WO2017061216A1 - Stainless steel pipe with excellent corrosion resistance - Google Patents

Stainless steel pipe with excellent corrosion resistance Download PDF

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Publication number
WO2017061216A1
WO2017061216A1 PCT/JP2016/076143 JP2016076143W WO2017061216A1 WO 2017061216 A1 WO2017061216 A1 WO 2017061216A1 JP 2016076143 W JP2016076143 W JP 2016076143W WO 2017061216 A1 WO2017061216 A1 WO 2017061216A1
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mass
stainless steel
steel pipe
less
polishing
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PCT/JP2016/076143
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French (fr)
Japanese (ja)
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知明 齋田
善一 田井
一成 今川
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日新製鋼株式会社
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

  • the present invention relates to a stainless steel pipe excellent in corrosion resistance.
  • Stainless steel is widely used in building materials such as roofing materials, wall materials, and building materials because it is excellent in weather resistance, workability, weldability, and the like. Moreover, since the stainless steel pipe is excellent in design, the surface is polished and used for applications such as handrails, fences, and pipe shutters.
  • polishing removal is performed to remove wrinkles and the like of the raw pipe before polishing, and then final polishing and gloss polishing are performed.
  • rough polishing and finish polishing in this polishing operation dry polishing using a flap wheel, a polishing belt, or the like is performed. Further, after the above process, wet polishing by buffing may be performed to obtain a desired surface.
  • stainless steel has excellent weather resistance as a material, but depending on the state of the polished finish, it may not exhibit the weather resistance inherent to the material and may cause significant bruising. This is one of the factors that eliminate the stability (reliability) of weather resistance. For example, it may occur in a short period of about one month after construction on an outdoor handrail.
  • the starting point is the oxide film and polishing marks remaining on the polished surface of the stainless steel pipe.
  • the remaining oxide film is a film generated due to heat generation during polishing, and a Cr-deficient layer is formed immediately below the oxide film.
  • the firing proceeds from the oxide film and the Cr-deficient layer immediately below the oxide film, and the corrosion resistance tends to deteriorate.
  • the polishing marks which are ridges carved on the surface of the stainless steel pipe by polishing, the deeper the recesses in the polishing marks, the more likely the oxide film generated by the flap wheel polishing or the like is difficult to be removed by buffing and remain. Since the height becomes higher and the concave portion of the polished eye becomes the starting point of the cracking, the cracking proceeds and the corrosion resistance tends to deteriorate.
  • Patent Document 1 proposes a stainless steel pipe capable of maintaining glossiness and weather resistance over a long period of time in a surface-polished state that does not generate sprout even in an outdoor environment in a short period of time.
  • Patent Document 1 is a stainless steel pipe having a surface roughness after final polishing of Ry 0.6 ⁇ m or less and an area ratio of the remaining oxide film of 7.0% or less. That is, by setting the surface roughness after final polishing to Ry 0.6 ⁇ m or less, an attempt is made to reduce the oxide film remaining in the recesses of the polishing eyes. Further, by setting the area ratio of the remaining oxide film to 7.0% or less, it is intended to suppress the progress of cracking and deterioration of corrosion resistance starting from the oxide film and the Cr-deficient layer immediately below the oxide film.
  • the remaining oxide film area ratio in the weather-resistant product is 3.1 to 6.8%, and the oxide film remains. For this reason, there still remains a problem that the rusting can progress and the corrosion resistance can be deteriorated starting from the remaining oxide film and the Cr-deficient layer directly therebelow.
  • Patent Document 2 describes that a stainless steel tube is immersed in a mixed solution of hydrofluoric acid and nitric acid to dissolve the oxidized scale on the surface of the stainless steel and the Cr-deficient layer immediately below the scale layer.
  • the object of the present invention is to solve the above-mentioned problems and to provide a stainless steel pipe excellent in corrosion resistance that does not start at an early stage even in a waterfront environment affected by sea salt particles.
  • the present inventors examined the stainless steel pipe described in Patent Document 1.
  • polishing by a flap wheel is performed.
  • the surface of the stainless steel pipe is heated at the time of flap wheel polishing, which is dry polishing, and an oxide film is generated, and there are surface defects along with polishing marks that are engraved by high grinding resistance by dry polishing.
  • the surface defects mentioned here are “burrs” or “covers” that are covered with the base material by polishing materials and paper continuously contacting the steel pipe surface when the steel pipe surface is polished, and the metal on the surface is partially peeled off. ".
  • the surface defect includes a portion where the metal is turned up like a strip shape or a bamboo leaf shape, and the maximum length from one end portion of the portion adhered to the substrate to the other end portion of the peeling tip is 5 ⁇ m. It is the above defect. Since the surface defect forms a minute gap with the surface base portion of the stainless steel pipe, corrosion tends to occur, which causes a reduction in the corrosion resistance of the steel pipe.
  • the stainless steel pipe is likely to be sprinkled, and the ordinary person skilled in the art is able to remove the oxide film and surface defect by pickling treatment.
  • the present inventors are a stainless steel pipe that is easily corroded due to the presence of colored oxide films and surface defects, and is early in the waterfront environment that is affected by sea salt particles even if it is not pickled after polishing.
  • the present invention has been found by investigating a stainless steel pipe excellent in corrosion resistance, which does not cause any problems.
  • the present invention provides the following (1) to (2) stainless steel pipes having excellent corrosion resistance.
  • (1) A longitudinally unidirectional polished surface is provided on the surface of a ferritic stainless steel tube, the pitting corrosion potential is 0.6 V or more, the 60 ° glossiness is 75 or less, and the composition is C: 0.020 mass.
  • the stainless steel pipe of the present invention has excellent design properties because it has a longitudinally polished surface on the surface of the ferritic stainless steel pipe, and has an antiglare property because its 60 degree gloss is 75 or less.
  • the colored oxide film is present on the surface of the stainless steel pipe and has surface defects, it has a predetermined composition and has a high pitting corrosion index (PI) of 30 or more. It is a stainless steel pipe excellent in corrosion resistance having a pitting potential of 0.6 V or more, in which the cracking starting from the Cr-deficient layer immediately below is suppressed.
  • Nb 0.1 to 1.0% by mass
  • Ti 0.05 to 0.3% by mass
  • Al 0.01 to 0.5% by mass
  • the stainless steel pipe of the present invention has a longitudinally polished surface on the surface of the ferritic stainless steel pipe, the pitting corrosion potential is 0.6 V or more, the 60 ° gloss is 75 or less, and the composition is C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4.00 mass%, P : 0.030% by mass or less, S: 0.020% by mass or less, Ni: 0.50% by mass or less, N: 0.020% by mass or less, with the balance being Fe and inevitable impurities, pitting corrosion resistance
  • the stainless steel pipe has a surface polished to give the surface unevenness and gloss.
  • the stainless steel pipe has a polished eye and becomes a stainless steel pipe excellent in design and antiglare properties.
  • Polishing eyes are ridges carved on the surface of a stainless steel pipe by polishing.
  • the polishing eye includes a polishing eye in one longitudinal direction.
  • a stainless steel pipe having a polishing mark in one longitudinal direction is excellent in antiglare property.
  • As the polishing finish in one longitudinal direction since wet polishing is difficult, dry polishing with a flap wheel or the like has been conventionally performed. However, when dry polishing is performed, the surface of the stainless steel tube becomes high temperature and oxidation with coloring is performed. A film is formed.
  • the polishing surface of the surface after polishing the deeper the recess of the polishing eye, the higher the possibility that the oxide film generated by flap wheel polishing or the like remains, the recess of the polishing eye becomes the starting point, Heating progresses and corrosion resistance tends to deteriorate.
  • the presence of a colored oxide film means that when an arbitrary 10 points on the surface of the stainless steel tube are observed with an optical microscope at a magnification of 400 times, the colored oxide film is 50 ⁇ m square. In the case of 10% or more by area ratio.
  • the coloration is not limited to a specific color, and any color that can be visually distinguished from the metal base or metallic luster of the stainless steel pipe is acceptable. A typical color for coloring is brown.
  • FIG. 1 is a photograph of an enlarged surface of a stainless steel tube with an optical microscope, (a) a surface in which surface defects are suppressed and (b) a surface in which surface defects are generated.
  • the surface of the stainless steel pipe in FIG. 1 (a) has polished eyes, but surface defects are suppressed.
  • the surface of the stainless steel pipe in FIG. 1 (b) is dry-polished, and the surrounding portions 1 to 9 show surface defects in which the metal on the surface is partially peeled and covered with the base portion.
  • the surface defect means that the maximum length from one end portion of the portion bonded to the substrate to the other end portion of the peeling tip has a size of 5 ⁇ m or more.
  • the average number of surface defects measured is In the case of 6 or more, the surface defect in the present invention is not suppressed.
  • the ferritic stainless steel pipe of the present invention having the composition and having a pitting corrosion index (PI) of 30 or higher has a high pitting corrosion potential of 0.6 V or higher and excellent corrosion resistance.
  • the SUS304 can be suppressed early, whereas the SUS304 can be suppressed. Moreover, even if there is a colored oxide film or a surface defect generated by polishing, it is possible to suppress the generation of wrinkles.
  • the stainless steel pipe of the present invention further includes Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, Al: 0.01 to 0.5% by mass, It is preferable that 2 or more types are included. By containing a predetermined amount of Nb, Ti and / or Al, the corrosion resistance tends to be further improved.
  • C is an element useful for obtaining the strength of steel, but when it is contained in a large amount, it tends to lower the corrosion resistance.
  • the C content is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
  • Si is an element useful as a deoxidizer and heat source in the steelmaking process, but when it is contained in a large amount, it tends to harden the steel.
  • the content of Si is preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.
  • Mn is an element useful as deoxidation in the steel making process, but when it is contained in a large amount, it tends to form an austenite phase.
  • the content of Mn is preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.
  • Cr is a useful element for ensuring corrosion resistance, but if it is contained in a large amount, it tends to decrease not only the cost but also the workability.
  • the content of Cr is preferably 25.00 to 31.50% by mass, and more preferably 25.00 to 31.00% by mass.
  • Mo is an element useful for improving the corrosion resistance of stainless steel in the presence of Cr, but if it is contained in a large amount, it tends to reduce not only the cost but also the workability.
  • the Mo content is preferably 1.50 to 4.00 mass%, more preferably 1.80 to 3.80 mass%.
  • the PP tends to reduce corrosion resistance.
  • the P content is preferably 0.025% by mass or less, and more preferably 0.020% by mass or less.
  • S has a tendency to lower the corrosion resistance.
  • the content of S is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
  • Ni is preferable because it is effective in suppressing the progress of corrosion and effective in improving the toughness of the ferritic stainless steel pipe, but if it is too much, it will cause the generation of austenite phase and high cost.
  • the content of Ni is preferably 0.45% by mass or less, and more preferably 0.40% by mass or less.
  • the N content is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
  • Nb is preferable in that it has a strong affinity with C and N, and suppresses intergranular corrosion of ferritic stainless steel pipes, but a large amount of Nb tends to inhibit toughness.
  • the content of Nb is more preferably 0.1 to 0.9% by mass, and further preferably 0.1 to 0.8% by mass.
  • Ti has a strong affinity with C and N, and is preferable in terms of suppressing intergranular corrosion of ferritic stainless steel pipes. However, a large amount of Ti tends to deteriorate the surface quality of steel.
  • the Ti content is more preferably 0.05 to 0.25% by mass, even more preferably 0.05 to 0.2% by mass.
  • Al is an element effective for refining and casting as a deoxidizer, but if added in excess, it degrades the surface quality and lowers the weldability and low temperature toughness of the steel.
  • the content of Al is more preferably 0.01 to 0.45% by mass, and further preferably 0.01 to 0.4% by mass.
  • FIG. 2 and 3 are diagrams showing surface defects and pitting corrosion potential
  • FIG. 2 (a) is an enlarged photograph showing the surface defects of the stainless steel pipe
  • FIG. 3 (a) shows the surface defects of the stainless steel pipe being suppressed
  • FIG. 2 (b) and FIG. 3 (b) are graphs showing the measurement results of the pitting potential of the stainless steel pipe of FIG. 2 (a) and FIG. 3 (a).
  • 2 and 3 are stainless steel pipes having a pitting corrosion index (PI) of about 24 and lower than the pitting corrosion index (PI) of the present invention.
  • PI pitting corrosion index
  • FIG. 2A there is a surface defect
  • the pitting corrosion potential is a low value of about 0.3 V as shown in FIG. Further, although surface defects are suppressed in FIG.
  • the pitting corrosion potential is a low value of about 0.5 V as shown in FIG. 3B.
  • the stainless steel pipe of the present invention has a high pitting potential of 0.6 V or more and is excellent in corrosion resistance. For this reason, even if there is a colored oxide film or a surface defect, it is possible to suppress the progress of cracking and the deterioration of corrosion resistance.
  • the pitting potential is more preferably 0.65V or more, and further preferably 0.7V or more.
  • Method B is a pitting potential measurement method by a kinetic potential method in a 3.5% by mass sodium chloride aqueous solution.
  • the pH of the aqueous sodium chloride solution is 7 and the temperature is 30 ° C.
  • the potential sweep rate is 20 mV / min.
  • the surface roughness Ra of the stainless steel pipe surface in the present invention is preferably 0.1 to 1.0 ⁇ m, and more preferably 0.2 to 0.5 ⁇ m.
  • the surface roughness Ra is less than 0.1 ⁇ m, the antiglare property is inferior, and the polishing residue is hardly maintained, and the design property tends to be difficult to ensure.
  • the glossiness of the stainless steel tube surface in the present invention is preferably 60 ° glossiness of 75 or less. More preferably, it is 60 or less.
  • the glossiness is measured according to JIS Z 8741, and can be measured by, for example, a gloss meter. Specifically, a light beam with a specified opening angle is incident on the sample surface at the time of glossiness measurement, and a light beam with a specified opening angle reflected in the reflection direction is measured with a light receiver.
  • the 60 degree glossiness is the glossiness when the specified incident angle is 60 degrees. When the 60 degree glossiness is 75 or less, the surface of the stainless steel tube has preferable antiglare properties.
  • Polishing was carried out in a line in which four flap wheels (# 80, # 80, # 80, # 150) were lined up so as to polish the longitudinal direction of the steel pipe surface (giving polishing marks in the longitudinal direction), and dry polishing was performed. . “# 80” or the like indicates the mesh granularity.
  • the stainless steel pipe of Example 1 has polished eyes on the surface of the stainless steel pipe, there are as many as 15 surface defects (see FIG. 4), and a colored oxide film is also present on the surface.
  • the stainless steel pipe of Example 1 was suppressed in sprinkling even by the CCT test (see FIG. 6), and proved to be excellent in corrosion resistance.
  • pitting corrosion did not generate

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Abstract

A stainless steel pipe with excellent corrosion resistance is provided which does not rust prematurely even in waterfront environments affected by sea salt particles, and a manufacturing method thereof are provided. This stainless steel pipe with excellent corrosion resistance has longitudinal unidirectional polishing marks on the surface of the ferrite-base stainless steel pipe. The pitting potential is 0.6 V or greater, the 60° gloss is 75 or less, the composition is C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4.00 mass%, P: 0.030 mass% or less, S: 0.020 mass% or less, Ni: 0.50 mass% or less and N: 0.020 mass% or less, the remainder consisting of Fe and unavoidable impurities, and the pitting index (PI = Cr mass% + 3 Mo mass%) being 30 or greater.

Description

耐食性に優れたステンレス鋼管Stainless steel pipe with excellent corrosion resistance
　本発明は、耐食性に優れたステンレス鋼管に関する。 The present invention relates to a stainless steel pipe excellent in corrosion resistance.
　ステンレス鋼は、耐候性、加工性、溶接性等に優れることから、屋根材、壁材、建築部材等の建材用途で多用されている。また、ステンレス鋼管は、意匠性にも優れるため、表面研磨されて手摺、フェンス、パイプシャッター等の用途で使用されている。 Stainless steel is widely used in building materials such as roofing materials, wall materials, and building materials because it is excellent in weather resistance, workability, weldability, and the like. Moreover, since the stainless steel pipe is excellent in design, the surface is polished and used for applications such as handrails, fences, and pipe shutters.
　このステンレス鋼管の一般的、工業的な研磨は、まず研磨前素管の疵等の除去のために、疵取り研磨を行い、次に仕上げ研磨および光沢研磨等を行っている。この研磨作業における粗研磨、仕上げ研磨では、フラップホイールや研磨ベルト等を使用した乾式研磨が行われている。さらに、上記工程後、所望の表面を得るためにバフ研磨による湿式研磨を行う場合がある。 In general and industrial polishing of this stainless steel pipe, first, polishing removal is performed to remove wrinkles and the like of the raw pipe before polishing, and then final polishing and gloss polishing are performed. In rough polishing and finish polishing in this polishing operation, dry polishing using a flap wheel, a polishing belt, or the like is performed. Further, after the above process, wet polishing by buffing may be performed to obtain a desired surface.
　従来より、ステンレス鋼は、素材として優れた耐候性を有しているものの、研磨仕上げの状態によっては、本来素材がもつ耐候性を発揮せず、著しく発銹を生じる場合があり、ステンレス鋼の耐候性の安定性（信頼性）をなくす要因の一つとなっている。例えば、屋外の手摺等へ施工した後、１ヶ月程度の短期間で発銹する場合がある。 Conventionally, stainless steel has excellent weather resistance as a material, but depending on the state of the polished finish, it may not exhibit the weather resistance inherent to the material and may cause significant bruising. This is one of the factors that eliminate the stability (reliability) of weather resistance. For example, it may occur in a short period of about one month after construction on an outdoor handrail.
　発銹については、ステンレス鋼管の研磨後の表面に残存している酸化皮膜や研磨目が起点になっていると考えられている。残存する酸化皮膜とは、研磨時の発熱に起因して生成された皮膜であり、酸化皮膜の直下にはＣｒ欠乏層が形成されている。このため、酸化皮膜が残存していると、該酸化皮膜及びその直下のＣｒ欠乏層を起点として発銹が進行し、耐食性が劣化しやすくなる。また、研磨によってステンレス鋼管表面に刻まれた疵である研磨目についても、研磨目の凹部が深いほど、フラップホイール研磨等で生成した酸化皮膜がバフ研磨で除去され難くなって残存する可能性が高くなり、その研磨目の凹部が発銹起点になることから、発銹が進行し、耐食性が劣化しやすくなる。 銹 It is thought that the starting point is the oxide film and polishing marks remaining on the polished surface of the stainless steel pipe. The remaining oxide film is a film generated due to heat generation during polishing, and a Cr-deficient layer is formed immediately below the oxide film. For this reason, if the oxide film remains, the firing proceeds from the oxide film and the Cr-deficient layer immediately below the oxide film, and the corrosion resistance tends to deteriorate. In addition, with respect to the polishing marks which are ridges carved on the surface of the stainless steel pipe by polishing, the deeper the recesses in the polishing marks, the more likely the oxide film generated by the flap wheel polishing or the like is difficult to be removed by buffing and remain. Since the height becomes higher and the concave portion of the polished eye becomes the starting point of the cracking, the cracking proceeds and the corrosion resistance tends to deteriorate.
　特許文献１では、屋外環境においても短期間で発銹が生じることのない表面研磨状態にして、長期にわたって光沢性、耐候性を維持できるステンレス鋼管を提案している。 Patent Document 1 proposes a stainless steel pipe capable of maintaining glossiness and weather resistance over a long period of time in a surface-polished state that does not generate sprout even in an outdoor environment in a short period of time.
　特許文献１に記載の発明は、最終研磨後の表面粗さがＲｙ０．６μｍ以下で、残存する酸化皮膜の面積率が７．０％以下のステンレス鋼管である。すなわち、最終研磨後の表面粗さをＲｙ０．６μｍ以下とすることによって、研磨目の凹部に残存する酸化皮膜を少なくしようとしている。また、残存する酸化皮膜の面積率が７．０％以下とすることによって、該酸化皮膜及びその直下のＣｒ欠乏層を起点とした発銹の進行及び耐食性の劣化を抑制しようとしている。 The invention described in Patent Document 1 is a stainless steel pipe having a surface roughness after final polishing of Ry 0.6 μm or less and an area ratio of the remaining oxide film of 7.0% or less. That is, by setting the surface roughness after final polishing to Ry 0.6 μm or less, an attempt is made to reduce the oxide film remaining in the recesses of the polishing eyes. Further, by setting the area ratio of the remaining oxide film to 7.0% or less, it is intended to suppress the progress of cracking and deterioration of corrosion resistance starting from the oxide film and the Cr-deficient layer immediately below the oxide film.
　しかしながら、特許文献１の実施例を参照すると、耐候性合格品における残存酸化皮膜面積率は３．１～６．８％であり、酸化皮膜は残存している。このため、残存した酸化皮膜及びその直下のＣｒ欠乏層を起点として発銹が進行し耐食性が劣化し得るという問題は、依然として残っている。 However, referring to the example of Patent Document 1, the remaining oxide film area ratio in the weather-resistant product is 3.1 to 6.8%, and the oxide film remains. For this reason, there still remains a problem that the rusting can progress and the corrosion resistance can be deteriorated starting from the remaining oxide film and the Cr-deficient layer directly therebelow.
　特許文献２には、フッ酸及び硝酸の混合液にステンレス鋼管を浸漬し、ステンレス鋼表面の酸化スケールやスケール層直下のＣｒ欠乏層を溶解することが記載されている。 Patent Document 2 describes that a stainless steel tube is immersed in a mixed solution of hydrofluoric acid and nitric acid to dissolve the oxidized scale on the surface of the stainless steel and the Cr-deficient layer immediately below the scale layer.
特開２００３－５６７５５号公報JP 2003-56755 A 特開２０００－１７４６９号公報JP 2000-17469 A
　近年、都市再開発などに伴い建築需要が増加しており、ウォーターフロント環境における建築需要が増加している。ウォーターフロント環境においては、大気中に含まれるエアロゾル粒子の一種であって、海水に由来する塩分からなる微粒子である海塩粒子の影響を建築部材が受けやすいという問題がある。このため、より高い耐食性を有する建築部材のニーズが高まっている。特許文献１では、耐候性に優れるステンレス鋼管の鋼種の一つとして、ＳＵＳ３０４を挙げている。しかしながら、海塩粒子の影響を受けるウォーターフロント環境では、ＳＵＳ３０４は早期に発銹してしまい、メンテナンスが必要になるという問題がある。 In recent years, building demand has increased due to urban redevelopment, etc., and building demand in the waterfront environment has increased. In the waterfront environment, there is a problem that a building member is easily affected by sea salt particles, which are a kind of aerosol particles contained in the atmosphere, and are fine particles composed of salt derived from seawater. For this reason, the needs for building members having higher corrosion resistance are increasing. In patent document 1, SUS304 is mentioned as one of the steel types of the stainless steel pipe excellent in a weather resistance. However, in a waterfront environment that is affected by sea salt particles, SUS304 is spawned at an early stage, and there is a problem that maintenance is required.
　また、高い耐食性に加え、防眩性に優れた建築部材へのニーズがある。防眩性を付与する手段として、ステンレス鋼管表面の長手一方向を研磨する研磨手段があるが、長手一方向の研磨目を付与するために湿式研磨を行おうとすると、ステンレス鋼管が滑って安定して搬送できず、均一に研磨できないという問題がある。このため、乾式研磨を行わざるを得ず、研磨後のステンレス鋼管表面に酸化皮膜などが生じやすいという問題がある。特許文献２では、ステンレス鋼管を酸洗することによって、鋼管表面の酸化皮膜などを除去することを記載している。しかしながら、研磨後のステンレス鋼管を酸洗する処理工程は、製造コストの増加につながる。このため、酸洗処理をしなくても早期の発銹を抑制できるステンレス鋼管が求められている。 There is also a need for building materials with excellent anti-glare properties in addition to high corrosion resistance. As a means for imparting anti-glare properties, there is a polishing means for polishing one longitudinal direction of the surface of the stainless steel pipe. However, when wet polishing is performed to provide a polishing mark in one longitudinal direction, the stainless steel pipe slides and becomes stable. Cannot be transported and cannot be uniformly polished. For this reason, there is a problem that dry polishing must be performed, and an oxide film or the like is likely to be formed on the surface of the polished stainless steel pipe. Patent Document 2 describes that an oxide film or the like on the surface of a steel pipe is removed by pickling the stainless steel pipe. However, the process of pickling the polished stainless steel pipe leads to an increase in manufacturing cost. For this reason, there is a need for a stainless steel pipe that can suppress early eruption without the pickling treatment.
　本発明は、上述した課題を解決し、海塩粒子の影響を受けるウォーターフロント環境でも、早期に発銹することのない、耐食性に優れたステンレス鋼管を提供することを目的とする。 The object of the present invention is to solve the above-mentioned problems and to provide a stainless steel pipe excellent in corrosion resistance that does not start at an early stage even in a waterfront environment affected by sea salt particles.
　本発明者らは、特許文献１に記載のステンレス鋼管について検討を行った。特許文献１の実施例においては、フラップホイールによる乾式研磨を行っている。このため、乾式研磨であるフラップホイール研磨時にステンレス鋼管表面が高温となり酸化被膜が発生すること、乾式研磨による高い研削抵抗によって刻まれた疵である研磨目とともに、表面欠陥が生じていること、を突き止めた。ここでいう表面欠陥とは、鋼管表面を研磨する時に研磨材や研磨紙が連続して鋼管表面に接触し、表面の金属が部分的に剥がされ、素地部分に被さった「バリ」や「かぶさり」と呼称されている。表面欠陥は、短冊状や笹の葉状のように金属がめくれている部分を含み、素地に接着している部分における一方の端部から剥がれの先端における他方の端部までの最大長さが５μｍ以上の欠陥である。当該表面欠陥はステンレス鋼管の表面素地部分と微小な隙間を形成することから、腐食を生じやすく、鋼管の耐食性低下の要因となる。 The present inventors examined the stainless steel pipe described in Patent Document 1. In the Example of patent document 1, the dry grinding | polishing by a flap wheel is performed. For this reason, the surface of the stainless steel pipe is heated at the time of flap wheel polishing, which is dry polishing, and an oxide film is generated, and there are surface defects along with polishing marks that are engraved by high grinding resistance by dry polishing. I found it. The surface defects mentioned here are “burrs” or “covers” that are covered with the base material by polishing materials and paper continuously contacting the steel pipe surface when the steel pipe surface is polished, and the metal on the surface is partially peeled off. ". The surface defect includes a portion where the metal is turned up like a strip shape or a bamboo leaf shape, and the maximum length from one end portion of the portion adhered to the substrate to the other end portion of the peeling tip is 5 μm. It is the above defect. Since the surface defect forms a minute gap with the surface base portion of the stainless steel pipe, corrosion tends to occur, which causes a reduction in the corrosion resistance of the steel pipe.
　上述のように、着色を有する酸化皮膜や表面欠陥が存在すると、ステンレス鋼管は発銹しやすくなり、酸洗処理で酸化皮膜や表面欠陥を除去しようとすることが、通常の当業者が行う解決手段である。しかしながら、本発明者らは、着色を有する酸化皮膜や表面欠陥が存在し腐食しやすいステンレス鋼管であって、研磨後に酸洗処理をしなくとも、海塩粒子の影響を受けるウォーターフロント環境で早期に発銹することのない、耐食性に優れたステンレス鋼管を検討し、本発明を見出したものである。 As described above, when there is a colored oxide film or surface defect, the stainless steel pipe is likely to be sprinkled, and the ordinary person skilled in the art is able to remove the oxide film and surface defect by pickling treatment. Means. However, the present inventors are a stainless steel pipe that is easily corroded due to the presence of colored oxide films and surface defects, and is early in the waterfront environment that is affected by sea salt particles even if it is not pickled after polishing. The present invention has been found by investigating a stainless steel pipe excellent in corrosion resistance, which does not cause any problems.
　すなわち、本発明は、以下の（１）～（２）の耐食性に優れたステンレス鋼管を提供する。
（１）長手一方向の研磨目をフェライト系ステンレス鋼管の表面に有し、孔食電位が０．６Ｖ以上であり、６０度光沢度が７５以下であり、組成が、Ｃ：０．０２０質量％以下、Ｓｉ：０．４０質量％以下、Ｍｎ：０．４０質量％以下、Ｃｒ：２５．００～３２．００質量％、Ｍｏ：１．００～４．００質量％、Ｐ：０．０３０質量％以下、Ｓ：０．０２０質量％以下、Ｎｉ：０．５０質量％以下、Ｎ：０．０２０質量％以下を含み、残部がＦｅ及び不可避的不純物からなり、耐孔食指数（ＰＩ＝Ｃｒ質量％＋３Ｍｏ質量％）が３０以上である、耐食性に優れたステンレス鋼管。 That is, the present invention provides the following (1) to (2) stainless steel pipes having excellent corrosion resistance.
(1) A longitudinally unidirectional polished surface is provided on the surface of a ferritic stainless steel tube, the pitting corrosion potential is 0.6 V or more, the 60 ° glossiness is 75 or less, and the composition is C: 0.020 mass. %: Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00 to 32.00 mass%, Mo: 1.00 to 4.00 mass%, P: 0.030 Mass% or less, S: 0.020 mass% or less, Ni: 0.50 mass% or less, N: 0.020 mass% or less, with the balance being Fe and inevitable impurities, pitting corrosion resistance (PI = A stainless steel pipe excellent in corrosion resistance, wherein Cr mass% + 3Mo mass%) is 30 or more.
　本発明のステンレス鋼管は、長手一方向の研磨目をフェライト系ステンレス鋼管の表面に有することから意匠性に優れ、６０度光沢度が７５以下であるため防眩性にも優れる。また、着色を有する酸化皮膜がステンレス鋼管表面上に存在し、表面欠陥が存在していても、所定の組成を有し、耐孔食指数（ＰＩ）が３０以上と高いことから、酸化皮膜及びその直下のＣｒ欠乏層を起点とする発銹が抑制された、孔食電位が０．６Ｖ以上の耐食性に優れたステンレス鋼管である。 The stainless steel pipe of the present invention has excellent design properties because it has a longitudinally polished surface on the surface of the ferritic stainless steel pipe, and has an antiglare property because its 60 degree gloss is 75 or less. In addition, since the colored oxide film is present on the surface of the stainless steel pipe and has surface defects, it has a predetermined composition and has a high pitting corrosion index (PI) of 30 or more. It is a stainless steel pipe excellent in corrosion resistance having a pitting potential of 0.6 V or more, in which the cracking starting from the Cr-deficient layer immediately below is suppressed.
（２）さらに、Ｎｂ：０．１～１．０質量％、Ｔｉ：０．０５～０．３質量％、Ａｌ：０．０１～０．５質量％のうち、１種又は２種以上を含む、（１）に記載のステンレス鋼管。 (2) Further, one or more of Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, and Al: 0.01 to 0.5% by mass The stainless steel pipe according to (1).
　本発明によれば、海塩粒子の影響を受けるウォーターフロント環境でも、早期に発銹することのない、耐食性に優れたステンレス鋼管を提供することができる。 According to the present invention, it is possible to provide a stainless steel pipe excellent in corrosion resistance that does not start early even in a waterfront environment affected by sea salt particles.
ステンレス鋼管の表面を光学顕微鏡で拡大した写真であり、（ａ）表面欠陥が抑制された表面と、（ｂ）表面欠陥が生じた表面である。It is the photograph which expanded the surface of the stainless steel pipe with the optical microscope, (a) The surface where the surface defect was suppressed, and (b) The surface where the surface defect produced. （ａ）ステンレス鋼管の表面欠陥を示す拡大写真と、（ｂ）孔食電位の測定結果を示すグラフである。(A) An enlarged photograph showing a surface defect of a stainless steel pipe, and (b) a graph showing a measurement result of pitting potential. （ａ）ステンレス鋼管の表面欠陥が抑制された表面を示す拡大写真と、（ｂ）孔食電位の測定結果を示すグラフである。(A) The enlarged photograph which shows the surface where the surface defect of the stainless steel pipe was suppressed, and (b) The graph which shows the measurement result of a pitting corrosion potential. 本発明のステンレス鋼管の表面を光学顕微鏡で拡大した写真である。It is the photograph which expanded the surface of the stainless steel pipe of this invention with the optical microscope. 実施例１の孔食電位の測定結果を示すグラフである。3 is a graph showing the measurement result of pitting corrosion potential of Example 1. 実施例１のＣＣＴ試験後の外観を示す写真である。2 is a photograph showing an appearance of Example 1 after a CCT test.
　以下に本発明を実施するための形態について説明する。なお、本発明は当該実施形態によって限定的に解釈されるものではない。 Hereinafter, embodiments for carrying out the present invention will be described. The present invention is not construed as being limited by the embodiment.
（ステンレス鋼管）
　本発明のステンレス鋼管は、長手一方向の研磨目をフェライト系ステンレス鋼管の表面に有し、孔食電位が０．６Ｖ以上であり、６０度光沢度が７５以下であり、組成が、Ｃ：０．０２０質量％以下、Ｓｉ：０．４０質量％以下、Ｍｎ：０．４０質量％以下、Ｃｒ：２５．００～３２．００質量％、Ｍｏ：１．００～４．００質量％、Ｐ：０．０３０質量％以下、Ｓ：０．０２０質量％以下、Ｎｉ：０．５０質量％以下、Ｎ：０．０２０質量％以下を含み、残部がＦｅ及び不可避的不純物からなり、耐孔食指数（ＰＩ＝Ｃｒ質量％＋３Ｍｏ質量％）が３０以上である、耐食性に優れたステンレス鋼管である。 (Stainless steel pipe)
The stainless steel pipe of the present invention has a longitudinally polished surface on the surface of the ferritic stainless steel pipe, the pitting corrosion potential is 0.6 V or more, the 60 ° gloss is 75 or less, and the composition is C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4.00 mass%, P : 0.030% by mass or less, S: 0.020% by mass or less, Ni: 0.50% by mass or less, N: 0.020% by mass or less, with the balance being Fe and inevitable impurities, pitting corrosion resistance This is a stainless steel pipe having an index (PI = Cr mass% + 3Mo mass%) of 30 or more and excellent in corrosion resistance.
　本発明において、ステンレス鋼管は表面に凹凸や光沢を付与するために表面の研磨仕上げが行われたものである。これにより、ステンレス鋼管は研磨目を備え、意匠性や防眩性に優れたステンレス鋼管となる。研磨目とは、研磨によってステンレス鋼管表面に刻まれた疵である。本発明において、研磨目は長手一方向の研磨目を含む。長手一方向の研磨目を有するステンレス鋼管は、防眩性に優れる。長手一方向の研磨仕上げとしては、湿式研磨が困難であることから、従来よりフラップホイール等による乾式研磨が行われているが、乾式研磨を行うとステンレス鋼管の表面が高温となり、着色を有する酸化皮膜が形成される。また、研磨後の表面の研磨目は、研磨目の凹部が深いほど、フラップホイール研磨等で生成した酸化皮膜が残存する可能性が高くなり、その研磨目の凹部が発銹起点になって、発銹が進行し、耐食性が劣化しやすくなる。本発明において、着色を有する酸化皮膜が存在するとは、ステンレス鋼管の表面の任意の１０点を光学顕微鏡で４００倍の倍率で観察したときに、着色を有するシミ状物質である酸化皮膜が５０μｍ四方において面積比率で１０％以上存在している場合をいう。ここで、着色は特定に限定されず、ステンレス鋼管の金属素地や金属光沢と目視で区別できる色であればよい。着色として代表的な色は、茶褐色である。 In the present invention, the stainless steel pipe has a surface polished to give the surface unevenness and gloss. As a result, the stainless steel pipe has a polished eye and becomes a stainless steel pipe excellent in design and antiglare properties. Polishing eyes are ridges carved on the surface of a stainless steel pipe by polishing. In the present invention, the polishing eye includes a polishing eye in one longitudinal direction. A stainless steel pipe having a polishing mark in one longitudinal direction is excellent in antiglare property. As the polishing finish in one longitudinal direction, since wet polishing is difficult, dry polishing with a flap wheel or the like has been conventionally performed. However, when dry polishing is performed, the surface of the stainless steel tube becomes high temperature and oxidation with coloring is performed. A film is formed. In addition, the polishing surface of the surface after polishing, the deeper the recess of the polishing eye, the higher the possibility that the oxide film generated by flap wheel polishing or the like remains, the recess of the polishing eye becomes the starting point, Heating progresses and corrosion resistance tends to deteriorate. In the present invention, the presence of a colored oxide film means that when an arbitrary 10 points on the surface of the stainless steel tube are observed with an optical microscope at a magnification of 400 times, the colored oxide film is 50 μm square. In the case of 10% or more by area ratio. Here, the coloration is not limited to a specific color, and any color that can be visually distinguished from the metal base or metallic luster of the stainless steel pipe is acceptable. A typical color for coloring is brown.
　また、研磨仕上げとしてフラップホイール等による乾式研磨を行うと、ステンレス鋼管表面に研磨材や研磨紙が連続して接触し、表面の金属が部分的に剥がされ素地部分に被さったバリやかぶさりである表面欠陥が生じる。該表面欠陥は、ステンレス鋼管の表面素地部分と微小な隙間が生じることから、隙間腐食の要因となる。図１は、ステンレス鋼管の表面を光学顕微鏡で拡大した写真であり、（ａ）表面欠陥が抑制された表面と、（ｂ）表面欠陥が生じた表面である。図１（ａ）のステンレス鋼管表面は、研磨目を有しているが表面欠陥は抑制されている。一方、図１（ｂ）のステンレス鋼管表面を乾式研磨したものであり、囲み部分１～９は、表面の金属が部分的に剥がされ素地部分に被さった表面欠陥を示している。本発明において、表面欠陥は、素地に接着している部分における一方の端部から剥がれの先端における他方の端部までの最大長さが５μｍ以上の大きさを有するものをいう。また、光学顕微鏡を用いて研磨されたステンレス鋼管表面の任意の１０点における１００μｍ×１００μｍ（０．０１ｍｍ２）の範囲を２００倍に拡大し観察した場合に、測定した表面欠陥の数の平均が６個以上の場合を、本発明における表面欠陥が抑制されていない状態とする。なお、表面欠陥の最大の長さ部分に上限はないが、測定する際の基準として上限を５０μｍとしてもよい。 Also, when dry polishing with a flap wheel or the like is performed as a polishing finish, the surface of the stainless steel pipe is continuously contacted with the abrasive or abrasive paper, and the metal on the surface is partially peeled off and the burrs and fogging covered the substrate Surface defects occur. The surface defect causes crevice corrosion because a minute gap is formed between the surface base portion of the stainless steel pipe. FIG. 1 is a photograph of an enlarged surface of a stainless steel tube with an optical microscope, (a) a surface in which surface defects are suppressed and (b) a surface in which surface defects are generated. The surface of the stainless steel pipe in FIG. 1 (a) has polished eyes, but surface defects are suppressed. On the other hand, the surface of the stainless steel pipe in FIG. 1 (b) is dry-polished, and the surrounding portions 1 to 9 show surface defects in which the metal on the surface is partially peeled and covered with the base portion. In the present invention, the surface defect means that the maximum length from one end portion of the portion bonded to the substrate to the other end portion of the peeling tip has a size of 5 μm or more. Moreover, when the range of 100 μm × 100 μm (0.01 mm 2 ) at an arbitrary 10 points on the surface of the stainless steel tube polished using an optical microscope is magnified 200 times, the average number of surface defects measured is In the case of 6 or more, the surface defect in the present invention is not suppressed. In addition, although there is no upper limit in the maximum length part of a surface defect, it is good also considering an upper limit as 50 micrometers as a reference | standard at the time of measuring.
　当業者の技術常識からすると、発銹の進行や耐食性の劣化を抑制するためには、研磨されたステンレス鋼管表面に、上述した着色を有する酸化皮膜が存在せず、図１（ａ）のようにバリやかぶさりである表面欠陥も存在しないことが好ましいと考え、酸化皮膜等を除去するために酸洗処理を用いてきた。しかしながら、本発明のステンレス鋼管においては、着色を有する酸化皮膜が存在してもよく、表面欠陥が抑制されていなくてもよく、酸洗処理を行わずに、発銹の進行や耐食性の劣化を抑制できる鋼管であることを特徴とする。なお、表面欠陥及び酸化皮膜を抑制する手段として、ヘアライン加工した鋼板を鋼管とすることも考えられるが、鋼管としての強度が十分ではない場合がある。 From the technical common knowledge of those skilled in the art, in order to suppress the progress of rusting and the deterioration of corrosion resistance, there is no oxide film having the above-mentioned coloring on the polished stainless steel pipe surface, as shown in FIG. In addition, it is preferable that no surface defects such as burrs and fogging exist, and pickling treatment has been used to remove oxide films and the like. However, in the stainless steel pipe of the present invention, a colored oxide film may be present, surface defects may not be suppressed, and the progress of cracking and deterioration of corrosion resistance may be performed without performing a pickling treatment. It is a steel pipe that can be suppressed. In addition, as a means for suppressing surface defects and oxide films, it is conceivable to use a steel plate that has undergone hairline processing as a steel pipe, but the strength as a steel pipe may not be sufficient.
　本発明のステンレス鋼管は、組成が、Ｃ：０．０２０質量％以下、Ｓｉ：０．４０質量％以下、Ｍｎ：０．４０質量％以下、Ｃｒ：２５．００～３２．００質量％、Ｍｏ：１．００～４．００質量％、Ｐ：０．０３０質量％以下、Ｓ：０．０２０質量％以下、Ｎｉ：０．５０質量％以下、Ｎ：０．０２０質量％以下を含み、残部がＦｅ及び不可避的不純物からなり、耐孔食指数（ＰＩ＝Ｃｒ質量％＋３Ｍｏ質量％）が３０以上である。該組成を備え、耐孔食指数（ＰＩ）が３０以上の本発明のフェライト系ステンレス鋼管は、孔食電位が０．６Ｖ以上と高く、耐食性に優れることから、耐孔食指数が１９と低いＳＵＳ３０４が海塩粒子の影響を受けるウォーターフロント環境では早期に発銹するのに対して、発銹を抑制することができる。また、研磨によって生じた、着色を有する酸化皮膜や表面欠陥が存在していても、発銹を抑制することができる。 The stainless steel pipe of the present invention has a composition of C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00 to 32.00 mass%, Mo : 1.00 to 4.00 mass%, P: 0.030 mass% or less, S: 0.020 mass% or less, Ni: 0.50 mass% or less, N: 0.020 mass% or less, the balance Consists of Fe and inevitable impurities, and the pitting resistance index (PI = Cr mass% + 3Mo mass%) is 30 or more. The ferritic stainless steel pipe of the present invention having the composition and having a pitting corrosion index (PI) of 30 or higher has a high pitting corrosion potential of 0.6 V or higher and excellent corrosion resistance. In the waterfront environment in which SUS304 is affected by sea salt particles, the SUS304 can be suppressed early, whereas the SUS304 can be suppressed. Moreover, even if there is a colored oxide film or a surface defect generated by polishing, it is possible to suppress the generation of wrinkles.
　本発明のステンレス鋼管は、さらに、Ｎｂ：０．１～１．０質量％、Ｔｉ：０．０５～０．３質量％、Ａｌ：０．０１～０．５質量％のうち、１種又は２種以上を含むことが好ましい。Ｎｂ，Ｔｉ及び／又はＡｌを所定量含有することによって、耐食性がさらに向上する傾向にある。 The stainless steel pipe of the present invention further includes Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, Al: 0.01 to 0.5% by mass, It is preferable that 2 or more types are included. By containing a predetermined amount of Nb, Ti and / or Al, the corrosion resistance tends to be further improved.
　以下、ステンレス鋼管の成分限定理由について説明する。
　Ｃは、鋼の強度を得るために有用な元素であるが、多量に含むと耐食性を低下させる傾向にある。Ｃの含有量は、０．０１５質量％以下が好ましく、０．０１０質量％以下がより好ましい。 Hereinafter, the reasons for limiting the components of the stainless steel pipe will be described.
C is an element useful for obtaining the strength of steel, but when it is contained in a large amount, it tends to lower the corrosion resistance. The C content is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
　Ｓｉは、製鋼工程における脱酸剤及び熱源として有用な元素であるが、多量に含むと鋼を硬化させる傾向にある。Ｓｉの含有量は、０．３５質量％以下が好ましく、０．３０質量％以下がより好ましい。 Si is an element useful as a deoxidizer and heat source in the steelmaking process, but when it is contained in a large amount, it tends to harden the steel. The content of Si is preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.
　Ｍｎは、製鋼工程における脱酸として有用な元素であるが、多量に含むとオーステナイト相を形成する傾向にある。Ｍｎの含有量は、０．３５質量％以下が好ましく、０．３０質量％以下がより好ましい。 Mn is an element useful as deoxidation in the steel making process, but when it is contained in a large amount, it tends to form an austenite phase. The content of Mn is preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.
　Ｃｒは、耐食性を確保するために有用な元素であるが、多量に含むと高コストだけでなく加工性が低下する傾向にある。Ｃｒの含有量は、２５．００～３１．５０質量％が好ましく、２５．００～３１．００質量％がより好ましい。 Cr is a useful element for ensuring corrosion resistance, but if it is contained in a large amount, it tends to decrease not only the cost but also the workability. The content of Cr is preferably 25.00 to 31.50% by mass, and more preferably 25.00 to 31.00% by mass.
　Ｍｏは、Ｃｒの存在下でステンレス鋼の耐食性を向上させるために有用な元素であるが、多量に含むと高コストだけでなく加工性が低下する傾向にある。Ｍｏの含有量は、１．５０～４．００質量％が好ましく、１．８０～３．８０質量％がより好ましい。 Mo is an element useful for improving the corrosion resistance of stainless steel in the presence of Cr, but if it is contained in a large amount, it tends to reduce not only the cost but also the workability. The Mo content is preferably 1.50 to 4.00 mass%, more preferably 1.80 to 3.80 mass%.
　Ｐは、耐食性を低下させる傾向にある。Ｐの含有量は、０．０２５質量％以下が好ましく、０．０２０質量％以下がより好ましい。 ＰP tends to reduce corrosion resistance. The P content is preferably 0.025% by mass or less, and more preferably 0.020% by mass or less.
　Ｓは、耐食性を低下させる傾向にある。Ｓの含有量は、０．０１５質量％以下が好ましく、０．０１０質量％以下がより好ましい。 S has a tendency to lower the corrosion resistance. The content of S is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
　Ｎｉは、腐食の進行を抑制する効果やフェライト系ステンレス鋼管の靱性改善に有効である点で好ましいが、多すぎるとオーステナイト相の生成やコスト高の原因となる。Ｎｉの含有量は、０．４５質量％以下が好ましく、０．４０質量％以下がより好ましい。 Ni is preferable because it is effective in suppressing the progress of corrosion and effective in improving the toughness of the ferritic stainless steel pipe, but if it is too much, it will cause the generation of austenite phase and high cost. The content of Ni is preferably 0.45% by mass or less, and more preferably 0.40% by mass or less.
　Ｎは、Ｃと同様に多量に含むと耐食性を低下させる傾向にある。Ｎの含有量は、０．０１５質量％以下が好ましく、０．０１０質量％以下がより好ましい。 N, like C, tends to lower the corrosion resistance when included in a large amount. The N content is preferably 0.015% by mass or less, and more preferably 0.010% by mass or less.
　Ｎｂは、Ｃ、Ｎとの親和力が強くフェライト系ステンレス鋼管の粒界腐食を抑制する点で好ましいが、多量のＮｂ含有は靱性を阻害する傾向にある。Ｎｂの含有量は、０．１～０．９質量％がより好ましく、０．１～０．８質量％がさらに好ましい。 Nb is preferable in that it has a strong affinity with C and N, and suppresses intergranular corrosion of ferritic stainless steel pipes, but a large amount of Nb tends to inhibit toughness. The content of Nb is more preferably 0.1 to 0.9% by mass, and further preferably 0.1 to 0.8% by mass.
　Ｔｉは、Ｃ、Ｎとの親和力が強くフェライト系ステンレス鋼管の粒界腐食を抑制する点で好ましいが、多量のＴｉ含有は鋼の表面品質を低下させる傾向にある。Ｔｉの含有量は、０．０５～０．２５質量％がより好ましく、０．０５～０．２質量％がさらに好ましい。 Ti has a strong affinity with C and N, and is preferable in terms of suppressing intergranular corrosion of ferritic stainless steel pipes. However, a large amount of Ti tends to deteriorate the surface quality of steel. The Ti content is more preferably 0.05 to 0.25% by mass, even more preferably 0.05 to 0.2% by mass.
　Ａｌは、脱酸剤として精錬や鋳造に有効な元素であるが、過剰に添加すると表面品質を劣化させるとともに、鋼の溶接性や低温靭性を低下させる。Ａｌの含有量は、０．０１～０．４５質量％がより好ましく、０．０１～０．４質量％がさらに好ましい。 Al is an element effective for refining and casting as a deoxidizer, but if added in excess, it degrades the surface quality and lowers the weldability and low temperature toughness of the steel. The content of Al is more preferably 0.01 to 0.45% by mass, and further preferably 0.01 to 0.4% by mass.
　図２及び図３は、表面欠陥と孔食電位を示す図であり、図２（ａ）はステンレス鋼管の表面欠陥を示す拡大写真、図３（ａ）はステンレス鋼管の表面欠陥が抑制された表面を示す拡大写真であり、図２（ｂ）及び図３（ｂ）は、図２（ａ）及び図３（ａ）のステンレス鋼管の孔食電位の測定結果を示すグラフである。図２、図３のステンレス鋼管は、耐孔食指数（ＰＩ）が２４程度と、本発明の耐孔食指数（ＰＩ）よりも低いステンレス鋼管である。図２（ａ）では表面欠陥を有しており、その孔食電位は図２（ｂ）に示すように約０．３Ｖ程度と低い値である。また、図３（ａ）では表面欠陥が抑制されているが、その孔食電位は図３（ｂ）に示すように約０．５Ｖ程度と低い値である。これに対し、本発明のステンレス鋼管は、孔食電位が０．６Ｖ以上と高く、耐食性に優れる。このため、着色を有する酸化皮膜や表面欠陥が存在していても、発銹の進行や耐食性の劣化を抑制することができる。孔食電位はより好ましくは０．６５Ｖ以上であり、さらに好ましくは０．７Ｖ以上である。 2 and 3 are diagrams showing surface defects and pitting corrosion potential, FIG. 2 (a) is an enlarged photograph showing the surface defects of the stainless steel pipe, and FIG. 3 (a) shows the surface defects of the stainless steel pipe being suppressed. FIG. 2 (b) and FIG. 3 (b) are graphs showing the measurement results of the pitting potential of the stainless steel pipe of FIG. 2 (a) and FIG. 3 (a). 2 and 3 are stainless steel pipes having a pitting corrosion index (PI) of about 24 and lower than the pitting corrosion index (PI) of the present invention. In FIG. 2A, there is a surface defect, and the pitting corrosion potential is a low value of about 0.3 V as shown in FIG. Further, although surface defects are suppressed in FIG. 3A, the pitting corrosion potential is a low value of about 0.5 V as shown in FIG. 3B. On the other hand, the stainless steel pipe of the present invention has a high pitting potential of 0.6 V or more and is excellent in corrosion resistance. For this reason, even if there is a colored oxide film or a surface defect, it is possible to suppress the progress of cracking and the deterioration of corrosion resistance. The pitting potential is more preferably 0.65V or more, and further preferably 0.7V or more.
　ステンレス鋼の孔食電位測定方法は、ＪＩＳ　Ｇ　０５７７に準拠し、Ｂ法を用いる。Ｂ法は、３．５質量％塩化ナトリウム水溶液中における動電位法による孔食電位測定法である。該塩化ナトリウム水溶液のｐＨは７とし、温度は３０℃とする。また、電位掃引速度は２０ｍＶ／分とする。 The method for measuring the pitting corrosion potential of stainless steel conforms to JIS G 0577 and uses the B method. Method B is a pitting potential measurement method by a kinetic potential method in a 3.5% by mass sodium chloride aqueous solution. The pH of the aqueous sodium chloride solution is 7 and the temperature is 30 ° C. The potential sweep rate is 20 mV / min.
　本発明におけるステンレス鋼管表面の表面粗さＲａは、０．１～１．０μｍであることが好ましく、０．２～０．５μｍであることがより好ましい。表面粗さＲａが０．１μｍ未満であると、防眩性に劣り、さらに研磨目残りが維持されにくく意匠性を確保しにくい傾向にある。 The surface roughness Ra of the stainless steel pipe surface in the present invention is preferably 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm. When the surface roughness Ra is less than 0.1 μm, the antiglare property is inferior, and the polishing residue is hardly maintained, and the design property tends to be difficult to ensure.
　本発明におけるステンレス鋼管表面の光沢度は、６０度光沢度が７５以下であることが好ましい。より好ましくは６０以下である。光沢度は、ＪＩＳ　Ｚ　８７４１に準拠して測定されたものであり、例えば光沢計によって測定できる。具体的には、光沢度測定時に試料面に規定された入射角で規定の開き角の光束を入射し、反射方向に反射する規定の開き角の光束を受光器で測る。６０度光沢度とは、規定された入射角が６０度の場合の光沢度である。６０度光沢度が７５以下であることによって、ステンレス鋼管表面は好ましい防眩性を有する。 The glossiness of the stainless steel tube surface in the present invention is preferably 60 ° glossiness of 75 or less. More preferably, it is 60 or less. The glossiness is measured according to JIS Z 8741, and can be measured by, for example, a gloss meter. Specifically, a light beam with a specified opening angle is incident on the sample surface at the time of glossiness measurement, and a light beam with a specified opening angle reflected in the reflection direction is measured with a light receiver. The 60 degree glossiness is the glossiness when the specified incident angle is 60 degrees. When the 60 degree glossiness is 75 or less, the surface of the stainless steel tube has preferable antiglare properties.
　ステンレス鋼管の造管、形状修正を行い、装飾用研磨仕上げを行った。ステンレス鋼管は以下の２種類を用いた。組成（質量％）及び寸法は以下のとおりである。 ¡Stainless steel pipe making, shape modification, and polishing finish for decoration. The following two types of stainless steel pipes were used. The composition (mass%) and dimensions are as follows.
　鋼種１（ＳＵＳ４４７Ｊ１）　Ｃｒ：３０％、Ｍｏ：２％、Ｔｉ：０．１５％、Ｎｂ：０．１５％、Ａｌ：０．０９％、残部Ｆｅ
　鋼種２（ＳＵＳ４４５Ｊ１）　Ｃｒ：２２％、Ｍｏ：１．０５％、Ｔｉ：０．２％、Ｎｂ：０．２％、Ａｌ：０．０９％、残部Ｆｅ
　鋼種３（ＳＵＳ３０４）　Ｃｒ：１８％、Ｎｉ：８％、Ｓｉ：０．６％、Ｍｎ：０．８％、残部Ｆｅ
　寸法：直径３４ｍｍ×厚み１．５ｍｍ×長さ４０００ｍｍ。 Steel type 1 (SUS447J1) Cr: 30%, Mo: 2%, Ti: 0.15%, Nb: 0.15%, Al: 0.09%, balance Fe
Steel type 2 (SUS445J1) Cr: 22%, Mo: 1.05%, Ti: 0.2%, Nb: 0.2%, Al: 0.09%, balance Fe
Steel type 3 (SUS304) Cr: 18%, Ni: 8%, Si: 0.6%, Mn: 0.8%, balance Fe
Dimensions: Diameter 34 mm x thickness 1.5 mm x length 4000 mm.
　研磨は、４つのフラップホイール（＃８０、＃８０、＃８０、＃１５０）が鋼管表面の長手方向を研磨する（長手方向の研磨目付与）ように並んだラインで行い、乾式研磨を行った。なお、「＃８０」等はメッシュ粒度を示す。 Polishing was carried out in a line in which four flap wheels (# 80, # 80, # 80, # 150) were lined up so as to polish the longitudinal direction of the steel pipe surface (giving polishing marks in the longitudinal direction), and dry polishing was performed. . “# 80” or the like indicates the mesh granularity.
（研磨条件）
　ライン速度：１．８ｍ／ｍｉｎ
　管の回転数：３８０ｒｐｍ
　ホイール回転数：１５００ｒｐｍ
　ホイール直径：４００ｍｍ (Polishing conditions)
Line speed: 1.8m / min
Tube rotation speed: 380 rpm
Wheel rotation speed: 1500rpm
Wheel diameter: 400mm
　研磨を行った後、一部のステンレス鋼管のみ酸洗処理を表１のとおり行った（比較例３、参考例１）。実施例１～３、比較例１、２については酸洗処理を行わなかった。 After polishing, only some of the stainless steel pipes were pickled as shown in Table 1 (Comparative Example 3, Reference Example 1). Examples 1 to 3 and Comparative Examples 1 and 2 were not pickled.
（表面欠陥）
　光学顕微鏡を用いて、実施例１～３及び比較例１～３、参考例１のステンレス鋼管表面の１００μｍ×１００μｍの範囲を２００倍に拡大して観察し、表面欠陥の数を測定した（表１参照）。 (Surface defect)
Using an optical microscope, the range of 100 μm × 100 μm on the surface of the stainless steel pipes of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example 1 was magnified 200 times, and the number of surface defects was measured (Table). 1).
（酸化皮膜）
　実施例１～３及び比較例１～３、参考例１のステンレス鋼管の表面を光学顕微鏡で４００倍の倍率で観察し、茶褐色のシミ状物質である酸化皮膜が５０μｍ四方において面積比率でどの程度存在しているかを算出した。残存酸化皮膜の面積比率１０％未満である場合は、着色を有する酸化皮膜が存在しないとして「なし」と評価し、面積比率１０％以上の場合は着色を有する酸化皮膜が存在するとして「あり」と評価した（表１参照）。 (Oxide film)
The surface of each of the stainless steel pipes of Examples 1 to 3 and Comparative Examples 1 to 3 and Reference Example 1 was observed with an optical microscope at a magnification of 400 times. The existence was calculated. When the area ratio of the remaining oxide film is less than 10%, it is evaluated as “none” because there is no colored oxide film, and when the area ratio is 10% or more, “colored” is present as if there is a colored oxide film. (See Table 1).
（孔食電位）
　実施例１～３及び比較例１～３、参考例１のステンレス鋼管の孔食電位を測定した。具体的には、ＪＩＳ　Ｇ　０５７７に準拠し、Ｂ法（３．５％（質量分率）塩化ナトリウム水溶液試験方法）を用い、３．５質量％塩化ナトリウム水溶液中における動電位法を用いた。該塩化ナトリウム水溶液のｐＨは７とし、温度は３０℃とした。また、電位掃引速度は２０ｍＶ／分とした（表１参照）。 (Pitting corrosion potential)
The pitting corrosion potentials of the stainless steel pipes of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example 1 were measured. Specifically, in accordance with JIS G 0577, Method B (3.5% (mass fraction) sodium chloride aqueous solution test method) was used, and the kinetic potential method in a 3.5 mass% sodium chloride aqueous solution was used. The pH of the aqueous sodium chloride solution was 7, and the temperature was 30 ° C. The potential sweep rate was 20 mV / min (see Table 1).
（研磨目残り）
　研磨目残りを評価するために、実施例１～３及び比較例１～３、参考例１のステンレス鋼管の表面粗度Ｒａを測定し、Ｒａ≧０．１μｍの場合には、研磨目が残り意匠性に優れるため「○」と評価した。一方、Ｒａ＜０．１μｍの場合には、研磨目の残りが少なく意匠性に優れないため「×」と評価した。表面粗度Ｒａは、ＪＩＳ　Ｂ　０６０１に準拠し測定し、接触式の表面粗度計を用いた（表１参照）。 (Polishing residue)
In order to evaluate the polishing residue, the surface roughness Ra of the stainless steel pipes of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example 1 was measured. If Ra ≧ 0.1 μm, the polishing residue remained. Since it was excellent in design property, it evaluated as "(circle)". On the other hand, in the case of Ra <0.1 μm, since the remaining polishing eyes are few and the design property is not excellent, “x” was evaluated. The surface roughness Ra was measured according to JIS B 0601, and a contact-type surface roughness meter was used (see Table 1).
（光沢度）
　ＪＩＳ　Ｚ　８７４１に準拠して、実施例１～３及び比較例１～３、参考例１のステンレス鋼管表面の６０度光沢度を、光沢計を用いて測定した。６０度光沢度が７５以下の場合を「○」、７５より大きい場合を「×」と評価した（表１参照）。 (Glossiness)
Based on JIS Z 8741, the 60 degree glossiness of the stainless steel pipe surfaces of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example 1 was measured using a gloss meter. The case where the 60 ° glossiness was 75 or less was evaluated as “◯”, and the case where it was greater than 75 was evaluated as “X” (see Table 1).
（耐食性試験）
　実施例１～３及び比較例１～３、参考例１のステンレス鋼管について、以下の条件で耐食性試験（塩乾湿複合サイクル試験（ＣＣＴ試験））を行った。
条件：（１）塩水噴霧　（３５℃、５％ＮａＣｌ、１５分）
　　　（２）乾燥　　（６０℃、３０％ＲＨ、６０分）
　　　（３）湿潤　　（５０℃、９５％ＲＨ、３時間）
　上記条件（１）～（３）を１サイクルとして、３０サイクル繰り返した。
評価：試験後の発銹面積が、鋼管表面全体の５％以内のときに耐食性が良好として「○」と評価し、５％より大きい場合は耐食性が不良として「×」と評価した（表１参照）。 (Corrosion resistance test)
The stainless steel pipes of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Example 1 were subjected to a corrosion resistance test (salt-dry-wet combined cycle test (CCT test)) under the following conditions.
Conditions: (1) Salt spray (35 ° C., 5% NaCl, 15 minutes)
(2) Drying (60 ° C., 30% RH, 60 minutes)
(3) Wet (50 ° C., 95% RH, 3 hours)
The above conditions (1) to (3) were set as one cycle, and 30 cycles were repeated.
Evaluation: When the surface area after the test is within 5% of the entire surface of the steel pipe, the corrosion resistance is evaluated as “Good”, and when it is larger than 5%, the corrosion resistance is evaluated as “Poor” (Table 1). reference).
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示すとおり、実施例１のステンレス鋼管は、研磨目をステンレス鋼管の表面に有し、表面欠陥が１５個と多く（図４参照）、着色を有する酸化皮膜も表面上に存在しているが、電位１．０Ｖでも孔食は発生しなかった（図５参照）。また、実施例１のステンレス鋼管は、ＣＣＴ試験によっても発銹は抑制されており（図６参照）、耐食性に優れていることを実証した。また、実施例２及び３のステンレス鋼管についても、実施例１と同様に、電位１．０Ｖでも孔食は発生せず、ＣＣＴ試験によっても発銹は抑制された。 As shown in Table 1, the stainless steel pipe of Example 1 has polished eyes on the surface of the stainless steel pipe, there are as many as 15 surface defects (see FIG. 4), and a colored oxide film is also present on the surface. However, no pitting corrosion occurred even at a potential of 1.0 V (see FIG. 5). In addition, the stainless steel pipe of Example 1 was suppressed in sprinkling even by the CCT test (see FIG. 6), and proved to be excellent in corrosion resistance. Moreover, also about the stainless steel pipe | tube of Example 2 and 3, similarly to Example 1, pitting corrosion did not generate | occur | produce even in the electric potential of 1.0V, and the cracking was suppressed also by the CCT test.
　１～９・・・表面欠陥
　２０・・・実施例１のステンレス鋼管 1 to 9 Surface defects 20 Stainless steel pipe of Example 1

Claims (2)

  1. 　長手一方向の研磨目をフェライト系ステンレス鋼管の表面に有し、
    　孔食電位が０．６Ｖ以上であり、
    　６０度光沢度が７５以下であり、
    　組成が、Ｃ：０．０２０質量％以下、Ｓｉ：０．４０質量％以下、Ｍｎ：０．４０質量％以下、Ｃｒ：２５．００～３２．００質量％、Ｍｏ：１．００～４．００質量％、Ｐ：０．０３０質量％以下、Ｓ：０．０２０質量％以下、Ｎｉ：０．５０質量％以下、Ｎ：０．０２０質量％以下を含み、残部がＦｅ及び不可避的不純物からなり、耐孔食指数（ＰＩ＝Ｃｒ質量％＋３Ｍｏ質量％）が３０以上である、耐食性に優れたステンレス鋼管。     Having a longitudinally polished surface on the surface of a ferritic stainless steel pipe,
    The pitting potential is 0.6V or more,
    60 degree gloss is 75 or less,
    Composition: C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4. 00% by mass, P: 0.030% by mass or less, S: 0.020% by mass or less, Ni: 0.50% by mass or less, N: 0.020% by mass or less, and the balance from Fe and inevitable impurities A stainless steel pipe excellent in corrosion resistance having a pitting corrosion index (PI = Cr mass% + 3Mo mass%) of 30 or more.
  2. 　さらに、Ｎｂ：０．１～１．０質量％、Ｔｉ：０．０５～０．３質量％、Ａｌ：０．０１～０．５質量％のうち、１種又は２種以上を含む、請求項１に記載のステンレス鋼管。 Further, one or more of Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, and Al: 0.01 to 0.5% by mass are included. Item 2. The stainless steel pipe according to Item 1.
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JPH05163557A (en) * 1991-12-13 1993-06-29 Kawasaki Steel Corp External stainless steel sheet provided with antidazzle characteristic and corrosion resistance
JPH06346196A (en) * 1993-06-14 1994-12-20 Nisshin Steel Co Ltd Highly corrosion resistant ferritic stainless steel excellent in antidazzle characteristic
JPH07113142A (en) * 1993-10-15 1995-05-02 Kawasaki Steel Corp Stainless steel plate for architectural material, excellent in contamination resistance and corrosion resistance
JPH1094968A (en) * 1996-09-24 1998-04-14 Nisshin Steel Co Ltd Grinding wheel for polishing high chromium ferrite stainess steel
JP2003027191A (en) * 2001-07-23 2003-01-29 Nisshin Steel Co Ltd Decorative tube made of ferrite stainless steel having excellent weather resistance and bending workability

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JPH05163577A (en) * 1991-12-11 1993-06-29 Hitachi Chem Co Ltd Catalytic liquid for electroless plating and production thereof

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Publication number Priority date Publication date Assignee Title
JPH05163557A (en) * 1991-12-13 1993-06-29 Kawasaki Steel Corp External stainless steel sheet provided with antidazzle characteristic and corrosion resistance
JPH06346196A (en) * 1993-06-14 1994-12-20 Nisshin Steel Co Ltd Highly corrosion resistant ferritic stainless steel excellent in antidazzle characteristic
JPH07113142A (en) * 1993-10-15 1995-05-02 Kawasaki Steel Corp Stainless steel plate for architectural material, excellent in contamination resistance and corrosion resistance
JPH1094968A (en) * 1996-09-24 1998-04-14 Nisshin Steel Co Ltd Grinding wheel for polishing high chromium ferrite stainess steel
JP2003027191A (en) * 2001-07-23 2003-01-29 Nisshin Steel Co Ltd Decorative tube made of ferrite stainless steel having excellent weather resistance and bending workability

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