form overlapping portions at the joints.
  • material (1) and material (2), material (1) and material (3), material (2) and material (5), and material (4) and material (5) each form overlapping portions at their joints.
  • Comparative Example 11 is a comparative example with the same conditions as Comparative Example 11 shown in Table 4.
  • the variation in martensite fraction is the value obtained by subtracting the minimum martensite fraction (%) from the maximum martensite fraction (%) in the cross section of the structural member at the position of the material having the minimum plate thickness t min , as described in the above embodiment.
  • the shape accuracy was evaluated based on how far apart the structural member was from the mating member at the overlapping portion of the structural member and mating member when the structural member was attached to another member, which was roughly hat-shaped in cross section.
  • Table 8 cases where the distance from the surface of the mating member was within ⁇ 2.0 mm are marked with an O, cases where it was between ⁇ 2.0 mm and ⁇ 3.0 mm, and cases where it was over ⁇ 3.0 mm are marked with an X.
  • door ring assembly parts were produced by spot welding door ring inner parts to each structural member (door ring outer part) of the examples and comparative examples shown in Table 8, and these were used as test specimens for partial structure evaluation. Then, the periphery of each test specimen was fixed with a restraining jig to reproduce the deformation during a vehicle collision, and a barrier was collided from the door ring outer part side (side of the vehicle body), and the maximum intrusion amount at this time was evaluated as impact absorption performance.
  • Impact absorption performance was evaluated based on the impact absorption performance of the door ring outer part formed by joining each material after forming it by hot stamping, and compared with the impact absorption performance of the base.
  • each example shown in Table 8 satisfies A 1 -A 2 >0, whereas each comparative example satisfies A 1 -A 2 ⁇ 0.
  • the variation in martensite fraction exceeded 20%, whereas in examples 14, 15A, and 16, the variation in martensite fraction was 20% or less.
  • the variation in martensite fraction was reduced to 15% or less.
  • the shape accuracy was also better than that of comparative examples 10A and 11.
  • Examples 14, 15A, and 16 where the variation in the martensite fraction was small, the impact absorption performance was improved compared to Comparative Examples 10A and 11.
  • Examples 14 and 15A where the variation in the martensite fraction was 10% or less, impact absorption performance equal to or greater than that of the base was ensured.
  • impact absorption performance equal to or greater than that of a structural component formed by joining the materials after press forming them individually was ensured.
  • Structural member 11 Member body 20, 20A, 20B: Blank 21: Steel plate (first steel plate) 22: Steel plate (second steel plate) 23: Steel plate 40: Mold 111: Front pillar 112: Center pillar 113: Locker

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  • Engineering & Computer Science (AREA)
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  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Heat Treatment Of Articles (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
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JP2004058082A (ja) * 2002-07-26 2004-02-26 Aisin Takaoka Ltd テーラードブランクプレス成形品の製造方法
JP2013501631A (ja) * 2010-11-03 2013-01-17 ヒュンダイ ハイスコ 熱処理硬化鋼板を用いた局部的に異種強度を有する自動車部品の製造方法
WO2013147035A1 (ja) * 2012-03-28 2013-10-03 新日鐵住金株式会社 ホットスタンプ用テーラードブランクおよびホットスタンプ部材ならびにそれらの製造方法
JP2019014935A (ja) * 2017-07-06 2019-01-31 新日鐵住金株式会社 熱間プレス用鋼板とその製造方法、ならびに熱間プレス成形部材およびその製造方法
JP2021528248A (ja) * 2018-06-25 2021-10-21 オートテック・エンジニアリング・ソシエダッド・リミターダＡｕｔｏｔｅｃｈ Ｅｎｇｉｎｅｅｒｉｎｇ， Ｓ．Ｌ． 車両のボディサイド構造フレーム
CN217893040U (zh) * 2022-08-12 2022-11-25 浙江吉利控股集团有限公司 侧围加强板、侧围加强板总成和车辆

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JP2004058082A (ja) * 2002-07-26 2004-02-26 Aisin Takaoka Ltd テーラードブランクプレス成形品の製造方法
JP2013501631A (ja) * 2010-11-03 2013-01-17 ヒュンダイ ハイスコ 熱処理硬化鋼板を用いた局部的に異種強度を有する自動車部品の製造方法
WO2013147035A1 (ja) * 2012-03-28 2013-10-03 新日鐵住金株式会社 ホットスタンプ用テーラードブランクおよびホットスタンプ部材ならびにそれらの製造方法
JP2019014935A (ja) * 2017-07-06 2019-01-31 新日鐵住金株式会社 熱間プレス用鋼板とその製造方法、ならびに熱間プレス成形部材およびその製造方法
JP2021528248A (ja) * 2018-06-25 2021-10-21 オートテック・エンジニアリング・ソシエダッド・リミターダＡｕｔｏｔｅｃｈ Ｅｎｇｉｎｅｅｒｉｎｇ， Ｓ．Ｌ． 車両のボディサイド構造フレーム
CN217893040U (zh) * 2022-08-12 2022-11-25 浙江吉利控股集团有限公司 侧围加强板、侧围加强板总成和车辆

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