WO2020251002A1 - Austenitic stainless steel and manufacturing method thereof - Google Patents
Austenitic stainless steel and manufacturing method thereof Download PDFInfo
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- WO2020251002A1 WO2020251002A1 PCT/JP2020/023152 JP2020023152W WO2020251002A1 WO 2020251002 A1 WO2020251002 A1 WO 2020251002A1 JP 2020023152 W JP2020023152 W JP 2020023152W WO 2020251002 A1 WO2020251002 A1 WO 2020251002A1
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- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims description 58
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 238000005098 hot rolling Methods 0.000 claims abstract description 39
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 32
- 239000010959 steel Substances 0.000 claims abstract description 32
- 238000001816 cooling Methods 0.000 claims abstract description 23
- 238000000034 method Methods 0.000 claims abstract description 16
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 12
- 238000009749 continuous casting Methods 0.000 claims abstract description 4
- 238000009826 distribution Methods 0.000 claims description 30
- 238000003892 spreading Methods 0.000 claims description 18
- 230000007480 spreading Effects 0.000 claims description 18
- 239000000203 mixture Substances 0.000 claims description 15
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 15
- 150000002910 rare earth metals Chemical class 0.000 claims description 15
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 239000000126 substance Substances 0.000 claims description 14
- 230000005291 magnetic effect Effects 0.000 claims description 10
- 230000008569 process Effects 0.000 claims description 10
- 230000009467 reduction Effects 0.000 claims description 9
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 230000035699 permeability Effects 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- 229910052787 antimony Inorganic materials 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 5
- 229910052745 lead Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052717 sulfur Inorganic materials 0.000 claims description 5
- 229910052718 tin Inorganic materials 0.000 claims description 5
- 229910052721 tungsten Inorganic materials 0.000 claims description 5
- 229910052727 yttrium Inorganic materials 0.000 claims description 5
- 229910052726 zirconium Inorganic materials 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 abstract description 8
- 238000005096 rolling process Methods 0.000 description 24
- 229910001220 stainless steel Inorganic materials 0.000 description 18
- 239000010935 stainless steel Substances 0.000 description 16
- 230000000694 effects Effects 0.000 description 13
- 238000010273 cold forging Methods 0.000 description 11
- 230000007797 corrosion Effects 0.000 description 10
- 238000005260 corrosion Methods 0.000 description 10
- 230000007423 decrease Effects 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 7
- 239000006104 solid solution Substances 0.000 description 7
- 229910001566 austenite Inorganic materials 0.000 description 5
- 230000000704 physical effect Effects 0.000 description 5
- 238000005482 strain hardening Methods 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 230000009471 action Effects 0.000 description 4
- 230000002411 adverse Effects 0.000 description 4
- 230000005389 magnetism Effects 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000005554 pickling Methods 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 229920006395 saturated elastomer Polymers 0.000 description 4
- 238000009628 steelmaking Methods 0.000 description 4
- 239000002344 surface layer Substances 0.000 description 4
- 238000003483 aging Methods 0.000 description 3
- 230000032683 aging Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 238000000137 annealing Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000005242 forging Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical class [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- -1 Mo: 0.01 to 3.00% Substances 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 206010070834 Sensitisation Diseases 0.000 description 1
- 229940069428 antacid Drugs 0.000 description 1
- 239000003159 antacid agent Substances 0.000 description 1
- 230000001458 anti-acid effect Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
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- 238000005530 etching Methods 0.000 description 1
- 230000005496 eutectics Effects 0.000 description 1
- 230000005294 ferromagnetic effect Effects 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
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- 239000002245 particle Substances 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000008313 sensitization Effects 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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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
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
-
- 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
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
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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
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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
- C21D8/0221—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
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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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- 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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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- 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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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
Definitions
- the present invention relates to austenitic stainless steel and a method for producing the same.
- the metal exterior members used for them are harshly cold in order to handle processing into complex shapes. After forging, the method of molding by cutting has come to be widely used. Further, depending on the design of the portable electronic device, mirror polishing may be performed after the cutting process.
- the exterior member of the portable electronic device is required not only to be non-magnetic in order to avoid adverse effects on the geomagnetic sensor and the like built in the own device, but also to have high strength. Further, since the above-mentioned electronic device is portable and is often used in an outdoor environment, the exterior member is also required to have higher corrosion resistance than the member for the electronic device which is supposed to be used indoors.
- Patent Document 1 describes a non-magnetic austenitic stainless steel sheet (hereinafter, simply referred to as "stainless steel sheet”) which has been cold forged and cut to form a non-magnetic member. ) Is disclosed.
- Patent Document 1 The method for manufacturing a stainless steel sheet described in Patent Document 1 is a good method for manufacturing non-magnetic and high-strength parts, but the manufacturing process is complicated and costly, and depending on the product shape, the manufactured stainless steel sheet may be used. There is a problem that it cannot be used.
- FIG. 8 shows the hardness distribution in the plate thickness direction of a stainless steel plate adjusted to a plate thickness of 8 mm and an average cross-sectional hardness of 300 HV.
- the strain of the surface layer is large and the strain at the center of the plate thickness is small. Therefore, the surface layer shows a hardness of 332 HV, while the center of the plate thickness shows only 275 HV. That is, the stainless steel sheet of Patent Document 1 has a problem that the hardness in the plate thickness direction becomes non-uniform when the plate thickness is increased to a certain level or more.
- One aspect of the present invention has been made in view of the above problems, and an object of the present invention is to reduce variations in cross-sectional hardness distribution in the thickness direction even though the thickness is a certain degree or more.
- the purpose is to realize austenitic stainless steel and its manufacturing method.
- the austenitic stainless steel according to one aspect of the present invention has a combined content of C and N of 0.08% or more in mass% and a cross-sectional hardness in the thickness direction.
- the average of the hardness distribution is 250 HV or more, the fluctuation range is 30 HV or less, and the thickness is 3 mm or more.
- the average cross-sectional hardness distribution in the thickness direction is 250 HV or more and the fluctuation range is 30 HV or less even though the thickness is 3 mm or more. Therefore, it is possible to provide an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is more than a certain level.
- the austenitic stainless steel according to one aspect of the present invention has a chemical composition of C: 0.003 to 0.12%, Si: 2.00% or less, Mn in mass%. : 2.00% or less, P: 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 Consists of ⁇ 0.20%, balance Fe and unavoidable impurities.
- the austenitic stainless steel according to one aspect of the present invention preferably has a relative magnetic permeability ⁇ of 1.1 or less. According to the above configuration, it is possible to provide a non-magnetic austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is a certain degree or more.
- the method for producing austenite-based stainless steel according to one aspect of the present invention is, in terms of mass%, C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, Contains P: 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20% However, the combined content of C and N is 0.08% or more in mass%, and the slab produced by continuous casting having a chemical composition composed of the balance Fe and unavoidable impurities is brought to 1000 to 1300 ° C.
- the finishing hot-rolling step which includes a cooling step of cooling the steel strip
- the reduction rate of the finishing hot-rolling is 60% or more
- the roll diameter of the finishing hot-rolling is 300 mm or more
- the finishing hot-rolling is performed.
- the temperature of the steel strip is 600 to 1100 ° C.
- the final pass temperature of the finishing heat spreading is 600 to 950 ° C.
- the final pass temperature of the finishing hot spreading of the steel strip is 750 ° C. or higher in the cooling step. Is a method of cooling to 750 ° C.
- a method for producing austenitic stainless steel capable of producing austenitic stainless steel in which variations in cross-sectional hardness distribution in the thickness direction are reduced even though the thickness is a certain degree or more is realized. be able to.
- the slab is further increased in mass%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al: 0.0080% or less, O: 0.0040 to 0.
- the slab further contains Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005 to 0.0030%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20%, REM (rare earth metal): 0.01 to 0.10%, Sn: 0.001 to 0. Contains one or more selected from 500% and Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50% [ 4] or [6], the method for producing austenitic stainless steel.
- an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is a certain degree or more.
- Austenitic stainless steel with reduced variation in cross-sectional hardness distribution in the thickness direction was realized despite having a certain thickness (3 mm or more), and (ii) austenitic stainless steel. If the final pass temperature of the finish hot-rolling is 750 ° C or higher, cool it to 750 ° C or lower at a cooling rate of 5 ° C / s or higher by heating the stainless steel to a high temperature and using a large-diameter roll to reduce it significantly.
- the point of the present invention is to find that the variation in the cross-sectional hardness distribution in the thickness direction can be reduced in the austenitic stainless steel having a thickness of 3 mm or more.
- the "austenitic stainless steel" described in the present specification includes both an austenitic stainless steel strip and an austenitic stainless steel sheet. In other words, the present invention is applicable to both austenitic stainless steel strips and austenitic stainless steel sheets.
- the present invention provides, for example, an austenitic stainless steel capable of manufacturing a structural member of an electronic device such as a smartphone by cutting, etching, electric discharge machining, etc. without performing complicated forging, and a method for manufacturing the austenitic stainless steel.
- the purpose is to realize.
- the austenitic stainless steel according to the embodiment of the present invention is applied as a structural member of a smartphone, if there is a soft portion (for example, a central portion in the thickness direction), it is likely to be scratched. Therefore, the value as a product is low. Further, even in a soft part, it is conceivable to make it sufficiently hard, but conversely, if a part that is harder than necessary is generated, the machinability is lowered.
- the austenitic stainless steel according to the embodiment of the present invention can be produced by subjecting each step of steelmaking, rough heat spreading, finishing hot spreading and cooling. More specifically, the slab produced by continuous casting is heated to 1000 to 1300 ° C. and then subjected to rough heat spreading to obtain a rough bar (steel strip) having a thickness of 25 mm (coarse heat spreading step). Then, the rough bar is hot-rolled for finishing at 600 ° C. or higher and 1100 ° C. or lower (finishing hot-rolling step).
- the reduction rate of the finishing hot-rolling is 60% or more
- the roll diameter of the finishing hot-rolling is 300 mm or more
- the final pass temperature of the finishing hot-rolling is 600 to 950 ° C.
- the manufactured steel strip is cooled to 750 ° C. or lower when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher at a cooling rate of 5 ° C./s or higher (cooling step).
- the obtained stainless steel may be pickled, if necessary, for the purpose of removing the oxide scale generated in the hot rolling process.
- the pickling treatment is carried out in an annealing pickling line in which the annealing step and the pickling step are connected.
- heat may be applied to the stainless steel in a temperature range (specifically, 900 ° C. or lower) at which the hardness of the stainless steel does not decrease.
- the average cross-sectional hardness distribution in the thickness direction can be 250 HV or more and the fluctuation range can be 30 HV or less even though the thickness is 3 mm or more. Therefore, it is possible to provide an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced.
- the cross-sectional hardness distribution in the thickness direction is a measurement of Vickers hardness at a plurality of points with a load of 1 kg so that the variation in cross-sectional hardness in the thickness direction can be seen for a cross section perpendicular to the rolling width direction.
- the stainless steel of Example A3 in which the thickness is 8 mm and the average cross-sectional hardness in the thickness direction is adjusted to 300 HV has a cross-sectional hardness distribution of 294 to 308 HV in the thickness direction as shown in FIG. It can be seen that the variation in the cross-sectional hardness distribution in the thickness direction is reduced as compared with the conventional technique.
- FIG. 2 is a graph showing the distribution of cross-sectional hardness of the austenitic stainless steel according to the embodiment of the present invention with respect to the thickness direction.
- FIG. 3 is a graph showing the relationship between the amount of C + N and the average cross-sectional hardness of austenitic stainless steel.
- the amount of C + N is the total content of C and N. Further, the amount of C + N includes the case where C is 0% or N is 0%.
- FIG. 3 shows the average of Examples A1 to A4 and Comparative Examples B1 and B2, which were rolled at a final pass temperature of 870 ° C. for hot rolling, cooled to 750 ° C. or lower at a cooling rate of 40 ° C./s, and wound up.
- the graph which plotted about the cross-sectional hardness is shown (see FIG. 4 for the chemical composition of each steel type of Examples A1 to A4 and Comparative Examples B1 and B2).
- A1 to A4 having a C + N amount of 0.08% or more had an average cross-sectional hardness of 250 HV or more, but B1 and B2 steels having a C + N amount of less than 0.08 had an average cross-sectional hardness of less than 250 HV. ..
- the relative magnetic permeability ⁇ is generally preferably 1.1 or less, more preferably 1.05 or less.
- the temperature is 600 ° C. or higher. Since it is rolled, process-induced martensite is not generated, but if ⁇ ferrite remains, the relative permeability increases.
- the austenitic stainless steel whose chemical composition has been adjusted as described above does not generate a work-induced martensite phase in the normal steel sheet manufacturing process and the subsequent cold forging process, magnetization due to the work-induced martensite phase occurs. Is avoided. However, a ⁇ ferrite phase may be formed at a high temperature during melting, and if this remains, non-magnetism with a magnetic permeability of 1.010 or less cannot be obtained. Further, if the ⁇ ferrite phase is mixed as a different phase in the product, the appearance of the mirror-polished product may be spoiled. Therefore, it is necessary that the ⁇ ferrite phase disappears at the stage of the steel sheet, which is the material used for cold forging. Since the ⁇ ferrite phase is ferromagnetic, its presence or absence is evaluated by magnetic permeability.
- the average cross-sectional hardness distribution of austenitic stainless steel in the thickness direction was aimed at 250 HV or more (SUS304CSP-1 / 2H standard). Further, the thickness of the austenitic stainless steel was aimed at 3 mm or more because, for example, the thickness range of the special metal Excel SUS301CSP is about 2.5 mm or less.
- the reduction rate of the finishing heat spread is preferably 60% or more.
- Condition No. in FIG. As shown in D001 to D006, when the reduction rate (total rolling rate) of the finish hot rolling is less than 60%, the rolling strain is not sufficiently applied and the target average cross-sectional hardness cannot be obtained.
- the roll diameter of the hot-rolled finish is preferably 300 mm or more. Condition No. in FIG. As shown in F01 to F19, when the roll diameter is small, the rolling strain cannot be applied to the center in the thickness direction, and the fluctuation range of the cross-sectional hardness becomes large at any rolling temperature.
- the roll diameter is the diameter of the cross section perpendicular to the rotation axis of the rolling roll.
- the temperature of the finishing heat spread is preferably 600 to 1100 ° C.
- the final pass temperature (final pass rolling temperature) of the hot rolling finish is preferably 600 to 950 ° C.
- the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, the desired cross-sectional hardness distribution cannot be obtained, and the temperature is too high for the final pass. It becomes difficult to adjust the rolling temperature to 950 ° C. or lower. Further, when the final pass rolling temperature exceeds 950 ° C., the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, and a desired cross-sectional hardness distribution cannot be obtained.
- a cooling step of cooling the steel strip subjected to the finishing hot-rolling to 750 ° C. or lower at a cooling rate of 5 ° C./s or more when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher is performed. It is preferable to have.
- the rolling strain accumulated in the material due to the hot rolling of the finish decreases immediately after the hot rolling of the finish when the stainless steel is kept at a high temperature. In order to reduce the reduction in rolling strain, it is preferable to quickly cool to a temperature range in which the reduction in rolling strain does not occur.
- FIG. 5 shows the physical properties of the austenitic stainless steel according to the embodiment of the present invention.
- FIGS. 6 and 7 show the physical properties of the austenitic stainless steel of the comparative example.
- the rolling temperature in FIGS. 5, 6 and 7 is the temperature of the steel sheet during rolling.
- No. 1 satisfying the above-mentioned manufacturing method conditions.
- the austenitic stainless steels produced by the production methods C01 to C25 had an average cross-sectional hardness distribution of 250 HV or more in the thickness direction and a fluctuation range of the cross-sectional hardness distribution of 30 HV or less.
- At least one of the above-mentioned manufacturing method conditions does not satisfy the above-mentioned manufacturing method conditions. Does not satisfy) No.
- the austenitic stainless steels produced by the production methods D01 to H06 had an average cross-sectional hardness distribution in the thickness direction of less than 250 HV and / or a fluctuation range of more than 30 HV.
- the chemical composition of the austenitic stainless steel according to the embodiment of the present invention is C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, P: in mass%. 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20%, balance Fe and Consists of unavoidable impurities.
- % in the steel composition means mass% unless otherwise specified.
- Mo 0.01 to 3.00%
- Cu 0.01 to 3.50%
- Al in mass%. 0.0080% or less
- O 0.0040 to 0.0100%
- V 0.01 to 0.5%
- B 0.001 to 0.01%
- Ti 0.01 to 0.50% It may contain one kind or two or more kinds of.
- Co 0.01 to 0.50%
- Zr 0.01 to 0.10%
- Nb 0.01 to 0.10%
- Mg 0.0005 to 0.0030%
- Ca 0.0003 to 0.0030%
- Y 0.01 to 0.20%
- REM rare earth metal
- C is an intrusive element and contributes to high strength by work hardening and strain aging. In addition, it is an element that stabilizes the austenite phase and is effective in maintaining non-magnetism. In the present invention, a C content of 0.003% or more is secured. However, excessive C content becomes a factor that hardens the steel and lowers the cold forging property. The C content is limited to 0.012% or less.
- Si is an element used as a deoxidizer for steel in the steelmaking process. Si has the effect of improving age hardening in the strain removing heat treatment. On the other hand, Si has a large solid solution strengthening action and also has an action of lowering stacking defect energy and increasing work hardening. Therefore, excessive Si content becomes a factor of lowering cold forging property. Therefore, the Si content is limited to 2.0% or less.
- Mn is an element that constitutes an oxide-based inclusion as MnO.
- Mn has a small solid solution strengthening action and is an austenite-forming element and has an action of suppressing process-induced martensitic transformation, so that it is an effective element for ensuring cold forging property and maintaining non-magnetism.
- the excessive Mn content causes a decrease in corrosion resistance.
- the Mn content is limited to 2.00% or less.
- P is an element that lowers the corrosion resistance, and excessive P reduction causes an increase in the steelmaking load, so it must be 0.040% or less.
- Cr is an element that improves corrosion resistance.
- the present invention targets steel having a Cr content of 16.0% or more.
- a large amount of Cr content causes a decrease in cold forging property.
- the upper limit of Cr content is limited to 22.0%.
- N is an intrusive element like C and contributes to high strength by work hardening and strain aging. In addition, it is an element that stabilizes the austenite phase and is effective in maintaining non-magnetism. In the present invention, an N content of 0.005% or more is secured. However, excessive N content becomes a factor that hardens the steel and lowers the cold forging property. The N content is limited to 0.20% or less.
- Mo is an element effective for improving the corrosion resistance of stainless steel.
- the Cr content is ensured and then added as needed.
- adding a large amount of Mo increases the cost. Therefore, when Mo is contained, the Mo content is 0.01%. It is ⁇ 3.00% or less.
- Cu is known to be effective in improving cold forging properties by suppressing work hardening of the austenite phase. Further, it is known that it is an element that causes age hardening in the heating temperature range of the strain removing heat treatment performed after cold forging. As a result of various studies, when Cu is contained, the Cu content is 0.01% to 3.5%.
- Al has a higher oxygen affinity than Si and Mn, and when the Al content is 0.0030% or more, coarse oxide-based inclusions which are the starting points of internal cracks in cold forging are likely to be formed. In addition, excessively low Al content increases the cost. Therefore, as a result of various studies, when Al is contained, the Al content is 0.0001% or more to 0.0080%.
- the O content When the O content is low, Mn, Si and the like are less likely to be oxidized, and the ratio of Al 2 O 3 in the inclusions is high. Further, if the O content is excessively high, coarse inclusions having a particle size of more than 5 ⁇ m are likely to be formed. Therefore, as a result of various studies, when O is contained, the O content is 40 ppm (0.0040%). It is ⁇ 100 ppm (0.0100%), preferably 80 ppm or less.
- V has the effect of enhancing the age hardening ability in the heating of the strain removing heat treatment performed after cold forging. Although it has an aging hardening effect, a large amount of V content leads to an increase in cost.
- V content is 0.01% to 0.05%.
- B is a factor that causes a decrease in workability due to the formation of boride. Therefore, when B is contained, the B content is 0.001 to 0.0100%, preferably 0.0050% or less.
- Ti is a carbonitride-forming element, which fixes C and N and suppresses a decrease in corrosion resistance due to sensitization. The above effect is exhibited when Ti is contained in an amount of 0.01% or more. Therefore, the Ti content is set to 0.01% or more. On the other hand, when the Ti content exceeds 0.50%, Ti is non-uniformly localized and precipitated in the steel as a carbide in a non-uniform size, which hinders the growth of sized recrystallized grains and is extremely difficult. Since it is expensive, the upper limit of the Ti content is set to 0.50%.
- Co has the effect of improving the crevice corrosion resistance. On the other hand, if Co is excessively contained, the steel is hardened and the bendability is adversely affected. Therefore, when Co is contained, the Co content is 0.01 to 0.50%, preferably 0.10% or less.
- Zr is an element having a high affinity for C and N, and is precipitated as a carbide or a nitride during hot rolling, and has an effect of reducing solid solution C and solid solution N in the matrix phase and improving workability. ..
- the Zr content is 0.01 to 0.10%, preferably 0.05% or less.
- Nb is an element having a high affinity for C and N, and is precipitated as a carbide or a nitride during hot rolling, and has an effect of reducing solid solution C and solid solution N in the matrix phase and improving workability. ..
- the Nb content is 0.01 to 0.10%, preferably 0.05% or less.
- Mg forms Mg oxide together with Al in molten steel and acts as an antacid.
- Mg is contained in an excessive amount, the toughness of the steel is lowered and the manufacturability is lowered. Therefore, when Mg is contained, the Mg content is 0.0005 to 0.0030%, preferably 0.0020% or less.
- Ca is an element that improves hot workability.
- the toughness of the steel is lowered and the manufacturability is lowered, and further, the corrosion resistance is lowered due to the precipitation of CaS. Therefore, when Ca is contained, the Ca content is 0.0003 to 0.0030%, preferably 0.0020% or less.
- Y is an element that reduces the decrease in viscosity of molten steel and improves cleanliness. On the other hand, if Y is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Y is contained, the Y content is 0.01 to 0.20%, preferably 0.10% or less.
- REM rare earth metal: an element having an atomic number of 57 to 71 such as La, Ce, Nd
- the REM content is 0.01 to 0.10%, preferably 0.05% or less.
- Sn is effective in improving workability by promoting the formation of a deformation zone during rolling. On the other hand, if Sn is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Sn is contained, the Sn content is 0.001 to 0.500%, preferably 0.200% or less.
- Sb is effective in improving workability by promoting the formation of a deformation band during rolling. On the other hand, if Sb is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Sb is contained, the Sb content is 0.001 to 0.500%, preferably 0.200% or less.
- Pb is set to 0.10% or less because there is a concern that the melting point of the grain boundaries will be lowered and the binding force of the grain boundaries will be lowered, leading to deterioration of hot workability such as liquefaction cracking due to melting of the grain boundaries.
- W has the effect of improving high temperature strength without impairing ductility at room temperature.
- the excessive addition produces coarse eutectic carbides and causes a decrease in ductility, so the content should be 0.50 or less.
- the present invention is used for, for example, structural members of electronic devices such as smartphones, steel belts, press plates, and austenitic stainless steel strips suitable for applications requiring relatively thick high-strength stainless steel. Can be done.
Abstract
This method involves a coarse hot rolling step for performing coarse hot rolling after heating a slab manufactured by continuous casting to 1000-1300°C, a finish hot rolling step for performing finish hot rolling on the manufactured steel strip after the coarse hot rolling step, and a cooling step for cooling the steel strip after the finish hot rolling step, wherein in the finish hot rolling step, the draft of the finish hot rolling is greater than or equal to 60%, the roll diameter of the finish hot rolling is greater than or equal to 300 mm, the temperature of the finish hot rolling is 600-1100°C, and the final pass temperature of the finish hot rolling is 600-950°C, and in the cooling step, if the final pass temperature of the finish hot rolling is greater than or equal to 750°C, then the steel strip is cooled at a cooling speed of at least 5°C/s until 750°C.
Description
本発明は、オーステナイト系ステンレス鋼およびその製造方法に関する。
The present invention relates to austenitic stainless steel and a method for producing the same.
スマートフォンに代表される携帯型電子機器は小型軽量化や意匠性向上のニーズが高いことから、それらに用いる金属製の外装部材の製造では、複雑形状への加工に対応するため、過酷な冷間鍛造を施した後、切削加工により成形する手法が多用されるようになってきた。さらに、携帯型電子機器のデザインによっては、切削加工後に鏡面研磨を施す場合もある。ここで、携帯型電子機器の外装部材は、自機器に内蔵される地磁気センサー等への悪影響を回避するために非磁性であることが要求されるだけでなく、高強度も要求される。また、上記の電子機器は携帯型であるため屋外環境で使用されることも多いことから、外装部材は、屋内での使用を前提とする電子機器用部材と比べて高い耐食性も要求される。
Since portable electronic devices such as smartphones are in high demand for smaller size and lighter weight and improved design, the metal exterior members used for them are harshly cold in order to handle processing into complex shapes. After forging, the method of molding by cutting has come to be widely used. Further, depending on the design of the portable electronic device, mirror polishing may be performed after the cutting process. Here, the exterior member of the portable electronic device is required not only to be non-magnetic in order to avoid adverse effects on the geomagnetic sensor and the like built in the own device, but also to have high strength. Further, since the above-mentioned electronic device is portable and is often used in an outdoor environment, the exterior member is also required to have higher corrosion resistance than the member for the electronic device which is supposed to be used indoors.
上記の外装部材の製造に用いられる金属材料として、例えば特許文献１には、冷間鍛造および切削加工を施して非磁性部材とされた非磁性オーステナイト系ステンレス鋼板（以下、単に「ステンレス鋼板」という）が開示されている。
As a metal material used for manufacturing the above-mentioned exterior member, for example, Patent Document 1 describes a non-magnetic austenitic stainless steel sheet (hereinafter, simply referred to as "stainless steel sheet") which has been cold forged and cut to form a non-magnetic member. ) Is disclosed.
特許文献１に記載のステンレス鋼板の製造方法は、非磁性、かつ高強度部品を製造する上で良い方法であるが、製造工程が複雑でコストがかかること、製品形状によっては製造したステンレス鋼板を利用できないという問題点がある。
The method for manufacturing a stainless steel sheet described in Patent Document 1 is a good method for manufacturing non-magnetic and high-strength parts, but the manufacturing process is complicated and costly, and depending on the product shape, the manufactured stainless steel sheet may be used. There is a problem that it cannot be used.
次に、図８に、焼鈍材に冷間圧延を施した場合、または板厚が厚い材料に冷間圧延（調質圧延）を施した場合に、表層に歪が集中し板厚方向の硬さの分布が不均一となる例を示す。具体的には、図８には、板厚８ｍｍ、平均断面硬さ３００ＨＶに調整したステンレス鋼板の板厚方向の硬さ分布を示している。一般的な冷間圧延では表層のひずみが大きく、板厚中央のひずみが小さいため、表層では３３２ＨＶの硬さを示す一方、板厚中央では２７５ＨＶしか示さなかった。すなわち、特許文献１のステンレス鋼板では、板厚を一定以上に厚くすると、板厚方向の硬さが不均一になってしまうという問題点がある。
Next, in FIG. 8, when the annealed material is cold-rolled or the thick material is cold-rolled (tempered rolling), strain is concentrated on the surface layer and the hardness in the plate thickness direction is hard. An example in which the distribution of shavings is uneven is shown. Specifically, FIG. 8 shows the hardness distribution in the plate thickness direction of a stainless steel plate adjusted to a plate thickness of 8 mm and an average cross-sectional hardness of 300 HV. In general cold rolling, the strain of the surface layer is large and the strain at the center of the plate thickness is small. Therefore, the surface layer shows a hardness of 332 HV, while the center of the plate thickness shows only 275 HV. That is, the stainless steel sheet of Patent Document 1 has a problem that the hardness in the plate thickness direction becomes non-uniform when the plate thickness is increased to a certain level or more.
本発明の一態様は、前記の問題点に鑑みて為されたものであり、その目的は、厚さが一定程度以上あるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼、およびその製造方法を実現することにある。
One aspect of the present invention has been made in view of the above problems, and an object of the present invention is to reduce variations in cross-sectional hardness distribution in the thickness direction even though the thickness is a certain degree or more. The purpose is to realize austenitic stainless steel and its manufacturing method.
前記の課題を解決するために、本発明の一態様に係るオーステナイト系ステンレス鋼は、ＣとＮとを合わせた含有量が、質量％で０．０８％以上であり、厚さ方向の断面硬さ分布の平均が２５０ＨＶ以上であり、かつ変動幅が３０ＨＶ以下であり、厚さが３ｍｍ以上である構成である。
In order to solve the above-mentioned problems, the austenitic stainless steel according to one aspect of the present invention has a combined content of C and N of 0.08% or more in mass% and a cross-sectional hardness in the thickness direction. The average of the hardness distribution is 250 HV or more, the fluctuation range is 30 HV or less, and the thickness is 3 mm or more.
前記構成によれば、厚さが３ｍｍ以上であるにも関わらず、厚さ方向の断面硬さ分布の平均が２５０ＨＶ以上であり、かつ変動幅が３０ＨＶ以下である。このため、厚さが一定程度以上あるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を提供することができる。
According to the above configuration, the average cross-sectional hardness distribution in the thickness direction is 250 HV or more and the fluctuation range is 30 HV or less even though the thickness is 3 mm or more. Therefore, it is possible to provide an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is more than a certain level.
［１］本発明の一態様に係るオーステナイト系ステンレス鋼は、前記オーステナイト系ステンレス鋼の化学組成は、質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％、残部Ｆｅおよび不可避的不純物からなる。
[1] The austenitic stainless steel according to one aspect of the present invention has a chemical composition of C: 0.003 to 0.12%, Si: 2.00% or less, Mn in mass%. : 2.00% or less, P: 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 Consists of ~ 0.20%, balance Fe and unavoidable impurities.
［２］前記化学組成に加えて、さらに質量％で、Ｍｏ：０．０１～３．００％、Ｃｕ：０．０１～３．５０％、Ａｌ：０．００８０％以下、Ｏ：０．００４０～０．０１００％、Ｖ：０．０１～０．５％、Ｂ：０．００１～０．０１％、Ｔｉ：０．０１～０．５０％の１種またが２種以上を含有する［１］に記載のオーステナイト系ステンレス鋼。
[2] In addition to the above chemical composition, in terms of mass%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al: 0.0080% or less, O: 0.0040. It contains one kind or two or more kinds of ~ 0.0100%, V: 0.01 ~ 0.5%, B: 0.001 ~ 0.01%, Ti: 0.01 ~ 0.50% [ 1] The austenitic stainless steel according to.
［３］前記化学組成に加えて、さらに質量％で、Ｃｏ：０．０１～０．５０％、Ｚｒ：０．０１～０．１０％、Ｎｂ：０．０１～０．１０％、Ｍｇ：０．０００５～０．００３０％、Ｃａ：０．０００３～０．００３０％、Ｙ：０．０１～０．２０％、ＲＥＭ（希土類金属）：０．０１～０．１０％、Ｓｎ：０．００１～０．５００％およびＳｂ：０．００１～０．５００％、Ｐｂ：０．０１～０．１０％、Ｗ：０．０１～０．５０％のうちから選んだ１種または２種以上を含有する［１］または［２］に記載のオーステナイト系ステンレス鋼。
[3] In addition to the above chemical composition, in terms of mass%, Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005 to 0.0030%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20%, REM (rare earth metal): 0.01 to 0.10%, Sn: 0. One or more selected from 001 to 0.500%, Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50% The austenitic stainless steel according to [1] or [2].
本発明の一態様に係るオーステナイト系ステンレス鋼は、比透磁率μが１．１以下であることが好ましい。前記構成によれば、厚さが一定程度以上あるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減された非磁性のオーステナイト系ステンレス鋼を提供することができる。
The austenitic stainless steel according to one aspect of the present invention preferably has a relative magnetic permeability μ of 1.1 or less. According to the above configuration, it is possible to provide a non-magnetic austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is a certain degree or more.
〔４〕本発明の一態様に係るオーステナイト系ステンレス鋼の製造方法は、質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％を含有し、かつＣとＮとを合わせた含有量が質量％で０．０８％以上であり、残部Ｆｅおよび不可避的不純物で構成された化学組成からなる連続鋳造によって製造したスラブを１０００～１３００℃に加熱した後、粗熱延を施す粗熱延工程と、前記粗熱延工程の後、製造された鋼帯に対して仕上熱延を施す仕上熱延工程と、前記仕上熱延工程の後、前記鋼帯を冷却する冷却工程とを含み、前記仕上熱延工程では、前記仕上熱延の圧下率が６０％以上であり、前記仕上熱延のロール径が３００ｍｍ以上であり、前記仕上熱延の温度が６００～１１００℃であり、前記仕上熱延の最終パス温度が６００～９５０℃であり、前記冷却工程では、前記鋼帯を前記仕上熱延の前記最終パス温度が７５０℃以上の場合は７５０℃以下まで、冷却速度５℃／ｓ以上で冷却する方法である。前記構成によれば、厚さが一定程度以上あるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を製造できる、オーステナイト系ステンレス鋼の製造方法を実現することができる。
[4] The method for producing austenite-based stainless steel according to one aspect of the present invention is, in terms of mass%, C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, Contains P: 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20% However, the combined content of C and N is 0.08% or more in mass%, and the slab produced by continuous casting having a chemical composition composed of the balance Fe and unavoidable impurities is brought to 1000 to 1300 ° C. After the rough heat spreading step of applying the rough heat spreading after heating, the finishing hot spreading step of applying the finishing hot spreading to the manufactured steel strip after the rough heat spreading step, and the finishing hot spreading step. In the finishing hot-rolling step, which includes a cooling step of cooling the steel strip, the reduction rate of the finishing hot-rolling is 60% or more, the roll diameter of the finishing hot-rolling is 300 mm or more, and the finishing hot-rolling is performed. When the temperature of the steel strip is 600 to 1100 ° C., the final pass temperature of the finishing heat spreading is 600 to 950 ° C., and the final pass temperature of the finishing hot spreading of the steel strip is 750 ° C. or higher in the cooling step. Is a method of cooling to 750 ° C. or lower at a cooling rate of 5 ° C./s or higher. According to the above configuration, a method for producing austenitic stainless steel capable of producing austenitic stainless steel in which variations in cross-sectional hardness distribution in the thickness direction are reduced even though the thickness is a certain degree or more is realized. be able to.
〔５〕前記スラブが、さらに質量％で、Ｍｏ：０．０１～３．００％、Ｃｕ：０．０１～３．５０％、Ａｌ：０．００８０％以下、Ｏ：０．００４０～０．０１００％、Ｖ：０．０１～０．５％、Ｂ：０．００１～０．０１％、Ｔｉ：０．０１～０．５０％の１種または２種以上を含有する〔４〕に記載のオーステナイト系ステンレス鋼の製造方法。
[5] The slab is further increased in mass%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al: 0.0080% or less, O: 0.0040 to 0. The description in [4], which contains one or more of 0100%, V: 0.01 to 0.5%, B: 0.001 to 0.01%, and Ti: 0.01 to 0.50%. How to make austenitic stainless steel.
〔６〕前記スラブが、さらに質量で、Ｃｏ：０．０１～０．５０％、Ｚｒ：０．０１～０．１０％、Ｎｂ：０．０１～０．１０％、Ｍｇ：０．０００５～０．００３０％、Ｃａ：０．０００３～０．００３０％、Ｙ：０．０１～０．２０％、ＲＥＭ（希土類金属）：０．０１～０．１０％、Ｓｎ：０．００１～０．５００％およびＳｂ：０．００１～０．５００％、Ｐｂ：０．０１～０．１０％、Ｗ：０．０１～０．５０％のうちから選んだ１種または２種以上を含有する〔４〕または〔６〕に記載のオーステナイト系ステンレス鋼の製造方法。
[6] The slab further contains Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005 to 0.0030%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20%, REM (rare earth metal): 0.01 to 0.10%, Sn: 0.001 to 0. Contains one or more selected from 500% and Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50% [ 4] or [6], the method for producing austenitic stainless steel.
本発明の一態様によれば、厚さが一定程度以上あるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を提供することができるという効果を奏する。
According to one aspect of the present invention, it is possible to provide an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced even though the thickness is a certain degree or more.
以下、本発明の一実施形態について詳細に説明する。なお、以下の記載は発明の趣旨をより良く理解させるためのものであり、特に指定のない限り、本発明を限定するものではない。
Hereinafter, one embodiment of the present invention will be described in detail. The following description is intended to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.
〔本発明のポイントおよび目的〕
（ｉ）一定程度以上（３ｍｍ以上）の厚さがあるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を実現した点、および、（ｉｉ）オーステナイト系ステンレス鋼を高温にし、大径ロールを用いて、大きく圧下し、圧下後に仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで冷却速度５℃／ｓ以上で冷却すれば、厚さが３ｍｍ以上のオーステナイト系ステンレス鋼において、厚さ方向の断面硬さ分布のばらつきを低減できることを見出した点が本発明のポイントである。なお、本明細書に記載の「オーステナイト系ステンレス鋼」は、オーステナイト系ステンレス鋼帯およびオーステナイト系ステンレス鋼板の両方を含む。言い換えれば、本発明は、オーステナイト系ステンレス鋼帯およびオーステナイト系ステンレス鋼板の両方に適用可能である。 [Points and Purposes of the Present Invention]
(I) Austenitic stainless steel with reduced variation in cross-sectional hardness distribution in the thickness direction was realized despite having a certain thickness (3 mm or more), and (ii) austenitic stainless steel. If the final pass temperature of the finish hot-rolling is 750 ° C or higher, cool it to 750 ° C or lower at a cooling rate of 5 ° C / s or higher by heating the stainless steel to a high temperature and using a large-diameter roll to reduce it significantly. The point of the present invention is to find that the variation in the cross-sectional hardness distribution in the thickness direction can be reduced in the austenitic stainless steel having a thickness of 3 mm or more. The "austenitic stainless steel" described in the present specification includes both an austenitic stainless steel strip and an austenitic stainless steel sheet. In other words, the present invention is applicable to both austenitic stainless steel strips and austenitic stainless steel sheets.
（ｉ）一定程度以上（３ｍｍ以上）の厚さがあるにも関わらず、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を実現した点、および、（ｉｉ）オーステナイト系ステンレス鋼を高温にし、大径ロールを用いて、大きく圧下し、圧下後に仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで冷却速度５℃／ｓ以上で冷却すれば、厚さが３ｍｍ以上のオーステナイト系ステンレス鋼において、厚さ方向の断面硬さ分布のばらつきを低減できることを見出した点が本発明のポイントである。なお、本明細書に記載の「オーステナイト系ステンレス鋼」は、オーステナイト系ステンレス鋼帯およびオーステナイト系ステンレス鋼板の両方を含む。言い換えれば、本発明は、オーステナイト系ステンレス鋼帯およびオーステナイト系ステンレス鋼板の両方に適用可能である。 [Points and Purposes of the Present Invention]
(I) Austenitic stainless steel with reduced variation in cross-sectional hardness distribution in the thickness direction was realized despite having a certain thickness (3 mm or more), and (ii) austenitic stainless steel. If the final pass temperature of the finish hot-rolling is 750 ° C or higher, cool it to 750 ° C or lower at a cooling rate of 5 ° C / s or higher by heating the stainless steel to a high temperature and using a large-diameter roll to reduce it significantly. The point of the present invention is to find that the variation in the cross-sectional hardness distribution in the thickness direction can be reduced in the austenitic stainless steel having a thickness of 3 mm or more. The "austenitic stainless steel" described in the present specification includes both an austenitic stainless steel strip and an austenitic stainless steel sheet. In other words, the present invention is applicable to both austenitic stainless steel strips and austenitic stainless steel sheets.
また、本発明は、例えば、スマートフォンなどの電子機器の構造部材を、複雑な鍛造加工を施すことなく、切削、エッチング、放電加工等で製造することが可能となるオーステナイト系ステンレス鋼およびその製造方法を実現することを目的とする。
Further, the present invention provides, for example, an austenitic stainless steel capable of manufacturing a structural member of an electronic device such as a smartphone by cutting, etching, electric discharge machining, etc. without performing complicated forging, and a method for manufacturing the austenitic stainless steel. The purpose is to realize.
（厚さ方向の断面硬さ分布のばらつきが低減されていることによるメリット）
スマートフォンの構造部材として本発明の実施形態に係るオーステナイト系ステンレス鋼を適用する場合、軟質な箇所（例えば厚さ方向の中央部）があると疵付きやすい。したがって製品としての価値が低くなる。また、軟質な箇所でも、十分に硬くすることで対応することも考えられるが、逆に必要以上に硬い部分が生じると切削性が低下する。 (Advantages due to reduced variation in cross-sectional hardness distribution in the thickness direction)
When the austenitic stainless steel according to the embodiment of the present invention is applied as a structural member of a smartphone, if there is a soft portion (for example, a central portion in the thickness direction), it is likely to be scratched. Therefore, the value as a product is low. Further, even in a soft part, it is conceivable to make it sufficiently hard, but conversely, if a part that is harder than necessary is generated, the machinability is lowered.
スマートフォンの構造部材として本発明の実施形態に係るオーステナイト系ステンレス鋼を適用する場合、軟質な箇所（例えば厚さ方向の中央部）があると疵付きやすい。したがって製品としての価値が低くなる。また、軟質な箇所でも、十分に硬くすることで対応することも考えられるが、逆に必要以上に硬い部分が生じると切削性が低下する。 (Advantages due to reduced variation in cross-sectional hardness distribution in the thickness direction)
When the austenitic stainless steel according to the embodiment of the present invention is applied as a structural member of a smartphone, if there is a soft portion (for example, a central portion in the thickness direction), it is likely to be scratched. Therefore, the value as a product is low. Further, even in a soft part, it is conceivable to make it sufficiently hard, but conversely, if a part that is harder than necessary is generated, the machinability is lowered.
〔プロセス〕
本発明の一実施形態に係るオーステナイト系ステンレス鋼は、図１に示すように、製鋼、粗熱延、仕上熱延および冷却の各工程を施すことで製造することができる。より具体的には、連続鋳造によって製造したスラブを１０００～１３００℃に加熱した後、粗熱延を施し、厚さ２５ｍｍの粗バー（鋼帯）とする（粗熱延工程）。その後、６００℃以上かつ１１００℃以下で上記粗バーに対して仕上熱延を施す（仕上熱延工程）。仕上熱延工程では、仕上熱延の圧下率を６０％以上、仕上熱延のロール径を３００ｍｍ以上、仕上熱延の最終パス温度を６００～９５０℃とする。仕上熱延工程の後、製造された鋼帯を、仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで、冷却速度５℃／ｓ以上で冷却する（冷却工程）。これらの条件を満たすことで所望の厚さ方向の断面硬さ分布およびその変動範囲のステンレス鋼を得ることができる。 〔process〕
As shown in FIG. 1, the austenitic stainless steel according to the embodiment of the present invention can be produced by subjecting each step of steelmaking, rough heat spreading, finishing hot spreading and cooling. More specifically, the slab produced by continuous casting is heated to 1000 to 1300 ° C. and then subjected to rough heat spreading to obtain a rough bar (steel strip) having a thickness of 25 mm (coarse heat spreading step). Then, the rough bar is hot-rolled for finishing at 600 ° C. or higher and 1100 ° C. or lower (finishing hot-rolling step). In the finishing hot-rolling step, the reduction rate of the finishing hot-rolling is 60% or more, the roll diameter of the finishing hot-rolling is 300 mm or more, and the final pass temperature of the finishing hot-rolling is 600 to 950 ° C. After the finishing hot-rolling step, the manufactured steel strip is cooled to 750 ° C. or lower when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher at a cooling rate of 5 ° C./s or higher (cooling step). By satisfying these conditions, a stainless steel having a desired cross-sectional hardness distribution in the thickness direction and a fluctuation range thereof can be obtained.
本発明の一実施形態に係るオーステナイト系ステンレス鋼は、図１に示すように、製鋼、粗熱延、仕上熱延および冷却の各工程を施すことで製造することができる。より具体的には、連続鋳造によって製造したスラブを１０００～１３００℃に加熱した後、粗熱延を施し、厚さ２５ｍｍの粗バー（鋼帯）とする（粗熱延工程）。その後、６００℃以上かつ１１００℃以下で上記粗バーに対して仕上熱延を施す（仕上熱延工程）。仕上熱延工程では、仕上熱延の圧下率を６０％以上、仕上熱延のロール径を３００ｍｍ以上、仕上熱延の最終パス温度を６００～９５０℃とする。仕上熱延工程の後、製造された鋼帯を、仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで、冷却速度５℃／ｓ以上で冷却する（冷却工程）。これらの条件を満たすことで所望の厚さ方向の断面硬さ分布およびその変動範囲のステンレス鋼を得ることができる。 〔process〕
As shown in FIG. 1, the austenitic stainless steel according to the embodiment of the present invention can be produced by subjecting each step of steelmaking, rough heat spreading, finishing hot spreading and cooling. More specifically, the slab produced by continuous casting is heated to 1000 to 1300 ° C. and then subjected to rough heat spreading to obtain a rough bar (steel strip) having a thickness of 25 mm (coarse heat spreading step). Then, the rough bar is hot-rolled for finishing at 600 ° C. or higher and 1100 ° C. or lower (finishing hot-rolling step). In the finishing hot-rolling step, the reduction rate of the finishing hot-rolling is 60% or more, the roll diameter of the finishing hot-rolling is 300 mm or more, and the final pass temperature of the finishing hot-rolling is 600 to 950 ° C. After the finishing hot-rolling step, the manufactured steel strip is cooled to 750 ° C. or lower when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher at a cooling rate of 5 ° C./s or higher (cooling step). By satisfying these conditions, a stainless steel having a desired cross-sectional hardness distribution in the thickness direction and a fluctuation range thereof can be obtained.
また、得られたステンレス鋼について、必要に応じて、熱延工程で生成した酸化スケールの除去を目的とし、酸洗処理を施してもよい。一般的に、酸洗処理は焼鈍工程と酸洗工程とが繋がった焼鈍酸洗ラインで実施される。酸洗処理を行う際は、ステンレス鋼の硬さの低下が発生しない温度範囲（具体的には、９００℃以下）において、ステンレス鋼に熱を加えてもよい。
Further, the obtained stainless steel may be pickled, if necessary, for the purpose of removing the oxide scale generated in the hot rolling process. Generally, the pickling treatment is carried out in an annealing pickling line in which the annealing step and the pickling step are connected. When the pickling treatment is performed, heat may be applied to the stainless steel in a temperature range (specifically, 900 ° C. or lower) at which the hardness of the stainless steel does not decrease.
以上の各工程によれば、厚さが３ｍｍ以上にも関わらず、厚さ方向の断面硬さ分布の平均が２５０ＨＶ以上であり、かつ変動幅が３０ＨＶ以下とすることができる。このため、厚さ方向の断面硬さ分布のばらつきが低減されたオーステナイト系ステンレス鋼を提供することができる。
According to each of the above steps, the average cross-sectional hardness distribution in the thickness direction can be 250 HV or more and the fluctuation range can be 30 HV or less even though the thickness is 3 mm or more. Therefore, it is possible to provide an austenitic stainless steel in which the variation in the cross-sectional hardness distribution in the thickness direction is reduced.
（厚さ方向の断面硬さ分布）
厚さ方向の断面硬さ分布とは、圧延幅方向に垂直な断面について、厚さ方向の断面硬さ変動が分かるように荷重１ｋｇでビッカース硬さを複数点測定したものである。例えば、厚さ８ｍｍ、厚さ方向の平均断面硬さを３００ＨＶに調整した実施例Ａ３（図４参照）のステンレス鋼は、図２に示すように厚さ方向の断面硬さ分布は２９４～３０８ＨＶの範囲であり、従来技術に比べて厚さ方向の断面硬さ分布のばらつきが低減されていることが分かる。図２は、本発明の実施の一形態に係るオーステナイト系ステンレス鋼の厚さ方向に対する断面硬さの分布を示すグラフである。 (Distribution of cross-sectional hardness in the thickness direction)
The cross-sectional hardness distribution in the thickness direction is a measurement of Vickers hardness at a plurality of points with a load of 1 kg so that the variation in cross-sectional hardness in the thickness direction can be seen for a cross section perpendicular to the rolling width direction. For example, the stainless steel of Example A3 (see FIG. 4) in which the thickness is 8 mm and the average cross-sectional hardness in the thickness direction is adjusted to 300 HV has a cross-sectional hardness distribution of 294 to 308 HV in the thickness direction as shown in FIG. It can be seen that the variation in the cross-sectional hardness distribution in the thickness direction is reduced as compared with the conventional technique. FIG. 2 is a graph showing the distribution of cross-sectional hardness of the austenitic stainless steel according to the embodiment of the present invention with respect to the thickness direction.
厚さ方向の断面硬さ分布とは、圧延幅方向に垂直な断面について、厚さ方向の断面硬さ変動が分かるように荷重１ｋｇでビッカース硬さを複数点測定したものである。例えば、厚さ８ｍｍ、厚さ方向の平均断面硬さを３００ＨＶに調整した実施例Ａ３（図４参照）のステンレス鋼は、図２に示すように厚さ方向の断面硬さ分布は２９４～３０８ＨＶの範囲であり、従来技術に比べて厚さ方向の断面硬さ分布のばらつきが低減されていることが分かる。図２は、本発明の実施の一形態に係るオーステナイト系ステンレス鋼の厚さ方向に対する断面硬さの分布を示すグラフである。 (Distribution of cross-sectional hardness in the thickness direction)
The cross-sectional hardness distribution in the thickness direction is a measurement of Vickers hardness at a plurality of points with a load of 1 kg so that the variation in cross-sectional hardness in the thickness direction can be seen for a cross section perpendicular to the rolling width direction. For example, the stainless steel of Example A3 (see FIG. 4) in which the thickness is 8 mm and the average cross-sectional hardness in the thickness direction is adjusted to 300 HV has a cross-sectional hardness distribution of 294 to 308 HV in the thickness direction as shown in FIG. It can be seen that the variation in the cross-sectional hardness distribution in the thickness direction is reduced as compared with the conventional technique. FIG. 2 is a graph showing the distribution of cross-sectional hardness of the austenitic stainless steel according to the embodiment of the present invention with respect to the thickness direction.
（Ｃ＋Ｎ）
Ｃ、Ｎはオーステナイト相の固溶強化および加工硬化に有効に作用するため、一定量必要である。種々検討の結果、安定して２５０ＨＶ以上の硬さを得るためにはＣ＋Ｎ量を０．０８％以上に調整する必要があることを見出した（図３参照）。なお、図３は、Ｃ＋Ｎの量と、オーステナイト系ステンレス鋼の平均断面硬さとの関係を示すグラフである。また、Ｃ＋Ｎ量は、ＣとＮとを合わせた含有量のことである。また、Ｃ＋Ｎ量には、Ｃが０％またはＮが０％の場合が含まれている。 (C + N)
A certain amount of C and N is required because they effectively act on the solid solution strengthening and work hardening of the austenite phase. As a result of various studies, it was found that it is necessary to adjust the amount of C + N to 0.08% or more in order to stably obtain a hardness of 250 HV or more (see FIG. 3). FIG. 3 is a graph showing the relationship between the amount of C + N and the average cross-sectional hardness of austenitic stainless steel. The amount of C + N is the total content of C and N. Further, the amount of C + N includes the case where C is 0% or N is 0%.
Ｃ、Ｎはオーステナイト相の固溶強化および加工硬化に有効に作用するため、一定量必要である。種々検討の結果、安定して２５０ＨＶ以上の硬さを得るためにはＣ＋Ｎ量を０．０８％以上に調整する必要があることを見出した（図３参照）。なお、図３は、Ｃ＋Ｎの量と、オーステナイト系ステンレス鋼の平均断面硬さとの関係を示すグラフである。また、Ｃ＋Ｎ量は、ＣとＮとを合わせた含有量のことである。また、Ｃ＋Ｎ量には、Ｃが０％またはＮが０％の場合が含まれている。 (C + N)
A certain amount of C and N is required because they effectively act on the solid solution strengthening and work hardening of the austenite phase. As a result of various studies, it was found that it is necessary to adjust the amount of C + N to 0.08% or more in order to stably obtain a hardness of 250 HV or more (see FIG. 3). FIG. 3 is a graph showing the relationship between the amount of C + N and the average cross-sectional hardness of austenitic stainless steel. The amount of C + N is the total content of C and N. Further, the amount of C + N includes the case where C is 0% or N is 0%.
図３に、仕上熱延の最終パス温度８７０℃で圧延を施し、７５０℃以下まで冷却速度４０℃／ｓで冷却して巻き取りを行った実施例Ａ１～Ａ４、比較例Ｂ１、Ｂ２の平均断面硬さについてプロットしたグラフを示す（実施例Ａ１～Ａ４および比較例Ｂ１、Ｂ２の各鋼種の化学組成については図４参照）。Ｃ＋Ｎ量が０．０８％以上であるＡ１～Ａ４は平均断面硬さが２５０ＨＶ以上であったが、Ｃ＋Ｎ量が０．０８未満であるＢ１、Ｂ２鋼の平均断面硬さは２５０ＨＶ未満であった。
FIG. 3 shows the average of Examples A1 to A4 and Comparative Examples B1 and B2, which were rolled at a final pass temperature of 870 ° C. for hot rolling, cooled to 750 ° C. or lower at a cooling rate of 40 ° C./s, and wound up. The graph which plotted about the cross-sectional hardness is shown (see FIG. 4 for the chemical composition of each steel type of Examples A1 to A4 and Comparative Examples B1 and B2). A1 to A4 having a C + N amount of 0.08% or more had an average cross-sectional hardness of 250 HV or more, but B1 and B2 steels having a C + N amount of less than 0.08 had an average cross-sectional hardness of less than 250 HV. ..
（比透磁率）
オーステナイト系ステンレス鋼を特徴付ける上で、一般的に比透磁率μは１．１以下が好ましく、より好ましくは、１．０５以下である、本発明の実施形態に係る製造方法では、６００℃以上で圧延するため、加工誘起マルテンサイトは生成しないが、δフェライトが残存すると比透磁率が高くなる。 (Permeability)
In characterizing austenitic stainless steel, the relative magnetic permeability μ is generally preferably 1.1 or less, more preferably 1.05 or less. In the production method according to the embodiment of the present invention, the temperature is 600 ° C. or higher. Since it is rolled, process-induced martensite is not generated, but if δ ferrite remains, the relative permeability increases.
オーステナイト系ステンレス鋼を特徴付ける上で、一般的に比透磁率μは１．１以下が好ましく、より好ましくは、１．０５以下である、本発明の実施形態に係る製造方法では、６００℃以上で圧延するため、加工誘起マルテンサイトは生成しないが、δフェライトが残存すると比透磁率が高くなる。 (Permeability)
In characterizing austenitic stainless steel, the relative magnetic permeability μ is generally preferably 1.1 or less, more preferably 1.05 or less. In the production method according to the embodiment of the present invention, the temperature is 600 ° C. or higher. Since it is rolled, process-induced martensite is not generated, but if δ ferrite remains, the relative permeability increases.
上記のように化学組成が調整されたオーステナイト系ステンレス鋼は、通常の鋼板製造工程や、その後の冷間鍛造工程で加工誘起マルテンサイト相が生成しないので、加工誘起マルテンサイト相に起因する磁性化は回避される。ただし、溶製時に高温でδフェライト相が生成することがあり、これが残存すると透磁率１.０１０以下の非磁性が得られない。また、製品中にδフェライト相が異相として混在していると、鏡面研磨品の外観を損なう場合もある。したがって、冷間鍛造に供する素材である鋼板の段階で、δフェライト相が消失している必要がある。δフェライト相は強磁性であるため、その存在有無は透磁率によって評価する。
Since the austenitic stainless steel whose chemical composition has been adjusted as described above does not generate a work-induced martensite phase in the normal steel sheet manufacturing process and the subsequent cold forging process, magnetization due to the work-induced martensite phase occurs. Is avoided. However, a δ ferrite phase may be formed at a high temperature during melting, and if this remains, non-magnetism with a magnetic permeability of 1.010 or less cannot be obtained. Further, if the δ ferrite phase is mixed as a different phase in the product, the appearance of the mirror-polished product may be spoiled. Therefore, it is necessary that the δ ferrite phase disappears at the stage of the steel sheet, which is the material used for cold forging. Since the δ ferrite phase is ferromagnetic, its presence or absence is evaluated by magnetic permeability.
（目標特性）
オーステナイト系ステンレス鋼の厚さ方向の断面硬さ分布の平均は、２５０ＨＶ以上（ＳＵＳ３０４ＣＳＰ－１／２Ｈ規格）を目指した。また、オーステナイト系ステンレス鋼の厚さは、例えば、特殊金属エクセルのＳＵＳ３０１ＣＳＰの厚さの範囲が２．５ｍｍ以下程度であるため、３ｍｍ以上を目指した。 (Target characteristics)
The average cross-sectional hardness distribution of austenitic stainless steel in the thickness direction was aimed at 250 HV or more (SUS304CSP-1 / 2H standard). Further, the thickness of the austenitic stainless steel was aimed at 3 mm or more because, for example, the thickness range of the special metal Excel SUS301CSP is about 2.5 mm or less.
オーステナイト系ステンレス鋼の厚さ方向の断面硬さ分布の平均は、２５０ＨＶ以上（ＳＵＳ３０４ＣＳＰ－１／２Ｈ規格）を目指した。また、オーステナイト系ステンレス鋼の厚さは、例えば、特殊金属エクセルのＳＵＳ３０１ＣＳＰの厚さの範囲が２．５ｍｍ以下程度であるため、３ｍｍ以上を目指した。 (Target characteristics)
The average cross-sectional hardness distribution of austenitic stainless steel in the thickness direction was aimed at 250 HV or more (SUS304CSP-1 / 2H standard). Further, the thickness of the austenitic stainless steel was aimed at 3 mm or more because, for example, the thickness range of the special metal Excel SUS301CSP is about 2.5 mm or less.
（圧下率）
仕上熱延の圧下率は６０％以上とすることが好ましい。図６中の条件Ｎｏ．Ｄ００１～Ｄ００６に示すように仕上熱延の圧下率（総圧延率）が６０％を下回った場合、圧延ひずみが十分に付与されず目標の平均断面硬さが得られない。なお、圧延ロールの入り口の厚さをｈ１、出口の厚さをｈ２とするとき、圧下率＝（ｈ１－ｈ２）／ｈ１の関係式が成立する。 (Reduction rate)
The reduction rate of the finishing heat spread is preferably 60% or more. Condition No. in FIG. As shown in D001 to D006, when the reduction rate (total rolling rate) of the finish hot rolling is less than 60%, the rolling strain is not sufficiently applied and the target average cross-sectional hardness cannot be obtained. When the thickness of the inlet of the rolling roll is h1 and the thickness of the outlet is h2, the relational expression of rolling ratio = (h1-h2) / h1 is established.
仕上熱延の圧下率は６０％以上とすることが好ましい。図６中の条件Ｎｏ．Ｄ００１～Ｄ００６に示すように仕上熱延の圧下率（総圧延率）が６０％を下回った場合、圧延ひずみが十分に付与されず目標の平均断面硬さが得られない。なお、圧延ロールの入り口の厚さをｈ１、出口の厚さをｈ２とするとき、圧下率＝（ｈ１－ｈ２）／ｈ１の関係式が成立する。 (Reduction rate)
The reduction rate of the finishing heat spread is preferably 60% or more. Condition No. in FIG. As shown in D001 to D006, when the reduction rate (total rolling rate) of the finish hot rolling is less than 60%, the rolling strain is not sufficiently applied and the target average cross-sectional hardness cannot be obtained. When the thickness of the inlet of the rolling roll is h1 and the thickness of the outlet is h2, the relational expression of rolling ratio = (h1-h2) / h1 is established.
（ロール径）
仕上熱延のロール径は３００ｍｍ以上とすることが好ましい。図６中の条件Ｎｏ．Ｆ０１～Ｆ１９に示すようにロール径が小さい場合は厚さ方向の中心まで圧延ひずみを付与することができず、いずれの圧延温度においても断面硬さの変動範囲が大きくなる。なお、ロール径は、圧延ロールの回転軸に垂直な断面の直径のことである。 (Roll diameter)
The roll diameter of the hot-rolled finish is preferably 300 mm or more. Condition No. in FIG. As shown in F01 to F19, when the roll diameter is small, the rolling strain cannot be applied to the center in the thickness direction, and the fluctuation range of the cross-sectional hardness becomes large at any rolling temperature. The roll diameter is the diameter of the cross section perpendicular to the rotation axis of the rolling roll.
仕上熱延のロール径は３００ｍｍ以上とすることが好ましい。図６中の条件Ｎｏ．Ｆ０１～Ｆ１９に示すようにロール径が小さい場合は厚さ方向の中心まで圧延ひずみを付与することができず、いずれの圧延温度においても断面硬さの変動範囲が大きくなる。なお、ロール径は、圧延ロールの回転軸に垂直な断面の直径のことである。 (Roll diameter)
The roll diameter of the hot-rolled finish is preferably 300 mm or more. Condition No. in FIG. As shown in F01 to F19, when the roll diameter is small, the rolling strain cannot be applied to the center in the thickness direction, and the fluctuation range of the cross-sectional hardness becomes large at any rolling temperature. The roll diameter is the diameter of the cross section perpendicular to the rotation axis of the rolling roll.
（仕上熱延の温度および仕上熱延の最終パス温度）
仕上熱延の温度は６００～１１００℃とすることが好ましい。また、仕上熱延の最終パス温度（最終パス圧延温度）は６００～９５０℃とすることが好ましい。仕上熱延の温度および最終パス圧延温度が６００℃を下回った場合、ロール径が大きくても板表層に付与されるひずみ量が厚さ方向の中心と比較して大きくなり、断面硬さの変動幅が大きくなる。一方、仕上熱延の温度が１１００℃を上回った場合、圧延ひずみが再結晶駆動力となり、圧延直後に再結晶が生じ所望の断面硬さ分布が得られないとともに、温度が高すぎて最終パス圧延温度を９５０℃以下に調整することが困難となる。また、最終パス圧延温度が９５０℃を超えた場合、圧延ひずみが再結晶駆動力となり、圧延直後に再結晶が生じ所望の断面硬さ分布が得られない。 (Temperature of hot-rolled finish and final pass temperature of hot-rolled finish)
The temperature of the finishing heat spread is preferably 600 to 1100 ° C. Further, the final pass temperature (final pass rolling temperature) of the hot rolling finish is preferably 600 to 950 ° C. When the finishing hot rolling temperature and the final pass rolling temperature are lower than 600 ° C, the amount of strain applied to the plate surface layer becomes larger than the center in the thickness direction even if the roll diameter is large, and the cross-sectional hardness fluctuates. The width increases. On the other hand, when the temperature of the finishing hot rolling exceeds 1100 ° C., the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, the desired cross-sectional hardness distribution cannot be obtained, and the temperature is too high for the final pass. It becomes difficult to adjust the rolling temperature to 950 ° C. or lower. Further, when the final pass rolling temperature exceeds 950 ° C., the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, and a desired cross-sectional hardness distribution cannot be obtained.
仕上熱延の温度は６００～１１００℃とすることが好ましい。また、仕上熱延の最終パス温度（最終パス圧延温度）は６００～９５０℃とすることが好ましい。仕上熱延の温度および最終パス圧延温度が６００℃を下回った場合、ロール径が大きくても板表層に付与されるひずみ量が厚さ方向の中心と比較して大きくなり、断面硬さの変動幅が大きくなる。一方、仕上熱延の温度が１１００℃を上回った場合、圧延ひずみが再結晶駆動力となり、圧延直後に再結晶が生じ所望の断面硬さ分布が得られないとともに、温度が高すぎて最終パス圧延温度を９５０℃以下に調整することが困難となる。また、最終パス圧延温度が９５０℃を超えた場合、圧延ひずみが再結晶駆動力となり、圧延直後に再結晶が生じ所望の断面硬さ分布が得られない。 (Temperature of hot-rolled finish and final pass temperature of hot-rolled finish)
The temperature of the finishing heat spread is preferably 600 to 1100 ° C. Further, the final pass temperature (final pass rolling temperature) of the hot rolling finish is preferably 600 to 950 ° C. When the finishing hot rolling temperature and the final pass rolling temperature are lower than 600 ° C, the amount of strain applied to the plate surface layer becomes larger than the center in the thickness direction even if the roll diameter is large, and the cross-sectional hardness fluctuates. The width increases. On the other hand, when the temperature of the finishing hot rolling exceeds 1100 ° C., the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, the desired cross-sectional hardness distribution cannot be obtained, and the temperature is too high for the final pass. It becomes difficult to adjust the rolling temperature to 950 ° C. or lower. Further, when the final pass rolling temperature exceeds 950 ° C., the rolling strain becomes a recrystallization driving force, recrystallization occurs immediately after rolling, and a desired cross-sectional hardness distribution cannot be obtained.
（冷却工程）
前記の仕上熱延工程の後、仕上熱延を施された鋼帯を仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで冷却速度５℃／ｓ以上で冷却する冷却工程を有することが好ましい。仕上熱延で材料中に蓄積される圧延ひずみは、ステンレス鋼が高温のまま保持されると仕上熱延直後から減少する。圧延ひずみの減少を低減するためには、圧延ひずみの減少が起こらない温度域まで速やかに冷却することが好ましい。 (Cooling process)
After the finishing hot-rolling step, a cooling step of cooling the steel strip subjected to the finishing hot-rolling to 750 ° C. or lower at a cooling rate of 5 ° C./s or more when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher is performed. It is preferable to have. The rolling strain accumulated in the material due to the hot rolling of the finish decreases immediately after the hot rolling of the finish when the stainless steel is kept at a high temperature. In order to reduce the reduction in rolling strain, it is preferable to quickly cool to a temperature range in which the reduction in rolling strain does not occur.
前記の仕上熱延工程の後、仕上熱延を施された鋼帯を仕上げ熱延の最終パス温度が７５０℃以上の場合は７５０℃以下まで冷却速度５℃／ｓ以上で冷却する冷却工程を有することが好ましい。仕上熱延で材料中に蓄積される圧延ひずみは、ステンレス鋼が高温のまま保持されると仕上熱延直後から減少する。圧延ひずみの減少を低減するためには、圧延ひずみの減少が起こらない温度域まで速やかに冷却することが好ましい。 (Cooling process)
After the finishing hot-rolling step, a cooling step of cooling the steel strip subjected to the finishing hot-rolling to 750 ° C. or lower at a cooling rate of 5 ° C./s or more when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher is performed. It is preferable to have. The rolling strain accumulated in the material due to the hot rolling of the finish decreases immediately after the hot rolling of the finish when the stainless steel is kept at a high temperature. In order to reduce the reduction in rolling strain, it is preferable to quickly cool to a temperature range in which the reduction in rolling strain does not occur.
図５に本発明の実施例のオーステナイト系ステンレス鋼の物性等を示す。また、図６および図７に比較例のオーステナイト系ステンレス鋼の物性等を示す。なお、図５、図６および図７における圧延温度は、圧延を行うときの鋼板の温度のことである。図５に示すように、上記の製造方法の条件を満たすＮｏ．Ｃ０１～Ｃ２５の製造方法で製造されたオーステナイト系ステンレス鋼は、厚さ方向の断面硬さ分布の平均が２５０ＨＶ以上であり、かつ断面硬さ分布の変動幅が３０ＨＶ以下であった。一方で、図６および図７に示すように、上記の製造方法の条件を満たさない（具体的には、板厚、ロール径、Ｃ＋Ｎ量および冷却速度のうち少なくとも１つが上記の製造方法の条件を満たさない）Ｎｏ．Ｄ０１～Ｈ０６の製造方法で製造されたオーステナイト系ステンレス鋼は、厚さ方向の断面硬さ分布の平均が２５０ＨＶ未満、および／または、変動幅が３０ＨＶよりも大きかった。
FIG. 5 shows the physical properties of the austenitic stainless steel according to the embodiment of the present invention. Further, FIGS. 6 and 7 show the physical properties of the austenitic stainless steel of the comparative example. The rolling temperature in FIGS. 5, 6 and 7 is the temperature of the steel sheet during rolling. As shown in FIG. 5, No. 1 satisfying the above-mentioned manufacturing method conditions. The austenitic stainless steels produced by the production methods C01 to C25 had an average cross-sectional hardness distribution of 250 HV or more in the thickness direction and a fluctuation range of the cross-sectional hardness distribution of 30 HV or less. On the other hand, as shown in FIGS. 6 and 7, at least one of the above-mentioned manufacturing method conditions (specifically, plate thickness, roll diameter, C + N amount, and cooling rate) does not satisfy the above-mentioned manufacturing method conditions. Does not satisfy) No. The austenitic stainless steels produced by the production methods D01 to H06 had an average cross-sectional hardness distribution in the thickness direction of less than 250 HV and / or a fluctuation range of more than 30 HV.
（鋼の化学組成）
本発明の一実施形態に係るオーステナイト系ステンレス鋼の化学組成は、質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％、残部Ｆｅおよび不可避的不純物からなる。以下、鋼組成における「％」は特に断らない限り質量％を意味する。 (Chemical composition of steel)
The chemical composition of the austenitic stainless steel according to the embodiment of the present invention is C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, P: in mass%. 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20%, balance Fe and Consists of unavoidable impurities. Hereinafter, "%" in the steel composition means mass% unless otherwise specified.
本発明の一実施形態に係るオーステナイト系ステンレス鋼の化学組成は、質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％、残部Ｆｅおよび不可避的不純物からなる。以下、鋼組成における「％」は特に断らない限り質量％を意味する。 (Chemical composition of steel)
The chemical composition of the austenitic stainless steel according to the embodiment of the present invention is C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, P: in mass%. 0.04% or less, S: 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20%, balance Fe and Consists of unavoidable impurities. Hereinafter, "%" in the steel composition means mass% unless otherwise specified.
本発明の一実施形態に係るオーステナイト系ステンレス鋼では、さらに、前記化学組成に加えて、質量％で、Ｍｏ：０．０１～３．００％、Ｃｕ：０．０１～３．５０％、Ａｌ：０．００８０％以下、Ｏ：０．００４０～０．０１００％、Ｖ：０．０１～０．５％、Ｂ：０．００１～０．０１％、Ｔｉ：０．０１～０．５０％の１種または２種以上を含有してもよい。
In the austenitic stainless steel according to the embodiment of the present invention, in addition to the chemical composition, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al in mass%. : 0.0080% or less, O: 0.0040 to 0.0100%, V: 0.01 to 0.5%, B: 0.001 to 0.01%, Ti: 0.01 to 0.50% It may contain one kind or two or more kinds of.
本発明の一実施形態に係るオーステナイト系ステンレス鋼では、さらに、任意成分として質量で、Ｃｏ：０．０１～０．５０％、Ｚｒ：０．０１～０．１０％、Ｎｂ：０．０１～０．１０％、Ｍｇ：０．０００５～０．００３０％、Ｃａ：０．０００３～０．００３０％、Ｙ：０．０１～０．２０％、ＲＥＭ（希土類金属）：０．０１～０．１０％、Ｓｎ：０．００１～０．５００％およびＳｂ：０．００１～０．５００％、Ｐｂ：０．０１～０．１０％、Ｗ：０．０１～０．５０％のうちから選んだ１種または２種以上を含有してもよい。
In the austenitic stainless steel according to the embodiment of the present invention, as an optional component, Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005 to 0.0030%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20%, REM (rare earth metal): 0.01 to 0. Select from 10%, Sn: 0.001 to 0.500%, Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50%. However, it may contain one kind or two or more kinds.
Ｃは、侵入型元素であり加工硬化および歪時効により高強度化に寄与する。また、オーステナイト相を安定化させる元素であり非磁性の維持に有効である。本発明では０．００３％以上のＣ含有量を確保する。ただし、過度のＣ含有は鋼を硬質化させ冷間鍛造性を低下させる要因となる。Ｃ含有量は０．０１２％以下に制限される。
C is an intrusive element and contributes to high strength by work hardening and strain aging. In addition, it is an element that stabilizes the austenite phase and is effective in maintaining non-magnetism. In the present invention, a C content of 0.003% or more is secured. However, excessive C content becomes a factor that hardens the steel and lowers the cold forging property. The C content is limited to 0.012% or less.
Ｓｉは、製鋼過程において鋼の脱酸剤として用いられる元素である。Ｓｉは歪取り熱処理において時効硬化性を向上させる作用を有する。一方、Ｓｉは固溶強化作用が大きく、かつ積層欠陥エネルギーを低下させて加工硬化を大きくする作用を有するので、過度のＳｉ含有は冷間鍛造性を低下させる要因となる。そのためＳｉ含有量は２．０％以下に制限される。
Si is an element used as a deoxidizer for steel in the steelmaking process. Si has the effect of improving age hardening in the strain removing heat treatment. On the other hand, Si has a large solid solution strengthening action and also has an action of lowering stacking defect energy and increasing work hardening. Therefore, excessive Si content becomes a factor of lowering cold forging property. Therefore, the Si content is limited to 2.0% or less.
Ｍｎは、ＭｎＯとして酸化物系介在物を構成する元素である。また、Ｍｎは固溶強化作用が小さく、かつオーステナイト生成元素であり加工誘起マルテンサイト変態を抑制させる作用を有するので、冷間鍛造性の確保と非磁性の維持には有効な元素である。ただし、過剰のＭｎ含有量は耐食性低下の要因となる。Ｍｎ含有量は２．００％以下に制限される。
Mn is an element that constitutes an oxide-based inclusion as MnO. In addition, Mn has a small solid solution strengthening action and is an austenite-forming element and has an action of suppressing process-induced martensitic transformation, so that it is an effective element for ensuring cold forging property and maintaining non-magnetism. However, the excessive Mn content causes a decrease in corrosion resistance. The Mn content is limited to 2.00% or less.
Ｐは、耐食性を低下させる元素であり、また、過度のＰ低減は製鋼負荷を増大させる要因となるため、０．０４０％以下とする必要がある。
P is an element that lowers the corrosion resistance, and excessive P reduction causes an increase in the steelmaking load, so it must be 0.040% or less.
Ｓは、ＭｎＳを形成して耐食性を劣化させる要因となり、また過度の脱Ｓは製鋼負荷を増大させる要因となるので、０．０３０％以下に制限される。
S is a factor that forms MnS and deteriorates corrosion resistance, and excessive de-S is a factor that increases the steelmaking load, so it is limited to 0.030% or less.
Ｃｒは、耐食性を向上させる元素である。携帯型電子機器の外装部材に適した耐食性を確保するために、本発明ではＣｒ含有量が１６．０％以上の鋼を対象とする。ただし、多量のＣｒ含有は冷間鍛造性を低下させる要因となる。Ｃｒ含有量の上限は２２．０％に制限される。
Cr is an element that improves corrosion resistance. In order to ensure corrosion resistance suitable for exterior members of portable electronic devices, the present invention targets steel having a Cr content of 16.0% or more. However, a large amount of Cr content causes a decrease in cold forging property. The upper limit of Cr content is limited to 22.0%.
Ｎは、Ｃと同様に侵入型元素であり加工硬化および歪時効により高強度化に寄与する。また、オーステナイト相を安定化させる元素であり非磁性の維持に有効である。本発明では０．００５％以上のＮ含有量を確保する。ただし、過度のＮ含有は鋼を硬質化させ冷間鍛造性を低下させる要因となる。Ｎ含有量は０．２０％以下に制限される。
N is an intrusive element like C and contributes to high strength by work hardening and strain aging. In addition, it is an element that stabilizes the austenite phase and is effective in maintaining non-magnetism. In the present invention, an N content of 0.005% or more is secured. However, excessive N content becomes a factor that hardens the steel and lowers the cold forging property. The N content is limited to 0.20% or less.
Ｍｏは、ステンレス鋼の耐食性向上に有効な元素である。本発明では、前記のＣｒ含有量を確保した上で、必要に応じて添加されるが、多量のＭｏ添加はコスト増になるため、Ｍｏを含有する場合は、Ｍｏ含有量は０．０１％～３．００％以下である。
Mo is an element effective for improving the corrosion resistance of stainless steel. In the present invention, the Cr content is ensured and then added as needed. However, adding a large amount of Mo increases the cost. Therefore, when Mo is contained, the Mo content is 0.01%. It is ~ 3.00% or less.
Ｃｕは、オーステナイト相の加工硬化を抑制し、冷間鍛造性の向上に有効であることが知られている。また、冷間鍛造後に行われる歪取り熱処理の加熱温度域で時効硬化をもたらす元素であることが知られている。種々検討の結果、Ｃｕを含有する場合は、Ｃｕ含有量は０．０１％～３．５％である。
Cu is known to be effective in improving cold forging properties by suppressing work hardening of the austenite phase. Further, it is known that it is an element that causes age hardening in the heating temperature range of the strain removing heat treatment performed after cold forging. As a result of various studies, when Cu is contained, the Cu content is 0.01% to 3.5%.
Ａｌは、酸素親和力がＳｉ、Ｍｎに比べて高く、０．００３０％以上のＡｌ含有量となると冷間鍛造での内部割れの起点となる粗大な酸化物系介在物が形成されやすくなる。また、過度に低Ａｌ化することはコスト増となるので、種々の検討の結果、Ａｌを含有する場合は、Ａｌ含有量は、０．０００１％以上～０．００８０％である。
Al has a higher oxygen affinity than Si and Mn, and when the Al content is 0.0030% or more, coarse oxide-based inclusions which are the starting points of internal cracks in cold forging are likely to be formed. In addition, excessively low Al content increases the cost. Therefore, as a result of various studies, when Al is contained, the Al content is 0.0001% or more to 0.0080%.
Ｏ含有量が低くなると、Ｍｎ、Ｓｉ等が酸化しにくくなり、介在物におけるＡｌ２Ｏ３の比率が高くなる。また、Ｏ含有量が過度に高いと粒子径５μｍを超える粗大な介在物が形成されやすくなることから、種々検討の結果、Ｏを含有する場合は、Ｏ含有量は４０ｐｐｍ（０．００４０％）～１００ｐｐｍ（０．０１００％）、好ましくは８０ｐｐｍ以下である。
When the O content is low, Mn, Si and the like are less likely to be oxidized, and the ratio of Al 2 O 3 in the inclusions is high. Further, if the O content is excessively high, coarse inclusions having a particle size of more than 5 μm are likely to be formed. Therefore, as a result of various studies, when O is contained, the O content is 40 ppm (0.0040%). It is ~ 100 ppm (0.0100%), preferably 80 ppm or less.
Ｖは、冷間鍛造後に行う歪取り熱処理の加熱において時効硬化能を高める作用があることが確認された。時効硬化作用があるものの、多量のＶ含有はコスト増につながる。Ｖを含有する場合は、Ｖ含有量は、０．０１％～０．０５％である。
It was confirmed that V has the effect of enhancing the age hardening ability in the heating of the strain removing heat treatment performed after cold forging. Although it has an aging hardening effect, a large amount of V content leads to an increase in cost. When V is contained, the V content is 0.01% to 0.05%.
多量のＢ含有は硼化物の生成による加工性低下を招く要因となる。そこで、Ｂを含有する場合は、Ｂ含有量は０.００１～０.０１００％、好ましくは０.００５０％以下である。
A large amount of B is a factor that causes a decrease in workability due to the formation of boride. Therefore, when B is contained, the B content is 0.001 to 0.0100%, preferably 0.0050% or less.
Ｔｉは、炭窒化物形成元素であり、Ｃ、Ｎを固定し、鋭敏化に起因する耐食性の低下を抑制する。上記効果はＴｉを０．０１％以上含有すると発揮される。よって、Ｔｉ含有量は０．０１％以上とする。一方、Ｔｉ含有量が０．５０％を超えると、Ｔｉは、炭化物として不均一なサイズで鋼中に不均一に局在して析出し、整粒な再結晶粒成長を阻害するとともに、大変高価であることからＴｉ含有量の上限を０．５０％とする。
Ti is a carbonitride-forming element, which fixes C and N and suppresses a decrease in corrosion resistance due to sensitization. The above effect is exhibited when Ti is contained in an amount of 0.01% or more. Therefore, the Ti content is set to 0.01% or more. On the other hand, when the Ti content exceeds 0.50%, Ti is non-uniformly localized and precipitated in the steel as a carbide in a non-uniform size, which hinders the growth of sized recrystallized grains and is extremely difficult. Since it is expensive, the upper limit of the Ti content is set to 0.50%.
Ｃｏは耐隙間腐食性を向上させる効果がある。一方、過剰にＣｏを含有すると、鋼を硬質化して曲げ性に悪影響を及ぼす。そのため、Ｃｏを含有する場合は、Ｃｏ含有量を０．０１～０．５０％、好ましくは０．１０％以下である。
Co has the effect of improving the crevice corrosion resistance. On the other hand, if Co is excessively contained, the steel is hardened and the bendability is adversely affected. Therefore, when Co is contained, the Co content is 0.01 to 0.50%, preferably 0.10% or less.
Ｚｒは、ＣおよびＮとの親和力の高い元素であり、熱間圧延時に炭化物あるいは窒化物として析出し、母相中の固溶Ｃおよび固溶Ｎを低減させ、加工性を向上させる効果がある。一方、過剰にＺｒを含有すると、鋼を硬質化し、曲げ性に悪影響を及ぼす。そのため、Ｚｒを含有する場合は、Ｚｒ含有量は０．０１～０．１０％、好ましくは０．０５％以下である。
Zr is an element having a high affinity for C and N, and is precipitated as a carbide or a nitride during hot rolling, and has an effect of reducing solid solution C and solid solution N in the matrix phase and improving workability. .. On the other hand, if Zr is excessively contained, the steel is hardened and the bendability is adversely affected. Therefore, when Zr is contained, the Zr content is 0.01 to 0.10%, preferably 0.05% or less.
Ｎｂは、ＣおよびＮとの親和力の高い元素であり、熱間圧延時に炭化物あるいは窒化物として析出し、母相中の固溶Ｃおよび固溶Ｎを低減させ、加工性を向上させる効果がある。一方、過剰にＮｂを含有すると、鋼を硬質化し、曲げ性に悪影響を及ぼす。そのため、Ｎｂを含有する場合は、Ｎｂ含有量は０．０１～０．１０％、好ましくは０．０５％以下である。
Nb is an element having a high affinity for C and N, and is precipitated as a carbide or a nitride during hot rolling, and has an effect of reducing solid solution C and solid solution N in the matrix phase and improving workability. .. On the other hand, if Nb is excessively contained, the steel is hardened and the bendability is adversely affected. Therefore, when Nb is contained, the Nb content is 0.01 to 0.10%, preferably 0.05% or less.
Ｍｇは、溶鋼中でＡｌとともにＭｇ酸化物を形成し脱酸剤として作用する。一方、過剰にＭｇを含有すると鋼の靱性が低下して製造性が低下する。そのため、Ｍｇを含有する場合は、Ｍｇ含有量は０．０００５～０．００３０％、好ましくは０．００２０％以下である。
Mg forms Mg oxide together with Al in molten steel and acts as an antacid. On the other hand, if Mg is contained in an excessive amount, the toughness of the steel is lowered and the manufacturability is lowered. Therefore, when Mg is contained, the Mg content is 0.0005 to 0.0030%, preferably 0.0020% or less.
Ｃａは、熱間加工性を向上させる元素である。一方、過剰にＣａを含有すると鋼の靱性が低下して製造性が低下するとともに、さらに、ＣａＳの析出により耐食性が低下する。そのため、Ｃａを含有する場合は、Ｃａ含有量は０．０００３～０．００３０％、好ましくは０．００２０％以下である。
Ca is an element that improves hot workability. On the other hand, if Ca is excessively contained, the toughness of the steel is lowered and the manufacturability is lowered, and further, the corrosion resistance is lowered due to the precipitation of CaS. Therefore, when Ca is contained, the Ca content is 0.0003 to 0.0030%, preferably 0.0020% or less.
Ｙは、溶鋼の粘度減少を減少させ、清浄度を向上させる元素である。一方、過剰にＹを含有するとその効果は飽和し、さらに、加工性が低下する。そのため、Ｙを含有する場合は、Ｙ含有量は０．０１～０．２０％、好ましくは０．１０％以下である。
Y is an element that reduces the decrease in viscosity of molten steel and improves cleanliness. On the other hand, if Y is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Y is contained, the Y content is 0.01 to 0.20%, preferably 0.10% or less.
ＲＥＭ（希土類金属：Ｌａ、Ｃｅ、Ｎｄなどの原子番号５７～７１の元素）は、耐高温酸化性を向上させる元素である。一方、過剰にＲＥＭを含有するとその効果は飽和し、さらに、熱間圧延の際に表面欠陥が生じ、製造性が低下する。そのため、ＲＥＭを含有する場合は、ＲＥＭ含有量は０．０１～０．１０％、好ましくは０．０５％以下である。
REM (rare earth metal: an element having an atomic number of 57 to 71 such as La, Ce, Nd) is an element that improves high temperature oxidation resistance. On the other hand, if an excessive amount of REM is contained, the effect is saturated, and surface defects occur during hot rolling, resulting in a decrease in manufacturability. Therefore, when REM is contained, the REM content is 0.01 to 0.10%, preferably 0.05% or less.
Ｓｎは、圧延時における変形帯生成の促進による加工性の向上に効果的である。一方、過剰にＳｎを含有するとその効果は飽和し、さらに加工性が低下する。そのため、Ｓｎを含有する場合は、Ｓｎ含有量は０．００１～０．５００％、好ましくは０．２００％以下である。
Sn is effective in improving workability by promoting the formation of a deformation zone during rolling. On the other hand, if Sn is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Sn is contained, the Sn content is 0.001 to 0.500%, preferably 0.200% or less.
Ｓｂは、圧延時における変形帯生成の促進による加工性の向上に効果的である。一方、過剰にＳｂを含有するとその効果は飽和し、さらに加工性が低下する。そのため、Ｓｂを含有する場合は、Ｓｂ含有量は０．００１～０．５００％、好ましくは０．２００％以下である。
Sb is effective in improving workability by promoting the formation of a deformation band during rolling. On the other hand, if Sb is contained in excess, the effect is saturated and the workability is further lowered. Therefore, when Sb is contained, the Sb content is 0.001 to 0.500%, preferably 0.200% or less.
Ｐｂは、粒界の融点を下げるとともに粒界の結合力を低下させ、粒界溶融に基づく液化割れなど、熱間加工性の劣化をまねく懸念があるため、０．１０％以下とする。
Pb is set to 0.10% or less because there is a concern that the melting point of the grain boundaries will be lowered and the binding force of the grain boundaries will be lowered, leading to deterioration of hot workability such as liquefaction cracking due to melting of the grain boundaries.
Ｗは、室温における延性を損なわずに、高温強度を向上させる作用を有する。しかし、その過剰な添加は粗大な共晶炭化物が生成し、延性の低下を引き起こすので、０．５０以下とする。
W has the effect of improving high temperature strength without impairing ductility at room temperature. However, the excessive addition produces coarse eutectic carbides and causes a decrease in ductility, so the content should be 0.50 or less.
〔付記事項〕
本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。さらに、各実施形態にそれぞれ開示された技術的手段を組み合わせることにより、新しい技術的特徴を形成することができる。 [Additional notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.
本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。さらに、各実施形態にそれぞれ開示された技術的手段を組み合わせることにより、新しい技術的特徴を形成することができる。 [Additional notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.
本発明は、例えば、スマートフォンなどの電子機器の構造部材、スチールベルト、プレスプレート等、比較的厚さが厚い高強度ステンレス鋼が必要な用途に好適な、オーステナイト系ステンレス鋼帯などに利用することができる。
The present invention is used for, for example, structural members of electronic devices such as smartphones, steel belts, press plates, and austenitic stainless steel strips suitable for applications requiring relatively thick high-strength stainless steel. Can be done.
Claims (8)
- ＣとＮとを合わせた含有量が、質量％で０．０８％以上であり、
厚さ方向の断面硬さ分布の平均が２５０ＨＶ以上であり、かつ変動幅が３０ＨＶ以下であり、
厚さが３ｍｍ以上であることを特徴とするオーステナイト系ステンレス鋼。 The total content of C and N is 0.08% or more in terms of mass%.
The average cross-sectional hardness distribution in the thickness direction is 250 HV or more, and the fluctuation range is 30 HV or less.
Austenitic stainless steel characterized by a thickness of 3 mm or more. - 前記オーステナイト系ステンレス鋼の化学組成は、質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％、残部Ｆｅおよび不可避的不純物からなることを特徴とする請求項１に記載のオーステナイト系ステンレス鋼。 The chemical composition of the austenitic stainless steel is C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, P: 0.04% or less, S in mass%. : 0.030% or less, Ni: 6.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20%, balance Fe and unavoidable impurities. The austenitic stainless steel according to claim 1, which is characterized.
- 前記化学組成に加えて、さらに質量％で、Ｍｏ：０．０１～３．００％、Ｃｕ：０．０１～３．５０％、Ａｌ：０．００８０％以下、Ｏ：０．００４０～０．０１００％、Ｖ：０．０１～０．５％、Ｂ：０．００１～０．０１％、Ｔｉ：０．０１～０．５０％の１種または２種以上を含有する請求項２に記載のオーステナイト系ステンレス鋼。 In addition to the above chemical composition, in terms of mass%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al: 0.0080% or less, O: 0.0040 to 0. The second aspect of claim 2, which contains one or more of 0100%, V: 0.01 to 0.5%, B: 0.001 to 0.01%, and Ti: 0.01 to 0.50%. Austenitic stainless steel.
- 前記化学組成に加えて、さらに質量％で、Ｃｏ：０．０１～０．５０％、Ｚｒ：０．０１～０．１０％、Ｎｂ：０．０１～０．１０％、Ｍｇ：０．０００５～０．００３０％、Ｃａ：０．０００３～０．００３０％、Ｙ：０．０１～０．２０％、ＲＥＭ（希土類金属）：０．０１～０．１０％、Ｓｎ：０．００１～０．５００％およびＳｂ：０．００１～０．５００％、Ｐｂ：０．０１～０．１０％、Ｗ：０．０１～０．５０％のうちから選んだ１種または２種以上を含有する、請求項２または３に記載のオーステナイト系ステンレス鋼。 In addition to the above chemical composition, in terms of mass%, Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005. ~ 0.0030%, Ca: 0.0003 ~ 0.0030%, Y: 0.01 ~ 0.20%, REM (rare earth metal): 0.01 ~ 0.10%, Sn: 0.001 ~ 0 Contains one or more selected from .500% and Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50%. , Austenitic stainless steel according to claim 2 or 3.
- 比透磁率μが１．１以下であることを特徴とする請求項１から４までの何れか１項に記載のオーステナイト系ステンレス鋼。 The austenitic stainless steel according to any one of claims 1 to 4, wherein the relative magnetic permeability μ is 1.1 or less.
- 質量％で、Ｃ：０．００３～０．１２％、Ｓｉ：２．００％以下、Ｍｎ：２．００％以下、Ｐ：０．０４％以下、Ｓ：０．０３０％以下、Ｎｉ：６．０～１５．０％、Ｃｒ：１６．０～２２．０％、Ｎ：０．００５～０．２０％を含有し、かつＣとＮとを合わせた含有量が質量％で０．０８％以上であり、残部Ｆｅおよび不可避的不純物で構成された化学組成からなる連続鋳造によって製造したスラブを１０００～１３００℃に加熱した後、粗熱延を施す粗熱延工程と、
前記粗熱延工程の後、製造された鋼帯に対して仕上熱延を施す仕上熱延工程と、
前記仕上熱延工程の後、前記鋼帯を冷却する冷却工程とを含み、
前記仕上熱延工程では、
前記仕上熱延の圧下率が６０％以上であり、
前記仕上熱延のロール径が３００ｍｍ以上であり、
前記仕上熱延の温度が６００～１１００℃であり、
前記仕上熱延の最終パス温度が６００～９５０℃であり、
前記冷却工程では、前記鋼帯を前記仕上熱延の前記最終パス温度が７５０℃以上の場合は７５０℃以下まで、冷却速度５℃／ｓ以上で冷却することを特徴とするオーステナイト系ステンレス鋼の製造方法。 By mass%, C: 0.003 to 0.12%, Si: 2.00% or less, Mn: 2.00% or less, P: 0.04% or less, S: 0.030% or less, Ni: 6 It contains 0.0 to 15.0%, Cr: 16.0 to 22.0%, N: 0.005 to 0.20%, and the combined content of C and N is 0.08 in mass%. A crude heat spreading step in which a slab produced by continuous casting having a chemical composition of% or more and composed of the balance Fe and unavoidable impurities is heated to 1000 to 1300 ° C. and then roughly heated.
After the rough heat spreading process, a finishing heat spreading process of applying a finishing heat spreading to the manufactured steel strip,
After the finishing heat spreading step, a cooling step of cooling the steel strip is included.
In the finishing heat spreading process,
The reduction rate of the finishing heat spread is 60% or more,
The roll diameter of the finished hot-rolled product is 300 mm or more.
The temperature of the finishing heat spread is 600 to 1100 ° C.
The final pass temperature of the finishing heat spread is 600 to 950 ° C.
In the cooling step, the austenitic stainless steel is characterized in that the steel strip is cooled to 750 ° C. or lower when the final pass temperature of the finishing hot-rolling is 750 ° C. or higher, and at a cooling rate of 5 ° C./s or higher. Production method. - 前記スラブが、さらに質量％で、Ｍｏ：０．０１～３．００％、Ｃｕ：０．０１～３．５０％、Ａｌ：０．００８０％以下、Ｏ：０．００４０～０．０１００％、Ｖ：０．０１～０．５％、Ｂ：０．００１～０．０１％、Ｔｉ：０．０１～０．５０％の１種または２種以上を含有する、請求項６に記載のオーステナイト系ステンレス鋼の製造方法。 The slab further contains, in terms of mass%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.50%, Al: 0.0080% or less, O: 0.0040 to 0.0100%, The austenitic stainless steel according to claim 6, which contains one or more of V: 0.01 to 0.5%, B: 0.001 to 0.01%, and Ti: 0.01 to 0.50%. Manufacturing method of austenitic stainless steel.
- 前記スラブが、さらに質量％で、Ｃｏ：０．０１～０．５０％、Ｚｒ：０．０１～０．１０％、Ｎｂ：０．０１～０．１０％、Ｍｇ：０．０００５～０．００３０％、Ｃａ：０．０００３～０．００３０％、Ｙ：０．０１～０．２０％、ＲＥＭ（希土類金属）：０．０１～０．１０％、Ｓｎ：０．００１～０．５００％およびＳｂ：０．００１～０．５００％、Ｐｂ：０．０１～０．１０％、Ｗ：０．０１～０．５０％のうちから選んだ１種または２種以上を含有する、請求項６または７に記載のオーステナイト系ステンレス鋼の製造方法。 In terms of mass%, the slab further contains Co: 0.01 to 0.50%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, Mg: 0.0005 to 0. 0030%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20%, REM (rare earth metal): 0.01 to 0.10%, Sn: 0.001 to 0.500% And Sb: 0.001 to 0.500%, Pb: 0.01 to 0.10%, W: 0.01 to 0.50%, and one or more selected from the above. The method for producing austenitic stainless steel according to 6 or 7.
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