Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/50—Treatment of iron or alloys based thereon

Definitions

• the present invention relates to a surface-treated steel sheet and a method for processing a surface-treated steel sheet.
• Hot stamping is known as one of the processing methods for steel sheets. Hot stamping is a processing method in which a steel sheet is heated to an austenite region of around 900 ° C., and molding and quenching are performed simultaneously in a mold.
• ultra-high-strength steel plates used in automobile cabins, etc.
• springback This occurs, and there is a problem that the dimensional accuracy tends to decrease.
• hot stamping steel that has been softened by heating to around 900 ° C. is placed in a die and pressed, and at the same time, the steel is cooled by contact with the die and quenched. Hot stamping has the features of excellent moldability and less springback.
• oxides formed by oxidizing Fe and the like in the steel may be generated on the surface of the processed steel sheet. From the viewpoint of increasing the productivity of the processed steel sheet, there is a demand for a method for processing the steel sheet so that this oxide is difficult to form.
• Patent Document 1 describes a stainless steel material in which the structure of a passivation film on the surface of stainless steel is Cr or a structure rich in Cr and Si, and an alkali silicate is adhered to the surface thereof. .. According to Patent Document 1, the stainless steel material is prevented from invading oxygen in the atmosphere and diffusing metal elements from the stainless steel substrate even when exposed to a high temperature such that the surface temperature reaches 650 ° C. or higher. Therefore, it is said that the generation of temper color due to the oxide produced by the reaction of these can be suppressed.
• Patent Document 2 describes a heat treatment steel sheet in which the amounts of C, Si, Mn, Cr and Ni are adjusted.
• the heat treatment steel sheet can be a medium to high carbon steel sheet having a C content of 0.3 to 1.2% by weight by setting the amount of Cr to 0.1 to 2% by weight.
• the peeling of the oxide scale during heat treatment can be prevented.
• Patent Document 1 even if stainless steel is exposed to a high temperature such that the surface temperature reaches 650 ° C. or higher, temper color due to Cr—Fe—O oxide can be suppressed.
• oxides are more likely to be generated than the test conditions of Patent Document 1 in which the steel sheet is heated only to around 700 ° C.
• hot stamping tends to produce thicker, grayer scales on the surface of the steel sheet. Therefore, processing of a steel sheet by hot stamping requires processing such as shot blasting to remove the scale, which may reduce productivity. Therefore, the steel sheet for hot stamping is required to further suppress the generation of oxides.
• Patent Document 2 in order to prevent the scale from peeling off in a process such as a press temper and causing an indentation defect, it is attempted to prevent the scale from peeling off. However, if the occurrence of scale is suppressed in the first place, the occurrence of indentation flaws can also be suppressed.
• the present invention has been made in view of this point, and an object of the present invention is to provide a surface-treated steel sheet in which scale is less likely to occur when a steel sheet is processed by hot stamping, and a method for processing the surface-treated steel sheet. And.
• the surface-treated steel sheet according to the embodiment of the present invention for solving the above problems is arranged in contact with a steel sheet having a Cr content of 0.2% by mass or more and 2.0% by mass or less and the surface of the steel sheet. It also has an alkaline silicate film.
• the method for processing the surface-treated steel sheet according to the embodiment of the present invention for solving the above-mentioned problems includes a step of heating the surface-treated steel sheet to a temperature range of Ac 3 points or more and 1100 ° C. or less of the steel sheet. It has a step of arranging a heated surface-treated steel sheet inside a die, hot-pressing it, and cooling the surface-treated steel sheet by the die.
• a surface-treated steel sheet in which scale is less likely to occur when the steel sheet is processed by hot stamping a method for processing the surface-treated steel sheet, and a processed surface treatment obtained by processing the surface-treated steel sheet.
• Steel sheets are provided.
• the present invention relates to a surface-treated steel sheet for hot stamping.
• the steel sheet may be any steel sheet having a Cr content of 0.2% by mass or more and 2.0% by mass or less.
• Examples of the steel sheet include nickel chrome steel sheet, chrome molybdenum steel sheet, nickel chrome molybdenum steel sheet (JIS G 4053: alloy steel for machine structure) and the like.
• the steel sheet may be a galvanized steel sheet, a Zn—Al alloy plated steel sheet, a Zn—Al—Mg alloy plated steel sheet, an aluminum plated steel sheet, or the like. Further, the steel sheet may be a cold-rolled steel sheet or a hot-rolled steel sheet.
• M is an alkali metal or an alkaline earth metal.
• X is M. When it is an alkali metal, it is 2, and when M is an alkaline earth metal, it is 1.
• n is, for example, an arbitrary number of 1 or more and 8 or less) and Si—Cr—M. -Forms an O-based reaction layer.
• the reaction layer is highly stable at high temperatures. Therefore, the reaction layer preferably suppresses the diffusion of atoms (particularly Fe) contained in the steel sheet from the steel sheet to the alkaline silicate film during hot stamping. As a result, the reaction layer suppresses the formation of oxides such as FeO, Fe 3 O 4 and Fe 2 O 3 due to the reaction of Fe diffused from the steel plate with oxygen (O 2 ) in the air during hot stamping. However, it is possible to suppress the generation of scale due to the deposition of these oxides.
• the Cr content in the steel sheet is 0.2% by mass or more, the reaction layer having a sufficient thickness is formed on the surface of the steel sheet, and the diffusion of Fe from the steel sheet can be sufficiently suppressed. Occurrence is also sufficiently suppressed.
• the Cr content in the steel sheet exceeds 2.0% by mass, the effect is saturated.
• the Cr content in the steel sheet is preferably 0.4% by mass or more and 1.7% by mass or less, and more preferably 0.6% by mass or more and 1.6% by mass or less.
• the steel sheet may contain elements other than Fe and Cr, such as C, Si, Mn, P, S, Mo, V, Ti, Bi and W.
• the content of these elements can be arbitrarily determined according to the characteristics required for the steel sheet and the like.
• the content of C can be 0.1% by mass or more and 1.2% by mass or less, preferably 0.2% by mass or more and 1.2% by mass or less, and 0.4% by mass or more. It is more preferably 1.0% by mass or less.
• the Si content can be 0.1% by mass or more and 2.5% by mass or less, and preferably 0.1% by mass or more and 1.5% by mass or less.
• the Mn content can be 0.4% by mass or more and 3.0% by mass or less, and preferably 0.4% by mass or more and 2.0% by mass or less.
• the thickness of the steel sheet may be such that it can be processed by hot stamping, for example, it may be about 0.5 mm or more and 4.0 mm or less.
• Alkaline silicate film is a film containing an alkali silicate that covers the surface of the steel plate.
• the alkali silicate film is formed in contact with the surface of the steel sheet.
• the alkali silicate film may be formed on only one surface of the steel sheet, or may be formed on both surfaces of the steel sheet.
• the alkali silicate film reacts with Cr contained in the steel sheet during hot stamping to form the Si—Cr—MO-based reaction layer described above.
• the alkaline silicate film suppresses the diffusion of Fe from the steel plate to the alkaline silicate film during hot stamping, and the diffused Fe reacts with oxygen (O 2 ) in the air. It is possible to suppress the formation of oxides and suppress the generation of scale due to the deposition of these oxides.
• the alkaline silicate film suppresses the invasion of oxygen (O 2 ) contained in the air into the steel sheet during hot stamping.
• oxygen O 2
• the alkali silicate film suppresses the formation of oxides such as FeO, Fe 3 O 4 and Fe 2 O 3 due to the reaction of oxygen that has entered the steel plate with Fe in the steel plate. It is also possible to suppress the generation of scale due to the deposition of these oxides.
• the alkaline silicate may be any compound represented by the general formula MXO ⁇ nSiO 2 .
• M is an alkali metal or an alkaline earth metal, and Li, Na, K or the like can be used as the alkali metal, and Mg, Ca or the like can be used as the alkaline earth metal.
• M is Li because it is possible to form an alkaline silicate film by firing even at a lower temperature, and since the melting temperature is higher, scale can be efficiently suppressed even during hot stamping at a higher temperature. Is more preferable.
• the alkali silicate may be a compound containing two different atoms of an alkali metal or an alkaline earth metal as M.
• X is 2 when M is an alkali metal and 1 when M is an alkaline earth metal.
• n is, for example, an arbitrary number of 3.5 or more and 7.5 or less.
• n is 3.5 or more, a sufficient amount of Si is present in the alkali silicate film, so that the above reaction layer having a sufficient thickness is formed on the surface of the steel sheet, and the scale due to the diffusion of Fe from the steel sheet is formed. Can be further suppressed. Further, when n is 3.5 or more, the amount of the alkaline component in the alkaline silicate film is not too large, so that the alkaline component remaining on the surface of the steel sheet after hot stamping is water in the air, carbon dioxide gas, or the like. It is also possible to further suppress the whitening phenomenon caused by the reaction product produced by the reaction of the above.
• n 7.5 or less
• a sufficient amount of alkaline component is present in the alkaline silicate film, so that the above reaction layer having a sufficient thickness is formed on the surface of the steel sheet, and Fe from the steel sheet is formed. It is possible to further suppress the generation of scale due to the diffusion of. Further, when n is 7.5 or less, a sufficient amount of alkaline component is present in the alkaline silicate film, so that the strength of the alkaline silicate can be further increased.
• the amount of the alkali silicate film adhered is preferably 0.05 g / m 2 or more and 1 g / m 2 or less in terms of Si.
• the amount of adhesion is 0.05 g / m 2 or more, the generation of scale can be sufficiently suppressed.
• the adhesion amount is 1 g / m 2 or more, the adhesion of the alkali silicate film to the steel sheet can be sufficiently enhanced.
• the alkaline silicate film can be formed by applying an aqueous solution containing the alkaline silicate on the surface of a steel sheet and firing it.
• the alkaline silicate film thus formed is a film mainly composed of a compound represented by the general formula MX O ⁇ nSiO 2 ⁇ yH 2 O.
• the amount of water retained in the alkaline silicate film is smaller (in the above general formula). Is smaller than y).
• the amount of the alkali silicate film adhering to the surface of the steel sheet can be adjusted.
• the surface of the steel sheet may be subjected to known pretreatment such as degreasing and pickling.
• Another embodiment of the present invention relates to a method for processing a surface-treated steel sheet, which heat-treats the above-mentioned surface-treated steel sheet.
• the heat treatment may be a high heat treatment of the surface-treated steel sheet, and may be any known heat treatment such as hot stamping, quenching, annealing (canning), and normalizing. This embodiment can be carried out in the same manner as the known heat treatment except that the surface-treated steel sheet is used as the steel sheet.
• the surface-treated steel sheet is heated to a temperature range in which the ferrite in the steel sheet transforms into austenite.
• the surface-treated steel sheet is heated to a temperature range of 800 ° C. or higher and 1100 ° C. or lower, preferably Ac 3 points or higher and 1100 ° C. or lower of the steel sheet.
• the temperature rising rate at this time may be adjusted in the range of 2 ° C./s or more.
• the heated surface-treated steel sheet is placed inside the mold and hot pressed. Then, at the same time as hot pressing, the surface-treated steel sheet is cooled by the die. Specifically, the surface-treated steel sheet may be cooled to the Mf point (martensite transformation end point) or less of the steel sheet. Further, the cooling rate at this time may be adjusted in the range of 5 ° C./s or more and 40 ° C./s or less.
• the surface-treated steel sheet processed in this way has a Si—Cr—MO reaction layer between the steel sheet and the alkali silicate film.
• the steel sheet preferably has an area ratio of martensite of 90% or more in its cross section.
• Each steel sheet was immersed in an alkaline aqueous solution at 40 ° C. having a pH of 14 with sodium orthosilicate for 30 seconds for alkaline degreasing.
• lithium silicate Li 2O ⁇ nSiO 2 : n is 3 to 8 manufactured by Nippon Kagaku Kogyo Co., Ltd. or water glass No. 3 manufactured by Kishida Chemical Co., Ltd.
• An aqueous solution obtained by diluting Na 2 O ⁇ nSiO 2 : n from 3 to 8) to a concentration of 5% was applied with bar coat # 3. After coating, it is heated to 180 ° C. in the air and fired to form an alkaline silicate film having an adhesion amount of 0.2 to 0.5 g / m 2 in terms of Si, and the surface-treated steel sheets 1 to surface are formed, respectively.
• a treated steel sheet 14 was obtained.
• a 50 mm ⁇ 50 mm test piece was cut out from each surface-treated steel sheet, and an atmospheric heating test was carried out in a heating furnace with an atmospheric temperature of 850 ° C or 900 ° C. The soaking time at this time was 10 minutes. After heating, the test piece was taken out from the furnace and allowed to cool at room temperature.
• a cross section of a sufficiently cooled test piece is observed by SEM and GDS (Glow Discharge Emission Spectroscopy), the thickness of the oxide film formed by the atmospheric heating test is measured, and each surface treatment is performed according to the following criteria.
• the steel plate was evaluated.
• ⁇ The thickness of the oxide film is 0.3 ⁇ m or less ⁇
• the thickness of the oxide film is larger than 0.3 ⁇ m and 1.0 ⁇ m or less ⁇
• the thickness of the oxide film is larger than 1.0 ⁇ m ⁇ ⁇
• the oxide film peels off Status
• Tables 2 and 3 show the surface-treated steel sheets used for the test, the types of alkaline silicates, the heating conditions in the atmospheric heating test, and the evaluation results.
• a surface-treated steel sheet 1, a surface-treated steel sheet 2, a surface-treated steel sheet 6, a surface-treated steel sheet 7, obtained by surface-treating a steel sheet having a Cr content of 0.4% by mass or more and 1.7% by mass or less. Even when the surface-treated steel sheet 12 and the surface-treated steel sheet 13 were subjected to atmospheric heating tests at 850 ° C. and 900 ° C., only an oxide film having a thickness of 0.3 ⁇ m or less was formed.
• the surface-treated steel sheet 5, the surface-treated steel sheet 9, and the surface-treated steel sheet 14 obtained by surface-treating a steel sheet having a Cr content of less than 0.2% by mass are heated to the atmosphere at 850 ° C or 900 ° C.
• an oxide film thicker than 1.0 ⁇ m was formed.
• the surface-treated steel sheet of the present invention is less likely to cause scale when processed by hot stamping. Therefore, it is possible to shorten or eliminate the process such as scale removal and to process the steel sheet by hot stamping more easily and inexpensively. Therefore, the surface-treated steel sheet of the present invention is expected to contribute to the further spread of processing of steel sheets by hot stamping.

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Citations (4)

• 2020
  • 2020-08-27 WO PCT/JP2020/032349 patent/WO2022044194A1/ja active Application Filing
  • 2020-08-27 CN CN202080104311.6A patent/CN116133768A/zh active Pending

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