EP4321631A2 - Formverfahren, wärmebehandlungssystem und formprodukt - Google Patents

Formverfahren, wärmebehandlungssystem und formprodukt Download PDF

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Publication number
EP4321631A2
EP4321631A2 EP23205839.6A EP23205839A EP4321631A2 EP 4321631 A2 EP4321631 A2 EP 4321631A2 EP 23205839 A EP23205839 A EP 23205839A EP 4321631 A2 EP4321631 A2 EP 4321631A2
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EP
European Patent Office
Prior art keywords
region
steel sheet
austenite state
forming
state
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23205839.6A
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English (en)
French (fr)
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EP4321631A3 (de
Inventor
Shun TAKAOKA
Takumi Satou
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G Tekt Corp
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G Tekt Corp
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Publication date
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Publication of EP4321631A2 publication Critical patent/EP4321631A2/de
Publication of EP4321631A3 publication Critical patent/EP4321631A3/de
Pending legal-status Critical Current

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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

Definitions

  • the present invention relates to a steel sheet forming method, a heat treatment system, and a formed product.
  • a part (vehicle body part) of a vehicle is required to have a high strength.
  • a steel sheet with a high strength such as a high tensile steel sheet
  • a vehicle body part is formed by press-forming a steel sheet, if a steel sheet with a high strength is used, defects of dimensional accuracy readily occur in press forming. The higher the strength of the steel sheet to be used is, the more conspicuous this is.
  • a vehicle part is sometimes provided with a portion that is plastically deformed and absorbs impact upon receiving the impact.
  • a technique of, for example, preventing quenching by cooling by maintaining a high temperature in a portion of a die corresponding to a region that should be plastically deformed has been proposed.
  • Patent Literature 1 Japanese Patent Laid-Open No. 2018-012113
  • the present invention has been made to solve the above-described problem, and has as its object to normally execute forming, by hot press, partially including a region that is not quenched.
  • a forming method comprises a heating step of heating a steel sheet and changing the steel sheet to an austenite state, a cooling step of forcibly cooling only a first region set on the steel sheet in the austenite state within a temperature range of a range where martensitic transformation does not occur, and a forming step of hot-press-forming the steel sheet including the first region that is not in the austenite state, and a second region other than the first region, which is in the austenite state.
  • the first region is cooled to a temperature at which a ferrite/pearlite phase is generated.
  • the heating step in the heating step, a whole region of the steel sheet is evenly heated.
  • the forming method further comprises a reheating step of, after the cooling step, heating the steel sheet to make the second region in the austenite state or maintain the austenite state of the second region, wherein the forming step is performed after the reheating step.
  • the second region in the cooling step, is cooled by natural cooling to maintain a state in which the temperature is higher than in the first region, in the reheating step, the steel sheet is heated under a condition of such a range that the first region is not made in the austenite state, and in the forming step, only the second region is transformed to martensite.
  • a plating layer made of aluminum is formed on a surface of the steel sheet, and in the heating step, a whole of the plating layer is alloyed, a composition ratio of iron is not less than a composition ratio of ⁇ -phase iron in an alloy of iron, aluminum, and silicon, and a thickness of a diffusion layer formed on a steel sheet side between the plating layer and the steel sheet is not more than 10 ⁇ m.
  • the steel sheet including the first region that is not in the austenite state, and the second region in the austenite state is hot-press-formed, a strength of the first region is set to not more than 780 MPa without a quenching process, and a strength of the second region is set to not less than 1,300 MPa after having undergone a quenching process, and the diffusion layer is evenly formed with a thickness of not more than 10 ⁇ m in a whole region including the first region and the second region.
  • a heat treatment system is a heat treatment system for forming, on a steel sheet, a first region that is not in an austenite state and a second region other than the first region to form a region to be partially plastically deformed by hot press forming of the steel sheet, the heat treatment system comprising a heat treatment apparatus configured to heat the steel sheet and make the steel sheet in the austenite state, and a cooling processing apparatus configured to forcibly cool only the first region set on the steel sheet in the austenite state within a temperature range of a range where martensitic transformation does not occur.
  • the heat treatment system is a heat treatment system configured to form the first region and the second region to form the region to be partially plastically deformed by hot-press-forming the steel sheet for which a plating layer of aluminum added with silicon is formed on a surface
  • the heat treatment apparatus heats the steel sheet to make the steel sheet in the austenite state, and to alloy a whole of the plating layer to have a composition ratio of iron which is not less than a composition ratio of iron of an ⁇ -phase alloy of iron, aluminum and silicon, and set a thickness of a diffusion layer formed on the side of the steel sheet on which the plating layer is formed not more than 10 ⁇ m.
  • the heat treatment system further comprises a reheat treatment apparatus configured to heat the steel sheet processed by the cooling processing apparatus under such a condition that the diffusion layer does not grow to make the second region in the austenite state or maintain the austenite state of the second region.
  • the reheat treatment apparatus comprises a heat source configured to irradiate the steel sheet with infrared rays, and a cover configured to cover the first region of the steel sheet, and in the cover, a plurality of through holes are formed in a surface irradiated with the infrared rays.
  • the cover is formed as a box body opening on a steel sheet side.
  • a formed product according to the present invention is a formed product obtained by forming a steel sheet for which a plating layer of aluminum added with silicon is formed on a surface, comprising a first region having a strength of not more than 780 MPa without a quenching process, and the second region having a strength of not less than 1,300 MPa after having undergone a quenching process, wherein a whole of the plating layer is alloyed, the formed product comprises a diffusion layer in which a composition ratio of iron is not less than a composition ratio of ⁇ -phase iron in an alloy of iron, aluminum, and silicon and which is formed on a steel sheet side of the plating layer, and the diffusion layer is evenly formed with a thickness of not more than 10 ⁇ m in a whole region including the first region and the second region.
  • a steel sheet is made in an austenite state in a heating step, and then, only the first region is forcibly cooled, thereby enabling normal execution of forming, by hot press, partially including a region that is not quenched.
  • heating step S101 a steel sheet is heated and made in an austenite state.
  • the whole region of the steel sheet is evenly heated, thereby changing the whole region of the steel sheet to the austenite state.
  • the steel sheet can be made in the austenite state by heating it to a temperature Ac3 or more at which the transformation to the austenite state starts.
  • the whole region of the steel sheet is heated to about 900°C using a heating apparatus such as an oven, thereby changing the whole region of the steel sheet to the austenite state.
  • the steel sheet is made of manganese boron steel, and can be made in the austenite state by heating it to 823°C or more.
  • cooling step S102 only a first region set on the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range of a range where martensitic transformation does not occur [(a) of Fig. 2 ].
  • the forcible cooling is performed in the range of temperatures higher than a temperature Ms at which generation of martensite starts. In this step, it is important to rapidly cool the first region to a temperature at which a ferrite/pearlite phase is generated.
  • the first region can be rapidly cooled by making it contact a cooling block cooled by water cooling.
  • only the first region can rapidly be cooled by blowing a gas such as air, water, mist, or the like only to the first region.
  • a second region other than the first region is cooled by natural cooling to maintain a state in which the temperature is higher than in the first region [(b) in Fig. 2 ].
  • the whole region of the process target steel sheet other than the first region is the second region.
  • the first region may rapidly be cooled to the lowest temperature within the range where martensitic transformation does not occur. In cooling step S102, however, it is important that the first region is at a temperature higher than a temperature at which bainitic transformation occurs. Depending on the type of steel forming the steel sheet, for example, in cooling step S102, only the first region is rapidly cooled to a temperature within the range of 550°C to 650°C.
  • the temperature instantaneously lowers to 750°C or less at which the ferrite phase is generated, forming a trigger of austenite -> ferrite transformation in the first region.
  • Ferrite transformation does not occur only by rapid cooling.
  • a state in which the first region is rapidly cooled is maintained for a predetermined time (several sec)
  • the structure grows from austenite to ferrite/pearlite. Since the rapid cooling of only the first region is performed outside a heating furnace in which the heating step is performed, the second region is naturally cooled. If the second region is cooled by natural cooling to a temperature lower than 750°C, ferrite is generated.
  • reheating step S103 the steel sheet is heated to make the second region other than the first region in the austenite state again, or the austenite state of the second region is maintained.
  • the whole region of the steel sheet is evenly heated, thereby changing the second region to the austenite state.
  • the steel sheet is heated under the condition of such a range that the first region is not made in the austenite state.
  • the above-described process can be performed by covering the first region with a thermal insulation material.
  • the width of the transition region can be adjusted by changing the size of the thermal insulation material.
  • cooling step S102 a difference is formed between the temperature of the first region and the temperature of the second region. For this reason, even if the whole region of the steel sheet is evenly heated, it is possible to make the second region in austenite and not to make the first region in the austenite state.
  • the heating process of reheating step S103 is a process for maintaining the austenite state of the second region to cause martensitic transformation in hot press forming of a post-process.
  • step S104 the steel sheet including the first region that is not in the austenite state and the second region that is in the austenite state is hot-press-formed. In this hot press forming, only the second region is transformed to martensite.
  • a heat treatment system configured to form the first region that is not in the austenite state and the second region other than the first region on the steel sheet in the above-described forming method will be described next with reference to Fig. 3 .
  • This heat treatment system is a system configured to form the first region that is not in the austenite state and the second region other than the first region on a steel sheet to form a region to be partially plastically deformed by hot press forming of the steel sheet.
  • the heat treatment system includes a heat treatment apparatus 101, a cooling processing apparatus 102, and a reheat treatment apparatus 103.
  • the heat treatment apparatus 101 heats a steel sheet to make it in the austenite state.
  • the heat treatment apparatus 101 can be formed by, for example, a well-known heating furnace.
  • the heat treatment apparatus 101 evenly heats the whole region of the steel sheet.
  • the cooling processing apparatus 102 forcibly cools only the first region set on the steel sheet in the austenite state within a temperature range of a range where martensitic transformation does not occur.
  • the cooling processing apparatus 102 cools the first region to a temperature at which a ferrite/pearlite phase is generated.
  • the cooling processing apparatus 102 is arranged outside the heat treatment apparatus 101 and can forcibly cool only the first region to the temperature at which a ferrite/pearlite phase is generated within the temperature range of a range where martensitic transformation does not occur, and set the second region in a state in which it is naturally cooled and cool the second region to a temperature lower than the temperature at which transformation to austenite starts.
  • the cooling processing apparatus 102 maintains a state in which the second region is at a temperature higher than in the first region.
  • the reheat treatment apparatus 103 heats the steel sheet processed by the cooling processing apparatus 102, and makes the second region in the austenite state, or maintains the austenite state of the second region. Immediately after the cooling processing apparatus 102, the reheat treatment apparatus 103 heats the steel sheet to make the second region in the austenite state, and at the same time, maintains the rapidly cooled state of the first region for a predetermined time to grow the ferrite/pearlite phase.
  • the reheat treatment apparatus 103 can heat the steel sheet under the condition of such a range that the first region is not made in the austenite state.
  • the reheat treatment apparatus 103 can be formed by, for example, a well-known heating furnace.
  • the reheat treatment apparatus 103 can be configured to include a heat source 131 that irradiates a steel sheet 141 with infrared rays, and a first cover 132 and a second cover 133, which cover a first region 151 of the steel sheet 141.
  • the first cover 132 and the second cover 133 are arranged to sandwich the steel sheet 141.
  • the first cover 132 and the second cover 133 are each formed as a box body opening on the side of the steel sheet 141.
  • the heat source 131 can be formed by, for example, an infrared lamp or a ceramic heater.
  • the first cover 132 covers the steel sheet 141 on the side of the heat source 131.
  • Each of the first cover 132 and the second cover 133 can be formed by a steel sheet having a predetermined thickness.
  • the heat source 131, the first cover 132, and the second cover 133 can be arranged in, for example, a sealable treatment furnace 135.
  • the first cover 132 and the second cover 133 are supported by a support structure (not shown) in the treatment furnace 135.
  • a plurality of through holes 134 are formed in a surface 132a irradiated with infrared rays. If the first cover 132 including the plurality of through holes 134 is used, it is possible to easily execute maintaining a second region 152 of the steel sheet 141 at a temperature at which it is in the austenite state and maintaining the first region 151 within such a range that it is not in the austenite state (a temperature range in which the ferrite/pearlite phase is generated).
  • the temperature difference between the first region 151 and the second region 152 can be set by conditions such as the hole diameter of the through hole 134 and the number of through holes 134 (the ratio of the total area of all through holes 134 on the surface 132a).
  • the first cover 132 and the second cover 133 are detachable/attachable and can therefore be used repetitively, and maintenability is high.
  • the second region is in a quenched state and becomes martensite.
  • the first region is in an annealed state and becomes a portion which is easy to be modified in composition.
  • the whole region has a low temperature at the stage of releasing the formed body from the die, a problem such as so-called spring back does not arise.
  • the first region can have a tensile strength of 780 MPa or less and a hardness of 220 HV or less
  • the second region can have a tensile strength of 1,300 MPa or more and a hardness of 400 HV or more.
  • a boundary region with a width of about 50 mm in which hardness gradually transitions can be formed between the first region and the second region.
  • a vehicle body part is provided with a portion that is plastically deformed and absorbs impact upon receiving the impact.
  • the first region is a region serving as this portion. If a state in which the ferrite/pearlite phase is generated is obtained, the first region becomes softer than bainite and obtains ductility. Since the first region in this state is more easily deformed, a deformation part can be limited in advance. In addition, if a state in which the ferrite/pearlite phase is generated is obtained, a state in which the ductility is high can be obtained, and the region hardly breaks at the time of deformation and is stretcheable and tough.
  • partial heating is also possible.
  • a facility for the partial heating is necessary, and the facility may be bulky.
  • a facility for partial cooling needs no bulky facility, unlike heating, and is considered to be advantageous in terms of cost.
  • a rust-proofing treatment or metal coating is performed for the surface of the part after the process.
  • a surface cleaning step or a surface treatment step is needed, and productivity lowers.
  • coating is performed for the steel sheet in advance. To make the coating correspond to the heating temperature in hot press forming, an aluminum plated steel sheet that has undergone coating of aluminum is used.
  • a plating layer of aluminum added with silicon is used.
  • the forming method according to the above-described embodiment can also be applied to a steel sheet including a plating layer.
  • the formed body can be used as, for example, a part such as the center pillar of a door of an automobile.
  • a steel sheet Al plated steel sheet including, on the surface, a plating layer of aluminum added with silicon
  • the steel sheet is heated to be in an austenitic state, and all of the plating layers are alloyed.
  • the thickness of a diffusion layer formed on the steel sheet side of the plating layer is 10 ⁇ m or less.
  • the diffusion layer is a layer in which the composition ratio of iron is equal to or more than the composition ratio of ⁇ -phase iron in the alloy of iron, aluminum, and silicon.
  • the steel sheet can be in an austenitic state by heating the steel sheet to the temperature Ac3 or more at which transformation to austenite occurs. For example, if the whole region of the steel sheet is heated to about 900°C, the whole region of the steel sheet can be in the austenite state.
  • the steel material can be made of manganese boron steel, and this can be made in the austenite state by heating it to 823°C or more.
  • Al-Fe-Si alloy layer has a high melting point which is about 1,150°C. For this reason, if a whole of the plating layer is alloyed, it is not molten at the heating temperature in the heating step.
  • ⁇ phase (FeSiAl 5 ) of the Al-Fe-Si alloy layer, ⁇ phase (FeSiAl 3 ) of the Al-Fe-Si alloy layer, and FeAl 3 mainly exist in the above-described alloy layer. It is confirmed that the FeAl 3 layer is a layer on the steel sheet side, and the FeSiAl 3 layer is formed in contact with the FeAl 3 layer.
  • the portion including both the FeAl 3 layer and the FeAl 3 layer in contact with it, in other words, the portion in which the composition ratio of iron is equal to or more than the composition ratio of ⁇ -phase iron in the alloy of iron, aluminum, and silicon is the diffusion layer.
  • the thickness of the diffusion layer is 10 ⁇ m or less, sufficient corrosion resistance can be obtained, and the above-described lowering of the joining strength can be suppressed.
  • the heating temperature is 700°C
  • the above-described diffusion layer starts being generated and grows.
  • the temperature range where the diffusion layer is generated in a low temperature region, even if an unalloyed portion exists, the growth of the diffusion layer is confirmed.
  • the reached temperature in the heating process is high, the whole portion is alloyed in a short process time, generation of the diffusion layer starts early, and the growth speed is high. For example, if heating is stopped, and cooling is started when the whole plating layer is alloyed, the growth of the diffusion layer stops before reaching 700°C.
  • heating step S101 a process time is set such that a whole of the plating layer is alloyed under heating temperature conditions for changing the steel sheet to the austenite state, and the diffusion layer is formed in the range of 10 ⁇ m or less in heating step S101.
  • cooling step S102 is the same as described above.
  • cooling step S102 only the first region set on the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range of a range where martensitic transformation does not occur.
  • the forcible cooling is performed in the range of temperatures higher than the temperature Ms at which generation of martensite starts. In this step, it is important to rapidly cool the first region to a temperature at which a ferrite/pearlite phase is generated.
  • the first region may rapidly be cooled to the lowest temperature within the range where martensitic transformation does not occur. In cooling step S102, however, it is important that the first region is at a temperature higher than a temperature at which bainitic transformation occurs. Depending on the type of steel forming the steel sheet, for example, in cooling step S102, only the first region is rapidly cooled to a temperature within the range of 550°C to 650°C.
  • the temperature instantaneously lowers to 750°C or less at which the ferrite phase is generated, forming a trigger of austenite -> ferrite transformation in the first region.
  • Ferrite transformation does not occur only by rapid cooling.
  • a state in which the first region is rapidly cooled is maintained for a predetermined time (several sec)
  • the structure grows from austenite to ferrite/pearlite. Since the rapid cooling of only the first region is performed outside a heating furnace in which the heating step is performed, the second region is naturally cooled. If the second region is cooled by natural cooling to a temperature lower than 750°C, ferrite is generated.
  • reheating step S103 described above is performed under the condition of the range where the diffusion layer does not grow.
  • the start of growth of the diffusion layer changes depending on the temperature condition and the process time. For example, even if the temperature is low, if the process time is long, growth of the diffusion layer starts. On the other hand, even if the temperature is high, if the process time is short, growth of the diffusion layer does not start.
  • the second region is made in the austenite state, or can be maintained in the austenite state. If the second region is heated to 823°C or more, it can be made in the austenite state, or can be maintained in the austenite state.
  • the temperature condition of reheating step S103 is set depending on the time for performing reheating step S103. For example, if the execution time is short, a higher temperature condition can be set. On the other hand, if the execution time is long, the temperature condition is set low.
  • step S104 the steel sheet including the first region that is not in the austenite state and the second region that is in the austenite state is hot-press-formed. In this hot press forming, only the second region is transformed to martensite.
  • This heat treatment system is a system configured to form the first region that is not in the austenite state and the second region other than the first region on a steel sheet to form a region to be partially plastically deformed by hot press forming of the steel sheet on which a plating layer of aluminum added with silicon is formed on the surface.
  • the heat treatment apparatus 101 described with reference to Fig. 3 has a configuration to be described below.
  • the heat treatment apparatus 101 in this case heats a steel sheet and make it in the austenite state, and the thickness of a diffusion layer which is formed on the steel sheet side of the plating layer and in which a whole of the plating layer is alloyed, and the composition ratio of iron is equal to or more than the composition ratio of ⁇ -phase iron in the alloy of iron, aluminum, and silicon is set to 10 ⁇ m or less.
  • the heat treatment apparatus 101 in this case can also be formed by, for example, a well-known heating furnace.
  • the heat treatment apparatus 101 evenly heats the whole region of the steel sheet.
  • the cooling processing apparatus 102 and the reheat treatment apparatus 103 are the same as described above.
  • the second region is in a quenched state and becomes martensite.
  • the first region is in an annealed state and becomes a portion which is easy to be modified in composition.
  • the whole region has a low temperature at the stage of releasing the formed body from the die, a problem such as so-called spring back does not arise.
  • a whole of the plating layer is alloyed, and the thickness of the diffusion layer formed in the alloyed plating layer can be set to 10 ⁇ m or less. Note that if the temperature on the low temperature side from the cooling step to the reheating step is controlled within the temperature range near a point where martensitic transformation occurs, structure transformation including a bainitic phase is also possible.
  • the process of heating the whole steel sheet for alloying is an essential process.
  • the whole region is heated, and after that, partial heating is performed again.
  • a plurality of facilities for heating are necessary, resulting in an increase of cost.
  • the heating step and the reheating step can be performed by the same heating facility, the cost does not increase.
  • the formed product formed using an Al plated steel sheet by the forming method according to the above-described embodiment includes a first region having a strength of 780 MPa or less without a quenching process, and a second region having a strength of 1,300 MPa or more after having undergone a quenching process, includes a plating layer a whole of which is alloyed, and includes a diffusion layer which is formed on the steel sheet side between the plating layer and the steel sheet and in which the composition ratio of iron is equal to or more than the composition ratio of ⁇ -phase iron in the alloy of iron, aluminum, and silicon.
  • the diffusion layer is evenly formed with a thickness of 10 ⁇ m or less in the whole region including the first region and the second region.
  • the thickness of the diffusion layer formed on the steel sheet side of the plating layer is set to 10 ⁇ m or less. For this reason, in forming partially including a region that is not quenched in the steel sheet with the plating layer of aluminum, the plating layer to be alloyed can appropriately be formed.
  • the conventional variation in the joining strength of welding is considered to occur due to the existence of a plating layer that is not appropriately alloyed. This is because the condition for appropriately forming the plating layer to be alloyed is not clear. According to the present invention, the condition for appropriately forming the plating layer to be alloyed is clear, and the above-described problem can be solved.

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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)
EP23205839.6A 2021-03-30 2022-03-30 Formverfahren, wärmebehandlungssystem und formprodukt Pending EP4321631A3 (de)

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JP2021056979A JP7052116B1 (ja) 2021-03-30 2021-03-30 成型方法
EP22781078.5A EP4316684A1 (de) 2021-03-30 2022-03-30 Formverfahren, wärmebehandlungssystem und formprodukt
PCT/JP2022/015940 WO2022210868A1 (ja) 2021-03-30 2022-03-30 成型方法、熱処理システムおよび成形品

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Publication number Priority date Publication date Assignee Title
JP2018012113A (ja) 2016-07-19 2018-01-25 東亜工業株式会社 熱間プレス装置、熱間プレス方法及び自動車車体部品の製造方法

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DE10208216C1 (de) * 2002-02-26 2003-03-27 Benteler Automobiltechnik Gmbh Verfahren zur Herstellung eines metallischen Bauteils
DE102010010156A1 (de) * 2010-03-04 2011-09-08 Kirchhoff Automotive Deutschland Gmbh Verfahren zur Herstellung eines Formteiles mit mindestens zwei Gefügebereichen unterschiedlicher Duktilität
KR101277874B1 (ko) * 2011-03-31 2013-06-21 주식회사 포스코 이종 강도 영역을 갖는 열간 성형품 및 그 제조방법
US9951395B2 (en) * 2012-03-13 2018-04-24 Asteer Co., Ltd. Method for strengthening steel plate member
EP2905346B1 (de) * 2014-01-23 2020-09-02 Schwartz GmbH Wärmebehandlungsverfahren
JP2019013936A (ja) * 2017-07-04 2019-01-31 東亜工業株式会社 プレス成形品の製造方法

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JP2018012113A (ja) 2016-07-19 2018-01-25 東亜工業株式会社 熱間プレス装置、熱間プレス方法及び自動車車体部品の製造方法

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EP4321631A3 (de) 2024-02-28
EP4316684A1 (de) 2024-02-07
US20240167115A1 (en) 2024-05-23
JP7052116B1 (ja) 2022-04-11
JP2022154099A (ja) 2022-10-13
US20240043957A1 (en) 2024-02-08

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