JP4727601B2 - Ferritic stainless steel with excellent crevice corrosion resistance - Google Patents
Ferritic stainless steel with excellent crevice corrosion resistance Download PDFInfo
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- 238000005260 corrosion Methods 0.000 title claims description 93
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 25
- 229910052758 niobium Inorganic materials 0.000 claims description 9
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 229910052791 calcium Inorganic materials 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052749 magnesium Inorganic materials 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
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- 229910052719 titanium Inorganic materials 0.000 description 7
- 229910052750 molybdenum Inorganic materials 0.000 description 6
- 238000009991 scouring Methods 0.000 description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 4
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- 230000035882 stress Effects 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
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- -1 CaS or MnS Chemical compound 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
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- 239000012530 fluid Substances 0.000 description 1
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- 238000005098 hot rolling Methods 0.000 description 1
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Description
本発明は、自動車部品、給水、給湯設備、建築設備等、構造上すきま部が存在し、塩化物環境で使用される機器、配管等において、優れた耐すきま腐食性が必要とされる部材に使用されるフェライト系ステンレス鋼に関する。 The present invention is a member that has a gap in structure such as automobile parts, water supply, hot water supply equipment, building equipment, etc., and that requires excellent crevice corrosion resistance in equipment, piping, etc. used in a chloride environment. It relates to the ferritic stainless steel used.
近年、フェライト系ステンレス鋼のもつ耐食性、加工性、コストパフォーマンスを利用して、さまざまな用途へ使用されるようになってきている。塩化物環境で使用されるステンレス鋼製の機器や配管部材の耐久性において、特に重要なのは、孔食、すきま腐食、応力腐食割れといった局部腐食であり、特にフェライト系ステンレス鋼においては、孔食、すきま腐食が重要である。溶接部、フランジ取り合い部など構造上すきまが存在する部材においては、特にすきま腐食が重要であり、すきま腐食に起因する孔あきにより、内部流体が漏洩することが問題となる。 In recent years, it has come to be used for various applications by utilizing the corrosion resistance, workability, and cost performance of ferritic stainless steel. Of particular importance in the durability of stainless steel equipment and piping components used in the chloride environment are local corrosion such as pitting corrosion, crevice corrosion, and stress corrosion cracking. Especially in ferritic stainless steel, pitting corrosion, Crevice corrosion is important. Crevice corrosion is particularly important for structural members such as welded parts and flange joints, and internal fluid leaks due to perforations caused by crevice corrosion.
こうしたすきま腐食により孔あきや、すきま腐食を起点とした応力腐食割れによる損傷を防止するために、特開２００３−２７７９９２号公報（下記特許文献１）、特許３５４５７５９号公報（下記特許文献２）には、塗装や犠牲防食による対策が提示されている。 In order to prevent perforation due to such crevice corrosion and damage due to stress corrosion cracking starting from crevice corrosion, Japanese Patent Application Laid-Open No. 2003-277792 (Patent Document 1) and Japanese Patent No. 3545759 (Patent Document 2) are disclosed. Measures by painting and sacrificial protection are presented.
塗装の場合には、その前処理工程で溶剤等を使用するため環境対応への負荷が大きく、また、犠牲防食の場合にはメンテナンスコストがかかるという問題点があった。そのため、塗装や犠牲防食に頼らずに無垢の材料で耐すきま腐食を担保することが望ましい。その一つとして、Cr、Moを多量に添加することで耐食性を向上させたフェライト系ステンレス鋼の適用が考えられるが、高Cr、高Moを含有する鋼種は成形性に劣る問題があるとともに、高価である。そのため、Moのように高価な元素を多量に添加することなく、耐食性と成形性が両立できるような材料が望まれていた。 In the case of painting, a solvent or the like is used in the pretreatment process, so that the burden on the environment is large, and in the case of sacrificial corrosion protection, there is a problem that a maintenance cost is required. Therefore, it is desirable to ensure crevice corrosion resistance with a solid material without resorting to painting or sacrificial protection. One of them is the application of ferritic stainless steel with improved corrosion resistance by adding a large amount of Cr and Mo, but steel types containing high Cr and high Mo have a problem of inferior formability, Expensive. Therefore, a material that can achieve both corrosion resistance and formability without adding a large amount of expensive elements such as Mo has been desired.
また、特許２８８０９０６号公報（下記特許文献３）には、P添加によって耐食性を高め、CaおよびAlを適正量添加することにより清浄度向上および介在物形態等の制御を狙ったフェライト系ステンレス鋼が開示されており、Mo、Cu、Ni、Coなどの選択添加が併せて記載されている。しかし、Pは溶接性を劣化させるため溶接構造物を製造するときの阻害要因になると共に、製造性を低下させるためコストが上昇する。また、Pによる加工性低下を補うために適量のCaおよびAlを添加しているが、適正範囲が狭く製鋼コストが増大するため、かえって高価な材料となりフェライト系ステンレス鋼を使用するメリットが薄れる。 In addition, Japanese Patent No. 2880906 (Patent Document 3 below) discloses a ferritic stainless steel that improves corrosion resistance by adding P and improves cleanliness and controls the form of inclusions by adding appropriate amounts of Ca and Al. The selective addition of Mo, Cu, Ni, Co and the like is also described. However, since P deteriorates weldability, it becomes an obstructive factor when manufacturing a welded structure, and the cost increases because manufacturability is reduced. Further, although appropriate amounts of Ca and Al are added to compensate for the workability deterioration due to P, the appropriate range is narrow and the steelmaking cost increases, so that the merit of using ferritic stainless steel becomes less expensive because it becomes an expensive material.
なお本発明のように、Sn、Sbを含むフェライト系ステンレス鋼については、特開２０００−１６９９４３（下記特許文献４）に高温強度に優れたフェライト系ステンレス鋼板が、特開２００１−２８８５４３（下記特許文献５）、特開２００１−２８８５４４（下記特許文献６）に表面特性及び耐食性に優れたフェライト系ステンレス鋼及びその製造方法が開示されている。前者の特許文献４では、Snの効果として高温強度の改善、特に長時間時効後の高温強度低下防止を挙げており、SbもSnと同様に記載されている。本発明での効果は耐すきま腐食性に対する効果であり、特許文献４におけるSn、Sbの効果とは異なる。一方、後者の特許文献５及び特許文献６は、MgとCaを基本として、これにTi、Ｃ、Ｎ、Ｐ、Ｓ、Ｏを加えて、これら元素の含有量をコントロールしてリジング特性と耐食性を改善させたことを特徴としており、Snは選択添加元素として記載されている。Snの効果として耐食性改善を挙げており、実施例では孔食電位で耐食性を評価している。孔食電位は孔食の発生に対する抵抗性を電気化学的に評価するものであるが、それに対し本発明ではすきま腐食を対象としている。後述するが、本発明では、Snの効果をすきま腐食発生後の成長抑制効果として見出しており、特許文献５及び特許文献６に記載されている孔食発生に対する抵抗性向上効果とは異なる。
本発明は、前述のような従来技術の問題点を解決し、耐すきま腐食性、とくにすきま部の耐孔あき性に優れたフェライト系ステンレス鋼を提供することを課題とする。 An object of the present invention is to solve the problems of the prior art as described above, and to provide a ferritic stainless steel having excellent crevice corrosion resistance, particularly excellent resistance to pores in a crevice portion.
本発明者等は、前述の課題を解決すべく鋭意検討の結果、Sn、Sbを適正量添加することで、耐すきま腐食性が向上し、すきま腐食によって孔あきにいたるまでの寿命が向上することを知見した。 As a result of intensive investigations to solve the above-mentioned problems, the present inventors have improved the crevice corrosion resistance by adding an appropriate amount of Sn and Sb, and the life until reaching the hole due to crevice corrosion is improved. I found out.
本発明は、Sn、Sbの耐すきま腐食性に対する効果、特にすきま部の耐孔あき性に対する
効果を基に、耐すきま腐食性に優れたフェライト系ステンレス鋼を提供するものであり、
その要旨とするところは、特許請求の範囲に記載した通りの下記内容である。
（１）質量％で、C：0.001〜0.02％、Ｎ：0.001〜0.02％、Si：0.01〜0.5％、Mn：0.05〜1％、P：0.04％以下、S：0.01％以下、Cr：12〜25％、Ti、Nbの１種または２種をTi：0.02〜0.5％、Nb：0.02〜1％の範囲で含み、かつ、Sn：0.005〜2％の範囲で含み、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耐すきま腐食性に優れたフェライト系ステンレス鋼。
（２）Sb：0.005〜1％、Ni：5%以下、Mo：3％以下の1種または２種を含むことを特徴とする（１）に記載の耐すきま腐食性に優れたフェライト系ステンレス鋼。
（３）Cu：1.5％以下、W：5％以下の1種または２種を含むを含むことを特徴とする（１）または（２）に記載の耐すきま腐食性に優れたフェライト系ステンレス鋼。
（４）Al：1％以下、Ca：0.002％以下、Mg：0.002％以下、B：0.005％以下の1種または２
種以上を含むことを特徴とする（１）〜（３）のいずれか一項に記載の耐すきま腐食性に
優れたフェライト系ステンレス鋼。
The present invention provides a ferritic stainless steel excellent in crevice corrosion resistance based on the effect on crevice corrosion resistance of Sn, Sb, particularly on the pore resistance of the gap portion.
The gist of the invention is as follows, as described in the claims.
(1) By mass%, C: 0.001 to 0.02%, N: 0.001 to 0.02%, Si: 0.01 to 0.5%, Mn: 0.05 to 1%, P: 0.04% or less, S: 0.01% or less, Cr: 12 to 25%, Ti, one kind or two kinds of Nb Ti: 0.02~0.5%, Nb: comprises at 0.02 to 1% range, and, Sn: includes at from 0.005 to 2% range, the balance being Fe and unavoidable Ferritic stainless steel with excellent crevice corrosion resistance, characterized by impurities.
(2) Ferritic stainless steel with excellent crevice corrosion resistance as described in (1), including one or two of Sb: 0.005 to 1%, Ni: 5% or less, Mo: 3% or less steel.
(3) Cu: 1.5% or less, W: characterized in that it comprises a containing 5% or less of one or (1) or (2) ferritic stainless steel excellent in crevice corrosion resistance according to .
(4) Al: 1% or less, Ca: 0.002% or less, Mg: 0.002% or less, B: 0.005% or less
Ferritic stainless steel excellent in crevice corrosion resistance according to any one of (1) to (3), characterized in that it contains seeds or more.
本発明によれば、耐すきま腐食性、特にすきま部の耐孔あき性に優れたフェライト系ステンレス鋼を提供することができるため、自動車部品、給水、給湯設備、建築設備に使用される部材のうち、構造上すきま部が存在し、塩化物環境で使用され、優れた耐すきま腐食性が必要とされる部材に対して、本発明の耐すきま腐食性に優れたフェライト系ステンレス鋼を適用することで、すきま部の耐孔あき性が向上するため部材の寿命延長に有効である。ここで、自動車部品としては排気系部材、燃料系部材があり、排気管、サイレンサー、燃料タンク、タンク固定用バンド、給油管等がある。 According to the present invention, it is possible to provide a ferritic stainless steel having excellent crevice corrosion resistance, and particularly excellent resistance to pores in the crevice portion. Therefore, the components used in automobile parts, water supply, hot water supply equipment, and building equipment can be provided. Among them, the ferritic stainless steel with excellent crevice corrosion resistance according to the present invention is applied to a member that has a crevice structure and is used in a chloride environment and requires excellent crevice corrosion resistance. As a result, the perforation resistance of the clearance is improved, which is effective for extending the life of the member. Here, there are an exhaust system member and a fuel system member as automobile parts, and there are an exhaust pipe, a silencer, a fuel tank, a tank fixing band, an oil supply pipe, and the like.
自動車部品、給水、給湯設備、建築設備等、構造上すきま部が存在し、塩化物環境で使用される機器、配管等においては、すきま腐食に起因する孔あきがその部材の寿命を決定する重要な因子となる。本発明者らは、すきま腐食により孔あきに至るまでの過程を、すきま腐食が発生するまでの誘導期間と、すきま腐食発生後の成長の期間の2つに分けて、鋭意研究を進めた。 その結果、フェライト系ステンレス鋼は、特に後者の腐食成長の期間が短いことが、孔あきまでの期間を短くする大きな要因であり、すきま腐食の成長速度を抑制することが耐孔あき寿命を向上させる重要な因子であることが判明した。 There are gaps in the structure of automobile parts, water supply, hot water supply facilities, building facilities, etc., and in equipment and piping used in chloride environments, perforations due to crevice corrosion are important to determine the life of the parts Factors. The inventors of the present invention diligently researched the process until crevice corrosion leads to perforation into two periods: an induction period until crevice corrosion occurs and a growth period after crevice corrosion occurs. As a result, for ferritic stainless steels, the short period of corrosion growth, especially the latter, is a major factor in shortening the period until perforation, and suppressing the growth rate of crevice corrosion improves the perforated life. It was found that this is an important factor.
その中で、種々の合金元素の影響を評価したところ、本発明者らが特開２００６−２５７５４４で示したNiと同様、Sn、Sbはすきま腐食の成長速度抑制に対し有効であり、NiやMoを複合した場合にさらに効果が高まり、すきま部の耐孔あき性が向上することを見出した。図1に模式図を示すように、腐食発生までの誘導期間を経過した後の腐食成長期間における侵食深さの成長速度は、Sn,Sb,Niを添加した場合に著しく低減する。 Among them, when the influence of various alloy elements was evaluated, Sn and Sb are effective for suppressing the growth rate of crevice corrosion, similar to Ni shown in Japanese Patent Application Laid-Open No. 2006-257544. It has been found that when Mo is combined, the effect is further enhanced and the perforation resistance of the gap is improved. As schematically shown in FIG. 1, the growth rate of the erosion depth during the corrosion growth period after the induction period until the occurrence of corrosion is significantly reduced when Sn, Sb, and Ni are added.
0.005C−0.1Si−0.1Mn−0.025P−0.001S−18Cr−0.15Ti−0.01Nをベース成分として、Sn、Sb 、Mo、Ni、Nb、Cuを単独または複合添加した冷延鋼板を作成した。なお、このうちMo以外の元素の添加量は、いずれも0.4％とした。これらを素材として、図２に示すスポット溶接試験片を用いて、図３に示す条件にて乾湿繰り返し試験を行い、スポット溶接すきまの最大侵食深さを実施例と同様の方法で評価した。結果を図４に示す。最大侵食深さの低減に対して、Sn、Sb添加はNi添加と同様な効果があり、複合添加するとさらに効果が高まる。また、Moと複合添加した場合でも、Niと同様な効果があり、Sn、Sbはすきま部の耐孔あき性向上に有効であり、NiやMoを複合した場合にさらに効果が高まることがわかる。 A cold-rolled steel sheet with 0.005C-0.1Si-0.1Mn-0.025P-0.001S-18Cr-0.15Ti-0.01N as a base component and Sn, Sb, Mo, Ni, Nb, Cu added alone or in combination was prepared. . Of these elements, the amount of elements other than Mo was 0.4%. Using these as raw materials, the wet and dry repeated test was conducted under the conditions shown in FIG. 3 using the spot welding test piece shown in FIG. 2, and the maximum erosion depth of the spot welding gap was evaluated in the same manner as in the example. The results are shown in FIG. Addition of Sn and Sb has the same effect as the addition of Ni with respect to the reduction of the maximum erosion depth. In addition, even when combined with Mo, it has the same effect as Ni, and Sn and Sb are effective in improving the perforation resistance of the gap portion, and it is understood that the effect is further enhanced when combining Ni and Mo. .
次に、乾湿繰り返し試験結果とすきま腐食成長挙動との関係を電気化学的に検討した。乾湿繰り返し試験に用いた材料のうち1Mo系の材料を用いて、pH1.5の20％NaCl溶液中でアノード分極曲線を測定した。この溶液は、すきま腐食発生後のすきま内模擬溶液と設定したものである。アノード分極曲線より求められる不動態化電流密度（活性態のピーク電流密度）と、乾湿繰り返し試験におけるすきま部の最大侵食深さとの関係を、図5に示す。両者にはよい対応関係が認められ、このことより、Sn、Sb添加はNi添加と同様、すきま腐食の成長速度を抑制する上で効果があることを知見した。 Next, the relationship between the wet and dry test results and crevice corrosion growth behavior was investigated electrochemically. An anodic polarization curve was measured in a 20% NaCl solution with a pH of 1.5 using a 1Mo-based material among the materials used in the wet and dry repeated test. This solution was set as a simulated solution in the crevice after crevice corrosion occurred. FIG. 5 shows the relationship between the passivating current density obtained from the anodic polarization curve (the peak current density in the active state) and the maximum erosion depth of the crevice in the wet and dry repeated test. There was a good correspondence between the two, and from this, it was found that the addition of Sn and Sb was effective in suppressing the growth rate of crevice corrosion, similar to the addition of Ni.
本発明は、このような知見に基づいてなされたものである。以下に本発明で規定される化学組成についてさらに詳しく説明する。
Ｃ： 耐粒界腐食性、加工性を低下させるため、その含有量を低く抑える必要がある。しかしながら、過度に低めることは精練コストを上昇させるため、0.001〜0.02％とした。
Ｎ：耐孔食性に有用な元素であるが、耐粒界腐食性、加工性を低下させるため、その含有量を低く抑える必要がある。しかしながら、過度に低めることは精練コストを上昇させるため、0.001〜0.02％とした。
Si： 脱酸元素として有用であると共に、耐食性に有効な元素であるが、加工性を低下させるため、その含有量を0.01〜0.5％とした。望ましくは0.05〜0.4％である。
Mn：脱酸元素として有用であるが、過剰に含有させると耐食性を劣化させるので、0.05〜1％とした。望ましくは0.05〜0.5％である。
P： 溶接性、加工性を低下させるので、その含有量を低く抑える必要がある。しかし、過度に低めることは、原料コスト、精練コストを高める。そのため、Pの含有量は0.04％以下とした。
Ｓ： Ｓは、CaS、MnSといった溶解しやすい硫化物として存在すると、孔食あるいはすきま腐食の起点となりうる。そのため、0.01％以下とした。
Cr： 耐すきま腐食性を確保する上で基本となる元素であり、少なくとも12％以上必要である。含有量を増加させるほど耐すきま腐食性は向上するが、本発明で特に必要としている耐孔あき性において、すきま腐食発生後の進展速度を低減させる効果が大きくない。また、加工性、製造性を低下させるため、上限を25％とした。望ましくは15〜22％である。
Ti、Nb：Ｃ、Ｎを固定し、溶接部の耐粒界腐食性、加工性を向上させる上で有用な元素であり、Ti、Nbの１種または２種を、Ti、Nb共に少なくとも0.02％以上含有させる必要がある。ここで、TiとNbを１種ずつ含有させる場合には、Tiは(Ｃ＋Ｎ)の和の４倍以上、Nbは（Ｃ＋Ｎ）の和の８倍以上含有させることが望ましい。TiとNbを複合して含有させる場合には（Ti＋Nb）/（Ｃ＋Ｎ）を６倍以上とすることが望ましい。しかしながら、Tiを過剰に添加すると、製造時の表面疵の原因となって製造性を劣化させる。一方、Nbを過剰に添加すると、成形性を劣化させる。そのため、Tiの上限を0.5％、Nbの上限を1％とした。望ましくは、Tiは0.03〜0.3％、Nbは0.05〜0.6％である。
Sn、Sb：耐すきま腐食性、特にすきま部の耐孔あき性において、すきま腐食発生後の進展速度を低減させるうえで、非常に有効な元素である。特に、Niとの複合、さらにはMoと複合させて含有させることで、その効果が高まる。その効果を発現させるには少なくともおのおの0.005％必要である。含有量を増加させるほどその効果は高まるが、過剰に含有させると、成形性、熱間加工性を低下させる。したがって、Snは0.005~2％、Sbは0.005~1％とした。望ましくはSnが0.01~1％、Sbが0.005~0.5％である。
Ni：耐すきま腐食性を向上させる上で、必要に応じて含有させることができる。すきま部の耐孔あき性（耐すきま腐食性）において、すきま腐食発生後の進展速度を低減させるうえで、非常に有効な元素である。単独でもSn、Sbと同様な効果があり、Sn、Sbと複合添加すると、さらに効果が高まる。その効果は0.2％から安定し、含有量の増加に伴いその効果は高まるが、過剰に含有させると、応力腐食割れの感受性が増加すると共に、成形性を低下させる。また、コストアップ要因にもなる。したがって、0.2〜5％の範囲で含有させるのが望ましい。
Mo：耐すきま腐食性を向上させる上で、必要に応じて含有させることができる。Moは特にすきま腐食の発生に対して効果的であることに加え、Sn、Sbとの複合、さらにはNiと複合させることで、すきま腐食発生後の進展速度抑制効果がより大きくなり、すきま部の耐孔あき性（耐すきま腐食性）を向上させることができる。その効果は0.3％から安定し、含有量の増加に伴いその効果は高まるが、過剰の添加は、加工性を劣化させると共に、高価であるためコストアップにつながる。したがって、0.3〜3％の範囲で含有させるのが望ましい。
Cu：耐すきま腐食性を確保する上で、必要に応じて含有させることができる。すきま腐食発生後の進展速度を低減させるうえで有効であり、0.1％以上含有させることが望ましい。しかしながら、過剰の添加は、加工性を劣化させる。したがって、0.1〜1.5％の範囲で含有させるのが望ましい。
V： 耐すきま腐食性をさらに向上させる目的で、必要に応じて含有させることができる。Vは、Moと同様特にすきま腐食の発生ならびにすきま腐食発生後の進展速度を低減させるうえで有効である。その効果は0.02％から安定し、含有量の増加に伴いその効果は高まるが、過剰の添加はコストアップ要因となる。したがって、0.02〜3.0％の範囲で含有させるのが望ましい。
W： 耐すきま腐食性をさらに向上させる目的で、必要に応じて含有させることができる。Wは、Mo、Vと同様特にすきま腐食の発生ならびにすきま腐食発生後の進展速度を低減させるうえで有効である。その効果は0.3％から安定し、含有量の増加に伴いその効果は高まるが、過剰の添加はコストアップ要因となる。したがって、0.3〜5％の範囲で含有させるのが望ましい。
Al：Alは脱酸効果等精練上有用な元素であり、成形性を向上させる効果があり、0.003〜1％の範囲で含有させることが望ましい。
Ca：Caは、Alと同様脱酸効果等精練上有用な元素であり、0.0002〜0.002％の範囲で含有させることが望ましい。
Mg：Al、Caと同様脱酸効果等精練上有用な元素であり、また、組織を微細化し、加工性、靭性の向上にも有用であることから、Mg：0.0002〜0.002％の範囲で含有させることが望ましい。
B：Bは２次加工性を向上させるのに有用な元素であり、0.0002〜0.005％の範囲で含有させることが望ましい。
The present invention has been made based on such knowledge. Hereinafter, the chemical composition defined in the present invention will be described in more detail.
C: In order to reduce intergranular corrosion resistance and workability, it is necessary to keep the content low. However, excessive reduction increases the scouring cost, so 0.001 to 0.02% was set.
N: Although it is an element useful for pitting corrosion resistance, its content needs to be kept low in order to reduce intergranular corrosion resistance and workability. However, excessive reduction increases the scouring cost, so 0.001 to 0.02% was set.
Si: An element that is useful as a deoxidizing element and effective in corrosion resistance, but its content is set to 0.01 to 0.5% in order to reduce workability. Desirably, it is 0.05 to 0.4%.
Mn: Useful as a deoxidizing element, but if contained excessively, corrosion resistance deteriorates, so 0.05 to 1% was set. Desirably, it is 0.05 to 0.5%.
P: Since weldability and workability are deteriorated, the content must be kept low. However, excessive reduction increases raw material costs and scouring costs. Therefore, the content of P is set to 0.04% or less.
S: When S is present as an easily soluble sulfide such as CaS or MnS, it can be a starting point for pitting corrosion or crevice corrosion. Therefore, it was made 0.01% or less.
Cr: Element that is fundamental for ensuring crevice corrosion resistance, and at least 12% is required. As the content is increased, crevice corrosion resistance is improved. However, in the pore resistance particularly required in the present invention, the effect of reducing the progress rate after crevice corrosion occurrence is not great. Moreover, in order to reduce workability and manufacturability, the upper limit was made 25%. Desirably, it is 15 to 22%.
Ti, Nb: An element useful for fixing C and N and improving the intergranular corrosion resistance and workability of welds. One or two of Ti and Nb and at least 0.02 for both Ti and Nb % Or more must be contained. Here, when Ti and Nb are contained one by one, it is desirable to contain Ti at least four times the sum of (C + N) and Nb at least eight times the sum of (C + N). When Ti and Nb are combined and contained, it is desirable that (Ti + Nb) / (C + N) be 6 times or more. However, if Ti is added excessively, it causes surface flaws during production and deteriorates productivity. On the other hand, if Nb is added excessively, moldability is deteriorated. Therefore, the upper limit of Ti is set to 0.5%, and the upper limit of Nb is set to 1%. Desirably, Ti is 0.03% to 0.3% and Nb is 0.05% to 0.6%.
Sn, Sb: Elements that are extremely effective in reducing crevice corrosion resistance, especially in the pore resistance of crevice, in reducing the rate of progress after crevice corrosion. In particular, the effect is enhanced by inclusion with Ni and further with Mo. At least 0.005% of each is required to exert the effect. The effect increases as the content increases, but if it is excessively contained, the moldability and hot workability are lowered. Therefore, Sn is 0.005 to 2%, and Sb is 0.005 to 1%. Desirably, Sn is 0.01 to 1% and Sb is 0.005 to 0.5%.
Ni: In order to improve crevice corrosion resistance, it can be contained if necessary. It is an extremely effective element in reducing the rate of progress after crevice corrosion in terms of pore resistance (crevice corrosion resistance) of the crevice. When used alone, the same effect as Sn and Sb is obtained, and when Sn and Sb are added together, the effect is further enhanced. The effect stabilizes from 0.2%, and the effect increases as the content increases. However, when the content is excessive, the susceptibility to stress corrosion cracking increases and the moldability decreases. Moreover, it becomes a cost increase factor. Therefore, it is desirable to make it contain in 0.2 to 5% of range.
Mo: Can be contained as necessary to improve crevice corrosion resistance. In addition to being effective for crevice corrosion, Mo is particularly effective for suppressing the growth rate after crevice corrosion by combining Sn, Sb, and Ni. Can improve the perforation resistance (crevice corrosion resistance). The effect stabilizes from 0.3%, and the effect increases as the content increases. However, excessive addition deteriorates processability and increases the cost because it is expensive. Therefore, it is desirable to make it contain in 0.3 to 3% of range.
Cu: In order to ensure crevice corrosion resistance, it can be contained if necessary. It is effective in reducing the rate of progress after crevice corrosion occurrence, and it is desirable to contain 0.1% or more. However, excessive addition deteriorates workability. Therefore, it is desirable to make it contain in 0.1 to 1.5% of range.
V: For the purpose of further improving crevice corrosion resistance, it can be contained as necessary. V, like Mo, is particularly effective in reducing the occurrence of crevice corrosion and the rate of progress after crevice corrosion. The effect stabilizes from 0.02%, and the effect increases as the content increases, but excessive addition causes a cost increase. Therefore, it is desirable to make it contain in 0.02 to 3.0%.
W: For the purpose of further improving crevice corrosion resistance, it can be contained as required. W, like Mo and V, is particularly effective in reducing crevice corrosion and the rate of progress after crevice corrosion. The effect stabilizes from 0.3%, and the effect increases as the content increases, but excessive addition causes a cost increase. Therefore, it is desirable to make it contain in 0.3 to 5% of range.
Al: Al is an element useful for scouring such as a deoxidizing effect, has an effect of improving moldability, and is desirably contained in a range of 0.003 to 1%.
Ca: Like Al, Ca is an element useful for scouring, such as a deoxidizing effect, and is desirably contained in a range of 0.0002 to 0.002%.
Mg: Similar to Al and Ca, it is an element useful for scouring, such as deoxidation effect. It is also useful for improving the workability and toughness by refining the structure. Therefore, Mg: contained in the range of 0.0002 to 0.002% It is desirable to make it.
B: B is an element useful for improving secondary workability, and is desirably contained in the range of 0.0002 to 0.005%.
表１に示す化学組成を有する鋼を溶製し、熱延、冷延、焼鈍工程を経て、板厚1.0mmの鋼板を製造した。この冷延鋼板を用いて耐すきま腐食性を評価した。 Steel having the chemical composition shown in Table 1 was melted, and a steel sheet having a thickness of 1.0 mm was manufactured through hot rolling, cold rolling, and annealing processes. Crevice corrosion resistance was evaluated using this cold-rolled steel sheet.
冷延鋼板より、幅60mm、長さ130mmと幅30mm、長さ60mmの試験片を切り出した後、エメリー紙にて#320まで湿式研磨を施した。その後、図２に示すような形状にスポット溶接を施し、幅60mm、長さ130mmの端面と裏面をシールテープにより被覆した。 A test piece having a width of 60 mm, a length of 130 mm, a width of 30 mm, and a length of 60 mm was cut out from the cold rolled steel sheet, and then wet-polished to # 320 with emery paper. Thereafter, spot welding was applied to the shape as shown in FIG. 2, and the end face and the back face having a width of 60 mm and a length of 130 mm were covered with a sealing tape.
この試験片を用いて、図３に示す条件にて乾湿繰り返し試験を行った。120サイクル完了後、大小試験片を分離した。その後、腐食生成物を除去して、スポット溶接隙間部の侵食深さを光学顕微鏡焦点深度法により測定した。深そうなところから10点以上測定した侵食深さの中から最大値を求めた。なお、ここに定めた試験条件以外については、自動車技術者協会規格の自動車用材料腐食試験方法であるJASO M609-91に規定される条件に準じた。 Using this test piece, a wet and dry repeated test was performed under the conditions shown in FIG. After 120 cycles were completed, the large and small test pieces were separated. Thereafter, the corrosion products were removed, and the erosion depth of the spot weld gap was measured by the optical microscope depth of focus method. The maximum value was obtained from the erosion depth measured from more than 10 points. The test conditions other than those specified here were in accordance with the conditions specified in JASO M609-91, which is the automotive material corrosion test method of the Automotive Engineers Association standard.
試験結果を表１に示す。 The test results are shown in Table 1.
本発明範囲内にあるＮｏ.１〜Ｎｏ.１３の鋼は、最大侵食深さが600μｍ以下と、耐すきま腐食性が良好である。Snの範囲が本発明から外れるＮｏ.１４、Sbの範囲が本発明から外れるＮｏ.１５、Crの範囲が本発明から外れるＮｏ.１６は、最大侵食深さが800μm以上と耐すきま腐食性に劣る。以上の実施例により本発明の効果が確認された。 The steels No. 1 to No. 13 within the scope of the present invention have a maximum crevice depth of 600 μm or less and good crevice corrosion resistance. No. 14 in which the Sn range deviates from the present invention, No. 15 in which the Sb range deviates from the present invention, and No. 16 in which the Cr range deviates from the present invention has a maximum erosion depth of 800 μm or more and is resistant to crevice corrosion. Inferior. The effects of the present invention were confirmed by the above examples.
本発明の耐すきま腐食性、特にすきま部の耐孔あき性に優れたフェライト系ステンレス鋼は、自動車部品、給水、給湯設備、建築設備等、構造上すきま部が存在し、塩化物環境で使用される機器、配管等において、優れた耐すきま腐食性が必要とされる部材に使用される部材として有用である。 The ferritic stainless steel with excellent crevice corrosion resistance, especially pore resistance of the crevice part of the present invention has a crevice part in the structure of automobile parts, water supply, hot water supply equipment, building equipment, etc., and is used in a chloride environment. It is useful as a member used for a member that requires excellent crevice corrosion resistance in equipment, piping, and the like.
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| JP2007026328A JP4727601B2 (en) | 2007-02-06 | 2007-02-06 | Ferritic stainless steel with excellent crevice corrosion resistance |
| CA2777715A CA2777715C (en) | 2006-05-09 | 2007-05-08 | Ferritic stainless steel excellent in resistance to crevice corrosion |
| PCT/JP2007/059501 WO2007129703A1 (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in crevice corrosion resistance and formability, and ferritic stainless steel excellent in crevice corrosion resistance |
| KR1020127010106A KR101261192B1 (en) | 2006-05-09 | 2007-05-08 | Ferritic stainless steel excellent in crevice corrosion resistance |
| KR1020087027083A KR20080110662A (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in crevice corrosion resistance and formability, and ferritic stainless steel excellent in crevice corrosion resistance |
| US12/226,592 US8470237B2 (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in resistance to crevice corrosion and formability, and ferritic stainless steel excellent in resistance to crevice corrosion |
| CA2776892A CA2776892C (en) | 2006-05-09 | 2007-05-08 | Ferritic stainless steel excellent in resistance to crevice corrosion and formability |
| KR1020117000666A KR101179408B1 (en) | 2006-05-09 | 2007-05-08 | Ferritic stainless steel excellent in crevice corrosion resistance |
| CN200780016464XA CN101437974B (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in resistance to crevice corrosion and formability, and ferritic stainless steel excellent inresistance to crevice |
| CA2650469A CA2650469C (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance, ferritic stainless steel excellent in resistance to crevice corrosion and formability, and ferritic stainless steel excellent in resistance to crevice corrosion |
| KR1020117000667A KR101120764B1 (en) | 2006-05-09 | 2007-05-08 | Stainless steel excellent in corrosion resistance |
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| JP2005146345A (en) * | 2003-11-14 | 2005-06-09 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel superior in oxidation resistance |
| JP2005220429A (en) * | 2004-02-09 | 2005-08-18 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel sheet having excellent corrosion resistance and workability |
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| US11215299B2 (en) | 2017-03-30 | 2022-01-04 | Nippon Steel Stainless Steel Corporation | Ferritic stainless steel pipe having excellent salt tolerance in gap, pipe-end-thickened structure, welding joint, and welded structure |
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