JP2004131796A - Chromium-containing steel for vessel material, welding method therefor, and vessel material - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は容器材料、特に２００質量ｐｐｍ以下のハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用の容器材料、具体的には水性塗料の保管容器の素材として用いるクロム含有鋼に関するもので、耐食性および靱性の劣化が問題となる溶接部の耐食性および靱性に優れたクロム含有鋼およびその溶接方法、ならびに容器材料に関するものである。
【０００２】
【従来の技術】
鋼製容器材料としては、塗装した鉄が一般的に使用されている。しかし、内容物が水溶液の場合、塗装した鉄では塗膜欠陥部から腐食が発生する恐れがある。特に、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器材料として、塗装した鉄を用いた場合、塗膜欠陥部からの腐食の発生は避けられない問題であり、代替材として、耐食性に優れたステンレス鋼の適用が考えられている。
【０００３】
しかし、耐食性に優れたステンレス鋼製容器といえども溶接部は耐食性が劣る部分であり、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液を保管する場合には、この溶接部での腐食の発生が問題となっている。ステンレス鋼製容器の溶接部分における腐食の発生を防止する方法として、例えば特許文献１および特許文献２には、溶接部の酸化スケールを硝酸とフッ酸の混酸を用いて除去し、耐食性を向上させる方法が開示されている。
【０００４】
上記特許文献１、特許文献２には、このステンレス鋼製容器に用いられているステンレス鋼の種類について全く記述がないが、容器材料として使用されているステンレス鋼は、通常、ＳＵＳ３０４鋼であることから、前記特許文献１，２において、実質対象としているステンレス鋼は、ＳＵＳ３０４鋼であるものと考えられる。しかし、ＳＵＳ３０４鋼は、合金コストの高いニッケルを約１０質量％含有したステンレス鋼であることから、ＳＵＳ３０４鋼を使用するステンレス鋼製容器は、塗装した鉄製容器と比較して大幅なコストアップとなってしまうことが、ステンレス鋼の容器への適用が進まない原因の一つとなっている。
【０００５】
現行のＳＵＳ３０４鋼よりも大幅な低コスト化を図るには、素材コストの低減が不可欠であり、それには、ニッケル無添加のクロム含有鋼の適用が望ましい。ただし、ニッケル無添加のクロム含有鋼を０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用容器に適用した場合、溶接部での耐食性劣化が顕著であり、前記特許文献１，２に示されている硝酸とフッ酸の混合溶液を用いた酸化スケール層の除去を実施しても、溶接部の耐食性は著しく低いままであるという欠点があった。さらには、ニッケル無添加のクロム含有鋼は、溶接部の靱性が低いという欠点も有する。
【０００６】
本発明者らは、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用容器への、ニッケル無添加のクロム含有鋼の適用を試みたが、耐食性に優れるＳＵＳ３０４鋼と比較して、溶接部での耐食性の劣化は顕著であり、溶接部耐食性を向上させない限り、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用容器への、ニッケル無添加のクロム含有鋼の適用は不可能であることを確認した。
【０００７】
さらに、本発明者らは、溶接部耐食性を向上させるために、ニッケル無添加のクロム含有鋼に対して鋼中クロム濃度の増加を試みたが、耐食性の改善は図れるものの、溶接部靭性は劣化してしまい、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用容器に適用するには必要特性を満足し得ないことを確認した。
【０００８】
すなわち、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管用容器材料には、素材の低コスト化と、ＳＵＳ３０４鋼並みの溶接部耐食性および溶接部靭性が望まれており、低コスト化に対してはニッケル無添加のクロム含有鋼で対応できるものの、溶接部耐食性と溶接部靭性の両立は不可能である。したがって現時点では、これらの特性を満足するクロム含有鋼はない。さらに、通常の容器の形成方法は、かしめや抵抗溶接による接合、あるいはプラズマ、ＭＩＧ、ＴＩＧのような溶融溶接法による接合を用いるため、隙間部や溶接部での耐食性の劣化や溶接部の靱性低下が問題となっている。
【０００９】
【特許文献１】
特公平１−３５０８０号公報
【特許文献２】
特公平４−１３２１８号公報
【００１０】
【発明が解決しようとする課題】
本発明は、上記課題に応えるべく、溶接部耐食性および溶接部靭性が確保でき、容器材料用素材、特に０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器用素材としてコスト面でも最適なニッケル無添加クロム含有鋼およびその溶接方法、ならびに容器材料を提供することを課題とする。
【００１１】
【課題を解決するための手段】
本発明者らは、ニッケル無添加のクロム含有鋼を容器材料、特に、０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器材料に適用すべく、容器材料の溶接部における耐食性および靭性を向上させるための種々の検討を行った。
【００１２】
その結果、溶接部の耐食性および靭性を向上させるには、鋼中にチタンおよび／またはニオブをそれぞれ規定量以上添加することにより、鋼中の炭素と窒素を安定化し、これに伴い、溶接部の耐食性および靭性が改善されることを新たに見出した。さらに、Ａｌの添加が、溶接部の耐食性及び靭性の向上に有効であることを見出した。またさらに、ＣａおよびＳは、所定量以上の添加で、母材の耐食性と、溶接部の耐食性および靱性の低下を生じさせる元素であることを見出した。そして、溶融溶接時にバックシールドを実施することにより、溶接部およびその周辺部に生成した酸化スケールを化学的処理により簡便に除去できることを見出した。また、接合部における隙間腐食の発生を防止するためには、隙間部を肉盛り溶接することが最も有効であることを見出した。
【００１３】
本発明は、上記知見に基づいてなし得たものであり、その要旨は以下のとおりである。
（１） 質量％で、Ｃｒ：９〜１９％、Ｃ＋Ｎ：０．０３％以下、Ａｌ：０．００２〜０．２％、Ｓ：０．０１％以下、を含有し、さらに、ＴｉおよびＮｂを単独または複合して含有し、前記Ｃ＋Ｎ含有量をｘ（質量％）とすると、Ｔｉの含有量ｙ（質量％）、およびＮｂの含有量ｚ（質量％）は、それぞれ単独で含有する場合は、８ｘ≦ｙ≦０．６、１８ｘ≦ｚ≦０．６、であり、複合して含有する場合は、１＜（ｙ／８ｘ）＋（ｚ／１８ｘ）、かつ、ｙ＋ｚ≦０．６であり、残部がＦｅおよび不可避的不純物からなることを特徴とする容器材料用クロム含有鋼。
（２） 前記鋼が、さらに、Ｃａを０．００５質量％以下含有することを特徴とする前記（１）に記載の容器材料用クロム含有鋼。
（３） 前記鋼が、さらに、Ｍｏ、Ｗ、およびＶの１種または２種以上を０．５〜３質量％含有することを特徴とする前記（１）または（２）に記載の容器材料用クロム含有鋼。
（４） 前記（１）〜（３）のいずれかに記載の鋼に、流量２０Ｌ／分以上のアルゴンガスを用いたバックシールドを実施しながら溶融溶接を行った後、さらに、該溶融溶接部およびその周囲に生じた酸化スケールを化学的に除去することを特徴とする容器材料用クロム含有鋼の溶接方法。
（５） 前記（１）〜（３）のいずれかに記載の鋼に、抵抗溶接またはかしめ構造による機械的接合を行った後、該溶接部または接合部に肉盛り溶接を行い、さらにその後、該肉盛り溶接部およびその周囲に生じた酸化スケールを化学的に除去することを特徴とする容器材料用クロム含有鋼の溶接方法。
（６） 前記肉盛り溶接が、溶接棒にオーステナイト系ステンレス鋼を用いるものであって、該溶接棒の含有成分が、質量％で、Ｃｒ：１６〜２５％、Ｎｉ：８〜１６％、Ｃ：０．０３％以下、Ｎ：０．０５％以下、Ｍｎ：２．００％以下で、残部がＦｅおよび不可避的不純物からなり、さらに、Ｃｒ当量およびＮｉ当量が下式を満たすことを特徴とする前記（５）に記載の容器材料用クロム含有鋼の溶接方法。
Ｃｒ当量×Ｎｉ当量＞１６０
（ただし、Ｃｒ当量＝Ｃｒ（質量％）＋Ｍｏ（質量％）＋１．５Ｓｉ（質量％）、Ｎｉ当量＝Ｎｉ（質量％）＋０．５Ｍｎ（質量％）＋３０Ｃ（質量％）＋３０Ｎ（質量％）、ＭｏおよびＳｉは不可避的不純物として含有されるものである。）
（７） 前記（１）〜（３）のいずれかに記載のクロム含有鋼を加工成形してなる容器材料。
（８） 前記容器材料が、２００質量ｐｐｍ以下のハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器の構成材料であることを特徴とする前記（７）に記載の容器材料。
【００１４】
【発明の実施の形態】
本発明の容器材料は、２００質量ｐｐｍ以下のハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器に用いられることを対象としている。従来の塗装した鉄製の容器では、特に、ハロゲン化物イオン濃度が０．０１質量ｐｐｍ以上の場合で腐食による損傷が問題となる。従って、本発明鋼は、特に０．０１〜２００質量ｐｐｍのハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液の保管容器に用いられることを対象としている。なお、保管温度は一般的な６０℃以下である。
【００１５】
２００質量ｐｐｍ以下のハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液とは、油相を含んでもよく、水相と油相がエマルション化したものであっても構わない。さらに、顔料等の添加剤を配合したものであっても構わない。
【００１６】
本発明のニッケル無添加のクロム含有鋼の添加成分の限定理由を以下に示す。なお、以下の説明において鋼の成分組成および化学物質の量はいずれも質量％である。
【００１７】
クロムは、母材の耐食性を確保するために必須の元素であり、耐食性を発現するためには９％以上の添加が必要である。しかし、１９％を超えて添加した場合、溶接部の靱性低下が顕著となることから、１９％を上限とする。
【００１８】
炭素および窒素は、溶接部の耐食性および靱性を劣化させる元素であり、これらの元素の算術和ｘ（質量％）を０．０３％以下とする。
【００１９】
チタンおよびニオブは、炭素と窒素を安定化するために添加する元素である。チタンおよびニオブは、単独あるいは複合で添加する。ただし、Ｔｉの添加量ｙ（質量％）およびＮｂの添加量ｚ（質量％）は、それぞれ単独添加の場合には、８ｘ≦ｙ≦０．６、１８ｘ≦ｚ≦０．６とし、複合添加の場合には、１＜（ｙ／８ｘ）＋（ｚ／１８ｘ）、かつ、ｙ＋ｚ≦０．６とする。チタンおよびニオブの添加量が前記関係式を満たす場合には、母材の炭素および窒素の固定による安定化が行われ、それに伴い、溶接部の耐食性および靱性の改善をもたらす。ただし、チタンおよびニオブの添加量が単独または複合添加で０．６％を超えると、逆に靱性に悪影響を及ぼすことから、０．６％を上限とする。
【００２０】
Ａｌは、母材の耐食性と、溶接部の耐食性および靱性の向上に必須の添加元素である。Ａｌは、０．００２％以上の添加により、母材の耐食性と、溶接部の耐食性および靱性を改善する。しかし、０．２％を超えて添加すると、溶接部の耐食性および靱性を低下させるので、０．２％を上限値とする。
【００２１】
Ｓは、母材の耐食性と、溶接部の耐食性および靱性の低下を生じさせる元素である。従って、Ｓの含有量は０．０１％以下とする必要がある。
【００２２】
本発明によるクロム含有鋼は、上記添加成分以外は、Ｆｅおよび不可避的不純物であるが、上記添加元素に加えて、必要に応じて、Ｃａを添加しても良い。Ｃａは、溶接部の耐食性および靭性の向上に有効であるが、０．００５％超を添加すると、母材の耐食性と、溶接部の耐食性および靱性の低下を生じさせるため、０．００５％を上限とする。
【００２３】
また、上記添加元素に加えて、さらに必要に応じて、Ｍｏ、Ｗ、およびＶを添加しても良い。
【００２４】
Ｍｏ、Ｗ、およびＶは、耐食性の向上に有効な添加元素であり、０．５％以上の添加により耐食性の向上を発現させる。しかし、３％を超えて添加すると、材料の強度上昇が顕著となり靱性低下を生じるため、３％を上限とする。なお、これらの元素は、単独あるいは複合で添加することができる。
【００２５】
次に、本発明鋼の溶接方法について説明する。
【００２６】
本発明が対象とする溶接方法は、容器の溶接方法として一般的な溶融溶接法による接合方法である。
【００２７】
溶融溶接法とは、ＭＩＧ（Ｍｅｔａｌ Ｉｎｅｒｔ Ｇａｓ）溶接法、ＴＩＧ（Ｔｕｎｇｓｔｅｎ Ｉｎｅｒｔ Ｇａｓ）溶接法、レーザー溶接法、およびプラズマ溶接法を意味する。溶融溶接法による溶接部は、一般的に耐食性が劣る場合が多いが、溶接条件によっては保護的な酸化スケールが形成され、耐食性向上に寄与する場合もある。本発明者らは、本発明鋼の溶接方法に関して、２００質量ｐｐｍ以下のハロゲン化物イオンを含有するｐＨ３〜１２の水相を含んでなる溶液中での溶接部耐食性を向上するための溶融溶接法について鋭意検討した結果、溶融溶接を行う際にアルゴンガスを用いたバックシールドの実施が、耐食性向上に極めて有効であることを見出した。
【００２８】
すなわち、本発明鋼の溶接方法は、ＭＩＧ溶接、ＴＩＧ溶接、レーザ溶接、およびプラズマ溶接の溶融溶接法であるが、溶融溶接を行う際に、アルゴンガスを用いたバックシールドを実施する。これは、溶接部に大気中の酸素および窒素が取り込まれることによる耐食性劣化を防止するのに不可欠な処置であり、アルゴンガスの流量は２０Ｌ／分以上が必要となる。２０Ｌ／分未満では、溶接時のシールド効果が不十分で、耐食性劣化の原因となる酸化スケールを形成するため、２０Ｌ／分以上の流量が必要となる。
【００２９】
しかし、上記バックシールドを実施して溶融溶接を行っても、溶接部およびその周囲に部分的に薄い酸化スケールが形成されることを全く防止することは困難である。本発明鋼の溶接では、酸化スケールが耐食性低下に関与するため、その除去は不可欠であり、酸化スケールを除去することにより溶接部耐食性が大幅に向上する。
【００３０】
本発明に係る前記酸化スケールの除去方法としては、機械的または化学的除去方法が挙げられるが、鋼材表面の粗度によっては、機械的除去方法のみでは酸化スケールの除去が十分に実施できないことがあるため、化学的除去方法の適用が好ましい。さらに、本発明鋼の溶接方法では、溶接時にアルゴンガスによるシールドを実施しているため、形成される酸化スケールの厚さは薄く、従って、ブラストや研磨等の前処理を実施することなく、化学的除去方法によって酸化スケールを除去することが可能である。
【００３１】
本発明に係る化学的除去方法は、硝酸とフッ酸の混酸による処理が好ましく、硝酸とフッ酸の濃度は、それぞれ５〜３０％、０．５〜５％が好ましい。硝酸濃度が５％未満では、十分な酸化力を得ることができず、酸化スケールの除去が不十分となる。ただし、３０％を超えるとＮＯｘ（窒素酸化物）の発生量が増大するため好ましくない。フッ酸については、０．５％未満では、鋼の溶解を促進する効果が少なく好ましくない。ただし、５％を超えて添加しても、鋼の溶解促進効果はほぼ飽和するため、５％を上限とする。
【００３２】
なお、処理温度および処理時間については、酸化スケールの厚みに依存するため、目視観察で酸化スケ−ルが除去できたと見なすことができる、すなわち着色部分が金属光沢になったと見なすことができる処理温度および時間を選定することが好ましい。
【００３３】
前記硝酸とフッ酸の混酸による化学的処理の具体的な実施形態は、溶接部およびその周囲に硝酸とフッ酸を含んだペーストを塗布しても良いし、あるいは硝酸とフッ酸を含んだ溶液をガーゼ、ろ紙等に染み込ませて、溶接部およびその周囲の部分に付着させても良い。ただし、後者の方法では、溶液が揮発しやすいため、ペースト状にしたものの方が扱いやすい。
【００３４】
前記方法の他に、中性塩溶液を用いた電解処理を行っても良い。中性塩電解は、１０〜３０％の硝酸ソーダや硫酸ソーダ等の電解質を溶解した水溶液を用い、前記水溶液を入れた電解槽中に本発明鋼とカソードとなるステンレス鋼板（たとえばＳＵＳ３０４鋼）を浸漬し、本発明鋼をアノードとして、０．０５〜３Ａ／ｃｍ２の電流密度で、酸化スケールの除去が目視で確認できるまで電解を行うことが好ましい。電流密度が０．０５Ａ／ｃｍ２未満では、酸化皮膜を過不働態溶解させることが難しく、酸化スケールが残存しやすいため好ましくない。ただし、３Ａ／ｃｍ２を超える電解電流密度では、過不働態溶解よりも、水の電気分解による酸素発生に電力が消費される割合が増大するため好ましくない。電解酸洗後は水洗することが好ましい。
【００３５】
前記化学的処理後、さらに、溶接部に研磨を行ってもよい。研磨によって、溶接部の表面粗度が低減し、溶接部の耐食性向上に寄与する。研磨は、研磨ベルト、カーボンブラシを用いて行うことができるが、溶接部の耐食性向上に寄与しないものの使用は好ましくなく、例えば、鉄系ブラシは、もらい錆びの原因となるため好ましくない。
【００３６】
なお、前記化学的処理および／または研磨を行った後に、フッ酸を含有しない硝酸溶液中への浸漬、あるいは前記硝酸を含んだペーストを塗布する、いわゆる不働態化処理も耐食性向上に有効に働く。前記硝酸濃度は、１０〜４０質量％が望ましい。硝酸濃度が１０質量％未満では酸化力が不十分なため、鋼表面にクロムを主体とした保護性の高い不働態皮膜を形成することが難しい。なお、硝酸濃度が４０質量％を超えると、硝酸の酸化力が極めて強くなるため、薬液のハンドリングに注意を必要とするため好ましくない。
【００３７】
なお、本発明鋼の溶接方法は、上記溶融溶接の他に、シーム溶接やスポット溶接のような抵抗溶接法、あるいはかしめ構造による機械的な接合方法も適用可能である。
【００３８】
抵抗溶接法は、溶融部分が直接外部環境と触れることがなく、かつ、溶接時間も短いことから、上述の溶融溶接の場合のようなバックシールドを実施する必要はないが、溶接により生成した酸化スケールの化学的除去の実施は不可欠であり、上述の化学的除去方法を行えばよい。
【００３９】
さらに、抵抗溶接やかしめ構造による接合では、接合部に隙間が形成されることによる隙間部における耐食性の劣化、すなわち、隙間腐食の発生を防止する必要がある。本発明者らは、隙間腐食の発生を確実に防止する方法について鋭意検討した結果、隙間部を肉盛り溶接する方法が最も防食効果が高いことを見出した。
【００４０】
すなわち、本発明に係る抵抗溶接部やかしめ構造による接合部では、肉盛り溶接を実施し、その後、溶接部およびその周囲の酸化スケール形成部に対して、上述の酸化スケールの化学的除去方法を行う。
【００４１】
本発明に係る肉盛り溶接は、溶接棒に、フェライト系ステンレス鋼の共金系、あるいはオーステナイト系ステンレス鋼のいずれも使用できる。
【００４２】
フェライト系ステンレス鋼の溶接棒としては、一般的なものが使用できる。ただし、フェライト系ステンレス鋼を用いた場合は、オーステナイト系ステンレス鋼を用いた場合と比較して、靱性に劣るため、オーステナイト系ステンレス鋼を用いることが好ましい。
【００４３】
次に、本発明に係る肉盛溶接に用いるオーステナイト系ステンレス鋼の溶接棒について説明する。
【００４４】
クロムは、溶接部の耐食性を確保するために１６％以上を必要とする。しかし、溶接部の耐食性は、溶接金属中のクロム含有量の増加と共に向上するが、２５％を超えると溶接部でのδフェライトの相分率が増加し、溶接部靱性の劣化原因となるので、２５％を上限とする。
【００４５】
ニッケルは、γ組織を得るのに不可欠な元素であり、８％以上の添加を必要とする。しかし、１６％を超えると、δフェライトの相分率が少ないため粒界にリンあるいは硫黄が偏析し、溶接冷却時の粒界割れを引き起こすので、１６％を上限とする。
【００４６】
マンガンも、γ組織を選るのに有効な元素であるが、２％を超えると耐食性に悪影響を及ぼすため、２％を上限とする。
【００４７】
モリブデンおよびシリコンは、特に積極的に添加する元素ではなく、不純物として存在するレベルで良いが、通常、モリブデンは０．２％以下、シリコンは０．４〜０．８％の含有量とすることが多い。
【００４８】
炭素および窒素の含有量は、炭素含有量は０．０３％以下、窒素含有量は０．０５％以下とする。炭素および窒素の含有量が前記範囲を超えると、母材粒界にクロム炭窒化物の析出を生じ、耐粒界腐食性を劣化させる。特に、耐食性と溶接割れの両者をバランスさせるには、下式（１）に基づいて、Ｃｒ当量およびＮｉ当量を乗したもの（Ｃｒ当量×Ｎｉ当量）が１６０超となることが望ましい。
【００４９】
Ｃｒ当量×Ｎｉ当量＞１６０ 式（１）
（ただし、Ｃｒ当量＝Ｃｒ％＋Ｍｏ％＋１．５Ｓｉ％、Ｎｉ当量＝Ｎｉ％＋０．５Ｍｎ％＋３０Ｃ％＋３０Ｎ％、ＭｏおよびＳｉは不可避的不純物として含有されるものである。）
本発明のニッケル無添加のクロム含有鋼は、電気炉あるいは溶銑のいずれを用いても製造することができる。本発明鋼は、上述の理由により、鋼中の炭素および窒素濃度を低減する必要があるため、電気炉あるいは溶銑のいずれの場合も、２次精錬工程が重要であり、鋼中の炭素および窒素濃度を十分低減する必要がある。このように成分調整された溶鋼は、通常、連続鋳造され、スラブ形状となる。スラブは、１０５０〜１２００℃の温度範囲で、鋼種に応じて選択される温度域で十分均熱後、所定の厚さになるまで熱間圧延する。続いて、８００〜９５０℃の温度域で固溶化熱処理を受け、ショット、酸洗工程を経て、製品とする。
【００５０】
【実施例】
ここで、本発明の実施例について説明するが、本発明は、実施例で用いた条件に限定されるものではない。
（実施例１）
表１に示す本発明鋼１〜８と比較鋼１〜５について、長さ１００ｍｍ×幅５０ｍｍ×厚み１．２ｍｍの試験片を作製した。次に、同一鋼種の試験片２枚に対して、長手方向に突き合わせで、３０Ｌ／ｍｉｎの流量のアルゴンガスを用いてバックシールドを行いながらＴＩＧ溶接を行った。
【００５１】
【表１】
溶接後、溶接部および溶接部周辺を１０質量％硝酸水溶液と３質量％フッ酸水溶液の混合溶液で酸洗して、溶接時に形成された酸化スケールを除去した。酸洗は、目視観察で酸化スケ−ルが除去できたと見なすことができる、すなわち着色部分が金属光沢になったと見なすことができる状態になるまで行った。酸洗後、水洗・乾燥した。
【００５３】
次に、上記溶接した試験片を用いて、（１）液温５０℃、ｐＨ３で塩化物イオン濃度が１００質量ｐｐｍの水溶液中に１ヶ月間浸漬、（２）液温５０℃、ｐＨ５で塩化物イオン濃度が１００質量ｐｐｍの水相と油相からなる溶液中に１ヶ月間浸漬、（３）液温４０℃、ｐＨ１１で塩化物イオン濃度が２００質量ｐｐｍのエマルション中に１ヶ月間浸漬、の３条件で浸漬試験を行った。
【００５４】
浸漬試験後の試験片の母材部および溶接部の耐食性の評価は目視観察により行い、◎：赤錆およびしみの発生が全くない、○：極めて軽微なしみ発生、△：明確なしみ発生、×：明らかな赤錆発生、の４段階で評価した。
【００５５】
表２に浸漬試験の結果を示す。本発明鋼１〜８の評価は、上記３条件のいずれの条件でも◎または〇であり、母材および溶接部での優れた耐食性を示したのに対して、比較鋼１〜５の評価は、上記３条件のいずれの条件でも×または△であり、いずれも溶接部において赤錆が発生した。
【００５６】
【表２】
（実施例２）
表１に示す本発明鋼１、３、７を用いて、実施例１と同様の形状の試験片を作製した。次に、同一鋼種の試験片２枚に対して、長手方向に突き合わせでシーム溶接を行い、さらに表３に示すオーステナイト系ステンレス鋼の溶接棒（本発明の溶接棒１〜３、比較例の溶接棒１、２）を用いて、表４の組み合わせで肉盛り溶接を行った。
【００５８】
【表３】
溶接後、実施例１と同様の混合溶液を用いて、溶接部および溶接部周辺を酸洗して、溶接時に形成された酸化スケールを除去した。酸化スケールが除去できたか否かの確認は、実施例１と同様の基準で行い、酸洗後、水洗・乾燥した。
【００６０】
次に、上記溶接した試験片を用いて、実施例１と同様の３条件で浸漬試験を行い、実施例１と同様の方法で、浸漬試験後の試験片の母材部および溶接部の耐食性の観察および評価を行った。
【００６１】
表４に浸漬試験結果を示す。本発明鋼および本発明法の溶接棒を使用した本発明例１〜３は、上記３条件のいずれの条件でも◎または〇であり、極めて良好な耐食性を示すのに対し、本発明鋼および比較例の溶接棒を使用した比較例１〜３は、上記３条件のいずれの条件でも×または△であり、いずれも溶接部において赤錆が発生した。
【００６２】
【表４】
【発明の効果】
本発明は、溶接部耐食性および溶接部靭性が確保でき、容器用素材としてコスト面でも最適なニッケル無添加クロム含有鋼およびその溶接方法、ならびに容器材料を提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a container material for storing a solution containing a water phase having a pH of 3 to 12 containing halide ions of 200 mass ppm or less, specifically, chromium used as a material for a storage container of an aqueous paint. The present invention relates to a chromium-containing steel excellent in corrosion resistance and toughness of a welded portion where deterioration of corrosion resistance and toughness is a problem, a welding method thereof, and a container material.
[0002]
[Prior art]
Painted iron is generally used as a steel container material. However, when the content is an aqueous solution, the painted iron may cause corrosion from a defective portion of the coating film. In particular, when coated iron is used as a storage container material for a solution containing an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of halide ions, corrosion from a defective portion of the coating film occurs. Is an inevitable problem, and as an alternative material, application of stainless steel having excellent corrosion resistance has been considered.
[0003]
However, even in a stainless steel container having excellent corrosion resistance, the welded portion is a portion having poor corrosion resistance, and stores a solution containing an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of halide ions. In this case, the occurrence of corrosion at the welded portion is a problem. As a method of preventing the occurrence of corrosion in a welded portion of a stainless steel container, for example, Patent Documents 1 and 2 disclose removing an oxide scale of a welded portion using a mixed acid of nitric acid and hydrofluoric acid to improve corrosion resistance. A method is disclosed.
[0004]
Patent Literature 1 and Patent Literature 2 have no description about the type of stainless steel used for the stainless steel container, but the stainless steel used as the container material is usually SUS304 steel. Therefore, it is considered that the stainless steels substantially targeted in Patent Documents 1 and 2 are SUS304 steel. However, SUS304 steel is a stainless steel containing about 10% by mass of nickel, which has a high alloy cost. Therefore, a stainless steel container using SUS304 steel has a significant cost increase compared to a painted iron container. This is one of the reasons why the application of stainless steel to containers has not progressed.
[0005]
In order to achieve a significant cost reduction over the current SUS304 steel, it is essential to reduce the material cost, and it is desirable to use a chromium-containing steel with no nickel added. However, when the chromium-containing steel containing no nickel is applied to a container for storing a solution containing an aqueous phase having a pH of 3 to 12 and containing halide ions of 0.01 to 200 mass ppm, the corrosion resistance of the welded portion is deteriorated. However, even if the oxide scale layer is removed using a mixed solution of nitric acid and hydrofluoric acid shown in Patent Documents 1 and 2, the corrosion resistance of the welded portion remains extremely low. there were. Further, the nickel-free chromium-containing steel also has a disadvantage that the toughness of the weld is low.
[0006]
The present inventors have attempted to apply nickel-free chromium-containing steel to a storage container of a solution containing an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of halide ions. However, compared to SUS304 steel having excellent corrosion resistance, the deterioration of corrosion resistance at the weld is remarkable, and unless the corrosion resistance of the weld is improved, pH 3 to 12 containing halide ions of 0.01 to 200 mass ppm is used. It has been confirmed that nickel-free chromium-containing steel cannot be applied to a container for storing a solution containing an aqueous phase.
[0007]
Further, the present inventors have tried to increase the chromium concentration in the steel for the chromium-containing steel without addition of nickel in order to improve the corrosion resistance of the weld, but the corrosion resistance can be improved, but the weld toughness is deteriorated. Therefore, it was confirmed that the characteristics required for application to a storage container for a solution containing an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 ppm by mass of halide ions could not be satisfied.
[0008]
That is, the material of the container for storing a solution containing an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of a halide ion has a low cost of the material, a welded portion corrosion resistance equivalent to that of SUS304 steel, and Although weld toughness is desired and cost reduction can be achieved by nickel-free chromium-containing steel, it is impossible to achieve both weld corrosion resistance and weld toughness. Therefore, at present, no chromium-containing steel satisfies these properties. Furthermore, since the usual container forming method uses joining by caulking or resistance welding or joining by fusion welding methods such as plasma, MIG, and TIG, deterioration of corrosion resistance in gaps and welds and toughness of welds are used. The decline is a problem.
[0009]
[Patent Document 1]
Japanese Patent Publication No. 1-35080 [Patent Document 2]
Japanese Patent Publication No. Hei 4-13218
[Problems to be solved by the invention]
In order to meet the above-mentioned problems, the present invention can ensure the corrosion resistance of the welded portion and the toughness of the welded portion, and contains a material for a container material, particularly, an aqueous phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of halide ions. An object of the present invention is to provide a nickel-free chromium-containing steel that is optimal in terms of cost as a material for a storage container for a solution, a welding method thereof, and a container material.
[0011]
[Means for Solving the Problems]
The present inventors have applied nickel-free chromium-containing steel to container materials, in particular, storage container materials for solutions comprising a pH 3-12 aqueous phase containing 0.01-200 ppm by weight of halide ions. In order to improve the corrosion resistance and toughness in the welded portion of the container material, various studies were made.
[0012]
As a result, in order to improve the corrosion resistance and toughness of the weld, carbon and nitrogen in the steel are stabilized by adding titanium and / or niobium to the steel in specified amounts or more, respectively. It was newly found that the corrosion resistance and toughness were improved. Further, it has been found that the addition of Al is effective for improving the corrosion resistance and toughness of the welded portion. Further, it has been found that Ca and S are elements that cause the corrosion resistance of the base material and the deterioration of the corrosion resistance and toughness of the welded portion when added in a predetermined amount or more. Then, it has been found that by performing the back shield at the time of the fusion welding, the oxide scale generated at the welded portion and its peripheral portion can be easily removed by a chemical treatment. In addition, it has been found that overlay welding of the gap portion is the most effective in preventing the occurrence of crevice corrosion at the joint portion.
[0013]
The present invention has been achieved based on the above findings, and the gist is as follows.
(1) In mass%, Cr: 9 to 19%, C + N: 0.03% or less, Al: 0.002 to 0.2%, S: 0.01% or less, and further, Ti and Nb When the C + N content is x (% by mass) and the Ti content y (% by mass) and the Nb content z (% by mass) are contained alone, Is 8x ≦ y ≦ 0.6, 18x ≦ z ≦ 0.6, and when contained in a complex form, 1 <(y / 8x) + (z / 18x) and y + z ≦ 0.6 Chromium-containing steel for a container material, the balance being Fe and unavoidable impurities.
(2) The chromium-containing steel for container materials according to (1), wherein the steel further contains Ca in an amount of 0.005% by mass or less.
(3) The container material according to (1) or (2), wherein the steel further contains one or more of Mo, W, and V in an amount of 0.5 to 3% by mass. For chromium-containing steel.
(4) After performing the melt welding on the steel according to any one of the above (1) to (3) while performing a back shield using an argon gas at a flow rate of 20 L / min or more, further, the molten welded portion And a method for welding chromium-containing steel for container material, which comprises chemically removing oxide scale generated around the chrome-containing steel.
(5) After mechanically joining the steel according to any one of the above (1) to (3) by resistance welding or caulking structure, build-up welding is performed on the welded portion or the joined portion, and further thereafter, A method for welding chromium-containing steel for a container material, wherein the build-up weld and the oxide scale generated around the weld are chemically removed.
(6) The build-up welding uses an austenitic stainless steel as a welding rod, and the components contained in the welding rod are, by mass%, Cr: 16 to 25%, Ni: 8 to 16%, C: : 0.03% or less, N: 0.05% or less, Mn: 2.00% or less, the balance being Fe and unavoidable impurities, and the Cr equivalent and the Ni equivalent satisfy the following formula. The method for welding a chromium-containing steel for a container material according to the above (5).
Cr equivalent × Ni equivalent> 160
(However, Cr equivalent = Cr (mass%) + Mo (mass%) + 1.5Si (mass%), Ni equivalent = Ni (mass%) + 0.5Mn (mass%) + 30C (mass%) + 30N (mass%), Mo and Si are contained as inevitable impurities.)
(7) A container material obtained by processing and forming the chromium-containing steel according to any one of (1) to (3).
(8) The container according to (7), wherein the container material is a constituent material of a storage container for a solution containing an aqueous phase having a pH of 3 to 12 and containing halide ions of 200 mass ppm or less. Container material.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The container material of the present invention is intended to be used as a storage container for a solution containing an aqueous phase having a pH of 3 to 12 and containing halide ions of 200 mass ppm or less. In a conventional painted iron container, damage due to corrosion is a problem particularly when the halide ion concentration is 0.01 mass ppm or more. Therefore, the steel of the present invention is intended to be used as a storage container for a solution containing a water phase having a pH of 3 to 12 containing 0.01 to 200 mass ppm of halide ions. The storage temperature is generally 60 ° C. or lower.
[0015]
The solution containing an aqueous phase having a pH of 3 to 12 containing 200 ppm by mass or less of halide ions may contain an oil phase, or may be an emulsion of the aqueous phase and the oil phase. Further, a mixture of additives such as a pigment may be used.
[0016]
The reasons for limiting the additive components of the nickel-free chromium-containing steel of the present invention are described below. In the following description, the composition of steel and the amount of chemical substances are all% by mass.
[0017]
Chromium is an essential element for ensuring the corrosion resistance of the base material, and it is necessary to add 9% or more to exhibit the corrosion resistance. However, if added in excess of 19%, the toughness of the welded portion is significantly reduced, so the upper limit is 19%.
[0018]
Carbon and nitrogen are elements that deteriorate the corrosion resistance and toughness of the weld, and the arithmetic sum x (% by mass) of these elements is set to 0.03% or less.
[0019]
Titanium and niobium are elements added to stabilize carbon and nitrogen. Titanium and niobium are added alone or in combination. However, the addition amount of Ti (mass%) and the addition amount z (mass%) of Nb are respectively set to 8x ≦ y ≦ 0.6 and 18x ≦ z ≦ 0.6 in the case of single addition. In the case of (1), 1 <(y / 8x) + (z / 18x) and y + z ≦ 0.6. When the added amounts of titanium and niobium satisfy the above relational expression, stabilization by fixing carbon and nitrogen of the base material is performed, and accordingly, the corrosion resistance and toughness of the welded portion are improved. However, if the addition amounts of titanium and niobium, alone or in combination, exceed 0.6%, on the contrary, the toughness is adversely affected, so the upper limit is 0.6%.
[0020]
Al is an essential element for improving the corrosion resistance of the base material and the corrosion resistance and toughness of the welded portion. Al improves the corrosion resistance of the base metal and the corrosion resistance and toughness of the welded portion by adding 0.002% or more. However, if added in excess of 0.2%, the corrosion resistance and toughness of the weld are reduced, so 0.2% is made the upper limit.
[0021]
S is an element that causes a reduction in the corrosion resistance of the base material and the corrosion resistance and toughness of the welded portion. Therefore, the content of S needs to be 0.01% or less.
[0022]
The chromium-containing steel according to the present invention is Fe and inevitable impurities other than the above-mentioned additional components. However, in addition to the above-mentioned additional elements, Ca may be added as necessary. Ca is effective in improving the corrosion resistance and toughness of the welded portion. However, if Ca is added in excess of 0.005%, the corrosion resistance of the base material and the decrease in the corrosion resistance and toughness of the welded portion are caused. Upper limit.
[0023]
Further, in addition to the above-mentioned additional elements, Mo, W, and V may be further added as necessary.
[0024]
Mo, W, and V are additive elements effective for improving the corrosion resistance, and exhibit an improvement in the corrosion resistance by adding 0.5% or more. However, if it is added in excess of 3%, the strength of the material will increase significantly and the toughness will decrease, so the upper limit is 3%. These elements can be added alone or in combination.
[0025]
Next, a method for welding the steel of the present invention will be described.
[0026]
The welding method targeted by the present invention is a joining method using a general fusion welding method as a method for welding a container.
[0027]
The fusion welding method means a MIG (Metal Inert Gas) welding method, a TIG (Tungsten Inert Gas) welding method, a laser welding method, and a plasma welding method. In general, the welded portion formed by the fusion welding method often has poor corrosion resistance. However, depending on the welding conditions, a protective oxide scale is formed, which may contribute to the improvement of the corrosion resistance. Means for Solving the Problems With respect to the method for welding the steel of the present invention, the present inventors have proposed a fusion welding method for improving the corrosion resistance of a weld in a solution containing an aqueous phase having a pH of 3 to 12 containing halide ions of 200 mass ppm or less. As a result of intensive studies, it was found that the implementation of a back shield using argon gas when performing fusion welding was extremely effective in improving the corrosion resistance.
[0028]
That is, the welding method of the steel of the present invention is a fusion welding method of MIG welding, TIG welding, laser welding, and plasma welding. When performing fusion welding, a back shield using argon gas is performed. This is an indispensable measure for preventing corrosion resistance deterioration due to the incorporation of atmospheric oxygen and nitrogen into the weld, and requires a flow rate of argon gas of 20 L / min or more. When the flow rate is less than 20 L / min, the shielding effect at the time of welding is insufficient, and an oxide scale causing deterioration of corrosion resistance is formed. Therefore, a flow rate of 20 L / min or more is required.
[0029]
However, even if the above-mentioned back shield is performed and the fusion welding is performed, it is difficult to completely prevent the formation of a thin oxide scale partially at and around the welded portion. In the welding of the steel of the present invention, the removal of the oxide scale is indispensable because the oxide scale is involved in the reduction of the corrosion resistance. By removing the oxide scale, the corrosion resistance of the welded portion is greatly improved.
[0030]
Examples of the method for removing the oxide scale according to the present invention include a mechanical or chemical removal method.However, depending on the roughness of the steel material surface, the removal of the oxide scale cannot be sufficiently performed only by the mechanical removal method. Therefore, application of a chemical removal method is preferable. Furthermore, in the method for welding steel of the present invention, since the shielding by argon gas is performed at the time of welding, the thickness of the formed oxide scale is small, and therefore, without performing pretreatment such as blasting or polishing, chemical treatment is performed. It is possible to remove the oxide scale by a selective removal method.
[0031]
In the chemical removal method according to the present invention, treatment with a mixed acid of nitric acid and hydrofluoric acid is preferable, and the concentrations of nitric acid and hydrofluoric acid are preferably 5 to 30% and 0.5 to 5%, respectively. When the nitric acid concentration is less than 5%, a sufficient oxidizing power cannot be obtained, and the removal of oxide scale becomes insufficient. However, if it exceeds 30%, the generation amount of NOx (nitrogen oxide) increases, which is not preferable. When the content of hydrofluoric acid is less than 0.5%, the effect of accelerating the dissolution of steel is small, which is not preferable. However, even if added over 5%, the effect of accelerating the dissolution of steel is almost saturated, so the upper limit is 5%.
[0032]
Since the treatment temperature and the treatment time depend on the thickness of the oxide scale, it can be regarded that the oxide scale has been removed by visual observation, that is, the treatment temperature at which the colored portion can be regarded as having a metallic luster. It is preferable to select the time and the time.
[0033]
In a specific embodiment of the chemical treatment using a mixed acid of nitric acid and hydrofluoric acid, a paste containing nitric acid and hydrofluoric acid may be applied to the weld and its surroundings, or a solution containing nitric acid and hydrofluoric acid May be impregnated into gauze, filter paper, or the like, and adhered to the welded portion and its surrounding portion. However, in the latter method, the solution is easily volatilized, so that the paste is easier to handle.
[0034]
In addition to the above method, an electrolytic treatment using a neutral salt solution may be performed. Neutral salt electrolysis uses an aqueous solution in which an electrolyte such as sodium nitrate or sodium sulfate of 10 to 30% is dissolved, and a stainless steel plate (for example, SUS304 steel) serving as a cathode and the present invention steel is placed in an electrolytic bath containing the aqueous solution. It is preferable to perform immersion and electrolysis using the steel of the present invention as an anode at a current density of 0.05 to 3 A / cm 2 until removal of oxide scale can be visually confirmed. If the current density is less than 0.05 A / cm 2 , it is difficult to dissolve the oxide film in a passive state, and the oxide scale tends to remain. However, an electrolytic current density exceeding 3 A / cm 2 is not preferable because the rate of power consumption for generating oxygen by electrolysis of water is increased as compared with overpassive dissolution. After electrolytic pickling, it is preferable to wash with water.
[0035]
After the chemical treatment, the weld may be further polished. The polishing reduces the surface roughness of the welded portion and contributes to the improvement of the corrosion resistance of the welded portion. Polishing can be performed using a polishing belt or a carbon brush, but it is not preferable to use one that does not contribute to improving the corrosion resistance of the welded portion. For example, an iron-based brush is not preferable because it causes rust.
[0036]
After performing the chemical treatment and / or polishing, immersion in a nitric acid solution containing no hydrofluoric acid, or application of a paste containing nitric acid, a so-called passivation treatment also effectively works to improve corrosion resistance. . The nitric acid concentration is desirably 10 to 40% by mass. If the nitric acid concentration is less than 10% by mass, the oxidizing power is insufficient, so that it is difficult to form a highly protective passive film mainly composed of chromium on the steel surface. If the nitric acid concentration exceeds 40% by mass, the oxidizing power of nitric acid becomes extremely strong, so that care must be taken in handling the chemical solution, which is not preferable.
[0037]
In addition to the above-described fusion welding, a resistance welding method such as seam welding or spot welding, or a mechanical joining method using a caulking structure can be applied to the welding method of the present invention steel.
[0038]
In the resistance welding method, since the molten portion does not come into direct contact with the external environment and the welding time is short, it is not necessary to perform a back shield as in the case of the above-described fusion welding, but the oxidation generated by welding is not necessary. The chemical removal of the scale is indispensable, and the above-described chemical removal method may be performed.
[0039]
Furthermore, in joining by resistance welding or caulking structure, it is necessary to prevent deterioration of corrosion resistance in the gap due to formation of a gap in the joint, that is, occurrence of gap corrosion. The present inventors have conducted intensive studies on a method for reliably preventing the occurrence of crevice corrosion, and as a result, have found that a method of overlay welding a gap portion has the highest anticorrosion effect.
[0040]
That is, in the resistance welded portion and the joint portion with the caulking structure according to the present invention, the build-up welding is performed, and then, the above-described method for chemically removing oxide scale is performed on the welded portion and the surrounding oxide scale forming portion. Do.
[0041]
In the overlay welding according to the present invention, either a ferritic stainless steel common metal or an austenitic stainless steel can be used for the welding rod.
[0042]
As the welding rod of ferritic stainless steel, a general welding rod can be used. However, when ferritic stainless steel is used, the toughness is inferior to that when austenitic stainless steel is used. Therefore, it is preferable to use austenitic stainless steel.
[0043]
Next, an austenitic stainless steel welding rod used for overlay welding according to the present invention will be described.
[0044]
Chromium requires more than 16% to ensure the corrosion resistance of the weld. However, the corrosion resistance of the weld increases with an increase in the chromium content in the weld metal. However, if it exceeds 25%, the phase fraction of δ-ferrite in the weld increases, causing deterioration of the weld toughness. , 25% as the upper limit.
[0045]
Nickel is an element indispensable for obtaining a γ-structure, and requires addition of 8% or more. However, if it exceeds 16%, the phase fraction of δ ferrite is small, so that phosphorus or sulfur segregates at the grain boundaries and causes grain boundary cracking during welding cooling, so the upper limit is 16%.
[0046]
Manganese is also an effective element for selecting the γ structure, but if it exceeds 2%, it adversely affects the corrosion resistance, so the upper limit is 2%.
[0047]
Molybdenum and silicon are not particularly actively added elements but may be present as impurities, but molybdenum and silicon are usually 0.2% or less, and silicon is 0.4 to 0.8%. There are many.
[0048]
Regarding the contents of carbon and nitrogen, the carbon content is 0.03% or less, and the nitrogen content is 0.05% or less. If the contents of carbon and nitrogen exceed the above ranges, precipitation of chromium carbonitride occurs at the grain boundary of the base material, deteriorating the intergranular corrosion resistance. In particular, in order to balance both corrosion resistance and weld cracking, it is desirable that the product of Cr equivalent and Ni equivalent (Cr equivalent × Ni equivalent) exceeds 160 based on the following equation (1).
[0049]
Cr equivalent × Ni equivalent> 160 Equation (1)
(However, Cr equivalent = Cr% + Mo% + 1.5Si%, Ni equivalent = Ni% + 0.5Mn% + 30C% + 30N%, Mo and Si are contained as unavoidable impurities.)
The nickel-free chromium-containing steel of the present invention can be produced using either an electric furnace or hot metal. For the steel of the present invention, it is necessary to reduce the concentration of carbon and nitrogen in the steel for the above-described reasons. Therefore, in both the electric furnace and hot metal, the secondary refining process is important, and the carbon and nitrogen in the steel are important. It is necessary to sufficiently reduce the concentration. The molten steel whose composition has been adjusted in this way is usually continuously cast to form a slab. The slab is sufficiently rolled in a temperature range of 1,050 to 1,200 ° C. in a temperature range selected according to the type of steel, and then hot-rolled to a predetermined thickness. Subsequently, a solution heat treatment is performed in a temperature range of 800 to 950 ° C., and a shot and a pickling process are performed to obtain a product.
[0050]
【Example】
Here, examples of the present invention will be described, but the present invention is not limited to the conditions used in the examples.
(Example 1)
Specimens of length 100 mm × width 50 mm × thickness 1.2 mm were prepared for inventive steels 1 to 8 and comparative steels 1 to 5 shown in Table 1. Next, two test pieces of the same steel type were subjected to TIG welding in the longitudinal direction while back-shielding using argon gas at a flow rate of 30 L / min.
[0051]
[Table 1]
After welding, the welded portion and the periphery of the welded portion were pickled with a mixed solution of a 10% by mass aqueous solution of nitric acid and a 3% by weight aqueous solution of hydrofluoric acid to remove oxide scale formed during welding. The pickling was carried out until it was considered that the oxide scale could be removed by visual observation, that is, the colored portion could be regarded as having a metallic luster. After pickling, it was washed with water and dried.
[0053]
Next, using the welded test piece, (1) immersion for one month in an aqueous solution having a chloride ion concentration of 100 mass ppm at a liquid temperature of 50 ° C. and pH 3, and (2) chloride at a liquid temperature of 50 ° C. and pH 5 (3) immersed in a solution consisting of an aqueous phase and an oil phase having a substance ion concentration of 100 mass ppm for one month; The immersion test was performed under the following three conditions.
[0054]
The corrosion resistance of the base material and the welded portion of the test piece after the immersion test was evaluated by visual observation, ◎: no occurrence of red rust and spots, ○: extremely slight spots, Δ: clear spots, × : Evaluated in four stages of obvious red rust.
[0055]
Table 2 shows the results of the immersion test. The evaluation of the steels 1 to 8 of the present invention was 〇 or Δ under any of the above three conditions, indicating excellent corrosion resistance in the base metal and the welded portions, whereas the evaluation of the comparative steels 1 to 5 wasで も or △ under any of the above three conditions, and red rust was generated at the welded portion.
[0056]
[Table 2]
(Example 2)
Using the steels 1, 3, and 7 of the present invention shown in Table 1, test pieces having the same shape as in Example 1 were produced. Next, seam welding was performed on two test pieces of the same steel type by butt in the longitudinal direction, and further, welding rods of austenitic stainless steel shown in Table 3 (welding rods 1 to 3 of the present invention, welding rods of comparative examples). Overlay welding was performed using the rods 1 and 2) in the combinations shown in Table 4.
[0058]
[Table 3]
After welding, the welded portion and the vicinity of the welded portion were pickled using the same mixed solution as in Example 1 to remove oxide scale formed at the time of welding. Confirmation as to whether or not the oxide scale could be removed was performed in the same manner as in Example 1. After pickling, washing and drying were performed.
[0060]
Next, an immersion test was performed on the welded test piece under the same three conditions as in Example 1, and in the same manner as in Example 1, the corrosion resistance of the base material and the welded portion of the test piece after the immersion test Was observed and evaluated.
[0061]
Table 4 shows the results of the immersion test. In the invention examples 1 to 3 using the steel of the invention and the welding rod of the method of the invention, 〇 or Δ was obtained under any of the above three conditions, indicating extremely good corrosion resistance. In Comparative Examples 1 to 3 using the welding rods of Examples, any of the above three conditions was × or Δ, and red rust occurred in the welded portions.
[0062]
[Table 4]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention can provide a nickel-free chromium-containing steel, a method for welding the same, and a container material, which can secure corrosion resistance and toughness of a weld portion and are optimal in terms of cost as a container material.
Claims (8)
Ｃｒ ：９〜１９％、
Ｃ＋Ｎ：０．０３％以下、
Ａｌ ：０．００２〜０．２％、
Ｓ ：０．０１％以下、
を含有し、さらに、ＴｉおよびＮｂを単独または複合して含有し、前記Ｃ＋Ｎ含有量をｘ（質量％）とすると、Ｔｉの含有量ｙ（質量％）、およびＮｂの含有量ｚ（質量％）は、それぞれ単独で含有する場合は、
８ｘ≦ｙ≦０．６、
１８ｘ≦ｚ≦０．６、
であり、複合して含有する場合は、
１＜（ｙ／８ｘ）＋（ｚ／１８ｘ）、かつ、ｙ＋ｚ≦０．６
であり、残部がＦｅおよび不可避的不純物からなることを特徴とする容器材料用クロム含有鋼。In mass%,
Cr: 9 to 19%,
C + N: 0.03% or less,
Al: 0.002 to 0.2%,
S: 0.01% or less,
Further, when Ti and Nb are contained alone or in combination, and the C + N content is x (% by mass), the Ti content y (% by mass) and the Nb content z (% by mass) ), When each is contained alone,
8x ≦ y ≦ 0.6,
18x ≦ z ≦ 0.6,
And if it is contained in combination,
1 <(y / 8x) + (z / 18x) and y + z ≦ 0.6
Chromium-containing steel for a container material, the balance being Fe and unavoidable impurities.
Ｃｒ：１６〜２５％、
Ｎｉ：８〜１６％、
Ｃ ：０．０３％以下、
Ｎ ：０．０５％以下、
Ｍｎ：２．００％以下
で、残部がＦｅおよび不可避的不純物からなり、さらに、Ｃｒ当量およびＮｉ当量が下式を満たすことを特徴とする請求項５に記載の容器材料用クロム含有鋼の溶接方法。
Ｃｒ当量×Ｎｉ当量＞１６０
｛ただし、Ｃｒ当量＝Ｃｒ（質量％）＋Ｍｏ（質量％）＋１．５Ｓｉ（質量％）、Ｎｉ当量＝Ｎｉ（質量％）＋０．５Ｍｎ（質量％）＋３０Ｃ（質量％）＋３０Ｎ（質量％）、ＭｏおよびＳｉは不可避的不純物として含有されるものである。｝The build-up welding uses austenitic stainless steel as a welding rod, and the content of the welding rod is, in mass%,
Cr: 16 to 25%,
Ni: 8 to 16%,
C: 0.03% or less,
N: 0.05% or less,
The chromium-containing steel for container material according to claim 5, wherein Mn: 2.00% or less, the balance being Fe and unavoidable impurities, and further, Cr equivalent and Ni equivalent satisfy the following formulas. Method.
Cr equivalent × Ni equivalent> 160
｛However, Cr equivalent = Cr (mass%) + Mo (mass%) + 1.5Si (mass%), Ni equivalent = Ni (mass%) + 0.5Mn (mass%) + 30C (mass%) + 30N (mass%), Mo and Si are contained as unavoidable impurities. ｝
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006097908A (en) * | 2004-09-28 | 2006-04-13 | Nisshin Steel Co Ltd | Hot water storage tank of welded structure and its construction method |
| JP2007254894A (en) * | 2007-03-28 | 2007-10-04 | Nippon Steel & Sumikin Stainless Steel Corp | Chromium-containing steel for vessel material and welding method therefor, and vessel material |
| WO2010090041A1 (en) * | 2009-02-09 | 2010-08-12 | 新日鐵住金ステンレス株式会社 | Ferrite stainless steel with low black spot generation |
| WO2012018074A1 (en) * | 2010-08-06 | 2012-02-09 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel |
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Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006097908A (en) * | 2004-09-28 | 2006-04-13 | Nisshin Steel Co Ltd | Hot water storage tank of welded structure and its construction method |
| JP2007254894A (en) * | 2007-03-28 | 2007-10-04 | Nippon Steel & Sumikin Stainless Steel Corp | Chromium-containing steel for vessel material and welding method therefor, and vessel material |
| WO2010090041A1 (en) * | 2009-02-09 | 2010-08-12 | 新日鐵住金ステンレス株式会社 | Ferrite stainless steel with low black spot generation |
| JP2010202973A (en) * | 2009-02-09 | 2010-09-16 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel with low black spot generation |
| AU2010211864B2 (en) * | 2009-02-09 | 2012-12-06 | Nippon Steel Stainless Steel Corporation | Ferrite stainless steel with low black spot generation |
| US8894924B2 (en) | 2009-02-09 | 2014-11-25 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferrite stainless steel with low black spot generation |
| WO2012018074A1 (en) * | 2010-08-06 | 2012-02-09 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel |
| JP2012036444A (en) * | 2010-08-06 | 2012-02-23 | Nippon Steel & Sumikin Stainless Steel Corp | Ferritic stainless steel with low blackspot generation |
| CN103052731A (en) * | 2010-08-06 | 2013-04-17 | 新日铁住金不锈钢株式会社 | Ferritic stainless steel |
| JP2022121577A (en) * | 2017-03-27 | 2022-08-19 | Ｊｆｅ建材株式会社 | Corrugated steel water channel member |
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