JP6056132B2 - Austenitic and ferritic duplex stainless steel for fuel tanks - Google Patents
Austenitic and ferritic duplex stainless steel for fuel tanks Download PDFInfo
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- 239000002828 fuel tank Substances 0.000 title claims description 31
- 229910001039 duplex stainless steel Inorganic materials 0.000 title claims description 24
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims 1
- 230000007797 corrosion Effects 0.000 description 42
- 238000005260 corrosion Methods 0.000 description 42
- 239000012071 phase Substances 0.000 description 20
- 239000000463 material Substances 0.000 description 19
- 238000005336 cracking Methods 0.000 description 17
- 229910000831 Steel Inorganic materials 0.000 description 11
- 229910001566 austenite Inorganic materials 0.000 description 11
- 239000010959 steel Substances 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 10
- 239000000446 fuel Substances 0.000 description 7
- 229910001220 stainless steel Inorganic materials 0.000 description 7
- 229910000859 α-Fe Inorganic materials 0.000 description 7
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 5
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 238000000137 annealing Methods 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- 239000002551 biofuel Substances 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 238000004381 surface treatment Methods 0.000 description 3
- 239000013585 weight reducing agent Substances 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 206010070834 Sensitisation Diseases 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000005097 cold rolling Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 229910001105 martensitic stainless steel Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 230000008313 sensitization Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 230000005068 transpiration Effects 0.000 description 2
- PCTMTFRHKVHKIS-BMFZQQSSSA-N (1s,3r,4e,6e,8e,10e,12e,14e,16e,18s,19r,20r,21s,25r,27r,30r,31r,33s,35r,37s,38r)-3-[(2r,3s,4s,5s,6r)-4-amino-3,5-dihydroxy-6-methyloxan-2-yl]oxy-19,25,27,30,31,33,35,37-octahydroxy-18,20,21-trimethyl-23-oxo-22,39-dioxabicyclo[33.3.1]nonatriaconta-4,6,8,10 Chemical compound C1C=C2C[C@@H](OS(O)(=O)=O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2.O[C@H]1[C@@H](N)[C@H](O)[C@@H](C)O[C@H]1O[C@H]1/C=C/C=C/C=C/C=C/C=C/C=C/C=C/[C@H](C)[C@@H](O)[C@@H](C)[C@H](C)OC(=O)C[C@H](O)C[C@H](O)CC[C@@H](O)[C@H](O)C[C@H](O)C[C@](O)(C[C@H](O)[C@H]2C(O)=O)O[C@H]2C1 PCTMTFRHKVHKIS-BMFZQQSSSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000008280 blood Substances 0.000 description 1
- 210000004369 blood Anatomy 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000003502 gasoline Substances 0.000 description 1
- 230000012447 hatching Effects 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、燃料タンクの素材として好適な燃料タンク用オーステナイト・フェライト系二相ステンレス鋼に関する。 The present invention relates to an austenitic ferritic duplex stainless steel for fuel tanks suitable as a material for fuel tanks.
従来、燃料タンクの素材としては、樹脂、表面処理を施した軟鋼、SUS304Lなどのオーステナイト系ステンレス鋼等の種々の素材が用いられている。
燃料タンクの素材としてオーステナイト系ステンレス鋼を用いたものとしては、例えば特許文献１に開示された「自動車の給油管および燃料タンク用オーステナイト系ステンレス鋼並びに自動車の給油管及び燃料タンク」がある。
Conventionally, various materials such as resin, mild steel subjected to surface treatment, and austenitic stainless steel such as SUS304L have been used as fuel tank materials.
As a material using austenitic stainless steel as a material for the fuel tank, there is, for example, “automotive oil supply pipe and austenitic stainless steel for fuel tank and automobile oil supply pipe and fuel tank” disclosed in Patent Document 1.
樹脂は燃料の耐蒸散性が劣るため、素材の肉厚を厚くする必要があり、燃料タンクの素材として樹脂を用いた場合、燃料タンクの外寸に対してタンク内容積が小さいという問題がある。
また、燃料タンクの素材として表面処理を施した軟鋼を用いた場合、溶接時に表面処理が欠落するため、燃料タンクを更に塗装する必要がある。
樹脂および表面処理を施した軟鋼に共通する課題として、両者共に燃料タンクの軽量化が困難であるという点が挙げられる。その理由は、樹脂では耐蒸散性を確保するために素材の肉厚を厚くする必要があるためであり、また、表面処理を施した軟鋼では素材強度が低いため、肉厚を厚くする必要があるためである。
また、両者ともに、バイオ燃料やアルコール燃料に対する耐久性が必ずしも十分ではなく、燃料と素材の種類の組合せによっては、長期使用の間にタンク素材表面と燃料が化学反応し劣化する場合があるという問題もあった。
Since resin has poor transpiration resistance of fuel, it is necessary to increase the thickness of the material. When resin is used as the material for the fuel tank, there is a problem that the volume of the tank is smaller than the outer dimensions of the fuel tank. .
Further, when using mild steel that has been subjected to surface treatment as a material for the fuel tank, the surface treatment is lost during welding, and thus the fuel tank needs to be further painted.
A problem common to both resin and surface-treated mild steel is that it is difficult to reduce the weight of the fuel tank. The reason is that it is necessary to increase the thickness of the material in order to ensure transpiration resistance in the resin, and it is necessary to increase the thickness because the material strength is low in the surface-treated mild steel. Because there is.
In addition, both of them are not necessarily durable against biofuels and alcohol fuels, and depending on the combination of fuel and material types, the tank material surface and fuel may chemically react and deteriorate during long-term use. There was also.
SUS304Lは軟鋼にくらべて強度が高く、燃料タンクの軽量化に寄与しうるとともに、延性が高いため複雑な形状の加工も可能である。また、SUS304Lは未加工部であればタンク外面の塩害などによる隙間腐食に対しても十分な耐性を示す。さらに、SUS304Lに限らずステンレス鋼は、タンク内面のバイオ燃料やアルコール燃料に対する耐久性も高い。このようにSUS304Lは燃料タンク用素材として好ましい特性を有している。 SUS304L has higher strength than mild steel, can contribute to weight reduction of the fuel tank, and can be processed into complicated shapes due to its high ductility. In addition, SUS304L exhibits sufficient resistance against crevice corrosion due to salt damage on the outer surface of the tank if it is an unprocessed part. Furthermore, not only SUS304L but also stainless steel has high durability against biofuel and alcohol fuel on the inner surface of the tank. Thus, SUS304L has preferable characteristics as a fuel tank material.
しかしながら、SUS304LはNiを多量に含有するため、素材のコストが高くなるという問題がある。また、SUS304Lは、タンク外面での塩害に対して、未加工部であれば十分な耐性を示すが、厳しい加工部では応力腐食割れの耐性が劣るため、防食のための塗装を施す必要があり、このような塗装は軽量化を妨げる要因となる。 However, since SUS304L contains a large amount of Ni, there is a problem that the cost of the material is increased. In addition, SUS304L is sufficiently resistant to salt damage on the outer surface of the tank if it is an unprocessed part, but it is inferior in stress corrosion cracking resistance in severely processed parts, so it is necessary to apply anticorrosion coating. Such a coating is a factor that hinders weight reduction.
本発明は、上記の問題点を解決するためになされたものであり、SUS304Lと同等の延性と耐隙間腐食性を有し、なおかつSUS304Lよりも省Niで、さらにSUS304Lよりも高強度の燃料タンク用オーステナイト・フェライト系二相ステンレス鋼を提供することを目的とする。 The present invention has been made to solve the above problems, and has a ductility and crevice corrosion resistance equivalent to those of SUS304L, is Ni-saving more than SUS304L, and has a higher strength than SUS304L. An object is to provide an austenitic-ferritic duplex stainless steel for use.
発明者は燃料タンク用に用いるステンレス鋼について鋭意検討した。
ステンレス鋼は、マルテンサイト系ステンレス鋼、フェライト系ステンレス鋼、オーステナイト系ステンレス鋼、オーステナイト・フェライト系二相ステンレス鋼に大別される。これらのうち、マルテンサイト系ステンレス鋼およびフェライト系ステンレス鋼では、SUS304Lのような高い延性は得られない。
他方、オーステナイト系ステンレス鋼では、SUS304Lが燃料タンク材として用いられているが、前述したような課題が有る。
The inventors diligently studied stainless steel used for fuel tanks.
Stainless steel is roughly classified into martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, and austenitic / ferritic duplex stainless steel. Among these, martensitic stainless steel and ferritic stainless steel cannot obtain high ductility like SUS304L.
On the other hand, in austenitic stainless steel, SUS304L is used as a fuel tank material, but there are problems as described above.
そこで、発明者はオーステナイト・フェライト系二相ステンレス鋼に着目し、種々の成分を有する省Ni型の二相ステンレス鋼についてその特性を評価した。
省NiでNおよびMnを含有したオーステナイト・フェライト系二相ステンレス鋼は、SUS304Lよりもはるかに高い強度を有することを知見した。また、この二相ステンレス鋼でCr当量およびNi当量を最適化することにより、大幅に延性が向上し、SUS304Lと同等以上の延性を有することも知見した。さらに、塩害に対する耐隙間腐食性もSUS304Lと同等以上であることを知見した。またさらに、Ni量の適正化により耐応力腐食割れ性がSUS304Lよりも優れることも知見した。
本発明は係る種々の知見に基づくものであり、具体的には以下の構成からなるものである。
Accordingly, the inventors focused on austenite-ferritic duplex stainless steel and evaluated the characteristics of Ni-saving duplex stainless steel having various components.
It was found that austenitic ferritic duplex stainless steel containing N and Mn with reduced Ni has much higher strength than SUS304L. It was also found that by optimizing the Cr equivalent and Ni equivalent of this duplex stainless steel, the ductility was significantly improved and the ductility was equal to or higher than that of SUS304L. Furthermore, it was found that the crevice corrosion resistance against salt damage is equivalent to or better than SUS304L. Furthermore, it was also found that stress corrosion cracking resistance is superior to SUS304L by optimizing the amount of Ni.
The present invention is based on such various findings, and specifically comprises the following configurations.
（１）本発明に係る燃料タンク用オーステナイト・フェライト系二相ステンレス鋼は、質量％にて、C：0.05%以下、Si：1%以下、Mn：2%以上8%以下、P：0.1%以下、S：0.02%以下、Cr：15%以上23%以下、Mo：4%以下、Ni：3.0%以下、Cu：2%以下、N：0.05%以上0.3%以下、残部がFeおよび不可避的不純物からなり、Cr当量、Ni当量が次の(1)式かつ(2)式の範囲内であることを特徴とするものである。
9≦Cr当量−Ni当量≦14 …(1)式
27≦Cr当量＋Ni当量≦32 …(2)式
ただし、Cr当量=1.5[Si]+[Cr]+[Mo]+2[Ti]+0.5[Nb]
Ni当量=30[C]+30[N]+0.5[Mn]+[Ni]+0.5[Cu]+0.5[Co]
なお、[元素記号]は[]内の元素の含有量（単位：質量％）を示す。
(1) The austenitic ferritic duplex stainless steel for fuel tank according to the present invention, in mass%, C: 0.05% or less, Si: 1% or less, Mn: 2% or more and 8% or less, P: 0.1% Below, S: 0.02% or less, Cr: 15% or more and 23% or less, Mo: 4% or less, Ni: 3.0% or less, Cu: 2% or less, N: 0.05% or more and 0.3% or less, the balance being Fe and inevitable It consists of impurities, and Cr equivalent and Ni equivalent are within the ranges of the following formulas (1) and (2).
9 ≦ Cr equivalent−Ni equivalent ≦ 14 (1)
27 ≦ Cr equivalent + Ni equivalent ≦ 32 (2) where Cr equivalent = 1.5 [Si] + [Cr] + [Mo] +2 [Ti] +0.5 [Nb]
Ni equivalent = 30 [C] +30 [N] +0.5 [Mn] + [Ni] +0.5 [Cu] +0.5 [Co]
[Element symbol] indicates the content (unit: mass%) of the element in [].
（２）また、上記（１）に記載のものにおいて、質量％にて、Ni：1.8%以下であることを特徴とするものである。
なお、本明細書において成分割合を示す「%」は「質量%」の意味である。
(2) Moreover, in the thing of said (1), it is Ni: 1.8% or less in the mass%, It is characterized by the above-mentioned.
In the present specification, “%” indicating the component ratio means “mass%”.
（３）また、上記（１）又は（２）に記載のものにおいて、質量％にて、Nb：1.0%以下を含有することを特徴とするものである。 (3) Moreover, in the thing as described in said (1) or (2), Nb: 1.0% or less is contained in the mass%, It is characterized by the above-mentioned.
（４）また、上記（１）乃至（３）のいずれかに記載のものにおいて、質量％にて、V：0.5%以下を含有することを特徴とするものである。 (4) Moreover, in the thing in any one of said (1) thru | or (3), it contains V: 0.5% or less in the mass%.
（５）また、上記（１）乃至（４）のいずれかに記載のものにおいて、質量％にて、Al：0.1%以下を含有することを特徴とするものである。 (5) Moreover, in the thing in any one of said (1) thru | or (4), it contains Al: 0.1% or less in the mass%.
（６）また、上記（１）乃至（５）のいずれかに記載のものにおいて、質量％にて、B：0.01%以下、Ca：0.01%以下、Mg：0.01%以下、REM：0.1%以下、Ti：0.3%以下のいずれか１種又は２種以上を含有することを特徴とするものである。 (6) Moreover, in the thing in any one of said (1) thru | or (5), in mass%, B: 0.01% or less, Ca: 0.01% or less, Mg: 0.01% or less, REM: 0.1% or less , Ti: Any one or more of 0.3% or less is contained.
本発明によれば、SUS304Lと同等の延性と耐隙間腐食性を有し、なおかつSUS304Lよりも省Niで、さらにSUS304Lよりも高強度となり、燃料タンク用に最適のオーステナイト・フェライト系二相ステンレス鋼となる。 According to the present invention, it has ductility and crevice corrosion resistance equivalent to SUS304L, is Ni-saving more than SUS304L, and has higher strength than SUS304L, and is an austenitic / ferritic duplex stainless steel optimal for fuel tanks. It becomes.
本発明に係る燃料タンク用オーステナイト・フェライト系二相ステンレス鋼について説明する。
本発明に係る燃料タンク用オーステナイト・フェライト系二相ステンレス鋼は、C：0.05%以下、Si：1%以下、Mn：2%以上8%以下、P：0.1%以下、S：0.02%以下、Cr：15%以上23%以下、Mo：4%以下、Ni：3.0%以下、Cu：2%以下、N：0.05%以上0.3%以下、残部がFeおよび不可避的不純物からなり、Cr当量、Ni当量が次の(1)式かつ(2)式の範囲内であることを特徴とするものである。
9≦Cr当量−Ni当量≦14 …(1)式
27≦Cr当量＋Ni当量≦32 …(2)式
ただし、Cr当量=1.5[Si]+[Cr]+[Mo]+2[Ti]+0.5[Nb]
Ni当量=30[C]+30[N]+0.5[Mn]+[Ni]+0.5[Cu]+0.5[Co]
なお、[元素記号]は[]内の元素の含有量（単位：質量％）を示す。
The austenitic ferritic duplex stainless steel for fuel tank according to the present invention will be described.
The austenitic ferritic duplex stainless steel for fuel tank according to the present invention is C: 0.05% or less, Si: 1% or less, Mn: 2% or more, 8% or less, P: 0.1% or less, S: 0.02% or less, Cr: 15% or more and 23% or less, Mo: 4% or less, Ni: 3.0% or less, Cu: 2% or less, N: 0.05% or more and 0.3% or less, the balance consisting of Fe and inevitable impurities, Cr equivalent, Ni The equivalent is within the range of the following formulas (1) and (2).
9 ≦ Cr equivalent−Ni equivalent ≦ 14 (1)
27 ≦ Cr equivalent + Ni equivalent ≦ 32 (2) where Cr equivalent = 1.5 [Si] + [Cr] + [Mo] +2 [Ti] +0.5 [Nb]
Ni equivalent = 30 [C] +30 [N] +0.5 [Mn] + [Ni] +0.5 [Cu] +0.5 [Co]
[Element symbol] indicates the content (unit: mass%) of the element in [].
以下において、本発明の燃料タンク用オーステナイト・フェライト系二相ステンレス鋼の成分組成を限定する理由及び、Cr当量、Ni当量の満たすべき範囲について説明する。なお、成分組成について、％はすべて質量%を意味する。 In the following, the reason for limiting the component composition of the austenite-ferritic duplex stainless steel for fuel tank of the present invention and the range to satisfy Cr equivalent and Ni equivalent will be described. In the component composition,% means mass%.
＜C：0.05%以下＞
溶接後冷却時の鋭敏化（Cr炭化物生成によるCr炭化物周辺のCr欠乏）による耐食性劣化を抑制するため、Cは0.05%以下とする。なお、Cは0.02%以下が好適である。
＜Si：1%以下＞
Siは脱酸材として必要に応じて含有できるが、フェライト生成元素であり、1%を超えると本発明に必要なオーステナイト相分率が得がたくなるのでSiは1%以下とする。なお、Siは0.5%以下が好適である。さらには、0.4%以下がより好適である。
<C: 0.05% or less>
In order to suppress corrosion resistance deterioration due to sensitization during cooling after welding (Cr deficiency around Cr carbide due to Cr carbide formation), C is made 0.05% or less. Note that C is preferably 0.02% or less.
<Si: 1% or less>
Si can be contained as needed as a deoxidizing material, but is a ferrite-forming element, and if it exceeds 1%, it becomes difficult to obtain the austenite phase fraction required for the present invention, so Si is made 1% or less. Si is preferably 0.5% or less. Furthermore, 0.4% or less is more preferable.
＜Mn：2%以上8%以下＞
Mnは固相でのN固溶度を高める元素であり、溶接後冷却時の鋭敏化を抑制するため2%以上含有させる。一方、Mnは過剰に含有させるとMnSを介して耐食性に悪影響をおよぼすため8%以下とする。なお、Mnは2.5%以上、5％以下が好適である。
＜P：0.1%以下＞
Pの含有量が0.1%を超えると耐食性が劣化するため0.1%以下とする。なお、Pは0.05%以下が好適である。
＜S：0.02%以下＞
Sの含有量が0.02%を超えると耐食性が劣化するため0.02%以下とする。なお、Sは0.01%以下が好適である。
<Mn: 2% to 8%>
Mn is an element that increases the solid solubility of N in the solid phase, and is contained in an amount of 2% or more in order to suppress sensitization during cooling after welding. On the other hand, if Mn is excessively contained, the corrosion resistance is adversely affected through MnS, so the content is made 8% or less. Mn is preferably 2.5% or more and 5% or less.
<P: 0.1% or less>
If the P content exceeds 0.1%, the corrosion resistance deteriorates, so the content is made 0.1% or less. P is preferably 0.05% or less.
<S: 0.02% or less>
If the S content exceeds 0.02%, the corrosion resistance deteriorates. S is preferably 0.01% or less.
＜Cr：15%以上23%以下＞
Crは耐食性を高める元素であり、耐食性確保のため含有量は15%以上必要である。一方、Crはフェライト生成元素であり、23%を超えると、本発明に必要なオーステナイト相分率が得がたくなるので23%以下とする。なお、Crは17%以上、22%以下が好適である。
＜Mo：4%以下＞
Moは耐食性を高める元素であり、必要に応じて含有させることができる。しかしながら、Moを4%を超えて含有させるとσ相などが析出しやすくなり加工性に悪影響をおよぼすので4%以下とした。なお、Moは2.5%以下が好適である。他方、Mo添加の明確な効果を得るには0.2%以上とするのが好適である。
<Cr: 15% to 23%>
Cr is an element that enhances corrosion resistance, and its content needs to be 15% or more to ensure corrosion resistance. On the other hand, Cr is a ferrite-forming element, and if it exceeds 23%, it becomes difficult to obtain the austenite phase fraction necessary for the present invention, so the content is made 23% or less. Note that Cr is preferably 17% or more and 22% or less.
<Mo: 4% or less>
Mo is an element that enhances corrosion resistance, and can be contained as necessary. However, if Mo is contained in an amount exceeding 4%, the σ phase and the like are liable to precipitate, and the workability is adversely affected. Mo is preferably 2.5% or less. On the other hand, in order to obtain a clear effect of addition of Mo, the content is preferably 0.2% or more.
＜Ni：3.0%以下＞
Niは強いオーステナイト相生成元素であり、本発明に必要な金属組織を得るために、必要に応じて含有させる。しかしながら、経済的観点および、Ni量が3%を超えると延性と耐応力腐食割れ性が低下するため上限を3.0%とする。
なお、耐応力腐食割れ性の観点から、Ni含有量は1.8%以下がさらに好ましい。また、耐隙間腐食性をより向上させたい場合は、0.2%以上とするのが好ましく、さらには、1.0%以上が好適である。
＜Cu：2%以下＞
Cuはオーステナイト生成元素であり、本発明に必要な金属組織を得るために、必要に応じて含有させることができる。しかしながら、2%を超える含有により、フェライト相中にCuが析出し耐食性に悪影響をおよぼすので2%以下とする。なお、Cuは1%以下が好適である。他方、Cu添加の明確な効果を得るには0.2%以上とするのが好適である。
<Ni: 3.0% or less>
Ni is a strong austenite phase-forming element, and is contained as necessary to obtain a metal structure necessary for the present invention. However, from an economic point of view, and if the Ni content exceeds 3%, the ductility and stress corrosion cracking resistance deteriorate, so the upper limit is made 3.0%.
From the viewpoint of stress corrosion cracking resistance, the Ni content is more preferably 1.8% or less. In order to further improve the crevice corrosion resistance, it is preferably 0.2% or more, and more preferably 1.0% or more.
<Cu: 2% or less>
Cu is an austenite-forming element and can be contained as necessary to obtain a metal structure necessary for the present invention. However, if the content exceeds 2%, Cu precipitates in the ferrite phase and adversely affects the corrosion resistance. Cu is preferably 1% or less. On the other hand, in order to obtain a clear effect of addition of Cu, the content is preferably 0.2% or more.
＜N：0.05%以上0.3%以下＞
Nはオーステナイト生成元素であり、強度を高める元素である。本発明に必要なオーステナイト相分率を確保するとともに、SUS304Lを超える強度を達成するため、Nの含有量は0.05%以上必要である。一方、Nの過剰含有により鋳片にブローホールが形成されやすくなるので上限は0.3%以下とする。なお、Nは0.1%以上、0.2%以下が好適である。さらには、Nは0.13%以上、0.17%以下がより好適である。
<N: 0.05% or more and 0.3% or less>
N is an austenite-generating element and is an element that increases the strength. In order to secure the austenite phase fraction necessary for the present invention and achieve strength exceeding SUS304L, the N content needs to be 0.05% or more. On the other hand, the upper limit is set to 0.3% or less because blow holes are easily formed in the slab due to excessive N content. N is preferably 0.1% or more and 0.2% or less. Furthermore, N is more preferably 0.13% or more and 0.17% or less.
＜Cr当量、Ni当量の範囲＞
本発明の燃料タンク用オーステナイト・フェライト系二相ステンレス鋼は、Cr当量、Ni当量が下記(1)式、(2)式の範囲内である。
9≦Cr当量−Ni当量≦14 …(1)式
27≦Cr当量＋Ni当量≦32 …(2)式
図１は、上記(1)式、(2)式の満たすべき範囲をグラフ上に示したものであり、縦軸がNi当量、横軸がCr当量を示している。図１のグラフにおいて、直線ＡＢは9＝Cr当量−Ni当量を、直線ＤＣはCr当量−Ni当量＝14を、直線ＡＤは27＝Cr当量＋Ni当量を、直線ＢＣはCr当量＋Ni当量＝32をそれぞれ表している。
したがって、(1)式及び(2)式を満たす範囲は、図１において斜線で示した正方形ＡＢＣＤの範囲である。
以下、本発明において、Cr当量、Ni当量を上記の範囲に限定した理由を説明する。
<Range of Cr equivalent, Ni equivalent>
The austenite-ferritic duplex stainless steel for fuel tank of the present invention has Cr equivalent and Ni equivalent within the ranges of the following formulas (1) and (2).
9 ≦ Cr equivalent−Ni equivalent ≦ 14 (1)
27 ≦ Cr equivalent + Ni equivalent ≦ 32 (2) Formula FIG. 1 shows the range to be satisfied by the above formulas (1) and (2) on the graph. The vertical axis is Ni equivalent and the horizontal axis is Cr equivalent is shown. In the graph of FIG. 1, line AB is 9 = Cr equivalent-Ni equivalent, line DC is Cr equivalent-Ni equivalent = 14, line AD is 27 = Cr equivalent + Ni equivalent, and line BC is Cr equivalent + Ni equivalent = 32. Respectively.
Therefore, the range satisfying the formulas (1) and (2) is the range of the square ABCD indicated by hatching in FIG.
Hereinafter, the reason why Cr equivalent and Ni equivalent are limited to the above ranges in the present invention will be described.
［9≦Cr当量−Ni当量≦14］
ただし、Cr当量=1.5[Si]+[Cr]+[Mo]+2[Ti]+0.5[Nb]
Ni当量=30[C]+30[N]+0.5[Mn]+[Ni]+0.5[Cu]+0.5[Co]
なお、[元素記号]は[]内の元素の含有量（単位：質量％）を示す。
Cr当量は鋼中でのフェライト相生成能を示す指標であり、Ni当量は鋼中でのオーステナイト相生成能を示す指標である。よって、Cr当量−Ni当量の値は、オーステナイト・フェライト系二相ステンレス鋼中でのフェライト相の分率を示す指標である。
[9 ≦ Cr equivalent−Ni equivalent ≦ 14]
However, Cr equivalent = 1.5 [Si] + [Cr] + [Mo] +2 [Ti] +0.5 [Nb]
Ni equivalent = 30 [C] +30 [N] +0.5 [Mn] + [Ni] +0.5 [Cu] +0.5 [Co]
[Element symbol] indicates the content (unit: mass%) of the element in [].
Cr equivalent is an index indicating the ability to form a ferrite phase in steel, and Ni equivalent is an index indicating the ability to form an austenite phase in steel. Therefore, the value of Cr equivalent-Ni equivalent is an index indicating the fraction of the ferrite phase in the austenite-ferritic duplex stainless steel.
Cr当量−Ni当量が9未満の場合、オーステナイト生成元素のNiやNを必要以上に含有させねばならなくなるが、Niの過剰含有は経済的観点から好ましくなく、Nの過剰含有はブローホール発生の点から好ましくない。
また、鋼中のフェライト相分率が必要とされる率よりも少なくなるため、応力腐食割れ性が劣化する。このような理由からCr当量−Ni当量は9以上としているが、11以上がより好適である。
他方、Cr当量−Ni当量が14を超える場合、鋼中のフェライト相分率が必要とされる率を超えて増加するため好ましい延性が得られなくなる。
When Cr equivalent-Ni equivalent is less than 9, it is necessary to contain Ni and N of austenite-generating elements more than necessary, but excessive Ni content is not preferable from an economic point of view, and excessive N content is an occurrence of blowholes. It is not preferable from the point.
Further, since the ferrite phase fraction in the steel is less than the required rate, the stress corrosion cracking property is deteriorated. For these reasons, Cr equivalent-Ni equivalent is 9 or more, but 11 or more is more preferable.
On the other hand, if the Cr equivalent-Ni equivalent exceeds 14, the ferrite phase fraction in the steel increases beyond the required rate, so that preferable ductility cannot be obtained.
［27≦Cr当量＋Ni当量≦32］
ただし、Cr当量=1.5[Si]+[Cr]+[Mo]+2[Ti]+0.5[Nb]
Ni当量=30[C]+30[N]+0.5[Mn]+[Ni]+0.5[Cu]+0.5[Co]
なお、[元素記号]は[]内の元素の含有量（単位：質量％）を示す。
Cr当量＋Ni当量の値はオーステナイト・フェライト系二相ステンレス鋼中のオーステナイト相の安定度を示す指標であり、Cr当量＋Ni当量の値が高いと安定度は増加し、Cr当量＋Ni当量の値が低いと安定度は低下する。省Ni型のオーステナイト・フェライト系二相ステンレス鋼では、オーステナイト相の安定度の最適化により著しく延性が向上する。
[27 ≦ Cr equivalent + Ni equivalent ≦ 32]
However, Cr equivalent = 1.5 [Si] + [Cr] + [Mo] +2 [Ti] +0.5 [Nb]
Ni equivalent = 30 [C] +30 [N] +0.5 [Mn] + [Ni] +0.5 [Cu] +0.5 [Co]
[Element symbol] indicates the content (unit: mass%) of the element in [].
The value of Cr equivalent + Ni equivalent is an index showing the stability of the austenite phase in the austenite-ferritic duplex stainless steel. The higher the Cr equivalent + Ni equivalent value, the higher the stability, and the Cr equivalent + Ni equivalent value. If it is low, the stability decreases. In Ni-saving austenitic and ferritic duplex stainless steels, ductility is significantly improved by optimizing the stability of the austenitic phase.
Cr当量＋Ni当量が27未満の場合、鋼中のオーステナイト相の安定度が低く加工時の変形初期にオーステナイト相の多くがマルテンサイト相に変態してしまうため、鋼は急激に硬化し高い延性が得られない。このような理由からCr当量＋Ni当量は27以上としているが、28以上がより好適である。
一方、Cr当量＋Ni当量が32を超える場合、鋼中のオーステナイト相の安定度が高く加工時にオーステナイト相がマルテンサイト変態しづらいためやはり高い延性が得られない。
Cr当量＋Ni当量が27以上32以下のときには、加工時に変形の著しい部位で適度にオーステナイト相がマルテンサイト変態し、ネッキングなどの局部変形が抑制されるため著しく高い延性が得られる。
When Cr equivalent + Ni equivalent is less than 27, the stability of the austenite phase in the steel is low, and most of the austenite phase transforms into the martensite phase at the beginning of deformation during processing, so the steel hardens rapidly and has high ductility. I can't get it. For these reasons, the Cr equivalent + Ni equivalent is 27 or more, but 28 or more is more preferable.
On the other hand, when the Cr equivalent + Ni equivalent exceeds 32, the austenite phase in the steel is highly stable and the austenite phase is difficult to martensite during processing, so that high ductility cannot be obtained.
When the Cr equivalent + Ni equivalent is 27 or more and 32 or less, the austenite phase is appropriately martensitic transformed at a remarkable deformation portion during processing, and local deformation such as necking is suppressed, so that extremely high ductility is obtained.
なお、上記の実施の形態で示した成分に加えて、Nbを、強度を高める任意成分として添加することができる。ただし、Nbが1.0%を超えると破断伸びが低下するので、Nbは1.0%以下とし、好ましくは0.6%以下とする。他方、強度を高めるという明確な効果を得るためには、0.05%以上とするのが好適である。 In addition to the components shown in the above embodiment, Nb can be added as an optional component that increases the strength. However, if Nb exceeds 1.0%, the elongation at break decreases, so Nb is 1.0% or less, preferably 0.6% or less. On the other hand, in order to obtain a clear effect of increasing the strength, 0.05% or more is preferable.
また、Vは鋼板の組織を微細化し、強度を高めるので任意成分として添加できる。ただし、0.5%を超えると、高温の焼鈍をしてもV析出物を減じることが困難であり、破断伸びが劣化するので、V量は0.5%以下に制限する。好ましくは0.2%以下とする。
他方、V添加の明確な効果を得るには0.05%以上とするのが好適である。
V can be added as an optional component because it refines the structure of the steel sheet and increases the strength. However, if it exceeds 0.5%, it is difficult to reduce V precipitates even after high-temperature annealing, and the elongation at break deteriorates, so the V content is limited to 0.5% or less. Preferably it is 0.2% or less.
On the other hand, 0.05% or more is suitable for obtaining a clear effect of V addition.
また、Alは強力な脱酸材であり、任意成分として添加できる。ただし0.1%を超えると、窒化物を形成し、鋼表面の疵の原因となるので、0.1%以下とする。好ましくは、0.05%以下とする。
他方、Al添加の明確な効果を得るには0.01%以上が好適である。
Al is a strong deoxidizer and can be added as an optional component. However, if it exceeds 0.1%, nitrides are formed and cause flaws on the steel surface. Preferably, it is 0.05% or less.
On the other hand, 0.01% or more is suitable for obtaining a clear effect of addition of Al.
また、Bは熱間加工性を向上させる任意成分として添加できる。しかしながら0.01%を超える添加は耐食性を劣化させるので、0.01%以下とする。好ましくは、0.005%以下とする。
他方、B添加の明確な効果を得るには0.0003%以上が好適である。
B can be added as an optional component for improving hot workability. However, addition over 0.01% degrades the corrosion resistance, so 0.01% or less. Preferably, it is 0.005% or less.
On the other hand, 0.0003% or more is suitable for obtaining a clear effect of addition of B.
また、Caは熱間加工性を向上させる任意成分として添加できる。しかしながら0.01%を超える添加は耐食性を劣化させるので、0.01%以下とする。好ましくは、0.005%以下とする。
他方、Ca添加の明確な効果を得るには0.0003%以上が好適である。
In addition, Ca can be added as an optional component that improves hot workability. However, addition over 0.01% degrades the corrosion resistance, so 0.01% or less. Preferably, it is 0.005% or less.
On the other hand, 0.0003% or more is suitable for obtaining a clear effect of addition of Ca.
また、Mgは熱間加工性を向上させる任意成分として添加できる。しかしながら0.01%を超える添加は耐食性を劣化させるので、0.01%以下とする。好ましくは、0.005%以下とする。
他方、Mg添加の明確な効果を得るには0.0003%以上が好適である。
Mg can be added as an optional component that improves hot workability. However, addition over 0.01% degrades the corrosion resistance, so 0.01% or less. Preferably, it is 0.005% or less.
On the other hand, 0.0003% or more is suitable for obtaining a clear effect of adding Mg.
また、REMは熱間加工性を向上させる任意成分として添加できる。しかしながら0.1%を超える添加は耐食性を劣化させるので、0.1%以下とする。好ましくは、0.05%以下とする。
他方、明確な効果を得るには0.01%以上が好適である。
REM can be added as an optional component that improves hot workability. However, addition exceeding 0.1% deteriorates the corrosion resistance, so it is made 0.1% or less. Preferably, it is 0.05% or less.
On the other hand, 0.01% or more is suitable for obtaining a clear effect.
また、Tiは熱間加工性を向上させる任意成分として添加できる。しかしながら0.3%を超える添加は窒化物を形成し、鋼表面の疵の原因になるので、0.3%以下とする。好ましくは、0.1%以下とする。
他方、Ti添加の明確な効果を得るには0.01%以上が好適である。
Ti can be added as an optional component that improves hot workability. However, addition over 0.3% forms nitrides and causes flaws on the steel surface, so it should be 0.3% or less. Preferably, it is 0.1% or less.
On the other hand, 0.01% or more is suitable for obtaining a clear effect of addition of Ti.
表１に示す記号1〜24の鋼を溶製し、熱延、熱延板焼鈍、冷延、冷延板焼鈍により0.8mm厚の冷延焼鈍板を作製した。冷延板焼鈍の条件は1050℃、1min保持、空冷である。
表１の記号1〜24のうち、記号1〜19が本発明例で、記号20〜24が比較例である。また、比較例として、0.8mm厚の市販のSUS304LおよびSUS436Lの冷延焼鈍板も準備した。
なお、表１における比較例において、本発明の数値範囲から外れる部分の欄には色を着けている。
Steels of symbols 1 to 24 shown in Table 1 were melted, and 0.8 mm thick cold-rolled annealed plates were produced by hot rolling, hot-rolled sheet annealing, cold rolling, and cold rolling sheet annealing. The conditions for cold-rolled sheet annealing are 1050 ° C., 1 min holding, and air cooling.
Among symbols 1 to 24 in Table 1, symbols 1 to 19 are examples of the present invention, and symbols 20 to 24 are comparative examples. As a comparative example, 0.8 mm thick commercially available SUS304L and SUS436L cold-rolled annealed plates were also prepared.
In addition, in the comparative example in Table 1, the column of the part which remove | deviates from the numerical range of this invention is colored.
上記の試験片に対して以下に示す試験を行った。
＜組織観察＞
断面全厚を露出したサンプルを作製し、研磨後、赤血塩溶液によりエッチングしフェライト相分率を測定した。
＜引張試験＞
長手方向が圧延方向に平行になるように採取した、JIS13号B試験片を用いて、標点間距離50mm、クロスヘッド速度10mm/minの条件で引張試験を行い、引張強度と破断伸びを測定した。
＜最大隙間腐食測定＞
各鋼種より60mm×80mm（下板サンプル）と30mm×40mm（上板サンプル）を採取し、それぞれ真中にボルト穴を開け、ボルトおよびナットで上板サンプルと下板サンプルを密着させた隙間形状試験体を作製した。これらの試験体を塩水を用いた複合サイクル腐食試験（自動車技術会規格JASO M 610-92、50サイクル）に供し、完了後、試験体を解体し、硝酸にて錆落とし後隙間部の最大侵食深さを測定した。
The following tests were performed on the above test pieces.
<Tissue observation>
A sample with the entire cross-section exposed was prepared, polished, and then etched with a red blood salt solution to measure the ferrite phase fraction.
<Tensile test>
Using a JIS13B test piece collected so that the longitudinal direction is parallel to the rolling direction, a tensile test is performed under the conditions of a distance between gauge points of 50 mm and a crosshead speed of 10 mm / min, and the tensile strength and elongation at break are measured. did.
<Maximum crevice corrosion measurement>
60mm x 80mm (lower plate sample) and 30mm x 40mm (upper plate sample) were taken from each steel type, a bolt hole was drilled in the middle, and the upper plate sample and lower plate sample were brought into close contact with the bolt and nut. The body was made. These specimens were subjected to a combined cycle corrosion test using salt water (Automobile Engineering Association Standard JASO M 610-92, 50 cycles). After completion, the specimens were disassembled, rust removed with nitric acid, and maximum erosion of gaps The depth was measured.
＜耐応力腐食割れ試験(i)＞
15mm×75mmの短冊状の試験片よりU曲げ試験片を作製し、30%CaCl2溶液（80℃）に4週間浸付けした。完了後表面の応力腐食割れ有無を判定した。
＜耐応力腐食割れ試験(ii)＞
15mm×75mmの短冊状の試験片よりU曲げ試験片を作製し、42%MgCl2溶液（143℃）に6時間浸付けした。完了後表面の応力腐食割れ有無を判定した。
特性評価結果を表2に示す。
<Stress corrosion cracking test (i)>
A U-bending test piece was prepared from a strip-shaped test piece of 15 mm × 75 mm and immersed in a 30% CaCl 2 solution (80 ° C.) for 4 weeks. After completion, the presence or absence of stress corrosion cracking on the surface was judged.
<Stress corrosion cracking test (ii)>
A U-bending test piece was prepared from a strip-shaped test piece of 15 mm × 75 mm, and immersed in a 42% MgCl 2 solution (143 ° C.) for 6 hours. After completion, the presence or absence of stress corrosion cracking on the surface was judged.
The characteristic evaluation results are shown in Table 2.
まず、比較例について検証する。
＜記号20＞
［Cr当量+Ni当量］が本発明範囲よりも大きい記号20の比較例では、Ｌ方向破断伸びが30%と小さく、高い延性が得られていない。
＜記号21＞
［Cr当量+Ni当量］が本発明範囲よりも小さい記号21の比較例の場合も、Ｌ方向破断伸びが20%と小さく、高い延性が得られていない。また、記号21では最大隙間腐食深さが81μｍと非常に深くなっている。
First, the comparative example is verified.
<Symbol 20>
In the comparative example indicated by symbol 20 in which [Cr equivalent + Ni equivalent] is larger than the range of the present invention, the L-direction breaking elongation is as small as 30%, and high ductility is not obtained.
<Symbol 21>
Also in the case of the comparative example indicated by the symbol 21 in which [Cr equivalent + Ni equivalent] is smaller than the range of the present invention, the L direction breaking elongation is as small as 20%, and high ductility is not obtained. Further, in symbol 21, the maximum crevice corrosion depth is as deep as 81 μm.
＜記号22＞
［Cr当量-Ni当量］が本発明範囲よりも大きい記号22の比較例では、Ｌ方向破断伸びが32%と小さく、引張強度も610MPaと小さく、高い延性が得られていない。
＜記号23＞
［Cr当量-Ni当量］が本発明範囲よりも小さい記号23の比較例では、耐応力腐食割れ性が劣る。
＜記号24＞
Ni含有率が本発明範囲よりも大きい記号24の比較例では、Ｌ方向破断伸びが31%と小さく、引張強度も683MPaと小さく、高い延性が得られておらず、また耐応力腐食割れが発生している。
<Symbol 22>
In the comparative example indicated by symbol 22 in which [Cr equivalent-Ni equivalent] is larger than the range of the present invention, the L-direction breaking elongation is as small as 32%, the tensile strength is as small as 610 MPa, and high ductility is not obtained.
<Symbol 23>
In the comparative example indicated by symbol 23 having a [Cr equivalent-Ni equivalent] smaller than the range of the present invention, the stress corrosion cracking resistance is inferior.
<Symbol 24>
In the comparative example of the symbol 24 where the Ni content is larger than the range of the present invention, the L direction breaking elongation is as small as 31%, the tensile strength is as small as 683 MPa, high ductility is not obtained, and stress corrosion cracking occurs. doing.
＜SUS304L＞
Mnの含有量が本発明範囲よりも少なく、Ni含有量が本発明範囲よりも大きいSUS304Lは、引張強度が583MPaと小さく、また耐応力腐食割れが発生している。
＜SUS436L＞
Mnの含有量が本発明範囲よりも少なく、［Cr当量-Ni当量］が本発明範囲よりも大きいSUS436Lは、Ｌ方向破断伸びが30%と小さく、引張強度も485MPaと小さく、さらに最大腐食深さが97μｍと深くなっている。
<SUS304L>
SUS304L having a Mn content smaller than the present invention range and a Ni content larger than the present range has a small tensile strength of 583 MPa, and stress corrosion cracking has occurred.
<SUS436L>
SUS436L with less Mn content than the present invention range and [Cr equivalent-Ni equivalent] larger than the present invention range has a small L direction breaking elongation of 30%, a small tensile strength of 485 MPa, and a maximum corrosion depth. Is as deep as 97μm.
上記の比較例に対して、本発明例である記号1〜19は、フェライト相分率はいずれも30〜70%の範囲である。引張強度はSUS304LやSUS436Lにくらべて100MPa以上高く、いずれも700MPa以上である。さらに、破断伸びはいずれも48%以上であり、SUS436Lに比べて遥かに高く、SUS304Lと同等水準あるいはそれ以上である。
最大隙間腐食深さは、いずれも50μｍ以下であり、SUS436Lよりもはるかに優れており、SUS304Lと同等以上の耐隙間腐食性を有していることが実証された。
また、応力腐食割れ試験の結果、記号1〜19は応力腐食割れ試験(i)で応力腐食割れが発生せずSUS304Lよりも優れていることが実証された。さらに条件の厳しい応力腐食割れ試験(ii)でも、Niが1.8%以下の二相ステンレス鋼(記号4、6〜19)は割れが発生せず耐応力腐食割れ性がいっそう優れることが実証された。
In contrast to the above comparative example, symbols 1 to 19 which are examples of the present invention all have a ferrite phase fraction in the range of 30 to 70%. Tensile strength is over 100MPa higher than SUS304L and SUS436L, both of which are over 700MPa. Further, the elongation at break is 48% or more, which is much higher than that of SUS436L, which is equal to or higher than that of SUS304L.
The maximum crevice corrosion depth is 50 μm or less, which is far superior to SUS436L and proved to have crevice corrosion resistance equivalent to or better than SUS304L.
Further, as a result of the stress corrosion cracking test, it was proved that the symbols 1 to 19 were superior to SUS304L because no stress corrosion cracking occurred in the stress corrosion cracking test (i). Furthermore, in severe stress corrosion cracking tests (ii), it was proved that duplex stainless steels (symbols 4, 6 to 19) with Ni of 1.8% or less do not generate cracks and have even better stress corrosion cracking resistance. .
以上のように、本発明のオーステナイト・フェライト系二相ステンレス鋼は、SUS304Lと同等の延性と耐隙間腐食性を有し、なおかつSUS304Lよりも省Niで、さらにSUS304Lよりも高強度であり、燃料タンク用素材としての適正に優れている。
つまり、本発明のオーステナイト・フェライト系二相ステンレス鋼は従来の燃料タンク用素材よりも高強度であるため燃料タンクの軽量化に寄与するところ大であり、延性が高いため複雑な形状の成型も可能である。また、耐食性にも優れている。さらに、省Niであることからコストを低減できる。
また、ガソリン燃料のみならず、アルコール燃料やバイオ燃料に対する耐性も高く、燃料タンク用素材として好適である。
As described above, the austenitic / ferritic duplex stainless steel of the present invention has ductility and crevice corrosion resistance equivalent to SUS304L, is Ni-saving more than SUS304L, and has higher strength than SUS304L. Excellent as a tank material.
In other words, the austenitic ferritic duplex stainless steel of the present invention has a higher strength than conventional fuel tank materials, and thus contributes to the weight reduction of the fuel tank. Is possible. It also has excellent corrosion resistance. Furthermore, since it is Ni-saving, cost can be reduced.
Moreover, it has high resistance to not only gasoline fuel but also alcohol fuel and biofuel, and is suitable as a material for fuel tanks.
Claims (5)
9≦Cr当量−Ni当量≦14 …(1)式
27≦Cr当量＋Ni当量≦32 …(2)式
ただし、Cr当量=1.5[Si]+[Cr]+[Mo]+2[Ti]+0.5[Nb]
Ni当量=30[C]+30[N]+0.5[Mn]+[Ni]+0.5[Cu]+0.5[Co]
なお、[元素記号]は[]内の元素の含有量（単位：質量％）を示す。 In mass%, C: 0.05% or less, Si: 1% or less, Mn: 2% or more and 8% or less, P: 0.1% or less, S: 0.02% or less, Cr: 15% or more and 23% or less, Mo: 4 %: Ni: 1.0% or more, 3.0% or less, Cu: 0.2% or more, 2% or less, N: 0.05% or more, 0.21% or less, V: 0.5% or less , the balance consisting of Fe and inevitable impurities An austenitic ferritic duplex stainless steel for fuel tanks, characterized in that the Cr equivalent and Ni equivalent are within the ranges of the following formulas (1) and (2):
9 ≦ Cr equivalent−Ni equivalent ≦ 14 (1)
27 ≦ Cr equivalent + Ni equivalent ≦ 32 (2) where Cr equivalent = 1.5 [Si] + [Cr] + [Mo] +2 [Ti] +0.5 [Nb]
Ni equivalent = 30 [C] +30 [N] +0.5 [Mn] + [Ni] +0.5 [Cu] +0.5 [Co]
[Element symbol] indicates the content (unit: mass%) of the element in [].
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