JP4190993B2 - Ferritic stainless steel sheet with improved crevice corrosion resistance - Google Patents
Ferritic stainless steel sheet with improved crevice corrosion resistance Download PDFInfo
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- 230000007797 corrosion Effects 0.000 title claims description 56
- 238000005260 corrosion Methods 0.000 title claims description 56
- 229910001220 stainless steel Inorganic materials 0.000 title claims description 24
- 229910000831 Steel Inorganic materials 0.000 claims description 16
- 229910052804 chromium Inorganic materials 0.000 claims description 16
- 239000010959 steel Substances 0.000 claims description 16
- 229910052759 nickel Inorganic materials 0.000 claims description 14
- 229910052802 copper Inorganic materials 0.000 claims description 9
- 229910000859 α-Fe Inorganic materials 0.000 claims description 8
- 239000011159 matrix material Substances 0.000 claims description 5
- 239000010935 stainless steel Substances 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 239000002436 steel type Substances 0.000 description 15
- 229910052750 molybdenum Inorganic materials 0.000 description 13
- 230000000694 effects Effects 0.000 description 11
- 150000003839 salts Chemical class 0.000 description 7
- 230000009471 action Effects 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000003628 erosive effect Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 230000000149 penetrating effect Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910000967 As alloy Inorganic materials 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 210000005036 nerve Anatomy 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
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- 230000001629 suppression Effects 0.000 description 1
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Description
本発明は、耐隙間腐食性を改善したフェライト系ステンレス鋼板に関する。 The present invention relates to a ferritic stainless steel sheet having improved crevice corrosion resistance.
フェライト系ステンレス鋼は、オーステナイト系ステンレス鋼に比べ応力腐食割れの問題が少なく、安価であることから、各種分野で広範に使用されている。しかしながらフェライト系ステンレス鋼は、オーステナイト系よりも隙間腐食の懸念が大きいという欠点を有している。このため、より信頼性の高いフェライト系ステンレス鋼を提供するためには、耐隙間腐食性の改善が望まれる。 Ferritic stainless steel is widely used in various fields because it has fewer problems of stress corrosion cracking and is less expensive than austenitic stainless steel. However, ferritic stainless steel has the disadvantage that there is greater concern about crevice corrosion than austenitic. For this reason, in order to provide a more reliable ferritic stainless steel, improvement in crevice corrosion resistance is desired.
下記特許文献１には、耐隙間腐食性の改善を図ったフェライト系ステンレス鋼が記載されている。これは、０.０４％を超えるＰと、５〜５０ｐｐｍのＣaを複合添加することにより耐隙間腐食性を向上させたものである。また、Ｎi，Ｃo，Ｃu等の元素も耐隙間腐食性向上に有効であるという。 Patent Document 1 listed below describes ferritic stainless steel with improved crevice corrosion resistance. This is an improvement of crevice corrosion resistance by adding P in excess of 0.04% and 5 to 50 ppm of Ca. Ni, Co, Cu and other elements are also effective in improving crevice corrosion resistance.
フェライト系ステンレス鋼にはＳＵＳ４３０やＳＵＳ４４４をはじめとする多くの規格鋼種があり、要求される耐食性レベルに応じてＣr含有量が規定され、高耐食用途ではＭo等の耐食性向上元素が添加される。Ｃrの増量やＭo添加による基本的耐食性レベルの向上に伴って一般的には耐隙間腐食性も向上する。しかし、耐隙間腐食性の改善目的のみでＣrやＭoを多量に含む高耐食鋼種を選択せざるを得ないのは不合理である。 Ferritic stainless steel includes many standard steel types such as SUS430 and SUS444, and the Cr content is defined according to the required corrosion resistance level. In high corrosion resistance applications, elements such as Mo are added. As the basic corrosion resistance level is increased by increasing the amount of Cr or adding Mo, generally the crevice corrosion resistance is also improved. However, it is unreasonable to select a high corrosion resistant steel type containing a large amount of Cr and Mo only for the purpose of improving crevice corrosion resistance.
また、特許文献１のフェライト系ステンレス鋼はＰを添加しているため、製造性があまり良好ではない。しかも、Ｃa含有量を微量範囲でコントロールする必要があり、製鋼での作業負担の増大を招く。このため、汎用のフェライト系鋼種と比べ製造コストが高くなり、本来安価であることを長所とするフェライト系鋼のメリットを十分に享受できない。 Moreover, since the ferritic stainless steel of patent document 1 has added P, manufacturability is not so good. In addition, it is necessary to control the Ca content within a very small range, which leads to an increase in work load in steelmaking. For this reason, compared with a general-purpose ferritic steel type, manufacturing cost becomes high and the merit of the ferritic steel which has the advantage that it is inexpensive originally cannot fully be enjoyed.
本発明は、鋼にとって有害要因の多いＰや、鋼中への歩留りコントロールに神経を使うＣa等の特殊元素を添加せず、一般的な汎用フェライト系ステンレス鋼と同等の工程負荷で容易に製造できる成分組成範囲において、ＣrやＭoの多量添加を必須とすることなく、耐隙間腐食性を顕著に改善したフェライト系ステンレス鋼板を提供することを目的とする。 The present invention does not add special elements such as P, which has many harmful factors for steel, and Ca, which uses nerves to control yield in steel, and is easily manufactured with the same process load as general-purpose ferritic stainless steel. It is an object of the present invention to provide a ferritic stainless steel sheet having markedly improved crevice corrosion resistance without requiring a large amount of Cr or Mo to be added in the component composition range.
既に多くの規格鋼種が存在する中、発明者らはフェライト系ステンレス鋼の耐隙間腐食性に及ぼす合金組成の影響を詳細に研究してきた。その結果、約１６質量％以上のＣrと、１質量％程度のＮiを複合添加したとき、耐隙間腐食性が顕著に向上することを発見した。Ｎiはオーステナイト形成元素であり、フェライト系鋼種では通常、添加量が制限される。しかし、合金成分全体のバランスを調整することにより、Ｎiを添加した場合でも十分にフェライト単相組織が得られることが確認された。また、ＣuやＭoを複合添加すると一層大きな耐隙間腐食性向上効果が得られた。さらに、他の合金成分の含有量を調整したり、Ｂを添加したりすることで、製造性や加工性レベルも従来鋼と同等以上に確保できることがわかった。本発明はこれらの知見に基づいて完成したものである。 While many standard steel grades already exist, the inventors have studied in detail the influence of the alloy composition on the crevice corrosion resistance of ferritic stainless steel. As a result, it was found that the crevice corrosion resistance is remarkably improved when about 16% by mass or more of Cr and about 1% by mass of Ni are added in combination. Ni is an austenite forming element, and the addition amount is usually limited in ferritic steel types. However, it was confirmed that by adjusting the balance of the entire alloy component, a ferrite single phase structure can be sufficiently obtained even when Ni is added. Further, when Cu or Mo was added in combination, a greater effect of improving crevice corrosion resistance was obtained. Further, it has been found that by adjusting the content of other alloy components or adding B, the manufacturability and workability level can be ensured to be equal to or higher than that of the conventional steel. The present invention has been completed based on these findings.
すなわち、上記目的は、Ｃ：０.０１５％以下，Ｓi：１.０％以下，Ｃr：１６.０〜２５.０％，Ｎi：０.６超え〜３.０％，Ｎ：０.０２％以下，Ｍo：３.０％以下，Ｃu：２.０％以下，Ｍn：２.０％以下，Ｔi：０.５％以下，Ｎb：０.５％以下，Ｂ：０.０１％以下を含有し、Ｐ：０.０４％以下，Ｓ：０.０２％以下に制限され、残部がＦeおよび不可避的不純物からなる鋼組成を有し、マトリクスがフェライト単相組織を呈する耐隙間腐食性を改善したステンレス鋼板によって達成される。 That is, the above purpose is as follows: C: 0.015% or less, Si: 1.0% or less, Cr: 16.0 to 25.0%, Ni: more than 0.6 to 3.0%, N: 0.02 %, Mo: 3.0% or less, Cu: 2.0% or less, Mn: 2.0% or less, Ti: 0.5% or less, Nb: 0.5% or less, B: 0.01% or less And P: 0.04% or less, S: 0.02% or less, the balance is a steel composition consisting of Fe and unavoidable impurities , and the matrix has a ferrite single-phase structure and is resistant to crevice corrosion. Achieved by improved stainless steel sheet.
本発明によれば、ＣrやＭoの多量添加の手法を採ることなく、且つ有害要因の多いＰや製鋼作業を繁雑にするＣaなどを添加することなく、フェライト系ステンレス鋼板の耐隙間腐食性を顕著に改善することができる。この鋼板は、一般的な汎用フェライト系ステンレス鋼と同等の工程負荷で容易に製造でき、Ｃr，Ｍo含有量が同レベルの既存鋼種と比べて製造コストの上昇はほとんどない。耐隙間腐食性以外の諸特性も十分に確保できる。したがって本発明は、隙間腐食の懸念があるためフェライト系鋼種を採用し難かった種々の用途において、当該鋼種の適用を可能にし、フェライト系ステンレス鋼板の用途拡大に寄与するものである。 According to the present invention, the crevice corrosion resistance of a ferritic stainless steel sheet can be improved without using a large amount of Cr or Mo addition method and without adding P, which has many harmful factors, or Ca, which complicates steelmaking operations. It can be remarkably improved. This steel sheet can be easily manufactured under the same process load as a general-purpose ferritic stainless steel, and there is almost no increase in manufacturing cost compared to existing steel types having the same Cr and Mo contents. Various characteristics other than crevice corrosion resistance can be sufficiently secured. Therefore, the present invention makes it possible to apply the steel type in various applications where it is difficult to adopt the ferritic steel type due to the concern of crevice corrosion, and contributes to the expansion of the use of the ferritic stainless steel sheet.
隙間腐食は、隙間内部で一旦腐食が発生すると隙間内部のpＨが２〜３あるいはそれ以下に低下し、さらに塩が濃縮することから、他の部分よりも著しく速く腐食が成長する現象である。Ｃr含有量を増大すること、あるいはさらにＭoを添加することにより、一般的には不動態皮膜が強化され、基本的な耐食性レベルは向上する。しかし、隙間内部は前記のように非常に厳しい腐食環境となるため、余程強固な不動態皮膜が形成されない限り、隙間内部での腐食の促進を阻止することは困難であると考えられる。 Crevice corrosion is a phenomenon in which once corrosion occurs in the gap, the pH inside the gap decreases to 2 to 3 or less, and the salt concentrates, so that the corrosion grows significantly faster than other parts. Increasing the Cr content or further adding Mo generally enhances the passive film and improves the basic corrosion resistance level. However, since the inside of the gap becomes a very severe corrosive environment as described above, it is considered difficult to prevent the promotion of corrosion inside the gap unless a very strong passive film is formed.
ところが発明者らの研究の結果、Ｃrを１６質量％以上含有させたフェライト系ステンレス鋼板において、Ｎiを０.６超え〜３.０質量％複合添加すると、隙間腐食に対する抵抗力が顕著に向上することがわかった。そのメカニズムは未解明であるが、種々のアノード分極曲線の解析によると、Ｎiは隙間腐食環境において、Ｃrとの相互作用により、極大電流密度を顕著に低減する作用を発揮するのではないかと考えられる。 However, as a result of the inventors' research, in a ferritic stainless steel sheet containing 16 mass% or more of Cr, when Ni is added in an amount of more than 0.6 to 3.0 mass%, the resistance to crevice corrosion is significantly improved. I understood it. Although the mechanism is not yet elucidated, according to the analysis of various anodic polarization curves, Ni is considered to exhibit the effect of significantly reducing the maximum current density by interaction with Cr in the crevice corrosion environment. It is done.
本発明では、Ｃr含有量は１６.０〜２５.０質量％に規定される。１６.０質量％未満では不動態皮膜の強化が基本的に不十分であると考えられ、Ｎiや、Ｍo，Ｃuを添加しても耐隙間腐食性の改善効果は小さい。一方、２５.０質量％を超えると素材の加工性、特に延性が低下し、汎用性の高いステンレス鋼板を得るのが難しくなる。 In this invention, Cr content is prescribed | regulated to 16.0-25.0 mass%. If the amount is less than 16.0% by mass, it is considered that the passive film is basically insufficiently strengthened. Even if Ni, Mo, or Cu is added, the effect of improving the crevice corrosion resistance is small. On the other hand, if it exceeds 25.0% by mass, the workability of the material, particularly the ductility, is lowered, and it becomes difficult to obtain a highly versatile stainless steel plate.
Ｎi含有量は０.６超え〜３.０質量％に規定される。０.６質量％を超えるＮi添加により耐隙間腐食性の改善効果が顕在化する。概ね１質量％以下の領域ではＮi含有量は多いほど良い。すなわち、０.７質量％以上とすることが好ましく、０.８質量％以上が一層好ましく、０.９質量％以上がさらに好ましい。Ｎi含有量の上限は、フェライト単相組織が得られる限り、耐隙間腐食性の観点からは特に制限しなくてもよいと考えられる。しかし、加工性と経済性を考慮すると、Ｎiは３.０質量％以下の範囲で添加することが望ましい。 The Ni content is specified to be more than 0.6 to 3.0% by mass. The effect of improving crevice corrosion resistance becomes obvious by adding Ni exceeding 0.6 mass%. In a region of approximately 1% by mass or less, the higher the Ni content, the better. That is, it is preferably 0.7% by mass or more, more preferably 0.8% by mass or more, and further preferably 0.9% by mass or more. The upper limit of the Ni content is considered to be not particularly limited from the viewpoint of crevice corrosion resistance as long as a ferrite single phase structure is obtained. However, considering workability and economy, it is desirable to add Ni in a range of 3.0% by mass or less.
Ｍoは、Ｃrとともに添加することで不動態皮膜を強化することが古くから知られている。しかし、Ｃr含有量が非常に高い高耐食鋼種でなければ、その不動態皮膜の強化による耐隙間腐食性の改善効果は十分に発揮されない。ところが、ＣrとＮiとＭoを複合添加する場合は、Ｃr含有量が概ね１６質量％以上の範囲で耐隙間腐食性の顕著な向上効果が見られる。つまりＭoは、ＣrとＮiの複合添加によってもたらされる耐隙間腐食性の向上作用を増長させる作用を有する。 Mo has long been known to strengthen the passive film by adding it together with Cr. However, unless the Cr content is a very high corrosion resistant steel, the effect of improving the crevice corrosion resistance due to the strengthening of the passive film is not sufficiently exhibited. However, when Cr, Ni, and Mo are added in combination, a remarkable improvement effect of crevice corrosion resistance is observed when the Cr content is approximately 16% by mass or more. That is, Mo has the effect of increasing the crevice corrosion resistance improving effect brought about by the combined addition of Cr and Ni.
Ｃuは、Ｎiと同様にオーステナイト形成元素であるが、隙間腐食に対する作用はＮiと異なる。Ｎiの場合、Ｃrとの複合添加で耐隙間腐食性は向上する（前述）。一方Ｃuの場合、単にＣrと複合添加しただけでは耐隙間腐食性の改善効果はほとんど認められない。しかしながら、ＣrとＮiとＣuを複合添加したときには、ＣrおよびＮiの含有量レベルが同等でＣuを含有しない場合に比べ、耐隙間腐食性は明らかに向上するのである。そのメカニズムも未解明であるが、恐らくＣuを添加すると、隙間腐食環境での極大電流密度自体はほとんど変化しないものの、電位を貴化する作用が起こり、ＮiとともにＣuを添加したときにはＣuによる電位貴化作用がＮiによる極大電流密度の低減作用と相俟って、結果的に隙間腐食の抑制効果を高めるのではないかと推察される。 Cu is an austenite-forming element like Ni, but its action on crevice corrosion is different from Ni. In the case of Ni, the crevice corrosion resistance is improved by the combined addition with Cr (described above). On the other hand, in the case of Cu, the effect of improving the crevice corrosion resistance is hardly recognized by simply adding it in combination with Cr. However, when Cr, Ni and Cu are added in combination, the crevice corrosion resistance is clearly improved as compared with the case where the Cr and Ni content levels are the same and Cu is not contained. The mechanism is still unclear, but perhaps when Cu is added, the maximum current density itself in the crevice corrosion environment hardly changes, but the action of making the potential noble occurs, and when Cu is added together with Ni, the potential due to Cu is nominated. It is presumed that the crystallization action, combined with the action of reducing the maximum current density by Ni, results in an increase in the crevice corrosion suppression effect.
このように、ＭoとＣuはいずれも、ＣrとＮiを含有するフェライト系鋼に添加したときに耐隙間腐食性を効果的に向上させる。このため、本発明ではＭoおよびＣuを添加する。Ｍoは、０.４質量％以上とすることが特に効果的である。ただし、多量のＭo添加は靱性の劣化やコスト増を招くので、Ｍo含有量の上限は３.０質量％に制限される。また、Ｃuは０.５質量％以上とすることが特に効果的である。ただし、多量のＣu添加は熱間加工性の劣化等を招くので、Ｃu含有量の上限は２.０質量％に制限される。 Thus, both Mo and Cu effectively improve crevice corrosion resistance when added to ferritic steel containing Cr and Ni. For this reason, Mo and Cu are added in the present invention. M o is particularly effective to 0.4 mass% or more. However, the addition of a large amount of Mo causes toughness deterioration and cost increase, so the upper limit of the Mo content is limited to 3.0% by mass. It is particularly effective to set Cu to 0.5% by mass or more. However, addition of a large amount of Cu causes deterioration of hot workability and the like, so the upper limit of the Cu content is limited to 2.0% by mass.
Ｃr，Ｎi，Ｍo，Ｃu以外の合金元素としては、耐食性，加工性，製造性等を阻害しない範囲で、通常のフェライト系ステンレス鋼に含まれる種々のものを含有することができる。例示すると以下のとおりである。 As alloy elements other than Cr, Ni, Mo, and Cu, various elements included in ordinary ferritic stainless steel can be contained within a range that does not impair corrosion resistance, workability, manufacturability, and the like. Examples are as follows.
Ｐは、熱間加工性の劣化を招くなど、鋼にとって有害要因の多い不純物元素である。また、本発明によれば特許文献１のようにＰ添加に頼らなくても対隙間腐食性を改善できる。本発明では、Ｐ含有量は０.０４質量％以下に制限される。 P is an impurity element having many harmful factors for steel, such as causing deterioration of hot workability. Further, according to the present invention, the corrosion resistance against crevice can be improved without relying on the addition of P as in Patent Document 1. In the present invention, the P content is limited to 0.04% by mass or less.
Ｓは、機械的性質や溶接性に有害な不純物であり、また、ＭnＳを形成し耐候性，耐発銹性，耐隙間腐食性を低下させる。本発明では、Ｓ含有量は０.０２質量％以下に制限される。 S is an impurity that is harmful to mechanical properties and weldability, and forms MnS to reduce weather resistance, rust resistance, and crevice corrosion resistance. In the present invention, the S content is limited to 0.02 mass% or less.
Ｃは、炭化物を形成し、それが最終焼鈍で再結晶核として働き、再結晶フェライト層の微細化と結晶方位のランダム化に有効となる。しかし、Ｃは冷延焼鈍後の強度を上昇させる元素であり、含有量が多くなると靱性低下を招くようになる。本発明では、Ｃは０.０１５質量％以下の範囲で含有させる。 C forms a carbide, which acts as a recrystallization nucleus in the final annealing, and is effective for refining the recrystallized ferrite layer and randomizing the crystal orientation. However, C is an element that increases the strength after cold rolling annealing, and as the content increases, the toughness decreases. In the present invention, C is contained in the range of 0.015% by mass or less.
Ｓiは、脱酸剤として添加される。耐酸化性や清浄度の向上に有効であり、また耐候性，耐発銹性の向上にも効果がある。しかし、含有量が多いと固溶強化により伸びと靱性の低下を招くので、Ｓiは１.０質量％以下の範囲で含有させる。 Si is added as a deoxidizer. It is effective in improving oxidation resistance and cleanliness, and is also effective in improving weather resistance and weathering resistance. However, since lowering the elongation and toughness by solid solution strengthening and high content, Si is Ru is contained in a range of 1.0 mass% or less.
Ｎは、窒化物を形成し、それが前記炭化物と同様に再結晶フェライト層の微細化と結晶方位のランダム化に有効に作用する。また、Ｎ含有量が多いと、Ｃと同様、靱性低下を招くようになる。本発明では、Ｎは０.０２質量％以下の範囲で含有させる。 N forms nitrides, which, like the carbides, effectively act to refine the recrystallized ferrite layer and randomize the crystal orientation. Moreover, when there is much N content, like C, toughness fall will be caused. In the present invention, N is the Ru is contained in an amount of 0.02 wt% or less.
Ｍnは、脱酸剤として有効である。しかし、高温域でオーステナイト相の生成を促進し、高温熱処理の冷却時にマルテンサイト相の生成を招く恐れがある。また、多量のＭn含有は熱間加工性の劣化を招く。このため、Ｍnの添加は２.０質量％以下の範囲で行う。 Mn is effective as a deoxidizer. However, the austenite phase may be generated at a high temperature range, and the martensite phase may be generated when the high temperature heat treatment is cooled. Also, a large amount of Mn content causes deterioration of hot workability. Therefore, addition of Mn is intends rows in the range of 2.0 wt% or less.
Ｔiは、Ｃ，Ｎを固定し、加工性および耐食性を向上させる。しかし、多量の添加は鋼材コストを増大させ、またＴi系介在物が表面欠陥の原因になる。このため、Ｔiの添加は０.５質量％以下の範囲で行う。Ｔiの特に好ましい含有量は０.０５〜０.５質量％である。 Ti fixes C and N and improves workability and corrosion resistance. However, a large amount of addition increases the steel material cost, and Ti inclusions cause surface defects. Therefore, the addition of T i is intends row in a range of 0.5 mass%. A particularly preferable content of Ti is 0.05 to 0.5% by mass.
Ｎbは、Ｃ，Ｎを固定し、耐衝撃特性や二次加工性の向上に有効である。また、Ｂ添加の場合に生じるＣr2Ｂの析出を抑制する作用を呈する。しかし、多量のＮb添加は材料の硬化を招き、加工性に悪影響を及ぼす。また再結晶温度の上昇を招く。このため、Ｎbの添加は０.５質量％以下の範囲で行う。Ｎbの特に好ましい含有量は０.１〜０.５質量％である。 Nb fixes C and N and is effective in improving impact resistance and secondary workability. Further, it exhibits the action of suppressing the precipitation of Cr 2 B that occurs when B is added. However, the addition of a large amount of Nb leads to hardening of the material and adversely affects workability. In addition, the recrystallization temperature increases. Therefore, the addition of Nb is intends rows in a range of 0.5 mass%. The particularly preferable content of Nb is 0.1 to 0.5% by mass.
Ｂは、Ｎを固定し、加工性を改善する作用を有する。しかし、過剰に添加するとＣr2Ｂを形成し、耐食性の低下を招くようになる。このため、Ｂの添加は０.０１質量％以下の範囲で行う。Ｂの特に好ましい含有量は０.０００５〜０.０１質量％である。 B has an effect of fixing N and improving workability. However, if added excessively, Cr 2 B is formed, leading to a decrease in corrosion resistance. Therefore, addition of B is intends rows in a range of 0.01 mass% or less. A particularly preferable content of B is 0.0005 to 0.01% by mass.
各合金元素の含有量を以上に述べた範囲内で調整することによって、マトリクスがフェライト単相組織になっている鋼板、すなわちオーステナイト相やマルテンサイト相を含まないフェライト系ステンレス鋼板を製造することができる。製造工程は、一般的なフェライト系ステンレス鋼板と同様の方法が採用できる。なお、マトリクス中には通常のフェライト系ステンレス鋼板に見られる析出物や介在物が含まれていて構わない。 By adjusting the content of each alloy element within the above-mentioned range, it is possible to produce a steel sheet in which the matrix has a ferrite single phase structure, that is, a ferritic stainless steel sheet that does not contain an austenite phase or a martensite phase. it can. The manufacturing process can employ the same method as that for a general ferritic stainless steel sheet. The matrix may contain precipitates and inclusions found in ordinary ferritic stainless steel sheets.
表１に示す成分値のフェライト系ステンレス鋼を溶製し、常法により熱間圧延、焼鈍、冷間圧延を行い、板厚１.２ｍｍの冷延鋼板を得た。各鋼板の表面に同一鋼種の鋼板の小片をスポット溶接で接合することにより隙間部を形成させ、「スポット溶接隙間試験片」とした。これを塩乾湿複合サイクル試験に供することにより耐隙間腐食性を調査した。
塩乾湿複合サイクル試験は、「５％ＮaＣl水溶液の塩水噴霧：１５分 → 湿度３５％，温度６０℃での乾燥：６０分 → 湿度９５％，温度５０℃の湿潤：１８０分」を１サイクルとして、これを３００サイクル実施し、試験後の試験片における隙間部の侵食深さを測定して耐隙間腐食性を評価した。
なお、鋼板の金属組織観察の結果、各鋼種ともマトリクスフェライト単相組織を呈していた。
Ferritic stainless steels having the component values shown in Table 1 were melted and hot-rolled, annealed, and cold-rolled by ordinary methods to obtain cold-rolled steel sheets having a thickness of 1.2 mm. A gap portion was formed by joining a small piece of a steel plate of the same steel type to the surface of each steel plate by spot welding to obtain a “spot weld gap test piece”. The crevice corrosion resistance was investigated by subjecting this to a combined salt / wet cycle test.
The salt dry-wet combined cycle test consists of “5% NaCl aqueous solution sprayed with salt: 15 minutes → humidity 35%, temperature 60 ° C. drying: 60 minutes → humidity 95%, temperature 50 ° C. wet: 180 minutes” This was carried out for 300 cycles, and the crevice corrosion resistance was evaluated by measuring the erosion depth of the gap portion in the test piece after the test.
As a result of observation of the metal structure of the steel sheet, each steel type exhibited a matrix ferrite single phase structure.
図１に、塩乾湿複合サイクル試験後の侵食深さの測定結果を示す。
比較例の鋼種ＡはＮi含有量が低いため、また鋼種ＥはＮiを含有していないため、いずれも板厚を貫通する隙間腐食が生じた。鋼種ＧはＣr量が低いため、Ｎiを適正量含有しているにもかかわらず板厚を貫通する隙間腐食が生じた。
In FIG. 1, the measurement result of the erosion depth after a salt dry-wet combined cycle test is shown.
Since steel type A of the comparative example has a low Ni content and steel type E does not contain Ni, crevice corrosion penetrating the plate thickness occurred. Since steel type G has a low Cr content, crevice corrosion that penetrates the plate thickness occurred despite containing an appropriate amount of Ni.
これに対し鋼種Ｂ，Ｃ，Ｄ，Ｆ，Ｉの場合は板厚を貫通する隙間腐食は生じなかった。上記の塩乾湿複合サイクル試験はフェライト系ステンレス鋼にとって非常に厳しい腐食条件であるが、ＣrとＮiの複合添加により隙間腐食の進行が抑制されることが実証された。特に、ＣrとＮiに加え更にＭoを複合添加した鋼種Ｂ，Ｃ，Ｄは、Ｍoを含有しない鋼種Ｉと比べ、一層優れた耐隙間腐食性を示した。また、Ｃr，Ｎi，Ｍo，Ｃuを複合添加した鋼種Ｆは、Ｃr，Ｎi，Ｍoの含有量レベルが同等でＣuを含有しない鋼種Ｃと比べ、一層顕著な耐隙間腐食性改善効果が認められた。 This pair Shi steel grade B, C, D, F, in the case of I did not occur crevice corrosion penetrating the plate thickness. Although the above-mentioned salt dry and wet combined cycle test is a very severe corrosion condition for ferritic stainless steel, it has been proved that the progress of crevice corrosion is suppressed by the combined addition of Cr and Ni. In particular, steel types B, C, and D in which Mo was added in addition to Cr and Ni exhibited much better crevice corrosion resistance than steel type I that did not contain Mo. In addition, the steel type F to which Cr, Ni, Mo, and Cu are added in combination shows a more remarkable crevice corrosion resistance improvement effect compared to the steel type C that has the same Cr, Ni, and Mo content levels and does not contain Cu. It was.
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| KR100643359B1 (en) | 2005-06-03 | 2006-11-10 | 주식회사 포스코 | Ti-mn free high drawability high strength steel sheet for automobile having excellent resistance to second work embrittleness and surface quality, and method for manufacturing the same |
| CN100580120C (en) * | 2005-08-17 | 2010-01-13 | 杰富意钢铁株式会社 | Ferritic stainless-steel sheet with excellent corrosion resistance and process for producing the same |
| JP4974542B2 (en) * | 2005-09-02 | 2012-07-11 | 日新製鋼株式会社 | Automotive exhaust gas flow path member |
| KR101261192B1 (en) | 2006-05-09 | 2013-05-09 | 닛폰 스틸 앤드 스미킨 스테인레스 스틸 코포레이션 | Ferritic stainless steel excellent in crevice corrosion resistance |
| JP4767146B2 (en) * | 2006-10-18 | 2011-09-07 | 日新製鋼株式会社 | Stainless steel container for high pressure water |
| JP5111910B2 (en) * | 2007-03-23 | 2013-01-09 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel with low surface defects and excellent weldability and crevice corrosion resistance |
| JP5109604B2 (en) * | 2007-05-31 | 2012-12-26 | Ｊｆｅスチール株式会社 | Ferritic stainless steel sheet with excellent crevice corrosion resistance |
| WO2009041430A1 (en) * | 2007-09-27 | 2009-04-02 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferritic stainless steel having excellent atmospheric corrosion resistance |
| JP2009097079A (en) * | 2007-09-27 | 2009-05-07 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel having excellent atmospheric corrosion resistance |
| JP5676896B2 (en) * | 2009-03-27 | 2015-02-25 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel with excellent local corrosion resistance |
| JP5992189B2 (en) * | 2012-03-26 | 2016-09-14 | 新日鐵住金ステンレス株式会社 | Stainless steel excellent in high temperature lactic acid corrosion resistance and method of use |
| FI125855B (en) * | 2012-06-26 | 2016-03-15 | Outokumpu Oy | Ferritic stainless steel |
| WO2016117458A1 (en) | 2015-01-19 | 2016-07-28 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel for exhaust system member having excellent corrosion resistance after heating |
| WO2016152622A1 (en) | 2015-03-26 | 2016-09-29 | 新日鐵住金ステンレス株式会社 | Ferrite-austenite stainless steel sheet with excellent sheared end face corrosion resistance |
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