JP5534119B1 - Ferritic stainless steel - Google Patents
Ferritic stainless steel Download PDFInfo
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- JP5534119B1 JP5534119B1 JP2013558250A JP2013558250A JP5534119B1 JP 5534119 B1 JP5534119 B1 JP 5534119B1 JP 2013558250 A JP2013558250 A JP 2013558250A JP 2013558250 A JP2013558250 A JP 2013558250A JP 5534119 B1 JP5534119 B1 JP 5534119B1
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 32
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 39
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 15
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 14
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 10
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 9
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 9
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 5
- 229910052802 copper Inorganic materials 0.000 claims abstract description 4
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 3
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 3
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 229910052787 antimony Inorganic materials 0.000 claims description 2
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052726 zirconium Inorganic materials 0.000 claims description 2
- 230000007797 corrosion Effects 0.000 abstract description 65
- 238000005260 corrosion Methods 0.000 abstract description 65
- 238000003466 welding Methods 0.000 abstract description 32
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 60
- 230000000694 effects Effects 0.000 description 25
- 206010070834 Sensitisation Diseases 0.000 description 24
- 230000008313 sensitization Effects 0.000 description 24
- 229910000831 Steel Inorganic materials 0.000 description 22
- 239000010959 steel Substances 0.000 description 22
- 238000000137 annealing Methods 0.000 description 17
- 230000007423 decrease Effects 0.000 description 16
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 15
- 229910052760 oxygen Inorganic materials 0.000 description 15
- 239000001301 oxygen Substances 0.000 description 15
- 239000011324 bead Substances 0.000 description 14
- 238000000034 method Methods 0.000 description 13
- 238000005554 pickling Methods 0.000 description 13
- 239000000047 product Substances 0.000 description 13
- 238000004519 manufacturing process Methods 0.000 description 12
- 239000000463 material Substances 0.000 description 12
- 239000012298 atmosphere Substances 0.000 description 11
- 239000007789 gas Substances 0.000 description 10
- 238000012360 testing method Methods 0.000 description 10
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 8
- 230000007547 defect Effects 0.000 description 8
- 239000007921 spray Substances 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 7
- 150000003839 salts Chemical class 0.000 description 7
- 229910000975 Carbon steel Inorganic materials 0.000 description 6
- 239000010962 carbon steel Substances 0.000 description 6
- 230000007935 neutral effect Effects 0.000 description 6
- 150000004767 nitrides Chemical class 0.000 description 6
- 238000001953 recrystallisation Methods 0.000 description 6
- 230000035515 penetration Effects 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 4
- 238000005097 cold rolling Methods 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 230000001681 protective effect Effects 0.000 description 4
- 230000007420 reactivation Effects 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 238000009864 tensile test Methods 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- 239000012141 concentrate Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000002950 deficient Effects 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 239000010410 layer Substances 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- -1 roofs and fittings Substances 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 241000219307 Atriplex rosea Species 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000006399 behavior Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000002932 luster Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000003566 sealing material Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 238000009423 ventilation 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
- C22C38/50—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
- C22C38/001—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
- C22C38/004—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
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- 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
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
十分なガスシールドを行えない溶接条件下においても、優れた耐食性を有するフェライト系ステンレス鋼を提供する。
質量%で、C:0.001〜0.030%、Si:0.05〜0.30%、Mn:0.05〜0.50%、P:0.05%以下、S:0.01%以下、Cr:18.0〜19.0%、Ni:0.05%以上0.50%未満、Cu:0.30〜0.60%、N:0.001〜0.030%、Al:0.10〜1.50%、Ti:0.05〜0.50%、Nb:0.002〜0.050%、V:0.01〜0.50%を含有し、かつ下記式(1)および(2)を満たし、残部がFeおよび不可避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。
0.40≦Si+1.5Al+1.2Ti≦2.4 ・・・・(1)
0.60≦1.2Nb+1.7Ti+V+2.2Al ・・・・(2)
なお、式中の元素記号は各元素の含有率(質量%)を表す。A ferritic stainless steel having excellent corrosion resistance even under welding conditions where sufficient gas shielding cannot be performed.
In mass%, C: 0.001 to 0.030%, Si: 0.05 to 0.30%, Mn: 0.05 to 0.50%, P: 0.05% or less, S: 0.01 % Or less, Cr: 18.0 to 19.0%, Ni: 0.05% or more and less than 0.50%, Cu: 0.30 to 0.60%, N: 0.001 to 0.030%, Al : 0.10 to 1.50%, Ti: 0.05 to 0.50%, Nb: 0.002 to 0.050%, V: 0.01 to 0.50%, and the following formula ( A ferritic stainless steel satisfying 1) and (2), with the balance being Fe and inevitable impurities.
0.40 ≦ Si + 1.5Al + 1.2Ti ≦ 2.4 (1)
0.60 ≦ 1.2Nb + 1.7Ti + V + 2.2Al (2)
In addition, the element symbol in a formula represents the content rate (mass%) of each element.
Description
本発明は、大気中から酸素あるいは窒素が、溶接相手材から窒素あるいは炭素が溶接ビード(weld bead)に侵入する溶接条件においても、耐食性の低下が起こりにくいフェライト系ステンレス鋼に関する。 The present invention relates to a ferritic stainless steel that is unlikely to deteriorate in corrosion resistance even under welding conditions in which oxygen or nitrogen enters the weld bead from the atmosphere and oxygen or nitrogen enters the weld bead.
フェライト系ステンレス鋼は、オーステナイト系ステンレス鋼と比較して少ないNi量で耐食性を確保できる。Niは高価な元素であることから、フェライト系ステンレス鋼はオーステナイト系ステンレス鋼に比べて低コストで製造することができる。また、フェライト系ステンレス鋼にはオーステナイト系ステンレス鋼に比べて熱伝導率が高く、熱膨張率が小さい、さらには応力腐食割れ(stress corrosion cracking)が起こりにくい等の優れた特性がある。このことから、フェライト系ステンレス鋼は、自動車排気系部材、屋根や建具などの建材、およびキッチンや貯水・貯湯タンクなどの水まわり用材料など幅広い用途に適用されてきた。 Ferritic stainless steel can ensure corrosion resistance with a smaller amount of Ni than austenitic stainless steel. Since Ni is an expensive element, ferritic stainless steel can be manufactured at a lower cost than austenitic stainless steel. In addition, ferritic stainless steel has superior properties such as higher thermal conductivity, lower thermal expansion coefficient, and less stress corrosion cracking than austenitic stainless steel. For this reason, ferritic stainless steel has been applied to a wide range of uses such as automobile exhaust system members, building materials such as roofs and fittings, and water-related materials such as kitchens and water / hot water storage tanks.
これらは、ステンレス鋼板をせん断やプレス加工等により加工した部品を、溶接により組み立てて製作されることが多い。溶接方法には、TIG溶接(tungsten inert gas welding)が多く用いられている。溶接される場合は、母材部と同様に溶接部も良好な耐食性を持つことが求められる。 These are often manufactured by assembling, by welding, parts obtained by processing a stainless steel plate by shearing or pressing. TIG welding (tungsten inert gas welding) is often used as the welding method. In the case of welding, the welded portion is required to have good corrosion resistance as well as the base material portion.
しかし、オーステナイト系ステンレス鋼、特にSUS304(18%Cr−8%Ni)(JIS(Japanese Industrial Standards)G 4305)等の鋼種とフェライト系ステンレス鋼をTIG溶接した場合、鋭敏化(sensitization)と呼ばれる現象により、溶接部の耐食性が母材より低下する場合がある。鋭敏化とは、溶接時の熱履歴によって鋼中のCrがC、Nと結合してCr炭化物(Cr23C6等)、またはCr窒化物(Cr2N等)として結晶粒界に析出し、溶接部の結晶粒界近傍に母材よりもCr濃度が低いCr欠乏層(Cr depletion layer)が生じることにより、結晶粒界での耐食性が低下する現象である。オーステナイト系ステンレス鋼、例えばSUS304等のCおよびN含有量がフェライト系ステンレス鋼より高い鋼とフェライト系ステンレス鋼を溶接した場合に鋭敏化が生じる場合がある。However, when austenitic stainless steel, especially SUS304 (18% Cr-8% Ni) (JIS (Japanese Industrial Standards) G4305) and other ferritic stainless steels are TIG welded, a phenomenon called sensitization is caused. Accordingly, the corrosion resistance of the welded portion may be lower than that of the base material. Sensitization means that Cr in steel combines with C and N due to the thermal history during welding and precipitates at grain boundaries as Cr carbide (Cr 23 C 6 etc.) or Cr nitride (Cr 2 N etc.). This is a phenomenon in which the corrosion resistance at the crystal grain boundary is lowered by the formation of a Cr depletion layer having a Cr concentration lower than that of the base material in the vicinity of the crystal grain boundary of the weld. Sensitization may occur when an austenitic stainless steel, for example, a steel having a C and N content higher than that of a ferritic stainless steel and a ferritic stainless steel, such as SUS304, is welded.
TIG溶接をおこなう場合、通常はアルゴンガス等の不活性ガスをシールドガスに用いて溶融池(weld metal pool)(溶接時に金属が溶けた状態の部分)への大気からの酸素や窒素の侵入を抑制する。しかし、近年では溶接部材の構造が複雑化することにともなって、溶接時に十分なガスシールドが行えず、溶融池に大気中の酸素や窒素が混入するような不完全な条件での溶接が増えている。大気から溶融池に侵入した窒素は溶接部の鋭敏化を助長し、耐食性の低下を招く。 When TIG welding is performed, oxygen or nitrogen from the atmosphere is usually introduced into the weld metal pool (the part where the metal has melted during welding) using an inert gas such as argon gas as the shielding gas. Suppress. However, in recent years, as the structure of the welded parts has become more complex, sufficient gas shielding cannot be performed at the time of welding, and welding under incomplete conditions in which oxygen and nitrogen in the atmosphere enter the molten pool has increased. ing. Nitrogen that has entered the molten pool from the atmosphere promotes sensitization of the welded portion and causes a decrease in corrosion resistance.
また、酸素は溶接部にテンパーカラー(temper color)と呼ばれるCr系の酸化皮膜を生成させ、この成長によって溶接部のCr濃度が低下し、耐食性が低下する。そのため、このような用途に適用されるフェライト系ステンレス鋼は、シールドガスによる大気からの窒素あるいは酸素の侵入を抑制できない場合においても、溶接部の耐食性を確保できる鋼成分であることが求められる。 Oxygen also forms a Cr-based oxide film called temper color in the welded portion, and this growth reduces the Cr concentration in the welded portion and lowers the corrosion resistance. Therefore, the ferritic stainless steel applied for such applications is required to be a steel component that can ensure the corrosion resistance of the welded part even when the penetration of nitrogen or oxygen from the atmosphere by the shielding gas cannot be suppressed.
一方、近年では従来のNo.2B仕上げやBA仕上げなどの光沢品に加え、外観を重視しない部材(自動車の排気系部材、各種電気製品および機械の内部部品など)に使用される、いわゆる機能品(functional products)の需要が増加している。機能品は製造コストを抑えるため、炭素鋼の焼鈍ラインを用いて、850〜900℃程度で焼鈍を行った後、例えば特許文献1に開示されるような高速酸洗手法を用いて製造される。したがって、No.2B仕上げ品やBA仕上げ品だけでなく、機能品をも製造するためには、炭素鋼の焼鈍ラインで焼鈍可能な再結晶温度を有し、かつ高速酸洗が可能となる鋼成分が求められる。 On the other hand, in recent years, the conventional no. In addition to glossy products such as 2B finish and BA finish, there is an increasing demand for so-called functional products that are used for parts that do not emphasize the appearance (automobile exhaust parts, various electrical products, machine internal parts, etc.) doing. Functional products are manufactured using a high-speed pickling technique as disclosed in Patent Document 1, for example, after annealing at about 850 to 900 ° C. using a carbon steel annealing line in order to reduce manufacturing costs. . Therefore, no. In order to produce not only 2B finished products and BA finished products but also functional products, steel components that have a recrystallization temperature that can be annealed in a carbon steel annealing line and that can be pickled at high speed are required. .
このような課題に対して、Crよりも炭素、窒素との親和力が大きいTiやNbを添加することで、Cr炭窒化物の生成をおさえて鋭敏化の発生を抑制する方法が開示されている。たとえば、特許文献2にはTiとNbを複合添加することでフェライト系ステンレス鋼の耐粒界耐食性(interglanular corrosion resistance)を向上させた鋼が開示されている。しかし、特許文献2に開示されているフェライト系ステンレス鋼は1.5%以上のMoの添加を必要とする。Moは母材の耐食性を向上させる元素ではあるが、強いフェライト生成元素であるため、1.5%ものMoが添加された場合、溶接部にフェライト相が生成して鋭敏化が発生して、十分な溶接部の耐食性を得ることができないことがある。 For such a problem, a method of suppressing the generation of sensitization by suppressing the formation of Cr carbonitride by adding Ti or Nb having a higher affinity for carbon and nitrogen than Cr is disclosed. . For example, Patent Document 2 discloses a steel in which interglanular corrosion resistance of ferritic stainless steel is improved by adding Ti and Nb in combination. However, the ferritic stainless steel disclosed in Patent Document 2 requires the addition of 1.5% or more of Mo. Mo is an element that improves the corrosion resistance of the base material, but because it is a strong ferrite-forming element, when 1.5% of Mo is added, a ferrite phase is generated in the weld and sensitization occurs, In some cases, sufficient corrosion resistance of the weld cannot be obtained.
また、溶接部の耐食性に優れたフェライト系ステンレス鋼としては、たとえば、特許文献3には溶接部の耐食性に優れたフェライト系ステンレス鋼が、特許文献4には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がそれぞれ開示されている。これらの開示例はいずれも0.1%以上のNb添加を必要としており、再結晶温度が高い。そのため、一般的な炭素鋼の焼鈍ラインを用いて、低コストで機能品を製造することができないという問題がある。
Moreover, as ferritic stainless steel excellent in the corrosion resistance of the welded part, for example, Patent Document 3 discloses a ferritic stainless steel excellent in the corrosion resistance of the welded part, and Patent Document 4 discloses a welded part with austenitic stainless steel. Ferritic stainless steels having excellent corrosion resistance are disclosed. All of these disclosed examples require 0.1% or more of Nb addition, and the recrystallization temperature is high. Therefore, there is a problem that a functional product cannot be manufactured at a low cost using a general carbon steel annealing line.
従来の技術思想に沿ってTiやNbを単純に増加することで鋭敏化の発生を抑制すると、TiN介在物に起因した表面欠陥の増加や、固溶していたNbが溶接部で粗大Nb析出物として析出して、溶接割れ(weld crack)などの問題が発生してしまう。 When the occurrence of sensitization is suppressed by simply increasing Ti and Nb in accordance with the conventional technical idea, the increase in surface defects due to TiN inclusions, and the dissolved Nb is coarse Nb precipitates at the weld. It precipitates as a product and causes problems such as weld cracks.
そこで、本発明では、フェライト系ステンレス鋼の溶接で、溶接部材の形状などが原因で十分なガスシールドを行えないために、溶融池に酸素が侵入して溶接部にテンパーカラー(酸化皮膜)が発生する溶接条件、窒素が侵入して鋭敏化が発生するような溶接条件や溶接相手材から窒素が溶接ビードに侵入する溶接条件において、優れた耐食性を有するフェライト系ステンレス鋼を提供することを目的とする。 Therefore, in the present invention, since sufficient gas shielding cannot be performed due to the shape of the welded member in the welding of ferritic stainless steel, oxygen enters the molten pool and a temper collar (oxide film) is formed in the weld. An object is to provide ferritic stainless steel having excellent corrosion resistance in welding conditions that occur, welding conditions that cause nitrogen to penetrate and sensitization, and welding conditions in which nitrogen enters a weld bead from a welding partner. And
本発明者らは、上記課題を解決するため、TIG溶接における酸素侵入によるテンパーカラーの生成と耐食性の関係、ならびに窒素侵入による鋭敏化の発生と耐食性の関係に対する各種添加元素の影響について、18.0〜19.0質量%Cr−0.15質量%Mn−0.1質量%Ni−0.35質量%Cuをベースに、Si、Al、Ti、NbおよびVを広範囲に変化させた鋼を用いて鋭意研究を行った。 In order to solve the above-mentioned problems, the present inventors have described the relationship between the generation of temper color due to oxygen penetration in TIG welding and the corrosion resistance, and the influence of various additive elements on the relationship between the occurrence of sensitization due to nitrogen penetration and the corrosion resistance. 0-19.0 mass% Cr-0.15 mass% Mn-0.1 mass% Ni-0.35 mass% A steel in which Si, Al, Ti, Nb and V are widely changed based on Cu We conducted intensive research using it.
その結果、酸素侵入によるテンパーカラーの生成による耐食性の変化と各種添加元素の関係は、Si+1.5Al+1.2Ti(以降OX値と表記する。なお、式中の元素記号は各元素の含有量(質量%)を表す)で整理することができ、OX値を0.40以上とすると耐食性が向上することを見出した。これは、OX値が0.40以上となるようにSi、AlおよびTiを複合添加すると、テンパーカラーは従来鋼に生成するCr系酸化物を主体とした酸化皮膜ではなく、Al、SiおよびTiが濃化した緻密で保護性のある酸化皮膜となり、テンパーカラーの成長による母材Cr濃度の低下が抑制されるためである。ただし、Si、AlおよびTiをOX値が2.4を超えるほど複合添加すると、酸化皮膜の結晶性が高まり、イオンなどの透過を抑制する効果が低下し、耐食性が再び低下することも明らかとなった。As a result, the relationship between the corrosion resistance of change and various additive elements due to the formation of temper color by oxygen intrusion, expressed as Si + 1.5Al + 1.2Ti (hereinafter O X value. The content of the element symbols each element in the formula ( wt%) can be organized in a representative), corrosion resistance of the O X value is 0.40 or higher can be improved. This, Si as O X value is 0.40 or more, when Al and Ti are added in combination, temper color is not the oxide film mainly composed of Cr-based oxide produced in conventional steel, Al, Si and This is because a dense and protective oxide film in which Ti is concentrated is formed, and a decrease in the base material Cr concentration due to the growth of the temper color is suppressed. However, Si, when Al and Ti O X value is added in combination as greater than 2.4, increasing the crystallinity of the oxide film, reduces the effect of suppressing the transmission of such ions, also clear that corrosion resistance decreases again It became.
また、窒素侵入による鋭敏化挙動と各種添加元素の関係を、Ox値を0.65〜0.70とした鋼を用いて調査した結果、JIS G0580(1986)に定義される再活性化率(reactivation rate)(鋭敏化の程度を示す指標であり、0.01%以下ではほとんど鋭敏化が生じていないことを意味する)は1.2Nb+1.7Ti+V+2.2Al(以降Ntr値と表記する。なお、式中の元素記号は各元素の含有量(質量%)を表す)で整理することができ、Ntr値が0.60以上の場合に再活性化率が0.01%以下となることを見出した。すなわち、Ntr値を0.60以上とすることにより、大気からの窒素侵入、あるいは窒素含有量の大きいオーステナイト系ステンレス鋼との溶接による溶接部への窒素侵入によって、通常のフェライト系ステンレス鋼では溶接部に鋭敏化が生じる溶接条件においても、良好な耐食性が得られる。Moreover, as a result of investigating the relationship between sensitization behavior due to nitrogen intrusion and various additive elements using a steel with an O x value of 0.65 to 0.70, the reactivation rate defined in JIS G0580 (1986) (Reactivation rate) (which is an index indicating the degree of sensitization, meaning that sensitization hardly occurs at 0.01% or less) is expressed as 1.2 Nb + 1.7 Ti + V + 2.2Al (hereinafter referred to as N tr value). In addition, the element symbol in a formula can be arranged by content (mass%) of each element, and when the N tr value is 0.60 or more, the reactivation rate becomes 0.01% or less. I found out. In other words, by setting the N tr value to 0.60 or more, intrusion of nitrogen from the atmosphere or penetration of nitrogen into the welded portion by welding with austenitic stainless steel having a large nitrogen content, Good corrosion resistance can be obtained even under welding conditions in which sensitization occurs in the weld.
なお、上記のOxならびにNtr値を求める各元素の係数は、その元素と酸素あるいは窒素との親和力に比例していると推定される。Note that the coefficient of each element for obtaining the above O x and N tr values is estimated to be proportional to the affinity between the element and oxygen or nitrogen.
本発明は、上記の知見に基づきなされたもので、その要旨は以下の通りである。 The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] 質量%で、C:0.001〜0.030%、Si:0.05〜0.30%、Mn:0.05〜0.50%、P:0.05%以下、S:0.01%以下、Cr:18.0〜19.0%、Ni:0.05%以上0.50%未満、Cu:0.30〜0.60%、N:0.001〜0.030%、Al:0.10〜1.50%、Ti:0.05〜0.50%、Nb:0.002〜0.05%、V:0.01〜0.50%を含有し、かつ下記式(1)および(2)を満たし、残部がFeおよび不可避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。
0.40≦Si+1.5Al+1.2Ti≦2.4 ・・・・(1)
0.60≦1.2Nb+1.7Ti+V+2.2Al ・・・・(2)
なお、式中の元素記号は各元素の含有率(質量%)を表す。[1] By mass%, C: 0.001 to 0.030%, Si: 0.05 to 0.30%, Mn: 0.05 to 0.50%, P: 0.05% or less, S: 0.01% or less, Cr: 18.0 to 19.0%, Ni: 0.05% or more and less than 0.50%, Cu: 0.30 to 0.60%, N: 0.001 to 0.030 %, Al: 0.10 to 1.50%, Ti: 0.05 to 0.50%, Nb: 0.002 to 0.05%, V: 0.01 to 0.50%, and A ferritic stainless steel satisfying the following formulas (1) and (2), the balance being Fe and inevitable impurities.
0.40 ≦ Si + 1.5Al + 1.2Ti ≦ 2.4 (1)
0.60 ≦ 1.2Nb + 1.7Ti + V + 2.2Al (2)
In addition, the element symbol in a formula represents the content rate (mass%) of each element.
[2] 更に、質量%で、Zr:0.01〜0.50%、W:0.01〜0.20%、REM:0.001〜0.10%、Co:0.01〜0.20%、B:0.0002〜0.010%、Mo:0.01〜1.0%の中から選ばれる1種以上を含有することを特徴とする上記[1]に記載のフェライト系ステンレス鋼。 [2] Further, in terms of mass%, Zr: 0.01 to 0.50%, W: 0.01 to 0.20%, REM: 0.001 to 0.10%, Co: 0.01 to 0. 0. 20%, B: 0.0002 to 0.010%, Mo: One or more selected from 0.01 to 1.0% are contained, The ferritic stainless steel according to the above [1] steel.
[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]に記載のフェライト系ステンレス鋼。 [3] The ferritic stainless steel according to the above [1] or [2], further comprising Sb: 0.05 to 0.30% by mass.
本発明によれば、大気から酸素あるいは窒素が、溶接相手材から窒素あるいは炭素が溶接ビードに侵入する溶接条件においても、優れた耐食性を有するフェライト系ステンレス鋼が得られる。 According to the present invention, a ferritic stainless steel having excellent corrosion resistance can be obtained even under welding conditions in which oxygen or nitrogen enters the weld bead from oxygen or nitrogen from the atmosphere.
以下に本発明の各構成要件の限定理由について説明する。 The reasons for limiting the respective constituent requirements of the present invention will be described below.
1.成分組成について
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。1. About component composition First, the reason which prescribed | regulated the component composition of the steel of this invention is demonstrated. In addition, all component% means the mass%.
C:0.001〜0.030%
C量が高いほど強度が向上し、少ないほど加工性が向上する。十分な強度を得るためには0.001%以上の含有が必要であるが、0.030%を超えて含有すると加工性の低下が顕著となるうえ、Cr炭化物の析出による局所的なCr欠乏に起因した耐食性の低下が生じやすくなる。そのため、C量は0.001〜0.030%の範囲とする。ただし、C量が低いほど耐食性および加工性の観点では好ましいが、C量を極度に低下させることは精錬に時間がかかり、製造上好ましくないため、好ましくは0.003〜0.018%の範囲である。より好ましくは0.005〜0.012%の範囲である。C: 0.001 to 0.030%
The higher the amount of C, the better the strength, and the lower the amount, the better the workability. In order to obtain sufficient strength, the content of 0.001% or more is necessary. However, if the content exceeds 0.030%, the workability deteriorates remarkably, and local Cr deficiency due to Cr carbide precipitation occurs. It becomes easy to produce the fall of corrosion resistance resulting from this. Therefore, the C content is in the range of 0.001 to 0.030%. However, the lower the amount of C, the better from the viewpoint of corrosion resistance and workability. However, extremely reducing the amount of C takes time for refining and is not preferable in production, so the range is preferably 0.003 to 0.018%. It is. More preferably, it is 0.005 to 0.012% of range.
Mn:0.05〜0.50%
Mnは不可避的に含まれる元素である。Mn量が0.50%を超えると、腐食の起点となるMnSの析出が促進され、耐食性が低下する。そのため、Mn量は0.50%以下とする。一方、Mn量は0.05%未満に低減することは製造コストの著しい上昇を招く。そのため、Mn量は0.05〜0.50%の範囲とする。好ましくは0.05〜0.40%の範囲である。より好ましくは0.05〜0.35%の範囲である。Mn: 0.05 to 0.50%
Mn is an element inevitably included. When the amount of Mn exceeds 0.50%, precipitation of MnS which becomes a starting point of corrosion is promoted, and the corrosion resistance is lowered. Therefore, the amount of Mn is 0.50% or less. On the other hand, reducing the amount of Mn to less than 0.05% causes a significant increase in manufacturing cost. Therefore, the amount of Mn is made 0.05 to 0.50% of range. Preferably it is 0.05 to 0.40% of range. More preferably, it is 0.05 to 0.35% of range.
P:0.05%以下
Pは鋼に不可避的に含まれる元素であり、過剰な含有は溶接性を低下させ、粒界腐食を生じやすくさせる。この傾向は0.05%超の含有で顕著となる。そのため、P量は0.05%以下とする。好ましくは0.03%以下である。P: 0.05% or less P is an element inevitably contained in steel. Excessive content decreases weldability and easily causes intergranular corrosion. This tendency becomes remarkable when the content exceeds 0.05%. Therefore, the P content is 0.05% or less. Preferably it is 0.03% or less.
S:0.01%以下
SもPと同様に鋼に不可避的に含まれる元素であり、0.01%超の含有によって、耐食性が低下する。そのため、S量は0.01%以下とする。好ましくは0.008%以下である。S: 0.01% or less S is an element inevitably contained in steel like P. Corrosion resistance is reduced by the inclusion of over 0.01%. Therefore, the S content is 0.01% or less. Preferably it is 0.008% or less.
Cr:18.0〜19.0%
Crは耐食性を確保するために最も重要な元素である。18.0%未満では、溶接による酸化で表層のCrが減少する溶接ビードやその周辺において十分な耐食性が得られない。特にSUS304等のオーステナイト系ステンレス鋼との異鋼種溶接の際、窒素の侵入によって鋭敏化が一層助長される。また、18.0%未満では、不動態(passivation)が不安定となり、後述するNtr値と再活性化率(reactivation rate)との関係が崩れ、鋭敏化による耐食性低下が起こる。一方、19.0%を超えて含有すると、酸洗時に地鉄の溶解速度が低下するため、特許文献1に開示されるような炭素鋼の酸洗ラインを使用しての高速酸洗方法ではスケールを除去しきれず、鋼板の端部などにスケール残りが生じる場合がある。そのため、Cr量は18.0〜19.0%の範囲とする。好ましくは、18.0〜18.7%の範囲である。より好ましくは18.3〜18.7%の範囲である。Cr: 18.0 to 19.0%
Cr is the most important element for ensuring corrosion resistance. If it is less than 18.0%, sufficient corrosion resistance cannot be obtained in the weld bead in which Cr on the surface layer decreases due to oxidation by welding or in the vicinity thereof. In particular, when different steel types are welded to austenitic stainless steel such as SUS304, sensitization is further promoted by the penetration of nitrogen. On the other hand, if it is less than 18.0%, the passivation becomes unstable, the relationship between the N tr value and the reactivation rate, which will be described later, is lost, and the corrosion resistance decreases due to sensitization. On the other hand, if the content exceeds 19.0%, the dissolution rate of the base iron decreases during pickling, and therefore, in the high-speed pickling method using the carbon steel pickling line as disclosed in Patent Document 1, In some cases, the scale cannot be completely removed, and a scale residue may occur at the end of the steel sheet. Therefore, the Cr content is in the range of 18.0 to 19.0%. Preferably, it is 18.0 to 18.7% of range. More preferably, it is 18.3 to 18.7% of range.
Ni:0.05%以上0.50%未満
Niはステンレス鋼の耐食性を向上させる元素であり、不動態皮膜(passive film)が形成できず活性溶解(active dissolution)が生じる腐食環境において腐食の進行を抑制する元素である。また、Niは強いオーステナイト生成元素であり、溶接部でのフェライト生成を抑制し、Cr炭窒化物の析出による鋭敏化を抑制する効果がある。これらの効果は0.05%以上の含有によって得られる。しかし、0.50%以上の含有では、加工性を低下させることに加えて、応力腐食割れの感受性が強くなる。さらには、Niは高価な元素であるため、製造コストの増大を招く。そのため、Ni量は0.05%以上0.50%未満の範囲とする。好ましくは0.10〜0.30%の範囲である。より好ましくは0.15〜0.25%の範囲である。Ni: 0.05% or more and less than 0.50% Ni is an element that improves the corrosion resistance of stainless steel. Progress of corrosion in a corrosive environment in which passive film cannot be formed and active dissolution occurs. It is an element which suppresses. Ni is a strong austenite generating element, and has the effect of suppressing ferrite formation at the weld and suppressing sensitization due to precipitation of Cr carbonitride. These effects are obtained when the content is 0.05% or more. However, if the content is 0.50% or more, in addition to lowering workability, the sensitivity to stress corrosion cracking becomes stronger. Furthermore, since Ni is an expensive element, the manufacturing cost increases. For this reason, the Ni content is in the range of 0.05% or more and less than 0.50%. Preferably it is 0.10 to 0.30% of range. More preferably, it is 0.15 to 0.25% of range.
Cu:0.30〜0.60%
Cuは耐食性を向上させる元素であり、水溶液中や弱酸性の水滴が付着した場合の母材および溶接部の耐食性を向上させるのに特に有効な元素である。また、CuはNiと同様に強いオーステナイト生成元素であり、溶接部でのフェライト生成を抑制し、Cr炭窒化物の析出による鋭敏化を抑制する効果がある。これらの効果は0.30%以上の含有で得られる。一方、0.60%を超えて含有すると、熱間加工性が低下するとともに、熱間圧延時に赤スケール(red scale)と呼ばれるCu起因の酸化物が鋼板表面に生成し、表面欠陥を生じるため好ましくない。そのため、Cu量は0.30〜0.60%の範囲とする。好ましくは0.30〜0.50%の範囲である。より好ましくは0.35〜0.45%の範囲である。Cu: 0.30 to 0.60%
Cu is an element that improves the corrosion resistance, and is an element that is particularly effective for improving the corrosion resistance of the base material and the welded part when an aqueous solution or weakly acidic water droplets adhere. Moreover, Cu is a strong austenite-forming element like Ni, and has the effect of suppressing ferrite formation at the weld and suppressing sensitization due to precipitation of Cr carbonitride. These effects are obtained when the content is 0.30% or more. On the other hand, if the content exceeds 0.60%, hot workability is reduced, and an oxide derived from Cu called red scale is generated on the steel sheet surface during hot rolling, resulting in surface defects. It is not preferable. Therefore, the amount of Cu is set to a range of 0.30 to 0.60%. Preferably it is 0.30 to 0.50% of range. More preferably, it is 0.35 to 0.45% of range.
N:0.001〜0.030%
N含有量が高いと強度が向上し、少ないほど加工性が向上する。十分な強度を得るためには0.001%以上の含有が適当であるが、含有量が0.030%を超えると加工性(伸び)が顕著に低下するうえ、Cr窒化物の析出を助長することによる耐食性の低下が生じるため好ましくない。そのため、N量は0.001〜0.030%の範囲とする。耐食性の観点から、Nは低いほど好ましいが、N量を低減するためには、精錬時間を増加させる必要があり、製造コストの上昇および生産性の低下を招くため、好ましくは0.003〜0.030%の範囲である。より好ましくは0.003〜0.015%の範囲である。さらに好ましくは0.005〜0.010%の範囲である。N: 0.001 to 0.030%
When the N content is high, the strength is improved, and as the N content is low, the workability is improved. In order to obtain sufficient strength, the content of 0.001% or more is appropriate. However, if the content exceeds 0.030%, the workability (elongation) is remarkably reduced and the precipitation of Cr nitride is promoted. This is not preferable because it causes a decrease in corrosion resistance. Therefore, the N amount is set in a range of 0.001 to 0.030%. From the viewpoint of corrosion resistance, N is preferably as low as possible. However, in order to reduce the amount of N, it is necessary to increase the refining time, leading to an increase in manufacturing cost and a decrease in productivity. 0.030% of the range. More preferably, it is 0.003 to 0.015% of range. More preferably, it is 0.005 to 0.010% of range.
Si+1.5Al+1.2Ti(OX値):0.40〜2.4
なお、式中の元素記号は各元素の含有率を表す。Si + 1.5Al + 1.2Ti (O X value): 0.40 to 2.4
In addition, the element symbol in a formula represents the content rate of each element.
Si、AlおよびTiは本発明において極めて重要な元素である。これら3元素はいずれも酸素との親和力が強い。そのため、これらの元素が添加されたステンレス鋼が酸化された場合、鋼板表面にSi、AlおよびTiを主成分とした酸化物の皮膜が形成される。この酸化物の皮膜は緻密で保護性が高いため、Crの酸化による母材中のCr濃度低下に起因した耐食性の低下を抑制する。この効果はOX値が0.40以上の場合に得られる。しかし、OX値が2.4を超えると、酸化物皮膜の結晶性が高まり、金属イオンなどの透過を抑制する効果が低下するため耐食性が再び低下する。そのため、OX値は0.40〜2.4の範囲とする。好ましくは0.40〜1.8の範囲である。さらに好ましくは0.50〜1.5の範囲である。Si, Al and Ti are extremely important elements in the present invention. All of these three elements have a strong affinity for oxygen. Therefore, when the stainless steel to which these elements are added is oxidized, an oxide film mainly composed of Si, Al and Ti is formed on the surface of the steel plate. Since this oxide film is dense and highly protective, it suppresses a decrease in corrosion resistance due to a decrease in Cr concentration in the base material due to oxidation of Cr. This effect is O X value is obtained in the case of 0.40 or more. However, if O X value exceeds 2.4, increases the crystallinity of the oxide film, the corrosion resistance to lower the effect of suppressing the transmission of such metal ions is lowered again. Therefore, O X value in the range of 0.40 to 2.4. Preferably it is the range of 0.40-1.8. More preferably, it is the range of 0.50-1.5.
1.2Nb+1.7Ti+V+2.2Al(Ntr値):0.60以上
なお、式中の元素記号は各元素の含有率を表す。1.2Nb + 1.7Ti + V + 2.2Al (N tr value): 0.60 or more In addition, the element symbol in a formula represents the content rate of each element.
溶接部における鋭敏化は、大気から溶融池に侵入する窒素、あるいは溶接相手材から侵入する窒素がCrと窒化物を形成して析出し、局所的なCr欠乏領域が生成することが原因である。CrよりもNとの親和力の大きいNb、Ti、VおよびAlを複合添加した場合、窒素はCrではなくこれら4元素の窒化物として析出する。そのため、Cr欠乏領域の生成を抑制することができ、溶接部の耐食性が向上する。この効果はNtr値が0.60以上の場合に得られる。さらに好ましくは、0.80以上である。
なお、Ntr値が4.00を超えるとTi系あるいはAl系の介在物に起因した表面欠陥が発生するため,上限値は、4.00とする。好ましくは2.50以下である。Sensitization in the weld is caused by nitrogen entering the molten pool from the atmosphere or nitrogen entering from the welding partner forming Cr and nitride, and forming a local Cr-deficient region. . When Nb, Ti, V, and Al having a higher affinity for N than Cr are added in combination, nitrogen precipitates as nitrides of these four elements instead of Cr. Therefore, the generation of a Cr-deficient region can be suppressed, and the corrosion resistance of the welded portion is improved. This effect is obtained when the N tr value is 0.60 or more. More preferably, it is 0.80 or more.
If the N tr value exceeds 4.00, surface defects due to Ti-based or Al-based inclusions are generated, so the upper limit value is 4.00. Preferably it is 2.50 or less.
Si、Al、Ti、NbおよびVは上記のOx値およびNtr値の好適な範囲を満たすように複合添加するが、本発明では各元素の添加量を下記の理由によりさらに規定する。Si, Al, Ti, Nb, and V are added in combination so as to satisfy the preferable ranges of the above O x value and N tr value. In the present invention, the addition amount of each element is further specified for the following reason.
Si:0.05〜0.30%
Siは上述したように、溶接によって形成されるテンパーカラーにAlやTiとともに濃縮して酸化皮膜の保護性を向上させ、溶接部の耐食性を良好なものとする元素である。この効果は0.05%以上の含有によって得ることができる。しかし、0.30%を超えてSiを含有すると、熱間圧延工程における圧延荷重の増大と、焼鈍工程においては鋼板表層でのSi濃化層の形成による酸洗性の低下がそれぞれ生じ、表面欠陥の増加や製造コストの上昇を招くため好ましくない。そのため、Si量は0.05〜0.30%の範囲とする。好ましくは0.05〜0.25%の範囲である。さらに好ましくは0.08〜0.20%の範囲である。Si: 0.05-0.30%
As described above, Si is an element that concentrates together with Al and Ti on the temper collar formed by welding to improve the protective property of the oxide film and to improve the corrosion resistance of the welded portion. This effect can be obtained when the content is 0.05% or more. However, if it contains Si exceeding 0.30%, an increase in rolling load in the hot rolling process and a drop in pickling due to the formation of a Si concentrated layer on the steel sheet surface layer occur in the annealing process, respectively. This is not preferable because it increases defects and increases manufacturing costs. Therefore, the amount of Si is set to a range of 0.05 to 0.30%. Preferably it is 0.05 to 0.25% of range. More preferably, it is 0.08 to 0.20% of range.
Al:0.10〜1.50%
AlもSiと同様に、SiおよびTiとともに溶接によって形成されるテンパーカラーに濃縮し、溶接部の耐食性を向上させる元素である。加えて、Alは窒素の親和力がCrよりも強いため、溶接部に窒素が混入した場合に、窒素をCr窒化物ではなくAl窒化物として析出させ、鋭敏化を抑制する効果がある。また、Alは製鋼工程における脱酸に有用な元素でもある。これらの効果は0.10%以上の含有で得られる。しかし、1.50%を超えてAlを含有すると、フェライト結晶粒が粗大化し、加工性や製造性が低下する。そのため、Al量は0.10〜1.50%の範囲とする。好ましくは、0.12〜0.80%の範囲である。さらに好ましくは0.15〜0.50%の範囲である。Al: 0.10 to 1.50%
Al, like Si, is an element that concentrates in a temper collar formed by welding together with Si and Ti and improves the corrosion resistance of the weld. In addition, since Al has a stronger affinity for nitrogen than Cr, when nitrogen is mixed in the weld, nitrogen is precipitated as Al nitride, not Cr nitride, and has the effect of suppressing sensitization. Al is also an element useful for deoxidation in the steel making process. These effects can be obtained with a content of 0.10% or more. However, if Al is contained in excess of 1.50%, ferrite crystal grains are coarsened, and workability and manufacturability are lowered. Therefore, the Al amount is set to a range of 0.10 to 1.50%. Preferably, it is 0.12 to 0.80% of range. More preferably, it is 0.15 to 0.50% of range.
Ti:0.05〜0.50%
TiもSiおよびAlと同様に、溶接によって形成されるテンパーカラーに濃縮し、酸化皮膜の保護性を向上させる元素である。また、TiはCおよびNと優先的に結合してCr炭窒化物の析出による鋭敏化に起因した耐食性の低下を抑制する元素でもある。これらの効果は、0.05%以上の添加によって得られる。しかし、0.50%を超えて添加すると、粗大なTi炭窒化物が生成し、表面欠陥を引き起こすため好ましくない。そのため、Ti量は0.05〜0.50%の範囲とする。好ましくは、0.10〜0.40%の範囲である。さらに好ましくは0.15〜0.35%の範囲である。Ti: 0.05 to 0.50%
Ti, like Si and Al, is an element that concentrates in a temper color formed by welding and improves the protective properties of the oxide film. Ti is also an element that preferentially binds to C and N and suppresses a decrease in corrosion resistance due to sensitization due to precipitation of Cr carbonitride. These effects can be obtained by adding 0.05% or more. However, adding over 0.50% is not preferable because coarse Ti carbonitrides are produced and cause surface defects. Therefore, the Ti amount is set in the range of 0.05 to 0.50%. Preferably, it is 0.10 to 0.40% of range. More preferably, it is 0.15 to 0.35% of range.
Nb:0.002〜0.050%
NbはCおよびNと優先的に結合してCr炭窒化物の析出による鋭敏化に起因した耐食性の低下を抑制する元素である。この効果は、0.002%以上の含有で得られる。一方で、Nbは再結晶温度を上昇させる元素でもあり、0.050%を超えて含有すると、再結晶に必要な焼鈍温度が高温化するため、炭素鋼の焼鈍ラインを用いた焼鈍および酸洗による機能品の安価な製造が困難になる。そのため、Nb量は0.002〜0.050%の範囲とする。好ましくは0.010〜0.045%の範囲である。さらに好ましくは0.015〜0.040%の範囲である。Nb: 0.002 to 0.050%
Nb is an element that preferentially binds to C and N and suppresses a decrease in corrosion resistance due to sensitization due to precipitation of Cr carbonitride. This effect is obtained when the content is 0.002% or more. On the other hand, Nb is also an element that raises the recrystallization temperature. If it contains more than 0.050%, the annealing temperature required for recrystallization increases, so annealing and pickling using an annealing line for carbon steel. This makes it difficult to inexpensively manufacture functional products. Therefore, the Nb amount is set to a range of 0.002 to 0.050%. Preferably it is 0.010 to 0.045% of range. More preferably, it is 0.015 to 0.040% of range.
V:0.01〜0.50%
Vは耐食性や加工性を向上させる元素である。溶接部に窒素が侵入した場合に、窒素をVNとして析出させて、鋭敏化を抑制する。この効果は、0.01%以上の含有で得られる。しかし、0.50%を超えて含有すると加工性が低下する。そのため、V量は0.01〜0.50%の範囲とする。好ましくは、0.05〜0.30%の範囲である。さらに好ましくは0.08〜0.20%の範囲である。V: 0.01 to 0.50%
V is an element that improves corrosion resistance and workability. When nitrogen penetrates into the weld, nitrogen is deposited as VN to suppress sensitization. This effect is obtained when the content is 0.01% or more. However, if it exceeds 0.50%, the workability decreases. Therefore, the V amount is in the range of 0.01 to 0.50%. Preferably, it is 0.05 to 0.30% of range. More preferably, it is 0.08 to 0.20% of range.
以上が本発明の基本化学成分であり、残部はFeおよび不可避不純物からなるが、不可避的不純物としては、Ca:0.0020%以下が許容できる。
さらに、溶接ビードの鋭敏化抑制および耐食性向上等の目的で以下の元素を含有しても良い。The above is the basic chemical component of the present invention, and the balance consists of Fe and unavoidable impurities, but Ca: 0.0020% or less is acceptable as an unavoidable impurity.
Further, the following elements may be contained for the purpose of suppressing the sensitization of the weld bead and improving the corrosion resistance.
Zr:0.01〜0.50%
ZrはC、Nと結合して鋭敏化を抑制する効果がある。この効果は0.01%以上の含有により得られるが、0.50%を超えて含有すると加工性が低下する。また、Zrは高価な元素であるため、過度な添加は製造コストの増加を招くため好ましくない。そのため、Zrを含有する場合は0.01〜0.50%の範囲とすることが好ましい。より好ましくは0.05〜0.35%の範囲である。Zr: 0.01 to 0.50%
Zr has an effect of binding to C and N to suppress sensitization. This effect is obtained when the content is 0.01% or more. However, if the content exceeds 0.50%, the workability decreases. Moreover, since Zr is an expensive element, excessive addition causes an increase in manufacturing cost, which is not preferable. Therefore, when it contains Zr, it is preferable to set it as 0.01 to 0.50% of range. More preferably, it is 0.05 to 0.35% of range.
W:0.01〜0.20%
WはMoと同様に耐食性を向上させる効果がある。この効果は0.01%以上の含有により得られるが、0.20%を超えて含有すると強度が上昇し、圧延荷重の増大等による製造性の低下を招くため好ましくない。そのため、Wを含有する場合は0.01〜0.20%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。W: 0.01-0.20%
W, like Mo, has the effect of improving corrosion resistance. This effect is obtained when the content is 0.01% or more. However, if the content exceeds 0.20%, the strength is increased, and the productivity is lowered due to an increase in rolling load and the like, which is not preferable. Therefore, when it contains W, it is preferable to set it as 0.01 to 0.20% of range. More preferably, it is 0.05 to 0.15% of range.
REM:0.001〜0.10%
REMは耐酸化性を向上させる効果があり、酸化スケールの成長速度を抑制することにより、溶接部のテンパーカラー直下におけるCr欠乏領域の形成の抑制に有効である。この効果を得るためには0.001%以上の含有が必要である。しかし、0.10%を超えて含有すると酸洗性などの製造性を低下させる。また、REMは高価な元素であるため、過度な含有は製造コストの増加を招くため好ましくない。そのため、REMを含有する場合は0.001〜0.10%の範囲とすることが好ましい。より好ましくは0.03〜0.08%の範囲である。REM: 0.001 to 0.10%
REM has the effect of improving oxidation resistance, and is effective in suppressing the formation of a Cr-deficient region immediately below the temper collar of the weld by suppressing the growth rate of the oxide scale. In order to acquire this effect, 0.001% or more needs to be contained. However, if the content exceeds 0.10%, productivity such as pickling properties is lowered. Moreover, since REM is an expensive element, excessive inclusion is not preferable because it causes an increase in manufacturing cost. Therefore, when it contains REM, it is preferable to set it as 0.001 to 0.10% of range. More preferably, it is 0.03 to 0.08% of range.
Co:0.01〜0.20%
Coは靭性を向上させる元素である。この効果は0.01%以上の含有によって得られる。一方、0.20%を超えて含有すると製造性を低下させる、そのため、Coを含有する場合は0.01〜0.20%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。Co: 0.01-0.20%
Co is an element that improves toughness. This effect is obtained when the content is 0.01% or more. On the other hand, if the content exceeds 0.20%, the productivity is lowered. Therefore, when Co is contained, the content is preferably in the range of 0.01 to 0.20%. More preferably, it is 0.05 to 0.15% of range.
B:0.0002〜0.010%
Bは二次加工脆性(secondary working embrittlement )を改善する元素であり、その効果は0.0002%以上の含有によって得られる。しかし、0.010%を超えて含有すると、過度な固溶強化( solid solution strengthening)による延性(ductility)の低下を生じる。そのため、Bを含有する場合は0.0002〜0.010%の範囲とすることが好ましい。より好ましくは0.0002〜0.007%の範囲である。さらに好ましくは0.0003〜0.003%の範囲である。B: 0.0002 to 0.010%
B is an element that improves secondary working embrittlement, and the effect is obtained when the content is 0.0002% or more. However, if the content exceeds 0.010%, ductility is reduced due to excessive solid solution strengthening. Therefore, when it contains B, it is preferable to set it as 0.0002 to 0.010% of range. More preferably, it is 0.0002 to 0.007% of range. More preferably, it is 0.0003 to 0.003% of range.
Mo:0.01〜1.0%
Moは、Cr含有量が18%以上の場合には、不動態皮膜の再不動態化(repassivation )を促進し、ステンレス鋼の耐食性を向上させる元素である。この効果は0.01%以上の含有によって得られる。しかし、1.0%を超えて含有すると、圧延負荷が大きくなり製造性が低下するとともに、鋼板強度の過度な上昇が生じる。また、Moは高価な元素であることから、多量の含有は製造コストを増大させる。そのため、Mo量を含有する場合は0.01〜1.0%の範囲とすることが好ましい。より好ましくは0.05〜0.5%の範囲である。Mo: 0.01 to 1.0%
Mo is an element that promotes the repassivation of the passive film and improves the corrosion resistance of stainless steel when the Cr content is 18% or more. This effect is obtained when the content is 0.01% or more. However, if the content exceeds 1.0%, the rolling load increases, the productivity decreases, and the steel sheet strength excessively increases. Moreover, since Mo is an expensive element, a large content increases the manufacturing cost. Therefore, when it contains Mo amount, it is preferable to set it as 0.01 to 1.0% of range. More preferably, it is 0.05 to 0.5% of range.
更に、窒素を安定化する目的でSbを選択元素として含有してもよい。 Furthermore, you may contain Sb as a selection element in order to stabilize nitrogen.
Sb:0.05〜0.30%
SbはAlと同じく、TIG溶接のガスシールドが不十分な場合に、大気から混入するNを捕らえる効果があり、十分なガスシールドを行うことが困難な複雑形状を有する構成体に適用する場合に、特に有効な添加元素である。この効果は0.05%以上の含有により得られるが、0.30%を超えて含有すると、製鋼工程において非金属介在物が生成し、表面性状が悪化する。また、熱延板の靭性を悪化させる。そのため、Sbを含有する場合は、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。Sb: 0.05-0.30%
Sb, like Al, has an effect of capturing N mixed in from the atmosphere when the gas shield of TIG welding is insufficient, and is applied to a structure having a complicated shape that makes it difficult to perform sufficient gas shield. It is a particularly effective additive element. This effect is obtained when the content is 0.05% or more. However, if the content exceeds 0.30%, nonmetallic inclusions are generated in the steel making process, and the surface properties are deteriorated. Moreover, the toughness of a hot-rolled sheet is deteriorated. Therefore, when it contains Sb, it is preferable to set it as 0.05 to 0.30% of range. More preferably, it is 0.05 to 0.15% of range.
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。上記した好適成分組成の溶鋼を、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法により鋼素材(スラブ)とする。このスラブを、1100〜1250℃で1〜24時間加熱するか、あるいは加熱することなく鋳造まま直接、熱間圧延して熱延板とする。2. Next, a preferred method for producing the steel of the present invention will be described. The molten steel having the above-mentioned preferred 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 forming method. This slab is heated at 1100 to 1250 ° C. for 1 to 24 hours, or directly hot-rolled as cast without heating to obtain a hot-rolled sheet.
通常、熱延板は800〜1100℃で1〜10分の熱延板の焼鈍が施されるが、用途によっては熱延板の焼鈍を省略しても良い。ついで、熱延板の酸洗後、冷間圧延により冷延板とした後、再結晶焼鈍、酸洗を施して製品とする。 Usually, the hot-rolled sheet is annealed at 800 to 1100 ° C. for 1 to 10 minutes, but depending on the application, the hot-rolled sheet may be omitted. Next, after pickling the hot-rolled sheet, it is made into a cold-rolled sheet by cold rolling, and then subjected to recrystallization annealing and pickling to obtain a product.
冷間圧延は伸び特性、曲げ特性、プレス成形性の確保および良好な形状を得るために50%以上の圧下率で行うことが望ましい。冷延板の再結晶焼鈍は、一般的にはJIS G 0203の表面仕上げ、No.2B仕上げ品の場合、良好な機械的性質を得ること、および酸洗で良好な表面性状を得るために800〜950℃で行うことが好ましい。 The cold rolling is desirably performed at a reduction rate of 50% or more in order to ensure elongation characteristics, bending characteristics, press formability, and obtain a good shape. In general, the recrystallization annealing of a cold-rolled sheet is performed according to JIS G 0203 surface finish, No. In the case of a 2B finished product, it is preferable to carry out at 800 to 950 ° C. in order to obtain good mechanical properties and to obtain good surface properties by pickling.
しかし、いわゆる機能品(タンデム冷間圧延(tandem cold rolling)−連続焼鈍プロセスにより製造される鋼板)の場合には、例えば特許文献1に開示されるような炭素鋼の連続焼鈍酸洗ラインを用いた安価なプロセスによる製造が最も好ましく、この際の焼鈍温度は800〜900℃で行うことが最も好ましい。また、より光沢を求める箇所の部材には仕上げにBA焼鈍(光輝焼鈍(bright annealing))を行うことが有効である。なお、冷間圧延後および加工後にさらに表面性状を向上させるために、研磨等を施すこともできる。 However, in the case of so-called functional products (tandem cold rolling-steel plate manufactured by a continuous annealing process), for example, a carbon steel continuous annealing pickling line as disclosed in Patent Document 1 is used. It is most preferable to carry out the production by an inexpensive process, and the annealing temperature at this time is most preferably 800 to 900 ° C. In addition, it is effective to perform BA annealing (bright annealing) for finishing the member where the luster is desired. In addition, grinding | polishing etc. can also be given in order to improve surface properties further after cold rolling and after a process.
以下、実施例に基づいて本発明をさらに詳しく説明する。 Hereinafter, the present invention will be described in more detail based on examples.
表1−1〜表1−4に示す化学組成を有するステンレス鋼を50kg小型真空溶解炉にて溶製した。なお、表1−2及び表1−4のOX値およびNtr値はそれぞれ、Si+1.5Al+1.2Tiおよび1.2Nb+1.7Ti+V+2.2Alで定義される(ただし、式中の元素記号は各元素の含有量(質量%)を表す)。これらのスラブを、Arガスでパージした炉内で1150℃に加熱後、熱間圧延を施して3.5mm厚の熱延板とした。ついで、これらの熱延板に950℃で1分間の熱延板の焼鈍を施した後、表面にガラスビーズを用いたショットブラスト処理を行った後、温度80℃、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。Stainless steels having chemical compositions shown in Table 1-1 to Table 1-4 were melted in a 50 kg small vacuum melting furnace. In Tables 1-2 and 1-4, the O X value and the N tr value are defined by Si + 1.5Al + 1.2Ti and 1.2Nb + 1.7Ti + V + 2.2Al, respectively. Content (mass%). These slabs were heated to 1150 ° C. in a furnace purged with Ar gas, and then hot-rolled to obtain 3.5 mm thick hot rolled sheets. Next, these hot-rolled sheets were annealed at 950 ° C. for 1 minute, and then subjected to shot blasting using glass beads on the surface, and then in a 20 mass% sulfuric acid solution at a temperature of 80 ° C. After dipping for 120 seconds, pickling was performed by dipping in a mixed acid composed of 15% by mass nitric acid and 3% by mass hydrofluoric acid at a temperature of 55 ° C. for 60 seconds, and descaling was performed.
さらに、板厚0.8mmまで冷間圧延し、弱還元性雰囲気(水素:5vol%、窒素:95vol%、露点:−40℃)において900℃で1分間の再結晶焼鈍を行い、冷延焼鈍板を得た。この冷延焼鈍板を、温度が50℃の15質量%硝酸および0.5質量%塩酸からなる混合酸液中で電解10A/dm2で2秒間)を2回行う高速脱スケール処理を行い、冷延焼鈍酸洗板を得た。作製した冷延板から、圧延方向と平行にJIS 13B号引張試験片を採取し、引張試験をJIS Z2201に準拠して行い、0.2%耐力(YS)、引張強度(TS)および破断伸び(El)をそれぞれ測定した。Further, it was cold-rolled to a thickness of 0.8 mm, recrystallized at 900 ° C. for 1 minute in a weak reducing atmosphere (hydrogen: 5 vol%, nitrogen: 95 vol%, dew point: −40 ° C.), and cold-rolled annealing I got a plate. This cold-rolled annealed plate is subjected to a high-speed descaling process in which a mixed acid solution composed of 15% by mass nitric acid and 0.5% by mass hydrochloric acid having a temperature of 50 ° C. is subjected to twice at 10 A / dm 2 for 2 seconds) A cold-rolled annealed pickled plate was obtained. A JIS 13B tensile test piece was taken from the produced cold-rolled sheet in parallel with the rolling direction, and the tensile test was conducted according to JIS Z2201, 0.2% proof stress (YS), tensile strength (TS) and elongation at break. (El) was measured respectively.
作製した冷延焼鈍酸洗板と市販のSUS304(C:0.07質量%、N:0.05質量%)の冷延板について突合せTIG溶接(butt TIG welding)を行った。溶接電流は90A、溶接速度は60cm/minとした。シールドガスは大気中からの窒素や酸素の侵入を想定して8vol%の窒素、2vol%の酸素を含有するアルゴンガスを15L/minで使用した。得られた表側の溶接ビードの幅はおよそ3mmであった。 Butt TIG welding was performed on the produced cold-rolled annealed pickled sheet and a commercially available cold-rolled sheet of SUS304 (C: 0.07 mass%, N: 0.05 mass%). The welding current was 90 A and the welding speed was 60 cm / min. As the shielding gas, an argon gas containing 8 vol% nitrogen and 2 vol% oxygen was used at 15 L / min assuming that nitrogen and oxygen enter from the atmosphere. The width of the obtained front-side weld bead was about 3 mm.
作製した溶接ビードを含む20mm角の試験片を採取し、10mm角の測定面を残してシール材で被覆し、溶接によるテンパーカラーを残したまま、30℃の3.5質量%NaCl溶液中で孔食電位(pitting potential)を測定した。試験片の研磨や不動態化処理は行わなかったが、それ以外の測定方法はJIS G 0577(2005)に準拠した。
さらに、溶接ビードを短辺の中心に長辺に平行に位置するようにして、60x80mmの試験片を採取した。この試験片に対して、表面を600番の研磨紙で研磨した後、中性塩水噴霧サイクル試験(neutral salt spray cyclic corrosion test)を5サイクル行って耐食性を調べた。塩水噴霧サイクル試験はJIS H 8502に準じ、5%NaCl噴霧(35℃、2hr)→乾燥(60℃、4hr、相対湿度20〜30%)→湿潤(40℃、2hr、相対湿度95%以上)を1サイクルとした。A 20 mm square test piece including the prepared weld bead was collected, covered with a sealing material leaving a 10 mm square measurement surface, and in a 3.5 mass% NaCl solution at 30 ° C. while leaving a temper collar by welding. The pitting potential was measured. The specimen was not polished or passivated, but the other measurement methods were based on JIS G 0577 (2005).
Further, a test piece of 60 × 80 mm was collected with the weld bead positioned in the center of the short side and parallel to the long side. The surface of the test piece was polished with No. 600 polishing paper, and then subjected to a neutral salt spray cyclic corrosion test for 5 cycles to examine the corrosion resistance. Salt water spray cycle test conforms to JIS H 8502, 5% NaCl spray (35 ° C., 2 hr) → Dry (60 ° C., 4 hr, relative humidity 20-30%) → Wet (40 ° C., 2 hr, relative humidity 95% or more) Was one cycle.
これらの評価を行い、母材の孔食電位150mVvs SCE以上、溶接ビードの孔食電位0mVvs SCE以上、中性塩水噴霧サイクル試験による腐食の発生がなく、引張試験における破断伸びが25%以上であり、かつ表面性状が良好な場合に本発明が提供する所定の材質が得られたと判断した。 As a result of these evaluations, the pitting corrosion potential of the base metal is 150 mV vs SCE or higher, the pitting corrosion potential of the weld bead is 0 mV vs SCE or higher, there is no corrosion due to the neutral salt spray cycle test, and the elongation at break in the tensile test is 25% or higher. And when the surface property was good, it was judged that the predetermined material provided by the present invention was obtained.
評価結果を表2−1、表2−2に示す。 The evaluation results are shown in Tables 2-1 and 2-2.
本発明の要件を満たすNo.1〜22の溶接ビードの孔食電位はいずれも0mV vs SCE以上であるとともに、中性塩水噴霧サイクル試験によっても腐食は発生せず、オーステナイト系ステンレス鋼との溶接部は十分な耐食性を示した。また、引張試験による破断伸びはいずれも25%以上と良好であり、表面欠陥も認められなかった。 No. satisfying the requirements of the present invention. The pitting corrosion potentials of the weld beads 1 to 22 were all 0 mV vs SCE or more, and no corrosion occurred even in the neutral salt spray cycle test, and the welded portion with the austenitic stainless steel showed sufficient corrosion resistance. . Further, the elongation at break by the tensile test was as good as 25% or more, and no surface defects were observed.
しかし、各元素の含有量は本発明の範囲内ではあるが、OX値、Ntr値のどちらか、あるいは両方が本発明の範囲を下回るNo.23、24、31および32、OX値が本発明の範囲を上回るNo.25では、150mVvs SCE以上の母材の孔食電位は得られたものの、溶接ビードの孔食電位はいずれも0mV vs SCE未満であるので、中性塩水噴霧試験中に溶接ビード部に腐食が発生し、所定の溶接部耐食性が得られなかった。However, the content of each element is within the scope of the present invention but, O X value, either N tr values, or both is less than the scope of the present invention No. No. 23, 24, 31 and 32, No. with O X values exceeding the range of the present invention. In No. 25, the pitting corrosion potential of the base metal of 150 mV vs SCE or higher was obtained, but the pitting corrosion potential of the weld bead was less than 0 mV vs SCE, so corrosion occurred in the weld bead during the neutral salt spray test. However, the predetermined weld corrosion resistance could not be obtained.
Si含有量が本発明の範囲を超えるNo.26では、焼鈍時に鋼板表層部にSiが濃化した強固な酸化スケール層が形成されたことに起因した酸洗工程後の酸化スケール残りが生じ、中性塩水噴霧サイクル試験中に酸化スケールを起点とした腐食が発生した。同様に、Alを本発明の範囲未満としたNo.27およびCuが本発明の範囲外であるNo.28では、所定のOX値およびNtr値であったにも関わらず、中性塩水噴霧サイクル試験中に腐食が発生した。No. Si content exceeding the range of the present invention. In No. 26, an oxide scale residue after the pickling process is caused due to the formation of a strong oxide scale layer in which Si is concentrated on the surface layer of the steel sheet during annealing, and the oxide scale is the starting point during the neutral salt spray cycle test. Corrosion occurred. Similarly, no. No. 27 and Cu are outside the scope of the present invention. In No. 28, corrosion occurred during the neutral salt spray cycle test despite the predetermined O X and N tr values.
Al、TiあるいはCu含有量が本発明の範囲を超えたNo.29〜31では、熱間圧延あるいは冷間圧延後に多量の表面欠陥が発生し、適正な表面性状を得ることができなかった。 No. Al, Ti or Cu content exceeded the scope of the present invention. In Nos. 29 to 31, a large amount of surface defects occurred after hot rolling or cold rolling, and appropriate surface properties could not be obtained.
これらの結果から、本発明が提供する所定の材料特性を表面欠陥無く得るためには、各元素の含有量だけでなく、OX値およびNtr値もそれぞれ本発明の範囲内に調整することが必要であることが確認された。From these results, in order to obtain the predetermined material properties provided by the present invention without surface defects, not only the content of each element but also the O X value and N tr value should be adjusted within the scope of the present invention. Was confirmed to be necessary.
本発明で得られるフェライト系ステンレス鋼は、溶接によって構造体の作製が行われる用途、たとえば、マフラー等の自動車排気系材料、建具や換気口、ダクト等の建築用材料などへの適用に好適である。 The ferritic stainless steel obtained by the present invention is suitable for applications in which structures are produced by welding, for example, automotive exhaust materials such as mufflers, building materials such as fittings, ventilation openings, ducts, etc. is there.
Claims (3)
0.40≦Si+1.5Al+1.2Ti≦2.4 ・・・(1)
0.60≦1.2Nb+1.7Ti+V+2.2Al ・・・(2)
なお、式中の元素記号は各元素の含有率(質量%)を表す。In mass%, C: 0.001 to 0.030%, Si: 0.05 to 0.30%, Mn: 0.05 to 0.50%, P: 0.05% or less, S: 0.01 % Or less, Cr: 18.0 to 19.0%, Ni: 0.05% or more and less than 0.50%, Cu: 0.30 to 0.60%, N: 0.001 to 0.030%, Al : 0.10 to 1.50%, Ti: 0.05 to 0.50%, Nb: 0.002 to 0.050%, V: 0.01 to 0.50%, and the following formula ( A ferritic stainless steel satisfying 1) and (2), with the balance being Fe and inevitable impurities.
0.40 ≦ Si + 1.5Al + 1.2Ti ≦ 2.4 (1)
0.60 ≦ 1.2Nb + 1.7Ti + V + 2.2Al (2)
In addition, the element symbol in a formula represents the content rate (mass%) of each element.
The ferritic stainless steel according to claim 1 or 2, further comprising Sb: 0.05 to 0.30% by mass.
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