JP4998132B2 - Ferritic stainless steel sheet for use around water - Google Patents
Ferritic stainless steel sheet for use around water Download PDFInfo
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- JP4998132B2 JP4998132B2 JP2007203958A JP2007203958A JP4998132B2 JP 4998132 B2 JP4998132 B2 JP 4998132B2 JP 2007203958 A JP2007203958 A JP 2007203958A JP 2007203958 A JP2007203958 A JP 2007203958A JP 4998132 B2 JP4998132 B2 JP 4998132B2
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 12
- 238000005868 electrolysis reaction Methods 0.000 claims description 12
- 229910017604 nitric acid Inorganic materials 0.000 claims description 12
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- 238000004519 manufacturing process Methods 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- 229910052748 manganese Inorganic materials 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- 229910052758 niobium Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- 229910052717 sulfur Inorganic materials 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- 230000007797 corrosion Effects 0.000 description 70
- 238000005260 corrosion Methods 0.000 description 70
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 32
- 238000005498 polishing Methods 0.000 description 26
- 239000000243 solution Substances 0.000 description 25
- 238000012360 testing method Methods 0.000 description 21
- 239000002253 acid Substances 0.000 description 17
- 229910052736 halogen Inorganic materials 0.000 description 17
- 150000002367 halogens Chemical class 0.000 description 17
- 229910052742 iron Inorganic materials 0.000 description 15
- 230000000694 effects Effects 0.000 description 14
- 238000000034 method Methods 0.000 description 11
- 238000004090 dissolution Methods 0.000 description 9
- 239000010410 layer Substances 0.000 description 8
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- 238000011156 evaluation Methods 0.000 description 7
- 238000007654 immersion Methods 0.000 description 6
- 239000002932 luster Substances 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 6
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 229910052801 chlorine Inorganic materials 0.000 description 5
- 239000000460 chlorine Substances 0.000 description 5
- 230000003628 erosive effect Effects 0.000 description 5
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- 239000010953 base metal Substances 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
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- 238000005728 strengthening Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 239000006061 abrasive grain Substances 0.000 description 1
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
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- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、フェライト系ステンレス鋼板に関し、特に、温水器の缶体や貯水槽、シンク等の厨房機器、浴槽などに用いて好適な、研磨性と耐食性に優れる水周り部材用フェライト系ステンレス鋼板に関するものである。 The present invention relates to a ferritic stainless steel sheet, and more particularly, to a ferritic stainless steel sheet for water-surrounding members excellent in abrasiveness and corrosion resistance, suitable for use in kitchen equipment such as water heater cans, water storage tanks, sinks, and bathtubs. Is.
ステンレス鋼板は、塗装などの防錆処理を施さずに使用することが多いため、優れた耐食性を有することが求められている。また、無垢のまま、シンク等の厨房機器や温水器の缶体、貯水槽、浴槽などの水周り部材に使用する場合には、耐食性のほか、金属特有の金属光沢を基調とした意匠性にも優れることが要求される。 Since stainless steel plates are often used without being subjected to rust prevention treatment such as painting, they are required to have excellent corrosion resistance. In addition, when used in kitchen equipment such as sinks, water heater cans, water storage tanks, bathtubs, and other water-related parts, it is not only corrosion resistant but also has a design that is based on a metallic luster unique to metals. It is required to be excellent.
このような水周り部材に用いられるステンレス鋼板としては、ＪＩＳに規定されているＳＵＳ４４４に代表されるフェライト系ステンレス鋼板がある。このフェライト系ステンレス鋼板は、Ｎｉを含まないため安価であり、オーステナイト系ステンレス鋼板と比較して、応力腐食割れ（ＳＣＣ）感受性が小さいという特長を有するため、このような用途に用いて好適である。 As a stainless steel plate used for such a water-surrounding member, there is a ferritic stainless steel plate represented by SUS444 specified in JIS. This ferritic stainless steel sheet is inexpensive because it does not contain Ni, and is less susceptible to stress corrosion cracking (SCC) than an austenitic stainless steel sheet, and is therefore suitable for use in such applications. .
ところで、水道水には、殺菌のために塩素が投入されており、０．１ｍｇ／Ｌ以上の多量の残留塩素が含まれている。そのため、この残留塩素の酸化作用に起因する材料の腐食が問題となる。特に、衛生対策を強化する観点から、２００３年に、建築物衛生法やビル管理法が改正され、特定建築物においては、給湯水にも０．１ｍｇ／Ｌ以上の残留塩素を含有することが求められることとなった。さらに、ウオーターフロントで使用される建材用の水周り部材の場合、酸やハロゲン等が多く存在する環境下あるいは飛来塩分等の多い大気環境下での耐食性が問題となる。そのため、水周り部材に用いられる材料への耐食性改善の要求はさらに高くなっている。この点、上述したＳＵＳ４４４（１８ｍａｓｓ％Ｃｒ−２ｍａｓｓ％Ｍｏ鋼）は、酸やハロゲン等が多く存在する環境下や飛来塩分等の多い大気環境下で使用された場合でも、発銹を抑制することができる優れた耐食性を有するものである。 By the way, the tap water is supplied with chlorine for sterilization and contains a large amount of residual chlorine of 0.1 mg / L or more. Therefore, corrosion of the material due to the oxidizing action of residual chlorine becomes a problem. In particular, from the viewpoint of strengthening hygiene measures, the Building Sanitation Law and Building Management Law were revised in 2003, and certain buildings may contain residual chlorine of 0.1 mg / L or more in hot water. It was required. Further, in the case of water-related members for building materials used at the waterfront, there is a problem of corrosion resistance in an environment where there are a lot of acids, halogens, etc. or in an atmospheric environment where there is a lot of flying salt. Therefore, the request | requirement of the corrosion resistance improvement to the material used for a water surrounding member is still higher. In this regard, the above-mentioned SUS444 (18 mass% Cr-2 mass% Mo steel) suppresses generation even when used in an environment where there are a lot of acids, halogens, etc. or in an atmospheric environment where there is a lot of incoming salt. It has excellent corrosion resistance.
しかし、ＳＵＳ４４４に代表されるＭｏ添加鋼は、その製造工程において、冷間圧延後、機械的性質を確保するための仕上焼鈍が施されるのが普通である。この焼鈍は、アンモニア分解ガスや水素ガス等のいわゆるＢＡ雰囲気と呼ばれる還元性雰囲気中で行われる場合と、コークス炉から排出されるガスと空気を混合させて燃焼させたガスような酸化性雰囲気中で行われる場合とがある。前者の焼鈍では、鋼板表面に酸化皮膜が生成しないため、焼鈍後も鋼板表面は光沢があり、研磨性もよいが、ＢＡ雰囲気とするために、製造コストが高くなるという問題がある。 However, the Mo-added steel represented by SUS444 is usually subjected to finish annealing in order to ensure mechanical properties after cold rolling in the manufacturing process. This annealing is performed in a reducing atmosphere called a so-called BA atmosphere such as ammonia decomposition gas or hydrogen gas, and in an oxidizing atmosphere such as a gas burned by mixing the gas discharged from the coke oven and air. It may be done in. In the former annealing, an oxide film is not formed on the surface of the steel sheet, so that the surface of the steel sheet is glossy and has good polishing properties even after annealing. However, since the BA atmosphere is used, there is a problem that the manufacturing cost increases.
一方、後者の焼鈍では、酸化性雰囲気での焼鈍によって、鋼板表面に酸化皮膜が形成されるため、これを除去するための工程を付加する必要がある。しかし、Ｍｏ添加鋼では、Ｍｏに起因した緻密な酸化皮膜が形成されるが、この緻密な酸化皮膜は、ステンレス製造において通常行われているＮａ２ＳＯ４等の溶液中での中性塩電解処理だけでは除去しきれないため、その後さらに、ハロゲンを含む酸溶液中で下地の母材までをも溶解させて脱スケールし、製品としている。 On the other hand, in the latter annealing, an oxide film is formed on the surface of the steel sheet by annealing in an oxidizing atmosphere. Therefore, it is necessary to add a process for removing this. However, in Mo-added steel, a dense oxide film due to Mo is formed. This dense oxide film is neutral salt electrolysis in a solution of Na 2 SO 4 or the like usually used in stainless steel production. Since it cannot be removed by treatment alone, the base material in the base is further dissolved and descaled in an acid solution containing halogen.
そのため、酸化性雰囲気で焼鈍されたＭｏ添加鋼は、金属光沢に劣り、また、金属光沢を出すための表面研磨性にも劣るという問題がある。さらに、良好な金属光沢を得るためには、地鉄を含めて大幅に溶解するか研削しなければならず、実質的に金属光沢を得ることが難しいという問題がある。 For this reason, the Mo-added steel annealed in an oxidizing atmosphere has a problem of being inferior in metallic luster and inferior in surface polishing for producing metallic luster. Furthermore, in order to obtain a good metallic luster, it is necessary to dissolve or grind the steel including the ground iron, and there is a problem that it is difficult to obtain the metallic luster substantially.
そこで、水周り用途に用いて好適な、耐食性に優れる材料の開発が別途進められている。例えば、特許文献１には、特に、溶接部の耐食性を向上することを目的とし、ステンレス鋼の高純度化精錬技術を活用してＰとＳ、ＣとＮを低減することにより、耐食性と加工性に優れた安価なフェライト系ステンレス鋼を得る技術が開示されている。また、特許文献２には、Ｔｉ添加量を制限した上で、ＴｉとＡｌを複合添加し、さらに適正量のＣｕを添加して溶接部の耐食性を向上させた、塩素イオンや残留塩素などを多く含んだ環境下で使用されるフェライト系ステンレス鋼が開示されている。さらに、特許文献３には、Ｎｂ，Ｔｉ，Ａｌの添加量を制限した低Ｃフェライト系ステンレス鋼板をかしめて接合することで、塩化物溶液中でも隙間部の発錆を抑えることができる温水器缶体が開示されている。
しかしながら、特許文献１〜３に開示された上記技術は、焼鈍後の鋼板表面の研磨性を改善することについては触れられていなかった。 However, the techniques disclosed in Patent Documents 1 to 3 have not been mentioned about improving the polishing properties of the steel sheet surface after annealing.
そこで、本発明の目的は、耐食性に優れるとともに、研磨性にも優れる水周り部材に用いて好適なフェライト系ステンレス鋼板を提供することおよびその鋼板を製造する有利な方法を提案することにある。 Therefore, an object of the present invention is to provide a ferritic stainless steel plate suitable for use in a water-surrounding member that is excellent in corrosion resistance and excellent in polishing properties, and to propose an advantageous method for manufacturing the steel plate.
発明者らは、従来技術が抱える上述した問題点を解決し、耐食性に優れるとともに、研磨性にも優れるステンレス鋼板を開発するべく、特に、仕上焼鈍時に形成される鋼板表層の酸化皮膜と、その酸化皮膜を酸溶液中で溶解した場合に残存する酸化皮膜とが、耐食性および研磨性に及ぼす影響について鋭意検討を重ねた。 The inventors have solved the above-mentioned problems of the prior art, and in order to develop a stainless steel plate that is excellent in corrosion resistance and excellent in polishing properties, in particular, an oxide film on the surface layer of the steel plate formed during finish annealing, and its Intensive study was conducted on the effects of the oxide film remaining when the oxide film was dissolved in an acid solution on the corrosion resistance and polishing properties.
その結果、Ｍｏ添加鋼では、Ｍｏの含有量によって焼鈍時に生成する酸化皮膜の緻密さが異なり、Ｍｏ含有量がある一定量を超えると酸化皮膜が緻密化し、従来の中性塩電解処理やそれに続く酸処理では、酸化皮膜が不均一に溶解するようになり、その結果、残留した酸化皮膜と地鉄との境界部が発錆の起点となりやすいことを見出した。 As a result, in the Mo-added steel, the density of the oxide film generated during annealing differs depending on the Mo content. When the Mo content exceeds a certain amount, the oxide film becomes dense, and conventional neutral salt electrolysis treatment and In the subsequent acid treatment, the oxide film became non-uniformly dissolved, and as a result, it was found that the boundary portion between the remaining oxide film and the base iron tends to be a starting point of rusting.
また、Ｃｒ濃度がある一定量を下回ると、地鉄表層の粒界におけるＣｒ濃度が低下し、ハロゲンを含む酸による粒界侵食孔が大きくなり、研磨性を阻害する。したがって、研磨性を確保するためには、ハロゲンを含む酸による粒界侵食孔の発生を極力抑える、つまりハロゲンを含む酸による溶解量を極力抑えることが重要であることを見出した。 On the other hand, when the Cr concentration falls below a certain amount, the Cr concentration at the grain boundary of the surface layer of the iron alloy decreases, and the grain boundary erosion holes due to the acid containing halogen increase, impairing the polishing properties. Therefore, it has been found that in order to ensure the polishing properties, it is important to suppress the generation of grain boundary erosion holes due to the acid containing halogen as much as possible, that is, to suppress the dissolution amount due to the acid containing halogen as much as possible.
さらに、ハロゲンを含む酸中での溶解量を抑えた場合には、鋼板表面に、薄い酸化皮膜が部分的に残留するが、鋼中のＣｒ濃度を増加させ、脱クロム層の濃度を一定値以上とすれば、酸化皮膜残留部や地鉄部の耐食性をむしろ向上できること、また、上記焼鈍後の酸処理によって、鋼板表面にＡｌ２Ｏ３、ＳｉＯ２を多く含むテンパーカラー状の薄い酸化皮膜を残留させれば、ハロゲンを含む酸中での耐食性が向上することを見出した。 Furthermore, when the amount of dissolution in a halogen-containing acid is suppressed, a thin oxide film partially remains on the steel plate surface, but the Cr concentration in the steel is increased, and the concentration of the dechromed layer is kept at a certain value. With the above, the corrosion resistance of the oxide film residual part and the base iron part can be rather improved, and the temper color thin oxide film containing a large amount of Al 2 O 3 and SiO 2 on the steel sheet surface by the acid treatment after the annealing. It has been found that the corrosion resistance in an acid containing a halogen is improved if is left.
本発明は、上記知見を踏まえて、フェライト系ステンレス鋼板のＭｏ，Ｃｒ，ＡｌおよびＳｉの成分を適切な範囲に制御するとともに、焼鈍後の酸処理によって鋼板表層に一定量の厚さの酸化皮膜を残留させることによって、耐食性と研磨性とを兼備したフェライト系ステンレス鋼板を開発するに至ったものである。 Based on the above knowledge, the present invention controls the Mo, Cr, Al, and Si components of the ferritic stainless steel sheet to an appropriate range, and has an oxide film with a certain thickness on the surface of the steel sheet by acid treatment after annealing. This has led to the development of a ferritic stainless steel sheet that has both corrosion resistance and abrasiveness.
すなわち、本発明は、Ｃ：０．０２０ｍａｓｓ％以下、Ｓｉ：０．３０〜１．００ｍａｓｓ％、Ｍｎ：０．５０ｍａｓｓ％以下、Ｐ：０．０４０ｍａｓｓ％以下、Ｓ：０．０１０ｍａｓｓ％以下、Ｃｒ：２０．０〜２８．０ｍａｓｓ％、Ｎｉ：０．６０ｍａｓｓ％以下、Ａｌ：０．０３〜０．１５ｍａｓｓ％以下、Ｎ：０．０２０ｍａｓｓ％以下、Ｏ：０．００２０〜０．０１５０ｍａｓｓ％、Ｍｏ：０．３０〜１．５ｍａｓｓ％、Ｎｂ：０．１０〜０．５０ｍａｓｓ％、Ｔｉ：０．１０ｍａｓｓ％以下を含有し、かつＣｒとＭｏが下記式；
２４ｍａｓｓ％≦Ｃｒ＋３．３Ｍｏ≦３２ｍａｓｓ％
を満たし、残部がＦｅおよび不可避的不純物からなり、鋼板表層に平均厚さ１０〜１００ｎｍの酸化皮膜を有する水周り部材用フェライト系ステンレス鋼板である。
That is, the present invention includes C: 0.020 mass% or less, Si: 0.30 to 1.00 mass%, Mn: 0.50 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr : 20.0 to 28.0 mass%, Ni: 0.60 mass% or less, Al: 0.03 to 0.15 mass%, N: 0.020 mass% or less, O: 0.0020 to 0.0150 mass%, Mo : 0.30 to 1.5 mass%, Nb: 0.10 to 0.50 mass%, Ti: 0.10 mass% or less, and Cr and Mo are represented by the following formula:
24 mass% ≦ Cr + 3.3Mo ≦ 32 mass%
And the balance consists of Fe and inevitable impurities, and a ferritic stainless steel sheet for water-surrounding members having an oxide film with an average thickness of 10 to 100 nm on the steel sheet surface layer.
本発明の鋼板は、上記成分組成に加えてさらに、Ｃｕ：０．２〜１．０ｍａｓｓ％およびＺｒ：０．１〜０．６ｍａｓｓ％のいずれか１種または２種を含有することを特徴とする。 The steel sheet of the present invention is characterized by further containing any one or two of Cu: 0.2 to 1.0 mass% and Zr: 0.1 to 0.6 mass% in addition to the above component composition. To do.
また本発明の鋼板は、酸化皮膜中のＳｉおよびＡｌのいずれか１つ以上の濃度が、母材濃度の３倍以上であることを特徴とする。 The steel sheet of the present invention is characterized in that the concentration of one or more of Si and Al in the oxide film is at least three times the base material concentration.
また本発明は、Ｃ：０．０２０ｍａｓｓ％以下、Ｓｉ：０．３０〜１．００ｍａｓｓ％、Ｍｎ：０．５０ｍａｓｓ％以下、Ｐ：０．０４０ｍａｓｓ％以下、Ｓ：０．０１０ｍａｓｓ％以下、Ｃｒ：２０．０〜２８．０ｍａｓｓ％、Ｎｉ：０．６０ｍａｓｓ％以下、Ａｌ：０．０３〜０．１５ｍａｓｓ％以下、Ｎ：０．０２０ｍａｓｓ％以下、Ｏ：０．００２０〜０．０１５０ｍａｓｓ％、Ｍｏ：０．３０〜１．５ｍａｓｓ％、Ｎｂ：０．１０〜０．５０ｍａｓｓ％、Ｔｉ：０．１０ｍａｓｓ％以下を含有し、かつＣｒとＭｏが下記式；
２４ｍａｓｓ％≦Ｃｒ＋３．３Ｍｏ≦３２ｍａｓｓ％
を満たし、残部がＦｅおよび不可避的不純物からなる鋼板を焼鈍して表層に酸化皮膜を形成し、次いで、硝弗酸溶液に浸漬して酸化皮膜の平均厚さを１０〜１００ｎｍに調整し、その後、硝酸溶液中で正電解、負電解を各１回以上行う水周り部材用フェライト系ステンレス鋼板の製造方法を提案する。
In the present invention, C: 0.020 mass% or less, Si: 0.30 to 1.00 mass%, Mn: 0.50 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr: 20.0 to 28.0 mass%, Ni: 0.60 mass% or less, Al: 0.03 to 0.15 mass% or less, N: 0.020 mass% or less, O: 0.0020 to 0.0150 mass%, Mo: 0.30 to 1.5 mass%, Nb: 0.10 to 0.50 mass%, Ti: 0.10 mass% or less, and Cr and Mo are represented by the following formula:
24 mass% ≦ Cr + 3.3Mo ≦ 32 mass%
An oxide film is formed on the surface layer by annealing a steel plate composed of Fe and the inevitable impurities, and then immersed in a nitric hydrofluoric acid solution to adjust the average thickness of the oxide film to 10 to 100 nm. We propose a method for producing a ferritic stainless steel sheet for a water-surrounding member in which positive electrolysis and negative electrolysis are performed at least once each in a nitric acid solution.
本発明によれば、製造性を害することなく、ハロゲンを含む溶液中でも優れた耐食性を有するとともに、研磨性にも優れるフェライト系ステンレス鋼板を得ることができる。したがって、本発明の鋼板は、水周り部材の素材として好適に用いることができる。 According to the present invention, it is possible to obtain a ferritic stainless steel sheet that has excellent corrosion resistance even in a halogen-containing solution and is excellent in abrasiveness without impairing manufacturability. Therefore, the steel plate of this invention can be used suitably as a raw material of a water surrounding member.
本発明のフェライト系ステンレス鋼が有すべき成分組成について説明する。
Ｃ：０．０２０ｍａｓｓ％以下
Ｃは、Ｃｒと結合して炭化物を形成しやすい元素であり、特に、溶接時に、熱影響部などに形成されやすい。このＣｒ炭化物の形成は、Ｃｒ欠乏層を発生させ、粒界腐食を引き起こす原因となるので、Ｃは低いほど好ましい。よって、本発明では、Ｃを０．０２０ｍａｓｓ％以下とする。好ましくは、０．０１５ｍａｓｓ％以下である。
The component composition that the ferritic stainless steel of the present invention should have will be described.
C: 0.020 mass% or less C is an element that is easily bonded to Cr to form a carbide, and is particularly easily formed in a heat-affected zone during welding. The formation of this Cr carbide generates a Cr-depleted layer and causes intergranular corrosion, so C is preferably as low as possible. Therefore, in the present invention, C is set to 0.020 mass% or less. Preferably, it is 0.015 mass% or less.
Ｓｉ：０．３０〜１．００ｍａｓｓ％
Ｓｉは、脱酸剤として添加される元素である。また、発明者らの研究によれば、鋼中にＳｉを含有させると、熱処理時に、Ｓｉが地鉄の最表層粒界部に酸化物（ＳｉＯ２）を形成し、これが、酸による粒界侵食を抑える働きがある。この効果は、特に、ハロゲンを含む酸やｐＨの低い溶液において大きく、粒界が深く掘られて、研磨性が悪化するのを防ぐことができる。また、ＳｉＯ２は、酸化皮膜として鋼板表面に連続的に存在している必要はなく、適度に表面に残留していることによっても、鋼の耐食性を向上する働きがある。これらの効果は、Ｓｉ含有量が０．３０ｍａｓｓ％以上で発現する。一方、Ｓｉ含有量が１．０ｍａｓｓ％を超えると、酸化皮膜を形成する時に、酸化皮膜と地鉄との界面に濃化し過ぎて、特に、最表層の粒界部にＳｉ酸化物が生成し過ぎて、逆に研磨性の劣化を招く。さらに、Ｓｉの過度の添加は、鋼を硬質化し、加工性の低下を招く。よって、本発明では、Ｓｉ含有量は、０．３０〜１．００ｍａｓｓ％の範囲とする。好ましくは、０．４〜０．６ｍａｓｓ％の範囲である。
Si: 0.30 to 1.00 mass%
Si is an element added as a deoxidizer. Further, according to the study by the inventors, when Si is contained in the steel, during the heat treatment, Si forms an oxide (SiO 2 ) at the outermost grain boundary part of the base iron, which is a grain boundary caused by acid. It works to suppress erosion. This effect is particularly great in a halogen-containing acid or a solution having a low pH, and it is possible to prevent the grain boundary from being dug deep and degrading the polishing property. Further, SiO 2 does not need to be continuously present on the surface of the steel sheet as an oxide film, and also has a function of improving the corrosion resistance of the steel by remaining on the surface appropriately. These effects are manifested when the Si content is 0.30 mass% or more. On the other hand, if the Si content exceeds 1.0 mass%, when an oxide film is formed, it is excessively concentrated at the interface between the oxide film and the base iron, and in particular, Si oxide is generated at the grain boundary portion of the outermost layer. On the contrary, the abrasiveness is deteriorated. Further, excessive addition of Si hardens the steel and causes a decrease in workability. Therefore, in this invention, Si content shall be the range of 0.30-1.00 mass%. Preferably, it is the range of 0.4-0.6 mass%.
Ｍｎ：０．５０ｍａｓｓ％以下
Ｍｎは、脱酸作用を有する元素であるが、鋼中に存在するＳと結合して、可溶性硫化物であるＭｎＳを形成し、耐食性を低下させる。また、過剰な添加は、固溶強化により加工性を損なう。さらに、Ｍｎは、０．５０ｍａｓｓ％を超えて添加すると、熱処理時に生成する酸化皮膜中に、特に外層に生成するスピネル酸化物中にＭｎが濃化し、テンパーカラー状の薄い酸化皮膜を残留させたときの耐食性を劣化させる。よって、本発明では、Ｍｎは低いほど好ましく、０．５０ｍａｓｓ％以下とする。好ましくは０．３ｍａｓｓ％以下である。
Mn: 0.50 mass% or less Mn is an element having a deoxidizing action, but combines with S present in steel to form MnS, which is a soluble sulfide, and lowers the corrosion resistance. Excessive addition impairs workability due to solid solution strengthening. Further, when Mn is added in excess of 0.50 mass%, Mn is concentrated in the oxide film generated during the heat treatment, particularly in the spinel oxide generated in the outer layer, and a temper color thin oxide film remains. Deterioration of corrosion resistance. Therefore, in this invention, Mn is so preferable that it is low, and it shall be 0.50 mass% or less. Preferably it is 0.3 mass% or less.
Ｐ：０．０４０ｍａｓｓ％以下
Ｐは、耐食性を害する元素であり、特に、含有量が０．０４０ｍａｓｓ％を超えると、その影響が大きくなる。よって、Ｐは０．０４０ｍａｓｓ％以下とする。好ましくは、０．０３０ｍａｓｓ％以下である。
P: 0.040 mass% or less P is an element that impairs corrosion resistance. In particular, when the content exceeds 0.040 mass%, the influence becomes large. Therefore, P is set to 0.040 mass% or less. Preferably, it is 0.030 mass% or less.
Ｓ：０．０１０ｍａｓｓ％以下
Ｓは、Ｍｎと結合してＭｎＳを形成し、初期発銹の起点となる。また、結晶粒界に偏析して粒界脆化を促進する有害元素でもある。特に、Ｓの含有量が０．０１０ｍａｓｓ％を超えると、その悪影響が顕著となる。よって、本発明においては、Ｓは０．０１０ｍａｓｓ％以下とする。好ましくは、０．００５ｍａｓｓ％以下である。
S: 0.010 mass% or less S combines with Mn to form MnS, which is the starting point of initial firing. It is also a harmful element that segregates at grain boundaries and promotes grain boundary embrittlement. In particular, when the S content exceeds 0.010 mass%, the adverse effect becomes significant. Therefore, in the present invention, S is 0.010 mass% or less. Preferably, it is 0.005 mass% or less.
Ｃｒ：２０．０〜２８．０ｍａｓｓ％
Ｃｒは、フェライト系ステンレス鋼の耐食性を決定する基本成分である。しかし、Ｃｒ含有量が２０．０ｍａｓｓ％未満では、鋼板表層に酸化皮膜が生成すると、皮膜と地鉄との界面のＣｒ濃度が局部的に低下するために、この部分が露出した場合には、短時間で発銹に至る。また、耐食性を向上させるＭｏの添加量を多くしても、耐食性は、Ｃｒが消費されてしまうと極端に低下する。しかし、Ｃｒの含有量が２０．０ｍａｓｓ％以上であれば、本発明が所期した程度の酸化皮膜の生成によって地鉄のＣｒ濃度が低下しても、粒界や粒内での脱クロム層の分布も腐食速度に影響を与えるような分布とはならない。一方、Ｃｒの含有量が２８．０ｍａｓｓ％を超えると、酸化物中のＣｒ濃度が上がり、前述した表層粒界でのＳｉ酸化物の生成が抑制されるため、本発明が所期した程度の酸化皮膜を残存させても、ハロゲンを含む酸やｐＨの低い溶液による選択的な粒界腐食を防止することができずに粒界侵食が起こり、研磨性を悪化させることになる。また、Ｃｒの含有量が２８．０ｍａｓｓ％を超えると、伸びが減少し、加工性が低下する。よって、Ｃｒの含有量は２０．０〜２８．０ｍａｓｓ％の範囲とする。好ましくは２２．０〜２５．０ｍａｓｓ％の範囲である。
Cr: 20.0-28.0 mass%
Cr is a basic component that determines the corrosion resistance of ferritic stainless steel. However, when the Cr content is less than 20.0 mass%, when an oxide film is generated on the steel sheet surface layer, the Cr concentration at the interface between the film and the ground iron is locally reduced. It starts in a short time. Moreover, even if the addition amount of Mo which improves corrosion resistance is increased, the corrosion resistance is extremely lowered when Cr is consumed. However, if the Cr content is 20.0 mass% or more, even if the Cr concentration of the ground iron is lowered by the formation of the oxide film as expected by the present invention, the chrominance layer in the grain boundary or in the grain The distribution of is not a distribution that affects the corrosion rate. On the other hand, if the Cr content exceeds 28.0 mass%, the Cr concentration in the oxide increases, and the generation of Si oxide at the surface grain boundary described above is suppressed, so the present invention is as expected. Even if the oxide film is left, selective intergranular corrosion due to an acid containing halogen or a solution having a low pH cannot be prevented, and intergranular erosion occurs, thereby degrading the polishability. Moreover, when content of Cr exceeds 28.0 mass%, elongation will reduce and workability will fall. Therefore, the Cr content is in the range of 20.0 to 28.0 mass%. Preferably it is the range of 22.0-25.0 mass%.
Ｎｉ：０．６０ｍａｓｓ％以下
Ｎｉは、靭性の向上に有効な元素であるが、０．６０ｍａｓｓ％を超えて含有すると、応力腐食割れ（ＳＣＣ）感受性が高くなる。よって、Ｎｉは０．６０ｍａｓｓ％以下にする。
Ni: 0.60 mass% or less Ni is an element effective for improving toughness, but if it exceeds 0.60 mass%, the stress corrosion cracking (SCC) sensitivity becomes high. Therefore, Ni is set to 0.60 mass% or less.
Ａｌ：０．０３〜０．１５ｍａｓｓ％
Ａｌは、Ｓｉと同じく、８００℃未満で酸化皮膜を形成するため、Ｓｉ，Ｍｏと並んで本発明においては重要な元素である。すなわち、Ａｌを鋼中に０．０３ｍａｓｓ％以上添加すると、熱処理した時に、Ｓｉ同様、Ａｌが地鉄の最表層に酸化皮膜を形成し、耐食性を向上する。一方、Ａｌの含有量が０．１５ｍａｓｓ％を超えると、酸化皮膜形成時に、その外層に生成する酸化物、特に、スピネル系の酸化物中のＡｌ濃度が上がり、耐食性が劣化する。よって、本発明では、Ａｌは０．０３〜０．１５ｍａｓｓ％とする。好ましくは、Ａｌの添加量は、０．０５〜０．１１ｍａｓｓ％の範囲である。
Al: 0.03-0.15 mass%
Al, like Si, forms an oxide film at less than 800 ° C., and thus is an important element in the present invention along with Si and Mo. That is, when Al is added to the steel in an amount of 0.03 mass% or more, when heat-treated, Al forms an oxide film on the outermost surface layer of the ground iron and improves the corrosion resistance when heat-treated. On the other hand, if the Al content exceeds 0.15 mass%, the concentration of Al in the oxide formed in the outer layer, particularly the spinel oxide, increases during the formation of the oxide film, and the corrosion resistance deteriorates. Therefore, in the present invention, Al is set to 0.03 to 0.15 mass%. Preferably, the amount of Al added is in the range of 0.05 to 0.11 mass%.
Ｎ：０．０２０ｍａｓｓ％以下
Ｎは、Ｃｒと結合してＣｒ窒化物を形成しやすい。特に、溶接時に、熱影響部にＣｒ窒化物が形成されると、粒界腐食の原因となるので、Ｎは低いほど好ましい。よって、本発明では、Ｎを０．０２０ｍａｓｓ％以下とする。
N: 0.020 mass% or less N is likely to form Cr nitride by combining with Cr. In particular, when Cr nitride is formed in the heat-affected zone during welding, it causes grain boundary corrosion, so N is preferably as low as possible. Therefore, in this invention, N shall be 0.020 mass% or less.
Ｏ：０．００２０〜０．０１５０ｍａｓｓ％
Ｏは、溶接時の溶け込み性を向上させる元素である。一方、多量の添加は、介在物を増加させ、耐食性の低下が顕著となる。よって、Ｏは、０．００２０〜０．０１５０ｍａｓｓ％の範囲とする。
O: 0.0020 to 0.0150 mass%
O is an element that improves the penetration during welding. On the other hand, addition of a large amount increases inclusions, and the deterioration of corrosion resistance becomes remarkable. Therefore, O is set to a range of 0.0020 to 0.0150 mass%.
Ｍｏ：０．３０〜１．５ｍａｓｓ％
Ｍｏは、耐食性の向上に極めて有効な元素である。鋼中のＭｏは、酸溶液中での不動態皮膜を強固にし、また、ハロゲンなどで破壊された不動態皮膜の再生を促進する働きが強いので、研磨後の耐食性を考慮した場合には、積極的に添加するのが好ましい。特に、温水器や水槽などのように、ハロゲンを含む水回りに使用する場合には、積極的に添加したほうがよい。上記Ｍｏの効果は、０．３０ｍａｓｓ％以上の添加で得られる。
Mo: 0.30 to 1.5 mass%
Mo is an element that is extremely effective in improving corrosion resistance. Mo in steel strengthens the passive film in the acid solution, and also has a strong effect of promoting the regeneration of the passive film destroyed by halogen, etc., so when considering the corrosion resistance after polishing, It is preferable to add it positively. In particular, when used around water containing halogen such as a water heater or a water tank, it is better to add it positively. The effect of Mo can be obtained by addition of 0.30 mass% or more.
しかし、発明者らが、Ｃｒ：２２．０〜２５．０ｍａｓｓ％、Ｓｉ：０．３〜０．６ｍａｓｓ％、Ｎｂ：０．２〜０．５ｍａｓｓ％を含有する鋼において、焼鈍時に形成される酸化皮膜の形態とＭｏ含有量との関係を調査したところ、Ｍｏが１．５ｍａｓｓ％を超えてしまうと、焼鈍時に形成される酸化皮膜はＣｒリッチなＣｒ２Ｏ３主体の皮膜となり、本発明において重要な働きをするＡｌやＳｉなどの元素の粒界での酸化を抑制してしまうことがわかった。これは、Ｍｏの添加により、酸化の初期において、Ｃｒ濃度の高い皮膜が生成されてしまうためと考えられる。さらに、Ｃｒ濃度の高い皮膜の生成は、粒界付近にＣｒ濃度の低いＣｒ欠乏領域を形成して粒界侵食を助長し、研磨性を劣化させることもわかった。したがって、本発明のように、若干の酸化皮膜を残留させて研磨性を確保するには、Ｍｏの上限を規制し、それによる不動態皮膜の低下をＣｒの添加で補償したほうが好ましいとの結論を得た。よって、本発明では、Ｍｏの含有量は０．３０〜１．５０ｍａｓｓ％の範囲とする。なお、ハロゲンなどを多く含む高温溶液中での耐食性を向上させるためには、Ｍｏの含有量は０．８〜１．２ｍａｓｓ％とするのが好ましい。 However, the inventors have formed during annealing in steel containing Cr: 22.0-25.0 mass%, Si: 0.3-0.6 mass%, Nb: 0.2-0.5 mass%. As a result of investigating the relationship between the form of the oxide film and the Mo content, if Mo exceeds 1.5 mass%, the oxide film formed during annealing becomes a film rich in Cr 2 O 3 , and the present invention. It has been found that the oxidation at the grain boundary of elements such as Al and Si, which play an important role in, is suppressed. This is presumably because a film having a high Cr concentration is generated at the initial stage of oxidation due to the addition of Mo. Furthermore, it has been found that the formation of a film with a high Cr concentration promotes grain boundary erosion by forming a Cr-deficient region with a low Cr concentration in the vicinity of the grain boundary and degrades the polishing property. Therefore, as in the present invention, in order to retain some oxide film and ensure polishability, it is concluded that it is preferable to limit the upper limit of Mo and compensate for the decrease of the passive film by adding Cr. Got. Therefore, in the present invention, the Mo content is in the range of 0.30 to 1.50 mass%. In order to improve the corrosion resistance in a high-temperature solution containing a large amount of halogen or the like, the Mo content is preferably 0.8 to 1.2 mass%.
Ｎｂ：０．１０〜０．５０ｍａｓｓ％
Ｎｂは、Ｃｒに優先して炭窒化物を形成する元素であり、熱延後にＣｒ炭窒化物が形成されるのを防ぎ、靭性の劣化を抑制する働きがある。この効果を得るためには、Ｎｂは、化学当量的な関係から、８×（Ｃ＋Ｎ）ｍａｓｓ％以上添加する必要がある。一方、０．５０ｍａｓｓ％を超え添加すると、逆に熱延板の靭性が劣化し、また溶接部での耐食性を低下させる。よって、Ｎｂは０．１０〜０．５０ｍａｓｓ％の範囲とする。なお、好ましいＮｂの添加量は０．２０〜０．４０ｍａｓｓ％である。
Nb: 0.10 to 0.50 mass%
Nb is an element that forms carbonitride in preference to Cr, and has the function of preventing the formation of Cr carbonitride after hot rolling and suppressing deterioration of toughness. In order to obtain this effect, Nb needs to be added in an amount of 8 × (C + N) mass% or more because of a chemical equivalent relationship. On the other hand, if added over 0.50 mass%, the toughness of the hot-rolled sheet deteriorates, and the corrosion resistance at the welded portion decreases. Therefore, Nb is set to a range of 0.10 to 0.50 mass%. In addition, the preferable addition amount of Nb is 0.20-0.40 mass%.
Ｔｉ：０．１０ｍａｓｓ％以下
Ｔｉは、Ｎｂと同様、Ｃｒよりも優先的に炭窒化物を形成し、溶接部などでの耐食性を向上させるので、耐食性の向上には好ましい元素である。しかし、０．１ｍａｓｓ％を超える添加は、熱延板のシャルピー吸収エネルギー低下の原因となり、破断しやすくなる。また、ＴｉＮのクラスター状介在物による表面傷の発生を招き、研磨性を著しく阻害する。よって、Ｔｉは０．１０ｍａｓｓ％以下とする。なお、好ましくは、Ｔｉは０．０３ｍａｓｓ％以下とする。
Ti: 0.10 mass% or less Ti, like Nb, forms carbonitride preferentially over Cr and improves corrosion resistance at welds and the like, and is therefore a preferable element for improving corrosion resistance. However, addition exceeding 0.1 mass% causes a reduction in the Charpy absorbed energy of the hot-rolled sheet, and breaks easily. Further, surface scratches are caused by TiN cluster-like inclusions, and the polishing property is remarkably impaired. Therefore, Ti is set to 0.10 mass% or less. In addition, Preferably, Ti shall be 0.03 mass% or less.
（Ｃｒ＋３．３Ｍｏ）：２４〜３２ｍａｓｓ％
本発明のフェライト系ステンレス鋼は、基本成分が上記組成範囲を満たしていることの外に、さらに、ＣｒとＭｏが下記（１）式；
２４ｍａｓｓ％≦Ｃｒ＋３．３Ｍｏ≦３２ｍａｓｓ％ ・・・（１）
を満たしていることが必要である。上記（１）式の左辺の値は、残留塩素濃度が高い温水器や水槽、シンクなどにおいても、耐食性を確保するために必要な条件を示したものである。一方、上記（１）の右辺の値は、母材の耐食性と溶接時のテンパーカラーの生成によって劣化した溶接部との耐食性の差が大きくなると、腐食が優先的にテンパーカラー部で起こるようになり、隙間腐食を助長するようになるので、これを防止するための条件を示したものである。
(Cr + 3.3Mo): 24-32 mass%
In the ferritic stainless steel of the present invention, in addition to the basic components satisfying the above composition range, Cr and Mo are further represented by the following formula (1):
24 mass% ≦ Cr + 3.3Mo ≦ 32 mass% (1)
It is necessary to satisfy. The value on the left side of the above equation (1) indicates the conditions necessary to ensure corrosion resistance even in a water heater, water tank, sink, etc. with a high residual chlorine concentration. On the other hand, the value on the right side of (1) indicates that the corrosion preferentially occurs in the temper collar portion when the difference between the corrosion resistance of the base metal and the weld portion deteriorated due to the generation of the temper collar at the time of welding increases. Therefore, crevice corrosion is promoted, and the conditions for preventing this are shown.
なお、本発明のフェライト系ステンレス鋼板は、上記必須成分に加えてさらに、ＣｕおよびＺｒを下記の範囲で添加することができる。
Ｃｕ：０．２〜１．０ｍａｓｓ％
Ｃｕは、Ｃｒを２０．０ｍａｓｓ％以上含有する鋼の母材の耐食性を向上させる効果を有する。この効果は、０．２ｍａｓｓ％以上の添加で発現し、特に、ハロゲンを含む低ｐＨの酸溶液中での、地鉄の溶解を少なくする効果が大きい。この理由は、十分に明らかとはなっていないが、ハロゲンを含む低ｐＨ溶液中で溶け出したＣｕが地鉄に再付着して、地鉄の耐溶解性を高めるためと推定している。一方、Ｃｕを１．０ｍａｓｓ％超え添加すると、逆に、Ｃｕの溶解が促進されて耐隙間腐食性が低下する。よって、Ｃｕは、０．２〜１．０ｍａｓｓ％の範囲で添加するのが好ましい。より好ましいＣｕの添加量は０．３〜０．７ｍａｓｓ％である。
In addition to the above essential components, the ferritic stainless steel sheet of the present invention can further contain Cu and Zr within the following range.
Cu: 0.2-1.0 mass%
Cu has the effect of improving the corrosion resistance of a steel base material containing 20.0 mass% or more of Cr. This effect is manifested by addition of 0.2 mass% or more, and in particular, the effect of reducing the dissolution of ground iron in a low pH acid solution containing halogen is great. The reason for this is not sufficiently clear, but it is presumed that Cu dissolved in a low pH solution containing halogen is reattached to the base iron to improve the dissolution resistance of the base iron. On the other hand, when Cu is added in excess of 1.0 mass%, conversely, dissolution of Cu is promoted and the crevice corrosion resistance is lowered. Therefore, it is preferable to add Cu in the range of 0.2 to 1.0 mass%. A more preferable addition amount of Cu is 0.3 to 0.7 mass%.
Ｚｒ：０．１〜０．６ｍａｓｓ％
Ｚｒは、Ｎｂと同様、Ｃｒよりも優先して炭窒化物を形成し、溶接部の耐食性を向上させる元素である。この効果は、０．１ｍａｓｓ％以上の添加で発現する。一方、０．６ｍａｓｓ％を超える過多の添加は、金属間化合物を形成して、熱延板の靭性を劣化させる。よって、本発明では、Ｚｒは０．１〜０．６ｍａｓｓ％の範囲で添加するのが好ましい。より好ましくは、Ｚｒは０．１５〜０．３５ｍａｓｓ％の範囲である。
Zr: 0.1 to 0.6 mass%
Zr, like Nb, is an element that forms carbonitride preferentially over Cr and improves the corrosion resistance of the weld. This effect is manifested by addition of 0.1 mass% or more. On the other hand, excessive addition exceeding 0.6 mass% forms an intermetallic compound and degrades the toughness of a hot-rolled sheet. Therefore, in the present invention, Zr is preferably added in the range of 0.1 to 0.6 mass%. More preferably, Zr is in the range of 0.15 to 0.35 mass%.
本発明に係るフェライト系ステンレス鋼板における上記成分以外の残部は、Ｆｅおよび不可避的不純物である。ただし、本発明の効果を害しない範囲であれば、その他の成分の含有を許容することができ、たとえば、Ｍｇ：０．００２０ｍａｓｓ％以下、Ｃａ：０．００２０ｍａｓｓ％以下を含有してもよい。 The balance other than the above components in the ferritic stainless steel sheet according to the present invention is Fe and inevitable impurities. However, the content of other components can be allowed as long as the effects of the present invention are not impaired. For example, Mg: 0.0020 mass% or less and Ca: 0.0020 mass% or less may be contained.
次に、本発明のフェライト系ステンレス鋼板において極めて重要な要件である鋼板表層の酸化皮膜について説明する。
本発明の鋼板は、上記成分組成を単に満たすだけでは、本発明が目的とする耐食性と研磨性とを両立させることは不可能であり、特に、優れた研磨性を得ることはできない。上記目的を達成するためには、上記成分組成条件を満たした上で、さらに、鋼板の表層に、特定の酸化皮膜を選択的に残留させる必要がある。
Next, the oxide film on the steel sheet surface layer, which is a very important requirement in the ferritic stainless steel sheet of the present invention, will be described.
The steel sheet of the present invention cannot satisfy both of the corrosion resistance and the abrasiveness intended by the present invention simply by satisfying the above component composition, and in particular, cannot obtain excellent abrasiveness. In order to achieve the above object, it is necessary to selectively leave a specific oxide film on the surface layer of the steel sheet after satisfying the above component composition conditions.
一般に、耐食性を確保する観点からは、焼鈍時に鋼板表面に生成する酸化皮膜は好ましいものではない。しかし、本発明は、この酸化皮膜を敢えて選択的に残留させることによって、地鉄の溶解を最小限に抑制し、研磨性を確保しようとするところに、従来技術にない特徴がある。なお、この酸化皮膜は、加工後、研磨して使用する際の耐食性にも、好ましい効果を発揮する。 In general, from the viewpoint of ensuring corrosion resistance, an oxide film formed on the surface of a steel sheet during annealing is not preferable. However, the present invention is characterized in that it does not exist in the prior art in that the oxide film is intentionally left selectively to suppress the dissolution of the base iron to the minimum and ensure the polishability. In addition, this oxide film exhibits a favorable effect also in the corrosion resistance at the time of grinding | polishing and using it after a process.
発明者らは、Ｃｒ：２０．０〜２８．０ｍａｓｓ％、Ｓｉ：０．２〜１．０ｍａｓｓ％、Ｃｕ：０．２〜１．０ｍａｓｓ％、Ｎｉ：０．１〜０．５ｍａｓｓ％、Ｍｏ：０．３〜１．５ｍａｓｓ％を含有する鋼板に、８００〜１０５０℃×１０〜６００秒の条件で焼鈍を施し、鋼板表面に種々の厚さの酸化皮膜を形成させた。そして、この時に生成した酸化皮膜の状態と地鉄表層部の粒界に生成したＳｉ酸化物の状態と、この鋼板を、ハロゲンを含む酸溶液中に浸漬したときの酸化皮膜の溶解形態と、上記溶解後に残留した酸化皮膜の厚さとが、鋼板の研磨性および耐食性（研磨後の耐食性も含む）に及ぼす影響について詳細に調査した。 The inventors have Cr: 20.0 to 28.0 mass%, Si: 0.2 to 1.0 mass%, Cu: 0.2 to 1.0 mass%, Ni: 0.1 to 0.5 mass%, Mo. : The steel plate containing 0.3 to 1.5 mass% was annealed under conditions of 800 to 1050 ° C. for 10 to 600 seconds to form oxide films with various thicknesses on the steel plate surface. And, the state of the oxide film generated at this time and the state of the Si oxide generated at the grain boundary of the surface layer portion of the base metal, and the dissolved form of the oxide film when this steel sheet is immersed in an acid solution containing halogen, The influence of the thickness of the oxide film remaining after the dissolution on the polishing properties and corrosion resistance (including corrosion resistance after polishing) of the steel sheet was investigated in detail.
その結果、酸溶解処理により、鋼板表面にＳｉ濃度の高くかつ平均厚さが１０〜１００ｎｍの酸化皮膜を残留させた場合には、非常に良好な研磨性が得られること、しかし、平均厚さが１００ｎｍを超えると、酸化皮膜外層のＭｎ，Ｆｅを多く含むスピネル酸化物が発錆の起点となり、短時間で発錆してしまうだけでなく、その酸化物を除去するのに要する研磨負荷が増大すること、一方、平均厚さが１０ｍｍ未満になるまで酸化皮膜を溶解してしまうと、鋼板表層の粒界の一部が深く掘られて、表面が白く曇りを生じて金属光沢が失われ、研磨性が劣化することを知見した。よって、本発明においては、酸溶解処理後、鋼板表層に残存する酸化皮膜の平均厚さを１０〜１００ｎｍの範囲に限定する。好ましくは、酸化皮膜の厚みは２０〜５０ｎｍである。 As a result, when an oxide film having a high Si concentration and an average thickness of 10 to 100 nm is left on the steel sheet surface by the acid dissolution treatment, very good polishing properties can be obtained, but the average thickness If the thickness exceeds 100 nm, the spinel oxide containing a large amount of Mn and Fe in the outer layer of the oxide film becomes the starting point of rusting, and not only does it rust in a short time, but also the polishing load required to remove the oxide is increased. On the other hand, if the oxide film is dissolved until the average thickness becomes less than 10 mm, part of the grain boundary of the steel sheet surface layer is deeply dug, the surface becomes white and cloudy, and the metallic luster is lost. It was found that the abrasiveness deteriorated. Therefore, in the present invention, after the acid dissolution treatment, the average thickness of the oxide film remaining on the steel sheet surface layer is limited to a range of 10 to 100 nm. Preferably, the thickness of the oxide film is 20 to 50 nm.
また、発明者らは、酸化皮膜中に含まれるＳｉ，Ａｌのうちのいずれか１以上の濃度が、母材（地鉄）中に含まれるそれらの濃度の３倍以上に濃化している場合には、その酸化皮膜は、優れた耐食性向上効果を発現することを知見した。 In addition, the inventors have a case where the concentration of any one or more of Si and Al contained in the oxide film is concentrated to 3 times or more of those contained in the base material (base metal). In addition, it was found that the oxide film exhibits an excellent effect of improving corrosion resistance.
なお、上記平均厚さが１０〜１００ｎｍの酸化皮膜を得るための冷延板を最終焼鈍した後の酸処理は、硝弗酸に浸漬して酸化皮膜の厚さを調整した後、硝酸溶液中で正電解、負電解をそれぞれ１回以上行うのが好ましい。硝弗酸浸漬処理では、溶解性の違いから、外層のＭｎ，Ｆｅを多く含むスピネル酸化物のみを除去することが容易であり、さらに、硝酸中で正電解、負電解処理を施すことにより、酸化物中と地鉄とのＳｉ，Ａｌ濃度比を上げて、酸化皮膜による耐食性向上効果をより高めることが可能となるからである。なお、硝弗酸浸漬処理の前工程で、通常行われている中性塩電解処理を施してもよいことは勿論である。 The acid treatment after the final annealing of the cold-rolled sheet for obtaining an oxide film having an average thickness of 10 to 100 nm is immersed in nitric hydrofluoric acid to adjust the thickness of the oxide film, and then in a nitric acid solution. It is preferable to perform positive electrolysis and negative electrolysis at least once each. In the nitric hydrofluoric acid immersion treatment, it is easy to remove only the spinel oxide containing a large amount of Mn and Fe in the outer layer due to the difference in solubility. Furthermore, by performing positive electrolysis and negative electrolysis in nitric acid, This is because the effect of improving the corrosion resistance by the oxide film can be further increased by increasing the Si and Al concentration ratio in the oxide and the base iron. Needless to say, a neutral salt electrolysis treatment which is usually performed may be performed in the pre-process of the nitric hydrofluoric acid immersion treatment.
次に、本発明に係るフェライト系ステンレス鋼板の製造方法について説明する。
本発明の鋼板の製造方法は、特に制限されるものではく、従来から用いられている公知のステンレス鋼板の製造方法を適用することができる。たとえば、上述した成分組成を有する溶鋼を、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−分塊法で鋼素材（スラブ）とし、この鋼素材を再加熱してから熱間圧延するかあるいは再加熱することなく直接熱間圧延して熱延板とし、次いで、この熱延板に、必要に応じて熱延板焼鈍を施し、酸洗し、冷間圧延して冷延板とするのが好ましい。
Next, the manufacturing method of the ferritic stainless steel sheet according to the present invention will be described.
The manufacturing method of the steel plate of this invention is not restrict | limited especially, The manufacturing method of the well-known stainless steel plate used conventionally can be applied. For example, molten steel having the above-described component composition is melted by a known method such as a converter, electric furnace, vacuum melting furnace or the like, and a steel material (slab) is obtained by a continuous casting method or an ingot-bundling method. The material is either reheated and then hot-rolled or directly hot-rolled without reheating to form a hot-rolled sheet, and then this hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, and pickled. And it is preferable to cold-roll and make a cold-rolled sheet.
その後、この冷延板を、コークス炉ガスと空気を空気比１．０〜１．５で混合し燃焼させたガス雰囲気中で、例えば、１０００℃×６０秒の焼鈍を行い、鋼板表面に酸化皮膜を形成してから、中性塩電解し、硝弗酸溶液（硝酸：５０ｇ／Ｌ、弗酸：３０ｇ／Ｌ、６０℃）に浸漬処理するのが好ましい。この浸漬処理の時間は、概ね３０秒前後であるが、この浸漬時間は、鋼板表層に残留させる酸化皮膜の平均厚さが１０〜１００ｎｍの範囲に収まるよう調節する。最後に、硝酸溶液（硝酸１００ｇ／Ｌ）中に、浸漬し、電解処理して製品とするのが好ましい。なお、上記硝弗酸溶液や硝酸溶液の濃度、浸漬時間および液温等は、単なる例示であり、これに限定されるものではなく、鋼中Ｃｒ濃度や形成される酸化皮膜厚さ、目標とする残留酸化皮膜の厚さ等に応じて、適宜変更するのが好ましい。 Then, this cold-rolled sheet is annealed at, for example, 1000 ° C. for 60 seconds in a gas atmosphere in which coke oven gas and air are mixed and burned at an air ratio of 1.0 to 1.5 to oxidize the steel sheet surface. After forming a film, neutral salt electrolysis is preferably carried out and immersed in a nitric hydrofluoric acid solution (nitric acid: 50 g / L, hydrofluoric acid: 30 g / L, 60 ° C.). The time for this dipping treatment is approximately 30 seconds, but this dipping time is adjusted so that the average thickness of the oxide film remaining on the steel sheet surface layer falls within the range of 10 to 100 nm. Finally, it is preferable to immerse it in a nitric acid solution (nitric acid 100 g / L) and subject it to electrolytic treatment to obtain a product. The concentration of nitric hydrofluoric acid solution and nitric acid solution, the immersion time, the liquid temperature, etc. are merely examples, and are not limited to these. The concentration of Cr in steel, the thickness of the oxide film to be formed, the target It is preferable to change appropriately according to the thickness etc. of the residual oxide film.
表１に示した成分組成を有する鋼を５０ｋｇの小型真空溶解炉で溶製し、鋼塊とした後、これらの鋼塊を１０５０〜１２５０℃に加熱し、仕上温度を７５０〜９５０℃とする熱間圧延により板厚４．０ｍｍの熱延板とし、保熱ボックスに保持することにより、巻取温度６５０〜８５０℃相当の熱処理を施した。次いで、これらの熱延板に対して、９００〜１１００℃の熱延板焼鈍を施した後、酸洗し、冷間圧延して板厚１．０ｍｍの冷延板とし、この冷延板に９８０℃×６０秒の焼鈍を施してから、中性塩溶液中（Ｎａ２ＳＯ４：２００g／Ｌ、８０℃）で電流（＋１００Ｃ／ｄｍ２、−１００Ｃ／ｄｍ２）の電解処理を行い、次いで、硝弗酸溶液（硝酸：５０ｇ／Ｌ、弗酸：２０ｇ／Ｌ、温度５５℃）に浸漬した。この時、浸漬時間を変化させることにより、表層の酸化皮膜の厚みを調整した。その後、１００ｇ／Ｌの硝酸を含む４５℃の硝酸溶液中で、＋３０Ｃ／ｄｍ２、−３０Ｃ／ｄｍ２の電解処理を各２回施して冷延製品板とした。なお、一部の鋼板については、硝酸溶液中での電解処理は行わなかった。 Steel having the composition shown in Table 1 is melted in a 50 kg small vacuum melting furnace to form steel ingots, and then these steel ingots are heated to 1050 to 1250 ° C., and the finishing temperature is set to 750 to 950 ° C. A hot-rolled sheet having a thickness of 4.0 mm was formed by hot rolling, and heat treatment corresponding to a coiling temperature of 650 to 850 ° C. was performed by holding the sheet in a heat retaining box. Next, these hot-rolled sheets were subjected to hot-rolled sheet annealing at 900 to 1100 ° C., and then pickled and cold-rolled to form cold-rolled sheets having a thickness of 1.0 mm. after annealed in 980 ° C. × 60 seconds, neutral salt solution: perform electrolytic treatment of (Na 2 SO 4 200g / L , 80 ℃) with a current (+ 100C / dm 2, -100C / dm 2), Next, it was immersed in a nitric hydrofluoric acid solution (nitric acid: 50 g / L, hydrofluoric acid: 20 g / L, temperature 55 ° C.). At this time, the thickness of the oxide film on the surface layer was adjusted by changing the immersion time. Then, at 45 ° C. in a nitric acid solution containing nitric acid 100g / L, + 30C / dm 2, and a cold-rolled product sheet is subjected twice each electrolytic treatment of -30C / dm 2. In addition, about some steel plates, the electrolytic treatment in a nitric acid solution was not performed.
上記のようにして得た冷延製品板を以下の試験に供した。
＜酸化皮膜の特性評価＞
上記冷延製品板から試験片を採取し、Ａｕｇｅｒ分光分析装置およびＧＤＳ分析装置を用いて、残留酸化皮膜の厚さを測定するとともに、酸化皮膜中および地鉄中のＳｉおよびＡｌの濃度を測定し、それぞれの強度比（皮膜濃度／地鉄濃度）を求めた。
＜研磨性の評価＞
上記冷延製品板から試験片を採取し、♯６００番のアルミナ砥粒を用いて、有機樹脂のバフロールにより１分間湿式研磨し、研磨後の板の光沢度を測定し、光沢度が４００以上を研磨性良と評価した。なお、光沢度の測定は、光沢度計ＨＧ−２６８（スガ試験機製）を用い、Ｌ方向（圧延方向）に平行に入射光の測定角度６０°で行った。
＜孔食電位の測定＞
上記研磨性評価の試験前および試験後の試験片について、ＪＩＳ Ｇ０５７７「ステンレス鋼の孔食電位測定方法」に準拠して、孔食電位（Ｖ’ｃ１０）を測定し、耐食性を評価した。なお、研磨前の測定に用いた試験片は、研磨は一切行わず、また、試験液への１０分間の浸漬も行うことなく、浸漬後、直ちに電位走査を開始した。なお、孔食電位による耐食性の評価は、研磨前は、３００ｍＶ以上を耐食性良好、研磨後は、４００ｍＶ以上を耐食性良好と評価した。
＜ＣＣＴ試験＞
上記冷延製品板から幅６０ｍｍ×長さ８０ｍｍの試験片を２枚採取し、そのうちの１枚を上記研磨性評価と同じ条件で研磨し、研磨前と研磨後の試験片を準備した。これらの試験片を、乾湿繰り返し試験（ＣＣＴ試験）に供して耐食性を評価した。ＣＣＴ試験に用いた試験片は、アルカリ洗浄液（脱脂液：ホメザリン：花王（株）製）に３０秒間浸漬して洗浄したのち試験面のエッジから５ｍｍまでの縁部とエッジそれに試験面の反対面を、ビニールテープでシールしてから耐食性試験に供した。ＣＣＴ試験は、噴霧（ＮａＣｌ：５％溶液、温度３５℃、０．５時間）→乾燥（温度６０℃、１時間）→湿潤（温度４０℃、湿度９５％、１時間）の２．５時間の行程を１サイクルとしてこれを繰り返して行い、初期錆が発生するまでの発錆時間を測定し、評価した。なお、発錆時間による耐食性の評価は、研磨前は、２００時間以上（８０サイクル以上）を耐食性良好、研磨後は、４００時間以上（１６０サイクル以上）を耐食性良好と評価した。
The cold-rolled product plate obtained as described above was subjected to the following test.
<Characteristic evaluation of oxide film>
Test specimens are taken from the cold-rolled product plate, and the thickness of the residual oxide film is measured using the Auger spectroscopic analyzer and GDS analyzer, and the concentrations of Si and Al in the oxide film and in the steel are measured. Each strength ratio (film concentration / base iron concentration) was determined.
<Abrasive evaluation>
A test piece was taken from the cold-rolled product plate, wet-polished with # 600 alumina abrasive grains with organic resin buffol for 1 minute, and the glossiness of the polished plate was measured. The glossiness was 400 or more. Was evaluated as having good polishing properties. The glossiness was measured using a gloss meter HG-268 (manufactured by Suga Test Instruments) at a measurement angle of incident light of 60 ° parallel to the L direction (rolling direction).
<Measurement of pitting potential>
About the test piece before and after the test of the polishing evaluation, the pitting potential (V ′ c10 ) was measured in accordance with JIS G0577 “Method for Measuring Pitting Corrosion Potential of Stainless Steel” to evaluate the corrosion resistance. The test piece used for the measurement before polishing was not polished at all, and the potential scan was started immediately after immersion without immersion for 10 minutes in the test solution. In addition, the evaluation of the corrosion resistance by the pitting corrosion potential was evaluated as good corrosion resistance at 300 mV or more before polishing, and as good corrosion resistance at 400 mV or more after polishing.
<CCT test>
Two test pieces each having a width of 60 mm and a length of 80 mm were collected from the cold-rolled product plate, and one of them was polished under the same conditions as in the evaluation of the polishing property to prepare test pieces before and after polishing. These test pieces were subjected to a dry and wet repeated test (CCT test) to evaluate the corrosion resistance. The test piece used for the CCT test was immersed for 30 seconds in an alkaline cleaning solution (degreasing solution: homezarin: manufactured by Kao Corporation), washed, and then the edge of the test surface from the edge to the edge of 5 mm, the edge and the opposite surface of the test surface After being sealed with vinyl tape, it was subjected to a corrosion resistance test. The CCT test was conducted by spraying (NaCl: 5% solution, temperature 35 ° C., 0.5 hour) → drying (temperature 60 ° C., 1 hour) → wetting (temperature 40 ° C., humidity 95%, 1 hour) for 2.5 hours. This process was repeated for one cycle, and the rusting time until the initial rust was generated was measured and evaluated. Evaluation of corrosion resistance by rusting time was evaluated as good corrosion resistance for 200 hours or more (80 cycles or more) before polishing and 400 hours or more (160 cycles or more) after polishing as good corrosion resistance.
以上の結果を総合評価して表２に示した。総合評価では、孔食電位、ＣＣＴ試験および光沢度の全てが良好あるいはそれ以上の評価になったものを◎、光沢度のみが良好未満であったものを△、ＣＣＴ試験および光沢度のいずれかが良好未満であったものを×とした。表１および表２の結果から、本発明範囲の成分組成を有するとともに、本発明範囲の酸化皮膜を有する鋼板はいずれも、耐食性と研磨性に優れていることがわかる。 The above results were comprehensively evaluated and are shown in Table 2. In the comprehensive evaluation, ◎ indicates that the pitting corrosion potential, CCT test and glossiness are all good or better, △ indicates that the glossiness is less than good, and CCT test and glossiness. Was less than good. From the results of Tables 1 and 2, it can be seen that any steel sheet having a component composition within the range of the present invention and having an oxide film within the range of the present invention is excellent in corrosion resistance and abrasiveness.
本発明のフェライト系ステンレス鋼板は、耐食性と研磨性に優れるため、水周り部材用途の外に、例えば、海上輸送コンテナーや建材、建具等の意匠性と耐食性を求められる部位の材料としても好適に用いることができる。さらに、本発明のステンレス鋼板は、不純物元素を低減した上で、安定化元素であるＮｂを添加し、さらに、Ｓｉ，Ａｌなどを添加しているので、溶接性に優れるのみならず、溶接部加工性や溶接部耐食性にも優れた特性を有するので、溶接して使用される用途にも用いることができる。 Since the ferritic stainless steel sheet of the present invention is excellent in corrosion resistance and polishability, it is also suitable as a material for parts requiring designability and corrosion resistance, such as maritime transport containers, building materials, joinery, etc. Can be used. Furthermore, since the stainless steel plate of the present invention is reduced in impurity elements and added with Nb which is a stabilizing element and further added with Si, Al, etc., not only has excellent weldability, but also welded parts. Since it has excellent properties in workability and welded portion corrosion resistance, it can also be used in applications that are used by welding.
Claims (4)
２４ｍａｓｓ％≦Ｃｒ＋３．３Ｍｏ≦３２ｍａｓｓ％
を満たし、残部がＦｅおよび不可避的不純物からなり、鋼板表層に平均厚さ１０〜１００ｎｍの酸化皮膜を有する水周り部材用フェライト系ステンレス鋼板。 C: 0.020 mass% or less, Si: 0.30 to 1.00 mass%, Mn: 0.50 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr: 20.0 to 28 0.0 mass%, Ni: 0.60 mass% or less, Al: 0.03 to 0.15 mass% or less, N: 0.020 mass% or less, O: 0.0020 to 0.0150 mass%, Mo: 0.30 to 1 0.5 mass%, Nb: 0.10 to 0.50 mass%, Ti: 0.10 mass% or less, and Cr and Mo are represented by the following formula:
24 mass% ≦ Cr + 3.3Mo ≦ 32 mass%
A ferritic stainless steel sheet for water-surrounding members having a balance of Fe and inevitable impurities and having an oxide film with an average thickness of 10 to 100 nm on the steel sheet surface layer.
２４ｍａｓｓ％≦Ｃｒ＋３．３Ｍｏ≦３２ｍａｓｓ％
を満たし、残部がＦｅおよび不可避的不純物からなる鋼板を焼鈍して表層に酸化皮膜を形成し、次いで、硝弗酸溶液に浸漬して酸化皮膜の平均厚さを１０〜１００ｎｍに調整し、その後、硝酸溶液中で正電解、負電解を各１回以上行う水周り部材用フェライト系ステンレス鋼板の製造方法。 C: 0.020 mass% or less, Si: 0.30 to 1.00 mass%, Mn: 0.50 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Cr: 20.0 to 28 0.0 mass%, Ni: 0.60 mass% or less, Al: 0.03 to 0.15 mass% or less, N: 0.020 mass% or less, O: 0.0020 to 0.0150 mass%, Mo: 0.30 to 1 0.5 mass%, Nb: 0.10 to 0.50 mass%, Ti: 0.10 mass% or less, and Cr and Mo are represented by the following formula:
24 mass% ≦ Cr + 3.3Mo ≦ 32 mass%
An oxide film is formed on the surface layer by annealing a steel plate composed of Fe and the inevitable impurities, and then immersed in a nitric hydrofluoric acid solution to adjust the average thickness of the oxide film to 10 to 100 nm. The manufacturing method of the ferritic stainless steel plate for water surrounding members which performs positive electrolysis and negative electrolysis at least once each in a nitric acid solution.
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