WO2016152870A1 - 熱延鋼板及びその製造方法、並びに冷延鋼板の製造方法 - Google Patents
熱延鋼板及びその製造方法、並びに冷延鋼板の製造方法 Download PDFInfo
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- WO2016152870A1 WO2016152870A1 PCT/JP2016/059027 JP2016059027W WO2016152870A1 WO 2016152870 A1 WO2016152870 A1 WO 2016152870A1 JP 2016059027 W JP2016059027 W JP 2016059027W WO 2016152870 A1 WO2016152870 A1 WO 2016152870A1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 187
- 239000010959 steel Substances 0.000 title claims abstract description 187
- 238000004519 manufacturing process Methods 0.000 title claims description 24
- 239000010960 cold rolled steel Substances 0.000 title claims description 16
- 239000010410 layer Substances 0.000 claims abstract description 170
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 148
- 239000013078 crystal Substances 0.000 claims abstract description 122
- 239000000463 material Substances 0.000 claims abstract description 48
- 229910052742 iron Inorganic materials 0.000 claims abstract description 47
- 239000002344 surface layer Substances 0.000 claims abstract description 12
- 238000005554 pickling Methods 0.000 claims description 94
- 229910004283 SiO 4 Inorganic materials 0.000 claims description 63
- 238000004804 winding Methods 0.000 claims description 36
- 238000005098 hot rolling Methods 0.000 claims description 34
- 238000000034 method Methods 0.000 claims description 33
- 238000005097 cold rolling Methods 0.000 claims description 26
- 229910021486 amorphous silicon dioxide Inorganic materials 0.000 claims description 20
- 230000008569 process Effects 0.000 claims description 13
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- 229910052761 rare earth metal Inorganic materials 0.000 claims description 11
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 14
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- 239000000956 alloy Substances 0.000 description 3
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- CWYNVVGOOAEACU-UHFFFAOYSA-N iron (II) ion Substances [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
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- OKIZCWYLBDKLSU-UHFFFAOYSA-M N,N,N-Trimethylmethanaminium chloride Chemical compound [Cl-].C[N+](C)(C)C OKIZCWYLBDKLSU-UHFFFAOYSA-M 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
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- 230000002411 adverse Effects 0.000 description 1
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- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/001—Heat treatment of ferrous alloys containing Ni
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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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
- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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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
- 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
- C21D8/0463—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 following hot rolling
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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
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by hot-rolling
Definitions
- the present invention relates to a steel sheet having a high Si and Mn content, hot-rolled steel sheet capable of shortening the pickling time of the steel sheet rolled up by hot rolling, a method for producing the same, and cold-rolling the hot-rolled steel sheet
- the present invention relates to a method for manufacturing a cold-rolled steel sheet.
- High-strength steel sheets used as skeleton materials for automobiles generally contain a large amount of Si and Mn in order to achieve both high strength and high ductility.
- metallic iron is used as the main parent phase for the ground iron directly below the oxide scale of the steel sheet surface layer portion.
- Si-based oxides are generated in the crystal grain boundaries and in the crystal grains. The generation of the oxide is called so-called internal oxidation, and usually occurs at a thickness of several ⁇ m to several tens of ⁇ m.
- a layer containing the oxide generated by internal oxidation (hereinafter referred to as “internal oxide layer”) has poor pickling property because the main component of the parent phase is metallic iron. For this reason, the internal oxidation layer cannot be removed with a pickling time equivalent to that of a general hot-rolled steel sheet having only an oxide scale, and several times the pickling time is required, so the productivity of the hot-rolled steel sheet is significantly reduced. To do. In addition, if cold rolling is performed without removing the internal oxide layer, the remaining internal oxide layer may be peeled off, causing cracks and deterioration of chemical conversion or forming a pickup on the surface of the hearth roll during annealing. It becomes.
- Internal oxidation occurs when the activity of the easily oxidizable element is high and exists under a specific oxygen potential, such as containing a certain amount of easily oxidizable elements Si and Mn in the steel material.
- a high-strength steel sheet in which internal oxidation occurs usually contains approximately 0.5 mass% or more of Si and 0.5 mass% or more of Mn.
- the oxide scale of the steel sheet surface layer portion produced by hot rolling becomes an oxygen source for internal oxidation.
- the temperature is a driving force for internal oxidation. Therefore, if the coiling temperature is high, the internal oxidation tends to be thicker.
- a Si oxide layer containing Fe and Mn may be formed at the interface between the oxide scale and the internal oxide layer, but this Si oxide layer can be handled as a part of the oxide scale.
- a Si ⁇ Mn-based oxide 21 of about 5 ⁇ m or more generated immediately below the scale layer of a hot-rolled steel sheet is used as a grain boundary 22.
- the grain boundary oxide layer and the internal oxide layer 20 in which the Si ⁇ Mn-based oxide 21 is precipitated in the metal matrix 23 are appropriately removed by pickling after hot rolling, and high strength cold rolling is performed. Techniques have been proposed that can effectively prevent poor chemical conversion properties of steel sheets. In this technique, the necessary pickling time is derived from the thickness of the grain boundary oxide layer and the dissolution time of the oxide scale layer.
- the grain boundary The oxide layer needs to be pickled for 90 seconds or longer at 10 ⁇ m, 135 seconds or longer for 10 ⁇ m, 180 seconds or longer for 15 ⁇ m, and 225 seconds or longer for 20 ⁇ m.
- this technique requires several times longer than the pickling time of a general hot-rolled steel sheet that requires only an oxide scale, a significant reduction in productivity is inevitable.
- Patent Document 2 although not a high-strength steel sheet with high Si and high Mn content, an antioxidant is applied to the surface of steel pieces of high nickel steel and high nickel-chromium steel containing 5 mass% or more of nickel.
- a technique has been proposed in which part or all of the surface is covered with a steel plate to prevent grain boundary oxidation during heating and to prevent ear cracks during hot rolling.
- this technique cannot be expected to suppress internal oxidation including grain boundary oxidation in a temperature range of 500 to 800 ° C. such as a steel sheet rolled by hot rolling.
- Patent Document 3 discloses a technique in which a hot-rolled Si-containing steel sheet is heat-treated at 700 ° C. or higher for 5 to 60 minutes in a nitrogen atmosphere in which O 2 is controlled to be less than 1% by volume.
- O 2 is controlled to be less than 1% by volume.
- the supply of oxygen to the surface of the steel sheet is suppressed to suppress the growth of oxide scale, and furthermore, the oxygen is sufficiently diffused from the oxide scale to the ground iron, thereby oxidizing the surface layer portion of the steel sheet.
- Si and Mn deficient layers are formed in the grain boundary oxidation part formed in the base iron directly under the scale.
- Patent Documents 4 to 6 disclose the shape of the internal oxide. However, none of the inventions disclosed in Patent Documents 4 to 6 are intended to improve pickling performance.
- JP 2013-237924 A Japanese Patent Publication No.63-11083 Japanese Patent No. 5271981 Japanese Patent No. 5315795 Japanese Patent No. 3934604 Japanese Patent No. 5267638 JP 2013-237101 A Japanese Patent Laid-Open No. 2-50908 JP 2014-227562 A
- the present invention aims to provide a hot-rolled steel sheet having an internal oxide layer structure excellent in acid solubility, a method for producing the hot-rolled steel sheet, and a method for producing a cold-rolled steel sheet.
- the present inventors examined manufacturing conditions in detail for a method for significantly improving the pickling performance without increasing the cost and without greatly reducing the productivity and satisfying the restrictions on the manufacturing process. As a result, it is possible to form an internal oxide layer structure that is easy to pickle while satisfying the characteristics required for high-strength steel sheets when the steel components and the control of the amount of heat after winding are in specific conditions. I found out.
- an internal oxide layer structure with high acid solubility can be obtained by controlling the Si / Mn ratio as a steel plate component and controlling the temperature after hot rolling. In this way, it is possible to improve the pickling performance of the internal oxide layer from a completely different approach from the conventional technology aiming at improving pickling performance by suppressing internal oxidation, and to significantly reduce pickling time. I found it.
- the present inventor has solved the problems that cannot be achieved by those skilled in the art, and has arrived at the present invention.
- the gist of the present invention is as follows. (1) C: 0.05 mass% to 0.45 mass%, Si: 0.5 mass% to 3.0 mass%, Mn: 0.50 mass% to 3.60 mass% or less, P: 0.030% by mass or less, S: 0.010 mass% or less, Al: 0% by mass to 1.5% by mass, N: 0.010% by mass or less, O: 0.010 mass% or less, Ti: 0% by mass to 0.150% by mass, Nb: 0% by mass to 0.150% by mass, V: 0% by mass to 0.150% by mass B: 0% by mass to 0.010% by mass, Mo: 0% by mass to 1.00% by mass, W: 0% by mass to 1.00% by mass, Cr: 0% by mass to 2.00% by mass, Ni: 0% by mass to 2.00% by mass, Cu: 0% by mass to 2.00% by mass, and one or more selected from the group consisting of Ca, Ce, Mg, Zr, Hf and REM: 0% by mass to 0.500% by
- Arbitrary crystal grain boundaries that are Si-containing oxides having a thickness of 10 nm to 200 nm, and that have one or more branches of the internal oxide in a cross section of 1 ⁇ m ⁇ 1 ⁇ m square and a length of 1 ⁇ m.
- a hot rolled steel sheet wherein one or more of the internal oxides are connected to the internal oxides of the crystal grain boundaries to form a network structure.
- a method for producing a hot-rolled steel sheet comprising: (6) C: 0.05 mass% to 0.45 mass%, Si: 0.5 mass% to 3.0 mass%, Mn: 0.50 mass% to 3.60 mass% or less, P: 0.030% by mass or less, S: 0.010 mass% or less, Al: 0% by mass to 1.5% by mass, N: 0.010% by mass or less, O: 0.010 mass% or less, Ti: 0% by mass to 0.150% by mass, Nb: 0% by mass to 0.150% by mass, V: 0% by mass to 0.150% by mass B: 0% by mass to 0.010% by mass, Mo: 0% by mass to 1.00% by mass, W: 0% by mass to 1.00% by mass, Cr: 0% by mass to 2.00% by mass
- a method for producing a cold-rolled steel sheet comprising:
- the pickling property of the hot-rolled steel sheet can be improved, the pickling time can be shortened, and the productivity can be greatly improved.
- FIG. 1 is an enlarged cross-sectional view of an internal oxide layer formed in the hot-rolled steel sheet of the present invention and the vicinity thereof.
- FIG. 2 is a schematic diagram of the internal oxide layer disclosed in Patent Document 1.
- FIG. 3A is a schematic diagram showing a connection state between internal oxides in crystal grains constituting the network structure in the present invention and oxides at grain boundaries.
- FIG. 3B is a diagram for explaining how to count the number of branches in the network structure according to the present invention.
- FIG. 4 is a schematic diagram showing the shape of the oxide in the internal oxide layer disclosed in Patent Document 4 and the presence of the oxide only in the vicinity of the grain boundary.
- the present inventors examined in detail the production conditions regarding the occurrence of internal oxidation of the winding material.
- Si / Mn ratio which is the mass ratio of the Si and Mn contents as the steel material component
- the calorific value after winding the internal oxide containing Si in the internal oxide layer that is generated It has been found that a network structure can be formed in the crystal grains by connecting to the crystal grain boundaries in the internal oxide layer. By adopting such a structure, the pickling time was significantly shortened.
- FIG. 1 is an enlarged cross-sectional view of an internal oxide layer 10 formed in the hot-rolled steel sheet of the present invention and the vicinity thereof.
- the internal oxide 1 having a network structure of the internal oxide layer 10 is an oxide containing Si having a thickness of 10 nm to 200 nm, and is connected from the crystal grain boundary 2 to the inside of the crystal grain as shown in FIG.
- the shape of the internal oxide 1 is a continuous network having an independent particle shape, linear shape, or branched structure in the crystal grains.
- the acid solution penetrates into the crystal grains from the interface between the network-like internal oxide 1 and the metal matrix 3 as a path through which the metal matrix 3 and the internal oxide 1 are dissolved.
- a path through which the metal matrix 3 and the internal oxide 1 are dissolved is referred to as a dissolution path.
- the acid solubility can be improved even in the case of a hardly soluble internal oxide layer because metal iron is originally used as a parent phase.
- the interface between the internal oxide layer 10 corresponding to the inner side of the internal oxide layer and the base iron 12 (internal oxide layer / base iron interface 13). If the network structure is formed in the vicinity in the vicinity, the inner side of the inner oxide layer 10 is dissolved first, so that the surface oxide scale 11 side, which is the outer side of the remaining inner oxide layer 10, It is also possible to peel and remove the whole.
- the Si / Mn ratio of the steel material component is set to 0.27 or more and 0.90 or less. Accordingly, it is necessary to generate an oxide and amorphous SiO 2 having a chemical composition of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1).
- an oxide represented by a chemical composition of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) elutes as Fe 2+ and Mn 2+ ions in an acid solution and gels Si oxidation. It will be a thing.
- Such an acid-soluble oxide is also effective for forming a dissolution path at the interface between the internal oxide having a network structure (network oxide) and the metal matrix 3.
- FIG. 3A shows a connection state between internal oxides in crystal grains constituting the network structure and internal oxides in crystal grain boundaries.
- the internal oxide 1a in the crystal grain is branched at the branch portion 32 in the crystal grain, and a part of the internal oxide in the crystal grain is a grain boundary 2. It is the structure connected with the internal oxide of this by the connection part 31.
- FIG. 3B is a diagram for explaining how to count the number of branches in the network structure.
- the number of branches of the network structure is the number of branches (from the original branch) in the oxide continuum observed during cross-sectional observation (5000 to 80000 times) with a transmission electron microscope (TEM) or scanning electron microscope (SEM). The number of derived branches).
- Si / Mn ratio 0.27 to 0.90>
- the Si content and the Mn content in the steel plate component of the base material are limited to a specific range in order to exhibit characteristics required for a high strength steel plate such as strength and ductility.
- the Si / Mn ratio is an important factor that determines the composition of the oxide to be produced in the process of internal oxidation of the wound material after hot rolling.
- Fe 2 SiO 4 , Mn 2 SiO 4 , FeSiO 3 , MnSiO 3 , and SiO 2 can be generated as internal oxides as Si-based oxides. it is conceivable that.
- the oxide composition and the amount of oxide to be generated are determined by the contents of Si and Mn and the oxygen potential.
- Al, Ti, Cr, etc. are also easier to oxidize than iron, so they can be internal oxidation elements.
- the structure and composition of the internal oxidation layer are almost unaffected within the range of the steel sheet content as targeted by the present invention. do not do.
- the oxide scale of the steel sheet surface layer is usually the oxygen source.
- the present inventors have found that control of the Si / Mn ratio is important in the composition of the Si-based internal oxide to be generated.
- Si / Mn ratio is high, Fe 2 SiO 4 and SiO 2 are generated, but Mn 2 SiO 4 is not generated.
- SiO 2 generated even at a lower oxygen potential, and Fe 2 SiO 4 that is an oxide of Fe, FeO, and SiO 2 that are the largest contained elements are preferentially generated. For the reason.
- the Si / Mn ratio of the base material needs to be 0.90 or less. I found out. When Si / Mn ratio exceeds 0.90, containing Mn (Fe x, Mn 1- x) 2 SiO 4 (0 ⁇ x ⁇ 1) is hardly generated, increasing the acid solubility of an internal oxide layer I can't. More preferably, the Si / Mn ratio is 0.70 or less.
- (Fe x , Mn 1-x ) 2 SiO 4 has a high Mn ratio (Fe x , Mn 1-x ) 2 in the range of 0 ⁇ x ⁇ 1.
- the formation region of SiO 4 is expanded, and the acid solubility of the entire internal oxide layer can be further increased.
- the lower limit of the Si / Mn ratio of the base material is 0.27. This expresses the characteristics of a high-strength steel sheet, and (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) and amorphous SiO 2 are formed in which the network oxide has a high Mn ratio.
- Patent Document 5 mainly on Si on the steel sheet in order to improve the coating film adhesion of the cold-rolled steel sheet The purpose is to suppress the formation of oxides.
- patent document 6 it aims at making it internally oxidize as complex oxide, without producing
- Patent Documents 5 and 6 also specify the Si / Mn ratio.
- Patent Documents 5 and 6 performs the heat quantity control as in the present invention, and the oxide is generated in the crystal grains by being connected to the crystal grain boundaries, and is also generated in the network in the crystal grains. It differs from the oxide structure.
- a network structure containing an oxide and an amorphous SiO 2 having a chemical composition of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) formed in the internal oxide layer of the present invention This is important in forming a dissolution path that is a starting point for acid dissolution in the crystal grains of the internal oxide layer.
- (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) and amorphous SiO 2 have a network structure is not clear, but the diffusion path of elements involved in internal oxidation is affected. it seems to do.
- (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) and amorphous SiO 2 have a thickness of several ⁇ m to several tens of ⁇ m unless they are formed almost all over the crystal grains.
- the pickling property of a certain internal oxide layer cannot be significantly improved.
- the crystal grain boundaries are dissolved first as described in Patent Document 1, but the parent phase is metallic iron inside the crystal grains, and the pickling solution contains Since it contains a pickling inhibitor (inhibitor) for the purpose of suppressing the overdissolution of iron, it is considered that the dissolution is slow and how to increase the solubility in the crystal grains in the presence of the pickling inhibitor is the key. It is done.
- each internal oxide is independent, and the dissolution path from the crystal grain boundary to the crystal grain Is not formed, and a long pickling time is required to dissolve and remove the internal oxide layer.
- Patent Document 4 refers to the existence shape of the oxide in the internal oxide layer 40 as shown in FIG. 4, but Patent Document 4 aims at anti-plating resistance at the time of high processing.
- the present invention is different from the present invention on the assumption that it is removed. Even if this structure is pickled, since the region of the dendritic oxide 41 generated in the crystal grain from the crystal grain boundary 42 is small with respect to the crystal grain having a grain size of at least several ⁇ m, Acid dissolution in the crystal grains having a large proportion of the metal base material 43 in which the oxide 41 does not exist is low, and the pickling property is not good.
- the network oxide in the present invention is (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) and amorphous SiO 2 , but Mn 2 SiO 4 is oxygen dissociated compared to Fe 2 SiO 4. Since the equilibrium pressure is low, it is formed inside the internal oxide layer. Therefore, in the region where (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) and amorphous SiO 2 having a high Mn content ratio are generated by the pickling solution that has dissolved and permeated the crystal grain boundaries The oxide / metal matrix interface dissolves first.
- the region to Fe 2 SiO 4 major internal oxides generated outward in the internal oxide layer, to exhibit the effect of reducing the pickling time since it peel each metal parent phase and internal oxide. Therefore, it is assumed that the internal oxide is present in more than 0% to 30% of the internal oxide layer thickness from the internal oxide layer / base metal interface toward the outer surface scale direction. More preferably, the internal oxide is present in more than 0% to 50% of the thickness of the internal oxide layer from the internal oxide layer / base metal interface toward the outer surface scale direction.
- the method for confirming the network oxide structure in the present invention is not particularly limited.
- a cross-section in the plate thickness direction of the wound material after hot rolling is processed by a focused ion beam (FIB), and transmission electron
- FIB focused ion beam
- the thickness of the oxide, the branching portion, and the connecting portion with the crystal grain boundary can be confirmed.
- a solution such as an acid by polishing the cross section of the wound material after hot rolling and etching with a solution such as an acid, the difference in solubility between the internal oxide and the metal matrix can be utilized to obtain the contour of the oxide.
- the shape of the internal oxide can be observed with a scanning electron microscope. It is also effective to observe the oxide residue recovered by electrolytic extraction of the above-described hot-rolled winding material with a scanning electron microscope or a transmission electron microscope.
- the network oxide structure defined in the present invention means that the internal oxide containing Si has a minor axis direction thickness of 10 nm or more and 200 nm or less, and crystal grains in an arbitrary field of view of 1 ⁇ m ⁇ 1 ⁇ m square. And a structure in which one or more branches of the internal oxide are present and one or more of the internal oxides in the crystal grains are connected to the internal oxide at the crystal grain boundaries at an arbitrary grain boundary of 1 ⁇ m in length. .
- the reason why the thickness of the internal oxide in the minor axis direction is limited to 10 nm or more and 200 nm or less is as follows.
- the thickness is less than 10 nm, the dissolution path at the interface between the internal oxide and the metal matrix becomes thin, and the pickling solution may not easily enter.
- the thickness is more than 200 nm, the surface area of the network oxide is small relative to the total amount of the internal oxide, and there may be a region where no network oxide is generated in the crystal grains.
- the steel material component has a Si / Mn ratio of 0.27 or more and 0.9 or less and a temperature range of 400 ° C. or more and 500 ° C. or less in a temperature range 50 to 100 ° C. lower than the temperature at which internal oxidation occurs.
- the oxide and amorphous SiO 2 represented by the chemical composition of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) are spread over almost the entire region in the crystal grains of the internal oxide layer. Generate with a mesh structure.
- (Fe x , Mn 1-x ) 2 SiO 4 is a total solid solution of Fe 2 SiO 4 and Mn 2 SiO 4 , and x can take an arbitrary value in the range of 0 to 1.
- the Si / Mn ratio of the steel material greatly affects the formation of (Fe x , Mn 1-x ) 2 SiO 4 .
- the Si / Mn ratio is 0.90 or less, the ratio of Fe decreases inward of the internal oxide layer in (Fe x , Mn 1-x ) 2 SiO 4 with respect to the thickness direction of the internal oxide layer, The inventors have found that the ratio of Mn tends to increase.
- Mn 2 SiO 4 has a lower dissociation equilibrium pressure than Fe 2 SiO 4 and Mn 2 SiO 4 is likely to be formed on the inner side of the internal oxide layer having a lower oxygen potential. Further, when the Si / Mn ratio exceeds 0.90, Mn is hardly contained in (Fe x , Mn 1-x ) 2 SiO 4 . Furthermore, a Mn-depleted layer is formed at the internal oxide layer / base metal interface. Therefore, Mn diffuses from the inner oxide layer / base metal interface along the grain boundary to the grain boundary of the inner oxide layer, and further diffuses from the grain boundary of the inner oxide layer into the crystal grain. Is thought to form.
- the internal oxide represented by the chemical composition of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) is eluted as Fe 2+ and Mn 2+ ions in the acid solution to form gel-like Si It is thought to be an oxide.
- Such an acid-soluble oxide is also effective in forming a dissolution path at the oxide / metal matrix interface when dissolving in the crystal grains of the internal oxide layer.
- the method for confirming the presence of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1) is not particularly limited.
- a wound material after hot rolling in which an internal oxide layer is formed Only the oxide scale is dissolved in an acid solution containing an inhibitor.
- the metal matrix phase of the inner oxide layer is dissolved electrochemically, and the resulting residue can be recovered by filtration to recover the inner oxide.
- the amount of metal in the matrix to be dissolved can be controlled by the amount of electricity during electrolysis. Therefore, it is possible to extract oxides in the depth direction by repeating electrolytic extraction with a predetermined amount of electricity a plurality of times.
- the obtained oxide residue can identify the structure of the internal oxide by X-ray diffraction.
- X of (Fe x , Mn 1-x ) 2 SiO 4 can be all values from 0 to 1, but the same diffraction can be obtained from the X-ray diffraction pattern of the internal oxide obtained by extracting the internal oxide layer in the depth direction. By comparing the lattice spacings of the surfaces, the change from Fe 2 SiO 4 to Mn 2 SiO 4 can be known.
- the thickness direction of the cross-section of the inner oxide layer was observed by a transmission electron microscope, when combined with elemental analysis by energy dispersive X-ray spectroscopy (EDX), (Fe x, Mn 1-x) 2
- EDX energy dispersive X-ray spectroscopy
- amorphous SiO 2 having a lower oxygen dissociation pressure is produced.
- the Si / Mn ratio specified by the present invention is 0.90 or less
- Amorphous SiO 2 is seen as a network structure.
- the method for confirming amorphous SiO 2 is not particularly limited. It can be recovered as an oxide residue by electrochemical dissolution of the internal oxide layer described above. However, since it is amorphous and cannot be confirmed by X-ray diffraction, there is a method of analyzing the obtained residue by, for example, the FT-IR method.
- a slab having a chemical composition described later is cast.
- a slab produced by a continuous casting slab, a thin slab caster or the like can be used.
- a process such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting may be used.
- the slab heating temperature is preferably 1050 ° C. or higher because there is a concern that the shape of the base steel sheet after rolling may be poor.
- the upper limit of the slab heating temperature is not particularly required, but it is not economically preferable to make the slab heating temperature excessively high. Therefore, the slab heating temperature is preferably 1350 ° C. or lower.
- the hot rolling is preferably completed at a finish rolling temperature equal to or higher than the Ar 3 transformation point temperature.
- the finish rolling temperature is lower than the Ar 3 transformation point, it becomes a two-phase rolling of ferrite and austenite, and the hot rolled sheet structure tends to be a heterogeneous mixed grain structure.
- tissue is not eliminated but there exists a possibility that ductility and bendability may fall.
- the upper limit of the finish rolling temperature is not particularly required, but when the finish rolling temperature is excessively high, the slab heating temperature must be excessively high in order to secure the temperature. Therefore, the finish rolling temperature is preferably 1100 ° C. or lower.
- Ar 3 transformation point (°C) is calculated by the following equation using the content of each element (mass%).
- Ar 3 901-325 ⁇ C + 33 ⁇ Si-92 ⁇ (Mn + Ni / 2 + Cr / 2 + Cu / 2 + Mo / 2) + 52 ⁇ Al
- the high-strength steel sheet that is the subject of the present invention has a slow phase transformation from hot rolling to winding due to its high alloy content, so when it is wound at a low temperature of less than 550 ° C., a large amount of martensite and retained austenite are generated. To do. In this case, the strength of the hot rolled original sheet is increased, and the steel sheet may be broken during cold rolling. Therefore, it is necessary to advance the ferrite transformation and the pearlite transformation by winding at a temperature of 550 ° C. or higher and to soften it to ensure cold rolling properties.
- 550 ° C. is the temperature at which internal oxidation occurs. This is the lower limit.
- the higher the winding temperature after hot rolling the easier it is to proceed with ferrite transformation and pearlite transformation, so the winding temperature is more preferably 600 ° C. or higher.
- the coiling temperature is 600 ° C. or higher, it is easy to complete the ferrite transformation and pearlite transformation, and the structure can be made more excellent in cold rolling.
- the higher the temperature the easier the internal oxidation grows and the more the film tends to become thicker. This is because the temperature factor becomes a driving force in the generation of internal oxidation, and therefore an excessive increase in the coiling temperature causes the internal oxide layer to become thicker and the pickling performance deteriorates. In particular, this tendency becomes remarkable when the coiling temperature exceeds 800 ° C., and the thickness of the internal oxide layer exceeds 30 ⁇ m, which is not preferable from the viewpoint of productivity and yield. Therefore, the upper limit of the coiling temperature is 800 ° C. In order to further improve the pickling property, the winding temperature is preferably 700 ° C. or lower.
- the internal oxidation grows in the thickness direction of the steel material and becomes thicker, so it is difficult to shorten the pickling time. Therefore, in the temperature range that is 50 to 100 ° C. lower than the temperature at which internal oxidation occurs, the conventional condition of about 1 to 5 hours is maintained for 10 hours or more, while preventing the thickening of the crystal of the internal oxide layer. Internal oxidation can proceed from the grain boundary into the crystal grain. Although this mechanism is not clear, a Si and Mn depletion layer is formed at the inner oxide layer / base metal interface, and Si and Mn diffuse into the inner oxide layer through the grain boundaries.
- the holding temperature after winding is 400 ° C. or more and 500 ° C. or less. If the holding temperature exceeds 500 ° C., it approaches 550 ° C., which is the temperature at which internal oxidation occurs, and thus growth in the plate thickness direction proceeds, which may lead to thickening. On the other hand, when the holding temperature is less than 400 ° C., the rate at which Si and Mn diffuse from the grain boundaries into the crystal grains becomes rate-determining, and the generation of internal oxides within the crystal grains becomes extremely slow.
- the lower limit of the holding time in this temperature range is 10 hours.
- the holding temperature is less than 10 hours, a region where no network oxide is generated may occur. More preferably, the holding temperature is 15 hours or more. If the holding temperature is 15 hours or longer, even in a crystal grain having a large grain size of several ⁇ m or more, the network oxide can be grown over the entire area in the crystal grain.
- the upper limit of the holding time is 20 hours. If the holding time exceeds 20 hours, inclusions such as carbides are generated in the ground iron, or productivity is lowered, which is not preferable.
- the holding time here requires 10 hours or more and 20 hours or less, but this is not a continuous process such as hot rolling, pickling, and cold rolling in the manufacturing process, and is out of the online process. The impact on performance and cost is relatively small.
- the steel material wound by hot rolling is subjected to pickling to remove the oxide scale and the internal oxide layer on the steel material surface layer.
- oxygen in the oxide scale is consumed by internal oxidation, so that a metal iron layer may be formed in the oxide scale and on the surface layer of the oxide scale, but this also needs to be removed by pickling.
- pickling it is possible to remove oxides on the surface of the steel sheet, improve the chemical conversion of the high-strength cold-rolled steel sheet of the final product, and cool it for hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets.
- Pickling is important in terms of improving the hot dipping property of the rolled steel sheet. Pickling may be performed only once or may be performed in multiple steps.
- the liquid composition used for pickling as the object of the present invention is not particularly limited as long as it is generally used for removing the oxide scale of the steel sheet.
- dilute hydrochloric acid, dilute sulfuric acid, or nitric acid is used. Can do.
- hydrochloric acid it is preferable to use hydrochloric acid.
- the concentration of hydrochloric acid is preferably 1% by mass or more and 20% by mass or less as hydrogen chloride. The higher the hydrochloric acid concentration, the higher the dissolution rate of the oxide scale and the inner oxide layer, but at the same time, the dissolution amount of the ground iron after dissolution increases.
- the above range is preferable because it causes a decrease in yield and increases the cost because it is necessary to supply high-concentration hydrochloric acid.
- iron (II) ions and iron (III) ions and other components derived from the steel sheet may be mixed by dissolution.
- the temperature of the acid solution is preferably 70 ° C or higher and 95 ° C or lower. The higher the temperature, the higher the dissolution rate of the oxide scale and the internal oxide layer, but at the same time, the amount of dissolution of the ground iron after dissolution increases the yield and increases the cost due to temperature rise. Therefore, the upper limit of the temperature of the acid solution is preferably 95 ° C.
- the lower limit of the temperature of the acid solution is preferably 70 ° C. More preferably, the temperature of the acid solution is 80 ° C. or higher and 90 ° C. or lower.
- a commercially available pickling inhibitor inhibitor
- a commercially available pickling promoter can also be added to the pickling solution to prevent overdissolution and yellowing of the base iron.
- a commercially available pickling promoter can also be added.
- the pickling solution that has permeated the crystal grain boundary dissolves the interface of the network oxide / metal matrix, thereby Progresses in dissolution.
- the interface that is the starting point of dissolution increases, and an internal oxide having high solubility exists. For this reason, the acid concentration is lower, the acid temperature is lower, and the iron ion concentration is lower than the conventional internal oxide layer that does not have a network oxide and needs to dissolve the metal matrix of the internal oxide layer.
- the thickness of the internal oxide layer is set to 1 ⁇ m or more and 30 ⁇ m or less in order to significantly shorten the pickling time.
- the pickling solution is formed using the oxide / metal matrix interface formed in the crystal grains connected from the crystal grain boundary as a dissolution path. The effect of penetrating into crystal grains is small.
- the thickness of the internal oxide layer exceeds 30 ⁇ m, there is an effect of allowing the pickling solution to penetrate into the crystal grains, but the time required for the pickling solution to penetrate to the crystal grain boundary below the internal oxide layer is long. Thus, the effect of shortening the pickling time as a whole is reduced. Moreover, it is not preferable from the viewpoint of yield.
- the hot rolled steel sheet having an internal oxidation structure that is easy to pickle, which is the subject of the present invention, is used as a cold rolled steel sheet by performing cold rolling after pickling.
- the strength of the hot-rolled steel sheet is too high, it causes breakage during cold rolling, and the cold-rollability cannot be secured. Therefore, it is necessary to complete the ferrite transformation and the pearlite transformation.
- the content of Mn in the steel material is too high, the weldability is deteriorated, so that the cold rolling property is also affected. If the Si / Mn ratio is 0.27 or more when the Mn content of the steel is 3.6 mass% and the Si content is 1.0 mass%, the cold rolling property can be secured.
- the present invention reduces the pickling time by maintaining the properties as a cold-rolled steel sheet and shortening the pickling time by making the structure of the internal oxide layer produced by winding after hot rolling easy to pickle. It is intended to improve the performance.
- the reason why the composition of the hot-rolled steel sheet and the slab is limited as described above will be described.
- a high-strength steel sheet containing C, Si, and Mn is targeted, but the reason for setting the contents of elements other than Fe in the steel sheet and slab will be described below.
- the Si / Mn ratio is 0.27 or more and 0.9 or less for the same reason as described above.
- C 0.05 mass% or more and 0.45 mass% or less>
- C is an element necessary for obtaining a retained austenite phase, and is contained in order to achieve both excellent moldability and high strength.
- the C content exceeds 0.45% by mass, weldability becomes insufficient, so the upper limit of the C content is set to 0.45% by mass.
- the C content is less than 0.05% by mass, it is difficult to obtain a sufficient amount of retained austenite phase, and the strength and formability deteriorate. From the viewpoint of strength and formability, the lower limit of the C content is set to 0.05% by mass.
- Si is an element that makes it easy to obtain a retained austenite phase by suppressing the formation of iron-based carbides in the steel sheet, and is necessary for enhancing strength and formability. If the Si content exceeds 3.00 mass%, the steel sheet becomes brittle and the ductility deteriorates, so the upper limit of the Si content was set to 3.00 mass%. On the other hand, when the Si content is less than 0.5% by mass, iron-based carbides are generated during cooling to room temperature after annealing, and a sufficiently retained austenite phase cannot be obtained. As a result, the strength and formability deteriorated, the activity was low, and internal oxidation during hot rolling was difficult to occur, so the lower limit of the Si content was set to 0.5% by mass.
- Mn 0.50 mass% or more and 3.60 mass% or less> Mn is contained in order to increase the strength of the steel sheet, and is an important element for stabilizing the austenite and obtaining characteristics as a high-strength steel sheet having excellent workability due to the formation of retained austenite.
- Mn content exceeds 3.60% by mass, embrittlement tends to occur, and the cast slab is likely to crack.
- Mn content exceeds 3.60 mass%, there exists a problem that weldability also deteriorates. For this reason, the upper limit of Mn content was 3.60 mass%.
- the Mn content is less than 0.50% by mass, a large amount of soft tissue is generated during cooling after annealing, making it difficult to ensure strength. Moreover, since the activity is low and internal oxidation during hot rolling hardly occurs, the lower limit of the Mn content is set to 0.50%.
- the hot-rolled steel sheet and slab of the present invention may contain the following alloy elements in addition to the above-described components in order to satisfy the characteristics as a high-strength steel sheet or as an unavoidable impurity in production.
- P tends to segregate at the center of the plate thickness of the steel sheet and has a characteristic of embrittlement of the weld. If the P content exceeds 0.030% by mass, the welded portion is significantly embrittled, so P is contained at 0.030% by mass or less. However, if the P content is less than 0.001%, the production cost is greatly increased. Therefore, the P content is preferably 0.001% by mass.
- S has an adverse effect on weldability and manufacturability at the time of casting and hot rolling, and forms coarse MnS in combination with Mn to reduce ductility and stretch flangeability, so the S content is 0. 0.0100% by mass or less. However, if the content of S is less than 0.0001% by mass, the production cost is greatly increased. Therefore, the S content is preferably 0.0001% by mass or more.
- Al is an element that makes it easy to obtain retained austenite by suppressing the formation of iron-based carbides, and improves the strength and formability of the steel sheet. Since weldability deteriorates when the Al content exceeds 1.500 mass%, the Al content is set to 1.500 mass% or less. However, Al is an element that is also effective as a deoxidizing material. If the Al content is less than 0.005% by mass, a sufficient effect as a deoxidizing material cannot be obtained. The Al content is preferably 0.005% by mass or more.
- N forms coarse nitrides and deteriorates ductility and stretch flangeability, so it is necessary to suppress the addition amount. If the N content exceeds 0.0100% by mass, this tendency becomes remarkable, so the N content is set to 0.0100% by mass or less. On the other hand, when the N content is less than 0.0001% by mass, the manufacturing cost is greatly increased. Therefore, the N content is preferably 0.0001% by mass or more.
- O forms an oxide
- the O content is set to 0.0100% by mass or less.
- the O content is preferably 0.0001% by mass or more.
- Ti is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization. If the Ti content exceeds 0.150% by mass, precipitation of carbonitrides increases and the formability deteriorates, so the Ti content is set to 0.150% by mass or less. Further, in order to sufficiently obtain the effect of increasing the strength due to Ti, the Ti content is preferably 0.005% by mass or more.
- Nb is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization. If the Nb content exceeds 0.150% by mass, precipitation of carbonitrides increases and the formability deteriorates, so the Nb content is set to 0.150% by mass or less. Moreover, in order to fully obtain the strength increasing effect by Nb, the Nb content is preferably 0.010% by mass or more.
- V is an element that contributes to increasing the strength of the steel sheet by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and dislocation strengthening by suppressing recrystallization. If the V content exceeds 0.150% by mass, precipitation of carbonitrides increases and the formability deteriorates, so the V content is set to 0.150% by mass or less. Further, in order to sufficiently obtain the effect of increasing the strength due to V, the V content is preferably 0.005% by mass or more.
- B is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and is contained in place of part of C or Mn. If the B content exceeds 0.0100 mass%, the hot workability is impaired and the productivity is lowered, so the B content is set to 0.0100 mass% or less. In order to sufficiently obtain the effect of increasing the strength due to B, the B content is preferably 0.0001% by mass or more.
- Mo 1.00% by mass or less> Mo is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and is contained in place of a part of C or Mn. If the Mo content exceeds 1.00% by mass, the hot workability is impaired and the productivity decreases, so the Mo content is set to 1.00% by mass or less. In order to sufficiently obtain the effect of increasing the strength due to Mo, the Mo content is preferably 0.01% by mass or more.
- W 1.00% by mass or less> W is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and is contained in place of a part of C or Mn. If the W content exceeds 1.00% by mass, the hot workability is impaired and the productivity is lowered, so the W content is set to 1.00% by mass or less. Moreover, in order to fully obtain the strength increasing effect by W, the content is preferably 0.01% by mass or more.
- Cr is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and is contained in place of a part of C or Mn. If the Cr content exceeds 2.00 mass%, the hot workability is impaired and the productivity is lowered, so the Cr content is 2.00 mass% or less. Further, in order to sufficiently obtain the effect of increasing the strength due to Cr, the Cr content is preferably 0.01% by mass or more.
- Ni is an element that suppresses phase transformation at high temperatures and is effective for increasing the strength, and is contained in place of a part of C or Mn.
- Ni content exceeds 2.00 mass%, weldability will be impaired, Therefore Ni content shall be 2.00 mass% or less. Further, in order to sufficiently obtain the effect of increasing the strength by Ni, the Ni content is preferably 0.01% by mass or more.
- Cu is an element that increases strength by being present in steel as fine particles, and is contained in place of a part of C or Mn.
- Cu content exceeds 2.00 mass%, weldability will be impaired, Therefore Cu content shall be 2.00 mass% or less.
- the Cu content is preferably 0.01% by mass or more.
- Ca, Ce, Mg, Zr, Hf, and REM are effective elements for improving moldability, and one or more of them are contained.
- REM is an abbreviation for Rare Earth Metal and indicates an element belonging to the lanthanoid series. If the total content of one or more selected from the group consisting of Ca, Ce, Mg, Zr, Hf and REM exceeds 0.5000% by mass, the ductility may be impaired. The total amount is 0.5000% by mass or less. In order to sufficiently obtain the effect of improving the formability of the steel sheet, the total content of the elements is preferably 0.0001% by mass or more.
- a hot-rolled steel sheet having the chemical composition shown in Table 1 and wound and heat-treated as shown in Table 2 has an internal oxide layer of 1000 to 5000 times within one field of view by means of a scanning electron microscope (manufactured by JEOL, JSM-6500F).
- the thickness of the internal oxide layer was determined from the average value obtained by observing 10 fields of view in the thickness direction of the hot-rolled steel sheet within the range. At this time, the thickness of the internal oxide layer was a distance from the oxide scale / internal oxide layer interface generated in the surface layer to the internal oxide layer / base metal interface.
- the depth in the plate thickness direction of the grain boundary oxide at the interface between the internal oxide layer and the base iron and the internal oxide in the crystal grains is not uniform and varies depending on the location of the cross section of the observation target. Therefore, in the above observation, the surface where the inner oxide of the crystal grain boundary located closest to the base metal side in the plate thickness direction and the end of the inner oxide in the crystal grain are connected is identified, and this surface is defined as the inner oxide layer. / It was set as the iron base interface.
- the presence or absence of internal oxide in the crystal grains and internal oxide in the crystal grain boundaries if there are internal oxides in the crystal grains and in the crystal grain boundaries in the 10-field cross section observed at a magnification of 5000, they are present. If there was something not to be done, it was deemed nothing.
- the thickness of the internal oxide layer is 0% to 30% from the internal oxide layer / base metal interface toward the surface oxide scale direction at 80000 times. These were determined by observing an arbitrary cross section of 1 ⁇ m ⁇ 1 ⁇ m square in the range. Further, in the observation, the surface where the internal oxide and the terminal end of the internal oxide of the grain boundary of the internal oxide layer located closest to the ground iron side with respect to the plate thickness direction are identified, and this surface is defined as the internal oxide layer. / It was set as the iron base interface.
- the thickness of the internal oxide in the internal oxide layer is ⁇ if the length in nm units in the minor axis direction is 10 nm or more and 200 nm or less for 20 oxides included in an arbitrary field of view, and other ranges If so, it was determined as x.
- the method for counting the number of branches of the internal oxide described above was calculated from the average value of the number of branches in 20 oxides included in an arbitrary field of view using the method shown in FIG. 3 as described above.
- the number of connections between the crystal grain boundaries and the internal oxides in the crystal grains is as follows. The average value was calculated from the number of internal oxides continuously present in the interior of 100 nm or more. In addition, for the internal oxide whose thickness was calculated, the number of branches of the internal oxide, the number of crystal grain boundaries, and the number of connections of the internal oxide, energy dispersive X-ray spectroscopy (manufactured by FEI, Tecnai G2 F30) Elemental analysis was carried out by means of "Yes” if the Si component was detected, and "No" if not detected. These measurement results are shown in Table 3.
- the composition of the oxide in the internal oxide layer was specified by the following procedure. First, the winding material was immersed in a 10 wt% citric acid aqueous solution at 50 ° C. containing 400 ppm of a commercially available inhibitor (Ibit 710, manufactured by Asahi Chemical Industry Co., Ltd.) until the oxide scale layer was dissolved.
- a commercially available inhibitor Ibit 710, manufactured by Asahi Chemical Industry Co., Ltd.
- electrolysis is performed at a current density of about 320 Am ⁇ 2 to electrochemically dissolve only metallic iron in a thickness of about 5 ⁇ m. It collect
- the extracted residue is subjected to X-ray diffraction by a continuous scan of the ⁇ / 2 ⁇ method (Rigaku, RINT 1500, scan speed: 0.4 ° min ⁇ 1 , sampling width: 0.010 °), (Fe x , Mn 1 -x) confirmed the existence of 2 SiO 4 (0 ⁇ x ⁇ 1).
- the electrolytically extracted residue and potassium bromide crystals were mixed, pressed into tablets, and then subjected to the FT-IR transmission method (detector TGS, resolution 4 cm ⁇ ) using FT / IR6100 manufactured by JASCO Corporation. 1 and the number of integration 100 times, measurement size 10 mm ⁇ ), and the presence or absence of amorphous SiO 2 was examined.
- the hot-rolled steel sheet having the chemical components shown in Table 1 and wound and heat-treated under the conditions shown in Table 2 was evaluated for pickling performance by the pickling completion time required to dissolve and remove the internal oxide layer.
- the wound material contains 80 g / L of iron (II) ions, 1 g / L of iron (III) ions, and 400 ppm of a commercially available inhibitor (Ibit 710, manufactured by Asahi Chemical Industry Co., Ltd.) 85 It was immersed in a 9 mass% hydrochloric acid aqueous solution at 0 ° C. And the time when the crystal grain containing the metal mother phase of an internal oxide layer was removed was made into pickling completion time.
- the pickling completion time was measured in units of 5 seconds due to the error range of the experimental work.
- the determination of the removal of the internal oxide layer was made by visually observing the steel surface and the cross section of the pickled hot-rolled steel sheet with a scanning electron microscope (JEOL, JSM-6500F) at a magnification of 1000 to 5000 times, and the internal oxide layer was one field of view It was done by observing within the range.
- the pickling completion time in the above-mentioned Patent Document 1 is 90 seconds or more when the grain boundary oxide layer is 5 ⁇ m, 135 seconds or more when it is 10 ⁇ m, and 15 ⁇ m.
- pickling is required for 180 seconds or more, and for 225 seconds or more for 20 ⁇ m, the time corresponding to 2/3 of the pickling time was set as the target pickling time.
- the pickling time is 60 seconds when the internal oxide layer thickness is 5 ⁇ m or less, 90 seconds when it is 5 ⁇ m or more and 10 ⁇ m or less, 120 seconds when it is 10 ⁇ m or more and 15 ⁇ m or less, and 150 seconds when it exceeds 15 ⁇ m.
- the processed hot-rolled steel sheet was subjected to a rolling process to a thickness of 1.5 mm by a cold rolling mill.
- the Si / Mn ratio is as low as 0.70 or less, the Mn ratio is higher inward, and x is close to 0 at the internal oxide layer / base metal interface (Fe x , Mn 1-x ) 2 SiO 4. Generated. Further, since the holding time in the temperature range from 400 ° C. to 500 ° C. is 15 hours, the network oxide was widely generated to about 50% or more outside of the internal oxide layer. As a result, the number of branches of the internal oxide in the crystal grains in the internal oxide layer increased, and the number of connections of the internal oxide in the crystal grain boundaries and crystal grains increased. From the above results, steel plate No. 2 to No. 4 shows that the pickling solution easily penetrates from the crystal grain boundary through the oxide / metal matrix interface as a dissolution path.
- steel plate No. In No. 1 the Si / Mn ratio was less than 0.27. In this case, the pickling completion time was as short as 45 seconds. Steel plate No. In No. 1, the Mn content was too high, embrittlement and deterioration of weldability were observed, and the characteristics as high strength steel were not satisfied. Steel plate No. In No. 7, the Si / Mn ratio was more than 0.90. In this case, the pickling completion time was 170 seconds. Steel plate No. No.
- Steel plate No. 8-No. No. 12 is common with 2.0% by mass of Si, and steel plate no. 13 and no. No. 14 has a common Si content of 3.0% by mass.
- steel plate No. 8-No. No. 14 is an example when the Si / Mn ratio is changed by setting the coiling temperature to 750 ° C. and the holding time in the temperature range of 400 ° C. to 500 ° C. to 15 hours.
- Steel plate No. 8 and no. 9 has a Si / Mn ratio of 0.27 or more and 0.70 or less, and the number of branches of the internal oxide in the crystal grains in the internal oxide layer, the number of crystal boundaries and the number of connections of the internal oxide in the crystal grains confirmed.
- the coiling temperature was as high as 750 ° C.
- the internal oxide layer was also thickened.
- the formation region of the network oxide structure in the thickness direction of the internal oxide layer is also the steel plate No. 2 to No. Since the ratio was lower than that of steel plate 4, steel plate No. 8 and no.
- the pickling completion time of 9 was 60 seconds.
- steel plate No. 10, no. 11 and no. No. 13 had a Si / Mn ratio of more than 0.70 and not more than 0.90, and the pickling completion time was 100 seconds to 120 seconds.
- steel plate No. 12 and no. No. 14 has a Si / Mn ratio exceeding 0.90. 12 and no.
- the completion time of pickling 14 was 180 to 200 seconds.
- the coiling temperature was 750 ° C., and the thickness of the internal oxide layer was This is considered to be because it was as thick as 25 ⁇ m or more.
- Steel plate No. Nos. 15 to 20 have the same Si / Mn ratio of 0.50, and the holding time from 400 ° C. to 500 ° C. after winding is 10 hours, but the winding temperature is different.
- steel plate No. No. 15 is a steel plate manufactured by performing a winding process at 530 ° C., an internal oxide layer was not formed, and the pickling completion time was as short as 45 seconds.
- steel plate No. No. 15 did not undergo ferrite transformation and pearlite transformation, and the strength of the steel sheet was too high to satisfy the strength characteristics required for cold rolling.
- Steel plate No. 21-No. No. 26 has a common Si / Mn ratio of 0.75, a common winding temperature of 710 ° C., and different holding times from 400 ° C. to 500 ° C. after winding.
- Mn is in the inward direction of the internal oxide layer of (Fe x , Mn 1-x ) 2 SiO 4 (0 ⁇ x ⁇ 1). A monotonous increase in the ratio was not observed, and the pickling completion time was 110 seconds.
- Steel plate No. No. 26 has a retention time of more than 20 hours after winding, and partly has a mesh shape over a wide range of 0% to 50% of the thickness of the internal oxide layer from the internal oxide layer / base metal interface toward the surface oxide scale. A structure was observed and the pickling completion time was 130 seconds. However, the formation of nitrides and carbides in the ground iron was noticeable, resulting in a decrease in ductility and stretch flangeability, and did not satisfy the requirements for steel.
- steel plate No. 1 slab cracking and poor welding occurred in the manufacturing process, and cold working could not be performed.
- Steel plate No. No. 15 was excluded from the evaluation because the strength of the steel sheet was too high and cold rolling could not be performed to a predetermined thickness, and the surface properties after cold rolling could not be confirmed.
- the present invention it is possible to shorten the pickling time of a steel sheet rolled up by hot rolling of a steel sheet having a high Si and Mn content, while maintaining the same characteristics as a conventional cold-rolled steel sheet. Productivity is greatly improved.
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Abstract
Description
(1)C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、
残部が鉄および不純物からなる鋼板において、
前記鋼板の母材の鋼材成分のSi/Mn比が質量比で0.27以上0.90以下であり、
鋼板表層部の酸化スケール直下に、厚さが1μm以上30μm以下の内部酸化層を有し、
前記内部酸化層の結晶粒内の内部酸化物は、前記内部酸化層と地鉄との界面から表層酸化スケール方向に向かって前記内部酸化層の厚さの0%超30%以下の範囲における結晶粒内において、太さ10nm以上200nm以下のSiを含む酸化物であり、かつ1μm×1μm四方の断面に前記内部酸化物の分岐が1本以上存在し、かつ長さ1μmの任意の結晶粒界において前記内部酸化物の1つ以上が前記結晶粒界の内部酸化物と連結して網目状構造を形成していることを特徴とする熱延鋼板。
(2)前記母材の鋼材成分のSi/Mn比が質量比で0.70以下であることを特徴とする(1)に記載の熱延鋼板。
(3)前記内部酸化層中には、前記鋼板の中心に向かってx値が減少する酸化物(Fex,Mn1-x)2SiO4(0≦x<1)および非晶質SiO2が存在することを特徴とする(1)又は(2)に記載の熱延鋼板。
(4)前記内部酸化層において、前記網目状構造を有するSiを含む酸化物が、前記内部酸化層と前記地鉄との界面から表層酸化スケール方向に向かって前記内部酸化層厚の0%超50%以下の範囲に存在していることを特徴とする(1)~(3)のいずれか1つに記載の熱延鋼板。
(5)C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、残部が鉄および不純物からなるスラブであって、Si/Mn比が質量比で0.27以上0.90以下であるスラブを加熱して熱間圧延を行う工程と、
前記熱間圧延された鋼板を550℃以上800℃以下で巻取る工程と、
前記巻取った巻取り材を冷却過程において400℃以上500℃以下の範囲で、10時間以上20時間以下保持して熱延鋼板を得る工程と、
を有することを特徴とする熱延鋼板の製造方法。
(6)C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、残部が鉄および不純物からなるスラブであって、Si/Mn比が質量比で0.27以上0.90以下であるスラブを加熱して熱間圧延を行う工程と、
前記熱間圧延された鋼板を550℃以上800℃以下で巻取る工程と、
前記巻取った巻取り材を冷却過程において400℃以上500℃以下の範囲で、10時間以上20時間以下保持して熱延鋼板を得る工程と、
前記熱延鋼板を酸洗する工程と、
前記酸洗した熱延鋼板に対して冷間圧延を行って冷延鋼板を得る工程と、
を有することを特徴とする冷延鋼板の製造方法。
内部酸化層10の網目構造となった内部酸化物1は、太さ10nm以上200nm以下のSiを含む酸化物で、図1に示すように結晶粒界2から結晶粒内まで連結している。また、内部酸化物1の形状はさらに結晶粒内でもそれぞれが独立した粒子状、線状、または分岐構造を有して連続した網目状である。それにより、表層酸化スケール11と内部酸化層10との結晶粒界を浸透した酸溶液が、網目状構造が形成された内部酸化層10の下部に到達し、結晶粒界2から結晶粒内へ到達する。そして、酸溶液が、金属母相3および内部酸化物1が溶解される経路として、網目状構造の内部酸化物1と金属母相3との界面から結晶粒内に浸透する。以下、この金属母相3および内部酸化物1が溶解される経路を溶解パスと呼ぶ。
図3Bは、網目状構造の分岐数の数え方の説明するための図である。網目状構造の分岐数は、透過型電子顕微鏡(TEM)または走査型電子顕微鏡(SEM)などで断面観察時(5000~80000倍)に見られる酸化物の連続体における枝分かれの数(元枝から派生する枝の数)とする。
母材の鋼板成分中のSi含有量およびMn含有量は、強度や延性などの高強度鋼板として求められる特性を発揮するために、特定の範囲内に限定される。一方、熱間圧延後の巻取り材が内部酸化する過程において、Si/Mn比は生成する酸化物組成を決める重要な因子となる。一般的には、SiおよびMnの含有量が高い高強度鋼板では、Si系酸化物として、Fe2SiO4、Mn2SiO4、FeSiO3、MnSiO3、SiO2が内部酸化物として生成しうると考えられる。一方、SiおよびMnの含有量や酸素ポテンシャルによって、生成する酸化物組成および酸化物量が決まる。Al、Ti、Crなども鉄よりも易酸化元素であるため内部酸化元素となりうるが、本発明が対象とするような鋼板の含有量の範囲では、内部酸化層の構造および組成にはほとんど影響しない。熱間圧延後の巻取り材においては、通常、鋼板表層部の酸化スケールが酸素源となる。また、Fe2SiO4およびMn2SiO4と、FeSiO3およびMnSiO3とはそれぞれ全率固溶することから、0≦x≦1の範囲で(Fex,Mn1-x)2SiO4および(Fex,Mn1-x)SiO3で示される組成の酸化物も生成すると考えられている。
本発明の内部酸化層中に生成する(Fex,Mn1-x)2SiO4(0≦x<1)の化学組成で示される酸化物および非晶質SiO2を含む網目状構造は、内部酸化層の結晶粒内の酸溶解の起点となる溶解パスを形成するうえで重要である。(Fex,Mn1-x)2SiO4(0≦x<1)および非晶質SiO2が網目状構造となる理由については明らかではないが、内部酸化に関与する元素の拡散経路が影響していると考えられる。すなわち、金属母相の主成分である鉄を除き、酸素は酸化スケールから拡散し、SiおよびMnは結晶粒界の近傍および内部酸化層/地鉄界面に欠乏層を形成しながら結晶粒界を通じて内部酸化層中へ拡散する。そのため、(Fex,Mn1-x)2SiO4(0≦x<1)および非晶質SiO2は、結晶粒界を起点として、結晶粒界から結晶粒内へと連続して成長しやすいためと推定される。Si/Mn比が低いと、よりMn比率の高い(Fex,Mn1-x)2SiO4(0≦x<1)が生成する。内部酸化層での酸素ポテンシャルの分布は板厚方向では内方ほど低いので、x値が減少し、Mnの比率が増加する。Mn比率の高い(Fex,Mn1-x)2SiO4(0≦x<1)を生成させられるほど、板厚方向に対して、易溶解領域が拡大できる。
鋼材成分のSi/Mn比が0.27以上0.9以下であり、かつ内部酸化が発生する温度よりも50~100℃低い温度域の400℃以上500℃以下の範囲において、10時間以上20時間以下保持すると、(Fex,Mn1-x)2SiO4(0≦x<1)の化学組成で示される酸化物および非晶質SiO2を内部酸化層の結晶粒内のほぼ全域にわたって網目状構造で生成する。
Si系内部酸化物が生成する鋼材成分において、より酸素解離圧の低い非晶質SiO2が生成する。とくに本発明が規定するSi/Mn比が0.90以下のときは、(Fex,Mn1-x)2SiO4(0≦x<1)の化学組成で示される内部酸化物の領域において、非晶質SiO2が網目状構造として見られる。
非晶質SiO2を確認する方法は、特に限定しない。上述の内部酸化層の電気化学的な溶解によって、酸化物残渣として回収することはできる。ところが、X線回折では非晶質のため確認できないため、得られた残渣を、たとえば、FT-IR法により分析する方法が挙げられる。
なお、Ar3変態点(℃)は、各元素の含有量(質量%)を用いた下式により計算する。
Ar3=901-325×C+33×Si-92×(Mn+Ni/2+Cr/2+Cu/2+Mo/2)+52×Al
本発明で対象とする高強度鋼板は、高い合金含有量により熱間圧延から巻取りまでの相変態が遅いため、550℃未満の低温で巻取った場合、多量のマルテンサイトおよび残留オーステナイトが生成する。この場合、熱延原板の強度が高くなり、鋼板が冷間圧延時に破断する恐れがある。そのため、550℃以上の温度で巻取ることでフェライト変態およびパーライト変態を進め、軟質化させて冷延性を確保する必要がある。経験的に550℃未満では内部酸化は発生しないか、発生しても板厚方向での成長速度は遅い。内部酸化の発生に関する温度と拡散との相関性は明確にはなっていないが、一般的にSiおよびMnを一定量以上含むような高強度鋼板においては、550℃が内部酸化が発生する温度の下限値である。また、熱間圧延後の巻取り温度が高いほど、よりフェライト変態およびパーライト変態を進めやすいため、より好ましくは、巻取り温度は600℃以上である。巻取り温度が600℃以上の場合、フェライト変態およびパーライト変態を完了させやすく、より冷延性に優れた組織とすることができる。
網目状酸化物の酸溶解性への効果について上述したが、ただ(Fex,Mn1-x)2SiO4(0≦x<1)の化学組成で示される酸化物および非晶質SiO2を生成させるだけでは、内部酸化層の酸洗性を大幅に向上させることはできない。内部酸化物を結晶粒界および粒界近傍だけでなく、結晶粒内のほぼ全域にわたって分散して、かつ結晶粒界から結晶粒内にも連続するように形成させる必要がある。そこで、Si/Mn比の制御に加え、内部酸化が成長する際の熱量を制御することで結晶粒内での網目状構造を有する酸化物を成長させられることを見出した。
熱間圧延を施して巻取った鋼材は、酸洗により鋼材表層部の酸化スケールおよび内部酸化層が除去される。場合によっては、酸化スケール中の酸素が内部酸化により消費されることで、酸化スケール中および酸化スケールの表層に金属鉄層が生成することもあるが、これも酸洗により除去する必要がある。酸洗によって、鋼板表面の酸化物を除去することが可能であり、最終製品の高強度冷延鋼板の化成性を向上させる点、および溶融亜鉛めっき鋼板用あるいは合金化溶融亜鉛めっき鋼板用の冷延鋼板の溶融めっき性を向上させる点から酸洗は重要である。酸洗は一回のみの処理でも良いし、複数回に分けて施してもよい。
本発明で対象としている、酸洗しやすい内部酸化構造を有する熱延鋼板は、酸洗後、冷間圧延が行われることによって、冷延鋼板として使用される。ただし、一般的に熱延鋼板の強度が高すぎると、冷間圧延時に破断などを引き起こす原因となり冷延性を確保できないため、フェライト変態およびパーライト変態を完了させる必要がある。また、鋼材中のMnの含有量が高すぎると、溶接性が劣化するため、冷延性にも影響を与える。鋼材のMn含有量が3.6質量%、Si含有量が1.0質量%のときのSi/Mn比0.27以上であれば、冷延性を確保できる。また、酸洗で内部酸化層を除去しきらないまま冷間圧延を施すと、残存する内部酸化層の剥離によりクラックが生じ、化成性が劣化したり、焼鈍時にハースロール表面へのピックアップが形成したりする原因となる。よって、冷延鋼板としての特性を得るためには、熱間圧延後の巻取り材の内部酸化層は酸洗によって完全に除去される必要がある。本発明は、冷延鋼板としての特性を維持したうえで、熱間圧延後の巻取りで生成される内部酸化層の構造を酸洗しやすいものにすることによって酸洗時間を短縮し、生産性の向上を図るものである。
Cは残留オーステナイト相を得るために必要な元素であり、優れた成形性と高強度とを両立するために含有される。C含有量が0.45質量%を超えると、溶接性が不十分となるため、C含有量の上限を0.45質量%とした。一方、C含有量が0.05質量%未満であると、十分な量の残留オーステナイト相を得ることが困難となり、強度および成形性が低下する。強度および成形性の観点から、C含有量の下限を0.05質量%とした。
Siは、鋼板における鉄系炭化物の生成を抑制することによって残留オーステナイト相を得やすくする元素であり、強度と成形性とを高めるために必要である。Si含有量が3.00質量%を超えると鋼板が脆化し、延性が劣化するので、Si含有量の上限を3.00質量%とした。一方、Si含有量が0.5質量%未満では、焼鈍後に室温まで冷却する間に鉄系炭化物が生成し、十分に残留オーステナイト相が得られない。その結果、強度および成形性が劣化し、活量が低く、熱間圧延での内部酸化が発生しにくいため、Si含有量の下限を0.5質量%とした。
Mnは、鋼板の強度を高めるために含有され、また、オーステナイトを安定化し、残留オーステナイトの生成による加工性に優れた高強度鋼板としての特性を得るのに重要な元素である。Mn含有量が3.60質量%を超えると、脆化が起こりやすくなり、鋳造したスラブの割れが起こりやすい。また、Mn含有量が3.60質量%を超えると、溶接性も劣化するという問題がある。このため、Mn含有量の上限を3.60質量%とした。一方、Mn含有量が0.50質量%未満であると、焼鈍後の冷却中に軟質な組織が多量に生成されるので、強度を確保することが難しくなる。また、活量が低く、熱間圧延での内部酸化が発生しにくいため、Mn含有量の下限を0.50%とした。
Pは、鋼板の板厚中央部に偏析する傾向があり、溶接部を脆化させる特性がある。Pの含有量が0.030質量%を超えると溶接部が大幅に脆化するので、Pは0.030質量%以下で含有する。ただし、P含有量を0.001%未満とすると製造コストが大幅に増加するため、P含有量は0.001質量%とすることが好ましい。
Sは、溶接性並びに鋳造時および熱間圧延時の製造性に悪影響を及ぼしたり、Mnと結びついて粗大なMnSを形成して延性および伸びフランジ性を低下させたりするので、S含有量は0.0100質量%以下とする。ただし、Sの含有量を0.0001質量%未満とすると製造コストが大幅に増加するため、S含有量は0.0001質量%以上とすることが好ましい。
Alは、鉄系炭化物の生成を抑えて残留オーステナイトを得やすくする元素であり、鋼板の強度および成形性を高める。Al含有量が1.500質量%を超えると溶接性が悪化するので、Al含有量は1.500質量%以下とする。ただし、Alは脱酸材としても有効な元素であり、Al含有量が0.005質量%未満では脱酸材としての効果が十分に得られないので、脱酸の効果を十分に得るには、Al含有量は0.005質量%以上含有していることが好ましい。
Nは、粗大な窒化物を形成し、延性および伸びフランジ性を劣化させるので、添加量を抑える必要がある。N含有量が0.0100質量%を超えると、この傾向が顕著となるので、N含有量は0.0100質量%以下とする。一方、N含有量を0.0001質量%未満にすると、製造コストが大幅に増加するため、N含有量は0.0001質量%以上とすることが好ましい。
Oは、酸化物を形成し、O含有量が0.0100質量%を超えると、延性および伸びフランジ性を劣化が顕著となるので、O含有量は0.0100質量%以下とする。一方、O含有量が0.0001質量%未満とすると、製造コストが大幅に増加するため、O含有量は0.0001質量%以上とすることが好ましい。
Tiは、析出物強化、フェライト結晶粒の成長抑制による細粒強化および再結晶の抑制を通じた転位強化により、鋼板の強度上昇に寄与する元素である。Ti含有量が0.150質量%を超えると、炭窒化物の析出が多くなって成形性が劣化するので、Ti含有量は0.150質量%以下とする。また、Tiによる強度上昇効果を十分に得るために、Ti含有量は0.005質量%以上であることが好ましい。
Nbは、析出物強化、フェライト結晶粒の成長抑制による細粒強化および再結晶の抑制を通じた転位強化により、鋼板の強度上昇に寄与する元素である。Nb含有量が0.150質量%を超えると、炭窒化物の析出が多くなって成形性が劣化するので、Nb含有量は0.150質量%以下とする。また、Nbによる強度上昇効果を十分に得るために、Nb含有量は0.010質量%以上であることが好ましい。
Vは、析出物強化、フェライト結晶粒の成長抑制による細粒強化および再結晶の抑制を通じた転位強化により、鋼板の強度上昇に寄与する元素である。V含有量が0.150質量%を超えると、炭窒化物の析出が多くなって成形性が劣化するので、V含有量は0.150質量%以下とする。また、Vによる強度上昇効果を十分に得るために、V含有量は0.005質量%以上であることが好ましい。
Bは、高温での相変態を抑制し、高強度化に有効な元素であり、CまたはMnの一部に代えて含有される。B含有量が0.0100質量%を超えると、熱間での加工性が損なわれ生産性が低下するので、B含有量は0.0100質量%以下とする。また、Bによる強度上昇効果を十分に得るために、B含有量は0.0001質量%以上であることが好ましい。
Moは、高温での相変態を抑制し、高強度化に有効な元素であり、CまたはMnの一部に代えて含有される。Mo含有量が1.00質量%を超えると、熱間での加工性が損なわれて生産性が低下するので、Mo含有量は1.00質量%以下とする。Moによる強度上昇効果を十分に得るために、Mo含有量は0.01質量%以上であることが好ましい。
Wは、高温での相変態を抑制し、高強度化に有効な元素であり、CまたはMnの一部に代えて含有される。W含有量が1.00質量%を超えると、熱間での加工性が損なわれて生産性が低下するので、W含有量は1.00質量%以下とする。また、Wによる強度上昇効果を十分に得るために、含有量は0.01質量%以上であることが好ましい。
Crは、高温での相変態を抑制し、高強度化に有効な元素であり、CまたはMnの一部に代えて含有される。Cr含有量が2.00質量%を超えると、熱間での加工性が損なわれて生産性が低下するので、Cr含有量は2.00質量%以下とする。また、Crによる強度上昇効果を十分に得るために、Cr含有量は0.01質量%以上であることが好ましい。
Niは、高温での相変態を抑制し、高強度化に有効な元素であり、CまたはMnの一部に代えて含有される。Ni含有量が2.00質量%を超えると、溶接性が損なわれるので、Ni含有量は2.00質量%以下とする。また、Niによる強度上昇効果を十分に得るために、Ni含有量は0.01質量%以上であることが好ましい。
Cuは、微細な粒子として鋼中に存在することで強度を高める元素であり、CまたはMnの一部に替えて含有される。Cu含有量が2.00質量%を超えると、溶接性が損なわれるので、Cu含有量は2.00質量%以下とする。また、Cuによる強度上昇効果を十分に得るには、Cu含有量は0.01質量%以上であることが好ましい。
Ca、Ce、Mg、Zr、Hf、およびREMは、成形性の改善に有効な元素であり、1種または2種以上が含有される。ここで、REMとは、Rare Earth Metalの略であり、ランタノイド系列に属する元素を示す。Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種又は2種以上の含有量が合計で0.5000質量%を超えると、延性を損なうおそれがあるので、各元素の含有量の合計は0.5000質量%以下とする。また、鋼板の成形性を改善する効果を十分に得るためには、各元素の含有量の合計が0.0001質量%以上であることが好ましい。
表1に示す鋼材No.A~Zの化学成分を有するスラブを鋳造し、1250℃に加熱し、仕上げ温度870℃~900℃で厚さ3.0mmまで熱間圧延を行った。その後、表2に示す温度で巻取りを施し、さらに400℃から500℃の温度域で一定時間保持しながら、冷却した。
表1に示す化学成分を有し、表2に示す巻取りおよび熱処理した熱延鋼板について、走査型電子顕微鏡(JEOL製、JSM-6500F)により、1000~5000倍の内部酸化層が一視野内に入る範囲で、熱延鋼板の板厚方向の任意の断面10視野を観察したときの平均値から、内部酸化層の厚さを求めた。このとき内部酸化層の厚さは、表層に生成する酸化スケール/内部酸化層界面から、内部酸化層/地鉄界面までの距離とした。ただし、内部酸化層/地鉄界面における粒界酸化物及び結晶粒内の内部酸化物の板厚方向の深さは均一では無く、観察対象の断面の箇所によってばらつきがある。そこで、前記観察において、板厚方向に対して最も地鉄側に位置する結晶粒界の内部酸化物及び結晶粒内の内部酸化物の末端が連結した面を特定し、この面を内部酸化層/地鉄界面とした。また、結晶粒内の内部酸化物及び結晶粒界の内部酸化物の有無については、5000倍で観察した断面10視野の結晶粒内および結晶粒界に、内部酸化物が存在すれば有、存在しないものがあれば無とした。
表1に示す化学成分を有し、表2に示す条件で巻取りおよび熱処理した熱延鋼板について、内部酸化層の結晶粒内の内部酸化物のSiの有無、結晶粒内の内部酸化物の太さ、結晶粒内の内部酸化物の分岐数、結晶粒界および結晶粒内の内部酸化物の連結数は、以下の手順で判定した。まず、内部酸化層の板厚方向の断面を集束イオンビーム(ZEISS製、Crossbeam 1540 ESB)で加工した薄片サンプルを作製した。そして、透過型電子顕微鏡(FEI製、Tecnai G2 F30)により、80000倍で、内部酸化層/地鉄界面から、表層酸化スケール方向に向かって内部酸化層の厚さの0%以上30%以下の範囲における1μm×1μm四方の任意の断面を観察してこれらを判定した。また、前記観察において、板厚方向に対して最も地鉄側に位置する内部酸化層の結晶粒界の内部酸化物及び内部酸化物の末端が連結した面を特定し、この面を内部酸化層/地鉄界面とした。
先に示した内部酸化物の分岐数の数え方は、前述したように図3に示した方法を用い、任意の視野に含まれる酸化物20個における分岐数の平均値から算出した。
また、内部酸化物の太さ、内部酸化物の分岐数、結晶粒界および内部酸化物の連結数を算出した内部酸化物については、エネルギー分散型X線分光法(FEI製、Tecnai G2 F30)により元素分析を行い、Si成分が検出されれば有、検出されなければ無とした。
これらの測定結果を、表3に示す。
内部酸化層中の酸化物の組成は、以下の手順で特定した。まず、巻取り材を400ppmの市販のインヒビター(朝日化学工業株式会社製、イビット710)を含有する50℃の10重量%くえん酸水溶液中に酸化スケール層が溶解するまで浸漬した。その後、10重量%アセチルアセトンおよび1重量%塩化テトラメチルアンモニウムを含むメタノール溶液中、電流密度約320Am-2で電解して電気化学的に金属鉄のみを5μm厚程度溶解させ、酸化物残渣を0.1μm×35mmφのフィルター上に回収した。この操作を内部酸化層の金属母相が溶解するまで複数回繰り返すことで、深さ方向の内部酸化物の抽出を行った。抽出した残渣は、θ/2θ法の連続スキャンでX線回折を行い(リガク製、RINT1500、スキャンスピード:0.4°min-1、サンプリング幅:0.010°)、(Fex,Mn1-x)2SiO4(0≦x<1)の存在有無を確認した。
また、電解抽出した残渣と臭化カリウム結晶とを混合させ、錠剤にプレス加工した後、日本分光(株)製FT/IR6100を用いてFT-IRの透過法(検出器TGS、分解能4 cm-1、積算回数100回、測定サイズ10 mmφ)により測定し、非晶質SiO2の存在有無を調べた。
また、Fe2SiO4およびMn2SiO4に共通する回折面の格子間隔を比較することで、(Fex,Mn1-x)2SiO4(0≦x<1)におけるFeおよびMnの含有比率の変化について調べた。(111)面の場合、格子間隔はFe2SiO4で3.556nmであり、Mn2SiO4で3.627nmである。まず、電解抽出により得られた残渣をθ/2θ法の連続スキャンでX線回折を行った(リガク製、RINT1500、スキャンスピード:0.4°min-1、サンプリング幅:0.010°)。その結果、(111)面の格子間隔が3.627nmに近づくほど、(Fex,Mn1-x)2SiO4におけるMnの比率が高いことを示しており、xの値が小さいと判定した。このとき、内部酸化層の内方になるほどMn比率が単調に増加すれば○、一部で増加せずに一定であれば△、すべてにおいて一定または減少した場合は×とした。これらの結果を、表4の項目「(Fex,Mn1-x)2SiO4(0≦x<1)のxが内方ほど小さい傾向」の欄に示す。
網目状構造を有するSiを含む酸化物が、内部酸化層/地鉄界面から表層酸化スケール方向に向かって内部酸化層の厚さの0%以上50%以下の範囲に存在しているか否かについては、前述と同様の方法で、その範囲における内部酸化物の太さ、内部酸化物の分岐の有無、結晶粒界および結晶粒内の内部酸化物の連結有無から判定した。このとき、透過型電子顕微鏡(FEI製、Tecnai G2 F30)により、80000倍で観察を行い、1μm×1μm四方の任意の10視野において、すべての視野で網目状酸化物が存在すれば○、1視野以上9視野以下で存在が確認された場合は△、1視野も存在が確認されなければ×とした。これらの測定結果を、表4の「内部酸化層/地鉄界面から内部酸化層厚の0-50%に網目状構造」の欄に示す。
表1に示す化学成分を有し、表2に示す条件で巻取りおよび熱処理した熱延鋼板は、内部酸化層を溶解除去するのに必要な酸洗完了時間によって、酸洗性を評価した。
酸洗では、巻取り材を80g/Lの鉄(II)イオンと、1g/Lの鉄(III)イオンおよび、400ppmの市販のインヒビター(朝日化学工業株式会社製、イビット710)を含有する85℃の9質量%の塩酸水溶液中に浸漬した。そして、内部酸化層の金属母相を含む結晶粒が除去された時間を酸洗完了時間とした。ただし、酸洗完了時間の測定は実験作業の誤差範囲上、5秒単位とした。また、内部酸化層の除去の判定は、鋼材表面の目視観察および酸洗した熱延鋼板の断面を走査型電子顕微鏡(JEOL社、JSM-6500F)で1000~5000倍で内部酸化層が一視野内に入る範囲で観察することで行った。
なお、酸洗完了時間は従来技術である前記特許文献1において、酸化スケールの溶解に45秒を要する熱延鋼板の場合、粒界酸化層が5μmでは90秒以上、10μmでは135秒以上、15μmでは180秒以上、20μmでは225秒以上酸洗する必要があることを提示されているが、その2/3に相当する時間を目標酸洗時間とした。
また、冷延性を評価するため、内部酸化層厚が5μm以下で60秒、5μm超10μm以下で90秒、10μm超15μm以下で120秒、15μm超で150秒という目標酸洗時間でそれぞれ酸洗処理をした熱延鋼板を、冷間圧延機により、板厚1.5mmにまで圧延処理を施した。
表2における鋼板No.1~No.7は、Siが1.0質量%で共通し、巻取り温度を650℃とし、400℃~500℃の温度域での保持時間を15時間として、Si/Mn比を変えたときの例である。
鋼板No.2~No.4は、Si/Mn比が0.27以上0.70以下であり、この場合、酸洗完了時間は45秒~55秒となった。このようにSi/Mn比が0.70以下と低いため、内方ほどMn比率が高く、内部酸化層/地鉄界面ではxが0に近い(Fex,Mn1-x)2SiO4が生成した。また、400℃から500℃での温度域での保持時間が15時間であるため、網目状酸化物が内部酸化層の外方50%程度以上に広く生成した。これによって、内部酸化層中の結晶粒内の内部酸化物の分岐数が増大し、結晶粒界および結晶粒内の内部酸化物の連結数が増大した。以上の結果から、鋼板No.2~No.4は、酸洗液が結晶粒界から酸化物/金属母相界面を溶解パスとして浸透しやすいとの結果が得られた。
続いて、冷延性への影響を確認するため、目標酸洗時間でそれぞれ酸洗処理した熱延鋼板を、冷間圧延機により板厚1.5mmに圧延処理を施した後、目視により表面に剥離およびむらがないかどうかを確認した。剥離やむらが認められなければ○、認められたものは×と判定した。
Claims (6)
- C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、
残部が鉄および不純物からなる鋼板において、
前記鋼板の母材の鋼材成分のSi/Mn比が質量比で0.27以上0.90以下であり、
鋼板表層部の酸化スケール直下に、厚さが1μm以上30μm以下の内部酸化層を有し、
前記内部酸化層の結晶粒内の内部酸化物は、前記内部酸化層と地鉄との界面から表層酸化スケール方向に向かって前記内部酸化層の厚さの0%超30%以下の範囲における結晶粒内において、太さ10nm以上200nm以下のSiを含む酸化物であり、かつ1μm×1μm四方の断面に前記内部酸化物の分岐が1本以上存在し、かつ長さ1μmの任意の結晶粒界において前記内部酸化物の1つ以上が前記結晶粒界の内部酸化物と連結して網目状構造を形成していることを特徴とする熱延鋼板。 - 前記母材の鋼材成分のSi/Mn比が質量比で0.70以下であることを特徴とする請求項1に記載の熱延鋼板。
- 前記内部酸化層中には、前記鋼板の中心に向かってx値が減少する酸化物(Fex,Mn1-x)2SiO4(0≦x<1)および非晶質SiO2が存在することを特徴とする請求項1又は2に記載の熱延鋼板。
- 前記内部酸化層において、前記網目状構造を有するSiを含む酸化物が、前記内部酸化層と前記地鉄との界面から表層酸化スケール方向に向かって前記内部酸化層厚の0%超50%以下の範囲に存在していることを特徴とする請求項1~3のいずれか1項に記載の熱延鋼板。
- C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、残部が鉄および不純物からなるスラブであって、Si/Mn比が質量比で0.27以上0.90以下であるスラブを加熱して熱間圧延を行う工程と、
前記熱間圧延された鋼板を550℃以上800℃以下で巻取る工程と、
前記巻取った巻取り材を冷却過程において400℃以上500℃以下の範囲で、10時間以上20時間以下保持して熱延鋼板を得る工程と、
を有することを特徴とする熱延鋼板の製造方法。 - C:0.05質量%~0.45質量%、
Si:0.5質量%~3.0質量%、
Mn:0.50質量%~3.60質量%以下、
P:0.030質量%以下、
S:0.010質量%以下、
Al:0質量%~1.5質量%、
N:0.010質量%以下、
O:0.010質量%以下、
Ti:0質量%~0.150質量%、
Nb:0質量%~0.150質量%、
V:0質量%~0.150質量%、
B:0質量%~0.010質量%、
Mo:0質量%~1.00質量%、
W:0質量%~1.00質量%、
Cr:0質量%~2.00質量%、
Ni:0質量%~2.00質量%、
Cu:0質量%~2.00質量%、および
Ca、Ce、Mg、Zr、HfおよびREMからなる群から選ばれる1種または2種以上の合計:0質量%~0.500質量%、を含有し、残部が鉄および不純物からなるスラブであって、Si/Mn比が質量比で0.27以上0.90以下であるスラブを加熱して熱間圧延を行う工程と、
前記熱間圧延された鋼板を550℃以上800℃以下で巻取る工程と、
前記巻取った巻取り材を冷却過程において400℃以上500℃以下の範囲で、10時間以上20時間以下保持して熱延鋼板を得る工程と、
前記熱延鋼板を酸洗する工程と、
前記酸洗した熱延鋼板に対して冷間圧延を行って冷延鋼板を得る工程と、
を有することを特徴とする冷延鋼板の製造方法。
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- 2016-03-22 WO PCT/JP2016/059027 patent/WO2016152870A1/ja active Application Filing
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KR20190073462A (ko) * | 2016-11-24 | 2019-06-26 | 아르셀러미탈 | 열간 스탬핑을 위한 열간 압연되고 코팅된 강 시트, 열간 스탬핑되고 코팅된 강 부품 및 이의 제조 방법 |
KR20210074405A (ko) * | 2016-11-24 | 2021-06-21 | 아르셀러미탈 | 열간 스탬핑을 위한 열간 압연되고 코팅된 강 시트, 열간 스탬핑되고 코팅된 강 부품 및 이의 제조 방법 |
KR102272870B1 (ko) * | 2016-11-24 | 2021-07-06 | 아르셀러미탈 | 열간 스탬핑을 위한 열간 압연되고 코팅된 강 시트, 열간 스탬핑되고 코팅된 강 부품 및 이의 제조 방법 |
KR102308581B1 (ko) | 2016-11-24 | 2021-10-05 | 아르셀러미탈 | 열간 스탬핑을 위한 열간 압연되고 코팅된 강 시트, 열간 스탬핑되고 코팅된 강 부품 및 이의 제조 방법 |
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WO2022097642A1 (ja) * | 2020-11-06 | 2022-05-12 | 日本製鉄株式会社 | 内部酸化層厚み推定装置、内部酸化層厚み推定方法、及びプログラム |
JP7425377B2 (ja) | 2020-11-06 | 2024-01-31 | 日本製鉄株式会社 | 内部酸化層厚み推定装置、内部酸化層厚み推定方法、及びプログラム |
WO2022196733A1 (ja) * | 2021-03-17 | 2022-09-22 | 日本製鉄株式会社 | 鋼板、鋼部材及び被覆鋼部材 |
Also Published As
Publication number | Publication date |
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US11066720B2 (en) | 2021-07-20 |
EP3276030A1 (en) | 2018-01-31 |
KR20170122723A (ko) | 2017-11-06 |
PL3276030T3 (pl) | 2020-09-21 |
JP6070907B1 (ja) | 2017-02-01 |
ES2800302T3 (es) | 2020-12-29 |
TW201700749A (zh) | 2017-01-01 |
KR101958130B1 (ko) | 2019-03-13 |
US20170369964A1 (en) | 2017-12-28 |
MX2017009418A (es) | 2017-11-08 |
EP3276030B1 (en) | 2020-05-06 |
CN107429343A (zh) | 2017-12-01 |
TWI588272B (zh) | 2017-06-21 |
JPWO2016152870A1 (ja) | 2017-04-27 |
EP3276030A4 (en) | 2018-10-10 |
BR112017014368A2 (ja) | 2018-01-02 |
CN107429343B (zh) | 2019-05-28 |
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