JP2022154099A - molding method - Google Patents

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JP2022154099A
JP2022154099A JP2021056979A JP2021056979A JP2022154099A JP 2022154099 A JP2022154099 A JP 2022154099A JP 2021056979 A JP2021056979 A JP 2021056979A JP 2021056979 A JP2021056979 A JP 2021056979A JP 2022154099 A JP2022154099 A JP 2022154099A
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steel plate
molding method
heating
cooling
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JP7052116B1 (en
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舜 ▲高▼岡
Shun Takaoka
匠 佐藤
Takumi Sato
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G Tekt Corp
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Priority to PCT/JP2022/015940 priority patent/WO2022210868A1/en
Priority to EP22781078.5A priority patent/EP4316684A1/en
Priority to US18/552,719 priority patent/US20240167115A1/en
Priority to EP23205839.6A priority patent/EP4321631A3/en
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    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0294—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a localised treatment
    • 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
    • C21D9/0062—Heat-treating apparatus with a cooling or quenching zone
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Abstract

To enable molding, in which a region which is not quenched partially is formed, to be executed normally by hot-pressing.SOLUTION: In a heating step S101, a steel plate is heated into an austenitic state. In the heating step S101, the whole area of the steel plate is heated evenly to bring the whole area of the steel plate into austenitic state. In a cooling step S102, only a preset first region of the steel plate brought into the austenitic state is forcibly cooled (rapidly quenched) in a temperature range which is a range in which martensitic transformation is not caused. In the cooling step S102, a second region other than the first region is cooled by natural cooling and is maintained at a temperature higher than in the first region.SELECTED DRAWING: Figure 1

Description

本発明は、鋼板の成型方法および成形品に関する。 TECHNICAL FIELD The present invention relates to a method of forming a steel plate and a formed product.

車輌を構成する部品（車体部品）には、高い強度が要求される。このため、部品を形成する材料には、例えば、高張力鋼板などの高強度な鋼板が用いられている。しかしながら、鋼板をプレス加工して車体部品としているため、高強度な鋼板を用いると、プレス加工において寸法精度不良が発生しやすいなどの問題が発生する。これは、用いる鋼板の強度が高いほど顕著となる。 High strength is required for parts (body parts) that constitute a vehicle. For this reason, high-strength steel plates such as high-strength steel plates are used as materials for forming parts. However, since a steel plate is pressed to form a vehicle body part, if a high-strength steel plate is used, problems such as poor dimensional accuracy tend to occur during press working. This becomes more pronounced as the strength of the steel plate used is higher.

上述した問題に対し、熱間プレスと呼ばれる技術が開発されている（特許文献１）。熱間プレスでは、加熱して鋼板を軟質化させた状態でプレス加工し、同時に型との接触による冷却で焼き入れをすることにより、高い強度および高い寸法精度の車体部品が形成可能となる。 A technique called hot pressing has been developed to address the above-described problem (Patent Document 1). In the hot press, the steel sheet is softened by heating and pressed, and at the same time, it is quenched by cooling due to contact with the mold, making it possible to form body parts with high strength and high dimensional accuracy.

ところで、自動車部品においては、衝撃を受けたときに受けた衝撃が吸収される塑性変形する部分を設ける場合がある。このような部品の成形のために、例えば、塑性変形させたい領域に対応する型の部分は、温度を高く維持し、冷却による焼き入れがなされないようにする技術が提案されている。 By the way, automobile parts may be provided with a plastically deformed portion that absorbs the impact received when receiving an impact. For molding such parts, for example, a technique has been proposed in which a portion of the mold corresponding to a region to be plastically deformed is maintained at a high temperature so that it is not quenched by cooling.

特開２０１８－０１２１１３号公報JP 2018-012113 A

しかしながら、上述した技術では、成型体を型から離型するときに、焼き入れがなされていない領域は高い温度が維持されているため、冷却の温度差による収縮差でねじれが発生するなどの問題が発生する。このように、従来の技術では、熱間プレスにより一部に焼き入れがなされない領域を形成しようとすると、正常な成形ができないという問題があった。 However, with the above-described technology, when the molded body is released from the mold, the area that is not quenched is maintained at a high temperature, so there are problems such as twisting due to the difference in shrinkage due to the difference in cooling temperature. occurs. As described above, the conventional technique has a problem that normal molding cannot be performed when an attempt is made to form a region that is partially not quenched by hot pressing.

本発明は、以上のような問題点を解消するためになされたものであり、一部に焼き入れがなされない領域を備える成形が、熱間プレスにより正常に実施できるようにすることを目的とする。 SUMMARY OF THE INVENTION The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to make it possible to normally carry out hot press forming that has a region that is not quenched in part. do.

本発明に係る成型方法は、鋼板を加熱してオーステナイト状態とする加熱工程と、オーステナイト状態とした鋼板の設定した第１領域のみをマルテンサイト変態しない範囲の温度範囲で強制的に冷却する冷却工程と、オーステナイト状態となっていない第１領域とオーステナイト状態とされた第２領域とを有する鋼板を熱間プレス成形する成形工程とを備える。 The forming method according to the present invention includes a heating step of heating a steel plate to an austenitic state, and a cooling step of forcibly cooling only the first region set in the steel plate in the austenitic state in a temperature range in which martensite transformation does not occur. and a forming step of hot press forming a steel sheet having a first region that is not in an austenitic state and a second region that is in an austenitic state.

上記成型方法の一構成例において、冷却工程は、第１領域を、フェライト・パーライト相が生成する温度に冷却する。 In one configuration example of the molding method, the cooling step cools the first region to a temperature at which a ferrite/pearlite phase is generated.

上記成型方法の一構成例において、加熱工程は、鋼板の全域を均一に加熱する。 In one configuration example of the forming method, the heating step uniformly heats the entire area of the steel sheet.

上記成型方法の一構成例において、冷却工程の後で、鋼板を加熱して、第１領域以外の第２領域をオーステナイト状態とする、または第２領域のオーステナイト状態を維持する再加熱工程をさらに備え、再加熱工程の後で、成形工程を実施する。 In one configuration example of the forming method, after the cooling step, a reheating step of heating the steel plate to bring the second region other than the first region into an austenitic state or maintain the austenitic state of the second region is further added. In preparation, the molding process is carried out after the reheating process.

上記成型方法の一構成例において、冷却工程は、第２領域は、自然冷却により冷却して第１領域より高い温度の状態を維持し、再加熱工程は、第１領域がオーステナイト状態とならない範囲の条件で鋼板を加熱し、成形工程は、第２領域のみをマルテンサイト変態させる。 In one configuration example of the molding method, in the cooling step, the second region is cooled by natural cooling to maintain a higher temperature state than the first region, and in the reheating step, the first region does not enter an austenitic state. The steel sheet is heated under the conditions of and the forming step transforms only the second region into martensite.

上記成型方法の一構成例において、鋼板は、表面にめっき層が形成され、加熱工程は、鋼板とめっき層とが合金化する温度に加熱する。 In one configuration example of the forming method, the steel sheet has a plating layer formed on its surface, and in the heating step, the steel sheet and the plating layer are heated to a temperature at which the steel sheet and the plating layer are alloyed.

上記成型方法の一構成例において、めっき層は、アルミニウムから構成されている。 In one structural example of the molding method, the plating layer is made of aluminum.

本発明に係る成形品は、めっきが形成され、形成されているめっきの層との間に拡散層が形成されている鋼板を成形した成形品であって、焼き入れ処理がされていない硬度が７８０ＭＰａ以下の第１領域と、焼き入れ処理がされた硬度が１３００ＭＰａ以上の第２領域とを備え、拡散層は、第１領域および第２領域を含めた全域に、厚さ１０μｍ以下で均一に形成されている。 The molded product according to the present invention is a molded product formed by molding a steel plate on which plating is formed and a diffusion layer is formed between the formed plating layer, and has a hardness that is not quenched. A first region having a hardness of 780 MPa or less and a second region having a hardened hardness of 1300 MPa or more. formed.

以上説明したように、本発明によれば、加熱工程により鋼板をオーステナイト状態とした後、第１領域のみを強制的に冷却するので、一部に焼き入れがなされない領域を備える成形が、熱間プレスにより正常に実施できる。 As described above, according to the present invention, after the steel sheet is brought into the austenitic state by the heating process, only the first region is forcibly cooled, so that forming having a region that is partially not quenched can be achieved by heating. It can be successfully performed by pressing between.

図１は、本発明の実施の形態１に係る成型方法を説明するフローチャートである。FIG. 1 is a flow chart illustrating a molding method according to Embodiment 1 of the present invention. 図２は、本発明の実施の形態１に係る成型方法における温度変化を示す特性図である。FIG. 2 is a characteristic diagram showing temperature changes in the molding method according to Embodiment 1 of the present invention.

以下、本発明の実施の形態に係る成型方法について図１、図２を参照して説明する。 A molding method according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG.

まず、加熱工程Ｓ１０１で、鋼板を加熱してオーステナイト状態とする。加熱工程Ｓ１０１では、鋼板の全域を均一に加熱して、鋼板の全域をオーステナイト状態とする。オーステナイトへ変態が開始する温度Ａｃ３以上に加熱することで、鋼板をオーステナイト状態とすることができる。例えば、オーブンなどの加熱装置を用い、鋼板の全域を約９００℃に加熱することで、鋼板の全域をオーステナイト状態とすることができる。例えば、鋼材は、マンガンボロン鋼から構成され、８２３℃以上に加熱することで、オーステナイト状態とすることができる。 First, in the heating step S101, the steel plate is heated to be in an austenite state. In the heating step S101, the entire area of the steel sheet is uniformly heated to bring the entire area of the steel sheet into an austenitic state. By heating to a temperature Ac3 or higher at which transformation to austenite starts, the steel sheet can be brought into an austenitic state. For example, by heating the entire area of the steel sheet to about 900° C. using a heating device such as an oven, the entire area of the steel sheet can be brought into an austenitic state. For example, the steel material is composed of manganese boron steel, and can be brought into an austenitic state by heating to 823° C. or higher.

次に、冷却工程Ｓ１０２で、オーステナイト状態とした鋼板の設定した第１領域のみをマルテンサイト変態しない範囲の温度範囲で強制的に冷却（急冷）する［図２の（ａ）］。マルテンサイトが生成し始める温度Ｍｓより高い温度の範囲で、強制的な冷却を実施する。この工程では、第１領域を、フェライト・パーライト相が生成する温度に急冷することが重要である。 Next, in the cooling step S102, only the set first region of the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range in which martensite transformation does not occur [FIG. 2(a)]. Forced cooling is carried out in a temperature range above the temperature Ms at which martensite begins to form. In this step, it is important to rapidly cool the first region to a temperature at which the ferrite-pearlite phase is formed.

例えば、水冷により冷却されている冷却ブロックを当接することで、第１領域のみを急冷することができる。また、第１領域のみに、空気などの気体、水、ミストなどを吹き付けることで、第１領域のみを急冷することができる。冷却工程Ｓ１０２においては、第１領域以外の第２領域は、自然冷却により冷却して第１領域より高い温度の状態を維持する［図２の（ｂ）］。例えば、処理対象の鋼板の、第１領域以外の全域が、第２領域である。 For example, by bringing a cooling block cooled by water cooling into contact, only the first region can be rapidly cooled. Also, by spraying a gas such as air, water, mist, or the like only on the first region, it is possible to rapidly cool only the first region. In the cooling step S102, the second area other than the first area is cooled by natural cooling and maintained at a higher temperature than the first area [FIG. 2(b)]. For example, the entire area other than the first area of the steel sheet to be processed is the second area.

なお、冷却工程Ｓ１０２では、第１領域がマルテンサイト変態しない範囲で、最も低い温度となる状態に急冷することもできる。ただし、冷却工程Ｓ１０２では、第１領域がベイナイト変態する温度より高い状態となっていることが重要となる。鋼板を構成する鋼の種類によっても異なるが、例えば、冷却工程Ｓ１０２では、第１領域のみを５５０～６５０℃の範囲のいずれかの温度にまで急冷する。 In the cooling step S102, the first region can also be rapidly cooled to the lowest temperature within a range in which martensitic transformation does not occur. However, in the cooling step S102, it is important that the temperature in the first region is higher than the bainite transformation temperature. For example, in the cooling step S102, only the first region is quenched to a temperature within the range of 550 to 650° C., depending on the type of steel forming the steel plate.

急速冷却を行うことで、フェライト相が生成する７５０℃以下まで瞬間的に温度が下がり、第１領域にオーステナイト→フェライト変態のきっかけが作られる。急速冷却しただけではフェライト変態しない。第１領域の急冷した状態を一定時間（数秒）維持することでオーステナイト→フェライト・パーライトへと組織が成長する。この、第１領域のみの急冷は、加熱工程を実施した加熱炉外で実施するため、第２領域が自然冷却される。この自然冷却により、第２領域が７５０℃より低い温度になると、フェライトが生成される。 By performing rapid cooling, the temperature is instantaneously lowered to 750° C. or less at which the ferrite phase is generated, and a trigger for austenite-to-ferrite transformation is created in the first region. Rapid cooling alone does not cause ferrite transformation. By maintaining the quenched state of the first region for a certain period of time (several seconds), the structure grows from austenite to ferrite/pearlite. Since this rapid cooling of only the first region is performed outside the heating furnace in which the heating step was performed, the second region is naturally cooled. Due to this natural cooling, ferrite is produced when the temperature of the second region is lower than 750°C.

次に、再加熱工程Ｓ１０３で、鋼板を加熱して、第１領域以外の第２領域を再度オーステナイト状態とする、または第２領域のオーステナイト状態を維持する。再加熱工程Ｓ１０３では、鋼板の全域を均一に加熱することで、第２領域をオーステナイト状態とする。再加熱工程Ｓ１０３は、第１領域がオーステナイト状態とならない範囲の条件で鋼板を加熱する。例えば、第１領域を断熱材で覆うことで、上述した処理を実施することができる。断熱材の大きさを変えることで遷移領域の幅を調整することができる。冷却工程Ｓ１０２の処理で、第１領域の温度と第２領域の温度との間に差が形成されているので、鋼板の全域を均一に加熱しても、第２領域はオーステナイトとし、第１領域はオーステナイト状態とならないようにすることができる。 Next, in a reheating step S103, the steel sheet is heated to bring the second region other than the first region back into an austenitic state, or maintain the austenitic state of the second region. In the reheating step S103, the second region is brought into an austenite state by uniformly heating the entire steel plate. In the reheating step S103, the steel plate is heated under conditions in which the first region does not enter the austenitic state. For example, by covering the first region with a heat insulating material, the processing described above can be implemented. The width of the transition region can be adjusted by varying the size of the insulation. In the cooling step S102, a difference is formed between the temperature of the first region and the temperature of the second region. The region can be kept out of the austenitic state.

また、冷却工程Ｓ１０２の処理を実施した後、再加熱工程Ｓ１０３を実施する段階で、第２領域のオーステナイト状態が維持されている場合、再加熱工程Ｓ１０３の加熱処理は、第２領域におけるオーステナイト状態を、後工程の熱間プレス成形でマルテンサイト変態をさせるために、維持するための処理となる。 Further, when the austenitic state in the second region is maintained at the stage of performing the reheating step S103 after the cooling step S102 is performed, the heat treatment in the reheating step S103 is performed in the austenitic state in the second region. is maintained in order to undergo martensite transformation in the subsequent hot press forming process.

また、冷却工程Ｓ１０２の処理を実施した後、再加熱工程Ｓ１０３を実施する段階で、第２領域のオーステナイト状態が十分に維持され、直後に後工程の熱間プレス成形が実施できる場合、再加熱工程Ｓ１０３を実施せず、次の成形工程Ｓ１０４が実施できる。 Further, after performing the cooling step S102, at the stage of performing the reheating step S103, the austenitic state of the second region is sufficiently maintained, and immediately after that, hot press forming in the post-process can be performed. The next molding step S104 can be performed without performing the step S103.

次に、成形工程Ｓ１０４で、オーステナイト状態となっていない第１領域とオーステナイト状態とされた第２領域とを有する鋼板を熱間プレス成形する。この熱間プレス成形においては、第２領域のみをマルテンサイト変態させる。 Next, in forming step S104, the steel plate having the first region not in the austenite state and the second region in the austenite state is hot press formed. In this hot press forming, only the second region undergoes martensite transformation.

上述した実施の形態によれば、熱間プレス成形の結果、第２領域は、焼き入れされた状態となってマルテンサイトとなる。一方、第１領域は、焼きなましされた状態となり、組成変改しやすい部分となる。また、実施の形態によれば、成型体を型から離型する段階で、全域が低い温度となっているため、いわゆるスプリングバックなどの問題が発生しない。このように、実施の形態によれば、一部に焼き入れがなされない領域を備える成形が、熱間プレスにより正常に実施できるようになる。なお、冷却工程から再加熱工程にかけての低温側温度を、マルテンサイト変態が起きる近辺の温度の範囲で制御することで、ベイナイト相を含む組織変態をすることもできる。 According to the embodiment described above, as a result of the hot press forming, the second region is in a quenched state and becomes martensite. On the other hand, the first region is in an annealed state and becomes a portion that is likely to change composition. Moreover, according to the embodiment, since the entire area is at a low temperature when the molded body is released from the mold, problems such as so-called springback do not occur. As described above, according to the embodiment, forming having a partially unquenched region can be performed normally by hot pressing. By controlling the temperature on the low temperature side from the cooling step to the reheating step within a temperature range around which martensitic transformation occurs, it is also possible to effect structural transformation including the bainite phase.

例えば、実施の形態によれば、熱間プレス成形により、第１領域は、引張強度７８０ＭＰａ以下、硬度２２０ＨＶ以下とし、第２領域は、引張強度１３００ＭＰａ以上、硬度４００ＨＶ以上とすることができる。また、第１領域と第２領域との間には、硬度が徐々に遷移する幅～５０ｍｍ程度の境界領域を形成することができる。 For example, according to the embodiment, by hot press forming, the first region can have a tensile strength of 780 MPa or less and a hardness of 220 HV or less, and the second region can have a tensile strength of 1300 MPa or more and a hardness of 400 HV or more. Further, between the first region and the second region, a boundary region having a width of about 50 mm can be formed in which the hardness gradually transitions.

前述したように、例えば、自動車部品においては、衝撃を受けたときに受けた衝撃が吸収される塑性変形する部分を設けるようにしている。第１領域は、この部分とするための領域である。第１領域を、フェライト・パーライト相が生成している状態とすることで、ベイナイトより柔らかく延性を持った状態とすることができる。このような状態となっている第１領域は、より変形しやすくなるので、予め変形部位を限定することができる。また、フェライト・パーライト相が生成している状態とすることで、延性が高い状態とすることができ、変形時に割れにくく伸びて粘るものとなる。 As described above, automobile parts, for example, are provided with a plastically deformable portion that absorbs the impact received. The first area is an area for this portion. By setting the first region to a state in which a ferrite/pearlite phase is generated, it can be made softer than bainite and have ductility. Since the first region in such a state is more easily deformed, the deformed portion can be limited in advance. In addition, by creating a state in which ferrite/pearlite phases are generated, a state of high ductility can be obtained, and the steel becomes hard to crack and stretches when deformed.

ところで、上述したような、プレス前において各々温度の異なる２つの領域を形成するために、部分的に加熱することも考えられる。しかしながらこの場合、部分的に加熱するための設備が必要となり、設備が大がかりとなる懸念がある。これに対し、部分的に冷却する設備は、加熱の場合と異なり、大がかりな設備を必要とせず、コストの点で有利なものと考えられる。 By the way, it is conceivable to partially heat in order to form two regions having different temperatures before pressing as described above. However, in this case, equipment for partially heating is required, and there is a concern that the equipment becomes large-scale. On the other hand, unlike the case of heating, equipment for partial cooling does not require large-scale equipment and is considered to be advantageous in terms of cost.

ところで、腐食を防止する観点から、一般に、鋼板の表面にめっき層を形成して用いている。例えば、アルミニウムから構成されためっき層を鋼板の表面に形成している。また、この種のめっき層は、加熱により鋼板との間に合金化した層を形成して用いられている。このように、めっき鋼板に対しても、上述した実施の形態に係る成型方法が適用可能である。成形された成型体は、例えば、自動車のドアのセンターピラーなどの部品として用いることができる。 By the way, from the viewpoint of preventing corrosion, a steel sheet is generally used with a plated layer formed on its surface. For example, a plated layer made of aluminum is formed on the surface of the steel plate. In addition, this type of plating layer is used by forming an alloyed layer with the steel sheet by heating. As described above, the forming method according to the above-described embodiment can also be applied to the plated steel sheet. The formed molded body can be used, for example, as a part such as a center pillar of an automobile door.

この場合、加熱工程において、めっき層が形成された鋼板を、鋼板とめっき層とが合金化する温度に加熱する。鋼板が、オーステナイト状態となる温度は、鋼板とめっき層とが合金化する温度であり、鋼板をオーステナイト状態となる温度に加熱することで、上述した合金化がなされるものとなる。例えば、アルミニウムによるめっき層が、厚さ３０μｍ程度形成されているマンガンボロン鋼による鋼板（Ａｌメッキ鋼板）の場合、６６０℃から合金化が始まり、６６０℃となった時点からおおよそ１５０秒後に、合金となっていない部分（未合金）がない状態とすることができる。従って、前述したように、オーステナイト状態とすることができる８２３℃以上に加熱することで、未合金のない状態に合金層を形成することもできる。 In this case, in the heating step, the steel sheet on which the plating layer is formed is heated to a temperature at which the steel sheet and the plating layer are alloyed. The temperature at which the steel sheet becomes austenite is the temperature at which the steel sheet and the coating layer are alloyed, and by heating the steel sheet to the temperature at which the steel sheet becomes austenite, the above-described alloying is performed. For example, in the case of a manganese boron steel steel plate (Al-plated steel plate) in which an aluminum plating layer is formed to a thickness of about 30 μm, alloying starts at 660 ° C., and about 150 seconds after reaching 660 ° C., the alloying It can be in a state where there is no portion (unalloyed) that is not. Therefore, as described above, by heating to 823° C. or higher at which an austenitic state can be obtained, an alloy layer can be formed without unalloyed.

なお、Ａｌメッキ鋼板では、加熱により合金化し、さらに鋼板が７５０℃以上であると、厚さ方向に拡散層が形成される。マンガンボロン鋼によるＡｌメッキ鋼板では、加熱を開始することで合金化が始まる。例えば、加熱炉の条件が９２０℃である場合、２５０秒加熱すると拡散層が形成され始める。拡散層の形成時間は、鋼板の種類や板厚や形状、加熱の温度、用いる加熱炉などの条件によって変化するが、拡散層の厚さは、１０μｍ以下とすることが好ましい。 In addition, in the Al-plated steel sheet, if the steel sheet is alloyed by heating and the steel sheet is heated to 750° C. or higher, a diffusion layer is formed in the thickness direction. In Al-plated steel sheets made of manganese boron steel, alloying starts when heating is started. For example, if the furnace condition is 920° C., the diffusion layer begins to form after heating for 250 seconds. The formation time of the diffusion layer varies depending on conditions such as the type, thickness and shape of the steel sheet, the heating temperature, and the heating furnace used, but the thickness of the diffusion layer is preferably 10 μm or less.

Ａｌメッキ鋼板を使用した熱間プレスでは、熱間プレスを実施する前に、合金化により形成される拡散層の厚さを制御する必要がある。一般的に、拡散層は、一度形成された後、加熱を続けることで厚さが増加する。加熱後の冷却工程でも拡散層は成長を続け厚さが増加する。拡散層は、厚すぎると溶接の接合強度が低下し、形成されないと材料に耐食性の問題が生じる。このため、Ａｌメッキ鋼板を熱間プレスする場合、熱間プレスをする前に実施する加熱処理は、拡散層がの厚さが、目的の品質が満たされる設定した状態となる必要がある。したがって冷却工程および再加熱工程において短時間で処理をすると、拡散層の品質が満たせる。 In hot pressing using an Al-plated steel sheet, it is necessary to control the thickness of the diffusion layer formed by alloying before hot pressing. In general, once the diffusion layer is formed, its thickness increases with continued heating. Even in the cooling process after heating, the diffusion layer continues to grow and its thickness increases. If the diffusion layer is too thick, the bonding strength of the weld will decrease, and if it is not formed, the material will suffer from corrosion resistance problems. Therefore, when hot-pressing an Al-plated steel sheet, the heat treatment performed before hot-pressing must bring the thickness of the diffusion layer into a set state that satisfies the desired quality. Therefore, if the treatment is performed in a short time in the cooling process and the reheating process, the quality of the diffusion layer can be satisfied.

このように、めっき層を備える鋼板が処理対象の場合、合金化のための、鋼板全域を加熱する処理は、必須の工程となる。この場合、部分的な加熱により部分的に焼き入れしない領域を設けるためには、全域を加熱した後、再度、部分的な加熱を実施することになる。この場合、加熱のための設備が、複数必要となり、コストの上昇を招くなどの問題がある。これに対し、上述した実施の形態に係る成型方法によれば、同一の加熱設備により、加熱工程および再加熱工程が実施できるため、コストの上昇を招くことがない。 Thus, when a steel sheet having a coating layer is to be processed, the process of heating the entire steel sheet for alloying is an essential step. In this case, in order to provide a region that is not partially quenched by partial heating, after heating the entire area, partial heating is performed again. In this case, a plurality of facilities for heating are required, which causes problems such as an increase in cost. On the other hand, according to the molding method according to the above-described embodiment, the heating process and the reheating process can be performed with the same heating equipment, so there is no cost increase.

上述した実施の形態における成型方法により成型された成形品は、めっきが形成され、形成されているめっきの層との間に拡散層が形成されている鋼板を成形した成形品であり、焼き入れ処理がされていない硬度が７８０ＭＰａ以下の第１領域と、焼き入れ処理がされた硬度が１３００ＭＰａ以上の第２領域とを備え、拡散層は、第１領域および第２領域を含めた全域に、厚さ１０μｍ以下で未合金無く均一に形成されている。 The molded product molded by the molding method in the above-described embodiment is a molded product obtained by molding a steel plate on which plating is formed and a diffusion layer is formed between the formed plating layer and is quenched. The diffusion layer comprises a first region having an untreated hardness of 780 MPa or less and a hardened second region having a hardness of 1300 MPa or more. It is uniformly formed with a thickness of 10 μm or less without being unalloyed.

以上に説明したように、本発明によれば、加熱工程により鋼板をオーステナイト状態とした後、第１領域のみを強制的に冷却するので、一部に焼き入れがなされない領域を備える成形が、熱間プレスにより正常に実施できるようになる。 As described above, according to the present invention, after the steel sheet is brought into the austenitic state by the heating process, only the first region is forcibly cooled, so that forming having a region that is not quenched in part is Hot pressing makes it possible to perform normally.

なお、本発明は以上に説明した実施の形態に限定されるものではなく、本発明の技術的思想内で、当分野において通常の知識を有する者により、多くの変形および組み合わせが実施可能であることは明白である。 It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by those skilled in the art within the technical concept of the present invention. It is clear.

本発明は、鋼板の成型方法に関する。 The present invention relates to a method for forming a steel plate.

成形品は、めっきが形成され、形成されているめっきの層との間に拡散層が形成されている鋼板を成形した成形品であって、焼き入れ処理がされていない硬度が７８０ＭＰａ以下の第１領域と、焼き入れ処理がされた硬度が１３００ＭＰａ以上の第２領域とを備え、拡散層は、第１領域および第２領域を含めた全域に、厚さ１０μｍ以下で均一に形成されている。 The molded product is a molded product formed from a steel sheet that is plated and has a diffusion layer formed between the formed plating layer, and has a hardness of 780 MPa or less without quenching. It comprises a first region and a hardened second region having a hardness of 1300 MPa or more. there is

Claims (8)

鋼板を加熱してオーステナイト状態とする加熱工程と、
オーステナイト状態とした前記鋼板の設定した第１領域のみをマルテンサイト変態しない範囲の温度範囲で強制的に冷却する冷却工程と、
オーステナイト状態となっていない前記第１領域と、オーステナイト状態とされた、前記第１領域以外の第２領域とを有する前記鋼板を熱間プレス成形する成形工程と
を備える成型方法。 A heating step of heating the steel plate to an austenitic state;
A cooling step of forcibly cooling only the set first region of the steel plate in the austenite state in a temperature range in which martensite transformation does not occur;
and a forming step of hot press forming the steel sheet having the first region that is not in an austenitic state and a second region that is in an austenitic state other than the first region. 請求項１記載の成型方法において、
前記冷却工程は、前記第１領域を、フェライト・パーライト相が生成する温度に冷却することを特徴とする成型方法。 In the molding method according to claim 1,
The molding method, wherein the cooling step cools the first region to a temperature at which a ferrite/pearlite phase is generated. 請求項１または２記載の成型方法において、
前記加熱工程は、前記鋼板の全域を均一に加熱することを特徴とする成型方法。 In the molding method according to claim 1 or 2,
The forming method, wherein the heating step uniformly heats the entire area of the steel plate. 請求項１～３のいずれか１項に記載の成型方法において、
前記冷却工程の後で、前記鋼板を加熱して、前記第２領域をオーステナイト状態とする、または前記第２領域のオーステナイト状態を維持する再加熱工程をさらに備え、
前記再加熱工程の後で、前記成形工程を実施することを特徴とする成型方法。 In the molding method according to any one of claims 1 to 3,
After the cooling step, further comprising a reheating step of heating the steel plate to bring the second region into an austenitic state or maintain the austenitic state of the second region,
A molding method, wherein the molding step is performed after the reheating step. 請求項４記載の成型方法において、
前記冷却工程は、前記第２領域は、自然冷却により冷却して前記第１領域より高い温度の状態を維持し、
前記再加熱工程は、前記第１領域がオーステナイト状態とならない範囲の条件で前記鋼板を加熱し、
前記成形工程は、前記第２領域のみをマルテンサイト変態させる
ことを特徴とする成型方法。 In the molding method according to claim 4,
In the cooling step, the second region is cooled by natural cooling to maintain a higher temperature state than the first region;
In the reheating step, the steel plate is heated under conditions in which the first region does not enter an austenitic state,
The molding method, wherein the molding step martensite-transforms only the second region. 請求項１～５のいずれか１項に記載の成型方法において、
前記鋼板は、表面にめっき層が形成され、
前記加熱工程は、前記鋼板と前記めっき層とが合金化する温度に加熱する
ことを特徴とする成型方法。 In the molding method according to any one of claims 1 to 5,
A plating layer is formed on the surface of the steel plate,
The forming method, wherein the heating step heats to a temperature at which the steel plate and the plating layer are alloyed. 請求項６記載の成型方法において、
前記めっき層は、アルミニウムから構成されていることを特徴とする成型方法。 In the molding method according to claim 6,
The molding method, wherein the plating layer is made of aluminum. めっきが形成され、形成されているめっきの層との間に拡散層が形成されている鋼板を成形した成形品あって、
焼き入れ処理がされていない強度が７８０ＭＰａ以下の第１領域と、
焼き入れ処理がされた強度が１３００ＭＰａ以上の第２領域と
を備え、
前記拡散層は、前記第１領域および前記第２領域を含めた全域に、厚さ１０μｍ以下で均一に形成されている
ことを特徴とする成形品。 A molded product formed by forming a steel plate with a plating layer and a diffusion layer formed between the plating layer,
a first region that is not quenched and has a strength of 780 MPa or less;
A second region having a hardened strength of 1300 MPa or more,
The molded product, wherein the diffusion layer is uniformly formed with a thickness of 10 μm or less over the entire area including the first region and the second region.
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WO2013137308A1 (en) * 2012-03-13 2013-09-19 株式会社アステア Method for strengthening steel plate member
JP2019013936A (en) * 2017-07-04 2019-01-31 東亜工業株式会社 Method for manufacturing press molded object

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