WO2013080518A1 - フェライト系ステンレス鋼 - Google Patents
フェライト系ステンレス鋼 Download PDFInfo
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- WO2013080518A1 WO2013080518A1 PCT/JP2012/007593 JP2012007593W WO2013080518A1 WO 2013080518 A1 WO2013080518 A1 WO 2013080518A1 JP 2012007593 W JP2012007593 W JP 2012007593W WO 2013080518 A1 WO2013080518 A1 WO 2013080518A1
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- corrosion resistance
- steel
- stainless steel
- rolled
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 33
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 17
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 17
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 10
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 5
- 229910052802 copper Inorganic materials 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 4
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 4
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract 2
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 239000010935 stainless steel Substances 0.000 claims description 6
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- 229910052787 antimony Inorganic materials 0.000 claims description 5
- 229910052720 vanadium Inorganic materials 0.000 claims description 5
- 230000007797 corrosion Effects 0.000 abstract description 84
- 238000005260 corrosion Methods 0.000 abstract description 84
- 229910000963 austenitic stainless steel Inorganic materials 0.000 abstract description 14
- 229910052804 chromium Inorganic materials 0.000 abstract description 4
- 229910052742 iron Inorganic materials 0.000 abstract description 3
- 239000002436 steel type Substances 0.000 description 56
- 238000012360 testing method Methods 0.000 description 39
- 239000010936 titanium Substances 0.000 description 38
- 238000003466 welding Methods 0.000 description 36
- 238000005554 pickling Methods 0.000 description 35
- 229910000831 Steel Inorganic materials 0.000 description 33
- 239000010959 steel Substances 0.000 description 33
- 230000007547 defect Effects 0.000 description 27
- 238000000137 annealing Methods 0.000 description 26
- 239000000463 material Substances 0.000 description 18
- 239000007789 gas Substances 0.000 description 16
- 230000000052 comparative effect Effects 0.000 description 15
- 238000000034 method Methods 0.000 description 13
- 150000003839 salts Chemical class 0.000 description 13
- 239000007921 spray Substances 0.000 description 13
- 206010070834 Sensitisation Diseases 0.000 description 11
- 230000008313 sensitization Effects 0.000 description 11
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 10
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 10
- 239000011324 bead Substances 0.000 description 10
- 229910000734 martensite Inorganic materials 0.000 description 9
- 239000000203 mixture Substances 0.000 description 9
- 238000005498 polishing Methods 0.000 description 9
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 8
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 8
- 238000005097 cold rolling Methods 0.000 description 8
- 239000002253 acid Substances 0.000 description 7
- 239000013078 crystal Substances 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 229910017604 nitric acid Inorganic materials 0.000 description 6
- 229910000975 Carbon steel Inorganic materials 0.000 description 5
- 239000010962 carbon steel Substances 0.000 description 5
- 150000004767 nitrides Chemical class 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 238000005336 cracking Methods 0.000 description 4
- 238000007598 dipping method Methods 0.000 description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 230000001737 promoting effect Effects 0.000 description 4
- 206010039509 Scab Diseases 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005422 blasting Methods 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 238000000227 grinding Methods 0.000 description 3
- 230000006911 nucleation Effects 0.000 description 3
- 238000010899 nucleation Methods 0.000 description 3
- 238000001953 recrystallisation Methods 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- 239000010937 tungsten Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 230000037303 wrinkles Effects 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 241000510097 Megalonaias nervosa Species 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 239000000571 coke Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 229910052726 zirconium Inorganic materials 0.000 description 2
- HSFWRNGVRCDJHI-UHFFFAOYSA-N Acetylene Chemical compound C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
- 241000219307 Atriplex rosea Species 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 239000004035 construction material Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 239000002932 luster Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 231100000957 no side effect Toxicity 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 230000003449 preventive effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- -1 titanium nitrides Chemical class 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/001—Interlayers, transition pieces for metallurgical bonding of workpieces
- B23K35/004—Interlayers, transition pieces for metallurgical bonding of workpieces at least one of the workpieces being of a metal of the iron group
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
-
- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- 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%
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
-
- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/005—Ferrite
Definitions
- the present invention relates to a ferritic stainless steel (ferritic stainless steel) which is excellent in corrosion resistance (corrosion) resistance) of the welded portion with austenitic stainless steel (austenitic stainless steel) and excellent in surface properties (surface quality) among corrosion resistances. Is.
- austenitic stainless steel SUS304 (18% Cr-8% Ni) (Japanese Industrial Standard, JIS G 4305) is widely used due to its excellent corrosion resistance.
- this steel type is expensive because it contains a large amount of Ni.
- stainless steel described in Patent Document 1 has been developed as a steel type having excellent corrosion resistance equivalent to SUS304.
- Patent Document 1 as component composition, C: 0.03% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.04% or less, S: 0.02% or less, Al: 0.1% or less, Cr: 20.5% or more, 22.5% or less, Cu: 0.3% or more, 0.8% or less, Ni: 1.0% or less, Ti: 4 ⁇ (C % + N%) or more, 0.35% or less, Nb: 0.01% or less, N: 0.03% or less, C + N: 0.05% or less, the balance being Fe and inevitable impurities
- a stainless steel sheet is disclosed.
- ferritic stainless steels such as JIS-SUS444 and JIS-SUS430J1L are also less sensitive to stress corrosion cracking (Stress Corrosion Cracking) than austenitic stainless steel, and do not contain Ni, which has a large price fluctuation. It is widely used as a material for automobile exhaust system members, water tanks, and construction materials.
- austenitic stainless steel is used for difficult-to-work parts that cannot be molded with ferritic stainless steel.
- a welding method TIG welding (Tungsten Inert Gas welding) is mainly used, and good corrosion resistance is required for the welded portion as well as the base material. It is done.
- the ferritic stainless steel disclosed in Patent Document 1 has good corrosion resistance in welded parts of the same steel type.
- the corrosion resistance of the welded part may be lower than that of the base material.
- the corrosion resistance of the welded portion is determined by the thermal history during welding, in which C and N in the steel are combined with Cr to form Cr carbide (Cr 23 C 6, for example), or Cr nitride (Cr- (precipitates at the grain boundaries) as nitrides) (CrN 2 etc.), resulting in a so-called sharpness caused by a Cr depletion layer having a lower Cr concentration than the base material at the grain boundaries. This is due to sensitization and deterioration of its corrosion resistance.
- Ti and N in the molten steel may react during solidification to precipitate as TiN.
- This TiN is poor in ductility at high temperature, and becomes a surface flaw in the hot rolling process and deteriorates the surface properties.
- the scratches generated in this way are deep and will not disappear even after hot-rolled sheet annealing (acidal pickling), subsequent cold rolling, cold-rolled sheet annealing, pickling, etc.
- the present invention has been made in view of such circumstances, and an object of the present invention is to provide a ferritic stainless steel which is excellent in corrosion resistance of a welded portion and excellent in surface properties even when welded to austenitic stainless steel.
- the present inventors have developed the corrosion resistance of the base metal part and the welded part and the surface defects of the steel sheet (scab, pin hole, pin scab, linear scab, Through careful investigation and examination of the influence of the chemical composition of steel on the occurrence of titanium stringer shape anomalies and white stripe pattern color defects, the following findings were obtained. (1) By optimizing the concentration of the ferrite phase promoting element, the so-called ferrite former element, the structure of the welded portion between the austenitic stainless steel and the ferritic stainless steel is reduced to the C and N solid solubility limit. It should be possible to prevent sensitization to some extent by using a large martensite phase.
- the ferritic stainless steel having excellent corrosion resistance and surface properties of the welded portion according to the above [1], further comprising Al: 0.01% to 0.5% by mass.
- the ferrite having excellent corrosion resistance and surface properties of the welded portion according to the above [1] or [2], further comprising Sb: 0.05% to 0.30% by mass% Stainless steel.
- the ferritic stainless steel of the present invention is suitable for kitchen equipment, building interior materials, industrial machinery, automobile parts and the like because it is excellent in corrosion resistance and surface properties of the welded portion even when welded with austenitic stainless steel.
- C 0.003-0.012%
- C is easy to combine with Cr to form Cr carbide, and when Cr carbide is formed in the heat-affected zone during welding, it causes intergranular corrosion. Therefore, C is preferably as low as possible. Therefore, C is set to 0.012% or less. On the other hand, even if it is too low, a great amount of time is required for refining, so the C content is in the range of 0.003 to 0.012%. Preferably, it is in the range of 0.003 to 0.010%.
- Si 0.30 to 0.60% Si is an important element in the present invention.
- Si the solubility product of Ti and N in the molten steel is lowered, and precipitation of the Ti nitrocarbon compound is promoted at a high temperature before columnar crystals are formed.
- N in the molten steel is lowered, and TiN is less likely to precipitate at the columnar grain boundaries during the subsequent columnar crystal growth.
- Si by adding 0.30% or more of Si, it is possible to suppress the precipitation of TiN on the columnar crystal grain boundaries that cause titanium stringer defects.
- the Si amount is in the range of 0.30 to 0.60%. Preferably it is 0.40 to 0.50% of range.
- Mn 0.10 to 0.35% Since Mn has a deoxidizing action, 0.10% or more is added. Further, since it is an austenite phase promoting element (austenite former element), it promotes the formation of a martensite phase in a welded portion (hereinafter referred to as a different steel type welded portion) with austenitic stainless steel. However, it combines with S present in the steel excessively to form MnS, which is a soluble sulfide, and lowers the corrosion resistance. Therefore, the Mn content is in the range of 0.10 to 0.35%. Preferably it is 0.10 to 0.25% of range.
- P 0.040% or less
- P is an element harmful to corrosion resistance. Furthermore, it is an element that reduces hot workability. In particular, these tendencies become prominent when it exceeds 0.040%. For this reason, the amount of P is made into 0.040% or less. Preferably it is 0.030% or less.
- S 0.020% or less S is an element harmful to corrosion resistance.
- MnS MnS is formed, which becomes a starting point of pitting corrosion and deteriorates corrosion resistance. Such an effect becomes remarkable when it exceeds 0.020%.
- the amount of S is made into 0.020% or less.
- it is 0.010% or less. More preferably, it is 0.006% or less.
- Cr 17.0 to 19.0% Cr is an element indispensable for forming a passive film on the surface of stainless steel and increasing the corrosion resistance of the base material. In order to obtain good corrosion resistance, addition of 17.0% or more is necessary, but addition exceeding 19.0% prevents martensite from being formed in a dissimilar steel type weld with SUS304 and prevents deterioration of corrosion resistance. Disappear. For this reason, the Cr content is in the range of 17.0 to 19.0%. Preferably it is 17.5 to 18.5% of range.
- Ni Over 0.10% to 0.30% Ni is an element that contributes to improvement of crevice corrosion resistance. Furthermore, since it is an austenite phase promoting element (austenite former element) like Mn, it promotes the formation of the martensite phase in the welded zone of different steel types. However, when added over 0.30%, SCC sensitivity increases. It is also an expensive element. For this reason, the Ni content is in the range of more than 0.10% to 0.30%. Preferably it is 0.20 to 0.30% of range.
- Nb 0.005% to less than 0.050%
- a small amount of Nb is also an important factor in the present invention.
- Nb preferentially forms carbonitride over Cr and Ti.
- Nb begins to form carbonitride at a temperature higher than that of Ti in a weld metal and a heat affected zone of a different steel type weld. The reason is not clear, but Ti generates this small amount of Nb carbonitride as a nucleation site in the subsequent cooling process. That is, the formation of Ti carbonitride is promoted by adding a small amount of Nb. Therefore, compared with the case where Nb is not included, the ability to fix C and N by the molten pool of the different steel type welded portion and Ti of the heat affected zone is increased.
- the Nb amount is set to 0.005% or more.
- the recrystallization temperature of the cold-rolled sheet is increased, and in order to obtain good mechanical properties, annealing must be performed at a higher temperature than when Nb is not added. You won't get. Therefore, it grows thicker than in the case where the oxide film produced during annealing is not added. For this reason, the pickling property of the cold-rolled sheet in the high-speed pickling method used in the carbon steel manufacturing facility described above is deteriorated and the productivity is lowered. Therefore, the Nb content is set to a range of 0.005 to less than 0.050%. Preferably it is 0.01% or more and less than 0.050% of range.
- Ti 0.10 to 0.40% Ti must be added in an amount of 0.10% or more in order to ensure the corrosion resistance of a welded part of a different steel type with austenitic stainless steel (to prevent sensitization). However, if added over 0.40%, TiN is formed at the columnar grain boundaries, the titanium stringer defects become stronger, and the surface of the hot rolled annealed pickled plate must be ground with a grinder to obtain good surface quality. I will have to. For this reason, the Ti amount is set to a range of 0.10 to 0.40%. Preferably it is 0.20 to 0.40% of range.
- Mo 0.20% or less
- Mo is an element that strengthens the passivation film and significantly improves the corrosion resistance, and the effect is obtained by adding 0.01% or more.
- Mo is a ferrite phase promoting element, a so-called ferrite former element, and if added over 0.20%, the welded zone of the different steel type with the austenitic stainless steel does not become martensite, and the solid solution amount of C and N Therefore, it becomes impossible to prevent sensitization. Therefore, Mo is 0.20% or less.
- Mo since Mo also reduces the toughness of a hot-rolled sheet, it is preferably 0.10% or less.
- N 0.005 to 0.015%
- N is likely to combine with Cr to form Cr nitride.
- Cr nitride When Cr nitride is formed in the welded zone and the heat-affected zone during welding, it causes grain boundary corrosion, so N is preferably as low as possible.
- the N content is in the range of 0.005 to 0.015%.
- the content is 0.005 to 0.012%.
- Cu 0.3% to 0.5%
- Cu is an element that enhances corrosion resistance, particularly corrosion resistance when an aqueous solution or weakly acidic water droplets adhere. This is presumed that Cu dissolves at a certain electrochemical potential in an aqueous solution or weakly acidic water droplets, and Cu reattaches to the base iron to suppress dissolution resistance.
- the Cu amount is set in the range of 0.3 to 0.5%. Preferably it is 0.3 to 0.4% of range.
- Mg Less than 0.0005% Mg is an impurity mainly mixed from bricks in the converter. Mg becomes the starting point of a wide variety of inclusions, and even if the amount is mixed, it becomes a nucleation site for other inclusions, and it is difficult to re-dissolve even if annealing is performed, hot-rolled annealing pickling plate, cold-rolling annealing pickling Deteriorates the surface properties of the plate. Therefore, the Mg content is less than 0.0005%. Preferably it is less than 0.0003%.
- the above are the basic chemical components of the present invention, and the balance consists of Fe and inevitable impurities.
- Al and Sb may be added as selective elements.
- Zr and V may be added as selective elements for the purpose of improving the corrosion resistance of the different steel type welds.
- Ca 0.0020% or less is acceptable.
- Al 0.01 to 0.5% Al needs to be added when the gas shield for TIG welding is insufficient.
- TIG welding welding is generally performed by shielding the rear surface and the front surface with gas.
- the shield is not sufficient, and N in the atmosphere is mixed into the molten pool, exceeding the solid solution limit of martensite. May not be able to be prevented.
- it is effective to add Al in advance to prevent sensitization. This is because the added Al reacts with N to produce AlN and captures N mixed in the molten pool. This effect can be obtained by adding 0.01% or more.
- the content is preferably in the range of 0.01 to 0.5%. More preferably, it is in the range of 0.1 to 0.5%. More preferably, it is in the range of 0.15 to 0.25%.
- Sb 0.05 to 0.30% Sb, like Al, has an effect of capturing N mixed in from the atmosphere when the gas shield for TIG welding is insufficient, and is an element that should be added in the case of a structure having a complicated shape.
- the Sb content is preferably in the range of 0.05 to 0.30%. More preferably, it is in the range of 0.05 to 0.15%.
- Zr 0.01 to 0.60%
- Zr forms carbonitride preferentially over Cr like Ti and improves corrosion resistance in welds of the same steel type and different steel types, and is an element to be added in consideration of the corrosion resistance of welds.
- Zr is considerably more expensive than Ti, and if added too much, an intermetallic compound is produced, and the toughness of the hot-rolled sheet deteriorates. Therefore, when Zr is added, the Zr content is preferably in the range of 0.01 to 0.60%. More preferably, it is in the range of 0.1 to 0.35%.
- V 0.01 to 0.50%
- V forms carbonitride preferentially over Cr and improves the corrosion resistance of welds of the same steel type and different steel types.
- the effect can be obtained by adding 0.01% or more. However, adding over 0.50% degrades the mechanical properties. Therefore, when V is added, the content is preferably in the range of 0.01% to 0.50%. More preferably, it is in the range of 0.02 to 0.05%.
- a preferred method for producing the steel of the present invention will be described.
- the steel having the above component composition is melted by a known method such as a converter, electric furnace, vacuum melting furnace or the like, and is made into a steel material (slab) by a continuous casting method or an ingot-bundling method.
- the steel material is then heated at 1100 to 1250 ° C. for 1 to 24 hours, or directly hot-rolled to form a hot-rolled sheet without heating.
- the hot-rolled sheet is usually subjected to hot-rolled sheet annealing at 800 to 1100 ° C. for 1 to 10 minutes. However, depending on the application, the hot-rolled sheet annealing may be omitted.
- the hot-rolled sheet after pickling the hot-rolled sheet, it is cold-rolled by cold rolling, and then recrystallized and annealed to obtain a product.
- a reduction rate in thickness of cold rolling can be achieved at a reduction rate of 50% or more in order to obtain good elongation, bendability and press formability, and for the purpose of shape correction. desirable.
- the recrystallization annealing of the cold-rolled sheet is preferably performed at 800 to 950 ° C. from the viewpoint of obtaining good mechanical properties and pickling properties in the case of the 2B product.
- the annealing temperature at this time is 800 Most preferably, it is carried out at ⁇ 900 ° C. Further, it is effective to perform BA annealing (Bright Annealing) for finishing the member where the luster is desired. Further, as described above, it is disadvantageous in terms of cost to further improve the surface properties after cold rolling and after processing, but there is no problem even if polishing is performed.
- Welding voltage 10V
- Welding current 90-110A
- Welding speed 600 mm / min
- Electrode 1.6 mm tungsten electrode
- Shielding gas Front bead side Ar 20 L / min
- Welding speed 600 mm / min
- Electrode 1.6 mm tungsten electrode
- Shielding gas Front bead side Ar 20 L / min
- Welding speed 600 mm / min
- Electrode 1.6 mm tungsten electrode
- Shielding gas Front bead side Ar 20 L / min
- the same specimen was subjected to a corrosion resistance test for a welded portion of a different steel type with SUS304.
- a plate taken from each test material and SUS304 having a thickness of 1.0 mmt were joined by TIG welding, and their surfaces were polished with # 600 abrasive paper, and then examined for corrosion resistance by CCT.
- TIG welding conditions are substantially the same
- the salt spray cycle test was performed by spraying 5% NaCl solution (35 ° C., 2 h) (spraying 5% NaCl aqueous solution at 35 ° C., 2 hr) ⁇ drying (60 ° C., 4 h, relative humidity 20-30%) (drying at 60 °C, 4hr, relative humidity 20 to 30%) ⁇ Wetting (40 °C, 2h, relative humidity 95% or more) .
- Table 2 The results are shown in Table 2.
- the criteria for each test are as follows. (1) Appearance after pickling with cold-rolled annealing: Judged by the ratio of the length of the portion with surface defects to the total length of the plate, the defect rate is less than 5% ⁇ (pass: super good), the defect rate is 5% or more, 10 % (Pass: good), defect rate 10% or more, less than 20% was ⁇ (fail), and defect rate 20% or more was judged as x (fail: very bad).
- Salt spray cycle test results of cold-rolled annealed pickling plate and # 600 polishing plate Rust area after 15-cycle test is less than 10% wrinkle rate ⁇ (pass: super good), 10% or more , Less than 20% was judged as ⁇ (pass: good), 20% or more, less than 30% was judged as ⁇ (failure), and 30% or more was judged as x (failure).
- pickling After being immersed in (sulfuric acid solution) for 120 seconds, pickling is performed by immersing in a mixed acid composed of 15 mass% nitric acid and 3 mass% hydrofluoric acid at a temperature of 55 ° C for 60 seconds. Then, descaling was performed to obtain a hot rolled annealed pickled coil. Further, the steel sheet was then cold rolled to a thickness of 1.0 mm, annealed in a coke oven gas combustion atmosphere with an air ratio of 1.3 at 900 ° C. for 2 minutes, and at a temperature of 80 ° C. and 20 mass% Na 2 SO 4 .
- Corrosion resistance was evaluated by CCT using this cold-rolled annealed pickling plate.
- the surface of the cold-rolled annealed pickling plate was polished with # 600 polishing paper, and corrosion resistance evaluation, welded portion corrosion resistance test, and SUS304 different steel type welded portion corrosion resistance test were performed. Table 4 shows the results obtained as described above.
- the criteria for each test are as follows. (1) Appearance after pickling with cold-rolled annealing: Judged by the ratio of the length of the portion with surface defects to the total length of the plate, the defect rate is less than 5% ⁇ (pass: super good), the defect rate is 5% or more, 10 % (Pass: good), defect rate 10% or more, less than 20% was ⁇ (fail), and defect rate 20% or more was judged as x (fail: very bad).
- Salt spray cycle test results of cold-rolled annealed pickling plate and # 600 polishing plate Rust area after 15-cycle test is less than 10% wrinkle rate ⁇ (pass: super good), 10% or more Less than 20% was judged as ⁇ (passed: good), 20% or more, less than 30% was judged as ⁇ (failed), and 30% or more was judged as x (failed: very bad).
- Corrosion resistance test results for the same steel type welds TIG butt welding between the same steel types, the temper color of the welds was removed with # 600 abrasive paper, and the same steel type welds were welded after 15 cycles of the salt spray cycle test.
- the defect rate is less than 10% ⁇ (pass: super good) 10% or more, less than 20% is ⁇ (pass: good), 20% or more, less than 30% is ⁇ (fail), 30% or more ⁇ (not good) Pass: very bad)
- Corrosion resistance test result of dissimilar steel type welded part with SUS304 After tempering the TIG butt weld with SUS304 and removing the temper color of the welded part with # 600 abrasive paper, the different steel type welded part after 15 cycles of salt spray cycle test , The sprout rate is less than 10% ⁇ (pass: super good) 10% or more, less than 20% ⁇ (pass: good), 20% or more, less than 30% ⁇ (fail), 30% or more ⁇ (Fail: very bad).
- This cold-rolled annealed plate was descaled by performing electrolysis (10 A / dm 2 ⁇ 2 seconds) twice in a solution comprising a temperature of 50 ° C., 15 mass% nitric acid and 0.5 mass% hydrochloric acid, and cold-rolled annealed acid A washboard was obtained.
- Corrosion resistance was evaluated by CCT using this cold-rolled annealed pickling plate. Further, after polishing the surface with # 600 polishing paper, the corrosion resistance was evaluated by CCT, and the TIG welded corrosion resistance test was conducted on the same steel type. In this test, two plates taken from each test material were joined by TIG welding, their surfaces were polished with # 600 abrasive paper, and the corrosion resistance was examined by CCT.
- the TIG welding conditions were as follows, and the welding current was controlled so that the back bead width was 3 mm or more.
- the evaluation surface was a back bead surface.
- Welding voltage 10V
- Welding current 90-110A
- Welding speed 600 mm / min
- Electrode 1.6 mm tungsten electrode
- Shielding gas Front bead side Ar + 20 vol% N 2 20 L / min
- the same specimen was subjected to a corrosion resistance test for a welded portion of a different steel type with SUS304.
- a plate taken from each test material and SUS304 having a thickness of 1.0 mm were joined by TIG welding, and their surfaces were polished with # 600 abrasive paper, and the corrosion resistance was investigated by CCT.
- TIG welding conditions are substantially the same as the above-described welding conditions for the same steel type.
- the salt spray cycle test consists of 5% NaCl solution spray (35 ° C, 2h) ⁇ dry (60 ° C, 4h, relative humidity 20-30%) ⁇ wet (40 ° C, 2h, relative humidity 95% or more) in one cycle. As a result, 15 cycles were performed. The results are shown in Table 6.
- the criteria for each test are as follows. (1) Appearance after pickling with cold-rolled annealing: Judged by the ratio of the length of the portion with surface defects to the total length of the plate, the defect rate is less than 5% ⁇ (pass: super good), the defect rate is 5% or more, 10 % (Pass: good), defect rate 10% or more, less than 20% was ⁇ (fail), and defect rate 20% or more was judged as x (fail: very bad).
- Salt spray cycle test results of cold-rolled annealed pickling plate and # 600 polishing plate Rust area after 15-cycle test is less than 10% wrinkle rate ⁇ (pass: super good), 10% or more Less than 20% was judged as ⁇ (passed: good), 20% or more, less than 30% was judged as ⁇ (failed), and 30% or more was judged as x (failed: very bad).
- Corrosion resistance test results for the same steel type welds TIG butt welding between the same steel types, the temper color of the welds was removed with # 600 abrasive paper, and the same steel type welds were welded after 15 cycles of the salt spray cycle test.
- the defect rate is less than 10% ⁇ (pass: super good) 10% or more, less than 20% is ⁇ (pass: good), 20% or more, less than 30% is ⁇ (fail), 30% or more ⁇ (not good) Pass: very bad) (4) Results of corrosion resistance test of welded part of different steel type with SUS304: TIG butt welding was performed with SUS304, and the temper color of the welded part was removed with # 600 abrasive paper.
- the weld rate after 15 cycles of the salt spray cycle test is less than 10% of the cracking rate ⁇ (pass: super good), 10% or more, less than 20% ⁇ (pass: good), 20% or more, Less than 30% was judged as ⁇ (failed), and 30% or more was judged as ⁇ (failed: very bad).
- Steel grades 23 to 28 and 33 within the scope of the present invention are cold-rolled annealed pickled plates, polished plates, welds of the same grade when the gas shield is insufficient, and SUS304 when the gas shield is insufficient. It was excellent in corrosion resistance and surface properties even in the welded zone of different steel types. In particular, the symbols 25 to 28 and 33 to which Al, Sb, Zr, and V were added were particularly excellent in corrosion resistance even in a dissimilar steel weld with SUS304 when the gas shield was insufficient. On the other hand, Comparative Example No. with a low Cr content of 16.8%. No. 29 had a large rusting area and poor corrosion resistance. Moreover, comparative steel No. with a high Cr addition amount of 19.8%. No.
- the ferritic stainless steel plate having good corrosion resistance of the base metal, corrosion resistance of the same steel type welded portion, corrosion resistance of the different steel type welded portion with SUS304, and surface properties of the cold-rolled annealed pickled plate is hot rolled. It has been clarified that any of the properties that can be obtained without grinding an annealed pickling plate is excellent.
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Abstract
Description
これは、溶接部の耐食性は、溶接時の熱履歴で鋼中のC,NがCrと結合してCr炭化物(Cr-carbides)(例えばCr23C6等)、またはCr窒化物(Cr-nitrides)(CrN2等)として粒界に析出する(precipitates at the grain boundaries)ことにより、粒界に母材よりCr濃度が低くなるCr欠乏層(chromium depletion layer)が生じることにより起こる、いわゆる鋭敏化(sensitization)をおこし、その耐食性を劣化させることによるものである。
しかし、この鋼板のC含有量が0.01%程度なのに対して、SUS304等はCの含有量が0.04~0.05%と高いために、通常、SUS304等の高C含有ステンレス鋼との接合で、同様のTi添加で鋭敏化を回避(防止)するためには、Ti添加量を1.0%程度までに高めなければならなくなる。
また、高価なTiを多量に添加することは、高価なNiを用いないという鋼種の利点を損なうことになるという問題もある。
(1)フェライト相促進元素、いわゆるフェライトフォーマー(ferritic former)元素の濃度を適正化することにより、オーステナイト系ステンレス鋼とフェライト系ステンレス鋼との溶接部の組織をC、Nの固溶限の大きなマルテンサイト相(martensite phase)とすることにより、鋭敏化をある程度防止できること。
(2)極微量のNbを添加すると、Tiより高温でNと析出物を生成し、その後の冷却過程でTi炭窒化物の核生成サイトとなり、Tiとの複合炭窒化物を生成し、Tiの鋭敏化防止効果が得られること。
(3)極微量のNbの添加であれば、鋼板の再結晶温度を上げる副作用はほとんどなく、例えば特許文献2に開示されるような炭素鋼の製造設備を用いた安価な高速焼鈍酸洗手法が適用できること。
(4)ガスシールドが不完全で大気中のNが溶接部に混入しても、Alの添加により溶接部にAlNが生成して鋭敏化を防止できること。Sbの添加でも溶接部にSbとNの化合物が生成して鋭敏化を防止できること。
(5)チタンストリンガー欠陥の主たる原因は柱状晶粒界部(columnar grain boundary)に発達したTiNによるものである。柱状晶部分のTiNは大きく発達するためである。柱状晶粒界部以外の部分のTiNは、通常の後工程の熱延板酸洗、冷延板酸洗で除去できる率が大きく、チタンストリンガー欠陥をほとんど起こさない。
(6)Si添加量を多くすると、溶鋼中でのTi、Nの溶解度積(solubility product)が下がり、柱状晶が生成する前の高温でTi炭窒化合物の析出が促進される。その結果溶鋼中のNが下がり、のちの柱状晶成長時に柱状晶粒界部にTiNが析出しにくくなる。このため、Si添加量を多くすると、Ti量がある程度高くても、チタンストリンガー欠陥の原因となる柱状晶結晶粒界へのTiNの析出を抑えることができる。
本発明は、以上の知見に基づきなされたもので、その要旨は以下のとおりである。
[2]更に、質量%で、Al:0.01%~0.5%を含有することを特徴とする上記[1]に記載の溶接部の耐食性および表面性状に優れたフェライト系ステンレス鋼。
[3]更に、質量%で、Sb:0.05%~0.30%を含有することを特徴とする上記[1]または[2]に記載の溶接部の耐食性および表面性状に優れたフェライト系ステンレス鋼。
[4]更に、質量%で、Zr:0.01%~0.60%、V:0.01%~0.50%の一種または二種を含有することを特徴とする上記[1]乃至[3]の何れかに記載の溶接部の耐食性および表面性状に優れたフェライト系ステンレス鋼。
はじめに、本発明の鋼の成分組成を規定した理由を説明する。なお、成分%は、すべて質量%を意味する。
Cは、Crと結合してCr炭化物を形成しやすく、溶接時に熱影響部にCr炭化物が形成されると粒界腐食の原因となるので、Cは低い程望ましい。そこで、Cは0.012%以下とする。一方、低すぎても精錬において多大な時間を必要とするため、C量は、0.003~0.012%の範囲とする。好ましくは、0.003~0.010%の範囲である。
Siは、本発明の中で重要な元素である。Siは適量添加すると、溶鋼中でのTi、Nの溶解度積が下がり、柱状晶が生成する前の高温でTi炭窒化合物の析出が促進される。その結果、溶鋼中のNが下がり、のちの柱状晶成長時に柱状晶粒界部にTiNが析出しにくくなる。本発明鋼の成分範囲では、Siを0.30%以上添加することにより、チタンストリンガー欠陥の原因となる柱状晶結晶粒界へのTiNの析出を抑えることができる。しかし、0.60%を超えて添加すると、前述した普通鋼製造設備で用いられる高速酸洗方法においての冷延板の酸洗性を劣化させ生産性を低下させる。また、添加しすぎると材質が硬くなり、加工性が劣化する。よって、Si量は0.30~0.60%の範囲とする。好ましくは0.40~0.50%の範囲である。
Mnは、脱酸作用があるので0.10%以上添加する。また、オーステナイト相促進元素(オーステナイトフォーマー元素)であるので、オーステナイト系ステンレス鋼との溶接部(以下異鋼種溶接部と呼ぶ)のマルテンサイト相の形成を促進させる。しかし、過剰に鋼中に存在するSと結合して、可溶性硫化物であるMnSを形成し、耐食性を低下させるので、Mn量は0.10~0.35%の範囲とする。好ましくは0.10~0.25%の範囲である。
Pは、耐食性に有害な元素である。さらには、熱間加工性を低下させる元素である。特に、これらの傾向は、0.040%を超えると顕著になる。このため、P量は0.040%以下とする。好ましくは0.030%以下である。
Sは、耐食性に有害な元素である。特に、Mnと同時に存在する場合、MnSを形成し、孔食の起点となり、耐食性を劣化させる。このような効果は0.020%を超えると顕著になる。このため、S量は0.020%以下とする。好ましくは0.010%以下である。さらに好ましくは0.006%以下である。
Crは、ステンレスの表面に不動態皮膜を形成させ、母材の耐食性を上げるのに不可欠な元素である。良好な耐食性を得るためには17.0%以上の添加が必要であるが、19.0%を超えての添加はSUS304との異鋼種溶接部でマルテンサイトが生成しなくなり耐食性低下を防止できなくなる。このため、Cr量は17.0~19.0%の範囲とする。好ましくは17.5~18.5%の範囲である。
Niは、耐隙間腐食性の改善に寄与する元素である。さらには、Mnと同じく、オーステナイト相促進元素(オーステナイトフォーマー元素)であるので、異鋼種溶接部のマルテンサイト相の形成を促進させる。しかし、0.30%を超えて添加するとSCC感受性が高くなる。また高価な元素でもある。このため、Ni量は0.10%超~0.30%の範囲とする。好ましくは0.20~0.30%の範囲である。
Nbの微量添加も本発明に重要な要素の一つである。Nbは、Cr、Tiよりも優先的に炭窒化物を形成する。特に異鋼種溶接部の溶融池(weld metal)、熱影響部(Heat Affected Zone)において、NbはTiより高温で炭窒化物の生成が始まる。理由は明らかではないが、後の冷却過程においてTiはこの微量のNb炭窒化物を核生成サイトとして生成する。つまり、微量のNb添加によって、Ti炭窒化物の生成が促進される。よって、Nbを含まない場合に比較して異鋼種溶接部の溶融池、熱影響部のTiによるC、Nの固定能力が増長されることになるのである。このためNb量は0.005%以上とする。
一方、Nbを0.050%以上添加すると、冷間圧延板の再結晶温度が上がり、良好な機械的性質を得るためには、Nbを添加しない場合に比較して、高温で焼鈍せざるを得なくなる。よって、この焼鈍時に生成する酸化皮膜が無添加の場合に比較して厚く成長する。このため、前述した炭素鋼製造設備で用いられる高速酸洗方法においての冷延板の酸洗性を劣化させ生産性を低下させる。よって、Nb量は0.005~0.050%未満の範囲とする。好ましくは0.01%以上、0.050%未満の範囲である。
Tiは、オーステナイト系ステンレス鋼との異鋼種溶接部の耐食性を確保するため(鋭敏化防止のため)に0.10%以上添加しなければならない。しかし、0.40%を超えて添加すると、TiNが柱状晶粒界に生成し、チタンストリンガー欠陥が強くなり、良好な表面品質を得るために熱延焼鈍酸洗板をグラインダーによる表面研削しなければならなくなる。このため、Ti量は0.10~0.40%の範囲とする。好ましくは0.20~0.40%の範囲である。
Moは、不動態皮膜(passivation film)を強固にし、耐食性を顕著に向上させる元素でありその効果は0.01%以上の添加で得られる。しかし、Moはフェライト相促進元素、いわゆるフェライトフォーマー元素であり、0.20%を超えて添加するとオーステナイト系ステンレス鋼との異鋼種溶接部がマルテンサイトにならなくなり、C、Nの固溶量の低いフェライト相となってしまい、鋭敏化を防ぐことができなくなる。よって、Moは0.20%以下とする。また、Moは熱延板の靭性をも低下させることから、好ましく0.10%以下である。
Nは、Crと結合してCr窒化物を形成しやすい。溶接時、異鋼種溶接部および熱影響部にCr窒化物が形成されると粒界腐食の原因となるので、Nは低い程望ましい。また、チタンストリンガー欠陥の原因とも成る元素であるので、できるだけ減らした方が良い。しかし、低すぎても精錬において多大な時間を必要とするため、N量は0.005~0.015%の範囲とする。好ましくは0.005~0.012%である。
Cuは、耐食性、特に水溶液中や弱酸性の水滴が付着した場合の耐食性を高める元素である。これは、Cuが水溶液や弱酸性水滴中のある電気化学的電位で溶解し、Cuが地鉄に再付着し耐溶解性を抑えるものと推定される。一方、Cuを0.5%超えて添加すると、熱間加工性が低下する他、熱延時に赤スケール(red scale)と呼ばれるCu起因の低融点酸化物が熱延スラブ上に生成し、表面欠陥の原因ともなる。よって、Cu量は0.3~0.5%の範囲とする。好ましくは0.3~0.4%の範囲である。
Mgは主に転炉の中のレンガより混入する不純物である。Mgは多種多様の介在物の起点となり、混入する量は微量でも他の介在物の核生成サイトとなり、焼鈍などを行っても再溶解しにくく、熱延焼鈍酸洗板、冷延焼鈍酸洗板の表面性状を劣化させる。よって、Mg量は0.0005%未満とする。好ましくは0.0003%未満である。
AlはTIG溶接のガスシールドが不十分な場合に、添加が必要となる。前述したようにTIG溶接の場合裏面、表面ガスシールドして溶接が行われるのが一般的である。しかし、異鋼種溶接部の形状が複雑な場合にはシールドが十分でなく、大気中のNが溶融池に混入し、マルテンサイトの固溶限を超え、あらかじめ添加したTiのみでは鋭敏化を完全に防止できなくなる場合がある。こうした場合には、あらかじめAlを添加しておくのが鋭敏化防止に効果的である。これは添加したAlがNと反応しAlNを生成し、溶融池に混入したNを捕らえるためである。この効果は0.01%以上の添加で得られる。しかし、Alを添加しすぎると、スラブ段階での非金属系介在物が生成し、表面性状が悪化する。また、熱延板への靭性をも悪化させる。このため、Alを添加する場合は、0.01~0.5%の範囲とすることが好ましい。より好ましくは0.1~0.5%の範囲である。さらに好ましくは0.15~0.25%の範囲である。
SbもAlと同じく、TIG溶接のガスシールドが不十分な場合に大気中より混入するNを捕らえる効果があり、複雑な形状を持った構成体の場合には添加したほうが良い元素である。しかし、一方でSbを添加しすぎると、スラブ段階での非金属系介在物が生成し、表面性状が悪化する。また、熱延板の靭性をも悪化させる。このため、Sbを添加する場合は、Sb量は0.05~0.30%の範囲とすることが好ましい。より好ましくは0.05~0.15%の範囲である。
Zrは、Tiと同様にCrよりも優先的に炭窒化物を形成し、同鋼種、異鋼種溶接部などでは耐食性を向上させるので、溶接部の耐食性を考慮した場合添加したい元素である。しかし、ZrはTiに比較してかなり高価であること、および添加しすぎると金属間化合物を生成し、熱延板の靭性が劣化する。このため、Zrを添加する場合は、Zr量は0.01~0.60%の範囲とすることが好ましい。より好ましくは0.1~0.35%の範囲である。
VもTi同様にCrよりも優先的に炭窒化物を形成し、同鋼種、異鋼種溶接部の耐食性を向上させる。その効果は0.01%以上の添加で得られる。しかし、0.50%を超えて添加すると機械的性質を劣化させる。このためVを添加する場合には、0.01%~0.50%の範囲とすることが好ましい。より好ましくは0.02~0.05%の範囲である
2.製造条件について
次に本発明鋼の好適製造方法について説明する。上記した成分組成の鋼を、転炉、電気炉、真空溶解炉等の公知の方法で溶製し、連続鋳造法あるいは造塊-分塊法により鋼素材(スラブ)とする。この鋼素材を、その後1100~1250℃×1~24時間の加熱をするか、あるいは加熱することなく直接、熱間圧延して熱延板とする。
熱延板には、通常、800~1100℃×1~10分の熱延板焼鈍が施される。しかし、用途によっては熱延板焼鈍を省略してもよい。ついで、熱延板酸洗後、冷間圧延により冷延板としたのち、再結晶焼鈍を施して、製品とする。冷間圧延の圧下率(a reduction rate in thickness of cold rolling)は良好な伸び性、曲げ性、プレス成形性を得るため、および形状矯正の目的から50%以上の圧下率で圧延を行うことが望ましい。冷延板の再結晶焼鈍は、一般的には2B品の場合、良好な機械的性質を得ること、および酸洗性の面から800~950℃で焼鈍を行うのが好ましい。
また、より光沢を求める箇所の部材には仕上げにBA焼鈍(Bright Annealing)を行うことが有効である。また、前述したが、冷間圧延後、および加工後に更に表面性状を上げるために、コスト的に不利にはなるが、研磨等を施しても何ら問題は無い。
ついで、これらの熱延板に対して大気中で950℃×1分間の熱延板焼鈍を施した後、表面をガラスビーズのショットブラスト処理を行った。その後、温度80℃の20質量%硫酸溶液中に120秒浸漬後、15質量%硝酸および3質量%弗酸よりなる温度55℃の混合酸中に60秒浸漬することにより酸洗を行い、脱スケールを行った。
さらに脱スケール後、冷間圧延を行い板厚1.0mmの冷間圧延板とし、大気開放炉で900℃×1分間の焼鈍を行い、冷延焼鈍板を得た。この冷延焼鈍板を、温度80℃、20質量%Na2SO4中で3A/dm2×10秒の電解を三回行った後、5質量%硝酸および3質量%弗酸よりなる温度55℃の混合酸に30秒間浸漬することにより脱スケールを行い、冷延焼鈍酸洗板を得た。
溶接電流 :90~110A
溶接速度 :600mm/min
電極 :1.6mmタングステン電極
シールドガス:表ビード側 Ar 20L/min
裏ビード側 Ar 20L/min
さらに、同じ供試材に対して、SUS304との異鋼種溶接部耐食性試験を行った。この試験では、それぞれの供試験材から採取した板と1.0mmt厚のSUS304をTIG溶接で接合し、それらの表面を♯600番の研磨紙で研磨した後、CCTにより耐食性を調査した。TIG溶接条件は前述した同鋼種同士の溶接条件とほぼ同じである。
塩水噴霧サイクル試験は、5質量%NaCl溶液噴霧(35℃、2h)(spraying 5% NaCl aqueous solution at 35℃, 2hr)→乾燥(60℃、4h、相対湿度20~30%)(drying at 60℃, 4hr, relative humidity 20 to 30%)→湿潤(40℃、2h、相対湿度95%以上)(wetting at 40℃, 2hr, relative humidity 95% or more)を1サイクルとして、15サイクルを行った。
それぞれの結果を表2に示す。
(1)冷延焼鈍酸洗後の外観:表面欠陥がある部分の長さの板全長に対する割合で判断し、欠陥率5%未満が◎(合格:超良好)、欠陥率5%以上、10%未満が○(合格:良好)、欠陥率10%以上、20%未満が△(不合格)、欠陥率20%以上を×(不合格:非常に悪い)と判定した。
一方、Cr含有量が16.1%と低い比較例No.9は、発銹面積が多く耐食性が劣っていた。
また、Cr添加量が19.5%と高い比較例No.10は、異鋼種溶接部での発銹面積が多く耐食性が劣っていた。フェライトフォーマー元素であるCr量が高いため、異鋼種溶接部がマルテンサイト化しないことが原因と考えられる。
また、Ti含有量が0.08%と少ない比較鋼No.11は、同鋼種溶接部および異鋼種溶接部での発銹面積が多く耐食性が劣っていた。
さらに、Nbが本発明範囲を超える比較例No.12では、母材の表面に若干のスケール残りが確認され、冷延焼鈍酸洗後の耐食性が劣っていた。
さらに、次いで、冷間圧延で板厚1.0mmとし、900℃×2分間、空気比1.3のコークス炉ガス燃焼雰囲気中で焼鈍し、温度80℃、20質量%Na2SO4中で3A/dm2×10秒の電解を三回行った後、5質量%硝酸および3質量%弗酸よりなる温度55℃の混合酸に30秒間浸漬することにより脱スケールを行い、冷延焼鈍酸洗板を得た。
この段階で、得られた冷延焼鈍酸洗板の表面性状の判定を目視で行った。
次にこの冷延焼鈍酸洗板の表面を♯600番の研磨紙で研磨して耐食性評価、溶接部耐食性試験、SUS304との異鋼種溶接部耐食性試験を行った。
以上により得られた結果を表4に示す。
(1)冷延焼鈍酸洗後の外観:表面欠陥がある部分の長さの板全長に対する割合で判断し、欠陥率5%未満が◎(合格:超良好)、欠陥率5%以上、10%未満が○(合格:良好)、欠陥率10%以上、20%未満が△(不合格)、欠陥率20%以上を×(不合格:非常に悪い)と判定した。
(2)冷延焼鈍酸洗板および♯600番研磨板の塩水噴霧サイクル試験結果:15サイクル試験後の発錆面積が、発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
(3)同鋼種溶接部耐食性試験結果:同鋼種同士でTIG突き合わせ溶接を行い♯600番の研磨紙で溶接部のテンパーカラーを除去後、塩水噴霧サイクル試験15サイクル後の同鋼種溶接部の発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
(4)SUS304との異鋼種溶接部耐食性試験結果:SUS304とTIG突き合わせ溶接を行い♯600番の研磨紙で溶接部のテンパーカラーを除去後、塩水噴霧サイクル試験15サイクル後の異鋼種溶接部の、発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
また、Cr添加量が19.7%と高い比較鋼No.20は、異鋼種溶接部での発銹面積が多く耐食性が劣っていた。フェライトフォーマー元素であるCr量が高いため、異鋼種溶接部がマルテンサイト化しないことが原因と考えられる。
また、Si含有量が本発明範囲より少ない比較鋼No.21、および、Si含有量が少なくかつMgが高い比較鋼No.22は表面性状に劣っていた。
ついで、これらの熱延板に対しては大気中で950℃×1分間の熱延板焼鈍を施した後、表面をガラスビーズのショットブラスト処理を行った。その後、温度80℃の20質量%硫酸溶液中に120秒浸漬後、15質量%硝酸および3質量%弗酸よりなる温度55℃の混合酸中に60秒浸漬することにより酸洗を行い、脱スケールを行った。
さらに脱スケール後、冷間圧延を行い板厚1.0mmの冷間圧延板とし、還元性雰囲気(H2:5%、N2:95%、露点-40℃)で900℃×1分間の焼鈍を行い、冷延焼鈍板を得た。この冷延焼鈍板を、温度50℃、15質量%硝酸および0.5質量%塩酸よりなる溶液中で電解(10A/dm2×2秒)を2回行う脱スケールを行い、冷延焼鈍酸洗板を得た。
さらに、♯600番の研磨紙で表面を研磨した後、CCTにより、耐食性評価、同鋼種でのTIG溶接部耐食性試験を行った。この試験では、それぞれの供試験材から採取した2枚の板をTIG溶接で接合し、それらの表面を♯600番の研磨紙で研磨して、CCTにより耐食性を調べた。TIG溶接条件は下記の通りで、裏ビード幅が3mm以上になるように、溶接電流を制御した。評価面は、裏ビード面とした。
溶接電流 :90~110A
溶接速度 :600mm/min
電極 :1.6mmタングステン電極
シールドガス:表ビード側 Ar+20vol%N2 20L/min
裏ビード側 Ar+20vol%N2 20L/min
さらに、同じ供試材に対して、SUS304との異鋼種溶接部耐食性試験を行った。この試験では、それぞれの供試験材から採取した板と1.0mm厚のSUS304をTIG溶接で接合し、それらの表面を♯600番の研磨紙で研磨してCCTにより耐食性を調査した。TIG溶接条件は前述した、同鋼種同士の溶接条件とほぼ同じである。塩水噴霧サイクル試験は、5質量%NaCl溶液噴霧(35℃、2h)→乾燥(60℃、4h、相対湿度20~30%)→湿潤(40℃、2h、相対湿度95%以上)を1サイクルとして、15サイクルを行った。結果を表6に示す。
(1)冷延焼鈍酸洗後の外観:表面欠陥がある部分の長さの板全長に対する割合で判断し、欠陥率5%未満が◎(合格:超良好)、欠陥率5%以上、10%未満が○(合格:良好)、欠陥率10%以上、20%未満が△(不合格)、欠陥率20%以上を×(不合格:非常に悪い)と判定した。
(2)冷延焼鈍酸洗板および♯600番研磨板の塩水噴霧サイクル試験結果:15サイクル試験後の発錆面積が、発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
(3)同鋼種溶接部耐食性試験結果:同鋼種同士でTIG突き合わせ溶接を行い♯600番の研磨紙で溶接部のテンパーカラーを除去後、塩水噴霧サイクル試験15サイクル後の同鋼種溶接部の発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
(4)SUS304との異鋼種溶接部耐食性試験結果:SUS304とTIG突き合わせ溶接を行い♯600番の研磨紙で溶接部のテンパーカラーを除去した。その後、塩水噴霧サイクル試験15サイクル後の異鋼種溶接部の、発銹率10%未満が◎(合格:超良好)、10%以上、20%未満が○(合格:良好)、20%以上、30%未満が△(不合格)、30%以上を×(不合格:非常に悪い)と判定した。
一方、Cr含有量が16.8%と低い比較例No.29は、発銹面積が多く耐食性が劣っていた。
また、Cr添加量が19.8%と高い比較鋼No.30は、異鋼種溶接部での発銹面積が多く耐食性が劣っていた。フェライトフォーマー元素であるCr量が高いため、異鋼種溶接部がマルテンサイト化しないことが原因と考えられる。
また、Si含有量が0.15%と少なく、Moが0.4%と高い比較鋼No.31、は表面性状も劣り、特にガスシールドが不十分な場合の同鋼種溶接部、ガスシールドが不十分な場合のSUS304との異鋼種溶接部においても耐食性、表面性状が劣っていた。
さらに、Si含有量が0.25%低く、Nbが0.10%と本発明範囲を超える比較鋼No.32では、炭素鋼ラインの高速酸洗ではスケール残りが確認され、母材(冷延焼鈍酸洗後)の耐食性が劣っていた。
Claims (5)
- 質量%で、C:0.003~0.012%、Si:0.30~0.60%、Mn:0.10~0.35%、P:0.040%以下、S:0.020%以下、Cr:17.0~19.0%、Ni:0.10超~0.30%、Ti:0.10~0.40%、Nb:0.005~0.050%未満、Mo:0.20%以下、N:0.005~0.015%、Cu:0.3~0.5%、Mg:0.0005%未満を含有し、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フェライト系ステンレス鋼。
- 更に、質量%で、Al:0.01~0.5%を含有することを特徴とする請求項1に記載のフェライト系ステンレス鋼。
- 更に、質量%で、Sb:0.05~0.30%を含有することを特徴とする請求項1または2に記載のフェライト系ステンレス鋼。
- 更に、質量%で、Zr:0.01~0.60%、V:0.01~0.50%の一種または二種を含有することを特徴とする請求項1または2に記載のフェライト系ステンレス鋼。
- 更に、質量%で、Zr:0.01~0.60%、V:0.01~0.50%の一種または二種を含有することを特徴とする請求項3に記載のフェライト系ステンレス鋼。
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US (1) | US20140294661A1 (ja) |
EP (1) | EP2787096B1 (ja) |
JP (1) | JP5713118B2 (ja) |
KR (1) | KR20140117370A (ja) |
CN (1) | CN103975086B (ja) |
ES (1) | ES2602800T3 (ja) |
IN (1) | IN2014KN00959A (ja) |
TW (1) | TWI519652B (ja) |
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Cited By (5)
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JP2013151733A (ja) * | 2011-12-26 | 2013-08-08 | Jfe Steel Corp | オーステナイト系ステンレス鋼との溶接部の耐食性に優れたフェライト系ステンレス鋼 |
WO2014050011A1 (ja) * | 2012-09-25 | 2014-04-03 | Jfeスチール株式会社 | フェライト系ステンレス鋼 |
CN105408511A (zh) * | 2013-07-29 | 2016-03-16 | 杰富意钢铁株式会社 | 焊接部的耐腐蚀性优良的铁素体系不锈钢 |
JP5900717B1 (ja) * | 2014-12-11 | 2016-04-06 | Jfeスチール株式会社 | ステンレス鋼板およびその製造方法 |
WO2016092713A1 (ja) * | 2014-12-11 | 2016-06-16 | Jfeスチール株式会社 | ステンレス鋼およびその製造方法 |
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ES2602800T3 (es) * | 2011-11-30 | 2017-02-22 | Jfe Steel Corporation | Acero inoxidable ferrítico |
US20150023832A1 (en) * | 2012-03-13 | 2015-01-22 | Jfe Steel Corporation | Ferritic stainless steel |
EP3118342B1 (en) * | 2014-05-14 | 2018-12-26 | JFE Steel Corporation | Ferritic stainless steel |
CA2984384A1 (en) * | 2015-07-01 | 2017-01-05 | Sandvik Intellectual Property Ab | A method of joining a fecral alloy with a fenicr alloy using a filler metal by welding |
JP6323623B1 (ja) * | 2016-06-10 | 2018-05-16 | Jfeスチール株式会社 | 燃料電池のセパレータ用ステンレス鋼板およびその製造方法 |
US10763517B2 (en) | 2016-06-10 | 2020-09-01 | Jfe Steel Corporation | Stainless steel sheet for fuel cell separators, and production method therefor |
KR102120695B1 (ko) * | 2018-08-28 | 2020-06-09 | 주식회사 포스코 | 산세성이 우수한 페라이트계 스테인리스강 |
CN113787278B (zh) * | 2021-09-01 | 2023-03-24 | 武汉轻工大学 | 一种氮钛复合强化高强钢的混合气体保护焊接工艺 |
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- 2012-11-27 US US14/359,782 patent/US20140294661A1/en not_active Abandoned
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Cited By (7)
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JP2013151733A (ja) * | 2011-12-26 | 2013-08-08 | Jfe Steel Corp | オーステナイト系ステンレス鋼との溶接部の耐食性に優れたフェライト系ステンレス鋼 |
WO2014050011A1 (ja) * | 2012-09-25 | 2014-04-03 | Jfeスチール株式会社 | フェライト系ステンレス鋼 |
CN105408511A (zh) * | 2013-07-29 | 2016-03-16 | 杰富意钢铁株式会社 | 焊接部的耐腐蚀性优良的铁素体系不锈钢 |
KR101809812B1 (ko) * | 2013-07-29 | 2017-12-15 | 제이에프이 스틸 가부시키가이샤 | 용접부의 내식성이 우수한 페라이트계 스테인레스강 |
JP5900717B1 (ja) * | 2014-12-11 | 2016-04-06 | Jfeスチール株式会社 | ステンレス鋼板およびその製造方法 |
WO2016092713A1 (ja) * | 2014-12-11 | 2016-06-16 | Jfeスチール株式会社 | ステンレス鋼およびその製造方法 |
US10626486B2 (en) | 2014-12-11 | 2020-04-21 | Jfe Steel Corporation | Stainless steel and production method therefor |
Also Published As
Publication number | Publication date |
---|---|
US20140294661A1 (en) | 2014-10-02 |
EP2787096B1 (en) | 2016-10-12 |
TW201331389A (zh) | 2013-08-01 |
JP5713118B2 (ja) | 2015-05-07 |
CN103975086B (zh) | 2016-06-22 |
IN2014KN00959A (ja) | 2015-10-09 |
KR20140117370A (ko) | 2014-10-07 |
EP2787096A1 (en) | 2014-10-08 |
CN103975086A (zh) | 2014-08-06 |
JPWO2013080518A1 (ja) | 2015-04-27 |
TWI519652B (zh) | 2016-02-01 |
EP2787096A4 (en) | 2015-07-15 |
ES2602800T3 (es) | 2017-02-22 |
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