JP2004238682A - Hot-dip al-plated steel sheet superior in corrosion resistance for material in automotive exhaust system - Google Patents
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Abstract
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【０００１】
【発明の属する技術分野】
本発明は、自動車の排気系部材として使用した際に、優れた耐食性を有する溶融Ａｌ系めっき鋼板に関するものである。
【０００２】
【従来の技術】
溶融Ａｌめっき鋼板は、高い耐食性と耐熱性、美しい外観等から、前記したような自動車部品、建材、家電部品等に広く使用されている。しかし、更なる耐食性向上、寿命長期化の要求がなされ、そのままのＡｌめっき鋼板では耐食性が不足するため、高耐食性Ａｌめっき鋼板として、種々の発明がなされている。そのアプローチの方法は主として２つに分けられ、Ａｌめっき層、あるいはその上の後処理皮膜層をより高耐食性化させるものと、鋼成分を変更して高耐食性を狙うものであった。
【０００３】
前者に関する発明を開示したものとして、Ｍｇ添加に関する特開２００１−８１５３９号公報（特許文献１）、Ｍｎ添加に関する特開平７−２００９１号公報（特許文献２）、後処理皮膜に関する技術を開示したものとして特開昭５８−８７０４４号公報（特許文献３）等が上げられ、また、後者に関する発明としては、主としてＣｒを鋼中に添加する技術が特開昭６１−２３１１５２号公報（特許文献４）、特開平３−２７７７６１号公報（特許文献５）に開示されている。これ以外にＣｒ−Ｃｕを複合添加する技術が特開昭６３−１８０４３号公報（特許文献６）に、またＣｕ−Ｐ複合添加する技術が特開平６−１０８２１８号公報（特許文献７）に開示されている。
【０００４】
前者、すなわち、Ａｌめっき層や後処理皮膜に関する発明に関しては、耐食性向上効果は認められるものの、耐食性を担うＡｌめっき層や後処理層の厚みはせいぜい５０μｍであり、鋼の板厚約１ｍｍの１／２０程度しかなく、この薄い層で耐食性を担保しなければならないという点に困難があった。また、Ａｌめっきの組成を変えることは浴組成を変えることであり、従って、他品種への影響等を調査する必要があった。また後処理皮膜にしてもこれらの皮膜を付与するためには別工程が必要で、コスト負担が大きなものであった。また、当然のことながら、疵付き部、溶接部等の耐食性確保についてはこれらの技術では限界があった。
【０００５】
次に、後者すなわち鋼中へのＣｒ等の添加に関しては、Ｃｒ単独で耐食性向上効果を得るには５％の添加量が必要で、このような量を添加するとメタルコスト、各種工程コストの増大となり、Ａｌめっき鋼板の特徴であ廉価で特性が優れるという点を損なう。Ｃｒ−Ｃｕ、Ｃｕ−Ｐ等の低合金鋼の適用も開示されているが、これらの開示内容を本発明者らが追試をしたところ、顕著な効果は認められなかった。
【０００６】
【引用文献】
（１）特許文献１（特開２００１−８１５３９号公報）
（２）特許文献２（特開平７−２００９１号公報）
（３）特許文献３（特開昭５８−８７０４４号公報）
（４）特許文献４（特開昭６１−２３１１５２号公報）
（５）特許文献５（特開平３−２７７７６１号公報）
（６）特許文献６（特開昭６３−１８０４３号公報）
（７）特許文献７（特開平６−１０８２１８号公報）
【０００７】
【発明が解決しようとする課題】
本発明は低廉な鋼成分、従来と変わらない製造工程、製造性で特に自動車排気系環境下において耐食性に優れる溶融Ａｌ系めっき鋼板を提供するものである。
【０００８】
【課題を解決するための手段】
本発明者らはこれまでＣｒ鋼ベースのＡｌめっき鋼板を開発してきた。この環境におけるＡｌめっき鋼板の腐食挙動についての知見を新日鉄技報第３６１号のｐ．５２に掲載している。すなわち、排気系材料は主として内面、排気ガス凝縮水環境下での腐食が問題となるもので、この環境はＳＯｘ、ＮＯｘ起因の硫酸根、アンモニウムイオンが主要な腐食因子である。凝結水そのものは中性から弱アルカリ性であるが、温度の上昇に伴いアンモニウムイオンが揮発して低ｐＨ環境となる。このときＡｌめっき鋼板のＡｌめっき層は鋼素地に対して電位が貴になる時間が長く、Ａｌめっき層の腐食が鋼素地に到達するとＡｌめっき層を残して鋼素地が優先して腐食し、早期に全面腐食の形態をとる。このとき、排気系内面環境でＡｌめっき層が鋼素地に対して貴であるために腐食が早期に広がりやすく、鋼中にＣｒを添加して鋼の電位を制御したものがＣｒ鋼へのＡｌめっき鋼板である。
【０００９】
本発明者らは排気系内面環境においてＣｒ以外で電位を貴な方向にシフトさせる元素を検討し、以下の知見を得た。Ｃ，Ｓｉ，Ａｌ，Ｃｒ，Ｓ等の元素を低く押さえ、かつＣｕを添加することで鋼の電位をＡｌめっき層よりも高く保持することが可能であった。近年では製鋼工程での高純化が進行しており、高純鋼へＣｕを添加した鋼で最もよい結果が得られた。不純物の多い鋼ではカソード反応の起点となるような析出物が多く、鉄の不働態化を妨げているものと推定しているが、詳細な機構は現在のところ不明である。
【００１０】
本発明の要旨とするところは以下の通りである。
（１）質量％で、Ｃ：０．０１％以下、Ｓｉ：０．４％以下、Ｍｎ：０．７％以下、Ｐ：０．０２％以下、Ｓ：０．０１５％以下、Ａｌ：０．０１％以下、Ｃｒ：０．１％以下、Ｃｕ：０．１〜０．５％を含有し、残部がＦｅ及び不可避的不純物からなる鋼板の表面にＡｌを５０％以上含有するＡｌ系めっき層を含有することを特徴とする耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。
【００１１】
（２）鋼中に更に、Ｓｂ：０．３％以下、Ｓｎ：０．３％以下、Ｎｉ：０．５％以下、Ｍｏ：０．５％以下、Ｔｉ：０．０２〜０．３％、Ｎｂ：０．０２〜０．２％、Ｖ：０．０５％以下、Ｂ：０．０１％以下の中の１種または２種以上を含有することを特徴とする前記（１）に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。
（３）Ａｌ系めっき層組成が、Ｓｉ：２〜１５％、Ｆｅ：３％以下、Ｃｒ：０．１％以下、残部がＡｌ及び不可避的不純物であることを特徴とする前記（１）または（２）に記載の耐食性に優れた自動車排気系材用溶融Ａｌめっき鋼板。
【００１２】
（４）Ａｌ系めっき層組成として、Ｚｎ：５０％以下、Ｓｉ：０．５〜１０％、Ｆｅ：３％以下、残部がＡｌ及び不可避的不純物であることを特徴とする前記（１）または（２）に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。
（５）Ａｌ系めっき層組成に更に、Ｍｇ：０．１〜１０％、Ｃａ：０．０１〜５％、Ｔｉ：０．１％以下、Ｍｎ：１％以下、ミッシュメタル：０．２％以下、Ｓｎ：１０％以下、Ｃｒ：０．５％以下、Ｎｉ：０．５％以下の中の１種または２種以上を含有することを特徴とする前記（３）または（４）に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板にある。
【００１３】
【発明の実施の形態】
次に、本発明に係る鋼成分の限定理由を説明する。
Ｃ：ＣはＴｉ，Ｃｒ等の金属と結合してカーバイトとして析出するため、耐食性の理由からできるだけ低くする事が望ましい。０．０１％を上限にする。より望ましくは０．００５％以下である。下限は設けないが、製鋼工程の能力から０．０００５％以上が実用上は望ましい。
Ｓｉ：Ｓｉは排気系内面環境下での電位変化に影響が大きい。添加量が高くなると電位が低下する傾向にあるため、低い方が好ましい。０．４％以下に限定するが、より望ましくは０．１％以下である。下限は設けないが、本発明はＳｉ脱酸となるため、０．０５％以上であることが望ましい。
【００１４】
Ｍｎ：ＭｎはＳと結合してＭｎＳを形成するため、これも低い方が望ましい。しかし、Ｓを低減することでＭｎＳ形成は抑制できるため、上限は０．７％である。より好ましくは０．４％以下である。下限は設けないが、熱間脆性を抑制するために０．０３％以上の添加が望ましい。
Ｐ：Ｐは一般に特にＣｕと複合添加して耐候性が向上することが知られ、耐候性へ添加されている。しかし、排気系内面環境下においては特にＰによる耐食性向上、電位向上効果は認められず、寧ろ耐食性は低下する傾向にある。このためＰの上限を０．０２％とする。より好ましくは０．０１％以下である。下限は設けないが、製鋼工程の能力から０．００２％以上であることが望ましい。
【００１５】
Ｓ：Ｓは本発明で重要な元素である。Ｓを低減することで鋼の電位を貴にシフトすることができる。その原因はＭｎＳの析出を抑制していると考えている。この目的からＳは０．０１５％以下とする。より望ましくは０．００５％以下である。
Ａｌ：Ａｌは脱酸の目的で添加されるが、Ａｌの添加量が多いとやはり鋼の電位が卑になりやすい。これはＡｌＮの析出であると考えている。このため、Ａｌ量は０．０１％以下とする。より望ましくは０．００５％以下である。下限は設けないが、０．００１％程度以下に下げることは困難である。
【００１６】
Ｃｒ：Ｃｒは鋼電位を上昇させる元素であるが、これはＣｒが３％以上添加されたときであり、これ以下の領域ではＣｒの添加は寧ろ鋼の電位を下げる傾向になるとの知見が得られた。このためＣｒ量は０．１％以下に限定する。下限は設けないが、不純物として０．０２％程度が混入しうる。
Ｃｕ：この元素は鋼の電位を高める効果があり、その効果を発揮するには０．１％以上が必要である。一方、Ｃｕは熱間脆性を引き起こす元素でもあり、この意味から上限を０．５％とする。
【００１７】
次に必要に応じて添加する元素の限定理由を説明する。
Ｓｂ，Ｓｎ，Ｍｏ：これらの元素は鋼の電位を上昇させる効果が認められるが、その効果はそう大きなものではない。従って、Ｃｕと複合添加することで、耐食性を安定的に得ることができる。しかし、これらの元素は鋼の加工性を低下させる元素でもあるため、Ｓｂ，Ｓｎの上限を０．３％にＭｏの上限を０．５％とするのが望ましい。
Ｎｉ，ＮｉはＣｕの熱間脆性を抑制する元素でもあり、添加が好ましい。しかし、高価な元素であり、過剰な添加は望ましくなく、上限を０．５％とするのが望ましい。
【００１８】
Ｔｉ，Ｎｂ，Ｖ：これらは炭化物形成元素であり、鋼の加工性に寄与する。しかし、前述したように析出物を作ることは耐食性上好ましくなく、Ｃを低下させてこれらの元素の添加量も少なくした方が好ましい。このような意味から各元素に上限を設け、その値はそれぞれ０．３％，０．２％，０．０５％が望ましい。一方、加工性を得るために必要な量がＴｉ，Ｎｂで０．０２％以上である。また、ＴｉはＡｌめっき鋼板の耐熱性にも寄与する元素であるため、これらの元素の中ではＴｉ添加が最も望ましい。
Ｂ：Ｂは粒界を強化して二次加工性を向上させる元素で、必要に応じ添加することができる。しかし、過剰な添加は加工性の低下に繋がることから上限を０．０１％に限定する。
【００１９】
次に、Ａｌ系めっき層の組成の限定理由を述べる。
まず、Ａｌめっき鋼板には通常合金層と呼ばれる金属間化合物層が鋼板−Ａｌめっきの界面に生成する。その厚みは通常３μｍ程度である。本発明で定義するＡｌめっき層はこの合金層を含まない層とする。このＡｌめっき層は通常タイプＩと呼ばれるＡｌ−１０％Ｓｉめっきが用いられることが多い。Ａｌめっき層の組成の限定については、次の理由による。
【００２０】
Ｓｉ：Ｓｉは通常Ａｌめっき鋼板の合金層成長抑制の目的で添加される。この目的のためにはＳｉは２％以上必要である。一方、Ｓｉを共晶点である１０％以上添加すると、粗大なＳｉ初晶が晶出して耐食性を低下させるため、上限を１５％に定める。
Ｆｅ：通常Ａｌ−Ｓｉめっき層中にＡｌ−Ｆｅ−Ｓｉ金属間化合物の形でＦｅが混入している。これは不可避的不純物であり、耐食性の理由から少ない方が好ましい。本発明においては３％以下が望ましい。
【００２１】
Ｃｒ：Ｃｒは浴中の機器の溶損に伴い若干浴に溶け出し、Ａｌめっき中にピックアップされる。通常この量は０．１％以下であり、本発明でもこの量以下が望ましい。
また、近年いわゆるガルバリュームという、５５％Ａｌ−１．５％Ｓｉ−Ｚｎめっき鋼板の使用が広まっている。本発明はガルバリューム原板にも使用することが可能で、このときのめっき層の限定理由を述べる。ガルバリュームも合金層を有し、ここでいうめっき層は合金層を含まないものとする。
【００２２】
Ｚｎ：Ｚｎは犠牲防食能を付与するために添加される。しかし、Ｚｎを添加するとその分めっき層自体の耐食性は低下する。Ｚｎが５０％を超えると、めっき層の耐食性低下が著しいため、Ｚｎ量は５０％以下とするのが望ましい。
Ｓｉ：Ｓｉはやはり合金層の成長を抑制するために添加される。このめっき組成の場合、浴温が低く、浴中Ａｌ量が少ないため、Ｓｉの添加量はＡｌめっき鋼板の場合よりも低くすることができる。合金層成長抑制に必要なＳｉ量は０．５％以上で、これを下限に、また過剰な添加はやはり耐食性低下につながるため、上限を１０％とするのが望ましい。
【００２３】
Ｆｅ：Ｆｅはやはり不可避的不純物で、少ない方が好ましく、上限を３％とする。これらの元素以外に、Ｍｇ，Ｃａ，Ｔｉ，Ｍｎ，ミッシュメタル，Ｓｎ，Ｃｒ，Ｎｉを添加することも可能である。これらの元素は主として耐食性の更なる改善に有効であり、添加することも可能である。しかし、Ａｌめっきの浴温から添加可能な量は上限があり、また、Ｍｇ，Ｃａについては過剰な添加は酸化物系のドロスの増加につながることからそれぞれ上限を持つ。その量はＭｇ：１０％、Ｃａ：５％、Ｔｉ：０．１％、Ｍｎ：１％、ミッシュメタル：０．２％、Ｓｎ：１０％、Ｃｒ：０．５％、Ｎｉ：０．５％とするのが望ましい。
【００２４】
Ａｌ系めっきの製造法については、現在一般的に使用されている溶融めっき法で行うものとする。溶融めっきプロセスとして、ゼンジマー法、ラジアントチューブファーネス法があるが、これらは特に限定するものではない。Ａｌ系めっきの前処理としてプレめっきを使用することも可能である。また、めっきの後処理として、化成処理（クロメート、ノンクロメート）、ゼロスパングル処理、焼鈍、調質圧延等が付与されることがあるが、これらについても特に限定せず、適用も可能である。また、Ａｌ系めっきの付着量についても、通常の付着量である両面６０〜２００ｇ／ｍ２ で特に問題はない。
【００２５】
次に、実施例で本発明をより詳細に説明する。
【実施例】
（実施例１）
通常の熱延、冷延工程を経た、表１に示すような鋼成分の冷延鋼板（板厚０．８ｍｍ）を材料として、溶融Ａｌめっきを行った。溶融Ａｌめっきは無酸化炉−還元炉タイプのラインを使用し、めっき後ガスワイピング法でめっき付着量を調節し、その後冷却し、ゼロスパングル処理としてアルミナを吹き付けた。この際のめっき浴組成としてはＡｌ−１０％−２％Ｆｅで、浴温を６６０℃とした。浴中のＦｅは浴中のめっき機器やストリップから供給される不可避のものである。めっき外観は不めっき等がなく良好であった。めっき付着量は両面１２０ｇ／ｍ２ で、両面均一であった。このようにして製造した溶融Ａｌめっき鋼板の耐食性を下に示した方法で評価した。評価結果を表２に示す。
【００２６】
【表１】
（１）耐食性評価
▲１▼排気系内面耐食性
寸法２５×１００ｍｍの試料を使用して、ＪＡＳＯ Ｍ ６１１−９２Ｂに規定する排気系内面評価法を４サイクル行い、腐食生成物を剥離した後の鋼素地の腐食深さを測定した。このとき各試料について１０点づつ腐食深さを測定してその最大腐食深さで評価した。
〔評価基準〕
○：腐食深さ０．０５ｍｍ未満
△：腐食深さ０．０５〜０．２ｍｍ
×：腐食深さ０．２ｍｍ超
【００２８】
▲２▼排気系外面耐食性（塩害耐食性）
寸法７０×１５０ｍｍの試料で、ＪＩＳ Ｚ ２３７１に準拠した塩水噴霧試験を３０日行い、腐食生成物を剥離して腐食減量を測定した。この腐食減量の表示はめっき片面に対しての値である。
〔評価基準〕
○：腐食減量２０ｇ／ｍ２ 未満
△：腐食減量３０ｇ／ｍ２ 以下
×：腐食減量３０ｇ／ｍ２ 超
表２に示すように、Ｓ，Ｐ，Ａｌ，Ｃｒ，Ｓｉ等の元素量が多いものは特に内面耐食性が低下する傾向にあることが分かる。外面耐食性はそれほど大きな影響は受けないが、排気系環境において寿命を決めるのは内面耐食性であることが多く、上記の元素を適正に制御することで優れた内面耐食性が得られる。
【００２９】
【表２】
（実施例２）
実施例１の表１中のＡの鋼を使用してめっき浴の組成を変えた試料を製造した。めっきは無酸化炉−還元炉タイプの溶融めっきラインを使用し、めっき後ガスワイピング法でめっき付着量を調節し、その後冷却した。めっき付着量は両面１２０ｇ／ｍ２ とした。均一な外観のめっきが得られた。更に後処理としてノンクロメート処理（Ｚｒ−Ｖ−シリカ系処理）を片面当たりの付着量５００ｍｇ／ｍ２ で両面に施した。これを実施例１と同一の方法、評価基準で評価した。めっき組成と評価結果を表３に示す。
表３に示したようなめっき成分で試験したが、良好な排気系内面耐食性を示した。但しめっき層のＺｎ量が多いと若干耐食性が低下する傾向がある。
【００３１】
【表３】
【発明の効果】
以上述べたように、本発明は、従来に比べて特に排気系内面環境下で耐食性に優れる溶融Ａｌ系めっき鋼板を提供するものである。本発明により廉価で加工性にも優れた排気系材料を供給することが可能となり、産業上の寄与は大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot-dip Al-coated steel sheet having excellent corrosion resistance when used as an exhaust system member of an automobile.
[0002]
[Prior art]
Hot-dip Al-plated steel sheets are widely used in automobile parts, building materials, home electric parts and the like as described above because of their high corrosion resistance, heat resistance, and beautiful appearance. However, there is a demand for further improvement in corrosion resistance and extension of life, and as it is, the corrosion resistance is insufficient with an Al-plated steel sheet as it is, various inventions have been made as a highly corrosion-resistant Al-plated steel sheet. The approach method is mainly divided into two methods. One is to increase the corrosion resistance of the Al plating layer or the post-treatment coating layer thereon, and the other is to aim at high corrosion resistance by changing the steel composition.
[0003]
JP-A-2001-81539 (Patent Document 1) relating to the addition of Mg and JP-A-7-20091 (Patent Document 2) relating to the addition of Mn disclose techniques relating to the post-treatment film. Japanese Patent Application Laid-Open No. 58-87044 (Patent Document 3) and the like, and as the invention relating to the latter, a technique of mainly adding Cr to steel is disclosed in Japanese Patent Application Laid-Open No. 61-231152 (Patent Document 4). And JP-A-3-277761 (Patent Document 5). In addition, a technique of adding Cr-Cu in a composite manner is disclosed in JP-A-63-18043 (Patent Document 6), and a technique of adding a Cu-P complex is disclosed in JP-A-6-108218 (Patent Document 7). Have been.
[0004]
In the former case, that is, in the invention relating to the Al plating layer and the post-treatment film, although the effect of improving the corrosion resistance is recognized, the thickness of the Al plating layer and the post-treatment layer responsible for the corrosion resistance is at most 50 μm, and the thickness of the steel sheet is about 1 mm. It was only about / 20, and there was difficulty in that the corrosion resistance had to be ensured by this thin layer. Further, changing the composition of Al plating means changing the bath composition, and therefore, it was necessary to investigate the influence on other types. Further, even for the post-treatment film, a separate step is required to apply these films, and the cost burden is large. Naturally, these techniques have limitations in ensuring the corrosion resistance of flawed parts, welded parts, and the like.
[0005]
Next, regarding the latter, that is, the addition of Cr and the like to steel, an addition amount of 5% is necessary to obtain the effect of improving corrosion resistance by Cr alone. If such an amount is added, metal cost and various process costs increase. This impairs the characteristics of the Al-plated steel sheet, which is inexpensive and has excellent characteristics. The application of low alloy steels such as Cr-Cu and Cu-P is also disclosed. However, when the present inventors conducted additional tests on these disclosures, no remarkable effect was found.
[0006]
[References]
(1) Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-81539)
(2) Patent Document 2 (Japanese Patent Laid-Open No. 7-20091)
(3) Patent Document 3 (JP-A-58-87044)
(4) Patent Document 4 (JP-A-61-231152)
(5) Patent Document 5 (JP-A-3-277761)
(6) Patent Document 6 (JP-A-63-18043)
(7) Patent Document 7 (JP-A-6-108218)
[0007]
[Problems to be solved by the invention]
The present invention provides an inexpensive steel component, a hot-dip Al-coated steel sheet that is excellent in corrosion resistance in a manufacturing process and manufacturability which are not different from those of the prior art, especially in an automobile exhaust system environment.
[0008]
[Means for Solving the Problems]
The present inventors have developed Al steel sheets based on Cr steel. Knowledge on the corrosion behavior of Al-plated steel sheets in this environment is described in Nippon Steel Technical Report No. 361, p. 52. That is, the exhaust system material has a problem of corrosion mainly in the inner surface, in an exhaust gas condensed water environment. In this environment, sulfate groups and ammonium ions caused by SOx and NOx are main corrosion factors. The condensed water itself is neutral to weakly alkaline, but as the temperature rises, ammonium ions volatilize, resulting in a low pH environment. At this time, the Al plating layer of the Al-plated steel sheet has a long time during which the potential is noble relative to the steel substrate, and when the corrosion of the Al plating layer reaches the steel substrate, the steel substrate preferentially corrodes leaving the Al plating layer, Early form of general corrosion. At this time, since the Al plating layer is noble relative to the steel substrate in the exhaust system inner surface environment, the corrosion easily spreads at an early stage. It is a plated steel sheet.
[0009]
The present inventors have studied elements that shift the potential in a noble direction other than Cr in the exhaust system inner surface environment, and have obtained the following knowledge. By keeping elements such as C, Si, Al, Cr, and S low and adding Cu, it was possible to keep the potential of the steel higher than that of the Al plating layer. In recent years, the purification of steel in the steelmaking process has been progressing, and the best results have been obtained with steel obtained by adding Cu to high purity steel. It is presumed that steel with many impurities has many precipitates that can be the starting point of the cathodic reaction and hinders passivation of iron, but the detailed mechanism is currently unknown.
[0010]
The gist of the present invention is as follows.
(1) In mass%, C: 0.01% or less, Si: 0.4% or less, Mn: 0.7% or less, P: 0.02% or less, S: 0.015% or less, Al: 0 Al-based plating containing 0.1% or less, Cr: 0.1% or less, Cu: 0.1 to 0.5%, and the balance being 50% or more Al on the surface of a steel sheet composed of Fe and unavoidable impurities. A hot-dip Al-coated steel sheet for automobile exhaust system materials having excellent corrosion resistance, characterized by containing a layer.
[0011]
(2) Sb: 0.3% or less, Sn: 0.3% or less, Ni: 0.5% or less, Mo: 0.5% or less, Ti: 0.02-0.3% in steel , Nb: 0.02 to 0.2%, V: 0.05% or less, B: 0.01% or less. Hot-dip Al-plated steel sheet for automobile exhaust system with excellent corrosion resistance.
(3) The above (1) or (1), wherein the composition of the Al-based plating layer is 2 to 15% of Si, 3% or less of Fe, 0.1% or less of Cr, and the balance is Al and inevitable impurities. (2) A hot-dip Al-plated steel sheet for automobile exhaust system excellent in corrosion resistance according to (2).
[0012]
(4) The composition according to (1), wherein the composition of the Al-based plating layer is Zn: 50% or less, Si: 0.5 to 10%, Fe: 3% or less, with the balance being Al and inevitable impurities. (2) A hot-dip Al-plated steel sheet for automobile exhaust system excellent in corrosion resistance according to (2).
(5) In addition to the Al-based plating layer composition, Mg: 0.1 to 10%, Ca: 0.01 to 5%, Ti: 0.1% or less, Mn: 1% or less, misch metal: 0.2% Hereinafter, (3) or (4), wherein one or more of Sn: 10% or less, Cr: 0.5% or less, and Ni: 0.5% or less are contained. Hot-dip Al-plated steel sheet for automobile exhaust system materials with excellent corrosion resistance.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the reasons for limiting the steel components according to the present invention will be described.
C: Since C combines with metals such as Ti and Cr and precipitates as carbide, it is desirable that the content be as low as possible for reasons of corrosion resistance. The upper limit is 0.01%. More preferably, it is 0.005% or less. Although there is no lower limit, 0.0005% or more is practically desirable in view of the performance of the steelmaking process.
Si: Si has a large influence on the potential change under the exhaust system inner surface environment. As the amount of addition increases, the potential tends to decrease. Although it is limited to 0.4% or less, it is more preferably 0.1% or less. Although no lower limit is provided, the content of the present invention is desirably 0.05% or more because Si deoxidation occurs.
[0014]
Mn: Since Mn combines with S to form MnS, it is preferable that Mn is also low. However, since MnS formation can be suppressed by reducing S, the upper limit is 0.7%. More preferably, it is 0.4% or less. Although no lower limit is provided, addition of 0.03% or more is desirable to suppress hot brittleness.
P: It is generally known that P is added in combination with Cu to improve weather resistance and is added to weather resistance. However, under the exhaust system inner surface environment, the effect of improving corrosion resistance and potential is not particularly observed by P, and the corrosion resistance tends to be rather lowered. Therefore, the upper limit of P is set to 0.02%. More preferably, it is 0.01% or less. Although no lower limit is provided, it is desirably 0.002% or more from the capacity of the steelmaking process.
[0015]
S: S is an important element in the present invention. By reducing S, the potential of the steel can be shifted preciously. It is thought that the cause is suppressing the precipitation of MnS. For this purpose, S is set to 0.015% or less. More preferably, it is 0.005% or less.
Al: Al is added for the purpose of deoxidation. However, if the amount of Al added is large, the electric potential of the steel tends to be low. This is considered to be AlN precipitation. For this reason, the Al content is set to 0.01% or less. More preferably, it is 0.005% or less. Although no lower limit is provided, it is difficult to lower it to about 0.001% or less.
[0016]
Cr: Cr is an element that raises the steel potential. This is when Cr is added in an amount of 3% or more, and it has been found that in a region below Cr, the addition of Cr tends to lower the potential of the steel. Was done. For this reason, the amount of Cr is limited to 0.1% or less. Although no lower limit is provided, about 0.02% may be mixed as an impurity.
Cu: This element has the effect of increasing the electric potential of steel, and 0.1% or more is required to exhibit the effect. On the other hand, Cu is also an element that causes hot embrittlement, and the upper limit is set to 0.5% in this sense.
[0017]
Next, the reasons for limiting the elements to be added as necessary will be described.
Sb, Sn, Mo: These elements have an effect of increasing the potential of steel, but the effect is not so great. Therefore, corrosion resistance can be stably obtained by adding it in combination with Cu. However, since these elements are also elements that lower the workability of steel, it is desirable to set the upper limits of Sb and Sn to 0.3% and the upper limit of Mo to 0.5%.
Ni, Ni is also an element that suppresses hot brittleness of Cu, and is preferably added. However, since it is an expensive element, excessive addition is not desirable, and the upper limit is desirably 0.5%.
[0018]
Ti, Nb, V: These are carbide forming elements and contribute to the workability of steel. However, as described above, it is not preferable to form a precipitate in terms of corrosion resistance, and it is more preferable to reduce C to reduce the amount of addition of these elements. For this reason, an upper limit is set for each element, and the values are preferably 0.3%, 0.2%, and 0.05%, respectively. On the other hand, the amount required for obtaining workability is 0.02% or more in Ti and Nb. Further, since Ti is an element that also contributes to the heat resistance of the Al-plated steel sheet, of these elements, the addition of Ti is most desirable.
B: B is an element that strengthens grain boundaries and improves secondary workability, and can be added as necessary. However, an excessive addition leads to a reduction in workability, so the upper limit is limited to 0.01%.
[0019]
Next, the reasons for limiting the composition of the Al-based plating layer will be described.
First, in an Al-plated steel sheet, an intermetallic compound layer usually called an alloy layer is formed at an interface between the steel sheet and the Al plating. Its thickness is usually about 3 μm. The Al plating layer defined in the present invention does not include this alloy layer. For this Al plating layer, Al-10% Si plating usually called type I is often used. The limitation of the composition of the Al plating layer is based on the following reasons.
[0020]
Si: Si is usually added for the purpose of suppressing the growth of the alloy layer of the Al-plated steel sheet. For this purpose, 2% or more of Si is required. On the other hand, if Si is added at 10% or more, which is the eutectic point, coarse Si primary crystals are crystallized to lower the corrosion resistance, so the upper limit is set to 15%.
Fe: Fe is usually mixed in the Al-Si plating layer in the form of an Al-Fe-Si intermetallic compound. This is an unavoidable impurity, and it is preferable that the amount is small because of corrosion resistance. In the present invention, 3% or less is desirable.
[0021]
Cr: Cr slightly dissolves into the bath due to erosion of equipment in the bath, and is picked up during Al plating. Usually, this amount is 0.1% or less, and it is desirable in the present invention that this amount is less than 0.1%.
In recent years, the use of so-called galvalume, a 55% Al-1.5% Si-Zn plated steel sheet, has been widely used. The present invention can also be used for a galvalume original plate, and the reasons for limiting the plating layer at this time will be described. Galvalume also has an alloy layer, and the plating layer here does not include an alloy layer.
[0022]
Zn: Zn is added to impart sacrificial corrosion protection. However, when Zn is added, the corrosion resistance of the plating layer itself is reduced. If Zn exceeds 50%, the corrosion resistance of the plating layer is significantly reduced. Therefore, the Zn content is desirably set to 50% or less.
Si: Si is also added to suppress the growth of the alloy layer. In the case of this plating composition, since the bath temperature is low and the amount of Al in the bath is small, the amount of Si added can be lower than in the case of the Al-plated steel sheet. The amount of Si required to suppress the growth of the alloy layer is 0.5% or more, and the lower limit is set to the lower limit. Since excessive addition also leads to a decrease in corrosion resistance, the upper limit is preferably set to 10%.
[0023]
Fe: Fe is also an unavoidable impurity, and it is preferable that Fe is small. The upper limit is 3%. In addition to these elements, Mg, Ca, Ti, Mn, misch metal, Sn, Cr, and Ni can be added. These elements are mainly effective for further improving the corrosion resistance, and can be added. However, there is an upper limit to the amount that can be added from the bath temperature of Al plating, and there is an upper limit for each of Mg and Ca since excessive addition leads to an increase in oxide dross. The amounts are Mg: 10%, Ca: 5%, Ti: 0.1%, Mn: 1%, misch metal: 0.2%, Sn: 10%, Cr: 0.5%, Ni: 0.5 % Is desirable.
[0024]
The method of producing Al-based plating is performed by a hot-dip plating method generally used at present. As the hot-dip plating process, there are a sendzimer method and a radiant tube furnace method, but these are not particularly limited. It is also possible to use pre-plating as a pretreatment for Al-based plating. In addition, as a post-treatment of plating, a chemical conversion treatment (chromate, non-chromate), a zero spangle treatment, an annealing, a temper rolling, or the like may be applied, but these are not particularly limited and can be applied. In addition, there is no particular problem with the amount of Al-based plating applied, which is 60 to 200 g / m 2 on both sides, which is a normal amount of adhesion.
[0025]
Next, the present invention will be described in more detail with reference to examples.
【Example】
(Example 1)
Hot-rolled Al plating was performed using a cold-rolled steel sheet (sheet thickness 0.8 mm) having a steel composition as shown in Table 1 after normal hot rolling and cold rolling steps. For the hot-dip Al plating, a non-oxidizing furnace-reduction furnace type line was used. After plating, the amount of plating was adjusted by a gas wiping method, then cooled, and alumina was sprayed as a zero spangle treatment. The composition of the plating bath was Al-10% -2% Fe, and the bath temperature was 660 ° C. The Fe in the bath is inevitable supplied from plating equipment and strips in the bath. The plating appearance was good without non-plating and the like. The plating adhesion amount was 120 g / m 2 on both sides, and both sides were uniform. The corrosion resistance of the hot-dip Al-plated steel sheet thus manufactured was evaluated by the method shown below. Table 2 shows the evaluation results.
[0026]
[Table 1]
(1) Corrosion resistance evaluation (1) Steel after removing corrosion products by performing four cycles of the exhaust system inner surface evaluation method specified in JASO M 611-92B using a sample having an exhaust system inner corrosion resistance dimension of 25 × 100 mm. The corrosion depth of the substrate was measured. At this time, the corrosion depth of each sample was measured at 10 points, and the maximum corrosion depth was evaluated.
〔Evaluation criteria〕
：: Corrosion depth less than 0.05 mm △: Corrosion depth 0.05 to 0.2 mm
×: Corrosion depth of more than 0.2 mm [0028]
(2) Corrosion resistance of the exhaust system outer surface (salt damage resistance)
A salt spray test in accordance with JIS Z 2371 was performed on a sample having a size of 70 × 150 mm for 30 days, and corrosion products were peeled off to measure corrosion weight loss. The indication of the corrosion weight loss is a value for one side of the plating.
〔Evaluation criteria〕
：: Corrosion weight loss of less than 20 g / m 2 △: Corrosion weight loss of 30 g / m 2 or less ×: Corrosion weight loss of more than 30 g / m 2 As shown in Table 2, the amount of elements such as S, P, Al, Cr, Si, etc. is large. In particular, it can be seen that the internal corrosion resistance tends to decrease. Although the external corrosion resistance is not so much affected, the life of the exhaust system environment is often determined by the internal corrosion resistance. By appropriately controlling the above elements, excellent internal corrosion resistance can be obtained.
[0029]
[Table 2]
(Example 2)
Using the steel of A in Table 1 of Example 1, a sample in which the composition of the plating bath was changed was manufactured. Plating was performed using a non-oxidizing furnace-reducing furnace type hot-dip plating line, and after plating, the amount of plating was adjusted by a gas wiping method, followed by cooling. The plating weight was 120 g / m 2 on both sides. Plating with a uniform appearance was obtained. Further, as a post-treatment, both surfaces were subjected to a non-chromate treatment (Zr-V-silica-based treatment) at an adhesion amount of 500 mg / m 2 per one surface. This was evaluated by the same method and evaluation criteria as in Example 1. Table 3 shows the plating composition and the evaluation results.
Tests were conducted with the plating components shown in Table 3 and showed good corrosion resistance on the inner surface of the exhaust system. However, when the Zn content of the plating layer is large, the corrosion resistance tends to be slightly lowered.
[0031]
[Table 3]
【The invention's effect】
As described above, the present invention provides a hot-dip Al-based steel sheet having excellent corrosion resistance particularly in an exhaust system inner surface environment as compared with the related art. According to the present invention, it is possible to supply an inexpensive exhaust system material which is inexpensive and has excellent workability, and has a great industrial contribution.
Claims (5)
Ｃ ：０．０１％以下、
Ｓｉ：０．４％以下、
Ｍｎ：０．７％以下、
Ｐ ：０．０２％以下、
Ｓ ：０．０１５％以下、
Ａｌ：０．０１％以下、
Ｃｒ：０．１％以下、
Ｃｕ：０．１〜０．５％
を含有し、残部がＦｅ及び不可避的不純物からなる鋼板の表面に質量％でＡｌを５０％以上含有するＡｌ系めっき層を含有することを特徴とする耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。In mass%,
C: 0.01% or less,
Si: 0.4% or less,
Mn: 0.7% or less,
P: 0.02% or less,
S: 0.015% or less,
Al: 0.01% or less,
Cr: 0.1% or less,
Cu: 0.1-0.5%
Characterized by containing an Al-based plating layer containing 50% or more by mass of Al on the surface of a steel plate comprising Fe and unavoidable impurities, with the balance being Fe, and having excellent corrosion resistance. System plated steel sheet.
Ｓｂ：０．３％以下、
Ｓｎ：０．３％以下、
Ｎｉ：０．５％以下、
Ｍｏ：０．５％以下、
Ｔｉ：０．０２〜０．３％、
Ｎｂ：０．０２〜０．２％、
Ｖ ：０．０５％以下、
Ｂ ：０．０１％以下、
の中の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に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。In addition to steel
Sb: 0.3% or less,
Sn: 0.3% or less,
Ni: 0.5% or less,
Mo: 0.5% or less,
Ti: 0.02 to 0.3%,
Nb: 0.02 to 0.2%,
V: 0.05% or less,
B: 0.01% or less,
The hot-dip Al-coated steel sheet for automobile exhaust system materials according to claim 1, wherein the steel sheet contains one or more of the following.
Ｓｉ：２〜１５％、
Ｆｅ：３％以下、
Ｃｒ：０．１％以下、
残部がＡｌ及び不可避的不純物であることを特徴とする請求項１または２に記載の耐食性に優れた自動車排気系材用溶融Ａｌめっき鋼板。Al-based plating layer composition is
Si: 2 to 15%,
Fe: 3% or less,
Cr: 0.1% or less,
3. The hot-dip Al-coated steel sheet for automobile exhaust system materials having excellent corrosion resistance according to claim 1, wherein the balance is Al and inevitable impurities.
Ｚｎ：５０％以下、
Ｓｉ：０．５〜１０％、
Ｆｅ：３％以下、
残部がＡｌ及び不可避的不純物であることを特徴とする請求項１または２に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。As the Al-based plating layer composition,
Zn: 50% or less,
Si: 0.5 to 10%,
Fe: 3% or less,
The hot-dip Al-coated steel sheet for automobile exhaust system materials according to claim 1 or 2, wherein the balance is Al and inevitable impurities.
Ｍｇ：０．１〜１０％、
Ｃａ：０．０１〜５％、
Ｔｉ：０．１％以下、
Ｍｎ：１％以下、
ミッシュメタル：０．２％以下、
Ｓｎ：１０％以下、
Ｃｒ：０．５％以下、
Ｎｉ：０．５％以下、
の中の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３または４に記載の耐食性に優れた自動車排気系材用溶融Ａｌ系めっき鋼板。In addition to the Al-based plating layer composition,
Mg: 0.1 to 10%,
Ca: 0.01-5%,
Ti: 0.1% or less,
Mn: 1% or less,
Misch metal: 0.2% or less,
Sn: 10% or less,
Cr: 0.5% or less,
Ni: 0.5% or less,
The hot-dip Al-coated steel sheet for automobile exhaust system materials having excellent corrosion resistance according to claim 3 or 4, wherein the hot-dip coated steel sheet has excellent corrosion resistance.
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006070326A (en) * | 2004-09-02 | 2006-03-16 | Nittetsu Steel Sheet Corp | Method for manufacturing hot-dip plated steel sheet with aluminum-zinc alloy |
| WO2008025066A1 (en) * | 2006-08-29 | 2008-03-06 | Bluescope Steel Limited | Metal-coated steel strip |
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2003
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| JP2006070326A (en) * | 2004-09-02 | 2006-03-16 | Nittetsu Steel Sheet Corp | Method for manufacturing hot-dip plated steel sheet with aluminum-zinc alloy |
| WO2008025066A1 (en) * | 2006-08-29 | 2008-03-06 | Bluescope Steel Limited | Metal-coated steel strip |
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| JP2020007641A (en) * | 2006-08-29 | 2020-01-16 | ブルースコープ・スティール・リミテッドＢｌｕｅｓｃｏｐｅ Ｓｔｅｅｌ Ｌｉｍｉｔｅｄ | Metal coated iron strip |
| JP2016194163A (en) * | 2006-08-29 | 2016-11-17 | ブルースコープ・スティール・リミテッドＢｌｕｅｓｃｏｐｅ Ｓｔｅｅｌ Ｌｉｍｉｔｅｄ | Metal coated iron strip |
| JP2014132121A (en) * | 2006-08-29 | 2014-07-17 | Bluescope Steel Ltd | Metal-coated iron strip |
| US11840763B2 (en) | 2008-03-13 | 2023-12-12 | Bluescope Steel Limited | Metal-coated steel strip |
| US11807941B2 (en) | 2009-03-13 | 2023-11-07 | Bluescope Steel Limited | Corrosion protection with Al/Zn-based coatings |
| US9464345B2 (en) | 2010-06-21 | 2016-10-11 | Nippon Steel & Sumitomo Metal Corporation | Hot dip Al coated steel sheet excellent in heat black discoloration resistance and method of production of same |
| KR101473550B1 (en) | 2010-06-21 | 2014-12-16 | 신닛테츠스미킨 카부시키카이샤 | Hot-dip al-coated steel sheet with excellent thermal blackening resistance and process for production of same |
| JP5218703B2 (en) * | 2010-06-21 | 2013-06-26 | 新日鐵住金株式会社 | Hot-dip Al-plated steel sheet excellent in heat blackening resistance and method for producing the same |
| WO2011161833A1 (en) * | 2010-06-21 | 2011-12-29 | 新日本製鐵株式会社 | Hot-dip al-coated steel sheet with excellent thermal blackening resistance and process for production of same |
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| JP2014503690A (en) * | 2010-12-27 | 2014-02-13 | ポスコ | Aluminum plated steel plate with excellent oxidation resistance and heat resistance |
| KR102531588B1 (en) * | 2014-07-16 | 2023-05-12 | 티센크루프 스틸 유럽 악티엔게젤샤프트 | Steel product with an anticorrosive coating of aluminium alloy and method for the production thereof |
| KR20170036700A (en) * | 2014-07-16 | 2017-04-03 | 티센크루프 스틸 유럽 악티엔게젤샤프트 | Steel product with an anticorrosive coating of aluminium alloy and method for the production thereof |
| CN107002213A (en) * | 2014-07-16 | 2017-08-01 | 蒂森克虏伯钢铁欧洲股份公司 | Product made from steel and its manufacture method with the corrosion protective layer being made up of aluminium alloy |
| US10287440B2 (en) * | 2014-07-16 | 2019-05-14 | Thyssenkrupp Steel Europe Ag | Steel product with an anticorrosive coating of aluminum alloy and method for the production thereof |
| CN104233149A (en) * | 2014-08-28 | 2014-12-24 | 河北钢铁股份有限公司 | High-temperature oxidation resistant plating layer material and hot dipping method for hot stamping formed steel |
| CN107083512A (en) * | 2017-03-30 | 2017-08-22 | 合肥金同维低温科技有限公司 | A kind of aluminum alloy materials for being used to manufacture freezer compressor cylinder block |
| KR20180123837A (en) * | 2017-05-10 | 2018-11-20 | 현대자동차주식회사 | Low-alloy and Corrosion-resistant Steel Having Improved Corrosion-resistant at Corrosive Environment and the Method Thereof |
| KR102373161B1 (en) * | 2017-05-10 | 2022-03-10 | 현대자동차주식회사 | Low-alloy and Corrosion-resistant Steel Having Improved Corrosion-resistant at Corrosive Environment and the Method Thereof |
| WO2020111889A1 (en) * | 2018-11-30 | 2020-06-04 | 주식회사 포스코 | Steel sheet having corrosion resistance in sulfuric acid and sulfuric acid/hydrochloric acid composite condensation environments, and manufacturing method therefor |
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