Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • 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
  • C22C38/06—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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • 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
  • 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
  • C23C2/04—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
  • C23C2/12—Aluminium 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
  • C23C2/26—After-treatment
  • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
• • 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
  • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C18/00—Alloys based on zinc
  • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent

Definitions

• the present invention relates to hot stamped bodies. This application claims priority based on Japanese Patent Application No. 2021-022063 filed in Japan on February 15, 2021, the content of which is incorporated herein.
• the members used for impact absorption and deformation control of the skeleton are required to be resistant to breakage due to deformation during a collision.
• vehicle body parts are required to have excellent bendability.
• the anisotropy of bendability is required to be small so that the occurrence of fracture can be suppressed even when deformed in various deformation modes at the time of collision.
• the bendability of the material is correlated with the tensile strength, and lowering the tensile strength improves the bendability. It is known that the main phase of the microstructure of hot stamped materials is martensite, and the tensile strength of martensite is greatly affected by C among the steel components.
• Patent Document 1 describes a carbide having an area ratio of martensite in the entire structure of 95% or more, a solid solution C of the martensite of 0.05% by mass or less, and a major axis of 200 nm or more. has a density of 50 pieces/ ⁇ m 3 or less and a tensile strength of 1270 MPa or more.
• Patent Document 2 discloses a non-heat treated high-strength steel plate having a yield strength of 885 MPa or more, characterized in that the microstructure is a mixed structure of martensite and lower bainite, and the total area ratio of both structures is 95% or more. disclosed.
• Patent Document 3 70% by volume or more of the metal structure is martensite phase or tempered martensite phase, and 50% by volume or more of the martensite phase or tempered martensite phase is generated from the non-recrystallized austenite phase.
• a high-strength steel with excellent delayed fracture resistance is disclosed which is characterized by a martensite phase or a tempered martensite phase.
• an object of the present invention is to provide a hot-stamped article that has high strength and excellent bendability, and that has low bendability anisotropy.
• a hot stamped article according to one aspect of the present invention has a chemical composition, in mass %, C: 0.050 to 0.150%, Si: 0.010 to 1.000%, Mn: 1.00-2.00%, Al: 0.001 to 0.500%, P: 0.100% or less, S: 0.0100% or less, N: 0.0100% or less, B: 0.0005 to 0.0050%, Cr: 0 to 0.50%, Mo: 0-0.500%, Ni: 0 to 3.00%, Cu: 0 to 3.00%, Co: 0-0.50%, Sn: 0 to 0.500%, Ca: 0 to 0.0050%, Mg: 0-0.0050%, Of the group containing REM: 0 to 0.0050% and Sb: 0 to 0.0200% and consisting of Ti: 0.005 to 0.100% and Zr: 0.005 to 0.100% containing one or two Nb: 0.015 to 0.
• the hot stamped body according to any one of [1] to [3] above has an average grain size of 20 to 500 nm in the metal structure, and is a group consisting of Nb, Ti, Zr and V. The number density of carbides containing one or more of these may be 0.3 to 10.0 pieces/ ⁇ m 2 .
• the hot-stamped article according to any one of [1] to [4] above may have a plating layer on its surface.
• the hot-stamped molded article according to the present embodiment will be described in detail below. First, reasons for limiting the chemical composition of the hot stamped body according to the present embodiment will be described.
• the hot stamped body according to the present embodiment has a chemical composition in mass % of C: 0.050 to 0.150%, Si: 0.010 to 1.000%, Mn: 1.00 to 2.00. %, Al: 0.001 to 0.500%, P: 0.100% or less, S: 0.0100% or less, N: 0.0100% or less, B: 0.0005 to 0.0050%, Cr: 0-0.50%, Mo: 0-0.500%, Ni: 0-3.00%, Cu: 0-3.00%, Co: 0-0.50%, Sn: 0-0.500 %, Ca: 0 to 0.0050%, Mg: 0 to 0.0050%, REM: 0 to 0.0050%, and Sb: 0 to 0.0200%, and Ti: 0.005 to 0 .100%, and Zr: 0.005-0.100% containing one or two of the group consisting of Nb: 0.015-0.100% and V: 0.005-0.100% containing one or two of the group consisting of
• C 0.050-0.150%
• C is an element that greatly affects the strength of the hot-stamped product. If the C content is less than 0.050%, the strength of the hot stamped product will be low. Therefore, the C content is made 0.050% or more. Preferably, it is 0.070% or more, 0.080% or more, or 0.090% or more. On the other hand, when the C content exceeds 0.150%, the strength of the hot-stamped product becomes too high, and bendability deteriorates. Therefore, the C content should be 0.150% or less. Preferably, it is 0.140% or less, 0.130% or less, 0.120% or less, 0.110% or less, or 0.100% or less.
• Si 0.010-1.000%
• Si has temper softening resistance, and has the effect of suppressing strength reduction due to auto-tempering during hot stamping quenching. If the Si content is less than 0.010%, the above effects may not be obtained and the desired strength may not be obtained, and the bendability may deteriorate. Therefore, the Si content is set to 0.010% or more. Preferably, it is 0.020% or more and 0.030% or more.
• the Si content exceeds 1.000%, the problem of surface scale arises. That is, after pickling the scale generated during hot rolling, patterns due to the surface unevenness are generated, and the surface appearance is inferior. Moreover, when the steel plate surface is plated, the plateability deteriorates. Therefore, the Si content is set to 1.000% or less. Preferably, it is 0.700% or less, 0.500% or less, or 0.300% or less.
• Mn 1.00-2.00%
• Mn is an element that improves the strength of hot stamped compacts and the hardenability of steel. If the Mn content is less than 1.00%, sufficient strength cannot be obtained in the hot-stamped product. Therefore, the Mn content is set to 1.00% or more. Preferably, it is 1.20% or more and 1.40% or more. On the other hand, even if the content of Mn exceeds 2.00%, the above effect is saturated and bendability is lowered. Therefore, the Mn content is set to 2.00% or less. Preferably, it is 1.80% or less and 1.60% or less.
• Al 0.001-0.500%
• Al is an element used as a deoxidizer for molten steel. Insufficient deoxidation reduces the bendability of the hot-stamped body due to excessive oxide formation.
• the Al content is set to 0.001% or more. Preferably, it is 0.010% or more and 0.030% or more.
• the Al content is set to 0.500% or less. Preferably, it is 0.300% or less, 0.200% or less, or 0.100% or less.
• P 0.100% or less
• P is an element that segregates at the grain boundary and reduces the strength of the grain boundary. If the P content exceeds 0.100%, the strength of the grain boundary is remarkably lowered, and the toughness and bendability of the hot-stamped product are lowered. Therefore, the P content is set to 0.100% or less. Preferably, it is 0.080% or less and 0.050% or less. Although the lower limit of the P content is not particularly specified, excessively reducing the P content increases the refining cost, so the P content may be 0.001% or more.
• the S content should be 0.0100% or less. Preferably, it is 0.0080% or less and 0.0050% or less. Although the lower limit of the S content is not particularly specified, the S content may be 0.0001% or more because excessively reducing the S content increases the manufacturing cost of the desulfurization step.
• N 0.0100% or less
• N is an impurity element, and forms nitrides in the steel that act as starting points for bending cracks, thereby deteriorating the bendability of the hot-stamped product. If the N content exceeds 0.0100%, coarse nitrides are formed in the steel and the bendability of the hot-stamped product is remarkably lowered. Therefore, the N content is set to 0.0100% or less.
• the N content is preferably 0.0080% or less and 0.0060% or less.
• the lower limit of the N content is not particularly limited, but if it is reduced to less than 0.0001%, the N removal cost will increase significantly, which is economically unfavorable. In actual operation, the N content may be 0.0001% or more and 0.0005% or more.
• B 0.0005 to 0.0050% B has the effect of improving the hardenability during hot stamping or during cooling after hot stamping, thereby improving the strength of the hot stamped product. If the B content is less than 0.0005%, the above effect cannot be obtained. Therefore, the B content is made 0.0005% or more. Preferably, it is 0.0007% or more and 0.0010% or more. On the other hand, when the B content exceeds 0.0050%, cracks may occur during hot rolling, the above effects may saturate, and the boride may reduce the bendability. Therefore, the B content is set to 0.0050% or less. Preferably, it is 0.0030% or less.
• Ti and Zr form carbonitrides in the steel, It has the effect of improving the strength of the hot-stamped product. Further, N is fixed as a nitride to suppress the formation of BN, and the effect of improving the hardenability of B is exhibited. In order to obtain these effects, one or more of Ti: 0.005% or more and Zr: 0.005% or more are contained. It is not necessary to contain both Ti and Zr, and any one of them may be contained in the above content. As long as at least one of Ti and Zr is included in the above content, elements other than that one may or may not be included in less than the above content.
• the content of the above elements is preferably one or more of Ti: 0.010% or more and Zr: 0.010% or more.
• the contents of Ti and Zr are each set to 0.100% or less.
• each is 0.080% or less.
• Nb 0.015 to 0.100% and V: 0.005 to 0.100% Nb and V form carbonitrides in steel, It has the effect of improving the strength of the hot-stamped product. Furthermore, as a solid-solution element, it has the effect of improving the strength and bendability of the hot-stamped product by refining the structure.
• one or more of Nb: 0.015% or more and V: 0.005% or more are contained. It is not necessary to contain both Nb and V, and any one of them may be contained in the above content. As long as at least one of Nb and V is included in the above content, elements other than the one may or may not be contained in less than the above content.
• the content of the above elements is preferably at least one of Nb: 0.020% or more and V: 0.010% or more.
• Nb 0.020% or more
• V 0.010% or more.
• the contents of Nb and V are each set to 0.100% or less.
• each is 0.080% or less.
• the left side of formula (1) is a formula for calculating the Ms point (°C). If the left side of formula (1) is 440° C. or less, the Ms point becomes low, and even if hot stamping is performed under favorable conditions, a desired amount of soft region cannot be obtained. Therefore, the left side (Ms point) of Equation (1) is set to over 440°C.
• the left side of formula (1) is preferably 450° C. or higher, more preferably 460° C. or higher. Although the upper limit of the left side of the formula (1) is not particularly defined, it may be 600° C. or less, 550° C. or less, or 500° C. or less.
• the left side of the formula (2) is a formula for calculating the nitrogen amount (mass %) fixed to the nitride containing Ti and Zr. If the left side of the formula (2) is equal to or less than the N content, BN is produced and the hardenability-enhancing effect of B cannot be sufficiently obtained. Therefore, the left side of the formula (2) is set to exceed the N content. Although the upper limit of the left side of the formula (2) is not specified, it may be 0.150% or less.
• the rest of the chemical composition of the hot stamped compact according to this embodiment may be Fe and impurities.
• impurities include elements that are inevitably mixed from steel raw materials or scraps and/or during the steelmaking process and that are permissible within a range that does not impair the properties of the hot stamped body according to the present embodiment.
• the hot-stamped compact according to the present embodiment may contain the following elements as arbitrary elements instead of part of Fe.
• the content is 0% when the following optional elements are not contained.
• Cr 0.005-0.50%
• Mo 0.005-0.500%
• Ni 0.005-3.00%
• Cu 0.005-3.00%
• Cr, Mo, Ni and Cu are elements that improve the hardenability of steel, and have the effect of improving the strength of hot stamped bodies. Therefore, one or more of these elements may be contained as necessary. In order to ensure this effect, the content of at least one of Cr, Mo, Ni and Cu is preferably 0.005% or more.
• the Cr content exceeds 0.50%, the Mo content exceeds 0.500%, or the Ni or Cu content exceeds 3.00%, cold rolling after hot rolling
• the carbides present after or after annealing may be stabilized and retard the dissolution of the carbides during heating during hot stamping, resulting in a decrease in hardenability. Therefore, the Cr content is 0.50% or less, the Mo content is 0.500% or less, and the Ni and Cu contents are each 3.00% or less.
• Co 0.005-0.50%
• Co is an element that has the effect of raising the Ms point and improves the bendability of the hot stamped product. Therefore, Co may be contained as necessary. In order to ensure the above effect, the Co content is preferably 0.005% or more. On the other hand, if the Co content exceeds 0.50%, the hardenability of the steel deteriorates. Therefore, the Co content is set to 0.50% or less.
• Sn 0.005-0.500% Since Sn has the effect of improving the corrosion resistance of the hot-stamped product, it may be contained as necessary. In order to ensure this effect, the Sn content is preferably 0.005% or more, more preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, even if the Sn content exceeds 0.500%, the above effect is saturated, so the Sn content is made 0.500% or less. Preferably, it is 0.300% or less and 0.150% or less.
• Ca, Mg and REM have the effect of refining inclusions in steel and preventing cracks from occurring during hot stamping due to inclusions. Therefore, one or more of these elements may be contained as necessary. In order to ensure the above effect, it is preferable that the content of at least one of Ca, Mg and REM is 0.0005% or more. On the other hand, when the content of Ca, Mg or REM exceeds 0.0050%, the effect of refining inclusions in steel is saturated and the alloy cost increases. Therefore, the contents of Ca, Mg and REM should each be 0.0050% or less.
• REM refers to a total of 17 elements consisting of Sc, Y and lanthanides, and the content of REM refers to the total content of these elements.
• Sb 0.0005-0.0200%
• Sb may be contained as necessary in order to suppress decarburization during hot working.
• the Sb content is preferably 0.0005% or more.
• the Sb content is made 0.0200% or less.
• the chemical composition of the hot stamped body according to the present embodiment in order to improve the properties of the hot stamped body, among the arbitrary elements described above, one or more of the group consisting of Co, Sn and Sb are added. It is preferable to contain in the above-mentioned content.
• the chemical composition of the hot stamped body described above can be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Incidentally, C and S may be measured using the combustion-infrared absorption method, and N may be measured using the inert gas fusion-thermal conductivity method.
• the chemical composition may be analyzed after removing the plated layer on the surface by mechanical grinding.
• the metal structure of the hot-stamped product according to the present embodiment contains martensite at 90 area % or more, and the soft region accounts for 5 to 25 area % of the martensite.
• Martensite 90 Area % or More Martensite is a structure necessary for obtaining desired strength. If the martensite is less than 90 area %, the desired strength cannot be obtained. Therefore, martensite shall be 90 area% or more. It is preferably 93 area % or more, 95 area % or more, or 97 area % or more. Martensite may be 100 area %.
• ferrite, pearlite, upper bainite, lower bainite, and retained austenite may be included as residual structures other than martensite.
• the total of these residual structures is preferably 10 area % or less in view of the relationship with the area ratio of martensite.
• the total amount of residual tissue is preferably 7 area % or less, 5 area % or less, 3 area % or less, and may be 0 area %.
• Soft region 5 to 25 area % of martensite
• the soft region is a region of martensite that has a low dislocation density and relatively low strength.
• the soft region means a region having an average Grain Average Image Quality value (average GAIQ value) of 123,000 to 200,000.
• the soft region should be 5 area % or more. Preferably, it is 10 area % or more and 15 area % or more.
• the soft region in the martensite should be 25 area % or less. Preferably, it is 23 area % or less and 20 area % or less.
• the present inventors speculate as follows. Since the soft region in martensite is softer than the surrounding area, plastic deformation is likely to occur during bending deformation, but crack generation is thought to be suppressed due to the high fracture limit. Furthermore, it is considered that there is also an effect of suppressing crack growth in crack propagation. Therefore, it is inferred that the bendability is improved. Also, the anisotropy of bendability is usually affected by inclusions extending in the rolling direction. In the hot-stamped article according to the present embodiment, the soft regions are uniformly dispersed, so it is thought that the influence of inclusions is alleviated. As a result, it is thought that the anisotropy of bendability can be reduced.
• the area ratio of martensite is measured by the following method. A sample is cut from an arbitrary position 50 mm or more away from the end face of the hot stamped product (a position other than the end if it cannot be sampled from this position) so that the thickness cross section can be observed. Although the size of the sample depends on the measuring device, it should be a size that allows observation of about 10 mm in the rolling direction.
• the cross section of the above sample is etched with a repeller reagent. 10 visual fields were observed at a magnification of 500 times at the 1/4 position of the plate thickness of the cross section etched with the repeller reagent (1/8 depth of the plate thickness from the surface to 3/8 depth of the plate thickness from the surface). , to obtain optical micrographs.
• the obtained optical micrograph is subjected to image analysis using Adobe's "Photoshop CS5" image analysis software to determine the area ratio of martensite.
• the maximum brightness value L max and the minimum brightness value L min of the image are obtained from the image, and the portion having pixels with brightness from L max ⁇ 0.3 (L max ⁇ L min ) to L max is A white region, a portion having pixels from L min to L min +0.3 (L max ⁇ L min ) is defined as a black region, and the other portion is defined as a gray region, and the area ratio of martensite, which is a white region, is calculated. do.
• Image analysis is performed in the same manner as above for a total of 10 observation fields to measure the area ratio of martensite. An average value of the obtained area ratios is calculated, and this average value is regarded as the area ratio of martensite. Thereby, the area ratio of martensite is obtained.
• the area ratio of the residual structure is obtained by subtracting the area ratio of martensite from 100%.
• the area ratio of the soft region is measured by the following method.
• a sample is cut from a position 50 mm or more away from the end face of the hot stamped product (a position avoiding the end if it cannot be sampled from this position) so that the thickness cross section can be observed.
• a diamond powder with a particle size of 1 to 6 ⁇ m is dispersed in a diluted solution such as alcohol or pure water to make a mirror surface. to finish.
• the sample is polished for 8 minutes with colloidal silica containing no alkaline solution at room temperature to remove strain introduced into the surface layer of the sample.
• an EBSD apparatus composed of a thermal field emission scanning electron microscope (JSM-7001F manufactured by JEOL) and an EBSD detector (DVC5 type detector manufactured by TSL) is used.
• JSM-7001F thermal field emission scanning electron microscope
• DVC5 type detector manufactured by TSL
• the degree of vacuum in the EBSD apparatus is 9.6 ⁇ 10 ⁇ 5 Pa or less
• the acceleration voltage is 15 kV
• the irradiation current level is 13
• the electron beam irradiation level is 62.
• the average grain size is 20 to 500 nm, and the number density of carbides containing one or more of the group consisting of Nb, Ti, Zr and V is 0.3 to 5. It may be 0/ ⁇ m 2 .
• An average particle size of 20 to 500 nm and a number density of carbides containing one or more of the group consisting of Nb, Ti, Zr and V of 0.3 to 5.0 pieces/ ⁇ m 2 the bendability of the hot-stamped product can be further improved.
• the precipitated state of the carbides contributes to crack propagation during bending deformation. It is believed that the larger the carbide size and the lower the number density, the lower the bendability.
• the above carbide number density is measured by the following method.
• a sample is cut from an arbitrary position 50 mm or more away from the end face of the hot stamped product (a position other than the end if it cannot be sampled from this position) so that the thickness cross section can be observed.
• the base metal is dissolved by the constant potential electrolytic etching method to make the precipitate appear.
• the conditions of the constant potential electrolytic etching method are as follows: a mixed liquid of 10% by volume acetylacetone, 1% by volume tetramethylammonium chloride, and the balance methyl alcohol is used as the electrolytic solution, the set potential is ⁇ 200 mV, and the amount of coulombs is 10 c/cm 2 .
• the composition of precipitates can be measured by EDS (energy dispersive X-ray spectrometer).
• carbides containing one or more of the group consisting of Nb, Ti, Zr and V are selected, and the major axis and minor axis of each carbide are measured from observation photographs. The average value of the major axis and the minor axis is determined, and the average value is regarded as the average grain size of the carbide.
• the average particle size is 20 to 500 nm, and one or two selected from the group consisting of Nb, Ti, Zr and V. Obtain the number density of carbides containing the above. If one or more of the group consisting of Nb, Ti, Zr and V and C are detected by EDS analysis of the precipitate, the precipitate is removed from Nb, Ti, Zr and V. It is regarded as a carbide containing one or more of the group.
• the hot-stamped article according to the present embodiment may have a plating layer on its surface for the purpose of further improving corrosion resistance.
• the plating layer is, for example, an Al-based plating layer such as a hot-dip aluminum plating layer and an aluminum-zinc plating layer, a Zn-based plating layer such as a hot-dip galvanizing layer, an alloyed hot-dip galvanizing layer, an electro-galvanizing layer, and a zinc-nickel plating layer. can be considered.
• the plating layer may be arranged on either one surface of the hot stamped article or may be arranged on both surfaces.
• adhesion amount is not particularly limited, Al-based plating layer: 15 to 120 g/m 2 per side, hot dip galvanizing layer: 30 to 120 g/m 2 per side, alloyed hot dip galvanizing layer: 30 to 120 g/m per side 2.
• Electrogalvanizing layer and zinc-nickel plating layer preferably 5 to 100 g/m 2 per side.
• the Al-based plating layer in the present embodiment means a plating layer containing 50% by mass or more of Al.
• Elements other than Al include Si: 0.1 to 20% by mass, Fe: 0.1 to 10% by mass, Zn: 0.1 to 45% by mass, and the balance (Cu, Na, K, Co, Ni, Mg etc.): may be contained in an amount of less than 0.5% by mass.
• the Zn-based plating layer means a plating layer containing 50% by mass or more of Zn.
• Elements other than Zn include Si: 0.01 to 20% by mass, Fe: 0.1 to 10% by mass, Al: 0.01 to 45% by mass, and the remainder (Cu, Na, K, Co, Ni, Mg etc.): may be contained in an amount of less than 0.5% by mass.
• the component analysis of the plating layer is performed by the following method.
• a sample is cut from an arbitrary position 50 mm or more away from the end face of the hot stamped product (a position other than the end if it cannot be sampled from this position) so that the thickness cross section can be observed.
• the size of the sample depends on the measuring device, it should be a size that allows observation of about 10 mm in the rolling direction.
• the layer structure of the plate thickness cross section is observed with a scanning electron microscope (SEM). Specifically, the specimen is observed with an SEM at a magnification in which the steel sheet and the plating layer are included in the observation field of view. For example, by observing a backscattered electron composition image (COMPO image), it is possible to infer how many layers the cross-sectional structure is composed of.
• SEM scanning electron microscope
• the range of 50 ⁇ m in the sheet surface direction and the plating layer thickness + 30 ⁇ m in the sheet thickness direction is analyzed by mapping.
• the plated layer is an Al-based plated layer
• the average values of the Fe concentration and the Al concentration in the sheet surface direction are obtained.
• the relationship between the thickness position and the Al concentration and the relationship between the thickness position and the Fe concentration are obtained.
• the plate thickness position where the Al concentration and Fe concentration are the same as the Al concentration and Fe concentration of the steel sheet may be determined as the interface between the steel sheet and the Al-based plating layer.
• the Al concentration and Fe concentration of the steel sheet referred to here are those obtained by measurement by EPMA.
• the plating layer is a Zn-based plating layer
• the average values of the Fe concentration and the Zn concentration in the sheet surface direction are obtained.
• the relationship between the thickness position and the Zn concentration and the relationship between the thickness position and the Fe concentration are obtained.
• the plate thickness position where the Zn concentration and Fe concentration are the same as the Zn concentration and Fe concentration of the steel sheet may be determined as the interface between the steel sheet and the Zn-based plating layer.
• the Zn concentration and Fe concentration of the steel sheet referred to here are those obtained by measurement by EPMA.
• Thickness of the hot stamped body according to the present embodiment is not particularly specified, but it may be 0.5 to 3.5 mm from the viewpoint of reducing the weight of the vehicle body.
• the hot stamped product according to the present embodiment preferably has a tensile strength of 980 MPa or more in order to enhance the effect of reducing the weight of the vehicle body. On the other hand, if the tensile strength is too high, the bendability decreases, so the tensile strength is preferably 1380 MPa or less. Tensile strength is determined according to the test method described in JIS Z 2241:2011 by preparing a No. 5 test piece described in JIS Z 2241:2011.
• a hot-rolled steel sheet is obtained by hot rolling.
• a steel slab (steel material) to be subjected to hot rolling may be a steel slab manufactured by a conventional method, for example, a steel slab manufactured by a general method such as a continuous casting slab or a thin slab caster.
• a billet having the chemical composition described above is subjected to hot rolling.
• the heating temperature before hot rolling is set to 1200 ° C. or higher, and the coiling temperature is set to It is preferable that the temperature is set to 600° C. or lower, and the time from the completion of finish rolling to the start of winding is set to 5 seconds or longer.
• the heating temperature By setting the heating temperature to 1200° C. or higher, carbides containing one or more of the group consisting of Nb, Ti, V and Zr can be dissolved, and the carbides are finely precipitated during rolling. be able to.
• the upper limit of the heating temperature is not particularly defined, it may be 1400° C. or less from the viewpoint of productivity.
• the winding temperature By setting the winding temperature to 600°C or lower, it is possible to preferably control the number density and average particle diameter of carbides containing one or more of the group consisting of Nb, Ti, V and Zr. Although the lower limit of the winding temperature is not particularly specified, it may be 400° C. or higher from the viewpoint of productivity.
• the upper limit is not particularly defined, and may be set so that the winding can be performed at the above winding temperature in consideration of the sheet threading speed and the cooling speed.
• the obtained hot-rolled steel sheet is coiled open, pickled, and then cold-rolled.
• the cumulative rolling reduction during cold rolling may be within a range that does not hinder productivity, and may be, for example, 30 to 80%.
• a cold-rolled steel sheet is thus obtained.
• the obtained cold-rolled steel sheet may be annealed for softening. It is preferable to perform temper rolling after annealing.
• the rolling reduction in the temper rolling of the steel sheet may be 2% or less as long as it does not hinder the productivity.
• a tension leveler may be used for shape correction.
• Al-based plating such as aluminum plating and aluminum-zinc plating, or Zn-based plating may be applied to the cold-rolled steel sheet as necessary.
• the composition of the plating is mainly composed of aluminum and zinc, elements such as Ni may be added to improve corrosion resistance.
• the plating may contain an element such as iron as an impurity.
• Plating should be applied under normal plating conditions.
• a suitable Si concentration in the bath is 5 to 12% by mass, with the balance being aluminum and impurities of less than 0.5%.
• a suitable Zn concentration in the bath is 40-50% by weight, the balance being aluminum and impurities less than 0.5%.
• Mg and Zn are mixed in the aluminum plating, and Mg is mixed in the aluminum-zinc plating.
• the atmosphere during plating may be normal plating conditions, whether it is a continuous plating facility having a non-oxidizing furnace or a continuous plating facility having no non-oxidizing furnace.
• galvanizing methods such as hot-dip galvanizing, electro-galvanizing, and galvannealing may be employed.
• Metal pre-plating may be applied to the surface of the steel sheet before plating.
• metal pre-plating include Ni pre-plating, Fe pre-plating, and other metal pre-plating that improves plating properties.
• a steel sheet for hot stamping is obtained by the above method.
• the following hot stamping conditions are applied to the steel sheet for hot stamping obtained by the method described above to manufacture the hot stamped body according to the present embodiment.
• a steel plate for hot stamping is heated to a temperature range of Ac 3 transformation point to 1000 ° C., held in the temperature range for 0.1 to 30.0 minutes, and then quickly conveyed onto a mold for hot stamping. . After that, the steel plate is pressed and the steel plate is cooled in the mold by heat transfer between the steel plate and the mold.
• the steel sheet temperature may be varied or may be kept constant.
• the Ac 3 transformation point can be obtained by the following formula.
• the surface pressure of the mold during hot stamping By setting the surface pressure of the mold during hot stamping to the smaller value (P max (MPa)) of Pa (MPa) represented by the following formula (3) and 200 MPa, hot stamping The rate of subsequent cooling can be preferably controlled. As a result, a desired amount of soft region can be obtained.
• the lower limit of the surface pressure of the mold during hot stamping is not particularly limited, it may be 0.1 MPa or more. This is because when the surface pressure is small, the heat transfer between the mold and the steel sheet is insufficient, and the cooling rate required for martensite transformation cannot be obtained.
• the surface pressure of the die during hot stamping may be controlled by changing the press load in holding the bottom dead center.
• a numerical simulation of press forming may be used to determine the press load when holding the bottom dead center. If the shape of the part is simple and the load in the normal direction of the part surface can be calculated from the press load, the surface pressure may be obtained by dividing the load in the normal direction by the surface area of the part.
• Ms in the above formula (3) is the Ms point (martensitic transformation start temperature) represented by the left side of the above formula (1).
• the cooling rate after hot stamping can be preferably controlled. As a result, a desired amount of soft region can be obtained.
• the temperature at which the hot-stamped product is removed from the mold is preferably the temperature at which the martensite transformation is completed or lower. Therefore, the temperature at which the hot-stamped product is removed from the mold is preferably 250° C. or lower.
• the take-out temperature here means the surface temperature of the hot-stamped product when it is taken out from the mold.
• Ms in the above formulas (5) and (6) is the Ms point (martensite transformation start temperature) represented by the left side of the above formula (1). It is conceivable that the holding at the dead point may be for a short period of time.
• the hot-stamped article according to the present embodiment can be manufactured.
• the conditions in the examples are one example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one example of conditions. It is not limited. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.
• CR no coating layer
• GA hot-dip galvanizing layer (target coating weight of 60 g/m 2 on one side, coating on both sides)
• GA Galvannealed layer (target weight per side: 45 g/m 2 , double-sided plating)
• AL Al-based plating layer (target coating weight of 80 g/m 2 on one side, plating on both sides)
• EG electrogalvanized layer (target weight per side: 40 g/m 2 , double-sided plating)
• Hot stamping was performed under the conditions shown in Tables 2A to 2C. Hot stamping was carried out by sandwiching a flat steel plate between water-cooled dies and applying pressure so as to facilitate preparation of test pieces for tensile testing and metallographic observation. As a result, hot stamped bodies shown in Tables 3A to 3C were obtained. In addition, manufacturing No. 77 was tempered by heating at 300° C. for 20 minutes after hot stamping. Next, observation of the metallographic structure and measurement of tensile strength were carried out by the methods described above.
• the obtained tensile strength was 980 MPa or more, it was judged to have high strength and to be accepted. On the other hand, when the obtained tensile strength was less than 980 MPa, it was determined to be unsatisfactory because it did not have high strength. Moreover, when the obtained tensile strength was more than 1380 MPa, it was determined that the strength was too high and was rejected.
• the bendability of the hot stamped product was evaluated by the following method.
• the bending angle ⁇ (°) was obtained by converting the displacement at the maximum load obtained in the bending test into an angle based on the VDA standard.
• Test piece size 60 mm (rolling direction) x 30 mm (direction parallel to plate width direction)
• Test piece plate thickness 1.6 mm
• Bending ridge line parallel to rolling direction, 45° direction, perpendicular direction
• Test method roll support, punch pushing Roll diameter: ⁇ 30 mm
• Punch shape: tip R 0.4 mm
• Distance between rolls 2.0 x plate thickness (mm) + 0.5 mm
• tests are performed in five directions at intervals of 22.5 ° . may be asked for. If the rolling direction is unknown even by this method, tests are performed in 10 directions at intervals of 11.25 °, and the direction in which the minimum value of the bending angle ⁇ is obtained is regarded as the rolling direction. may be asked for.
• ⁇ m is affected by plate thickness and tensile strength. In addition, ⁇ m is also affected by the plating layer of the hot-stamped product.
• a hard Fe—Al alloy layer is formed on the surface by heating with hot stamping, so ⁇ m is higher than GA, GI, CR (shot blasted after hot stamping) or EG. becomes low.
• corrosion resistance was evaluated by the method specified in JASO M609-91 established by the Society of Automotive Engineers of Japan. Specifically, it was evaluated by the following method.
• a sample was taken from the hot-stamped product, and a 70 mm-long linear scratch was made with a cutter on the flat surface of the sample to which an electrodeposition coating film with a thickness of 15 ⁇ m was applied, and the sample was subjected to a cyclic corrosion test. After 120 cycles, the sample was taken out and immersed in a commercially available coating remover for 30 minutes, and then the coating was removed with a brush. After that, the sample was immersed in a 5% by volume ammonium citrate aqueous solution containing an inhibitor for steel plates, and rust formed on the corroded portion was removed with a brush.
• the center part in the longitudinal direction of the 70 mm flaw is a boundary, and the thickness reduction from the reference surface is measured every 35 mm in length from both ends of the flaw. got the maximum value.
• the reference surface was the surface of a portion that had not been corroded after the paint film had been peeled off, regardless of the presence or absence of plating. The average value of the maximum values of the two plate thickness reductions obtained was calculated.
• the average value of the obtained maximum thickness reduction values was evaluated according to the following criteria.
• the hot-stamped products had particularly excellent corrosion resistance when the evaluations were E1, E2, and V1.
• the evaluations were E1, E2, and V1.
• the hot stamped product had particularly excellent corrosion resistance.
• the hot-stamped product having an evaluation of G or higher was judged to have particularly excellent corrosion resistance.
• B, G, V2, V1, E2 and E1 indicate that corrosion resistance is superior in that order.
• E1 (Excellent-1): Less than 0.03 mm
• E2 (Excellent-2): 0.03 mm or more and less than 0.05 mm
• V1 (Very Good-1): 0.05 mm or more and less than 0.07 mm V2 (Very Good-2 ): 0.07 mm or more and less than 0.10 mm G (Good): 0.10 mm or more and less than 0.15 mm B (Bad): 0.15 mm or more
• Tables 3A to 3C The above results are shown in Tables 3A to 3C. From Tables 3A to 3C, it can be seen that hot-stamped bodies having high strength, excellent bendability, and small anisotropy in bendability were obtained in the examples of the present invention. On the other hand, it can be seen that one or more of the above characteristics did not satisfy the acceptance criteria in the comparative example.

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• 2022
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