JP3828067B2

JP3828067B2 - High corrosion resistance austenitic stainless steel with good cold workability

Info

Publication number: JP3828067B2
Application number: JP2002325151A
Authority: JP
Inventors: 雄介及川; 好宣多田; 健中野
Original assignee: Nippon Steel and Sumikin Stainless Steel Corp
Current assignee: Nippon Steel Stainless Steel Corp
Priority date: 2002-11-08
Filing date: 2002-11-08
Publication date: 2006-09-27
Anticipated expiration: 2022-11-08
Also published as: JP2004156126A

Description

【０００１】
【発明の属する技術分野】
本発明は臨海環境等で用いられ、従来材より軟質で熱間および冷間加工性に優れた高耐食オーステナイト系ステンレス鋼に関するものである。
【０００２】
【従来の技術】
ステンレス鋼はその高耐食の性質を利用し比較的過酷な環境でも発銹を生じ難い金属建材として用いられており、例えば屋根，ビルの外壁，フェンス等に板や線材等様々な形状のものが使用されている。これらにはステンレスの汎用鋼であるＳＵＳ３０４やＳＵＳ３１６が使われることが多い。
【０００３】
しかしながら、当該材は臨海環境では耐食性が十分とは言えず、ウォーターフロント開発等の活発化等に合わせ臨海地区でも十分な耐食性を有するステンレス鋼が望まれている。
【０００４】
それらの用途に対して、例えば特許文献１に開示されている高Ｃｒ高Ｍｏ高Ｎオーステナイト系ステンレス鋼や、例えば特許文献２に開示されている高Ｃｒ高Ｍｏフェライト系ステンレス鋼が発明され、屋根や外壁等の平板材としてはかなり広く使用されている。
【０００５】
【特許文献１】
特開昭４９−１３５８１２号公報
【特許文献２】
特開平６−２７９９５３号公報
【０００６】
【発明が解決しようとする課題】
建材には、屋根等の平板だけでなく、フェンス等に用いられる線材、モニュメント等の複雑形状材、更に、屋根を締結するファスナー材等がある。これらは、曲げや冷間鍛造といった冷間加工によって所定の形状に加工される。
【０００７】
しかしながら、従来材は冷間加工性が低く、上記形状に加工するのは困難であり、温間加工といった特別な加工を行うか、あるいは耐食性を犠牲にしてＳＵＳ３１６等の汎用鋼を用いることさえあった。
【０００８】
前記特許文献１等に開示されている高Ｃｒ高Ｍｏ高Ｎオーステナイト系ステンレス鋼については、化学工業用機器や海水を使用する熱交換器等の用途に開発されたものであり、耐孔食性や熱間加工性について考慮されているが、強度については高強度狙いであり、熱間加工性冷間加工性何れについても劣る。
【０００９】
また、前記特許文献２に開示されている高Ｃｒ高Ｍｏフェライト系ステンレス鋼については、高純フェライト系であるため軟質かつ熱間加工性良好であるが、靱性が比較的低く、冷間鍛造等を行うのは至難である。
【００１０】
本発明は、臨海環境等で使用される建材として十分な耐食性を有し、かつ軟質で冷間，熱間加工性共に良好なオーステナイト系ステンレス鋼を提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
上記目的を達成する本発明の要旨は、以下の通りである。
【００１２】
まず、基本成分として、
（１）まず、基本成分として、質量％にてＣ：≦０．０３％
Ｓｉ：０．１〜１．０％
Ｍｎ：０．１〜０．８％
Ｎｉ：２１．０〜２５．０％
Ｃｒ：１８．０〜２２．０％
Ｍｏ：５．０〜７．０％
Ｃｕ：０．３〜３．０％
Ｎ：０．０５％未満を含有し、残部がＦｅおよび不可避的不純物からなり、（１）式で表されるδＦｅ（ｃａｌ）値が−７．５以下とする。
δＦｅ（ｃａｌ）＝３（Ｃｒ＋Ｍｏ＋１．５Ｓｉ）―２．８｛Ｎｉ＋０．５（Ｍｎ＋Ｃｕ）＋３０（Ｃ＋Ｎ）｝―１９．８・・・（１）
（２）更に質量％でＣ＋Ｎ：０．０５％以下とすることで、冷間加工性を更に向上できる。
（３）更に質量％でＢ：０．００１〜０．００５％添加することで、冷間加工性を更に向上できる。
（４）更に質量％でＡｌ：０．００５〜０．０６％、Ｍｇ：０．０００５〜０．００４％、ＲＥＭ：０．０００５〜０．００３％の１種または２種以上を添加することで、脱酸材や脱硫材として添加した場合の加工性や耐食性の劣化を防止できる。
（５）更に質量％でＴｉ：０．０５〜０．４％、Ｎｂ：０．０５〜０．２５％、Ｚｒ：０．０５〜０．３％、Ｔａ：０．０５〜０．２％の１種または２種以上を添加することで、耐食性を向上できる。
（６）更に質量％でＶ：０．５％以下、Ｗ：０．５％以下、Ｓｎ：０．１％以下の１種または２種以上を添加することで、耐食性を更に向上できる。
【００１３】
【発明の実施の形態】
本発明者らは、オーステナイト系ステンレス鋼の熱間加工性、冷間加工性、耐食性に及ぼす主要元素の影響について研究した結果、以下の知見を得た。
【００１４】
まず、熱間加工性即ち高温における強度については、特にＣ、Ｎ、Ｃｒ、Ｍｏが高強度化に大きく寄与し、増加により低強度化する元素は無い。
【００１５】
冷間加工性については、熱間と同様Ｃ，Ｎ，Ｃｒ，Ｍｏの増加により高強度化するが、熱間と比較してＣｒ，Ｍｏに対するＣ，Ｎの寄与が大きい。また、Ｓｉの増加によっても高強度化する。逆にＮｉ，Ｃｕの増加は低強度側に寄与する。
【００１６】
一方、耐食性についてはＣｒ，Ｍｏ，Ｎの３元素が増加により耐食性向上に寄与する。
【００１７】
これらの結果から言えることは、耐食性向上元素であるＣｒ，Ｍｏ，Ｎは何れも高強度化に寄与するため、耐食性と軟質化の両方を満足させることは困難であるということである。そこで、本発明者らは下記の考えによりこの問題を解決するに到った。
【００１８】
即ち、高強度化に対する寄与が特に大きいＮについてはできる限り低減し、耐食性は高Ｃｒ，高Ｍｏ化にて担保すると言うことである。更に冷間加工時の軟質化を確保すべく、Ｎｉ，Ｃｕの添加を行った。
【００１９】
もう一つ考慮しなければならないのがσ相の問題である。σ相はＦｅ，Ｃｒ，Ｍｏの金属間化合物であり、当該材のような高Ｃｒ高Ｍｏ鋼で成分的にオーステナイト安定度が低い場合に生成し、成品の冷間加工性と耐食性を著しく損ねる。これについては実験を重ねた結果、下記（１）式で規定されるδＦｅ（ｃａｌ）値が−５．０以下になるように成分調整し、適切な熱処理を行うことにより、σ相の影響を無害化できることを突き止めた。望ましいδＦｅ（ｃａｌ）値は−７．５以下である。

【００２０】
次に各々の合金元素の成分範囲を規定した理由について説明する。
【００２１】
ＣはＮと同様に侵入型固溶元素として鋼の強度を非常に増加させる元素である。更にクロム炭化物の析出等により耐食性も減ずるため、０．０３％以下にする必要がある。望ましい範囲は０．０２％以下である。
【００２２】
Ｓｉは冷間加工時における強度を高める元素であり、軟質化のためには低減した方がよいが、脱酸剤として精錬上必要である上、高温における耐酸化性を高め熱処理時のスケールロスを抑制する効果があるためある程度の添加は必要である。このため、Ｓｉの範囲は０．１〜１．０％にした。望ましい範囲は０．１５〜０．７％である。
【００２３】
ＭｎはＳｉと同様に脱酸剤として働くが、１．０％超の添加は耐食性を劣化させるためＭｎの範囲は０．１〜１．０％にした。望ましい範囲は０．３〜０．８％である。
【００２４】
Ｎｉは前述の通り軟質化とσ相抑制のために２１．０％以上の添加が必要であるが、２５．０％を超えて添加してもコスト高に見合う効果が得られないため上限を２５．０％とした。望ましい範囲は２２．０％を超え２４．０％未満である。
【００２５】
Ｃｒは耐食性を高める主元素であり、Ｃｒ量が増えるほど耐食性は良くなる。しかしながら過度の添加は高強度化とσ相発生に寄与するため範囲を１８．０〜２２．０％にした。望ましい範囲は１９．０〜２１．０％である。
【００２６】
Ｍｏは耐食性を向上させるが、Ｃｒと同様高強度化とσ相発生に寄与するため範囲を５．０〜７．０％にした。望ましい範囲は５．５〜６．５％である。
【００２７】
Ｃｕは軟質化に寄与し、かつ隙間腐食性を向上させるが、多量に添加すると熱間加工割れの原因となるため０．３〜３．０％とした。望ましい範囲は０．５〜２．０％である。
【００２８】
Ｎは耐食性を高めるが、熱間冷間共に強度を著しく高めるため、本発明では極力低減することとした。但し、低窒素化は精錬時の能率を悪化させるため上限を０．０５％とした。望ましい範囲は精錬時の能率、コストの面から下限も設け０．０１〜０．０３％である。
【００２９】
なお、侵入型固溶強化元素であるＣとＮを合計で０．０５％以下に抑制すると、本発明鋼の冷間加工性を更に向上させる事が出来る。
【００３０】
また、Ｂを０．００１％以上添加することにより固溶ＣとＮをホウ化物として析出させ、更に冷間加工性を向上させることができる。但し、過剰の添加は過剰析出ホウ化物により却って熱間、冷間加工性を損ねるので上限を０．００５％とする。
【００３１】
Ａｌは０．００５％以上の添加により鋼の強力な脱酸材として働くが、過剰に添加すると介在物による冷間加工割れを生じるため上限を０．０６％とした。
【００３３】
Ｍｇも０．０００５％以上の添加により同様の効果があるが、過剰に添加すると介在物の量を増加して耐食性等を損なうことから上限を０．００４％とした。
【００３４】
ＲＥＭも０．０００５％以上の添加により同様の効果があるが、過剰に添加すると介在物の量を増加して耐食性等を損なうことから上限を０．００３％とした。
【００３５】
Ｔｉ，Ｎｂ，Ｚｒ，Ｔａは何れも０．０５％以上の添加により鋼中のＣを炭化物として固定し、耐食性を向上させる。しかし過剰に添加すると強度を高め熱間、冷間加工性を損ねる。各元素で強度の増加代が異なるので、上限についてはＴｉが０．４％、Ｎｂが０．２５％、Ｚｒが０．３％、Ｔａが０．２％とした。
【００３６】
Ｖ、Ｗは添加により何れも鋼の耐食性を向上させるが、強度を高め熱間、冷間加工性を損ね、σ相を析出させやすくなるので上限は０．５％とした。Ｓｎも鋼の耐食性を向上させるが、過剰に添加すると熱間加工割れを生じるので上限を０．１％とした。
【００３７】
【実施例】
表１および表２に示す成分組成で残部がＦｅおよび不可避的不純物からなるＮｏ．１から４９までのステンレス鋼について、直径１７０ｍｍφの連続鋳造鋳片を１２００℃に加熱し、連続線材圧延ラインで５．５ｍｍφまで熱間圧延を行った後、１１００℃で焼鈍を行った。
【００３８】
当該材について、以下の特性を評価した。
【００３９】
熱間強度は、鋳片熱処理を行った後の鋳片表層から試験片を採取し、１０００℃における熱間強度を測定した。表面疵は圧延後の線材成品を目視検査し、疵の有無を判定した。σ相量は線材を非水溶媒中で電解することにより析出物を抽出し、その質量％を求めた。引張強さは線材をＪＩＳ準拠法で試験して求めた。孔食電位は線材表面研磨材を５０℃、２０％ＮａＣｌ水溶液中で、その他の条件はＪＩＳ準拠法で求めた。
【００４０】
評価結果を表３に示す。
【００４１】
Ｎｏ．１〜１０は本発明の請求項１の実施例であるが、成分、δＦｅ（ｃａｌ）が本発明範囲内にあり、鋳片熱間強度、表面疵、引張強さ、耐食性何れも狙いを満足している。Ｎｏ．１１は本発明の請求項２を満足する、Ｃ＋Ｎを低減させたものである。この場合、引張強さが更に低下し冷間加工性がより向上する。Ｎｏ．１２は本発明の請求項３を満足する、Ｂを添加しているものである。引張強さが更に低下し冷間加工性がより向上する。
【００４２】
Ｎｏ．１３〜１６は本発明の請求項４を満足する、Ａｌ，Ｍｇ，ＲＥＭの何れかを添加したものである。何れの特性も狙いを満足しており、更にＭｇ，ＲＥＭ添加材は熱間加工割れ防止効果により表面疵が極小になっている。Ｎｏ．１７〜２０は本発明の請求項５を満足する、Ｔｉ，Ｎｂ，Ｚｒ，Ｔａの何れかを添加したものである。何れの特性も狙いを満足しており、更に耐食性がより良好になっている。Ｎｏ．２１〜２３は本発明の請求項６を満足する、Ｖ，Ｗ，Ｓｎの何れかを添加したものである。何れの特性も狙いを満足しており、更に耐食性がより良好になっている。
【００４３】
Ｎｏ．２４はＣが本発明範囲上限以上の場合で、冷間強度が高い上、耐食性も劣る。Ｎｏ．２５はＳｉが本発明範囲上限以上の場合で、冷間強度が高く加工性に劣る。Ｎｏ．２６はＭｎが本発明範囲上限以上の場合で、Ｍｎの過度の添加のため目標とする耐食性が得られていない。
【００４４】
Ｎｏ．２７はＮｉが本発明範囲下限以下の場合で冷間強度が高く加工性に劣る。Ｎｏ．２８はＣｒが本発明範囲下限以下の場合で耐食性が悪い。Ｎｏ．２９はＣｒが本発明範囲上限以上の場合で熱間、冷間強度が高い。Ｎｏ．３０はＭｏが本発明範囲下限以下の場合で耐食性が悪い。Ｎｏ．３１はＭｏが本発明範囲上限以上の場合で熱間、冷間強度が高い。Ｎｏ．３２はＣｕが本発明範囲下限以下の場合で冷間強度が高い。Ｎｏ．３３はＣｕが本発明範囲上限以上の場合で、熱間加工性が悪く線材全長に熱間加工割れ起因の表面疵が発生し、製造性が悪い。Ｎｏ．３４はＮが本発明範囲上限以上の場合で、熱間、冷間強度何れも高い。Ｎｏ．３５はδＦｅ（ｃａｌ）が本発明範囲外であるが、適正な熱処理を行ってもσ相が大量に残存し、耐食性が大幅に劣化する。
【００４５】
Ｎｏ．３６はＢが本発明範囲上限以上の場合で、熱間加工性が悪く線材全長に熱間加工割れ起因の表面疵が発生し、製造性が悪い。Ｎｏ．３７はＡｌが本発明範囲上限以上の場合で、冷間加工時に介在物起因の割れを生じる。Ｎｏ．３９〜４０はＭｇ，ＲＥＭが本発明範囲上限以上の場合で、介在物起点の孔食を生じ耐食性が悪い。Ｎｏ．４１〜４６はＴｉ，Ｎｂ，Ｚｒ，Ｔａ，Ｖ，Ｗが本発明範囲上限以上の場合で、熱間強度が高く加工が困難となる。Ｎｏ．４７はＳｎが本発明範囲上限以上の場合で、熱間加工性が悪く線材全長に熱間加工割れ起因の表面疵が発生し、製造性が悪い。
【００４６】
Ｎｏ．４８、４９は発明鋼の比較として既存高耐食ステンレス鋼であるＳＵＳ３２９Ｊ３Ｌ，ＳＵＳ３１７Ｊ２の引張強さと耐食性を示したものである。発明鋼は両鋼より低強度高耐食であることが判る。
【００４７】
【表１】

【００４８】
【表２】

【００４９】
【表３】

【００５０】
【発明の効果】
本発明法により、臨海環境等で使用される建材向けに十分な耐食性を有し、かつ軟質で熱間，冷間加工性共に良好なオーステナイト系ステンレス鋼を提供し、それにより臨海環境の締結材やフェンス材の製造、加工の容易さと耐久性を両立することが出来、産業上有効な効果をもたらす。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a highly corrosion-resistant austenitic stainless steel that is used in a coastal environment and is softer than conventional materials and excellent in hot and cold workability.
[0002]
[Prior art]
Stainless steel is used as a metal building material that uses its high corrosion resistance properties and is unlikely to generate fire even in relatively harsh environments. For example, it has various shapes such as roofs, building outer walls, and fences, such as plates and wires. in use. For these, SUS304 and SUS316, which are general-purpose stainless steels, are often used.
[0003]
However, the material cannot be said to have sufficient corrosion resistance in the coastal environment, and stainless steel having sufficient corrosion resistance in the coastal area is desired in accordance with the activation of waterfront development and the like.
[0004]
For these applications, for example, high Cr high Mo high N austenitic stainless steel disclosed in Patent Document 1 and high Cr high Mo ferritic stainless steel disclosed in Patent Document 2, for example, are invented, It is widely used as a flat plate material for outer walls.
[0005]
[Patent Document 1]
JP 49-135812 A [Patent Document 2]
JP-A-6-279953 [0006]
[Problems to be solved by the invention]
Building materials include not only flat plates such as roofs but also wire materials used for fences and the like, complex shaped materials such as monuments, and fastener materials for fastening the roof. These are processed into a predetermined shape by cold working such as bending or cold forging.
[0007]
However, the conventional material has low cold workability and is difficult to process into the above shape, and special processing such as warm processing is performed, or even general-purpose steel such as SUS316 is used at the expense of corrosion resistance. It was.
[0008]
About the high Cr high Mo high N austenitic stainless steel currently disclosed by the said patent document 1 etc., it was developed for uses, such as a heat exchanger using a chemical industry apparatus or seawater, pitting corrosion resistance, Although hot workability is considered, the strength is aimed at high strength, and the hot workability and cold workability are both poor.
[0009]
The high Cr high Mo ferritic stainless steel disclosed in Patent Document 2 is soft and has good hot workability because it is a high purity ferritic steel, but has a relatively low toughness, such as cold forging. It is very difficult to do.
[0010]
An object of the present invention is to provide an austenitic stainless steel that has sufficient corrosion resistance as a building material used in a coastal environment and the like, is soft, and has good cold and hot workability.
[0011]
[Means for Solving the Problems]
The gist of the present invention that achieves the above object is as follows.
[0012]
First, as a basic component
(1) First, C: ≦ 0.03% in terms of mass% as a basic component
Si: 0.1 to 1.0%
Mn: 0.1 to 0.8%
Ni: 21.0-25.0%
Cr: 18.0 to 22.0%
Mo: 5.0-7.0%
Cu: 0.3 to 3.0%
N: It contains less than 0.05%, the remainder consists of Fe and inevitable impurities, and the δFe (cal) value represented by the formula (1) is −7.5 or less .
δFe (cal) = 3 (Cr + Mo + 1.5Si) −2.8 {Ni + 0.5 (Mn + Cu) +30 (C + N)} − 19.8 (1)
(2) The cold workability can be further improved by setting C + N: 0.05% or less in terms of mass%.
(3) The cold workability can be further improved by adding B: 0.001 to 0.005% by mass%.
(4) Add one or more of Al: 0.005-0.06% , Mg: 0.0005-0.004%, REM: 0.0005-0.003% by mass%. Therefore, deterioration of workability and corrosion resistance when added as a deoxidizer or desulfurizer can be prevented.
(5) Further, in terms of mass%, Ti: 0.05 to 0.4%, Nb: 0.05 to 0.25%, Zr: 0.05 to 0.3%, Ta: 0.05 to 0.2% Corrosion resistance can be improved by adding 1 type or 2 types or more.
(6) Corrosion resistance can be further improved by adding one or more of V: 0.5% or less, W: 0.5% or less, and Sn: 0.1% or less in terms of mass%.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a result of studying the influence of main elements on hot workability, cold workability, and corrosion resistance of austenitic stainless steel, the present inventors have obtained the following knowledge.
[0014]
First, regarding hot workability, that is, strength at high temperatures, C, N, Cr, and Mo particularly contribute greatly to increasing strength, and there is no element that decreases strength due to increase.
[0015]
The cold workability is increased by increasing C, N, Cr, and Mo as in hot, but the contribution of C and N to Cr and Mo is larger than that in hot. Further, the strength is increased by increasing Si. Conversely, an increase in Ni and Cu contributes to the low strength side.
[0016]
On the other hand, with respect to corrosion resistance, three elements of Cr, Mo, and N contribute to improvement of corrosion resistance.
[0017]
What can be said from these results is that it is difficult to satisfy both corrosion resistance and softening because Cr, Mo, and N, which are elements for improving corrosion resistance, all contribute to high strength. Accordingly, the present inventors have solved this problem based on the following idea.
[0018]
In other words, N, which has a particularly large contribution to increasing the strength, is reduced as much as possible, and the corrosion resistance is secured by increasing the Cr and Mo. Furthermore, Ni and Cu were added to ensure softening during cold working.
[0019]
Another issue to consider is the σ phase problem. The sigma phase is an intermetallic compound of Fe, Cr, Mo, and is produced when the high austenite stability is low in the high Cr high Mo steel such as the material, and significantly deteriorates the cold workability and corrosion resistance of the product. . As a result of repeated experiments, the effect of the σ phase is reduced by adjusting the components so that the δFe (cal) value defined by the following formula (1) is −5.0 or less and performing an appropriate heat treatment. I found out that it can be detoxified. A desirable δFe (cal) value is −7.5 or less.

[0020]
Next, the reason why the component ranges of each alloy element are specified will be described.
[0021]
C, like N, is an element that greatly increases the strength of steel as an interstitial solid solution element. Furthermore, since corrosion resistance also decreases due to precipitation of chromium carbide, it is necessary to make it 0.03% or less. A desirable range is 0.02% or less.
[0022]
Si is an element that increases the strength during cold working and should be reduced for softening. However, it is necessary for refining as a deoxidizer, and it increases the oxidation resistance at high temperatures and scale loss during heat treatment. It is necessary to add a certain amount because of the effect of suppressing the above. For this reason, the range of Si was made into 0.1 to 1.0%. A desirable range is 0.15 to 0.7%.
[0023]
Mn works as a deoxidizer like Si, but the addition of more than 1.0% deteriorates the corrosion resistance, so the range of Mn was made 0.1 to 1.0%. A desirable range is 0.3 to 0.8%.
[0024]
As described above, Ni needs to be added in an amount of 21.0% or more for softening and suppressing the σ phase, but even if added over 25.0%, an effect commensurate with high cost cannot be obtained, so the upper limit is set The content was 25.0%. A desirable range is more than 22.0% and less than 24.0%.
[0025]
Cr is a main element that enhances corrosion resistance, and the corrosion resistance improves as the Cr content increases. However, excessive addition contributes to high strength and generation of σ phase, so the range was made 18.0 to 22.0%. A desirable range is 19.0 to 21.0%.
[0026]
Mo improves the corrosion resistance, but in the same way as Cr, it contributes to increasing the strength and generating the σ phase, so the range was made 5.0 to 7.0%. A desirable range is 5.5 to 6.5%.
[0027]
Cu contributes to softening and improves crevice corrosion, but if added in a large amount, it causes hot working cracks, so it was made 0.3 to 3.0%. A desirable range is 0.5 to 2.0%.
[0028]
N increases the corrosion resistance, but significantly increases the strength in both hot and cold conditions. However, lowering the nitrogen content deteriorates the efficiency during refining, so the upper limit was made 0.05%. A desirable range is 0.01 to 0.03% with a lower limit provided in terms of efficiency and cost during refining.
[0029]
In addition, when C and N which are interstitial solid solution strengthening elements are suppressed to 0.05% or less in total, the cold workability of the steel of the present invention can be further improved.
[0030]
Further, by adding B in an amount of 0.001% or more, solid solution C and N are precipitated as borides, and cold workability can be further improved. However, excessive addition causes excessive hot precipitated boride to deteriorate hot and cold workability, so the upper limit is made 0.005%.
[0031]
Al acts as a strong deoxidizing material for steel when added in an amount of 0.005% or more, but if added in excess, cold work cracking due to inclusions occurs, so the upper limit was made 0.06%.
[0033]
Mg has the same effect when added in an amount of 0.0005% or more, but if added in excess, the amount of inclusions is increased and the corrosion resistance is impaired, so the upper limit was made 0.004%.
[0034]
REM has the same effect when added in an amount of 0.0005% or more, but if added excessively, the amount of inclusions is increased and the corrosion resistance is impaired, so the upper limit was made 0.003%.
[0035]
Ti, Nb, Zr, and Ta all add 0.05% or more to fix C in the steel as carbides and improve corrosion resistance. However, excessive addition increases strength and impairs hot and cold workability. Since the amount of increase in strength is different for each element, the upper limits were set to 0.4% for Ti, 0.25% for Nb, 0.3% for Zr, and 0.2% for Ta.
[0036]
V and W both improve the corrosion resistance of the steel when added, but the strength is increased, hot and cold workability are impaired, and the σ phase is easily precipitated, so the upper limit was made 0.5%. Sn also improves the corrosion resistance of the steel, but if added excessively, hot working cracks occur, so the upper limit was made 0.1%.
[0037]
【Example】
In the composition shown in Table 1 and Table 2, the balance is No. which consists of Fe and inevitable impurities. For stainless steels 1 to 49, a continuous cast slab having a diameter of 170 mmφ was heated to 1200 ° C., hot-rolled to 5.5 mmφ in a continuous wire rolling line, and then annealed at 1100 ° C.
[0038]
The following properties were evaluated for the material.
[0039]
For the hot strength, a test piece was taken from the slab surface layer after the slab heat treatment, and the hot strength at 1000 ° C. was measured. The surface defects were visually inspected after rolling to determine the presence or absence of defects. The amount of σ phase was determined by extracting precipitates by electrolyzing the wire in a non-aqueous solvent and calculating the mass%. The tensile strength was obtained by testing the wire according to a JIS compliant method. The pitting corrosion potential was determined by a wire surface polishing material at 50 ° C. in a 20% NaCl aqueous solution, and other conditions were determined according to JIS standards.
[0040]
The evaluation results are shown in Table 3.
[0041]
No. 1 to 10 are embodiments of claim 1 of the present invention, but the component, δFe (cal) is within the scope of the present invention, and the slab hot strength, surface flaw, tensile strength, and corrosion resistance satisfy all objectives. is doing. No. No. 11 satisfies the second aspect of the present invention, and C + N is reduced. In this case, the tensile strength is further reduced and the cold workability is further improved. No. No. 12 satisfies the third aspect of the present invention, and B is added. The tensile strength is further reduced and the cold workability is further improved.
[0042]
No. Nos. 13 to 16 are obtained by adding any one of Al , Mg, and REM , which satisfies claim 4 of the present invention. Any characteristics also satisfy the aims, further Mg, REM additives are surface defects by hot working cracking prevention effect becomes minimized. No. Nos. 17 to 20 are obtained by adding any one of Ti, Nb, Zr, and Ta satisfying claim 5 of the present invention. All the characteristics satisfy the aim, and the corrosion resistance is further improved. No. Nos. 21 to 23 are obtained by adding any one of V, W and Sn satisfying the sixth aspect of the present invention. All the characteristics satisfy the aim, and the corrosion resistance is further improved.
[0043]
No. No. 24 is a case where C is not less than the upper limit of the range of the present invention, and the cold strength is high and the corrosion resistance is also poor. No. 25 is the case where Si is not less than the upper limit of the range of the present invention, and the cold strength is high and the workability is poor. No. No. 26 is a case where Mn is not less than the upper limit of the range of the present invention, and the target corrosion resistance is not obtained due to excessive addition of Mn.
[0044]
No. 27 is a case where Ni is below the lower limit of the range of the present invention, and the cold strength is high and the workability is inferior. No. 28 is a case where Cr is less than the lower limit of the range of the present invention, and the corrosion resistance is poor. No. 29 is a case where Cr is not less than the upper limit of the range of the present invention, and the hot and cold strength is high. No. 30 is a case where Mo is below the lower limit of the range of the present invention, and the corrosion resistance is poor. No. 31 is a case where Mo is not less than the upper limit of the range of the present invention, and the hot and cold strength is high. No. 32 is a case where Cu is below the lower limit of the range of the present invention, and the cold strength is high. No. No. 33 is a case where Cu is not less than the upper limit of the range of the present invention, hot workability is poor, surface flaws due to hot work cracking occur in the entire length of the wire, and manufacturability is poor. No. 34 is a case where N is equal to or higher than the upper limit of the range of the present invention, and both hot and cold strengths are high. No. No. 35 has a δFe (cal) outside the range of the present invention, but a large amount of the σ phase remains even after appropriate heat treatment, and the corrosion resistance is greatly deteriorated.
[0045]
No. No. 36 is a case where B is not less than the upper limit of the range of the present invention, hot workability is poor, surface flaws due to hot working cracks occur in the entire length of the wire, and manufacturability is poor. No. 37 is a case where Al is not less than the upper limit of the range of the present invention, and cracks due to inclusions occur during cold working. No. Nos. 39 to 40 are cases where Mg and REM are more than the upper limit of the range of the present invention, resulting in pitting corrosion of inclusion starting points and poor corrosion resistance. No. Nos. 41 to 46 are cases where Ti, Nb, Zr, Ta, V, and W are not less than the upper limit of the range of the present invention, and the hot strength is high, making it difficult to process. No. 47 is a case where Sn is not less than the upper limit of the range of the present invention, hot workability is poor, surface flaws due to hot work cracking occur in the entire length of the wire, and manufacturability is poor.
[0046]
No. 48 and 49 show the tensile strength and corrosion resistance of SUS329J3L and SUS317J2 which are existing high corrosion resistance stainless steels as a comparison with the invention steel. It can be seen that the inventive steel has lower strength and higher corrosion resistance than both steels.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
[Table 3]

[0050]
【The invention's effect】
The method of the present invention provides austenitic stainless steel that has sufficient corrosion resistance for building materials used in coastal environments, etc., and is soft and has good hot and cold workability. It is possible to achieve both the ease of manufacturing and processing of fence materials and the durability, and industrially effective effects.

Claims

In mass% C: ≦ 0.03%
Si: 0.1 to 1.0%
Mn: 0.1 to 0.8%
Ni: 21.0-25.0%
Cr: 18.0 to 22.0%
Mo: 5.0-7.0%
Cu: 0.3 to 3.0%
N: Less than 0.05%, the balance is Fe and inevitable impurities, and δFe (cal) value represented by the formula (1) is −7.5 or less , cold work High corrosion resistance austenitic stainless steel with good properties.
δFe (cal) = 3 (Cr + Mo + 1.5Si)
-2.8 {Ni + 0.5 (Mn + Cu) +30 (C + N)}
―19.8 (1)

A high-corrosion-resistant austenitic stainless steel with good cold workability, which is the austenitic stainless steel according to claim 1 and further has a C + N ratio of 0.05% or less by mass%.

The austenitic stainless steel according to claim 1 or 2, further comprising B: 0.001 to 0.005% by mass%, and having high cold workability and high corrosion resistance austenitic stainless steel steel.

The austenitic stainless steel according to any one of claims 1 to 3, wherein Al: 0.005 to 0.06% , Mg: 0.0005 to 0.004%, REM: 0.0005 in mass%. High corrosion-resistant austenitic stainless steel with good cold workability, characterized by containing one or more of ˜0.003%.

The austenitic stainless steel according to any one of claims 1 to 4, further in terms of mass%, Ti: 0.05 to 0.4%, Nb: 0.05 to 0.25%, Zr: 0.05 A high corrosion resistance austenitic stainless steel with good cold workability, characterized by containing one or more of ˜0.3% and Ta: 0.05 to 0.2%.

The austenitic stainless steel according to any one of claims 1 to 5, and further, in mass%, V: 0.5% or less, W: 0.5% or less, Sn: 0.1% or less, or High corrosion-resistant austenitic stainless steel with good cold workability, characterized by containing two or more.