JP3549397B2

JP3549397B2 - Corrosion resistant steel

Info

Publication number: JP3549397B2
Application number: JP16358798A
Authority: JP
Inventors: 謙治加藤; 將夫黒崎; 康秀森本; 英俊新頭
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1998-06-11
Filing date: 1998-06-11
Publication date: 2004-08-04
Anticipated expiration: 2018-06-11
Also published as: JPH11350087A

Description

【０００１】
【発明の属する技術分野】
本発明は、耐食鋼に係り、更に詳しくは、例えば、（１）自動車や船舶等の内燃機関排気系統、ボイラ排気系統、低温熱交換機、焼却炉床等の高温湿潤腐食環境、（２）橋梁、支柱、建築内外装材、屋根材、建具、厨房部材、各種手すり、ガードレール、各種フック、ルーフドレイン、鉄道車両等の大気腐食環境、（３）各種貯蔵タンク、支柱、杭、矢板等の土壌腐食環境、（４）缶容器、各種容器、低温熱交換機、浴室部材、自動車構造部材等の結露腐食環境（冷凍、湿潤、乾燥が複合する腐食環境を含む）、（５）貯水槽、給水管、給湯管、缶容器、各種容器、食器、調理機器、浴槽、プール、洗面化粧台等の水道水腐食環境、（６）缶容器、各種容器、食器、調理機器等の飲料水腐食環境、（７）各種鉄筋構造物、支柱等のコンクリート腐食環境、（８）船舶、橋梁、杭、矢板、海洋構造物等の海水腐食環境等の、種々の腐食環境において優れた耐食性を有する耐食鋼に関する。
【０００２】
【従来の技術】
従来、自動車を中心とする内燃機関の排気系統には、内面あるいは外面からの腐食を抑制するために普通鋼にアルミニウムメッキや亜鉛メッキを施した鋼が使用されてきた。環境汚染を抑制するために排気ガス浄化の目的で触媒等が排気系統に具備されたためにこうしたメッキ鋼材では耐食性が充分ではなくなり、鋼素地の耐食性向上を目的として５〜１０％のＣｒを含有させた鋼が、特開昭６３−１４３２４０号公報や特開昭６３−１４３２４１号公報で開示されている。しかし、近年の車両の使用期間および保証期間の延長に伴なって、更にＣｒを１８％程度まで含有させ、あるいは更にＭｏを添加した高級ステンレス鋼が排気系統に多く使用されている。
【０００３】
しかし、このような高級ステンレス鋼であっても孔食状の局部腐食が発生する場合があるなど、耐食性は必ずしも充分ではない。また、こうした高級ステンレス鋼はＣｒやＭｏを多量に含有するために加工性が悪く、排気系部材のような複雑な形状を形成するためには、製造に非常な困難を伴い、製造工程が著しく複雑になるために加工コストも高くなるという難点がある。かつ、素材コストも高い。
【０００４】
上記の排気系統を代表として、一般にＣｒをある程度含有する鋼では使用腐食環境が厳しくなると局部腐食が発生し易く、これに対する手段として腐食に対する抵抗を向上させるためには、更にＣｒあるいはＭｏの含有量を増加させるのが極めて一般的な技術的手段であった。また、ＣｒおよびＭｏを用いて耐食性を保有させる場合、排気ガス環境に対しては充分な耐食性を有する場合でも、米国やカナダの寒冷地のように、冬季に道路路面の凍結を防止する目的で多量の塩を散布する場合には、かかる塩分によって外面から排気系部材が侵食されることも問題となっている。
【０００５】
近年、特開平５−２７９７９１号公報、特開平６−１７９９４９号公報、特開平６−１７９９５０号公報、特開平６−１７９９５１号公報、特開平６−２１２２５６号公報、特開平６−２１２２５７号公報、特開平７−３３８８号公報において、耐食性の向上あるいは耐食性と加工性の向上を目的としたＣｒにＡｌを添加した鋼が開示されている。これらの鋼は、排気系内面耐食性あるいは排気系内面耐食性と加工性の向上にはある程度有効と認められるが、塩害耐食性を中心とする湿潤耐食性に関しては改善の余地を残しているのが現状である。
【０００６】
【発明が解決しようとする課題】
本発明は、こうした現状に鑑みて、内燃機関の排気系統をはじめとする高温湿潤腐食環境、結露腐食環境、更には大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の様々な腐食環境における耐食性の優れた低コスト耐食鋼を提供することを目的としている。
【０００７】
【課題を解決するための手段】
本発明者らは上記の目的を達成すべく、内燃機関の排気系統をはじめとする高温湿潤腐食環境、結露腐食環境、更には大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の様々な腐食環境において優れた耐食性を有する鋼を開発するべく、種々の観点から検討してきた。
【０００８】
まず、本発明者らは最も腐食に対して厳しい排気系統の内面腐食環境について検討し、内燃機関排気系統の腐食は排気ガス中に含まれる塩化物、硫酸イオン等が８０〜１５０℃に加熱された環境において起こることを見出した。
更に、該腐食環境において耐食性を向上させる手段を種々検討した結果、Ａｌを０．１〜１０％添加したＣｒを０．５〜９．９％含む鋼が排気系統をはじめとする腐食環境で非常に優れた耐食性を示すことを見出した。
【０００９】
更に本発明者らはより優れた鋼にせんとして検討を続けた結果、Ｃｒを０．５〜９．９％、Ａｌを０．１〜１０％含有する鋼のＣおよびＮを低減した上でＮｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆを特定の条件を満足するように添加すると、耐食性の改善と加工性の向上に効果があること、脱酸および強化元素としてはＳｉおよびＭｎが適切であること、上記の鋼にＣｕ，Ｍｏ，Ｓｂ，Ｎｉ，Ｗを単独あるいは組み合わせて添加するとより優れた耐食性が得られることを見出した。
【００１０】
一方で本発明者らは、排気系統の内面腐食環境に次ぐ厳しい腐食環境である塩害腐食や塩水等の乾湿繰り返しに対する腐食抵抗を高めた鋼材を得る手段についても別途並行して検討した結果、Ｃｒを０．１〜９．９％含有し、Ａｌを０．１％以上含有する鋼を基材として、その表面に、水溶液環境における電位が基材よりも卑なる金属の層を形成すると、優れた耐食性、特に優れた耐塩害腐食性が得られることを見い出した。特に基材中へのＡｌの添加は、基材表面に被覆した電位が基材よりも卑なる金属の層が部分的に消失し、ごくわずかに基材表面が腐食環境に露出した後の耐食性向上に効果が顕著であり、更に、被覆金属に、Ｍｇ，Ｉｎのうちのいずれか１種以上を、重量％で０．０５％以上、１０％以下含有せしめたものがより一層優れた耐食性を実現することを見出した。
【００１１】
このＡｌの基材中への添加による耐食性向上挙動は、上述した基材の耐食性とは全く異なる現象であり、基材表面に被覆した電位が基材よりも卑なる金属の層が存在し、かつ、この金属層が部分的に消失したときに初めて認められる現象であることを確認している。
見出した著しい耐食性向上の理由には現状では不明点が多いが、基材にＡｌを添加することで、基材表面が腐食環境に露出した後の残存する基材表面に被覆した、電位が基材よりも卑なる金属の層の消失速度が著しく低下し、従って基材表面の腐食環境に露出される面積の拡大速度が著しく低下し、同時に、露出した基材部分に対する基材表面に被覆した電位が基材よりも卑なる金属の層の基材露出部分に対する保護作用が長期にわたって継続することによって、耐食性が向上していることを確認している。
【００１２】
このような効果が認められる基材表面の腐食環境への露出部分は顕微鏡観察で初めて確認できるもので、絶対値では約０．０５ｍｍ^２程度以下の微小面積で、全腐食面積に対する比率では０．２％以下のわずかなものであり、実使用を想定した巨視的な肉眼外観上は全く赤錆の発生がないことはもとより、一般的には基材の腐食が認められないと判断される外観を呈している。しかもこのような状態が長期間維持されることが特徴である。
【００１３】
従来の知見では、基材表面に被覆した電位が基材よりも卑なる金属の層が存在し、かつ、この金属層が部分的に消失したときには、表面に被覆した金属層の腐食速度は基材金属の腐食を抑制するために増大し、従って基材金属の腐食環境への露出面積は急速に拡大し、速やかに基材金属の腐食に移行すると考えるのが一般的であることを考えると、基材金属中へのＡｌの添加による上述した耐食性向上は、従来全く知られていなかった本願発明の根本となる耐食性向上手段であり、本願発明のこのような新たな知見に基づいてなされたものである。
【００１４】
更に耐食性の向上を目的に引き続き検討を行い、このような基材中へのＡｌの添加に伴い、鋼中に従来安定的に添加することが困難とされてきた各種元素を添加することが可能となることを新たに見出した。特に、Ａｌを０．１〜１０％含有する鋼に、Ｍｇを添加することでより一層、上述した基材と被覆金属の相互作用による耐食性向上が著しいことを新たに見出した。
【００１５】
本発明者らは、基材表面に被覆した電位が基材よりも卑なる金属の層が存在する基材金属中へのＡｌとＭｇの同時添加による耐食性向上効果を更に高めるための手段について種々検討を重ね、基材へのＳｉ，Ｍｎ，Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆ，Ｃｕ，Ｍｏ，Ｓｂ，Ｎｉ，Ｗの添加が有効であることを明らかにした。
【００１６】
更に、本発明者らは検討を続け、水溶液環境における電位が基材よりも卑なる金属として、アルミニウム、アルミニウムを主体とする合金、亜鉛、亜鉛を主体とする合金、クロム、クロムを主体とする合金、マンガン、マンガンを主体とする合金、が本発明の目的に適する金属であることをも見出した。
本発明は主に上記の知見に基づいてなされたものであり、本願第１発明の要旨は、重量％で、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：０．０１〜３．０％、
Ｃｒ：０．１〜９．９％、
Ａｌ：０．１〜１０％、
残部Ｆｅおよび不可避的不純物からなり、該不可避的不純物のうちＣを０．０２％以下、Ｐを０．０３％以下、Ｓを０．０１％以下、Ｎを０．０２％以下に制限した鋼を基材とし、該基材の表面に、水溶液環境における電位が該基材よりも卑なる金属の被覆層を０．５〜５００μｍ厚さに形成した耐食鋼において、
該被覆層の金属が、重量％で、ＭｇおよびＩｎのうち少なくとも１種を単独含有量で０．０５〜１０％含有することを特徴とする耐食鋼にある。
【００１７】
第２発明の要旨は、第１発明の鋼において、基材が付加成分として更に、重量％で、
Ｃｕ：０．０１〜５．０％、
Ｍｏ：０．０５〜１０％、
Ｓｂ：０．０１〜０．５％、
Ｎｉ：０．０１〜１０％、
Ｗ：０．０５〜３．０％、
の１種または２種以上を含有することを特徴とする耐食鋼にある。
【００１８】
第３発明の要旨は、第１発明、第２発明の鋼において、基材が付加成分として更に、重量％で、
希土類元素：０．００１〜０．１％、Ｃａ：０．０００１〜０．０５％
の１種または２種以上を含有することを特徴とする耐食鋼にある。
第４発明の要旨は、第１発明、第２発明、第３発明の鋼において、基材が付加成分として更に、重量％で、Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆの中から選ばれる１種あるいは２種以上の元素を単独含有量で０．０１〜１％含有し、かつ次式を満足することを特徴とする耐食鋼にある。
【００１９】
Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９≧０．８×（Ｃ／１２＋Ｎ／１４）
第５発明の要旨は、第１発明、第２発明、第３発明、第４発明において、被覆層の金属が、アルミニウムあるいはアルミニウムを主体とする合金のいずれかであることを特徴とする耐食鋼にある。
【００２０】
第６発明の要旨は、第１発明、第２発明、第３発明、第４発明において、被覆層の金属が、亜鉛あるいは亜鉛を主体とする合金のいずれかであることを特徴とする耐食鋼にある。
第７発明の要旨は、第１発明、第２発明、第３発明、第４発明において、被覆層の金属が、クロムあるいはクロムを主体とする合金のいずれかであることを特徴とする耐食鋼にある。
【００２１】
第８発明の要旨は、第１発明、第２発明、第３発明、第４発明において、被覆層の金属が、マンガンあるいはマンガンを主体とする合金のいずれかであることを特徴とする耐食鋼にある。
【００２２】
【発明の実施の形態】
以下に、本発明において基材の各成分の範囲を限定した理由を述べる。
Ｓｉ：Ｓｉは、基材表面に、水溶液環境における電位が基材よりも卑なる金属の層を０．０５〜５００μｍ厚さに形成せしめた場合の耐食性を向上する効果をもたらすが、０．０１％未満では効果が認められず、３％を超えて添加してもその効果が飽和する。従って、含有量範囲を０．０１％以上３％以下に限定する。更にＣｒを０．１％以上含有する鋼にＳｉを添加することで脱酸剤および強化元素としての添加が有効であるが、含有量が０．０１５％未満ではその脱酸効果が充分ではなく、１．５％以上を含有するともはやその効果は飽和している上に加工性をやや低下させる。従って、０．０１５％以上１．５％以下の範囲で添加することがより望ましい。
【００２３】
Ｍｎ：Ｍｎは、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．０１％未満では効果が認められず、３％を超えて添加してもその効果が飽和する。従って、含有量範囲を０．０１％以上３％以下に限定する。更にＭｎは鋼の脱酸剤として有効で、０．０５％以上を含有させる必要があるが、１．２％を超えて含有させてもその効果はもはや飽和しているばかりか、過剰にＭｎを含有させると加工性をが低下する。従って、０．０５％以上１．２％以下の範囲で添加することがより望ましい。
【００２４】
Ｃｒ：Ｃｒは、Ａｌを０．１％以上含有する鋼にＣｒを添加することで、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．１％未満では効果が十分ではなく、一方９．９％を超えて添加してもその効果が飽和する。従ってＣｒの含有量は０．１％以上９．９％以下に限定する。更に排気ガス環境等に対する基材単体での耐食性を確保するためにＡｌを０．１％以上含有する鋼に０．５％以上を含有させることが必要であるが、９．９％を超えて含有させても加工性が低下するので、上限含有量は９．９％とする。従って、０．５％以上９．９％以下の範囲で添加することがより望ましい。
【００２５】
Ａｌ：Ａｌは本発明において耐食性を確保するために最も重要な元素であって、Ｃｒを０．１％以上９．９％以下含有する鋼にＡｌを添加することで、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．１％未満では効果が十分ではなく、１０％を超えて添加してもその効果が飽和するものであるから、Ａｌの含有量は０．１％以上１０％以下に限定する。
【００２６】
Ｃ，Ｎ：ＣおよびＮは、鋼板の加工性を低下させる上に、ＣはＣｒと炭化物を生成して耐食性を低下させるので、またＮは靱性を低下させるので、ＣおよびＮ量は少ない方が望ましく、上限含有量はいずれも０．０２％とし、いずれも少ないほど好ましい。更に、優れた加工性を確保するためには、Ｃ＋Ｎの合計量を低減する必要があり、本発明の望ましい態様による鋼としては、Ｃ＋Ｎを０．０３％以下とする。
【００２７】
Ｐ：Ｐは、多量に存在すると靱性を低下させるので少ない方が望ましく、上限含有量は０．０３％とする。
Ｓ：Ｓも、多量に存在すると耐孔食性を低下させるので少ない方が望ましく、上限含有量は０．０１％とする。
以上が本発明が対象とする耐食性に優れた鋼の基材の基本的成分であるが、本発明においては、必要に応じて更に以下の元素を添加して耐食性を一段と向上させた鋼材も対象としている。
【００２８】
Ｃｕ：Ｃｕは、Ａｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．０１％未満では効果が認められず、一方５％を超えて添加してもその効果が飽和する。従って、その範囲を０．０１％以上５％以下の範囲に限定する。更に０．０５％以上添加すると、基材単体での全面腐食に対する抵抗を向上させる効果があり、２．５％を超えて添加するとその効果は飽和する。従って、０．０５％以上２．５％以下の範囲で添加することがより望ましい。
【００２９】
Ｍｏ：ＭｏはＡｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に添加することで、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．０５％未満では効果が認められず、一方１０％を超えて添加してもその効果が飽和する。従って、その範囲を０．０５％以上１０％以下に限定する。更にＭｏは０．１％以上添加すると、基材単体での孔食の発生と成長を抑制する効果があるが、３．０％を超えて添加してもそのその効果は飽和するばかりか加工性を低下させる。従って、０．１％以上３％以下の範囲で添加することがより望ましい。
【００３０】
Ｓｂ：Ｓｂは、Ａｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に０．０１％以上添加すると、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、０．０１％未満では効果が認められず、一方０．５％を超えて添加してもその効果が飽和する。従って、その範囲を０．０１％以上０．５％以下に限定する。更にＳｂを添加することで、基材単体での孔食および全面腐食に対する抵抗を向上させる効果があるが、０．３％を超えて添加すると熱間加工性をやや低下させる。従って、０．０１５％以上０．３％以下の範囲で添加することがより望ましい。
【００３１】
Ｎｉ：Ｎｉは、Ａｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に０．０１％以上添加すると、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、一方１０％を超えて添加してもその効果が飽和する。従って、その範囲を０．０１％以上１０％以下に限定する。更にＮｉを０．１％以上添加することで、基材単体での孔食を抑制する効果があるが、６％を超えて添加しても効果が飽和する。従って、０．１％以上６％以下の範囲で添加することがより望ましい。
【００３２】
Ｗ：Ｗは、Ａｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に０．０５％以上添加すると、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、一方３％を超えて添加してもその効果が飽和する。従って、その範囲を０．０５％以上３％以下に限定する。更にＷを添加することで、基材単体での孔食の発生と成長を抑制する効果があるが、０．１％未満では効果は十分ではなく、一方２．０％を超えて添加しても効果が飽和するばかりか加工性を低下させる。従って、０．１％以上２％以下の範囲で添加することがより望ましい。
【００３３】
希土類元素（ＲＥＭ）、Ｃａ：希土類元素（ＲＥＭ）やＣａはＡｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に添加することで、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、ＲＥＭでは０．００１％未満では効果が認められず、Ｃａでは０．０００１％未満では効果が認められず、一方ＲＥＭでは０．１％を超えて、Ｃａでは０．０５％を超えて添加してもその効果が飽和する。従って、ＲＥＭの範囲を０．００１％以上０．１％以下、Ｃａの範囲を０．０００１％以上０．０５％以下にそれぞれ限定する。更にＲＥＭおよびＣａは熱間加工性の向上と基材単体での耐孔食性の改善に効果のある元素であるが、添加量がＲＥＭでは０．０１％未満、Ｃａでは０．００５％未満ではその効果が充分ではなく、Ｃａでは０．０１％を、ＲＥＭでは０．０５％を超えて添加すると、それぞれ粗大な非金属介在物を生成して逆に熱間加工性や耐孔食性を劣化させる。従って、Ｃａは０．００５％以上０．０１％以下の範囲で、ＲＥＭは０．０１％以上０．０５％以下の範囲でそれぞれ添加することがより望ましい。なお、本発明において希土類元素（ＲＥＭ）とは原子番号が５７〜７１番および８９〜１０３番の元素およびＹを指す。
【００３４】
Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆ：Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，ＨｆはＡｌを０．１％以上含有しＣｒを０．１％以上９．９％以下含有する鋼に添加することで、基材表面に水溶液環境における電位が基材よりも卑なる金属の層を０．５〜５００μｍ厚さに形成せしめた場合に耐食性を向上する効果をもたらすが、各元素共に０．０１％未満では効果が認められず、一方約１．０％を超えて添加してもその効果が飽和する。従ってＮｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆの含有量は０．０１％以上１．０％以下に限定する。更に、Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆは含Ｃｒ鋼中のＣおよびＮを炭化物として固定することによって基材単体での耐食性の向上や加工性の改善に顕著な効果があり、各元素単独の添加あるいは２種以上の元素を複合して添加することができるが、単独での添加量が０．０５％未満では効果がなく、０．８％を超えて添加するといたずらにコストを上昇させるとともに圧延疵等の原因となる。従って、Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆは０．０５％以上０．８％以下の範囲で添加することがより望ましい。かつ、加工性を有効に改善するためには、Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆの添加量の合計が次式を満足することが必要である。
【００３５】
Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９≧０．８×（Ｃ／１２＋Ｎ／１４）
本発明においては、鋼基材表面、特に、少なくとも腐食環境に曝される面を、基材よりも電位が卑なる金属で被覆する。基材よりも電位が卑なる金属で被覆する厚さが０．５μｍ以下では、基材にＡｌを添加することによる、基材表面が腐食環境に露出した後の残存する基材表面に被覆した、電位が基材よりも卑なる金属の層の消失速度の低下と、基材表面の腐食環境に露出される面積の拡大速度の著しい低下、同時に、露出した基材部分に対する基材表面に被覆した電位が基材よりも卑なる金属の層の基材露出部分に対する保護作用が長期にわたって継続するという効果の発現が充分ではなく、５００μｍを超える厚さまで被覆しても、もはやその効果は飽和しているのに対して、生産性を低下させて徒にコストを上昇させるだけであるから、被覆層の厚さは０．５〜５００μｍとする。
【００３６】
上記被覆層の金属が、ＭｇおよびＩｎのうちの少なくとも１種を単独含有量で０．０５〜１０％含有することにより、より一層優れた耐食性が得られる。
Ｍｇ，Ｉｎの含有量を上記範囲に限定した理由は下記のとおりである。すなわち、それぞれの添加量が、０．０５％未満では耐食性を向上させる効果が見られず、逆に１０％を超えて添加しても効果が飽和するばかりで、本発明鋼の特徴である低コストを損なう。従って、Ｍｇ，Ｉｎはそれぞれ、０．０５〜１０％の範囲で添加する。
【００３７】
被覆層を形成する、水溶液環境における電位が基材よりも卑なる金属としては、アルミニウム、亜鉛、クロム、マンガン、およびこれらを主体とする合金を使用することができる。
また、被覆のプロセスは該金属が基材に充分に固着されていればそのプロセスを限定するものではない。用途やコスト等を考慮した上で選択すれば良く、溶融メッキ、電着メッキ、溶融塩電解メッキ、真空蒸着、スパッタリング、イオンプレーティング、溶射等を使用することができ、それらを併用することも可能である。また、被覆およびそのための処理の前後にいかなる処理を行なってもよい。
【００３８】
亜鉛を主体とする合金とは、合金成分のうち最大量を占める成分が亜鉛である合金すなわち亜鉛基合金であり、一般に亜鉛基合金に含有されるアルミニウム等の合金成分および不純物成分を含んでよい。
アルミニウムを主体とする合金とは、合金成分のうち最大量を占める成分がアルミニウムである合金すなわちアルミニウム基合金であり、一般にアルミニウム基合金に含有されるシリコン、亜鉛等の合金成分および不純物成分を含んでよい。
【００３９】
クロムを主体とする合金とは、合金成分のうち最大量を占める成分がクロムである合金すなわちクロム基合金であり、一般にクロム基合金に含有されるシリコン等の合金成分および不純物成分を含んでよい。
マンガン主体とする合金とは、合金成分のうち最大量を占める成分がマンガンである合金すなわちマンガン基合金であり、一般にマンガン基合金に含有されるアルミニウム等の合金成分および不純物成分を含んでよい。
【００４０】
また、使用上の目的から、鋼管や板材等のように表裏面を有する材料の一方の面だけに被覆されていれば良い場合には、卑なる金属を被覆するプロセスから片面のみが被覆される鋼を使用してもよい。このような場合に片面だけの被覆を使用するか、あるいは両面に被覆された鋼を使用するかは、コストや溶接性等の他の要因を考慮して選択すれば良い。
【００４１】
上記被覆を施す時期については、コイル、板、棒、ケーブル、穿孔鋼管等の鋼材の一般的な形状とした後に、本発明の被覆やそのための処理を行ってもよいし、被覆・処理後の本発明鋼をプレスやロール成形等で所定の形状に成形し、更に加工・溶接して製品として製造しても良いし、本発明の鋼を例えば電縫鋼管等としてまず鋼管の形状にした後に、２次加工および溶接等によって製品としても良く、更に、本発明の被覆・処理を施す前に鋼材を上述したようなプロセスによって目的の形状とした後に本発明の表面被覆処理を施すことも可能であり、その他のプロセスも含めて本発明で限定する組成および処理条件の組み合わせを有する鋼は、いずれも本発明の対象とするところであって、コストや既存製造設備の制約等によって最適な製品製造工程を選択することができ、どの製造工程を選択したとしてもそれをもって本発明の範囲を逸脱するものではない。
【００４２】
以上の本発明において提案する鋼は、内燃機関の排気系統をはじめとする高温湿潤腐食環境、結露腐食環境はもとより、大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の種々の腐食環境に適用することができる。
【００４３】
【実施例】
以下に本発明の実施例について説明する。
〔耐食性の評価〕
表１，２に成分を示す鋼を溶製し、熱延、冷延等の通常の鋼板製造工程によって肉厚１ｍｍの鋼板とし、９００℃にて焼鈍を施した後、両面それぞれに、片面あたり１５±２μｍの条件で被覆を施した。表１，２に示した被覆１はアルミニウム被覆、被覆２は亜鉛被覆、被覆３はマンガン被覆、被覆４はクロム被覆をそれぞれ示す。
【００４４】
次に、これらの鋼板から幅５０ｍｍ、長さ７０ｍｍの試験片を採取して、以下に述べる各種の腐食試験に供した。
高温湿潤腐食試験は、硫酸イオン１０００ｐｐｍ、塩化物イオン１０００ｐｐｍ、重炭酸イオン５０００ｐｐｍをアンモニウム塩の形で添加した水溶液５０ｃｃ中に試験片を半分まで浸漬し、試験容器ごと１３０℃の雰囲気に保持して試験溶液が完全に蒸発・揮散することを７５回繰り返す試験とした。本試験は自動車排気系の内面環境に相当する腐食試験であり、実車の約４年以下の走行に対応する厳しい試験方法である。試験結果を表１，２に併せて示した。腐食試験結果の◎は最大腐食深さが０．１０ｍｍ未満、○は０．２ｍｍ未満、△は０．３ｍｍ未満、×は０．３ｍｍ以上であったことをそれぞれ示す。
【００４５】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は塩化物を含む高温湿潤という非常に厳しい腐食環境であっても良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
また、大気環境や自動車排気系外面の塩害腐食を想定した試験としては、５０℃−１時間の塩水噴霧後、６０℃で湿度９６％の環境に５時間保持した後、更に１時間の冷凍保持を行うことを６００回繰り返す塩害腐食試験とした。試験後の試験片について最大孔食深さを測定し、試験結果とした。得られた結果を表１，２に併せて示した。最大孔食深さが０．２ｍｍ以下のものは◎、最大孔食深さが０．２ｍｍを超え０．４ｍｍ以下のものは○、最大孔食深さが０．４ｍｍを超え０．８ｍｍ以下のものは×、最大孔食深さが０．８ｍｍを超えるものは××で表示することとした。
【００４６】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は塩害腐食という非常に厳しい腐食環境であっても良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。土壌腐食試験は、含水率１５％、比抵抗３５０Ω・ｃｍに塩化ナトリウム含有量で調整した砂中に試験片を埋め込み、５０℃に保持して約７００日放置する試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は最大腐食深さが０．０５ｍｍ未満、○は０．１ｍｍ未満、△は０．５ｍｍ未満、×は０．５ｍｍ以上であったことをそれぞれ示す。
【００４７】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は土壌腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
コンクリート中腐食試験は、塩化物を含む海砂を用いて混練したポルトランドセメント中に試験片を埋め込みサンプルとなし、凝固させた後、人工海水中にサンプルを半分まで浸漬し、５５℃の環境に約１０００日放置する試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は腐食の発生が認められなかったもの、○は発錆面積率が５％未満、△は発錆面積率が１０％未満、×は１０％以上であったことをそれぞれ示す。
【００４８】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）はコンクリート中腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
水道水環境腐食試験は、水道水中に試験片を浸漬し、５０℃の雰囲気に２４ケ月間保持する試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は腐食の発生が認められなかったもの、○は発錆面積率が５％未満、△は発錆面積率が１０％未満、×は１０％以上であったことをそれぞれ示す。
【００４９】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は水道水腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
海水環境腐食試験は、海岸飛沫帯に試験片を２６ケ月間暴露する試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は腐食深さ０．０５ｍｍ未満だったもの、○は０．１ｍｍ未満、△は０．３ｍｍ未満、×は０．３ｍｍ以上であったことをそれぞれ示す。
【００５０】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は海水腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
結露腐食試験は、−２０℃の環境に２時間保持後湿度９８％、３０℃の環境に４時間保持することを２１００回繰り返す試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は腐食の発生が認められなかったもの、○は発錆面積率が５％未満、△は発錆面積率が１０％未満、×は１０％以上であったことをそれぞれ示す。
【００５１】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は結露腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
大気腐食試験は、海岸から約２３ｍの位置に試験片を約９００日暴露する試験とした。試験結果を表１，２に併せて示した。腐食試験結果の◎は腐食が認められなかったもの、○は発錆面積率が３％未満、△は発錆面積率が１０％未満、×は１０％以上であったことをそれぞれ示す。
【００５２】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は大気腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
飲料水環境腐食試験は、水酸化ナトリウムを用いてｐＨを２．３に調整し、高純度窒素ガスを通して脱気し、２７℃に保持した、（ａ）０．５％リン酸溶液、（ｂ）０．５％クエン酸溶液、（ｃ）０．５％クエン酸−０．５％塩化ナトリウム溶液等の溶液８５０ｃｃ中に試験片を４５日間浸漬し、溶液中に溶出した鉄イオン量を分析する試験とした。なお本試験のみ、被覆１のアルミニウム被覆、被覆４のクロム被覆について試験を実施した。試験結果を表１，２に併せて示した。腐食試験結果の◎は溶液中への鉄イオンの溶出量が１ｐｐｍ以下、○は３ｐｐｍ未満、△は５ｐｐｍ未満、×は５ｐｐｍ以下であったことをそれぞれ示す。
【００５３】
表１，２から明らかなように、本発明鋼（番号１〜４０，５１〜９０）は飲料水腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
すなわち本発明鋼（番号１〜４０，５１〜９０）は高温湿潤腐食環境、結露腐食環境、大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の種々の腐食環境で良好な耐食性を示しているのに対して、比較鋼（番号４１〜５０，１００〜１０９）は耐食性に劣ることがわかる。
〔加工性の評価〕
表２に成分を示す鋼を溶製し、熱延、冷延など通常の鋼板製造工程によって、厚さ１．０ｍｍの鋼板とし、８５０℃にて焼鈍を施した。これらの鋼板から幅１００ｍｍ長さ１００ｍｍの試験片を採取し、絞り比１．８の円筒絞り試験を行なって割れの有無で判定した。試験結果を表２に併せて示した。表２の加工性において○は円筒絞り試験結果が良好であったことを示し、×は円筒絞り試験で割れを生じたことを示している。尚、表２中のＸ値は、次式によって算出したものを記載した。
【００５４】
Ｘ＝Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９−０．８×（Ｃ／１２＋Ｎ／１４）
表２から明らかなように、本発明鋼において特に加工性を向上させたもの（番号５１〜９０）は良好な耐食性を示し、かつ加工性も良好である。すなわち、高温湿潤腐食環境、結露腐食環境、大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の種々の腐食環境で良好な耐食性を示し、かつ加工性も優れている。これに対して、比較鋼（番号１００〜１０９）は耐食性と加工性が同時に達成できないことがわかる。
【００５５】
【表１】

【００５６】
【表２】

【００５７】
【表３】

【００５８】
【表４】

【００５９】
【表５】

【００６０】
【表６】

【００６１】
【表７】

【００６２】
【表８】

【００６３】
【発明の効果】
以上述べたように、本発明によれば、例えば自動車等の内燃機関の排気系統といった高温湿潤腐食環境、結露腐食環境をはじめとして、大気腐食環境、水道水腐食環境、土壌腐食環境、コンクリート腐食環境、海水腐食環境、飲料水腐食環境等の種々の腐食環境において耐食性に優れる耐食鋼が低コストで提供される。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to corrosion-resistant steel, and more specifically, for example, (1) a high-temperature wet-corrosion environment such as an exhaust system for an internal combustion engine of a car or ship, a boiler exhaust system, a low-temperature heat exchanger, an incinerator floor, and (2) a bridge , Struts, building interior and exterior materials, roofing materials, fittings, kitchen components, various handrails, guardrails, various hooks, roof drains, atmospheric corrosion environments such as railway vehicles, (3) soils such as various storage tanks, struts, piles, sheet piles, etc. Corrosion environment, (4) canned containers, various containers, low-temperature heat exchangers, bathroom members, automobile structural members, etc. Dew condensation corrosion environment (including corrosive environment where freezing, wetting and drying are combined), (5) water storage tank, water supply pipe , Hot water supply pipes, can containers, various containers, tableware, cooking equipment, bathtubs, pools, vanities, etc., tap water corrosive environments, (6) can containers, various containers, tableware, cooking equipment, etc. drinking water corrosive environments, ( 7) Concrete for various rebar structures, columns, etc. Corrosive environments, (8) ships, bridges, piles, sheet piles, seawater corrosive environments such as marine structures, to corrosion resistant steel having excellent corrosion resistance in various corrosive environments.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an exhaust system of an internal combustion engine mainly for automobiles, steel in which ordinary steel is subjected to aluminum plating or galvanization in order to suppress corrosion from an inner surface or an outer surface has been used. Since a catalyst or the like is provided in the exhaust system for the purpose of purifying exhaust gas in order to suppress environmental pollution, such a plated steel material does not have sufficient corrosion resistance, and contains 5 to 10% Cr for the purpose of improving the corrosion resistance of the steel base. Steels are disclosed in JP-A-63-143240 and JP-A-63-143241. However, with the extension of the service period and the warranty period of vehicles in recent years, high-grade stainless steel further containing about 18% of Cr or further adding Mo is widely used in exhaust systems.
[0003]
However, even such a high-grade stainless steel does not always have sufficient corrosion resistance such that pitting-like local corrosion may occur. In addition, such high-grade stainless steel contains a large amount of Cr and Mo, and thus has poor workability. In order to form a complicated shape such as an exhaust system member, the production is extremely difficult, and the production process is remarkably difficult. There is a disadvantage that the processing cost increases due to the complexity. Also, the material cost is high.
[0004]
As represented by the above-mentioned exhaust system, in general, steel containing a certain amount of Cr is liable to cause local corrosion when the use corrosion environment becomes severe, and in order to improve the resistance to corrosion as a measure against this, the content of Cr or Mo is further increased. Was a very common technical measure. Also, when Cr and Mo are used to maintain corrosion resistance, even if they have sufficient corrosion resistance to the exhaust gas environment, they are used to prevent freezing of road surfaces in winter, such as in the cold regions of the United States and Canada. When spraying a large amount of salt, there is also a problem that the exhaust system member is eroded from the outer surface by the salt.
[0005]
In recent years, JP-A-5-279793, JP-A-6-179949, JP-A-6-179950, JP-A-6-179951, JP-A-6-212256, JP-A-6-212257, Japanese Patent Application Laid-Open No. 7-3388 discloses a steel in which Al is added to Cr for the purpose of improving corrosion resistance or improving corrosion resistance and workability. Although these steels are recognized to be effective to some extent in improving the exhaust system inner corrosion resistance or the exhaust system inner surface corrosion resistance and workability, there is still room for improvement in wet corrosion resistance, especially salt corrosion resistance. .
[0006]
[Problems to be solved by the invention]
In view of these circumstances, the present invention provides a high-temperature wet corrosion environment including an exhaust system of an internal combustion engine, a dew condensation corrosion environment, an air corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion environment, a seawater corrosion environment. It is an object of the present invention to provide a low-cost corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as a drinking water corrosive environment.
[0007]
[Means for Solving the Problems]
The present inventors, in order to achieve the above object, high-temperature wet corrosion environment including the exhaust system of the internal combustion engine, condensation corrosion environment, further atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, In order to develop steel having excellent corrosion resistance in various corrosive environments such as a seawater corrosive environment and a drinking water corrosive environment, studies have been made from various viewpoints.
[0008]
First, the present inventors examined the internal corrosion environment of the exhaust system which is the most severe against corrosion. In the corrosion of the internal combustion engine exhaust system, chloride, sulfate ions, etc. contained in the exhaust gas were heated to 80 to 150 ° C. And what happens in an environment.
Furthermore, as a result of various studies on means for improving the corrosion resistance in the corrosive environment, steel containing 0.5 to 9.9% of Cr to which Al is added in an amount of 0.1 to 10% has been found to be extremely difficult in a corrosive environment such as an exhaust system. And excellent corrosion resistance.
[0009]
Furthermore, the present inventors have continued their studies as a better steel, and as a result, after reducing C and N of steel containing 0.5 to 9.9% of Cr and 0.1 to 10% of Al. When Nb, V, Ti, Zr, Ta, and Hf are added to satisfy specific conditions, they are effective in improving corrosion resistance and workability, and Si and Mn are suitable as deoxidizing and strengthening elements. Certainly, it has been found that more excellent corrosion resistance can be obtained by adding Cu, Mo, Sb, Ni, W alone or in combination to the above steel.
[0010]
On the other hand, the present inventors separately and in parallel studied a means of obtaining a steel material having an increased corrosion resistance to salt damage corrosion, which is a severe corrosive environment next to the inner corrosive environment of the exhaust system, and repeated wet and dry conditions such as salt water. It is excellent to form a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material on the surface of a steel base material containing 0.1 to 9.9% of Al and 0.1% or more of Al. Corrosion resistance, particularly excellent salt corrosion resistance. In particular, the addition of Al to the substrate causes corrosion resistance after the metal layer whose potential applied to the substrate surface is more base than the substrate partially disappears and the substrate surface is slightly exposed to the corrosive environment. The effect is remarkable in the improvement. Further, a coating metal containing at least one of Mg and In in a content of 0.05% or more and 10% or less by weight% has more excellent corrosion resistance. I found it to be realizable.
[0011]
The corrosion resistance improving behavior by the addition of Al into the base material is a phenomenon completely different from the corrosion resistance of the base material described above, and there is a metal layer in which the potential coated on the base material surface is lower than the base material, In addition, it has been confirmed that this phenomenon is observed only when the metal layer partially disappears.
At present, there are many unknown reasons for the remarkable improvement in corrosion resistance found, but by adding Al to the base material, the potential based on the potential applied to the remaining base material surface after the base material surface was exposed to the corrosive environment. The rate of disappearance of the metal layer, which is more base than the material, is significantly reduced, and therefore, the rate of expansion of the area exposed to the corrosive environment on the substrate surface is significantly reduced, and at the same time, the substrate surface is coated on the exposed substrate portion. It has been confirmed that the corrosion resistance is improved by continuing the protective action on the exposed portion of the base material of the metal layer having a potential lower than that of the base material over a long period of time.
[0012]
The exposed portion of the substrate surface to the corrosive environment where such an effect is recognized can be confirmed for the first time by microscopic observation, and the absolute value is about 0.05 mm. ² It is a very small area of about less than 0.2%, which is a small percentage of less than 0.2% of the total corrosion area. In addition to the fact that there is no red rust on the macroscopic appearance assuming actual use, Has an appearance determined that no corrosion of the substrate is observed. Moreover, such a state is characterized by being maintained for a long time.
[0013]
According to conventional knowledge, when a metal layer coated on the surface of a base material has a potential lower than that of the base material, and when the metal layer partially disappears, the corrosion rate of the metal layer coated on the surface is reduced to a base value. Considering that it is common to think that the area exposed to the corrosive environment of the base metal increases rapidly in order to suppress the corrosion of the base metal, and that the base metal corrodes rapidly. The above-mentioned improvement in corrosion resistance by the addition of Al to the base metal is a means for improving corrosion resistance that has never been known before and is the basis of the present invention, and has been made based on such new findings of the present invention. Things.
[0014]
Further studies were conducted for the purpose of improving corrosion resistance, and with the addition of Al to such a base material, it is possible to add various elements that have conventionally been difficult to stably add to steel. Was newly found. In particular, it has been newly found that by adding Mg to steel containing 0.1 to 10% of Al, the corrosion resistance is significantly improved by the interaction between the base material and the coated metal.
[0015]
The present inventors have proposed various means for further improving the corrosion resistance improving effect by simultaneous addition of Al and Mg to a base metal in which a metal layer having a base potential lower than that of the base is present on the base metal surface. Through repeated studies, it was clarified that the addition of Si, Mn, Nb, V, Ti, Zr, Ta, Hf, Cu, Mo, Sb, Ni, and W to the base material was effective.
[0016]
Further, the present inventors have continued to study, as a metal whose potential in an aqueous solution environment is lower than that of the base material, aluminum, an alloy mainly containing aluminum, zinc, an alloy mainly containing zinc, chromium, mainly containing chromium It has also been found that alloys, manganese, and manganese-based alloys are metals suitable for the purpose of the present invention.
The present invention has been mainly made on the basis of the above findings, and the gist of the first invention of the present application is
Si: 0.01 to 3.0%,
Mn: 0.01 to 3.0%,
Cr: 0.1 to 9.9%,
Al: 0.1 to 10%,
Steel with the balance being Fe and unavoidable impurities, of which C is 0.02% or less, P is 0.03% or less, S is 0.01% or less, and N is 0.02% or less. In a corrosion-resistant steel in which a coating layer of a metal whose potential in an aqueous environment is lower than that of the base material is formed to a thickness of 0.5 to 500 μm on the surface of the base material,
The corrosion-resistant steel is characterized in that the metal of the coating layer contains 0.05 to 10% by weight of at least one of Mg and In alone.
[0017]
The gist of the second invention is that, in the steel of the first invention, the base material further includes, as an additional component,
Cu: 0.01 to 5.0%,
Mo: 0.05 to 10%,
Sb: 0.01-0.5%,
Ni: 0.01 to 10%,
W: 0.05 to 3.0%,
Corrosion-resistant steel comprising one or more of the following.
[0018]
The gist of the third invention is that in the steels of the first invention and the second invention, the base material is further added as an additional component by weight%.
Rare earth element: 0.001-0.1%, Ca: 0.0001-0.05%
Corrosion-resistant steel comprising one or more of the following.
The gist of the fourth invention is that, in the steel of the first invention, the second invention, and the third invention, the base material is further selected as an additional component from Nb, V, Ti, Zr, Ta, and Hf by weight%. Corrosion resistant steel comprising one or more elements in a single content of 0.01 to 1% and satisfying the following expression.
[0019]
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)
The gist of the fifth invention is the corrosion-resistant steel according to the first invention, the second invention, the third invention, and the fourth invention, wherein the metal of the coating layer is either aluminum or an alloy mainly composed of aluminum. It is in.
[0020]
The gist of the sixth invention is that in the first invention, the second invention, the third invention, and the fourth invention, the metal of the coating layer is any one of zinc or an alloy mainly containing zinc. It is in.
The gist of the seventh invention is that in the first invention, the second invention, the third invention, and the fourth invention, the metal of the coating layer is any one of chromium and an alloy mainly composed of chromium. It is in.
[0021]
The gist of the eighth invention is the corrosion-resistant steel according to the first, second, third and fourth inventions, wherein the metal of the coating layer is either manganese or an alloy mainly containing manganese. It is in.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the reason for limiting the range of each component of the substrate in the present invention will be described.
Si: Si has the effect of improving the corrosion resistance when a metal layer having a potential lower than that of the base material in an aqueous solution environment is formed to a thickness of 0.05 to 500 μm on the base material surface, but 0.01%. If the amount is less than 3%, the effect is not recognized, and even if added over 3%, the effect is saturated. Therefore, the content range is limited to 0.01% or more and 3% or less. Further, the addition of Si as a deoxidizing agent and a strengthening element is effective by adding Si to steel containing 0.1% or more of Cr, but if the content is less than 0.015%, the deoxidizing effect is not sufficient. , 1.5% or more, the effect is no longer saturated and the processability is slightly reduced. Therefore, it is more desirable to add in the range of 0.015% or more and 1.5% or less.
[0023]
Mn: Mn has an effect of improving corrosion resistance when a metal layer having a potential lower than that of a base material in an aqueous solution environment is formed to a thickness of 0.5 to 500 μm on a base material surface, but 0.01% If the amount is less than 3%, the effect is not recognized, and even if added over 3%, the effect is saturated. Therefore, the content range is limited to 0.01% or more and 3% or less. Further, Mn is effective as a deoxidizing agent for steel, and it is necessary to contain Mn in an amount of 0.05% or more. However, if Mn is contained in excess of 1.2%, the effect is not only saturated, but Mn is excessively increased. When it is contained, the processability decreases. Therefore, it is more desirable to add in the range of 0.05% or more and 1.2% or less.
[0024]
Cr: Cr is formed by adding Cr to steel containing 0.1% or more of Al to form a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material on the base material surface to a thickness of 0.5 to 500 μm. When formed, the effect of improving the corrosion resistance is brought about, but if it is less than 0.1%, the effect is not sufficient, while if it exceeds 9.9%, the effect is saturated. Therefore, the content of Cr is limited to 0.1% or more and 9.9% or less. Further, in order to ensure the corrosion resistance of the base material alone against the exhaust gas environment and the like, it is necessary to make the steel containing 0.1% or more of Al contain 0.5% or more, but exceeding 9.9%. Even if it is contained, the workability decreases, so the upper limit content is set to 9.9%. Therefore, it is more desirable to add in the range of 0.5% or more and 9.9% or less.
[0025]
Al: Al is the most important element for securing corrosion resistance in the present invention. By adding Al to steel containing 0.1% or more and 9.9% or less of Cr, an aqueous solution environment is formed on the surface of the base material. When a metal layer having a potential lower than that of the base material is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained. Since the effect is saturated even if added in excess, the Al content is limited to 0.1% or more and 10% or less.
[0026]
C, N: C and N reduce the workability of the steel sheet, and C generates carbides with Cr to reduce the corrosion resistance, and N decreases the toughness. It is desirable that the upper limit content is set to 0.02% in each case, and the lower the content in each case, the more preferable. Furthermore, in order to ensure excellent workability, it is necessary to reduce the total amount of C + N, and as a steel according to a desirable embodiment of the present invention, C + N is set to 0.03% or less.
[0027]
P: If P is present in a large amount, the toughness is reduced. Therefore, it is desirable that P is small, and the upper limit content is 0.03%.
S: Since the presence of a large amount of S lowers the pitting corrosion resistance, the smaller the amount, the better. The upper limit content is 0.01%.
The above are the basic components of the steel substrate excellent in corrosion resistance targeted by the present invention, but in the present invention, steel materials with further improved corrosion resistance by further adding the following elements as necessary are also included. And
[0028]
Cu: Cu has a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material on the surface of a steel base material containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr. When formed to a thickness of 5 to 500 μm, the effect of improving the corrosion resistance is obtained. However, if the content is less than 0.01%, the effect is not recognized. On the other hand, if the addition exceeds 5%, the effect is saturated. Therefore, the range is limited to the range of 0.01% to 5%. Further, if added in an amount of 0.05% or more, there is an effect of improving resistance to general corrosion of the base material alone, and if added in an amount exceeding 2.5%, the effect is saturated. Therefore, it is more desirable to add in the range of 0.05% or more and 2.5% or less.
[0029]
Mo: Mo is a metal whose potential in an aqueous solution environment is lower than that of the base material on the base material surface by being added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr. Is formed in a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained. However, if the content is less than 0.05%, the effect is not recognized. Saturates. Therefore, the range is limited to 0.05% or more and 10% or less. Further, when Mo is added in an amount of 0.1% or more, the effect of suppressing the generation and growth of pitting corrosion in the base material alone is obtained. However, even if added in excess of 3.0%, the effect is not only saturated but also processed. Reduce the nature. Therefore, it is more desirable to add in the range of 0.1% or more and 3% or less.
[0030]
Sb: When Sb is added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr to 0.01% or more, the potential in an aqueous solution environment on the surface of the substrate becomes higher than that of the substrate. When the base metal layer is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained. However, if the content is less than 0.01%, the effect is not recognized, while the addition exceeds 0.5%. Even so, the effect is saturated. Therefore, the range is limited to 0.01% or more and 0.5% or less. Further, the addition of Sb has the effect of improving the resistance to pitting corrosion and general corrosion of the substrate alone, but adding more than 0.3% slightly reduces hot workability. Therefore, it is more desirable to add in the range of 0.015% or more and 0.3% or less.
[0031]
Ni: When Ni is added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr and 0.01% or more of Ni, the electric potential in an aqueous solution environment on the surface of the substrate is higher than that of the substrate. When the base metal layer is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. On the other hand, the effect is saturated even if it exceeds 10%. Therefore, the range is limited to 0.01% or more and 10% or less. Further, by adding 0.1% or more of Ni, there is an effect of suppressing pitting corrosion of the base material alone, but the effect is saturated even if it exceeds 6%. Therefore, it is more desirable to add in the range of 0.1% or more and 6% or less.
[0032]
W: When W is added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr to 0.05% or more of W, the potential of an aqueous solution environment on the surface of the substrate is higher than that of the substrate. When the base metal layer is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained. On the other hand, the effect is saturated even if it exceeds 3%. Therefore, the range is limited to 0.05% or more and 3% or less. Further, the addition of W has the effect of suppressing the occurrence and growth of pitting corrosion in the base material alone, but the effect is not sufficient if it is less than 0.1%, while adding more than 2.0%. This not only saturates the effect but also lowers the workability. Therefore, it is more desirable to add in the range of 0.1% or more and 2% or less.
[0033]
Rare earth element (REM) and Ca: Rare earth element (REM) and Ca are added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr, so that the surface of the base material is added. When a metal layer having a potential lower than that of a base material in an aqueous solution environment is formed to a thickness of 0.5 to 500 μm, the effect of improving corrosion resistance is obtained. However, the effect is not recognized at less than 0.001% in REM. , Ca has no effect if it is less than 0.0001%, while REM exceeds 0.1% and Ca does not exceed the effect even if Ca exceeds 0.05%. Therefore, the range of REM is limited to 0.001% or more and 0.1% or less, and the range of Ca is limited to 0.0001% or more and 0.05% or less. Further, REM and Ca are elements that are effective in improving hot workability and pitting corrosion resistance of the base material alone. However, if the addition amount is less than 0.01% in REM and less than 0.005% in Ca, The effect is not sufficient. If Ca is added in more than 0.01% and REM is added in more than 0.05%, coarse non-metallic inclusions are respectively formed, and conversely, hot workability and pitting corrosion resistance are deteriorated. Let it. Therefore, it is more preferable that Ca is added in the range of 0.005% to 0.01%, and REM is added in the range of 0.01% to 0.05%. In the present invention, the rare earth element (REM) refers to an element having an atomic number of 57 to 71 or 89 to 103 and Y.
[0034]
Nb, V, Ti, Zr, Ta, Hf: Nb, V, Ti, Zr, Ta, Hf are added to steel containing 0.1% or more of Al and 0.1% or more and 9.9% or less of Cr. By doing so, when a metal layer having a potential lower than that of the substrate in an aqueous solution environment is formed to a thickness of 0.5 to 500 μm on the surface of the substrate, the effect of improving the corrosion resistance is brought about. If it is less than 01%, no effect is observed, while if it exceeds about 1.0%, the effect is saturated. Therefore, the contents of Nb, V, Ti, Zr, Ta, and Hf are limited to 0.01% or more and 1.0% or less. Further, Nb, V, Ti, Zr, Ta, and Hf have remarkable effects on the improvement of corrosion resistance and workability of the base material alone by fixing C and N in the Cr-containing steel as carbides. The element can be added alone or two or more elements can be added in combination. However, if the addition amount is less than 0.05%, there is no effect. If the addition amount exceeds 0.8%, the cost is unnecessarily increased. It raises and causes a rolling crack etc. Therefore, it is more desirable to add Nb, V, Ti, Zr, Ta, and Hf in a range of 0.05% or more and 0.8% or less. In addition, in order to effectively improve the workability, the total amount of Nb, V, Ti, Zr, Ta, and Hf needs to satisfy the following expression.
[0035]
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)
In the present invention, the surface of the steel substrate, particularly at least the surface exposed to the corrosive environment, is coated with a metal having a potential lower than that of the substrate. At a thickness of 0.5 μm or less for coating with a metal whose potential is lower than that of the base material, the remaining base material surface after the base material surface was exposed to the corrosive environment was coated by adding Al to the base material. , The rate of disappearance of the metal layer whose potential is lower than that of the base material and the rate of expansion of the area exposed to the corrosive environment of the base material surface are significantly reduced, and at the same time, the base material surface is coated on the exposed base part. The effect of protecting the exposed portion of the base material of the metal layer having a base potential lower than that of the base material over a long period of time is not sufficient, and even when coating is performed to a thickness exceeding 500 μm, the effect is no longer saturated. On the other hand, the thickness of the coating layer is set to 0.5 to 500 μm because it only lowers the productivity and increases the cost.
[0036]
When the metal of the coating layer contains at least one of Mg and In in a single content of 0.05 to 10%, more excellent corrosion resistance can be obtained.
The reasons for limiting the contents of Mg and In to the above ranges are as follows. That is, if the amount of each addition is less than 0.05%, the effect of improving the corrosion resistance is not seen. Conversely, if it exceeds 10%, the effect is only saturated, and the low characteristic which is a feature of the steel of the present invention. Hurt costs. Therefore, each of Mg and In is added in the range of 0.05 to 10%.
[0037]
Aluminum, zinc, chromium, manganese, and alloys based on these can be used as the metal forming the coating layer and having a lower potential in an aqueous solution environment than the base material.
The coating process is not limited as long as the metal is sufficiently fixed to the substrate. It may be selected in consideration of the application, cost, etc., and hot-dip plating, electrodeposition plating, molten salt electrolytic plating, vacuum deposition, sputtering, ion plating, thermal spraying, etc. can be used, and they can be used together It is possible. Further, any treatment may be performed before and after the coating and the treatment therefor.
[0038]
The alloy mainly composed of zinc is an alloy in which the component occupying the largest amount among the alloy components is zinc, that is, a zinc-based alloy, and may generally include an alloy component such as aluminum and an impurity component contained in the zinc-based alloy. .
An alloy mainly composed of aluminum is an alloy in which the component occupying the largest amount among the alloy components is aluminum, that is, an aluminum-based alloy, and generally includes an alloy component such as silicon and zinc and an impurity component contained in the aluminum-based alloy. Is fine.
[0039]
The chromium-based alloy is an alloy in which the component occupying the largest amount among the alloy components is chromium, that is, a chromium-based alloy, and may generally include an alloy component such as silicon and an impurity component contained in the chromium-based alloy. .
The alloy mainly composed of manganese is an alloy in which the component occupying the largest amount among the alloy components is manganese, that is, a manganese-based alloy, and may generally include an alloy component such as aluminum and an impurity component contained in the manganese-based alloy.
[0040]
In addition, for the purpose of use, when it is sufficient that only one surface of a material having front and back surfaces such as a steel pipe or a plate material is coated, only one surface is coated from a process of coating a base metal. Steel may be used. In such a case, whether to use coating on one side only or to use steel coated on both sides may be selected in consideration of other factors such as cost and weldability.
[0041]
About the time of the coating, after the coil, plate, rod, cable, and the general shape of steel material such as perforated steel pipe, the coating of the present invention and the treatment therefor may be performed, or after coating and processing The steel of the present invention may be formed into a predetermined shape by press or roll forming or the like, and may be further processed and welded to be manufactured as a product. It may be made into a product by secondary processing and welding, etc. Further, before coating and treatment of the present invention, the steel material can be subjected to the surface coating treatment of the present invention after being formed into a target shape by the above-described process. Any steel having a combination of composition and processing conditions limited by the present invention, including other processes, is the subject of the present invention, and is optimally manufactured due to costs, restrictions on existing manufacturing facilities, and the like. Can select the manufacturing process, it with a do not depart from the scope of the present invention even on the choice of manufacturing process.
[0042]
The steel proposed in the present invention described above can be used not only in a high-temperature wet corrosion environment including an exhaust system of an internal combustion engine, in a condensation corrosion environment, but also in an air corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion environment, and a seawater corrosion environment. It can be applied to various corrosive environments such as drinking water corrosive environment.
[0043]
【Example】
Hereinafter, examples of the present invention will be described.
[Evaluation of corrosion resistance]
The steels having the components shown in Tables 1 and 2 were melted and formed into a steel plate having a thickness of 1 mm by a normal steel plate manufacturing process such as hot rolling or cold rolling, and then subjected to annealing at 900 ° C. The coating was applied under the conditions of 15 ± 2 μm. In Tables 1 and 2, coating 1 indicates aluminum coating, coating 2 indicates zinc coating, coating 3 indicates manganese coating, and coating 4 indicates chromium coating.
[0044]
Next, test pieces having a width of 50 mm and a length of 70 mm were collected from these steel sheets and subjected to various corrosion tests described below.
In the high-temperature wet corrosion test, the test piece was immersed in half in 50 cc of an aqueous solution to which 1000 ppm of sulfate ion, 1000 ppm of chloride ion, and 5000 ppm of bicarbonate ion were added in the form of ammonium salt. The test was repeated 75 times in which the test solution was completely evaporated and volatilized. This test is a corrosion test corresponding to the internal environment of an automobile exhaust system, and is a strict test method corresponding to running of an actual vehicle for about four years or less. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the maximum corrosion depth was less than 0.10 mm, ○ indicates that the depth was less than 0.2 mm, Δ indicates that the depth was less than 0.3 mm, and X indicates that the depth was 0.3 mm or more.
[0045]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance even in a very severe corrosive environment such as high-temperature wet containing chloride. Thus, it can be seen that the comparative steels (Nos. 41 to 50 and 100 to 109) are inferior in corrosion resistance.
As a test assuming salt damage corrosion of the air environment and the outer surface of the automobile exhaust system, the test was carried out by spraying salt water at 50 ° C. for 1 hour, maintaining the temperature at 60 ° C. in an environment of 96% humidity for 5 hours, and further holding for 1 hour by freezing. Is repeated 600 times to obtain a salt damage corrosion test. The maximum pit depth of the test piece after the test was measured and used as the test result. The obtained results are also shown in Tables 1 and 2. If the maximum pit depth is 0.2 mm or less, ◎, if the maximum pit depth is more than 0.2 mm and 0.4 mm or less, ○, the maximum pit depth is more than 0.4 mm and 0.8 mm or less , And those having a maximum pit depth exceeding 0.8 mm are indicated by XX.
[0046]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance even in a very severe corrosive environment such as salt damage corrosion, while the comparative steels (Nos. 41 to 50 and 100 to 109) are inferior in corrosion resistance. The soil corrosion test was a test in which a test piece was embedded in sand adjusted to have a water content of 15% and a specific resistance of 350 Ω · cm with a sodium chloride content, and was left at 50 ° C. for about 700 days. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the maximum corrosion depth was less than 0.05 mm, ○ indicates that it was less than 0.1 mm, Δ indicates that it was less than 0.5 mm, and x indicates that it was 0.5 mm or more.
[0047]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in a soil corrosion environment, whereas the comparative steels (Nos. 109) is inferior in corrosion resistance.
The corrosion test in concrete is performed by embedding a test piece in Portland cement kneaded with sea sand containing chloride to form a sample, solidifying the sample, immersing the sample in half in artificial seawater, and placing it in a 55 ° C environment. A test was performed in which the sample was left for about 1000 days. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, △ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more. .
[0048]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in a corrosive environment in concrete, whereas the comparative steels (Nos. 41 to 50 and 100). To 109) are inferior in corrosion resistance.
The tap water environment corrosion test was a test in which a test piece was immersed in tap water and kept in a 50 ° C. atmosphere for 24 months. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, △ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more. .
[0049]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in tap water corrosive environments, while the comparative steels (Nos. 41 to 50, 100). To 109) are inferior in corrosion resistance.
The seawater environment corrosion test was a test in which a test piece was exposed to a shore splash zone for 26 months. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the corrosion depth was less than 0.05 mm, ○ indicates that the corrosion depth was less than 0.1 mm, Δ indicates that the corrosion depth was less than 0.3 mm, and X indicates that the depth was 0.3 mm or more.
[0050]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in a seawater corrosive environment, while the comparative steels (Nos. 109) is inferior in corrosion resistance.
The dew condensation corrosion test was a test in which holding in an environment of −20 ° C. for 2 hours and then holding in an environment of 98% humidity and 30 ° C. for 4 hours was repeated 2100 times. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, △ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more. .
[0051]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in a dew condensation corrosion environment, whereas the comparative steels (Nos. 109) is inferior in corrosion resistance.
The atmospheric corrosion test was a test in which a test piece was exposed to a position about 23 m from the coast for about 900 days. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 3%, △ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more.
[0052]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in an atmospheric corrosion environment, while the comparative steels (Nos. 109) is inferior in corrosion resistance.
In the drinking water environmental corrosion test, the pH was adjusted to 2.3 using sodium hydroxide, degassed through high-purity nitrogen gas, and kept at 27 ° C. (A) 0.5% phosphoric acid solution, (b) ) A test piece was immersed in 850 cc of a solution of 0.5% citric acid solution, (c) 0.5% citric acid-0.5% sodium chloride solution for 45 days, and the amount of iron ions eluted in the solution was analyzed. Test. Only in this test, the test was performed for the aluminum coating of the coating 1 and the chromium coating of the coating 4. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the amount of iron ions eluted into the solution was 1 ppm or less, ○ indicates less than 3 ppm, Δ indicates less than 5 ppm, and × indicates 5 ppm or less.
[0053]
As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in a drinking water corrosive environment, whereas the comparative steels (Nos. 41 to 50, 100). To 109) are inferior in corrosion resistance.
That is, the steels of the present invention (Nos. 1 to 40 and 51 to 90) are used in high-temperature wet corrosion environment, dew condensation corrosion environment, atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, seawater corrosion environment, drinking water corrosion environment and the like. It can be seen that the comparative steels (Nos. 41 to 50, 100 to 109) are inferior in corrosion resistance, while exhibiting good corrosion resistance in various corrosion environments.
[Evaluation of workability]
A steel having the components shown in Table 2 was melted, and a steel sheet having a thickness of 1.0 mm was formed by a normal steel sheet manufacturing process such as hot rolling or cold rolling, and annealed at 850 ° C. Test pieces having a width of 100 mm and a length of 100 mm were sampled from these steel sheets, and subjected to a cylindrical drawing test with a drawing ratio of 1.8 to determine the presence or absence of cracks. The test results are also shown in Table 2. In the workability in Table 2, ○ indicates that the result of the cylindrical drawing test was good, and × indicates that cracks were generated in the cylindrical drawing test. In addition, the X value in Table 2 described what was calculated by the following formula.
[0054]
X = Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179-0.8.times. (C / 12 + N / 14)
As is clear from Table 2, the steels of the present invention with particularly improved workability (Nos. 51 to 90) show good corrosion resistance and good workability. That is, it shows good corrosion resistance in various corrosive environments such as high temperature wet corrosive environment, dew condensate corrosive environment, atmospheric corrosive environment, tap water corrosive environment, soil corrosive environment, concrete corrosive environment, seawater corrosive environment, drinking water corrosive environment, and Excellent workability. On the other hand, it can be seen that the comparative steels (numbers 100 to 109) cannot simultaneously achieve corrosion resistance and workability.
[0055]
[Table 1]

[0056]
[Table 2]

[0057]
[Table 3]

[0058]
[Table 4]

[0059]
[Table 5]

[0060]
[Table 6]

[0061]
[Table 7]

[0062]
[Table 8]

[0063]
【The invention's effect】
As described above, according to the present invention, for example, a high-temperature wet corrosion environment such as an exhaust system of an internal combustion engine of an automobile, a condensation corrosion environment, an atmospheric corrosion environment, a tap water corrosion environment, a soil corrosion environment, and a concrete corrosion environment. Corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as a seawater corrosive environment and a drinking water corrosive environment is provided at low cost.

Claims

In weight percent,
Si: 0.01 to 3.0%,
Mn: 0.01 to 3.0%,
Cr: 0.1 to 9.9%,
Al: 0.1 to 10%,
Steel with the balance being Fe and unavoidable impurities, of which C is 0.02% or less, P is 0.03% or less, S is 0.01% or less, and N is 0.02% or less. In a corrosion-resistant steel in which a metal coating layer having a potential lower than that of the base material in an aqueous solution environment is formed to a thickness of 0.5 to 500 μm on the surface of the base material,
Corrosion-resistant steel characterized in that the metal of the coating layer contains at least one of Mg and In in a single content of 0.05 to 10% by weight.

The base steel further comprises, in weight%,
Cu: 0.01 to 5.0%,
Mo: 0.05 to 10%,
Sb: 0.01-0.5%,
Ni: 0.01 to 10%,
W: 0.05 to 3.0%,
The corrosion-resistant steel according to claim 1, comprising one or more of the following.

The base steel further comprises, in weight%,
Rare earth element: 0.001-0.1%, Ca: 0.0001-0.05%
The corrosion-resistant steel according to claim 1, comprising one or more of the following.

The steel of the base material further contains, in terms of% by weight, any one or more selected from Nb, V, Ti, Zr, Ta, and Hf in a single content of 0.01 to 1%, The corrosion-resistant steel according to claim 1, wherein the steel satisfies the following expression.
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)

The corrosion-resistant steel according to claim 1, 2, 3, or 4, wherein the metal of the coating layer is one of aluminum and an alloy mainly containing aluminum.

The corrosion-resistant steel according to claim 1, 2, 3, or 4, wherein the metal of the coating layer is one of zinc and an alloy mainly containing zinc.

The corrosion-resistant steel according to claim 1, 2, 3, or 4, wherein the metal of the coating layer is one of chromium and an alloy mainly composed of chromium.

5. The corrosion-resistant steel according to claim 1, wherein the metal of the coating layer is one of manganese and an alloy mainly containing manganese.