WO2023182525A1 - Procédé de fabrication de tôle d'acier galvanisée haute résistance par immersion à chaud - Google Patents

Procédé de fabrication de tôle d'acier galvanisée haute résistance par immersion à chaud Download PDF

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WO2023182525A1
WO2023182525A1 PCT/JP2023/012038 JP2023012038W WO2023182525A1 WO 2023182525 A1 WO2023182525 A1 WO 2023182525A1 JP 2023012038 W JP2023012038 W JP 2023012038W WO 2023182525 A1 WO2023182525 A1 WO 2023182525A1
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steel sheet
hot
heating
strength
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PCT/JP2023/012038
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English (en)
Japanese (ja)
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俊佑 山本
友美 金澤
祥吾 田牧
克弥 星野
克利 ▲高▼島
央海 澤西
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Ｊｆｅスチール株式会社
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Priority to JP2023577502A priority Critical patent/JP7468819B2/ja
Publication of WO2023182525A1 publication Critical patent/WO2023182525A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • 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
    • C22C38/04—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
    • C22C38/60—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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • 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

Definitions

  • the present invention relates to a method for manufacturing a hot-dip galvanized steel sheet with excellent resistance weld cracking resistance and delayed fracture resistance.
  • Delayed fracture is when a high-strength steel material is subjected to static load stress (load stress less than tensile strength) and after a certain period of time, it suddenly occurs without any apparent plastic deformation. This is a phenomenon that causes brittle fracture.
  • This kind of delayed fracture is often caused by hydrogen that has entered the steel sheet due to corrosion caused by the usage environment, but hydrogen that has entered the steel sheet during the annealing process of a continuous galvanizing line (CGL) In particular, it deteriorates the mechanical properties of steel plates with a tensile strength exceeding 980 PMa, causing brittle fracture.
  • CGL continuous galvanizing line
  • Patent Document 1 oxidizes the surface of Si-added steel by heating it to 700°C or higher in an atmosphere containing O 2 to remove oxides on the surface layer of the steel sheet.
  • a method of reduction in an atmosphere containing H 2 having a dew point of 5° C. or higher is disclosed.
  • the amount of oxidation in the steel sheet is large, and oxides adhere to the inside of the furnace during reduction annealing, which poses a problem of impairing the appearance quality of the steel sheet.
  • Patent Document 2 the surface of Si-added steel is oxidized by heating to 600°C or higher and 850°C or lower in an atmosphere containing O 2 , and the oxides on the surface layer of the steel plate are oxidized to 500 volume ppm or higher with a dew point of 5°C or higher, 5000 °C or higher.
  • a method is disclosed for reducing an oxidized steel sheet in an atmosphere containing H 2 O and H 2 in a volume ppm or less.
  • Patent Document 3 the surface of Si-added steel is oxidized by increasing the air ratio of a direct-fired heating furnace (DFF), and the oxides on the surface layer of the steel sheet are reduced to log (P H2O /P H2 ) of -3.4 or more.
  • DFF direct-fired heating furnace
  • the present invention prevents deterioration of the appearance quality of the steel sheet due to adhesion of in-furnace oxides during reduction annealing, which occurs when the amount of oxidation of the steel sheet is excessive, and provides excellent LME cracking resistance and ductility. It is an object of the present invention to provide a method for manufacturing a high-strength galvanized steel sheet that can simultaneously suppress deterioration of delayed fracture resistance caused by hydrogen embrittlement.
  • the present inventors ensured the appearance quality of the steel sheet by optimizing the O 2 concentration and temperature during oxidation of the steel sheet according to the Si concentration and Mn concentration contained in the steel sheet and suppressing excessive oxidation, and further improved the appearance quality during reduction annealing.
  • optimizing the H 2 O concentration, H 2 concentration, and log (P H2O /P H2 ) it is possible to have excellent resistance weld cracking resistance and at the same time suppress the deterioration of delayed fracture resistance caused by hydrogen embrittlement. They discovered this and completed the present invention.
  • the present invention has been made based on the above findings. That is, the gist of the present invention is as follows. [1] A slab containing, in mass%, C: 0.05% or more and 0.30% or less, Si: 0.45% or more and 2.0% or less, and Mn: 1.0% or more and 4.0% or less. After hot rolling, the hot rolling process involves winding the coil into a coil at a temperature equal to or lower than the temperature T C (°C) calculated from the following formula (1) and pickling it; and the hot rolling process obtained in the hot rolling process.
  • T C °C
  • a method for producing a high-strength hot-dip galvanized steel sheet, which is subjected to continuous annealing and then hot-dip galvanizing In the direct-fired heating furnace, in the first stage, the steel plate is heated to 400° C. or more and 670° C.
  • the steel plate is heated to 600°C or more and 700°C or less in an atmosphere containing 500 volume ppm or less of O2 ,
  • the H 2 O concentration in the furnace atmosphere is 5000 volume ppm or more and 40000 volume ppm or less, and the H 2 concentration is 2 volume % or more and 20 volume % or less
  • the steel plate temperature was set at 650°C in an atmosphere where the ratio of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ), log (P H2O /P H2 ), was -1.1 or more and 0.5 or less.
  • a method for manufacturing a high-strength hot-dip galvanized steel sheet which is maintained at a temperature of 900° C. or less for 90 seconds or more.
  • T C -30([Si]+[Mn])+775...(1)
  • [Si] is the Si content (mass%) contained in the steel plate
  • [Mn] is the Mn content (mass%) contained in the steel sheet [2]
  • the atmosphere satisfies the ratio log (P H2O /P H2 ) of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ) from ⁇ 0.99 to 0.5 [ The method for producing a high-strength hot-dip galvanized steel sheet according to any one of [1] to [3].
  • the atmosphere is such that the ratio log (P H2O /P H2 ) of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ) is -0.9 or more and 0.5 or less [ The method for producing a high-strength hot-dip galvanized steel sheet according to any one of [1] to [4].
  • the atmosphere is such that the ratio log (P H2O /P H2 ) of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ) satisfies -0.7 or more and 0.5 or less [
  • the present invention it is possible to provide a high-strength steel plate that has excellent resistance weld cracking resistance in welded parts and good appearance quality, and has sufficiently reduced hydrogen in the steel, which is a factor in deterioration of delayed fracture resistance. be able to.
  • FIG. 1 is a structural diagram of a test material for evaluating LME cracking resistance.
  • the upper figure in Figure 2 is a plan view of the plate assembly with welded parts, and the lower figure shows a cross section in the plate thickness direction after cutting the plate assembly with welded parts at the cutting position shown in the upper figure. It is a drawing.
  • the unit of the content of each element in the composition of the Si-containing slab and the content of each element in the composition of the plating layer is "% by mass", and unless otherwise specified, "%" is simply used.
  • a numerical range expressed using “ ⁇ ” means a range that includes the numerical values written before and after " ⁇ ” as lower and upper limits.
  • the steel plate having "high strength” means that the tensile strength TS of the steel plate measured in accordance with JIS Z 2241 (2011) is 590 MPa or more.
  • Si 0.45% or more and 2.0% or less Si has a large effect of increasing the strength of steel through solid solution (solid solution strengthening ability) without significantly impairing workability, so it achieves high strength of steel sheets. It is an effective element for On the other hand, Si is also an element that has a negative effect on the resistance weld cracking resistance in the weld zone. When adding Si to increase the strength of a steel sheet, it is necessary to add 0.45% or more. Furthermore, if the Si content is less than 0.45%, no particular problem arises in resistance weld cracking resistance in the welded portion, and there is little need to apply the present invention.
  • Si is added in a range of 0.45% or more and 3.0% or less.
  • the amount of Si is preferably 0.7% or more, more preferably 0.9% or more. Further, the amount of Si is preferably 2.5% or less, more preferably 2.0% or less.
  • C 0.30% or less C improves the workability of a steel plate by forming martensite or the like as a steel structure.
  • the amount of C is preferably 0.8% or less, more preferably 0.30% or less.
  • the lower limit of C is not particularly limited, but in order to obtain good workability, it is preferable to contain C at 0.03% or more, and more preferably at 0.05% or more.
  • Mn 1.0% or more and 4.0% or less Mn has the effect of solid solution strengthening the steel to increase its strength, increasing hardenability, and promoting the formation of retained austenite, bainite, and martensite. It is an element. Such an effect is produced by containing 1.0% or more of Mn. On the other hand, if the Mn content is 4.0% or less, the above effects can be obtained without causing an increase in cost. Therefore, the amount of Mn is preferably 1.0% or more, and preferably 4.0% or less. It is more preferable that the Mn amount is 1.8% or more. Moreover, it is more preferable that the amount of Mn is 3.3% or less.
  • P 0.1% or less (not including 0%) By suppressing the P content, deterioration in weldability can be prevented. Furthermore, it is possible to prevent P from segregating at grain boundaries, thereby preventing deterioration of ductility, bendability, and toughness. Furthermore, when a large amount of P is added, the crystal grain size becomes large by promoting ferrite transformation. Therefore, the amount of P is preferably 0.1% or less.
  • the lower limit of P is not particularly limited, but is more than 0% due to production technology constraints, and is usually 0.001% or more.
  • the amount of S is preferably 0.03% or less, more preferably 0.02% or less.
  • the amount of S is preferably 0.03% or less, more preferably 0.02% or less.
  • Al 0.1% or less (not including 0%) Since Al is thermodynamically the easiest to oxidize, it oxidizes before Si and Mn, suppressing the oxidation of Si and Mn in the outermost layer of the steel sheet, and promoting the oxidation of Si and Mn inside the steel sheet. This effect is obtained when the amount of Al is 0.01% or more. On the other hand, if the amount of Al exceeds 0.1%, the cost will increase. Therefore, when added, the amount of Al is preferably 0.1% or less.
  • the lower limit of Al is not particularly limited and is more than 0%, usually 0.001% or more.
  • N 0.010% or less (not including 0%)
  • the content of N is preferably 0.010% or less.
  • N forms coarse nitrides with Ti, Nb, and V at high temperatures, thereby increasing the strength of steel sheets by adding Ti, Nb, and V. can be prevented from being damaged.
  • the content of N is preferably 0.005% or less, more preferably 0.003% or less, and still more preferably 0.002% or less.
  • the lower limit of the N content is not particularly limited, but is more than 0% due to production technology constraints, and is usually 0.0005% or more.
  • the component composition may further optionally be B: 0.005% or less, Ti: 0.2% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Nb: 0.20% or less, V: 0.5% or less, Sb: 0.200% or less, Ta: 0.1% or less, W: 0.5% or less, Zr: 0. 1% or less, Sn: 0.20% or less, Ca: 0.005% or less, Mg: 0.005% or less, and REM (Rare Earth Metal): 0.005% or less. It may contain more than one species.
  • B 0.005% or less B is an effective element for improving the hardenability of steel.
  • the amount of B is preferably 0.0003% or more, more preferably 0.0005% or more.
  • the amount of B is preferably 0.005% or less.
  • Ti 0.2% or less Ti is effective for precipitation strengthening of steel.
  • the lower limit of Ti is not particularly limited, but in order to obtain the effect of adjusting strength, it is preferably 0.005% or more. However, if Ti is added excessively, the hard phase becomes too large and the formability decreases, so when adding Ti, the amount of Ti is preferably 0.2% or less, and preferably 0.05% or less. is more preferable.
  • the amount of Cr is preferably 0.005% or more. By setting the Cr content to 0.005% or more, hardenability can be improved and the balance between strength and ductility can be improved.
  • the amount of Cr is preferably 1.0% or less from the viewpoint of preventing cost increases.
  • the amount of Cu is preferably 0.005% or more. By setting the Cu amount to 0.005% or more, the formation of the residual ⁇ phase can be promoted. Further, when adding Cu, the amount of Cu is preferably 1.0% or less from the viewpoint of preventing cost increases.
  • Ni 1.0% or less
  • the amount of Ni is preferably 0.005% or more. By setting the Ni amount to 0.005% or more, the formation of the residual ⁇ phase can be promoted. Further, when adding Ni, the amount of Ni is preferably 1.0% or less from the viewpoint of preventing cost increases.
  • the amount of Mo is preferably 0.005% or more. By setting the amount of Mo to 0.005% or more, the effect of adjusting strength can be obtained.
  • the amount of Mo is more preferably 0.05% or more. Further, when adding Mo, the amount of Mo is preferably 1.0% or less from the viewpoint of preventing cost increases.
  • Nb 0.20% or less By containing Nb at 0.005% or more, the effect of improving strength can be obtained. Further, when Nb is contained, the amount of Nb is preferably 0.20% or less from the viewpoint of preventing cost increases.
  • V 0.5% or less By containing V at 0.005% or more, the effect of improving strength can be obtained. Further, when V is contained, the amount of V is preferably 0.5% or less from the viewpoint of preventing cost increases.
  • Sb 0.200% or less
  • Sb can be contained from the viewpoint of suppressing nitridation, oxidation, or decarburization of the steel plate surface to a depth of several tens of microns caused by oxidation.
  • Sb suppresses nitridation and oxidation on the surface of the steel sheet, thereby preventing the production amount of martensite from decreasing on the surface of the steel sheet and improving the fatigue properties and surface quality of the steel sheet.
  • the amount of Sb is preferably 0.001% or more.
  • the amount of Sb is preferably 0.200% or less.
  • Ta 0.1% or less By containing Ta at 0.001% or more, the effect of improving strength can be obtained. Further, when Ta is contained, the amount of Ta is preferably 0.1% or less from the viewpoint of preventing cost increases.
  • W 0.5% or less
  • the amount of W is preferably 0.5% or less from the viewpoint of preventing cost increases.
  • Zr 0.1% or less
  • the amount of Zr is preferably 0.1% or less from the viewpoint of preventing cost increase.
  • Sn 0.20% or less
  • Sn is an element that suppresses denitrification, deborizing, etc., and is effective in suppressing a decrease in strength of steel.
  • the content is preferably 0.002% or more.
  • the amount of Sn is preferably 0.20% or less.
  • Ca 0.005% or less Ca can control the morphology of sulfides and improve ductility and toughness by containing 0.0005% or more. Moreover, from the viewpoint of obtaining good ductility, the amount of Ca is preferably 0.005% or less.
  • Mg 0.005% or less
  • the amount of Mg is preferably 0.005% or less from the viewpoint of preventing cost increases.
  • REM 0.005% or less REM can control the morphology of sulfides and improve ductility and toughness by containing 0.0005% or more. Further, when containing REM, the amount of REM is preferably 0.005% or less from the viewpoint of obtaining good toughness.
  • the Si-containing steel plate may be either a cold-rolled steel plate or a hot-rolled steel plate.
  • the hot rolling process is a process in which the above-mentioned slab is hot rolled, then wound into a coil at a temperature equal to or lower than the temperature T C (° C.) calculated from the following formula (1), and pickled.
  • the results of investigating the amount of internal oxidation at the center in the longitudinal direction and the center in the width direction of the coil formed after hot rolling and cooling using steel with varying Si and Mn contents By winding it into a coil at a temperature equal to or lower than the temperature T C (°C) calculated from the following formula (1), the total amount of Si internal oxide and Mn internal oxide formed in the hot rolling process is reduced to 0.10 g. /m 2 or less.
  • Tc -30([Si]+[Mn])+775...(1)
  • Tc is the winding temperature after rolling
  • [Si] and [Mn] are the Si content and Mn content in the steel, respectively.
  • Tc is preferably 400°C or higher.
  • the heating temperature before hot rolling and the finishing temperature of hot rolling are not particularly limited, but from the viewpoint of microstructural control, the slab is heated to 1100 to 1300°C, soaked, and finished at 800 to 1000°C. Preferably, rolling is completed.
  • pickling is performed to remove scale.
  • the pickling method is not particularly limited, and any conventional method may be used.
  • the cold rolling process is a process in which the hot rolled sheet obtained in the above hot rolling process is subjected to cold rolling.
  • the cold rolling conditions are not particularly limited, and for example, the cooled hot rolled sheet may be cold rolled at a predetermined rolling reduction of 30 to 80%.
  • the annealing process of the present invention includes a process of oxidizing the cold-rolled steel plate obtained in the above-mentioned cold rolling process using a direct-fired heating furnace having two or more separated zones, and a process of radiant tube heating. This process consists of reducing the oxidized steel plate using a furnace or holding furnace.
  • Si and Mn can be removed inside the steel sheet by strictly controlling the annealing conditions (oxidation treatment conditions + reduction annealing conditions) before hot-dip galvanizing treatment. It is possible to improve the plating properties by oxidizing the steel sheet, and also to improve the reactivity between the plating and the steel sheet, thereby improving the adhesion of the plating. Then, in the annealing step, oxidation treatment is performed to oxidize Si and Mn inside the steel sheet and prevent oxidation on the surface of the steel sheet. In particular, it is necessary to obtain a certain amount or more of iron oxide through oxidation treatment. After that, it is effective to perform reduction annealing, hot-dip plating, and alloying treatment if necessary.
  • annealing conditions oxidation treatment conditions + reduction annealing conditions
  • the atmosphere is controlled by controlling the air ratio of the direct-fired heating furnace.
  • a direct-fired heating furnace heats a steel plate by directly applying a burner flame made by mixing air with a fuel such as coke oven gas (COG), which is a by-product gas of a steel mill, to the surface of the steel plate.
  • COG coke oven gas
  • the air ratio is increased to increase the ratio of air to fuel, unreacted oxygen remains in the flame, and the oxygen can promote oxidation of the steel sheet.
  • the fuel for the direct-fired heating furnace in addition to coke oven gas, natural gas, hydrogen gas, ammonia gas, etc. may be used. Oxidation products generated when these fuels are combusted include CO, CO2 , H2O , NOX , and the like.
  • N 2 in the combustion air is also present in the atmosphere.
  • the process of oxidizing a steel plate using a direct-fired heating furnace requires having two or more separated areas and heating in two or more different atmospheres. Next, the heating zone front stage and the heating zone rear stage will be explained.
  • the steel plate is heated from 400°C to 670°C in an atmosphere containing 1000 volume ppm or more of O 2 and 1000 volume ppm or more of H 2 O.
  • the air ratio is adjusted to create an atmosphere of 1000 volume ppm or more, and the cold rolled steel plate is heated.
  • O 2 is 1000 volume ppm or less and H 2 O is 1000 volume ppm or less
  • the oxidation of the steel sheet will be insufficient.
  • O 2 is less than 1000 volume ppm and H 2 O is less than 1000 volume ppm, the influence of O 2 and H 2 O concentration on the oxidation of the steel sheet is small, and the influence of the temperature of the steel sheet becomes large, so the upper limit is particularly Not provided.
  • O 2 is preferably 10,000 volume ppm or less
  • H 2 O is preferably 10,000 volume ppm or less.
  • the steel plate is heated to a temperature of 400°C or higher and 670°C or lower. If the temperature of the steel plate is less than 400°C, the oxidation of the steel plate will be insufficient, and if it exceeds 670°C, the oxidation of the steel plate will be excessive, resulting in the above-mentioned pickup onto the rolls. Therefore, in the present invention, it is essential to heat the steel plate so that the temperature is in the range of 400°C or higher and 670°C or lower.
  • heating is performed to suppress the aforementioned roll pickup and to obtain a beautiful surface appearance free of scratches. This is an important requirement for inventions.
  • it is important to reduce a portion of the surface (surface layer) of the steel sheet that has been oxidized.
  • the air ratio is adjusted in the latter stage of the heating zone so that the atmosphere contains O 2 at 500 volume ppm or less, and the steel plate that has passed through the first stage of the heating zone is heated.
  • the steel sheet will be excessively oxidized, and the aforementioned pickup onto the rolls will occur.
  • the steel plate is heated to a temperature of 600°C or higher and 700°C or lower. If the temperature of the steel plate is less than 600°C, part of the surface of the steel plate (surface layer) is insufficiently reduced, and if it exceeds 700°C, part of the surface of the steel plate (surface layer) is not reduced and oxidation is promoted. The aforementioned pickup to the roll may occur. Therefore, in the present invention, it is essential to heat the steel plate so that the temperature is in the range of 600°C or higher and 700°C or lower.
  • Radiant tube type heating and holding can be used for reduction annealing.
  • H 2 O concentration of the atmosphere by controlling the H 2 O concentration of the atmosphere to 5000 volume ppm or more and 40000 volume ppm or less, LME cracking can be suppressed and dehydrogenation can be promoted. If the H 2 O concentration is less than 5000 ppm by volume, the LME cracking resistance and dehydrogenation promoting effect cannot be said to be sufficient. On the other hand, if the H 2 O concentration exceeds 40,000 volume ppm, there is a concern that equipment damage may occur, so it is preferably 40,000 volume ppm or less. Here, the difference in H 2 O concentration between the upper and lower parts of the furnace needs to be 2000 volume ppm or less.
  • the H 2 concentration during reduction annealing also greatly influences the formation of the internal oxidation layer.
  • the H 2 concentration needs to be from 2% by volume to 20% by volume. Further, the ratio of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ) needs to satisfy the following formula (2). If the H 2 concentration is less than 2% by volume, the reduction of the oxidized steel sheet is insufficient, and non-plating defects may occur during hot-dip galvanizing, or plating adhesion may be inhibited.
  • the formation of the internal oxide layer is influenced by the ratio of the partial pressure of H 2 O (P H2O ) to the partial pressure of H 2 (P H2 ).
  • log(P H2O /P H2 ) needs to be -1.1 or more and 0.5 or less.
  • log(P H2O /P H2 ) is less than -1.1, a sufficient internal oxidation layer may not be formed, and good LME cracking resistance and dehydrogenation promoting effect may not be obtained.
  • log(P H2O /P H2 ) exceeds 0.5, there is a fear of equipment damage, so log(P H2O /P H2 ) is preferably 0.5 or less.
  • log (P H2O /P H2 ) is also effective for the bendability required for the formability of high-strength steel sheets.
  • the mechanism for this is not clear, but the formability is improved by the reduction of hydrogen in the steel sheet, and the presence of an internal oxidation layer on the surface layer, which has relatively good formability, improves strain dispersion. This is thought to be due to changes.
  • log (P H2O /P H2 ) By setting log (P H2O /P H2 ) to -1.1 or more, the bendability is improved, but by setting log (P H2O /P H2 ) to -0.99 or more, the bendability is further improved. It may be set to -0.90 or more, and further improvement can be achieved by setting it to -0.7 or more.
  • the upper limit of log( PH2O / PH2 ) is preferably 0.5 or less.
  • N 2 in the reducing annealing atmosphere, except for H 2 O and H 2 , it is preferable to use N 2 from the viewpoint of cost.
  • NOx , SOx , CO, CO2, etc. may be mixed in.
  • the temperature of reduction annealing needs to be 650°C or higher and 900°C or lower. If the temperature is less than 650°C, the formation of an internal oxidation layer, which is necessary for improving LME cracking resistance and promoting dehydrogenation, may become insufficient. Further, if the temperature exceeds 900°C, there is a concern that the furnace body of the annealing furnace may be damaged, so the temperature is preferably 900°C or lower.
  • the reducing atmosphere described above only needs to be partially or completely filled in the furnace. If a part of the part satisfies the atmosphere described above, the annealing time in the specified atmosphere is required to be 90 seconds or more. As long as the annealing is performed in the specified atmosphere for 90 seconds or more, the atmosphere for reduction annealing does not need to be controlled throughout the furnace.
  • the cooling/heating process refers to cooling after reduction annealing at an average cooling rate of 10°C/sec or more, from the final holding temperature in reduction annealing to the final cooling temperature of 150 to 350°C, and then cooling to a cooling temperature of 350 to 600°C. This is a step of heating to the reheating temperature and holding at that temperature for 10 to 600 seconds. By performing this cooling and heating step, the mechanical properties can be further improved. Note that in the present invention, the cooling and heating step is not an essential step, and may be performed as necessary.
  • the cooling rate from the final holding temperature in reduction annealing is less than 10° C./sec, pearlite will be produced and TS ⁇ EL and hole expandability will decrease. Therefore, the cooling rate from the final holding temperature in reduction annealing is preferably 10° C./second or more.
  • the final holding temperature in reduction annealing refers to the temperature at which the steel sheet, which has been annealed within a range that satisfies the requirements of the annealing temperature, hydrogen concentration, dew point, and holding time, deviates from at least one of the above requirements. .
  • the temperature of the plating bath increases in the subsequent hot-dip plating process, which may promote the generation of dross that impairs the surface appearance quality. Therefore, the ultimate cooling temperature is preferably 600°C or less. Mechanical properties can be improved by setting the cooling temperature to 350° C. or lower. Moreover, when the cooling temperature reached is lower than 150° C., most of the austenite transforms into martensite during cooling, and the amount of untransformed austenite decreases. Therefore, the temperature reached by cooling is preferably in the range of 150 to 350°C. As for the cooling method, any cooling method such as gas jet cooling, mist cooling, water cooling, metal quenching, etc. may be used as long as the target cooling rate and cooling stop temperature (achieved cooling temperature) can be achieved.
  • any cooling method such as gas jet cooling, mist cooling, water cooling, metal quenching, etc. may be used as long as the target cooling rate and cooling stop temperature (achieved cooling temperature) can be achieved.
  • the untransformed austenite at the time of stopping cooling will transform into pearlite, and it will eventually become impossible to obtain residual austenite with an area ratio of 3% or more. If the holding time during reheating is less than 10 seconds, the stabilization of austenite will be insufficient, and if it exceeds 600 seconds, the untransformed austenite at the time of stopping cooling will transform into bainite, and a sufficient amount of residual austenite will eventually be obtained. I won't be able to do it. Therefore, when reheating, the temperature should be in the range of 350 to 600°C, and the holding time in that temperature range should be 10 to 600 seconds.
  • the hot-dip galvanizing process is a process in which the annealed plate after the annealing process is subjected to hot-dip galvanizing in a hot-dip galvanizing bath containing 0.12 to 0.22% by mass of Al.
  • the Al concentration in the galvanizing bath is set to 0.12 to 0.22% by mass. If it is less than 0.12% by mass, a Fe--Zn alloy phase is formed during plating, which may deteriorate plating adhesion or cause uneven appearance. If it exceeds 0.22% by mass, the Fe--Al alloy phase generated at the plating/substrate interface during plating will be thick, resulting in poor weldability. Furthermore, since there is a large amount of Al in the bath, a large amount of Al oxide film is formed on the surface of the plated steel sheet, which may impair not only the weldability but also the appearance.
  • the Al concentration in the plating bath when performing alloying treatment is preferably 0.12 to 0.17% by mass. If it is less than 0.12% by mass, a Fe--Zn alloy phase is formed during plating, which may deteriorate plating adhesion or cause uneven appearance. If it exceeds 0.17% by mass, the Fe-Al alloy phase that forms at the plating/substrate interface during plating will form thickly and become a barrier to the Fe-Zn alloying reaction, resulting in a high alloying temperature and poor mechanical properties. It may deteriorate.
  • hot-dip galvanizing bath temperature is in the normal range of 440 to 500°C
  • the steel plate is immersed in the plating bath at a plate temperature of 440 to 550°C.
  • the amount of adhesion can be adjusted using gas wiping, etc.
  • the alloying process is a process in which the steel plate after the hot-dip galvanizing process is subjected to an alloying process at a temperature of 450 to 550°C for 10 to 60 seconds.
  • the degree of alloying after the alloying treatment is not particularly limited, but the degree of alloying is preferably 7 to 15% by mass. If it is less than 7% by mass, the ⁇ phase remains and the press formability is poor, and if it exceeds 15% by mass, the plating adhesion is poor.
  • the amount of internal oxidation is measured by "impulse furnace melting - infrared absorption method".
  • the oxygen concentration in the steel was measured before and after polishing a 10 mm x 70 mm area of the surface layer portion (center of the coil (width center and longitudinal center)) on both sides of the hot rolled sheet by 10 ⁇ m. Further, from the difference between these measured values, the amount of oxygen per unit area of one side existing in a region 10 ⁇ m from the surface of the steel plate was determined, and this was determined as the amount of internal oxidation of Si and/or Mn (g/m 2 ).
  • the internal oxide formed on the surface layer of the hot-rolled sheet is an oxide of Si and/or Mn can be confirmed by SEM observation and EDS (energy dispersive This was confirmed by elemental analysis using a line spectrometer.
  • Table 3 shows the amount of internal oxidation.
  • the sheet was annealed at CGL and hot-dipped. Heating was performed under the conditions shown in Table 2 using a direct-fired heating furnace equipped with a nozzle mix type burner in the front stage of the heating furnace. Next, the latter part of the heating furnace was heated in a direct-fired heating furnace equipped with a premix burner under the conditions shown in Table 2. Note that the oxidation start temperature was 300°C. Since the oxidation starting temperature does not particularly affect the appearance of the plating, the oxidizing atmosphere may be set to less than 400°C. Reduction annealing was performed in a radiant tube type heating and holding furnace under the conditions shown in Table 2, followed by cooling.
  • hot-dip galvanizing was performed using a 460° C. zinc bath containing 0.135% Al as shown in Table 2, and the basis weight was adjusted to about 50 g/m 2 by gas wiping. Alloying treatment was performed under some conditions.
  • a test piece was cut from a hot-dip galvanized steel sheet into a size of 150 mm in the longitudinal direction and 50 mm in the transverse direction, with the rolling direction (TD) as the long side and the rolling direction as the short side.
  • a test galvanized steel plate (thickness 1.2 mm, TS: 980 MPa class) with a coating weight of 50 g/m 2 was stacked to form a plate assembly. This plate assembly was assembled so that the hot-dip galvanized layer of the test piece was aligned with the hot-dip galvanized layer surface of a commercially available hot-dip galvanized steel sheet.
  • this plate assembly is fixed to a fixed base via a 2.0 mm thick spacer with an angle of 5°, which is the maximum inclination expected for some parts shapes.
  • the spacer was a pair of steel plates measuring 50 mm in the longitudinal direction x 45 mm in the transversal direction x 2.0 mm in thickness, and was arranged so that the longitudinal end faces of each of the pair of steel plates were aligned with both end faces in the transverse direction of the plate assembly. Therefore, the distance between the pair of steel plates constituting the spacer is 60 mm.
  • the fixing base is a single plate with a hole in the center.
  • the pair of electrodes applied pressure to the plate assembly from above and below in the vertical direction, and the lower electrode applied pressure to the test piece through the hole in the fixing table.
  • the lower electrode and the fixing base are fixed so that the lower electrode of the pair of electrodes contacts a plane that is an extension of the surface where the spacer and the fixing base are in contact, and the upper electrode is movable. did.
  • the upper electrode was placed in contact with the center of the test hot-dip galvanized steel sheet.
  • the hold time refers to the time from when the welding current finishes flowing until the electrode starts to open.
  • the nugget diameter refers to the distance between the end portions 10 of the nugget in the longitudinal direction of the plate set, as shown in FIG.
  • the plate set with the welded part was cut to include the welded part (nugget), and the cross section of the welded part was observed with an optical microscope (200x magnification), and it was evaluated according to the following criteria.
  • the resistance weld cracking characteristics of the weld zone were evaluated.
  • the upper diagram in FIG. 2 is a plan view of the plate assembly with welded parts, and shows the cutting position.
  • the lower figure in FIG. 2 is a drawing showing a cross section in the plate thickness direction of the plate set after cutting, and schematically shows cracks that occurred in the test piece. Note that if cracks occur in the hot-dip galvanized steel sheet for testing, the stress in the test piece will be dispersed and the evaluation will not be appropriate. For this reason, data in which no cracks occurred in the hot-dip galvanized steel sheet for testing were adopted as examples.
  • the resistance welding cracking resistance of the welded part is judged to be good or excellent, respectively, and if it is "x”, the resistance welding cracking resistance of the welded part is judged to be poor. It was judged.
  • ⁇ Dehydrogenation behavior> A strip-shaped test piece with a major axis length of 30 mm and a short axis length of 5 mm was taken from the center of the width of a hot-dip galvanized steel sheet, the plating layer of the test piece was removed using a router, and immediately subjected to temperature-programmed desorption analysis. Using a device, hydrogen was analyzed under the conditions of an analysis start temperature of 25°C, an analysis end temperature of 300°C, and a heating rate of 200°C/hour, and the released hydrogen amount (mass ppm /min) was measured. The total amount of hydrogen released from the analysis start temperature to 300° C. was calculated as the amount of diffusible hydrogen in the steel.
  • the streak speed was 50 mm/min, and a decisive push was applied to the die for 5 seconds with a load of 10 tons.
  • Tests were conducted by varying the tip R of the V-shaped punch in 0.5 steps, and the vicinity of the test piece ridgeline was observed with a 20x lens to confirm the presence or absence of cracks. Calculate R/t from the minimum R at which no cracks occurred and the plate thickness of the test piece (tmm, use the value rounded to the nearest thousandth), and calculate this. was used as an index of bendability. The smaller R/t is, the better the bendability is.
  • the present invention example is a high-strength hot-dip galvanized steel sheet containing C, Si, and Mn, it has excellent LME cracking resistance, a good plating appearance, and an amount of diffusible hydrogen in the steel sheet. It can be expected to have good delayed fracture resistance, less damage to the furnace body, and excellent ductility and bendability.
  • comparative examples manufactured outside the scope of the present invention are inferior in any one or more of LME cracking resistance, plating appearance, amount of diffusible hydrogen in the steel sheet, and damage to the furnace body.
  • the high-strength galvanized steel sheet obtained by the manufacturing method of the present invention has excellent appearance quality and resistance weld cracking resistance, and at the same time can suppress deterioration of delayed fracture resistance caused by hydrogen embrittlement, and can be used for automobile bodies. It can be used as a surface-treated steel sheet to reduce weight and increase strength.

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Abstract

L'invention concerne un procédé de fabrication d'une tôle d'acier galvanisée haute résistance par immersion à chaud qui empêche la dégradation de la qualité de l'aspect d'une plaque d'acier, qui présente une résistance à la fissuration LME, une ductilité et une aptitude au pliage supérieures, et qui permet la suppression de la détérioration de la résistance à la fracture retardée due à la fragilisation par l'hydrogène. Le procédé de fabrication d'une tôle d'acier galvanisée haute résistance par immersion à chaud, dans lequel une galvanisation par immersion à chaud est effectuée après un recuit continu, consiste : dans un premier étage d'un four de chauffage à chauffage direct, à chauffer une plaque d'acier à une température de 400 °C à 670 °C dans une atmosphère contenant 1 000 ppm en volume ou plus d'O2 et 1 000 ppm en volume ou plus de H2O ; dans un étage suivant du four de chauffage à chauffage direct, à chauffer la plaque d'acier à une température de 600 °C à 700 °C dans une atmosphère contenant 500 ppm en volume ou moins d'O2 ; et dans un four de chauffage et de maintien, à maintenir la plaque d'acier à une température de 650 °C à 900 °C pendant au moins 90 secondes dans une atmosphère dans laquelle la concentration de H2 de l'atmosphère de four est de 5 000 ppm en volume à 40 000 ppm en volume, la concentration de H2 étant de 2 pour cent en volume à 20 pour cent en volume, et une mesure spécifique (PH2O/PH2) d'une pression partielle de H2O (PH2O) et d'une pression partielle de H2 (PH2) satisfaisant à -1,1 à 0,5.
PCT/JP2023/012038 2022-03-25 2023-03-24 Procédé de fabrication de tôle d'acier galvanisée haute résistance par immersion à chaud WO2023182525A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013136809A (ja) * 2011-12-28 2013-07-11 Nippon Steel & Sumitomo Metal Corp Ｓｉ含有高強度溶融亜鉛めっき鋼板、及びＳｉ含有高強度合金化溶融亜鉛めっき鋼板の製造方法
WO2015087549A1 (fr) * 2013-12-13 2015-06-18 Ｊｆｅスチール株式会社 Procédé de fabrication d'une tôle d'acier de résistance élevée galvanisée à chaud
JP2015113504A (ja) * 2013-12-12 2015-06-22 Ｊｆｅスチール株式会社 加工性に優れた高強度溶融亜鉛めっき鋼板およびその製造方法
WO2016038801A1 (fr) * 2014-09-08 2016-03-17 Ｊｆｅスチール株式会社 Procédé et appareil de fabrication de tôle d'acier haute résistance galvanisée à chaud au trempé

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013136809A (ja) * 2011-12-28 2013-07-11 Nippon Steel & Sumitomo Metal Corp Ｓｉ含有高強度溶融亜鉛めっき鋼板、及びＳｉ含有高強度合金化溶融亜鉛めっき鋼板の製造方法
JP2015113504A (ja) * 2013-12-12 2015-06-22 Ｊｆｅスチール株式会社 加工性に優れた高強度溶融亜鉛めっき鋼板およびその製造方法
WO2015087549A1 (fr) * 2013-12-13 2015-06-18 Ｊｆｅスチール株式会社 Procédé de fabrication d'une tôle d'acier de résistance élevée galvanisée à chaud
WO2016038801A1 (fr) * 2014-09-08 2016-03-17 Ｊｆｅスチール株式会社 Procédé et appareil de fabrication de tôle d'acier haute résistance galvanisée à chaud au trempé

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