JP4184481B2 - Corrosion resistant steel - Google Patents
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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めっきや亜鉛めっき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めっき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の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、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腐食に対する腐食抵抗を高めた鋼材を得る手段について検討した結果、Ａｌを０．３％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出した。
【０００８】
そして、この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ることを見出した。
このＡｌの基材中への添加による耐食性向上挙動は、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。
【０００９】
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。
【００１０】
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０．５ｍｍ２ 程度以下の微小面積で、全腐食面積に対する比率では０．５％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。
【００１１】
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、本願発明はこのような新たな発見に基づいてなされたものである。
【００１２】
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０．３〜４．９６％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。
【００１３】
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の添加あるいは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。
【００１４】
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、アルミニウム合金、亜鉛、亜鉛合金、クロム、クロム合金、マンガン、マンガン合金、が本発明の目的に適する金属であることをも見出した。
これらの被覆金属についても、基材との相互作用による耐食性向上の観点から種々の検討を重ねた結果、アルミニウム、アルミニウム合金、亜鉛、亜鉛合金、クロム、クロム合金、マンガン、マンガン合金、のいずれかにＭｇ，Ｉｎのうちいずれか一種以上を、質量％で単独含有量にて０．０５〜１０％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。
【００１５】
本発明は主に以上の知見に基づいてなされたものであり、第１発明の要旨は、質量％で、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：０．０１〜１．２％、
Ａｌ：０．３〜４．９６％
を含有し、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０．２５％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基材よりも卑なる金属の被覆層を０．０５〜５００μｍ厚さに形成したことを特徴とする耐食鋼にある。
【００１６】
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、質量％で、
Ｍｇ：０．０００３〜０．０５％
を含有することを特徴とする耐食鋼にある。
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、質量％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。
【００１７】
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、質量％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５発明の要旨は、第１発明、第２発明、第３発明、第４発明の鋼において、基材が付加成分として更に、質量％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。
【００１８】
Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９≧０．８×（Ｃ／１２＋Ｎ／１４）
第６発明の要旨は、第１発明、第２発明、第３発明、第４発明、第５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合金のいずれかである耐食鋼にある。
【００１９】
第７発明の要旨は、第１発明、第２発明、第３発明、第４発明、第５発明において、被覆層の金属が、亜鉛あるいは亜鉛合金のいずれかである耐食鋼にある。
第８発明の要旨は、第１発明、第２発明、第３発明、第４発明、第５発明において、被覆層の金属が、クロムあるいはクロム合金のいずれかである耐食鋼にある。
【００２０】
第９発明の要旨は、第１発明、第２発明、第３発明、第４発明、第５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合金のいずれかである耐食鋼にある。
第１０発明の要旨は、第６発明、第７発明、第８発明、第９発明の鋼において、被覆層の金属が更に、質量％で、ＭｇおよびＩｎのうちの少なくとも一種を単独含有量で０．０５〜１０％含有することを特徴とする耐食鋼にある。
【００２１】
【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、鋼の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０．０１％未満ではその脱酸効果が充分ではなく、３％を超えて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低下させるので、含有量範囲を０．０１％以上３％以下に限定する。更にＳｉ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０．０５〜５００μｍ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、０．０１５％未満では効果が認められず、１．５％を超えて添加してもその効果が飽和する。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。
【００２２】
Ｍｎ： Ｍｎは、鋼の脱酸剤として必要で、０．０１％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が低下するので、上限含有量は１．２％とする。更にＭｎ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、０．０５％未満では効果が認められず、１．２％を超えて添加してもその効果が飽和する。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。
【００２３】
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、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、０．３％未満では効果が十分ではなく、４．９６％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０．３％以上４．９６％以下に限定する。４．０％を超えて添加すると加工性を低下させるものであるから、Ａｌの含有量は０．３％以上４．０％以下とする事が好ましい。
【００２４】
Ｃ，Ｎ： ＣおよびＮは、鋼板の加工性を低下させる上に、Ｃは炭化物を生成して基材の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Ｃは０．２５％以下、Ｎは０．０２％以下とする。いずれも少ないほど好ましいが、特にＣを０．０３以下とすることで、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が顕著であり、Ｃは０．０３％以下とすることがより望ましい。
【００２５】
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。
【００２６】
Ｍｇ： Ｍｇは、本発明において耐食性を更に向上させるために添加する元素であって、Ａｌを０．３〜４．９６％含有する鋼に、Ｍｇ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、０．０００３％未満では効果が十分ではなく、０．０５％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、Ｍｇの含有量は０．０００３％以上０．０５％以下に限定する。
【００２７】
Ｃｕ： Ｃｕは、Ａｌを０．３％以上４．９６％以下含有する鋼に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、５．０％を超えて添加するとその効果は飽和する。更に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％未満では効果が認められず、一方約２．５％を超えて添加してもその効果が飽和する。従って、０．１％以上２．５％以下の範囲で添加することがより望ましい。
【００２８】
Ｍｏ： Ｍｏは、Ａｌを０．３％以上４．９６％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ので上限を１０％とする。更にＭｏは、Ａｌを０．３％以上含有する鋼に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。
【００２９】
Ｓｂ： Ｓｂは、Ａｌを０．３％以上４．９６％以下含有する鋼に０．０１％以上添加すると、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、０．５％を超えて添加すると熱間加工性を低下させるので、上限含有量は０．５％とする。更にＳｂ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、０．０１５％未満では効果が認められず、一方０．３％を超えて添加してもその効果が飽和する。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。
【００３０】
Ｎｉ： Ｎｉは、Ａｌを０．３％以上４．９６％以下含有する鋼に０．０１％以上添加すると、基材単体での孔食を抑制する効果があるが、１０％を超えて添加しても効果が飽和するばかりか熱間加工性を低下させるので、上限含有量は１０％とする。更にＮｉ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％未満では効果が認められず、一方６％を超えて添加してもその効果が飽和する。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。
【００３１】
Ｗ： Ｗは、Ａｌを０．３％以上４．９６％以下含有する鋼に０．０５％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効果が飽和するばかりか加工性を低下させるので、上限含有量は３．０％とする。更にＷ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％未満では効果が認められず、一方２％を超えて添加してもその効果が飽和する。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。
【００３２】
希土類元素（ＲＥＭ）、Ｃａ： 希土類元素（ＲＥＭ）およびＣａは熱間加工性の改善に効果のある元素であるが、添加量がＲＥＭでは０．００１％未満、Ｃａでは０．０００１％未満ではその効果が充分ではなく、ＲＥＭでは０．１％を超えて、Ｃａでは０．０５％（０．０１％）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ので、上限含有量はＲＥＭでは０．１％、Ｃａでは０．０５％とした。更にＲＥＭやＣａはＡｌを０．３％以上４．９６％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、Ｃａでは０．００５％未満では効果が認められず、ＲＥＭでは０．０１％未満では効果が認められず、一方Ｃａでは０．０１％を、ＲＥＭ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、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。
【００３３】
Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆ： Ｎｂ，Ｖ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆは鋼中の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０．０１％未満では効果がなく、１．０％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もなるので上限含有量は１．０％とする。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。
【００３４】
Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９≧０．８×（Ｃ／１２＋Ｎ／１４）
更にＴｉ，Ｚｒ，Ｔａ，Ｈｆを、Ａｌを０．３％以上４．９６％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、各元素共に約０．０５％未満では効果が認められず、一方約０．８％を超えて添加してもその効果が飽和する。従って、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。
【００３５】
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未満では、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】
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、およびこれらの合金を使用することができる。
上記被覆層の金属が更に、ＭｇおよびＩｎのうちの少なくとも一種を単独含有量で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。
【００３７】
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。
【００３８】
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、溶融めっき、電着めっき、溶融塩電解めっき、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必要に応じていかなる処理を行なってもよい。
【００３９】
亜鉛合金とは、合金成分のうちの最大量を占める成分が亜鉛である合金であり、一般に亜鉛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であり、一般にアルミニウム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。
【００４０】
クロム合金とは、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であり、一般にクロム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であり、 一般にマンガン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。
【００４１】
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。
【００４２】
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。
【００４３】
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。
【００４４】
【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℃にて焼純を施した後、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。
【００４５】
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１００ｐｐｍ、塩化物イオン２５０ｐｐｍ、重炭酸イオン５００ｐｐｍをアンモニウム塩の形で添加した水溶液５０ｃｃ中の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７０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年以上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。
【００４６】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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１５０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。
【００４７】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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４００Ω・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、３０℃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。
【００４８】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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、４５℃の環境に約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２〜４０，５２〜９０）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、４５℃の雰囲気に６ヶ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。
【００５０】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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１５ヶ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。
【００５１】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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９２％，３０℃の環境に４時間保持することを１０００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。
【００５２】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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４００ｍの位置に試験片を約７００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。
【００５３】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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２．８に調整し、高純度窒素ガスを通気して脱気し、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２５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 以上であったことをそれぞれ示す。
【００５４】
表１，２から明らかなように、本発明鋼（番号２〜４０，５２〜９０）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２〜４０，５２〜９０）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。
【００５５】
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高めたもの（番号５２〜９０）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。
【００５６】
【表１】
【表２】
【表３】
【表４】
【表５】
【表６】
【表７】
【表８】
【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、更に大気腐食環境、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]
BACKGROUND OF THE INVENTION
The present invention relates to corrosion-resistant steel. More specifically, for example, (1) high-temperature and wet-corrosion environment such as an exhaust system of an internal combustion engine such as an automobile or a ship, a boiler exhaust system, a low-temperature heat exchanger, and an incinerator floor; , Struts, interior / exterior materials, roofing materials, joinery, kitchen members, various handrails, guardrails, various hooks, roof drains, railcars, etc., (3) various storage tanks, struts, piles, sheet piles, etc. Corrosive environment, (4) Condensed corrosive environment such as can containers, various containers, low temperature heat exchangers, bathroom members, automobile structural members (including corrosive environments where freezing, wetting and drying are combined), (5) water storage tank, water supply pipe , Hot water pipes, can containers, various containers, tableware, cooking equipment, bathtubs, pools, bathroom vanities, etc., (6) drinking water corrosive environments such as can containers, various containers, tableware, cooking equipment, ( 7) Concrees such as various reinforcing steel structures and struts 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]
Conventionally, the exhaust system of internal combustion engines, mainly automobiles, has been made of ordinary steel to suppress corrosion from the inside or outside.Aluminum platingAndZinc platingSteel has been used. In order to control environmental pollution, the exhaust system was equipped with a catalyst for the purpose of exhaust gas purification.Plated steelHowever, the corrosion resistance is not sufficient, and steel containing 5 to 10% Cr for the purpose of improving the corrosion resistance of the steel substrate is disclosed in Japanese Patent Laid-Open Nos. 63-143240 and 63-143241. . However, with the extension of the use period and warranty period of vehicles in recent years, high-grade stainless steel further containing Cr up to about 18% or further containing Mo is used in the exhaust system.
[0003]
However, even such high-grade stainless steel does not always have sufficient corrosion resistance, such as pitting corrosion-like local corrosion. In addition, these high-grade stainless steels contain a large amount of Cr and Mo, so that the processability is poor, and in order to form a complicated shape such as an exhaust system member, it is very difficult to manufacture and the manufacturing process is remarkably high. Due to the complexity, there is a problem that the processing cost is high. In addition, the material cost is high.
[0004]
As a representative of the above-mentioned exhaust system, in general, steel containing a certain amount of Cr tends to generate local corrosion when the corrosive environment becomes severe. In order to improve the resistance against corrosion as a means against this, the content of Cr or Mo is further increased. It was a very common technical measure to increase. In addition, when Cr and Mo are used to maintain corrosion resistance, even if they have sufficient corrosion resistance to the exhaust gas environment, the purpose is to prevent freezing of road surfaces in the winter, as in the cold regions of the United States and Canada. When spraying a large amount of salt, the exhaust system member is eroded from the outer surface by such salt.
[0005]
In recent years, Japanese Patent Application Laid-Open Nos. Hei 5-279791, Hei 6-179949, Hei 6-179950, Hei 6-179951, Hei 6-212256, Hei 6-212257, Japanese Patent Application Laid-Open No. 7-3388 discloses steel in which Al is added to Cr for the purpose of improving corrosion resistance or improving corrosion resistance and workability. These steels are recognized to be effective to some extent in improving exhaust system inner surface corrosion resistance or exhaust system inner surface corrosion resistance and workability, but there is still room for improvement in terms of wet corrosion resistance centering on salt corrosion resistance. .
[0006]
[Problems to be solved by the invention]
In view of such a current situation, the present invention is a high temperature wet corrosion environment including an exhaust system of an internal combustion engine, a condensation corrosion environment, an air corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion environment, a seawater corrosion environment. Another object of the present invention is to provide a low-cost corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as drinking water corrosive environments.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have studied a means for obtaining a steel material having increased corrosion resistance against dry and wet repeated corrosion such as salt damage corrosion and salt water which is a severe corrosive environment, and as a result, Al is contained 0.3% or more. It has been found that when a steel layer is used as a base material and a metal layer whose potential in an aqueous solution environment is lower than that of the base material is formed on the surface, excellent corrosion resistance, particularly excellent salt corrosion resistance is obtained.
[0008]
This addition of Al is effective in improving the corrosion resistance after the metal layer whose potential is coated on the substrate surface partially disappears and the substrate surface is exposed to a corrosive environment. Was found to be prominent.
The corrosion resistance improvement behavior due to the addition of Al to the base material is a phenomenon completely different from the corrosion resistance of the base material, and there is a metal layer in which the potential coated on the base material surface is lower than the base material, and It has been confirmed that this is the first phenomenon observed when this metal layer partially disappears.
[0009]
The reasons for the significant improvement in corrosion resistance that we have found are currently unknown, but by adding Al to the base material, the potential of the base material surface covered after the base material surface is exposed to the corrosive environment is covered. The disappearance rate of the metal layer that is lower than the material is significantly reduced, and therefore the expansion rate of the area exposed to the corrosive environment of the substrate surface is significantly reduced, and at the same time, the substrate surface is coated on the exposed substrate part. It has been confirmed that the corrosion resistance has been improved by continuing the protective action for the exposed portion of the base material of the metal layer whose potential is lower than that of the base material.
[0010]
The part of the substrate surface where such an effect is recognized can be confirmed for the first time by microscopic observation. The absolute value is a minute area of about 0.5 mm 2 or less, and the ratio to the total corrosion area is 0.5. The appearance is generally judged that corrosion of the base material is not observed, as well as the occurrence of red rust on the macroscopic macroscopic appearance assuming actual use. ing. Moreover, such a state is characterized by being maintained for a long time.
[0011]
According to the conventional knowledge, when there is a metal layer with a lower potential applied to the substrate surface than the substrate, and the metal layer partially disappears, the corrosion rate of the metal layer coated on the surface is Considering that it is common to think that the area exposed to the corrosive environment of the base metal will rapidly expand and quickly shift to the corrosion of the base metal. The above-described improvement in corrosion resistance due to the addition of Al to the base metal is a means for improving corrosion resistance, which has never been known so far, and is based on such a new discovery. Is.
[0012]
Furthermore, we will continue to study 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 add stably to steel Newly found to be.
In particular,Contains Al 0.3 to 4.96%It was newly found that by adding Mg to steel, the corrosion resistance is significantly improved by the interaction between the base material and the coated metal described above.
[0013]
In order to further enhance the effect of improving corrosion resistance by adding Al to a base metal in which a metal layer having a lower potential than the base is present or the simultaneous addition of Al and Mg is present. Various studies were made on the above means, and it was revealed that the addition of Si, Mn, Nb, V, Ti, Zr, Ta, Hf, Cu, Mo, Sb, Ni, and W to the base material was effective.
[0014]
Furthermore, the present inventors continue to study, as a metal whose electric potential in an aqueous solution environment is lower than that of the substrate, aluminum,Aluminum alloy,zinc,Zinc alloy,chromium,Chrome alloy,manganese,Manganese alloyHas also been found to be a suitable metal for the purposes of the present invention.
As for these coated metals, as a result of various examinations from the viewpoint of improving corrosion resistance by interaction with the base material, aluminum,Aluminum alloy,zinc,Zinc alloy,chromium,Chrome alloy,manganese,Manganese alloy, Any one or more of Mg and In,In mass%It has been found that a material containing 0.05 to 10% in a single content achieves even better corrosion resistance.
[0015]
The present invention has been made mainly based on the above findings, and the gist of the first invention is mass%,
Si: 0.01-3.0%,
Mn: 0.01 ~1.2%,
Al: 0.3-4.96%
ContainingSteel comprising the balance Fe and unavoidable impurities, C of which is limited to 0.25% or less, P is 0.03% or less, S is 0.01% or less, and N is 0.02% or less. And a metal coating layer having a lower potential in an aqueous solution environment than the base material is formed on the surface of the base material in a thickness of 0.05 to 500 μm.
[0016]
The gist of the second invention is that in the steel of the first invention, the base material is further added as an additional component.% By mass
Mg: 0.0003 to 0.05%
It exists in the corrosion-resistant steel characterized by containing.
The gist of the third invention is that in the steel of the first invention and the second invention, the base material is further added as an additional component.% By mass
Cu: 0.01 to 5.0%,
Mo: 0.05 to 10%,
Sb: 0.01 to 0.5%,
Ni: 0.01 to 10%,
W: 0.05-3.0%
It is in the corrosion-resistant steel characterized by containing 1 type, or 2 or more types.
[0017]
The gist of the fourth invention is the steel of the first invention, the second invention, and the third invention, wherein the base material is further added as an additional component,% By mass
Rare earth elements: 0.001 to 0.1%, Ca: 0.0001 to 0.05%
It is in the corrosion-resistant steel characterized by containing 1 type, or 2 or more types.
The gist of the fifth invention is the steel of the first invention, the second invention, the third invention, and the fourth invention, wherein the base material is further added as an additional component,% By massCorrosion resistance characterized by containing one or more elements selected from Nb, V, Ti, Zr, Ta, and Hf in a single content of 0.01 to 1% and satisfying the following formula: In steel.
[0018]
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)
The gist of the sixth invention is that in the first invention, the second invention, the third invention, the fourth invention, and the fifth invention, the metal of the coating layer is aluminum orAluminum alloyIt is one of the corrosion-resistant steel.
[0019]
The gist of the seventh invention is that in the first invention, the second invention, the third invention, the fourth invention, and the fifth invention, the metal of the coating layer is zinc orZinc alloyIt is one of the corrosion-resistant steel.
The gist of the eighth invention is that in the first invention, the second invention, the third invention, the fourth invention, and the fifth invention, the metal of the coating layer is chromium orChrome alloyIt is one of the corrosion-resistant steel.
[0020]
The gist of the ninth invention is that in the first invention, the second invention, the third invention, the fourth invention, and the fifth invention, the metal of the coating layer is manganese orManganese alloyIt is one of the corrosion-resistant steel.
The tenth aspect of the present invention is the steel of the sixth aspect, the seventh aspect, the eighth aspect, and the ninth aspect, wherein the metal of the coating layer is further% By massThe corrosion-resistant steel is characterized by containing at least one of Mg and In in a single content of 0.05 to 10%.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The reason why the range of each component of the substrate is limited in the present invention will be described below.
Si: Si is effective to add steel as a deoxidizer and strengthening element. However, if the content is less than 0.01%, the deoxidation effect is not sufficient, and if it exceeds 3%, the effect is no longer effective. Saturates and lowers workability, so the content range is limited to 0.01% to 3%. Further, by adding Si, an effect of improving the corrosion resistance when a metal layer having a lower potential in an aqueous solution environment than the base material is formed to a thickness of 0.05 to 500 μm on the surface of the base material is brought about. If less than 0.15%, no effect is observed, and even if added over 1.5%, the effect is saturated. Therefore, it is more desirable to add in the range of 0.015% to 1.5%.
[0022]
Mn: Mn is necessary as a deoxidizer for steel and needs to contain 0.01% or more.1.2The effect is no longer saturated even if it is contained in excess of%, but if Mn is contained excessively, the workability is reduced, so the upper limit content is1.2%. Further, by adding Mn, when a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. If it is less than 0.05%, no effect is observed, and even if added over 1.2%, the effect is saturated. Therefore, it is more desirable to add in the range of 0.05% or more and 1.2% or less.
[0023]
Al: Al is the most important element for securing corrosion resistance in the present invention, and by adding Al, a layer of a metal whose potential in an aqueous solution environment is lower than that of the base material is added to the surface of the base material by 0.0. When it is formed to a thickness of 5 to 500 μm, it brings about the effect of improving the corrosion resistance.Less than 0.3%The effect is not enough4. Over 96%Even if added, the effect is saturated, so the Al content is0.3% to 4.96%Limited to. 4. If added over 0%, workability will be reduced, so the Al content should be 0.3% or more and 4.0% or less.PreferGood.
[0024]
C, N: C and N decrease the workability of the steel sheet, and C generates carbides and decreases the corrosion resistance of the base material. Also, N decreases the toughness, so the amount of C and N is small. The upper limit content is preferably 0.25% or less for C and 0.02% or less for N. The smaller the number, the better. However, when C is set to 0.03 or less, a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the base material surface to a thickness of 0.5 to 500 μm. In addition, the effect of improving the corrosion resistance is remarkable, and C is more preferably 0.03% or less.
[0025]
P: When P is present in a large amount, the toughness is lowered, so the smaller one is desirable, and the upper limit content is 0.03%.
S: If S is present in a large amount, the pitting corrosion resistance is deteriorated, so that it is desirable that the content is small. The upper limit is 0.01%.
The above is the basic component of the steel base material excellent in corrosion resistance targeted by the present invention, but in the present invention, steel materials whose corrosion resistance is further improved by adding the following elements as necessary are also targeted. It is said.
[0026]
Mg: Mg is an element added to further improve the corrosion resistance in the present invention.Contains 0.3 to 4.96%By adding Mg to the steel, the effect of improving the corrosion resistance is brought about when a metal layer having a lower potential in the aqueous solution environment is formed on the surface of the base material to a thickness of 0.5 to 500 μm than the base material. However, if it is less than 0.0003%, the effect is not sufficient, and even if added over 0.05%, the effect is saturated, so the Mg content is 0.0003% or more and 0.05% or less Limited to.
[0027]
Cu: Cu is AlContaining 0.3% or more and 4.96% or lessWhen 0.05% or more is added to the steel to be added, there is an effect of improving the resistance against the general corrosion of the base material alone, and when it exceeds 5.0%, the effect is saturated. Furthermore, when a metal layer having a lower potential in the aqueous solution environment on the surface of the substrate is formed to have a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. On the other hand, adding more than about 2.5% saturates the effect. Therefore, it is more desirable to add in the range of 0.1% to 2.5%.
[0028]
Mo: Mo stands for AlContaining 0.3% or more and 4.96% or lessWhen added to steel, the effect of improving the corrosion resistance is brought about when a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm. If it is less than 0.05%, no effect is observed. On the other hand, even if added over 10%, the effect is saturated, so the upper limit is made 10%. Mo is also AlContains 0.3% or moreAdding 0.1% or more to the steel to be used has the effect of suppressing the occurrence and growth of pitting corrosion on the base material alone, but adding more than 3.0% not only saturates the effect but also processability ReduceThe ObedienceTherefore, it is more desirable to add in the range of 0.1% to 3%.
[0029]
Sb: Sb is AlContaining 0.3% or more and 4.96% or lessWhen added to the steel to be added in an amount of 0.01% or more, there is an effect of improving the resistance to pitting corrosion and overall corrosion of the base material alone, but adding over 0.5% lowers the hot workability, so the upper limit The content is 0.5%. Further, by adding Sb, when a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. If it is less than 0.15%, no effect is observed. On the other hand, adding over 0.3% saturates the effect. Therefore, it is more desirable to add in the range of 0.015% to 0.3%.
[0030]
Ni: Ni stands for AlContaining 0.3% or more and 4.96% or lessWhen added to steel to 0.01% or more, there is an effect of suppressing pitting corrosion of the base material alone, but adding more than 10% not only saturates the effect, but also reduces hot workability, The upper limit content is 10%. Further, by adding Ni, when a metal layer having a lower potential in an aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. If the amount is less than 1%, no effect is observed, while if the amount exceeds 6%, the effect is saturated. Therefore, it is more desirable to add in the range of 0.1% to 6%.
[0031]
W: W is AlContaining 0.3% or more and 4.96% or lessAddition of 0.05% or more to the steel to be used has the effect of suppressing the occurrence and growth of pitting corrosion in the base material alone, but adding more than 3.0% not only saturates the effect but also improves workability. Since the content is reduced, the upper limit content is set to 3.0%. Furthermore, by adding W, when a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is brought about. If the amount is less than 1%, the effect is not recognized, and if the amount exceeds 2%, the effect is saturated. Therefore, it is more desirable to add in the range of 0.1% to 2%.
[0032]
Rare earth elements (REM), Ca: Rare earth elements (REM) and Ca are elements that are effective in improving hot workability, but if the amount added is less than 0.001% for REM and less than 0.0001% for Ca The effect is not sufficient. When REM exceeds 0.1% and Ca exceeds 0.05% (0.01%), coarse non-metallic inclusions are formed, respectively. Since the workability and pitting corrosion resistance are deteriorated, the upper limit content is set to 0.1% for REM and 0.05% for Ca. Furthermore, REM and Ca are Al.Containing 0.3% or more and 4.96% or lessWhen added to the steel, the effect of improving the corrosion resistance is brought about when a metal layer having a lower potential in the aqueous solution environment than the base material is formed on the surface of the base material to a thickness of 0.5 to 500 μm. In REM, if less than 0.005%, no effect is observed. In REM, if less than 0.01%, no effect is observed. On the other hand, even if Ca is added in an amount of 0.01% and REM exceeds 0.05%, the effect is not observed. The effect is saturated. Therefore, it is more desirable to add Ca in the range of 0.005% to 0.01% and REM in the range of 0.01% to 0.05%. In the present invention, the rare earth element (REM) refers to an element having atomic numbers 57 to 71 and 89 to 103 and Y.
[0033]
Nb, V, Ti, Zr, Ta, and Hf: Nb, V, Ti, Zr, Ta, and Hf have a remarkable effect on improving workability by fixing C and N in steel as carbides. Can be added alone or in combination of two or more elements, but if the added amount alone is less than 0.01%, there is no effect, and adding more than 1.0% unnecessarily increases the cost. In addition, the upper limit content is set to 1.0%. And in order to improve workability effectively, it is necessary for the sum total of the addition amount of Nb, V, Ti, Zr, Ta, and Hf to satisfy the following formula.
[0034]
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)
Furthermore, Ti, Zr, Ta, HfAl content of 0.3% or more and 4.96% or lessWhen added to the steel, the effect of improving the corrosion resistance is brought about when a metal layer whose potential in the aqueous solution 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. If both elements are less than about 0.05%, the effect is not recognized, while the effect is saturated even if added over about 0.8%. Therefore, it is more desirable to add in the range of 0.05% or more and 0.8% or less.
[0035]
In the present invention, the steel substrate surface, particularly at least the surface exposed to the corrosive environment, is coated with a metal having a lower potential than the substrate. Thickness to cover with metal whose potential is lower than the base materialIf it is less than 0.5 μm,By adding Al to the base material, the remaining base material surface after the base material surface is exposed to the corrosive environment is coated, and the disappearance rate of the metal layer whose potential is lower than that of the base material is reduced. Significantly lowering the expansion rate of the area exposed to the corrosive environment of the surface, and at the same time, protecting the substrate exposed portion of the metal layer where the potential coated on the substrate surface with respect to the exposed substrate portion is lower than the substrate The effect of continuing for a long time is not enough, and even if it is coated to a thickness exceeding 500 μm, the effect is no longer saturated, but it only reduces the productivity and increases the cost. Therefore, the thickness of the coating layer is set to 0.5 to 500 μm.
[0036]
Metals that form a coating layer and whose potential in an aqueous solution environment is lower than that of the substrate include aluminum, zinc, chromium, manganese, andThese alloysCan be used.
Further excellent corrosion resistance can be obtained when the metal of the coating layer further contains at least one of Mg and In in an independent content of 0.05 to 10%.
[0037]
The reason why the contents of Mg and In are limited to the above range is as follows. That is, when the addition amount is less than 0.05%, the effect of improving the corrosion resistance is not seen. Conversely, even if the addition amount exceeds 10%, the effect is only saturated, and the low characteristic of the steel of the present invention is low. Reduce costs. Therefore, Mg and In are added in a range of 0.05 to 10%, respectively.
[0038]
The coating process is not limited as long as the metal is sufficiently fixed to the substrate. You only have to select it after considering its usage and cost.Hot dipping, electrodeposition plating, hot salt electroplating,Vacuum deposition, sputtering, ion plating, thermal spraying, or the like can be used, and these can be used in combination. Moreover, you may perform what kind of process as needed before and after covering and the process for it.
[0039]
Zinc alloyAnd the component occupying the maximum amount of the alloy components is zincAlloy, generally zinc alloyAn alloy component such as aluminum and an impurity component may be included.
Aluminum alloyAnd the component occupying the maximum amount among the alloy components is aluminumAlloy, generally aluminum alloyIt may contain alloy components such as silicon and zinc and impurity components.
[0040]
Chrome alloyMeans that the largest component of the alloy components is chromiumAlloy, generally chromium alloyAn alloy component such as silicon and an impurity component may be included.
Manganese alloyAnd the component that occupies the maximum amount among the alloy components is manganeseAlloy, Generally manganese alloyAn alloy component such as aluminum and an impurity component may be included.
[0041]
In addition, for the purpose of use, if only one surface of a material having front and back surfaces such as a steel pipe or a plate material may be coated, only one surface is coated from the process of covering a base metal. Steel may be used. In such a case, whether to use only one side coating or to use steel coated on both sides may be selected in consideration of other factors such as cost and weldability.
[0042]
About the timing of applying the coating, after the general shape of the steel material such as a coil, a plate, a rod, a cable, a perforated steel pipe, etc., the coating of the present invention and the processing for the same may be performed, The steel of the present invention may be formed into a predetermined shape by pressing or roll forming, and further processed and welded to produce a product. The steel of the present invention is first formed into a steel pipe shape, for example, as an electric resistance steel pipe It may be made into a product by secondary processing and welding, etc. Furthermore, before applying the coating and processing of the present invention, it is possible to apply the surface coating treatment of the present invention after making the steel material into the target shape by the process described above. Steels having a combination of composition and processing conditions limited in the present invention, including other processes, are all objects of the present invention, and are optimally manufactured depending on costs, constraints on existing manufacturing equipment, etc. 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.
[0043]
The steel proposed in the present invention described above is not only high-temperature humid corrosion environment, condensation corrosion environment including exhaust system of internal combustion engine, but also atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, seawater corrosion environment It can be applied to various corrosive environments such as drinking water corrosive environments.
[0044]
【Example】
Examples of the present invention will be described below.
[Evaluation of corrosion resistance]
Steels having the components shown in Tables 1 and 2 are melted and made into a steel plate having a thickness of 1 mm by a normal steel plate manufacturing process such as hot rolling and cold rolling. The coating was applied under the condition of 15 ± 2 μm per unit. The coating 1 shown in Tables 1 and 2 is an aluminum coating, the coating 2 is a zinc coating, the coating 3 is a manganese coating, and the coating 4 is a chromium coating.
[0045]
Next, test pieces having a width of 50 mm and a length of 70 mm were collected from these steel plates and subjected to various corrosion tests described below.
In the high temperature wet corrosion test, a test piece in 50 cc of an aqueous solution to which 100 ppm of sulfate ion, 250 ppm of chloride ion and 500 ppm of bicarbonate ion were added in the form of ammonium salt was immersed in half and kept in an atmosphere of 130 ° C. together with the test container. It was set as the test which repeats 70 times that a test solution evaporates and volatilizes completely. This test is a corrosion test that corresponds to the internal environment of the automobile exhaust system, and is a rigorous test method that can be used for running a real vehicle for about four years or more. The test results are also shown in Tables 1 and 2. In the corrosion test results, ◎ indicates that the maximum corrosion depth was less than 0.10 mm, ◯ was less than 0.2 mm, Δ was less than 0.3 mm, and x was 0.3 mm or more.
[0046]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance even in a very severe corrosive environment of high temperature humidity containing chloride, whereas the comparative steels (Nos. 41 to 50, 100 to 109) are inferior in corrosion resistance.
In addition, as a test assuming salt damage corrosion of the air environment and the outer surface of an automobile exhaust system, after spraying salt water at 50 ° C. for 1 hour, holding it in an environment of 96% humidity at 60 ° C. for 5 hours, and then holding it frozen for another hour The salt damage corrosion test was repeated 150 times. The maximum pitting corrosion 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. The maximum pitting depth is 0.2 mm or less, ◎, the maximum pitting depth is more than 0.2 mm to 0.4 mm or less, and the maximum pitting depth is more than 0.4 mm to 0.8 mm or less. Those with a maximum pitting corrosion depth exceeding 0.8 mm are indicated with xx.
[0047]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance even in a very severe corrosive environment of salt damage corrosion, whereas the comparative steels (Nos. 41 to 50, 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%, a specific resistance of 400 Ω · cm and a sodium chloride content, and kept at 30 ° C. for about 700 days. The test results are also shown in Tables 1 and 2. In the corrosion test results, ◎ indicates that the maximum corrosion depth was less than 0.05 mm, ◯ was less than 0.1 mm, Δ was less than 0.5 mm, and x was 0.5 mm or more.
[0048]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a soil corrosive environment, while comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
In the concrete corrosion test, the test piece was embedded in Portland cement kneaded with sea sand containing chloride, solidified, and then half-immersed in artificial seawater in a 45 ° C environment. The test was allowed to stand for about 700 days. The test results are also shown in Tables 1 and 2. Corrosion test results ◎ indicate that no corrosion was observed, ○ indicates that the rusting area ratio is less than 5%, △ indicates that the rusting area ratio is less than 10%, and X indicates that it is 10% or more. .
[0049]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a corrosive environment in concrete, while comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
The tap water environmental corrosion test was a test in which a test piece was immersed in tap water and held in a 45 ° C. atmosphere for 6 months. The test results are also shown in Tables 1 and 2. Corrosion test results ◎ indicate that no corrosion was observed, ○ indicates that the rusting area ratio is less than 5%, △ indicates that the rusting area ratio is less than 10%, and X indicates that it is 10% or more. .
[0050]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a tap water corrosive environment, while comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
The seawater environment corrosion test was a test in which the test piece was exposed to the coastal splash zone for 15 months. The test results are also shown in Tables 1 and 2. In the corrosion test results, “◎” indicates that the corrosion depth was less than 0.05 mm, “◯” indicates less than 0.1 mm, “Δ” indicates less than 0.3 mm, and “x” indicates 0.3 mm or more.
[0051]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a seawater corrosive environment, while the comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
The condensation corrosion test was a test that was repeated 1000 times by holding for 2 hours in an environment of -20 ° C and then holding for 4 hours in an environment of 30% humidity and 30 ° C. The test results are also shown in Tables 1 and 2. Corrosion test results ◎ indicate that no corrosion was observed, ○ indicates that the rusting area ratio is less than 5%, △ indicates that the rusting area ratio is less than 10%, and X indicates that it is 10% or more. .
[0052]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a condensation corrosion environment, while the comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
The atmospheric corrosion test was a test in which a test piece was exposed to a position about 400 m from the coast for about 700 days. The test results are also shown in Tables 1 and 2. In the corrosion test results, “◎” indicates that no corrosion was observed, “◯” indicates that the rusting area ratio is less than 3%, “Δ” indicates that the rusting area ratio is less than 10%, and “x” indicates 10% or more.
[0053]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in an atmospheric corrosive environment, whereas the comparative steels (Nos. 41 to 50, 100 to 109) are inferior in corrosion resistance.
In the drinking water environmental corrosion test, pH was adjusted to 2.8 using sodium hydroxide, high-purity nitrogen gas was vented and degassed, and maintained at 27 ° C. (a) 0.5% phosphoric acid solution , (B) 0.5% citric acid solution, (c) 0.5% citric acid-0.5% sodium chloride solution, etc. It was a test to analyze the amount. Only in this test, the test was conducted on the aluminum coating of coating 1 and the chromium coating of coating 4. The test results are also shown in Tables 1 and 2. In the corrosion test results, “◎” indicates that the elution amount of iron ions in the solution was 1 ppm or less, “◯” was less than 3 ppm, “Δ” was less than 5 ppm, and “x” was 5 ppm or more.
[0054]
As is clear from Tables 1 and 2, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in a drinking water corrosive environment, whereas comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
That is, the steel of the present invention(Numbers 2-40, 52-90)Shows good corrosion resistance in various corrosive environments such as high temperature wet corrosive environment, condensation corrosive environment, air corrosive environment, tap water corrosive environment, soil corrosive environment, concrete corrosive environment, seawater corrosive environment, drinking water corrosive environment, etc. On the other hand, it can be seen that the comparative steels (numbers 41 to 50, 100 to 109) are inferior in corrosion resistance.
[Evaluation of workability]
Steels having the components shown in Table 2 were melted and made into steel plates having a thickness of 1.0 mm by normal steel plate manufacturing processes such as hot rolling and cold rolling, and annealed at 850 ° C. Test pieces having a width of 100 mm and a length of 100 mm were collected from these steel plates, and subjected to a cylindrical drawing test with a drawing ratio of 1.8 to determine whether or not there was a crack. 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 cracking occurred in the cylindrical drawing test. The X values in Table 2 are those calculated by the following formula.
[0055]
X = Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179−0.8 × (C / 12 + N / 14)
As is apparent from Table 2, the steel of the present invention has particularly improved workability.(Numbers 52-90)Exhibits good corrosion resistance and good workability. That is, it shows good corrosion resistance in various corrosive environments such as high temperature and wet corrosive environment, condensation corrosive environment, air 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 steel (numbers 100 to 109) cannot achieve corrosion resistance and workability at the same time.
[0056]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
[Table 6]
[Table 7]
[Table 8]
【The invention's effect】
As described above, according to the present invention, for example, an exhaust system of an internal combustion engine such as an automobile, a high temperature wet corrosion environment, a condensation corrosion environment, an air corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion, and the like. Corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as the environment, seawater corrosive environment and drinking water corrosive environment is provided at low cost.
Claims (10)
Ｓｉ：０．０１〜３．０％、
Ｍｎ：０．０１〜１．２％、
Ａｌ：０．３〜４．９６％
を含有し、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０．２５％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の厚さに形成したことを特徴とする耐食鋼。% By mass
Si: 0.01-3.0%,
Mn: 0.01 to 1.2 %,
Al: 0.3-4.96%
And the balance Fe and unavoidable impurities, of which C is 0.25% or less, P is 0.03% or less, S is 0.01% or less, and N is 0.02% or less Corrosion-resistant, characterized in that a steel coating layer having a thickness of 0.5 to 500 μm is formed on the surface of the base material, and the surface of the base material has a lower potential in an aqueous solution environment than the base material. steel.
Ｍｇ：０．０００３〜０．０５％
を含有することを特徴とする請求項１に記載の耐食鋼。The steel of the base material is further mass%,
Mg: 0.0003 to 0.05%
The corrosion-resistant steel according to claim 1, comprising:
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請求項１または２に記載の耐食鋼。The steel of the base material is further mass%,
Cu: 0.01 to 5.0%,
Mo: 0.05 to 10%,
Sb: 0.01 to 0.5%,
Ni: 0.01 to 10%,
The corrosion-resistant steel according to claim 1 or 2, comprising one or more of W: 0.05 to 3.0%.
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請求項１，２または３に記載の耐食鋼。The steel of the base material is further mass%,
Rare earth elements: 0.001 to 0.1%, Ca: 0.0001 to 0.05%
The corrosion-resistant steel according to claim 1, 2 or 3, characterized by containing one or more of the following.
Ｎｂ／９３＋Ｖ／５１＋Ｔｉ／４８＋Ｚｒ／９１＋Ｔａ／１８１＋Ｈｆ／１７９≧０．８×（Ｃ／１２＋Ｎ／１４）The base steel further contains, in mass%, any one or two or more selected from Nb, V, Ti, Zr, Ta, and Hf in an amount of 0.01 to 1%. The corrosion-resistant steel according to claim 1, 2, 3 or 4, wherein the following formula is satisfied.
Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta / 181 + Hf / 179 ≧ 0.8 × (C / 12 + N / 14)
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| JP16344698A JP4184481B2 (en) | 1998-06-11 | 1998-06-11 | Corrosion resistant steel |
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| JP4184481B2 true JP4184481B2 (en) | 2008-11-19 |
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| FR2836930B1 (en) * | 2002-03-11 | 2005-02-25 | Usinor | HOT ROLLED STEEL WITH HIGH RESISTANCE AND LOW DENSITY |
| JP4577158B2 (en) * | 2005-08-31 | 2010-11-10 | Ｊｆｅスチール株式会社 | Corrosion resistant steel for crude oil tanks |
| JP5042694B2 (en) * | 2007-04-13 | 2012-10-03 | 新日本製鐵株式会社 | High strength low specific gravity steel plate excellent in ductility and workability and method for producing the same |
| JP5332894B2 (en) * | 2009-05-15 | 2013-11-06 | 新日鐵住金株式会社 | Low specific gravity steel sheet excellent in ductility, fatigue characteristics and toughness and method for producing the same |
| CN109359431B (en) * | 2018-11-30 | 2022-12-20 | 中国航空工业集团公司沈阳飞机设计研究所 | Simulation method for material surface pitting in flowing seawater |
| KR102225742B1 (en) * | 2020-09-11 | 2021-03-11 | 주식회사 하이콘엔지니어링 | Method for reinforcing of bridge pier |
| CN116083820B (en) * | 2023-01-13 | 2024-06-25 | 桂林理工大学 | Method for preparing low-cost high-strength high-corrosion-resistance antimony-containing reinforcing steel bar from high-phosphorus copper-containing iron ore |
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