WO2012042677A1 - High-strength steel sheet and method for producing same - Google Patents
High-strength steel sheet and method for producing same Download PDFInfo
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- WO2012042677A1 WO2012042677A1 PCT/JP2010/067612 JP2010067612W WO2012042677A1 WO 2012042677 A1 WO2012042677 A1 WO 2012042677A1 JP 2010067612 W JP2010067612 W JP 2010067612W WO 2012042677 A1 WO2012042677 A1 WO 2012042677A1
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- 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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/12—Oxidising using elemental oxygen or ozone
- C23C8/14—Oxidising of ferrous surfaces
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- 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
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface treatment
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- 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
- C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
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- 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
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- 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
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- 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
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- 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
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
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- 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
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- 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
- C23C22/07—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 containing phosphates
- C23C22/08—Orthophosphates
- C23C22/18—Orthophosphates containing manganese cations
- C23C22/182—Orthophosphates containing manganese cations containing also zinc cations
- C23C22/184—Orthophosphates containing manganese cations containing also zinc cations containing also nickel cations
Definitions
- the present invention relates to a high-strength steel sheet having excellent chemical conversion properties and corrosion resistance after electrodeposition coating even when the Si content is large, and a method for producing the same.
- Si is oxidized even when annealing is performed in a reducing N 2 + H 2 gas atmosphere in which Fe does not oxidize (reducing Fe oxide), and Si oxide is formed on the outermost layer of the steel sheet. (SiO 2 ) is formed. Since this SiO 2 inhibits the formation reaction of the chemical conversion film during the chemical conversion treatment, a minute region (hereinafter also referred to as “ske”) where the chemical conversion film is not formed is formed, and the chemical conversion treatment performance is lowered.
- Patent Document 1 discloses a method of forming an iron coating layer of 20 to 1500 mg / m 2 on a steel sheet using an electroplating method.
- this method there is a problem that the cost is increased due to the additional steps required for the electroplating equipment.
- Patent Document 2 the Mn / Si ratio is defined, and in Patent Document 3, Ni is added to improve the phosphate processability.
- the effect depends on the Si content in the steel sheet, and it is considered that further improvement is necessary for the steel sheet having a high Si content.
- Patent Document 4 by setting the dew point during annealing to ⁇ 25 to 0 ° C., an internal oxide layer made of an Si-containing oxide is formed within a depth of 1 ⁇ m from the surface of the steel sheet substrate, and the steel sheet surface length is 10 ⁇ m. A method is disclosed in which the proportion of the Si-containing oxide is 80% or less.
- the area for controlling the dew point since the area for controlling the dew point is premised on the entire inside of the furnace, the controllability of the dew point is difficult and stable operation is difficult.
- Patent Document 5 describes a method in which a steel sheet temperature reaches 350 to 650 ° C. in an oxidizing atmosphere to form an oxide film on the steel sheet surface, and then heated and cooled to a recrystallization temperature in a reducing atmosphere.
- a steel sheet temperature reaches 350 to 650 ° C. in an oxidizing atmosphere to form an oxide film on the steel sheet surface, and then heated and cooled to a recrystallization temperature in a reducing atmosphere.
- this method there is a difference in the thickness of the oxide film formed on the surface of the steel sheet due to the oxidation method, and sufficient oxidation does not occur, or the oxide film becomes too thick, and in subsequent annealing in a reducing atmosphere. Oxide film may remain or peel off, and surface properties may deteriorate.
- a technique for oxidizing in the air is described, but oxidation in the air generates a thick oxide and subsequent reduction is difficult, or a reducing atmosphere with a high hydrogen concentration is required. There are problems such as.
- Patent Document 6 a cold-rolled steel sheet containing 0.1% or more of Si and / or 1.0% or more of Mn by mass%, the steel sheet surface in an iron oxidizing atmosphere at a steel sheet temperature of 400 ° C. or more. Describes a method in which an oxide film is formed, and then the oxide film on the surface of the steel sheet is reduced in an iron reducing atmosphere. Specifically, after oxidizing Fe on the steel sheet surface using a direct fire burner at 400 ° C. or higher and an air ratio of 0.93 or higher and 1.10 or lower, annealing is performed in an N 2 + H 2 gas atmosphere that reduces Fe oxide.
- Patent Document 6 does not specifically describe the heating temperature of an open flame burner, but when it contains a large amount of Si (approximately 0.6% or more), the amount of oxidation of Si that is easier to oxidize than Fe. As a result, the oxidation of Fe is suppressed, and the oxidation of Fe itself becomes too small. As a result, the formation of the surface Fe reduction layer after reduction may be insufficient, or SiO 2 may be present on the steel sheet surface after reduction, resulting in the occurrence of a conversion coating.
- JP-A-5-320952 JP 2004-323969 A Japanese Patent Application Laid-Open No. 6-10096 JP 2003-113441 A JP 55-145122 A JP 2006-45615 A
- the present invention has been made in view of such circumstances, and provides a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating, and a method for producing the same, even when the content of Si is large. With the goal.
- the dew point or oxygen concentration was increased by simply increasing the steam partial pressure or oxygen partial pressure in the entire annealing furnace to excessively oxidize the inside of the steel sheet.
- Various problems have occurred, such as problems, unevenness in chemical conversion treatment, and deterioration of corrosion resistance after electrodeposition coating. Therefore, the present inventors have studied a method for solving the problem by a new method not confined to the conventional idea.
- high strength with excellent chemical conversion treatment and corrosion resistance after electrodeposition coating by controlling the structure and structure of the steel sheet surface layer, which may be the starting point of corrosion resistance degradation after electrodeposition coating It has been found that a steel plate can be obtained.
- the dew point of the atmosphere is set to ⁇ 10 in a limited temperature range of the heating furnace temperature in the heating process: A ° C. or higher and B ° C. or lower (A: 600 ⁇ A ⁇ 780, B: 800 ⁇ B ⁇ 900).
- Annealing and chemical conversion treatment are performed while controlling the temperature to be equal to or higher.
- selective surface oxidation can be suppressed, surface concentration can be suppressed, and a high-strength steel sheet excellent in chemical conversion treatment properties and corrosion resistance after electrodeposition coating can be obtained.
- having excellent chemical conversion property means having a non-scaling and uneven appearance after chemical conversion treatment.
- the high-strength steel plate obtained by the above method has Fe, Si, Mn, Al, P, and also B, Nb, Ti, Cr, Mo, Cu, Ni on the steel plate surface layer portion within 100 ⁇ m from the steel plate surface.
- At least one oxide selected from the inside is formed in an amount of 0.010 to 0.50 g / m 2 per side, and in the region from the steel plate surface to 10 ⁇ m, crystalline Si is present in the iron grains within 1 ⁇ m from the grain boundary.
- the structure and structure in which Mn-based oxides are deposited are obtained. As a result, the deterioration of the corrosion resistance after electrodeposition coating can be realized and the chemical conversion processability is excellent.
- the present invention is based on the above findings, and features are as follows.
- the heating furnace temperature A method for producing a high-strength steel sheet, wherein a temperature range of A ° C. or higher and B ° C. or lower is performed at an atmospheric dew point of ⁇ 10 ° C. or higher.
- the steel sheet has a component composition by mass%, and B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 ⁇ 0.05%, Cr: 0.001 to 1.0%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0%
- B 0.001 to 0.005%
- Nb 0.005 to 0.05%
- Ti 0.005 ⁇ 0.05%
- Cr 0.001 to 1.0%
- Mo 0.05 to 1.0%
- Cu 0.05 to 1.0%
- Ni 0.05 to 1.0%
- Fe, Si, Mn, Al, P, B, Nb, Ti, Cr are formed on a steel sheet surface layer within 100 ⁇ m from the steel sheet surface.
- At least one oxide selected from Mo, Cu and Ni is formed at 0.010 to 0.50 g / m 2 per side, and in the region within 10 ⁇ m from the steel plate surface, the grain boundary of the steel plate A high-strength steel sheet characterized by the presence of crystalline Si and Mn-based oxides in grains within 1 ⁇ m.
- the high strength means that the tensile strength TS is 340 MPa or more.
- the high-strength steel sheet of the present invention includes both cold-rolled steel sheets and hot-rolled steel sheets.
- the dew point of the atmosphere is ⁇ 10 in the limited temperature range of the heating furnace temperature: A ° C. or higher and B ° C. or lower (A: 600 ⁇ A ⁇ 780, B: 800 ⁇ B ⁇ 900).
- an appropriate amount of oxides of oxidizable elements (Si, Mn, etc.) (hereinafter referred to as internal oxidation) within the steel sheet surface layer within 10 ⁇ m. It is possible to suppress the selective surface oxidation (hereinafter referred to as surface concentration) in the steel sheet surface layer of Si, Mn, etc. in steel, which is present and deteriorates the chemical conversion property after annealing.
- the lower limit temperature A is 600 ⁇ A ⁇ 780 is as follows. In the temperature range lower than 600 ° C., the dew point control is not performed and the internal oxidation is not formed, so the surface concentration is originally low, and the chemical conversion treatment property is not hindered. Further, when the temperature is raised to a temperature exceeding 780 ° C. without controlling the dew point, the surface is heavily concentrated, so that the inward diffusion of oxygen is inhibited and internal oxidation is less likely to occur. Therefore, the dew point must be controlled to at least ⁇ 10 ° C. from the temperature range of at least 780 ° C. From the above, the allowable range of A is A: 600 ⁇ A ⁇ 780, and for the reason described above, it is desirable that A is as low as possible within this range.
- the reason why the upper limit temperature B is set to 800 ⁇ B ⁇ 900 is as follows.
- a region (hereinafter referred to as a deficient layer) in which the solid solution amount of the internal oxidizable elements (Si, Mn, etc.) within 10 ⁇ m of the steel sheet surface layer is reduced is formed. Suppresses surface diffusion of easily oxidizable elements.
- B needs to satisfy 800 ⁇ B ⁇ 900.
- the temperature is lower than 800 ° C., sufficient internal oxidation is not formed.
- the temperature exceeds 900 ° C. the amount of internal oxidation formed becomes excessive, which becomes a starting point for corrosion resistance deterioration after electrodeposition coating.
- the reason why the dew point in the temperature range of A ° C. or higher and B ° C. or lower is ⁇ 10 ° C. or higher is as follows.
- By increasing the dew point it is possible to increase the O 2 potential resulting from the decomposition of H 2 O and promote internal oxidation.
- the amount of internal oxidation formed is small.
- the upper limit of the dew point is not particularly defined, but if it exceeds 90 ° C, the amount of Fe oxidation increases, and there is concern about deterioration of the annealing furnace wall and roll.
- C 0.01 to 0.18% C improves workability by forming martensite or the like as a steel structure. For that purpose, 0.01% or more is necessary. On the other hand, if it exceeds 0.18%, the elongation is reduced, the material is deteriorated, and the weldability is further deteriorated. Therefore, the C content is 0.01% or more and 0.18% or less.
- Si 0.4 to 2.0% Si is an element effective for strengthening steel and improving elongation to obtain a good material, and 0.4% or more is necessary to obtain the intended strength of the present invention. If Si is less than 0.4%, the strength within the scope of the present invention cannot be obtained, and there is no particular problem with chemical conversion treatment. On the other hand, when it exceeds 2.0%, the steel strengthening ability and the effect of improving elongation become saturated. Furthermore, it becomes difficult to improve the chemical conversion processability. Therefore, the Si amount is set to 0.4% or more and 2.0% or less.
- Mn 1.0 to 3.0% Mn is an element effective for increasing the strength of steel. In order to ensure mechanical properties and strength, it is necessary to contain 1.0% or more. On the other hand, if it exceeds 3.0%, it becomes difficult to secure weldability and the balance between strength and ductility. Therefore, the Mn content is 1.0% or more and 3.0% or less.
- Al 0.001 to 1.0% Al is added for the purpose of deoxidizing molten steel.
- the effect of deoxidation of molten steel is obtained at 0.001% or more.
- the cost increases.
- the surface concentration of Al increases and it becomes difficult to improve chemical conversion properties. Therefore, the Al content is 0.001% or more and 1.0% or less.
- P 0.005 to 0.060% or less
- P is an element inevitably contained, and in order to make it less than 0.005%, there is a concern about an increase in cost, so 0.005% or more
- P exceeds 0.060% weldability deteriorates.
- the chemical conversion processability is greatly deteriorated, and even with the present invention, it is difficult to improve the chemical conversion processability. Therefore, the P content is 0.005% or more and 0.060% or less.
- S 0.01% S is one of the elements inevitably contained.
- the lower limit is not specified, but if it is contained in a large amount, the weldability and corrosion resistance deteriorate, so the content is made 0.01% or less.
- B 0.001 to 0.005%
- Nb 0.005 to 0.05%
- Ti 0.005 to 0.05%
- Cr 0.001
- B 0.001 to 0.005%
- B amount shall be 0.001% or more and 0.005% or less.
- Nb 0.005 to 0.05% If Nb is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when it contains, Nb amount shall be 0.005% or more and 0.05% or less.
- Ti 0.005 to 0.05% If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, chemical conversion processability is deteriorated. Therefore, when it contains, Ti amount shall be 0.005% or more and 0.05% or less.
- Cr 0.001 to 1.0%
- Cr 0.001 to 1.0%
- Mo 0.05 to 1.0% If Mo is less than 0.05%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Mo content is 0.05% or more and 1.0% or less.
- Cu 0.05 to 1.0% If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual ⁇ phase. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Cu content is 0.05% or more and 1.0% or less.
- Ni 0.05 to 1.0% If Ni is less than 0.05%, the effect of promoting the formation of residual ⁇ phase is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when it contains, Ni amount shall be 0.05% or more and 1.0% or less. The balance other than the above is Fe and inevitable impurities.
- the steel having the above chemical components is hot-rolled, cold-rolled, and then annealed in a continuous annealing facility, followed by chemical conversion treatment.
- the temperature in the heating furnace A ° C. or higher and B ° C. or lower (A: 600 ⁇ A ⁇ 780, B: 800 ⁇ B ⁇ 900)
- Dew point -10 ° C or higher. This is the most important requirement in the present invention.
- the oxygen potential is increased and the easily oxidizable elements such as Si and Mn are internally oxidized in advance immediately before the chemical conversion treatment, and Si and Mn in the steel sheet surface layer portion.
- the activity of is reduced.
- external oxidation of these elements is suppressed, and as a result, chemical conversion property improves.
- annealing may be performed as it is without performing cold rolling.
- Hot rolling Usually, it can be performed on the conditions performed.
- the pickling treatment is preferable to perform a pickling treatment after hot pickling.
- the black scale formed on the surface in the pickling process is removed, and then cold-rolled.
- the pickling conditions are not particularly limited.
- Cold rolling is preferably performed at a rolling reduction of 40% to 80%. If the rolling reduction is less than 40%, the recrystallization temperature is lowered, and the mechanical characteristics are likely to deteriorate. On the other hand, if the rolling reduction exceeds 80%, the steel sheet is a high-strength steel plate, so that not only the rolling cost is increased, but also the surface concentration during annealing is increased, so that the chemical conversion property may be deteriorated.
- Cold-rolled steel sheet or hot-rolled steel sheet is annealed and then subjected to chemical conversion treatment.
- a heating process is performed in which the steel sheet is heated to a predetermined temperature in a preceding heating zone, and a soaking process is performed in which the temperature is maintained at a predetermined temperature for a predetermined time in a subsequent soaking zone.
- a cooling process is performed.
- the dew point of the atmosphere becomes ⁇ 10 ° C. or higher in the temperature range of the heating furnace temperature: A ° C. or higher and B ° C. or lower (A: 600 ⁇ A ⁇ 780, B: 800 ⁇ B ⁇ 900).
- Annealing is performed in such a manner as to control.
- the dew point of the atmosphere in the annealing furnace other than the region of A ° C. or higher and B ° C. or lower is not particularly limited, but is preferably in the range of ⁇ 50 ° C. to ⁇ 10 ° C.
- the gas component in the annealing furnace consists of nitrogen, hydrogen and unavoidable impurities. Other gas components may be included as long as the effects of the present invention are not impaired. If the hydrogen concentration in the atmosphere in the annealing furnace is less than 1 vol%, the activation effect by reduction cannot be obtained and the chemical conversion treatment performance deteriorates. The upper limit is not particularly specified, but if it exceeds 50 vol%, the cost increases and the effect is saturated. Therefore, the hydrogen concentration is preferably 1 vol% or more and 50 vol% or less.
- the gaseous component in an annealing furnace consists of nitrogen gas and an unavoidable impurity gas other than hydrogen gas. Other gas components may be included as long as the effects of the present invention are not impaired.
- tempering is preferably performed at a temperature of 150 to 400 ° C. This is because the elongation tends to deteriorate when the temperature is lower than 150 ° C., and the hardness tends to decrease when the temperature exceeds 400 ° C.
- the present invention good chemical conversion treatment can be ensured without carrying out electrolytic pickling, but a small amount of surface condensate inevitably generated during annealing is removed to ensure better chemical conversion treatment.
- the conditions of the electrolytic pickling are not particularly limited, but in order to efficiently remove the inevitably surface-enriched Si and Mn oxides formed after annealing, an alternating electrolysis with a current density of 1 A / dm 2 or more is used. It is desirable.
- the reason for alternating electrolysis is that the pickling effect is small when the steel plate is held at the cathode, and conversely, Fe that is eluted during electrolysis accumulates in the pickling solution while the steel plate is held at the anode. This is because if the Fe concentration increases and adheres to the surface of the steel sheet, problems such as dry dirt occur.
- the pickling solution used for the electrolytic pickling is not particularly limited, but nitric acid and hydrofluoric acid are not preferable because they are highly corrosive to equipment and require careful handling. Hydrochloric acid is not preferred because it may generate chlorine gas from the cathode. For this reason, use of sulfuric acid is preferable in consideration of corrosivity and environment.
- the sulfuric acid concentration is preferably 5% by mass or more and 20% by mass or less. If the sulfuric acid concentration is less than 5% by mass, the electrical conductivity will be low, so that the bath voltage during electrolysis will rise and the power load may become large. On the other hand, if it exceeds 20% by mass, a loss due to drag-out is large, which causes a problem in cost.
- the temperature of the electrolytic solution is preferably 40 ° C. or higher and 70 ° C. or lower. Since the bath temperature rises due to heat generated by continuous electrolysis, the pickling effect may be reduced at less than 40 ° C. Moreover, it may be difficult to maintain the temperature below 40 ° C. Moreover, it is not preferable that temperature exceeds 70 degreeC from a durable viewpoint of the lining of an electrolytic cell.
- the high-strength steel sheet of the present invention is obtained. And it has the characteristic in the structure of the steel plate surface as follows. On the steel sheet surface layer portion within 100 ⁇ m from the steel sheet surface, Fe, Si, Mn, Al, P, and further one or more oxides selected from B, Nb, Ti, Cr, Mo, Cu, and Ni are contained. A total of 0.010 to 0.50 g / m 2 is formed per side. Further, in the region from the steel plate surface to 10 ⁇ m, crystalline Si and Mn-based composite oxide exist in the ground iron grains within 1 ⁇ m from the grain boundary.
- the dew point control is performed as described above in order to increase the oxygen potential in the annealing process in order to ensure chemical conversion treatment.
- easily oxidizable elements such as Si and Mn are internally oxidized in advance immediately before the chemical conversion treatment, and the activities of Si and Mn in the steel sheet surface layer portion are lowered.
- this improvement effect is at least one selected from Fe, Si, Mn, Al, P, and B, Nb, Ti, Cr, Mo, Cu, Ni on the steel sheet surface layer portion within 100 ⁇ m from the steel sheet surface. There will be 0.010 g / m 2 or more of the seed or more oxide per side. On the other hand, since this effect is saturated even if it exceeds 0.50 g / m 2 , the upper limit is 0.50 g / m 2 .
- the dew point of the atmosphere is ⁇ 10 in the temperature range of the heating furnace temperature: A ° C. or higher and B ° C. or lower (A: 600 ⁇ A ⁇ 780, B: 800 ⁇ B ⁇ 900).
- the temperature is controlled to be higher than or equal to ° C., internal oxidation is performed not only at the grain boundaries but also within the grains.
- crystalline Si and Mn-based composite oxides are present in the ground iron grains within 1 ⁇ m from the grain boundary.
- the presence of oxide in the ground iron grains reduces the amount of solid solution Si and Mn in the ground iron grains near the oxide. As a result, concentration on the surface due to intragranular diffusion of Si and Mn can be suppressed.
- the structure of the steel sheet surface of the high-strength steel sheet obtained by the production method of the present invention is as described above. For example, there is no problem even if the oxide grows in a region exceeding 100 ⁇ m from the steel sheet surface. . Further, in the region exceeding 10 ⁇ m from the surface of the steel plate, there is no problem even if crystalline Si and Mn-based composite oxide are present in the ground iron grains of 1 ⁇ m or more from the grain boundary.
- the hot-rolled steel sheet having the steel composition shown in Table 1 was pickled, and after removing the black scale, it was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some did not carry out cold rolling, but prepared the hot-rolled steel plate (thickness 2.0 mm) after removing the black scale.
- the cold-rolled steel plate and hot-rolled steel plate obtained above were charged into a continuous annealing facility.
- the temperature inside the heating furnace and the dew point were controlled and passed through the plate and annealed, and then tempered between 300 ° C. and 140 s after water quenching.
- electrolytic pickling was performed by alternating electrolysis in which the test material was in the order of anode and cathode for 3 seconds each in the order of the current density conditions shown in Table 2 in a sulfuric acid aqueous solution of 5% by mass at 40 ° C. Obtained.
- region which controlled the said dew point was based on -35 degreeC.
- the atmospheric gas components were nitrogen gas, hydrogen gas, and inevitable impurity gas, and the dew point was controlled by dehumidifying or absorbing and removing moisture in the atmosphere.
- the hydrogen concentration in the atmosphere was basically 10 vol%.
- TS and El were measured with respect to the obtained test material in accordance with JIS Z 2241 Metal Material Tensile Test Method.
- the chemical conversion property and corrosion resistance were investigated with respect to the obtained test material.
- the amount of oxide (internal oxidation amount) present in the steel sheet surface layer up to 100 ⁇ m just below the steel sheet surface layer was measured. The measurement method and evaluation criteria are shown below.
- Corrosion resistance after electrodeposition coating A test piece having a size of 70 mm x 150 mm was cut out from the test material subjected to chemical conversion treatment obtained by the above method, and cation electrodeposition was performed using PN-150G (registered trademark) manufactured by Nippon Paint Co., Ltd. Coating (baking conditions: 170 ° C. ⁇ 20 minutes, film thickness 25 ⁇ m) was performed. Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material.
- PN-150G registered trademark
- Coating (baking conditions: 170 ° C. ⁇ 20 minutes, film thickness 25 ⁇ m) was performed. Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material.
- a JIS No. 5 tensile test piece is taken from the sample in a direction of 90 ° with respect to the rolling direction, and a tensile test is performed at a constant crosshead speed of 10 mm / min in accordance with the provisions of JIS Z 2241.
- (TS / MPa) and elongation (El%) were measured, and when TS was less than 650 MPa, TS ⁇ El ⁇ 22000 was judged good and TS ⁇ El ⁇ 22000 was judged poor.
- TS was 650 MPa or more and 900 MPa
- TS ⁇ El ⁇ 20000 was judged good, and TS ⁇ El ⁇ 20000 was judged poor.
- TS was 900 MPa or more, TS ⁇ El ⁇ 18000 was judged good, and TS ⁇ El ⁇ 18000 was judged poor.
- the internal oxidation amount in the region up to 100 ⁇ m of the steel sheet surface layer is measured by “impulse furnace melting-infrared absorption method”.
- the surface layer portions on both surfaces of the high-strength steel plate after continuous annealing are polished by 100 ⁇ m or more in the steel.
- Measure the oxygen concentration set the measured value as the amount of oxygen OH contained in the material, measure the oxygen concentration in the steel in the entire thickness direction of the high-strength steel sheet after continuous annealing, and measure the measured value internally.
- the subsequent oxygen amount OI was used.
- single-sided unit area i.e. 1 m 2
- the high-strength steel sheet produced by the method of the present invention is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si and Mn, but the chemical conversion treatment property, electrodeposition It can be seen that it has excellent corrosion resistance and workability after painting. On the other hand, in the comparative example, any one or more of chemical conversion property, corrosion resistance after electrodeposition coating, and workability is inferior.
- the high-strength steel sheet of the present invention is excellent in chemical conversion property, corrosion resistance, and workability, and can be used as a surface-treated steel sheet for reducing the weight and strength of an automobile body.
- the steel sheet can be applied in a wide range of fields such as home appliances and building materials as a surface-treated steel sheet provided with rust prevention.
Abstract
Description
一般に自動車用鋼板は塗装して使用されており、その塗装の前処理として、リン酸塩処理と呼ばれる化成処理が施される。鋼板の化成処理は塗装後の耐食性を確保するための重要な処理の一つである。 In recent years, from the viewpoint of improving the fuel efficiency of automobiles and improving the collision safety of automobiles, there is an increasing demand for reducing the thickness of the vehicle body by increasing the strength of the vehicle body material and reducing the weight of the vehicle body. Therefore, application of high-strength steel sheets to automobiles is being promoted.
In general, steel plates for automobiles are used after being coated, and as a pretreatment for the coating, a chemical conversion treatment called a phosphate treatment is performed. The chemical conversion treatment of the steel sheet is one of the important treatments for ensuring the corrosion resistance after painting.
本発明は上記知見に基づくものであり、特徴は以下の通りである。 And the high-strength steel plate obtained by the above method has Fe, Si, Mn, Al, P, and also B, Nb, Ti, Cr, Mo, Cu, Ni on the steel plate surface layer portion within 100 μm from the steel plate surface. At least one oxide selected from the inside is formed in an amount of 0.010 to 0.50 g / m 2 per side, and in the region from the steel plate surface to 10 μm, crystalline Si is present in the iron grains within 1 μm from the grain boundary. The structure and structure in which Mn-based oxides are deposited are obtained. As a result, the deterioration of the corrosion resistance after electrodeposition coating can be realized and the chemical conversion processability is excellent.
The present invention is based on the above findings, and features are as follows.
焼鈍炉内の加熱過程で、加熱炉内温度:A℃以上B℃以下(A:600≦A≦780、B:800≦B≦900)の限定された温度域において、雰囲気の露点を−10℃以上となるように制御して連続焼鈍した後化成処理することで、鋼板表層10μm以内の内部に易酸化性元素(Si、Mnなど)の酸化物(以下、内部酸化と称する)を適量に存在させ、焼鈍後の化成処理性を劣化させる鋼中Si、Mn等の鋼板表層における選択的表面酸化(以後、表面濃化と称する)を抑制することが可能となる。 First, annealing atmosphere conditions that determine the structure of the steel sheet surface, which is the most important requirement in the present invention, will be described.
In the heating process in the annealing furnace, the dew point of the atmosphere is −10 in the limited temperature range of the heating furnace temperature: A ° C. or higher and B ° C. or lower (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900). By performing chemical conversion treatment after continuous annealing controlled to be at or above ° C., an appropriate amount of oxides of oxidizable elements (Si, Mn, etc.) (hereinafter referred to as internal oxidation) within the steel sheet surface layer within 10 μm. It is possible to suppress the selective surface oxidation (hereinafter referred to as surface concentration) in the steel sheet surface layer of Si, Mn, etc. in steel, which is present and deteriorates the chemical conversion property after annealing.
Cは、鋼組織としてマルテンサイトなどを形成させることで加工性を向上させる。そのためには0.01%以上必要である。一方、0.18%を超えると伸びが低下し材質が劣化し、さらに溶接性が劣化する。したがって、C量は0.01%以上0.18%以下とする。 C: 0.01 to 0.18%
C improves workability by forming martensite or the like as a steel structure. For that purpose, 0.01% or more is necessary. On the other hand, if it exceeds 0.18%, the elongation is reduced, the material is deteriorated, and the weldability is further deteriorated. Therefore, the C content is 0.01% or more and 0.18% or less.
Siは鋼を強化し伸びを向上させ良好な材質を得るのに有効な元素であり、本発明の目的とする強度を得るためには0.4%以上が必要である。Siが0.4%未満では本発明の適用範囲とする強度が得られず、化成処理性についても特に問題とならない。一方、2.0%を超えると鋼の強化能や伸び向上効果が飽和してくる。さらに、化成処理性の改善が困難になってくる。したがって、Si量は0.4%以上2.0%以下とする。 Si: 0.4 to 2.0%
Si is an element effective for strengthening steel and improving elongation to obtain a good material, and 0.4% or more is necessary to obtain the intended strength of the present invention. If Si is less than 0.4%, the strength within the scope of the present invention cannot be obtained, and there is no particular problem with chemical conversion treatment. On the other hand, when it exceeds 2.0%, the steel strengthening ability and the effect of improving elongation become saturated. Furthermore, it becomes difficult to improve the chemical conversion processability. Therefore, the Si amount is set to 0.4% or more and 2.0% or less.
Mnは鋼の高強度化に有効な元素である。機械特性や強度を確保するためは1.0%以上含有させることが必要である。一方、3.0%を超えると溶接性や、強度と延性のバランスの確保が困難になる。したがって、Mn量は1.0%以上3.0%以下とする。 Mn: 1.0 to 3.0%
Mn is an element effective for increasing the strength of steel. In order to ensure mechanical properties and strength, it is necessary to contain 1.0% or more. On the other hand, if it exceeds 3.0%, it becomes difficult to secure weldability and the balance between strength and ductility. Therefore, the Mn content is 1.0% or more and 3.0% or less.
Alは溶鋼の脱酸を目的に添加される。溶鋼の脱酸の効果は0.001%以上で得られる。一方、1.0%を超えるとコストアップになる。さらに、Alの表面濃化が多くなり、化成処理性の改善が困難になってくる。したがって、Al量は0.001%以上1.0%以下とする。 Al: 0.001 to 1.0%
Al is added for the purpose of deoxidizing molten steel. The effect of deoxidation of molten steel is obtained at 0.001% or more. On the other hand, if it exceeds 1.0%, the cost increases. Furthermore, the surface concentration of Al increases and it becomes difficult to improve chemical conversion properties. Therefore, the Al content is 0.001% or more and 1.0% or less.
Pは不可避的に含有される元素のひとつであり、0.005%未満にするためには、コストの増大が懸念されるため、0.005%以上とする。一方、Pが0.060%を超えて含有されると溶接性が劣化する。さらに、化成処理性の劣化が激しくなり、本発明をもってしても化成処理性を向上させることが困難となる。したがって、P量は0.005%以上0.060%以下とする。 P: 0.005 to 0.060% or less P is an element inevitably contained, and in order to make it less than 0.005%, there is a concern about an increase in cost, so 0.005% or more And On the other hand, if P exceeds 0.060%, weldability deteriorates. Furthermore, the chemical conversion processability is greatly deteriorated, and even with the present invention, it is difficult to improve the chemical conversion processability. Therefore, the P content is 0.005% or more and 0.060% or less.
Sは不可避的に含有される元素のひとつである。下限は規定しないが、多量に含有されると溶接性及び耐食性が劣化するため0.01%以下とする。 S ≦ 0.01%
S is one of the elements inevitably contained. The lower limit is not specified, but if it is contained in a large amount, the weldability and corrosion resistance deteriorate, so the content is made 0.01% or less.
これらの元素を添加する場合における適正添加量の限定理由は以下の通りである。 In order to control the balance between strength and ductility, B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001 Requires one or more elements selected from -1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0% It may be added depending on.
The reason for limiting the appropriate addition amount in the case of adding these elements is as follows.
Bは0.001%未満では焼き入れ促進効果が得られにくい。一方、0.005%超えでは化成処理性が劣化する。よって、含有する場合、B量は0.001%以上0.005%以下とする。 B: 0.001 to 0.005%
When B is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 0.005%, chemical conversion processability deteriorates. Therefore, when it contains, B amount shall be 0.001% or more and 0.005% or less.
Nbは0.005%未満では強度調整の効果が得られにくい。一方、0.05%超えではコストアップを招く。よって、含有する場合、Nb量は0.005%以上0.05%以下とする。 Nb: 0.005 to 0.05%
If Nb is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when it contains, Nb amount shall be 0.005% or more and 0.05% or less.
Tiは0.005%未満では強度調整の効果が得られにくい。一方、0.05%超えでは化成処理性の劣化を招く。よって、含有する場合、Ti量は0.005%以上0.05%以下とする。 Ti: 0.005 to 0.05%
If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, chemical conversion processability is deteriorated. Therefore, when it contains, Ti amount shall be 0.005% or more and 0.05% or less.
Crは0.001%未満では焼き入れ促進効果が得られにくい。一方、1.0%超えではCrが表面濃化するため、溶接性が劣化する。よって、含有する場合、Cr量は0.001%以上1.0%以下とする。 Cr: 0.001 to 1.0%
When Cr is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 1.0%, the surface of Cr is concentrated, so that the weldability is deteriorated. Therefore, when it contains, Cr amount shall be 0.001% or more and 1.0% or less.
Moは0.05%未満では強度調整の効果が得られにくい。一方、1.0%超えではコストアップを招く。よって、含有する場合、Mo量は0.05%以上1.0%以下とする。 Mo: 0.05 to 1.0%
If Mo is less than 0.05%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Mo content is 0.05% or more and 1.0% or less.
Cuは0.05%未満では残留γ相形成促進効果が得られにくい。一方、1.0%超えではコストアップを招く。よって、含有する場合、Cu量は0.05%以上1.0%以下とする。 Cu: 0.05 to 1.0%
If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Cu content is 0.05% or more and 1.0% or less.
Niは0.05%未満では残留γ相形成促進効果が得られにくい。一方、1.0%超えではコストアップを招く。よって、含有する場合、Ni量は0.05%以上1.0%以下とする。
上記以外の残部はFeおよび不可避的不純物である。 Ni: 0.05 to 1.0%
If Ni is less than 0.05%, the effect of promoting the formation of residual γ phase is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when it contains, Ni amount shall be 0.05% or more and 1.0% or less.
The balance other than the above is Fe and inevitable impurities.
例えば、上記化学成分を有する鋼を熱間圧延した後、冷間圧延し、次いで、連続式焼鈍設備において焼鈍を行った後、化成処理を行う。なお、この時、本発明においては、焼鈍時の加熱過程では、加熱炉内温度:A℃以上B℃以下(A:600≦A≦780、B:800≦B≦900)の温度域を雰囲気の露点:−10℃以上で行うこととする。これは本発明において、最も重要な要件である。このように焼鈍工程において露点、すなわち雰囲気中酸素分圧を制御することで、酸素ポテンシャルを高め易酸化性元素であるSiやMn等が化成処理直前に予め内部酸化し鋼板表層部におけるSi、Mnの活量が低下する。そして、これらの元素の外部酸化が抑制され、結果的に化成処理性が改善することになる。また、上記において、熱間圧延終了後、冷間圧延を施さずに、そのまま焼鈍を行う場合もある。 Next, the manufacturing method of the high strength steel plate of the present invention and the reason for limitation will be described.
For example, the steel having the above chemical components is hot-rolled, cold-rolled, and then annealed in a continuous annealing facility, followed by chemical conversion treatment. At this time, in the present invention, in the heating process at the time of annealing, the temperature in the heating furnace: A ° C. or higher and B ° C. or lower (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900) Dew point: -10 ° C or higher. This is the most important requirement in the present invention. In this way, by controlling the dew point, that is, the oxygen partial pressure in the atmosphere in the annealing process, the oxygen potential is increased and the easily oxidizable elements such as Si and Mn are internally oxidized in advance immediately before the chemical conversion treatment, and Si and Mn in the steel sheet surface layer portion. The activity of is reduced. And external oxidation of these elements is suppressed, and as a result, chemical conversion property improves. In the above, after the hot rolling, annealing may be performed as it is without performing cold rolling.
通常、行われる条件にて行うことができる。 Hot rolling Usually, it can be performed on the conditions performed.
熱間圧延後は酸洗処理を行うのが好ましい。酸洗工程で表面に生成した黒皮スケールを除去し、しかる後冷間圧延する。なお、酸洗条件は特に限定しない。 It is preferable to perform a pickling treatment after hot pickling. The black scale formed on the surface in the pickling process is removed, and then cold-rolled. The pickling conditions are not particularly limited.
40%以上80%以下の圧下率で行うことが好ましい。圧下率が40%未満では再結晶温度が低温化するため、機械特性が劣化しやすい。一方、圧下率が80%超えでは高強度鋼板であるため、圧延コストがアップするだけでなく、焼鈍時の表面濃化が増加するため、化成処理性が劣化する場合がある。 Cold rolling is preferably performed at a rolling reduction of 40% to 80%. If the rolling reduction is less than 40%, the recrystallization temperature is lowered, and the mechanical characteristics are likely to deteriorate. On the other hand, if the rolling reduction exceeds 80%, the steel sheet is a high-strength steel plate, so that not only the rolling cost is increased, but also the surface concentration during annealing is increased, so that the chemical conversion property may be deteriorated.
そして、上述したように、加熱炉内温度:A℃以上B℃以下(A:600≦A≦780、B:800≦B≦900)の温度域において、雰囲気の露点が−10℃以上となるように制御して焼鈍を行う。A℃以上B℃以下の領域以外の焼鈍炉内雰囲気の露点は特に限定されないが、好ましくは−50℃~−10℃の範囲が望ましい。 In the annealing furnace, a heating process is performed in which the steel sheet is heated to a predetermined temperature in a preceding heating zone, and a soaking process is performed in which the temperature is maintained at a predetermined temperature for a predetermined time in a subsequent soaking zone. Next, a cooling process is performed.
Then, as described above, the dew point of the atmosphere becomes −10 ° C. or higher in the temperature range of the heating furnace temperature: A ° C. or higher and B ° C. or lower (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900). Annealing is performed in such a manner as to control. The dew point of the atmosphere in the annealing furnace other than the region of A ° C. or higher and B ° C. or lower is not particularly limited, but is preferably in the range of −50 ° C. to −10 ° C.
750℃以上の温度域から冷却後、必要に応じて焼入れ、焼き戻しを行っても良い。この条件は特に限定しないが、焼き戻しは150~400℃の温度で行うのが望ましい。150℃未満では伸びが劣化する傾向にあり、400℃超えでは硬度が低下する傾向にあるためである。 The gas component in the annealing furnace consists of nitrogen, hydrogen and unavoidable impurities. Other gas components may be included as long as the effects of the present invention are not impaired. If the hydrogen concentration in the atmosphere in the annealing furnace is less than 1 vol%, the activation effect by reduction cannot be obtained and the chemical conversion treatment performance deteriorates. The upper limit is not particularly specified, but if it exceeds 50 vol%, the cost increases and the effect is saturated. Therefore, the hydrogen concentration is preferably 1 vol% or more and 50 vol% or less. In addition, the gaseous component in an annealing furnace consists of nitrogen gas and an unavoidable impurity gas other than hydrogen gas. Other gas components may be included as long as the effects of the present invention are not impaired.
After cooling from a temperature range of 750 ° C. or higher, quenching and tempering may be performed as necessary. This condition is not particularly limited, but tempering is preferably performed at a temperature of 150 to 400 ° C. This is because the elongation tends to deteriorate when the temperature is lower than 150 ° C., and the hardness tends to decrease when the temperature exceeds 400 ° C.
電解酸洗の条件は特に限定しないが、焼鈍後に形成された不可避的に表面濃化したSiやMnの酸化物を効率的に除去するため、電流密度が1A/dm2以上の交番電解とすることが望ましい。交番電解とする理由は、鋼板を陰極に保持したままでは酸洗効果が小さく、逆に鋼板を陽極に保持したままでは電解時に溶出するFeが酸洗液中に蓄積し、酸洗液中のFe濃度が増大してしまい、鋼板表面に付着すると乾き汚れ等の問題が発生してしまうためである。 In the present invention, good chemical conversion treatment can be ensured without carrying out electrolytic pickling, but a small amount of surface condensate inevitably generated during annealing is removed to ensure better chemical conversion treatment. For the purpose, it is preferable to perform electrolytic pickling.
The conditions of the electrolytic pickling are not particularly limited, but in order to efficiently remove the inevitably surface-enriched Si and Mn oxides formed after annealing, an alternating electrolysis with a current density of 1 A / dm 2 or more is used. It is desirable. The reason for alternating electrolysis is that the pickling effect is small when the steel plate is held at the cathode, and conversely, Fe that is eluted during electrolysis accumulates in the pickling solution while the steel plate is held at the anode. This is because if the Fe concentration increases and adheres to the surface of the steel sheet, problems such as dry dirt occur.
そして、以下のように、鋼板表面の構造に特徴を有することになる。
鋼板表面から100μm以内の鋼板表層部には、Fe、Si、Mn、Al、P、さらには、B、Nb、Ti、Cr、Mo、Cu、Niの中から選ばれる1種以上の酸化物が合計で片面あたり0.010~0.50g/m2形成される。また、鋼板表面から10μmまでの領域においては、粒界から1μm以内の地鉄粒内に結晶性Si、Mn系複合酸化物が存在する。 As described above, the high-strength steel sheet of the present invention is obtained.
And it has the characteristic in the structure of the steel plate surface as follows.
On the steel sheet surface layer portion within 100 μm from the steel sheet surface, Fe, Si, Mn, Al, P, and further one or more oxides selected from B, Nb, Ti, Cr, Mo, Cu, and Ni are contained. A total of 0.010 to 0.50 g / m 2 is formed per side. Further, in the region from the steel plate surface to 10 μm, crystalline Si and Mn-based composite oxide exist in the ground iron grains within 1 μm from the grain boundary.
表1に示す鋼組成からなる熱延鋼板を酸洗し、黒皮スケールを除去した後、冷間圧延し、厚さ1.0mmの冷延鋼板を得た。なお、一部は冷間圧延を実施せず、黒皮スケール除去後の熱延鋼板(厚さ2.0mm)ままのものも用意した。 Hereinafter, the present invention will be specifically described based on examples.
The hot-rolled steel sheet having the steel composition shown in Table 1 was pickled, and after removing the black scale, it was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some did not carry out cold rolling, but prepared the hot-rolled steel plate (thickness 2.0 mm) after removing the black scale.
得られた供試材に対してJIS Z 2241 金属材料引張試験方法 に従い、TS、Elを測定した。また、得られた供試材に対して、化成処理性及び耐食性を調査した。鋼板表層直下の100μmまので鋼板表層部に存在する酸化物の量(内部酸化量)を測定した。測定方法および評価基準を下記に示す。
TS and El were measured with respect to the obtained test material in accordance with JIS Z 2241 Metal Material Tensile Test Method. Moreover, the chemical conversion property and corrosion resistance were investigated with respect to the obtained test material. The amount of oxide (internal oxidation amount) present in the steel sheet surface layer up to 100 μm just below the steel sheet surface layer was measured. The measurement method and evaluation criteria are shown below.
化成処理性の評価方法を以下に記載する。
化成処理液は日本パーカライジング(株)製の化成処理液(パルボンドL3080(登録商標))を用い、下記方法で化成処理を施した。
日本パーカライジング(株)製の脱脂液ファインクリーナー(登録商標)で脱脂したのち、水洗し、次に日本パーカライジング(株)製の表面調整液プレパレンZ(登録商標)で30s表面調整を行い、43℃の化成処理液(パルボンドL3080)に120s浸漬した後、水洗し、温風乾燥した。
化成処理後の供試材を走査型電子顕微鏡(SEM)で倍率500倍で無作為に5視野を観察し、化成処理皮膜のスケ面積率を画像処理により測定し、スケ面積率によって以下の評価を行った。○が合格レベルである。
○:10%以下
×:10%超 The chemical conversion property evaluation method of chemical conversion property is described below.
A chemical conversion treatment liquid (Palbond L3080 (registered trademark)) manufactured by Nihon Parkerizing Co., Ltd. was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed by the following method.
After degreasing with a degreasing liquid Fine Cleaner (registered trademark) manufactured by Nihon Parkerizing Co., Ltd., washing with water, and then adjusting the surface for 30 s with surface conditioning solution preparen Z (registered trademark) manufactured by Nihon Parkerizing Co., Ltd. After being immersed in a chemical conversion treatment solution (Palbond L3080) for 120 s, it was washed with water and dried with warm air.
The sample after the chemical conversion treatment was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, the scale area ratio of the chemical conversion film was measured by image processing, and the following evaluation was made based on the scale area ratio. Went. ○ is an acceptable level.
○: 10% or less ×: Over 10%
上記の方法で得られた化成処理を施した供試材より寸法70mm×150mmの試験片を切り出し、日本ペイント(株)製のPN−150G(登録商標)でカチオン電着塗装(焼付け条件:170℃×20分、膜厚25μm)を行った。その後、端部と評価しない側の面をAlテープでシールし、カッターナイフにて地鉄に達するクロスカット(クロス角度60°)を入れ、供試材とした。
次に、供試材を5質量%NaCl水溶液(55℃)中に、240時間浸漬後に取り出し、水洗、乾燥後にクロスカット部をテープ剥離し、剥離幅を測定し、以下の評価を行った。○が合格レベルである。
○:剥離幅が片側2.5mm未満
×:剥離幅が片側2.5mm以上 Corrosion resistance after electrodeposition coating A test piece having a size of 70 mm x 150 mm was cut out from the test material subjected to chemical conversion treatment obtained by the above method, and cation electrodeposition was performed using PN-150G (registered trademark) manufactured by Nippon Paint Co., Ltd. Coating (baking conditions: 170 ° C. × 20 minutes, film thickness 25 μm) was performed. Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material.
Next, the test material was taken out after being immersed in a 5% by mass NaCl aqueous solution (55 ° C.) for 240 hours, washed with water and dried, and then the tape was peeled off, the peel width was measured, and the following evaluation was performed. ○ is an acceptable level.
○: Peel width is less than 2.5 mm on one side ×: Peel width is 2.5 mm or more on one side
加工性は、試料から圧延方向に対して90°方向にJIS5号引張試験片を採取し、JIS Z 2241の規定に準拠してクロスヘッド速度10mm/min一定で引張試験を行い、引張り強度(TS/MPa)と伸び(El%)を測定し、TSが650MPa未満の場合は、TS×El≧22000のものを良好、TS×El<22000のものを不良とした。TSが650MPa以上900MPaの場合は、TS×El≧20000のものを良好、TS×El<20000のものを不良とした。TSが900MPa以上の場合は、TS×El≧18000のものを良好、TS×El<18000のものを不良とした。 Workability As for workability, a JIS No. 5 tensile test piece is taken from the sample in a direction of 90 ° with respect to the rolling direction, and a tensile test is performed at a constant crosshead speed of 10 mm / min in accordance with the provisions of JIS Z 2241. (TS / MPa) and elongation (El%) were measured, and when TS was less than 650 MPa, TS × El ≧ 22000 was judged good and TS × El <22000 was judged poor. When TS was 650 MPa or more and 900 MPa, TS × El ≧ 20000 was judged good, and TS × El <20000 was judged poor. When TS was 900 MPa or more, TS × El ≧ 18000 was judged good, and TS × El <18000 was judged poor.
内部酸化量は、「インパルス炉溶融−赤外線吸収法」により測定する。ただし、素材(すなわち焼鈍を施す前の高強度鋼板)に含まれる酸素量を差し引く必要があるので、本発明では、連続焼鈍後の高強度鋼板の両面の表層部を100μm以上研磨して鋼中酸素濃度を測定し、その測定値を素材に含まれる酸素量OHとし、また、連続焼鈍後の高強度鋼板の板厚方向全体での鋼中酸素濃度を測定して、その測定値を内部酸化後の酸素量OIとした。このようにして得られた高強度鋼板の内部酸化後の酸素量OIと、素材に含まれる酸素量OHとを用いて、OIとOHの差(=OI−OH)を算出し、さらに片面単位面積(すなわち1m2)当たりの量に換算した値(g/m2)を内部酸化量とした。
以上により得られた結果を製造条件と併せて表2に示す。 The internal oxidation amount in the region up to 100 μm of the steel sheet surface layer is measured by “impulse furnace melting-infrared absorption method”. However, since it is necessary to subtract the amount of oxygen contained in the material (that is, the high-strength steel plate before annealing), in the present invention, the surface layer portions on both surfaces of the high-strength steel plate after continuous annealing are polished by 100 μm or more in the steel. Measure the oxygen concentration, set the measured value as the amount of oxygen OH contained in the material, measure the oxygen concentration in the steel in the entire thickness direction of the high-strength steel sheet after continuous annealing, and measure the measured value internally. The subsequent oxygen amount OI was used. The difference between OI and OH (= OI-OH) is calculated using the oxygen amount OI after internal oxidation of the high-strength steel plate thus obtained and the oxygen amount OH contained in the material, and further, single-sided unit area (i.e. 1 m 2) value converted into the amount per (g / m 2) as an internal oxide amount.
The results obtained as described above are shown in Table 2 together with the production conditions.
一方、比較例では、化成処理性、電着塗装後の耐食性、加工性のいずれか一つ以上が劣る。 As is apparent from Table 2, the high-strength steel sheet produced by the method of the present invention is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si and Mn, but the chemical conversion treatment property, electrodeposition It can be seen that it has excellent corrosion resistance and workability after painting.
On the other hand, in the comparative example, any one or more of chemical conversion property, corrosion resistance after electrodeposition coating, and workability is inferior.
Claims (4)
- 質量%で、C:0.01~0.18%、Si:0.4~2.0%、Mn:1.0~3.0%、Al:0.001~1.0%、P:0.005~0.060%、S≦0.01%を含有し、残部がFeおよび不可避的不純物からなる鋼板に、連続焼鈍を施す際に、
加熱過程では、加熱炉内温度:A℃以上B℃以下の温度域を雰囲気の露点:−10℃以上で行うことを特徴とする高強度鋼板の製造方法。ただし、A:600≦A≦780、B:800≦B≦900である。 By mass%, C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0%, P: When steel plate containing 0.005 to 0.060%, S ≦ 0.01%, the balance being Fe and inevitable impurities, is subjected to continuous annealing,
In the heating process, a method for producing a high-strength steel sheet, characterized in that the temperature in the furnace is A ° C. or higher and B ° C. or lower at a dew point of the atmosphere: −10 ° C. However, A: 600 ≦ A ≦ 780 and B: 800 ≦ B ≦ 900. - 前記鋼板は、成分組成として、質量%で、さらに、B:0.001~0.005%、Nb:0.005~0.05%、Ti:0.005~0.05%、Cr:0.001~1.0%、Mo:0.05~1.0%、Cu:0.05~1.0%、Ni:0.05~1.0%の中から選ばれる1種以上の元素を含有することを特徴とする請求項1に記載の高強度鋼板の製造方法。 The steel sheet has a component composition in mass%, and B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0 One or more elements selected from 0.001 to 1.0%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ni: 0.05 to 1.0% The manufacturing method of the high strength steel plate of Claim 1 characterized by the above-mentioned.
- 前記連続焼鈍を行った後、硫酸を含む水溶液中で電解酸洗を行うことを特徴とする請求項1または2に記載の高強度鋼板の製造方法。 The method for producing a high-strength steel sheet according to claim 1 or 2, wherein after the continuous annealing, electrolytic pickling is performed in an aqueous solution containing sulfuric acid.
- 請求項1~3のいずれか一項に記載の製造方法により製造され、鋼板表面から100μm以内の鋼板表層部にFe、Si、Mn、Al、P、B、Nb、Ti、Cr、Mo、Cu、Niの中から選ばれる少なくとも1種以上の酸化物を、片面あたり0.010~0.50g/m2形成し、更に、鋼板表面から10μm以内の領域において、鋼板結晶粒界から1μm以内の粒内に結晶性Si、Mn系酸化物が存在していることを特徴とする高強度鋼板。 It is manufactured by the manufacturing method according to claim 1, and Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu are formed on a steel plate surface layer portion within 100 μm from the steel plate surface. In addition, at least one oxide selected from Ni is formed in an amount of 0.010 to 0.50 g / m 2 per side, and in a region within 10 μm from the surface of the steel plate, within 1 μm from the grain boundary of the steel plate. A high-strength steel sheet characterized by the presence of crystalline Si and Mn-based oxides in the grains.
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US10837074B2 (en) | 2012-03-19 | 2020-11-17 | Jfe Steel Corporation | Method for manufacturing high strength galvanized steel sheet and high strength galvanized steel sheet |
WO2014136412A1 (en) * | 2013-03-04 | 2014-09-12 | Jfeスチール株式会社 | High-strength steel sheet, method for manufacturing same, high-strength molten-zinc-plated steel sheet, and method for manufacturing same |
CN105026600A (en) * | 2013-03-04 | 2015-11-04 | 杰富意钢铁株式会社 | High-strength steel sheet, method for manufacturing same, high-strength molten-zinc-plated steel sheet, and method for manufacturing same |
CN105026600B (en) * | 2013-03-04 | 2018-04-06 | 杰富意钢铁株式会社 | High-strength steel sheet and its manufacture method and high-strength hot-dip zinc-coated steel sheet and its manufacture method |
US10174411B2 (en) | 2013-03-04 | 2019-01-08 | Jfe Steel Corporation | High-strength steel sheet and production method therefor and high-strength galvanized steel sheet and production method therefor (as amended) |
JP2014169487A (en) * | 2013-03-05 | 2014-09-18 | Jfe Steel Corp | Method of producing high strength hot-dip galvanized steel sheet and high strength hot-dip galvanized steel sheet |
US10301701B2 (en) | 2014-02-18 | 2019-05-28 | Jfe Steel Corporation | High-strength hot-dip galvanized steel sheet and method for producing same |
JP2019531408A (en) * | 2016-08-30 | 2019-10-31 | 宝山鋼鉄股▲分▼有限公司 | Cold-rolled high-strength steel sheet with excellent phosphatability and formability and method for producing the same |
JP2019531409A (en) * | 2016-08-30 | 2019-10-31 | 宝山鋼鉄股▲分▼有限公司 | Cold-rolled high-strength steel sheet having excellent phosphatability and formability and method for producing the same |
Also Published As
Publication number | Publication date |
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CA2811489A1 (en) | 2012-04-05 |
EP2623631A1 (en) | 2013-08-07 |
CN103154297B (en) | 2016-05-18 |
CN103154297A (en) | 2013-06-12 |
EP2623631A4 (en) | 2016-11-23 |
BR112013007163A2 (en) | 2016-06-14 |
EP2623631B1 (en) | 2022-11-02 |
US20130327452A1 (en) | 2013-12-12 |
KR20130049820A (en) | 2013-05-14 |
CA2811489C (en) | 2016-11-22 |
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