US20180216219A1 - Method for Manufacturing Hot-Pressed Member - Google Patents

Method for Manufacturing Hot-Pressed Member Download PDF

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Publication number
US20180216219A1
US20180216219A1 US15/747,880 US201615747880A US2018216219A1 US 20180216219 A1 US20180216219 A1 US 20180216219A1 US 201615747880 A US201615747880 A US 201615747880A US 2018216219 A1 US2018216219 A1 US 2018216219A1
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steel sheet
zinc
hot
coated steel
coating layer
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English (en)
Inventor
Seiji Nakajima
Satoru Ando
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JFE Steel Corp
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JFE Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-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
    • 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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • 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
    • B21D22/208—Deep-drawing by heating the blank or deep-drawing associated with heat treatment
    • 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
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F17/00—Multi-step processes for surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by subclass C21D or C22F or class C25
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C25D5/50—After-treatment of electroplated surfaces by heat-treatment
    • 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
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

  • the present disclosure relates to a method for manufacturing a hot-pressed member which can preferably be used for, for example, chassis and body structure members of an automobile.
  • chassis and body structure members of an automobile have usually been manufactured by performing press working on steel sheets having a specified strength.
  • efforts are being made to reduce the thickness of a steel sheet which is used for an automobile body by increasing the strength of the steel sheet.
  • an increase in the strength of steel sheets causes a deterioration in press workability, and therefore there is an increase in the number of cases where it is difficult to form a steel sheet into desired shapes of the members.
  • Patent Literature 1 proposes a working technique called hot pressing which makes it possible to realize an improvement in workability and an increase in strength at the same time by performing working and rapid cooling at the same time on a heated steel sheet by using a mold which is composed of a die and a punch.
  • this hot pressing since a steel sheet is heated to a high temperature of about 950° C. before hot pressing is performed, scale (iron oxide) is generated on the surface of the steel sheet, and the flaking of the scale occurs when hot pressing is performed, which results in a problem in that a mold is damaged or the surface of a member is damaged after the hot pressing. Also, scale which remained on the surface of a member causes a deterioration in surface appearance and paint adhesiveness. Therefore, scale which is present on the surface of a member is usually removed by performing a treatment such as pickling or shot blasting. However, such a treatment makes a manufacturing process complex, and thus there is a decrease in productivity.
  • chassis and body structure members of an automobile are also required to have excellent corrosion resistance.
  • a hot-pressed member which is manufactured by using the process described above, is not provided with an anti-corrosion film such as a coating layer, the member is very poor in terms of corrosion resistance.
  • a hot-pressing technique is desired with which the generation of scale can be inhibited when heating is performed before hot pressing and with which the corrosion resistance of a hot-pressed member can be improved, and thus a steel sheet to be hot-pressed whose surface is coated with a film such as a coating layer and a method for hot pressing which utilizes the steel sheet have been proposed.
  • Patent Literature 2 discloses a method for manufacturing a hot-pressed member excellent in terms of corrosion resistance whose surface is coated with a Zn—Fe-based compound or a Zn—Fe—Al-based compound by performing hot pressing on a steel sheet, which is coated with Zn or a Zn-based alloy.
  • Patent Literature 3 discloses a hot-pressed member excellent in terms of scale resistance, paint adhesiveness, after-painting corrosion resistance, and hydrogen entry resistance which is manufactured by forming a Ni diffusion region, a layer of an intermetallic compound, which is equivalent to the ⁇ phase of a Zn—Ni alloy, and a ZnO layer in the surface layer of a steel sheet.
  • Patent Literature 4 discloses a steel sheet to be hot-pressed which is manufactured by forming a ZnO layer, which inhibits the vaporization of Zn, in the surface layer of a Zn-based coating layer in advance, and indicates that it is possible to obtain a hot-pressed product having good surface appearance, excellent paint adhesiveness, and excellent after-painting corrosion resistance by using the steel sheet.
  • a hot-pressed member which is manufactured by using the method described in Patent Literature 2
  • a zinc-coated steel sheet or a zinc-aluminum-coated steel sheet, whose coating layer has a low melting point is used, the melting of the coating layer or the vaporization of zinc which occurs in a heating process before hot pressing is significant.
  • a hot-pressed member, which is finally obtained has, for example, a spotty inhomogeneous surface appearance or many white or black point-like defects. Therefore, it is difficult to obtain a hot-pressed member having a homogeneous and good surface appearance.
  • Patent Literature 3 which is manufactured by using a steel sheet coated with a Zn—Ni-alloy coating layer, which has a melting point higher than that of Zn
  • a hot-pressed member described in Patent Literature 3 which is manufactured by using a steel sheet coated with a Zn—Ni-alloy coating layer, which has a melting point higher than that of Zn
  • Patent Literature 4 In the case where a steel sheet to be hot-pressed described in Patent Literature 4 is used, there is an improvement in the surface appearance of a hot-pressed member to some extent through the effect of a ZnO layer which is formed in the surface layer of the steel sheet. However, there is still a problem in that local point-like defects are generated in a portion in which the result of a treatment for forming a ZnO layer is inhomogeneous.
  • the present disclosure has been completed in order to solve the problems of the conventional techniques described above, and an object of the present disclosure is to provide a method for manufacturing a hot-pressed member excellent in terms of surface appearance with which it is possible to stably manufacture a hot-pressed member having a homogeneous and good surface appearance without causing a significant increase in cost.
  • the present inventors in order to solve the problems described above, diligently conducted investigations regarding a method for manufacturing a hot-pressed member excellent in terms of surface appearance. First, investigations regarding a state in which point-like defects are generated on the surface of a hot-pressed member were conducted. As a result, it was found that the position or number of point-like defects is not necessarily the same even if the same kind of zinc-based coated steel sheet is heated under the same condition.
  • a method for manufacturing a hot-pressed member having an excellent surface appearance including heating a zinc-based coated steel sheet to a temperature range from the Ac3 transformation temperature to 1000° C., performing hot pressing work, and performing cooling, in which a surface-cleaning treatment is performed on the zinc-based coated steel sheet before the heating is performed.
  • a method for manufacturing a hot-pressed member having an excellent surface appearance including performing cold pressing work on a zinc-based coated steel sheet, heating the zinc-based coated steel sheet to a temperature range from the Ac3 transformation temperature to 1000° C., and cooling the heated steel sheet, in which a surface-cleaning treatment is performed on the zinc-based coated steel sheet before the heating is performed.
  • % used when describing the chemical composition of steel or a coating layer always means mass %.
  • the hot-pressed member which is manufactured by using the present disclosure can preferably be used for the chassis and body structure members of an automobile.
  • FIG. 1 is a diagram illustrating typical examples of the surface appearance of a hot-pressed member, where (a) is a photograph indicating a product having a good surface appearance and (b) is a photograph indicating a product having point-like defects.
  • FIG. 2 is a diagram illustrating typical examples of the surface appearance of point-like defects, where (a) is an enlarged photograph of a white defect and (b) is an enlarged photograph of a black defect.
  • a zinc-based coated steel sheet having a zinc-based coating layer on one or both sides thereof is used.
  • a zinc-based coating layer include, but are not limited to, a galvanizing layer, a galvannealing layer, a hot-dip zinc-aluminum-alloy coating layer, a hot-dip zinc-aluminum-magnesium-alloy coating layer, a zinc electroplating layer, and a zinc-nickel-alloy electroplating layer, and all of the known zinc-based coating layers containing zinc may be used.
  • the coating weight on the surface of such a zinc-based coated steel sheet be 10 g/m 2 to 90 g/m 2 per side.
  • the coating weight per side (hereinafter, also simply referred to as “coating weight”) is 10 g/m 2 or more, the corrosion resistance does not become insufficient.
  • the coating weight is 90 g/m 2 or less, there is no increase in cost.
  • the coating weight be 20 g/m 2 to 80 g/m 2 .
  • the coating weight of the coating layer should be derived from the amount of decrease in mass at this time.
  • the zinc-based coated steel sheet described above be a Zn—Ni-alloy-coated steel sheet having a coating layer on one or both sides thereof, in which the coating layer having a chemical composition containing 10 mass % to 25 mass % of Ni and the balance being Zn and inevitable impurities.
  • the Ni content in the coating layer is 10 mass % to 25 mass %
  • the structure of the coating layer becomes a ⁇ phase structure, and since this ⁇ phase has a high melting point of 881° C., there is an increase in the effect of inhibiting the generation of point-like defects to a higher level.
  • a ⁇ phase has one of the crystal structures of Ni 2 Zn 11 , NiZn 3 , and Ni 5 Zn 21 , and it is possible to identify the structure by using an X-ray diffraction method.
  • an underlying coating layer such as a coating layer mainly containing, for example, Ni may be formed under the above-described coating layer.
  • a hot-rolled steel sheet or a cold-rolled steel sheet having a chemical composition containing, by mass %, C: 0.15% to 0.50%, Si: 0.05% to 2.00%, Mn: 0.5% to 3.0%, P: 0.10% or less, S: 0.05% or less, Al: 0.10% or less, N: 0.010% or less, and the balance being Fe and inevitable impurities may be used as a base steel sheet for a zinc-based coating layer.
  • a hot-rolled steel sheet or a cold-rolled steel sheet having such a chemical composition is used as a base steel sheet, it is possible to obtain a hot-pressed member having a desired high strength of, for example, 980 MPa or more.
  • C is a chemical element which increases the strength of steel, and it is necessary that the C content be 0.15% or more in order to control the tensile strength (hereinafter, also referred to as “TS”) of a hot-pressed member to be 980 MPa or more.
  • TS tensile strength
  • the C content be 0.15% to 0.50%.
  • Si is, like C, a chemical element which increases the strength of steel, and it is necessary that the Si content be 0.05% or more in order to control the TS of a hot-pressed member to be 980 MPa or more.
  • the Si content is more than 2.00%, there is a significant increase in the amount of a surface defect, which is called red scale, generated when hot rolling is performed, there is an increase in rolling load, and there is a deterioration in the ductility of a hot-rolled steel sheet.
  • the Si content is more than 2.00%, there may be a negative effect on coatability when a coating treatment is performed in order to form a coating film containing mainly Zn and Al on the surface of a steel sheet. Therefore, it is preferable that the Si content be 0.05% to 2.00%.
  • Mn is a chemical element which is effective for improving hardenability by inhibiting ferrite transformation and which is effective for decreasing a heating temperature before hot pressing is performed, because Mn decreases the Ac 3 transformation temperature. It is necessary that the Mn content be 0.5% or more in order to realize such effects. On the other hand, in the case where the Mn content is more than 3.0%, since Mn is segregated, there is a deterioration in the homogeneity of the properties of a steel sheet as a material and a hot-pressed member. Therefore, it is preferable that the Mn content be 0.5% to 3.0%.
  • the P content is more than 0.10%, since P is segregated, there is a deterioration in the homogeneity of the properties of a steel sheet as a material and a hot-pressed member, and there is a significant decrease in toughness. Therefore, it is preferable that the P content be 0.10% or less.
  • the S content is more than 0.05%, there is a decrease in the toughness of a hot-pressed member. Therefore, it is preferable that the S content be 0.05% or less.
  • the Al content is more than 0.10%, there is a deterioration in the blanking performance and hardenability of a steel sheet as a material. Therefore, it is preferable that the Al content be 0.10% or less.
  • the N content is more than 0.010%, since nitrides of AlN are formed when hot rolling is performed or when heating is performed before hot pressing work is performed, there is a deterioration in the blanking performance and hardenability of a steel sheet as a material Therefore, it is preferable that the N content be 0.010% or less.
  • At least one selected from Cr: 0.01% to 1.0%, Ti: 0.01% to 0.20%, and B: 0.0005% to 0.0800% and Sb: 0.003% to 0.030% be added separately or at the same time in addition to the chemical composition described above for the reasons described below.
  • Cr is a chemical element which is effective for increasing the strength of steel and improving hardenability of steel. It is preferable that the Cr content be 0.01% or more in order to realize such effects. On the other hand, in the case where the Cr content is more than 1.0%, there is a significant increase in cost. Therefore, it is preferable that the upper limit of the Cr content be 1.0%.
  • Ti is a chemical element which is effective for increasing the strength of steel and which is effective for increasing toughness by decreasing a crystal grain size.
  • Ti is a chemical element which is effective for realizing the effect of improving hardenability through the use of solid solution B by forming nitrides more readily than B, which will be described below. Therefore, it is preferable that the Ti content be 0.01% or more. However, in the case where the Ti content is more than 0.20%, there is a significant increase in rolling load when hot rolling is performed, and there is a decrease in the toughness of a hot-pressed member. Therefore, it is preferable that the upper limit of the Ti content be 0.20%.
  • B is a chemical element which is effective for improving hardenability when hot pressing is performed and for increasing toughness after the hot pressing. It is preferable that the B content be 0.0005% or more in order to realize such effects. On the other hand, in the case where the B content is more than 0.0800%, there is a significant increase in rolling load when hot rolling is performed, and, for example, cracking occurs in a steel sheet due to the formation of a martensite phase and a bainite phase after the hot rolling. Therefore, it is preferable that the upper limit of the B content be 0.0800%.
  • Sb is effective for inhibiting the formation of a decarburized layer in the surface layer of a steel sheet in a process in which a zinc-based coated steel sheet is subjected to heating followed by hot pressing work and cooling. It is necessary that the Sb content be 0.003% or more in order to realize such an effect. On the other hand, in the case where the Sb content is more than 0.030%, since there is an increase in rolling load, there is a decrease in productivity. Therefore, it is preferable that the Sb content be 0.003% to 0.030%.
  • a hot-pressed member is manufactured by using one of the processes in the two embodiments described below as a hot pressing process.
  • the two embodiments discussed herein are exemplary embodiments.
  • the first embodiment is a method for manufacturing a hot-pressed member and is a hot pressing process called direct process in which a zinc-based coated steel sheet is subjected to heating to a temperature range from the Ac3 transformation temperature to 1000° C. followed by hot pressing work and cooling.
  • the heating temperature is lower than the Ac3 transformation temperature, since there is an insufficient degree of quenching of a steel sheet, there may be a case where it is not possible to achieve the desired strength.
  • the heating temperature is higher than 1000° C., there is an economic disadvantage from the viewpoint of energy, and it is difficult to manufacture a hot-pressed member having a homogeneous and good surface appearance due to the significant generation of point-like defects.
  • cooling after hot pressing work may be performed by using a mold at the same time as hot pressing work, or the cooling may be performed by using a coolant such as water at the same time as hot pressing work or immediately after the hot pressing work.
  • the second embodiment is a method for manufacturing a hot-pressed member and is a hot pressing process called indirect process in which a zinc-based coated steel sheet is subjected to cold pressing work followed by heating to a temperature range from the Ac3 transformation temperature to 1000° C. and cooling.
  • cold pressing work is first performed before a zinc-based coated steel sheet is heated.
  • the cold-pressed member is subjected to heating followed by cooling.
  • the heating temperature is set to be in a temperature range from the Ac3 transformation temperature to 1000° C. for the reasons described above.
  • Cooling may be performed by using a mold which is used for cooling a member or by using a coolant such as water.
  • work may be added by performing hot pressing.
  • heating temperature means the maximum end-point temperature of a steel sheet.
  • examples of a method for performing the heating described above include heating which utilizes, for example, an electric furnace or a gas furnace, direct-fired heating, electrical heating, high-frequency heating, and induction heating.
  • a surface-cleaning treatment is performed on a zinc-based coated steel sheet before the zinc-based coated steel sheet is heated in order to remove stains due to, for example, dirt, dust, and fingerprint which are adhered to the surface of a coating layer.
  • This surface-cleaning treatment is an important requirement in the present disclosure.
  • point-like defects are generated as illustrated in FIG. 1( b ) .
  • a surface-cleaning treatment it is possible to manufacture a product having a good surface appearance as illustrated in FIG. 1( a ) .
  • examples of point-like defects include a white defect illustrated in FIG.
  • a surface-cleaning treatment is a treatment which removes the origins of point-like defects.
  • a surface-cleaning treatment may be performed on a steel sheet in the form of a coiled steel sheet or in the form of a cut steel sheet or a steel sheet blank, which has been cut out of the coiled steel sheet, or on a cold-pressed member after cold pressing work.
  • a surface-cleaning treatment be performed on a steel sheet in the form of a steel sheet blank, because this facilitates the treatment with a high level of surface-cleaning effect.
  • a method for performing a surface-cleaning treatment includes one in which the surface of a steel sheet is wiped with waste cloth, one in which the surface of a steel sheet is brushed by using, for example, a nylon brush, one in which the surface of a steel sheet is brushed after a liquid such as a wash oil, which has no negative effect on a steel sheet, has been applied to the surface, and one in which alkaline degreasing or solvent degreasing is performed.
  • a method in which a liquid is in contact with the surface of a steel sheet such as a combined method of wash-oil application and brushing, an alkaline degreasing method, or a solvent degreasing method has a higher cleaning effect than a physical method such as one in which wiping with waste cloth or brushing is performed, it is preferable that a method in which a liquid be in contact with the surface of a steel sheet be performed to clean the surface of a steel sheet completely.
  • alkaline degreasing is performed as a surface-cleaning treatment by using an alkaline degreasing liquid having a pH of 12.5 or more
  • the pH of the alkaline degreasing liquid is set to be less than 12.5.
  • the process of a surface-cleaning treatment have a low cost.
  • apparatuses for cold pressing work has an apparatus for performing the combination of wash-oil application and brushing, such equipment can preferably be used for hot pressing work, because it is possible to perform a treatment at low cost with a high cleaning effect by using such equipment.
  • This cold-rolled steel sheet was coated with one of a galvanizing layer, a hot-dip Zn—Al-alloy coating layer (Al content: 55 mass %), a galvannealing layer (Fe content: 10 mass %), a Zn electroplating layer, and a Zn—Ni-alloy electroplating layer (Ni content: 12 mass %) and cut into a sample having a size of 200 mm ⁇ 300 mm.
  • a surface-cleaning treatment was performed by using one of A: a wiping method with waste cloth, B: a brushing method, C: a combined method of wash-oil application and brushing, D: an alkaline degreasing method (pH: 12.0), and E: a solvent degreasing method.
  • a surface-cleaning treatment was performed by using one of A: a wiping method with waste cloth, B: a brushing method, C: a combined method of wash-oil application and brushing, D: an alkaline degreasing method (pH: 12.0), and E: a solvent degreasing method.
  • F strong alkaline degreasing (pH: 13.0) and samples which had not been subjected to a surface-cleaning treatment were also prepared.
  • Wiping with waste cloth was performed by using waste cloth (Cleaning White Stockinet Waste (Cotton) produced by Nihon Waste Co., Ltd.) and by wiping the surface of a sample twice with a reciprocating movement of a hand.
  • Brushing was performed by using a nylon-fiber plant brush (SK-type Straight Brush produced by Showa Kogyo Co., Ltd.) and by brushing the surface of a sample twice with a reciprocating movement of a hand.
  • SK-type Straight Brush produced by Showa Kogyo Co., Ltd.
  • wash-oil application and brushing were performed by performing brushing as described above after having applied a wash rust-prevention oil (PRETON R352L produced by Sugimura Chemical Industrial Co., Ltd.) to the surface of a sample so that the amount of oil applied was 2.0 g/m 2 .
  • a wash rust-prevention oil PRETON R352L produced by Sugimura Chemical Industrial Co., Ltd.
  • Alkaline degreasing was performed by spraying a sample with an alkaline degreasing liquid (CL-N364S, 20 g/L, 60° C., produced by Nihon Parkerizing Co., LTD.) for 10 seconds, and thereafter performing water washing followed by drying.
  • an alkaline degreasing liquid (CL-N364S, 20 g/L, 60° C., produced by Nihon Parkerizing Co., LTD.) for 10 seconds, and thereafter performing water washing followed by drying.
  • the pH of the alkaline degreasing liquid was 12.0.
  • Solvent degreasing was performed by immersing a sample in a combined solvent of toluene and ethanol having a mixture ratio of 1:1, and thereafter performing ultrasonic cleaning for one minute and drying.
  • Strong alkaline degreasing which was performed as a comparative example, was performed by immersing a sample in a strong alkaline degreasing liquid (NaOH aqueous solution, pH: controlled to be 13.0, 50° C.) for seconds, and thereafter performing water washing followed by drying.
  • a strong alkaline degreasing liquid NaOH aqueous solution, pH: controlled to be 13.0, 50° C.
  • the sample was heated in an electric furnace at a temperature of 950° C. so that duration of the sample in the electric furnace was 8 minutes, the sample was taken out of the furnace immediately after completion of heating, and then held in a flat, mold made of Al in order to perform a rapid cooling treatment (cooling rate: 50° C./s).
  • Ten samples were each prepared under the same condition in order to increase the judgment accuracy of surface appearance. After having performed a visual test regarding the state of point-like defects of the samples, surface appearance was judged on the basis of the judgment criteria below, and the case of ⁇ or ⁇ was judged as satisfactory.
  • the effect of the present disclosure was evaluated on the basis of the evaluation of the surface appearance after having heated and cooled a flat sheet as described above without performing practical press forming which utilized a direct process or an indirect process
  • the results of the present evaluation are the same as those of the evaluation of the surface appearance after having performed practical press forming which utilizes the above-mentioned two processes, because the surface appearance after having performed heating and cooling depends on whether or not stain components exist on the surface of the sample and on the effect of removing the stain components.

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  • Metallurgy (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Electrochemistry (AREA)
  • Coating With Molten Metal (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Heat Treatment Of Articles (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Chemically Coating (AREA)
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CN114525389A (zh) * 2022-02-16 2022-05-24 南京钢铁股份有限公司 一种镍系钢板表面质量的控制方法

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WO2017017905A1 (fr) 2017-02-02
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EP3330016B1 (fr) 2023-09-06
CN107921509A (zh) 2018-04-17
KR102050175B1 (ko) 2019-11-28
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JP6409878B2 (ja) 2018-10-24
JPWO2017017905A1 (ja) 2017-07-27

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