JP2004211151A

JP2004211151A - Al-plated steel sheet for high-temperature press forming superior in lubricity

Info

Publication number: JP2004211151A
Application number: JP2002381773A
Authority: JP
Inventors: Masahiro Fuda; 雅裕布田; Jun Maki; 純真木; Masayoshi Suehiro; 正芳末廣; Toshihiro Miyakoshi; 寿拓宮腰
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-12-27
Filing date: 2002-12-27
Publication date: 2004-07-29

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-plated steel sheet for high-temperature press forming superior in lubricity, which can give a high-strength formed article having attractive appearance and superior corrosion resistance, by controlling the occurrence of flaw during press forming. <P>SOLUTION: The steel sheet has a composition consisting of by mass%, 0.1% or more but 0.6% or less C, 0.1% or more but 3.0% or less Mn, 0.1% or less P, 0.02% or less S, 0.005% or more but 0.1% or less Al, at least one element of 0.01% or more but 0.5% or less Si, 0.0002% or more but 0.01% or less B, 0.005% or more but 0.2% or less Ti and 0.005% or more but 1.0% or less Cr, and the balance Fe with unavoidable impurities. The Al plated steel sheet for high-temperature press forming superior in lubricity has an aluminum coating comprising 3% or more but 15% or less Si and the balance Al with unavoidable impurities plated on the above steel sheet, and further either one film thereon among an inorganic compound film, an organic compound film and the organic and inorganic composite compounds film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、高温でのプレス成形性に優れ、かつ極めて高い機械強度を有し、良好な耐食性、外観を有する溶融アルミめっき鋼板に関するものである。
【０００２】
【従来の技術】
近年、環境保護と地球温暖化を防止するため、化石燃料の消費を抑制する動きが強まっており、移動手段として我々の生活に欠かせない自動車においても、車体の軽量化が強く求められている。この軽量化を達成するためには、従来に比べ、高い機械強度を有する材料を使用することが必要になるが、一般に、高い強度を有する材料は、曲げ加工等の成形加工において、形状凍結性が低下する傾向にあり、また、複雑な形状のものに対しては、成形そのものが困難である。これらの問題を解決する方法の一つとして、８００℃以上の高温に加熱し、プレス加工を行った後、冷却する、いわゆる高温プレスによる方法が有望である。この手法によれば、材料を一旦高温に加熱して、軟化した状態にすれば、容易にプレス成形でき、さらに、成形後の冷却時の焼入れ効果により、高強度化を可能にしたもので、良好な形状凍結性と高強度を有した成形品が得られる。しかし、材料として鋼板を用いた場合、８００℃程度の高温に加熱するため、表面に酸化物（スケール）が発生し、それを取り除くための工程が発生する。また、耐食性を必要とする部材等では、加工後に表面へ防錆処理や金属被覆する必要があり、表面清浄化工程、表面処理工程が必要となる。
【０００３】
これらの欠点を克服する方法として、所定の鋼成分を有する鋼に、Ａｌ系の金属被覆を施した鋼板を用いる方法が示されている（例えば、特許文献１参照）。しかしながら、この方法では、目的とする材料強度は得られるものの、プレス前の予備加熱条件によっては、鋼板のＦｅとめっき層のＡｌによる合金層が成長しすぎて、表面が荒れ、成型時の金型との接触により表面に加工傷が形成され、外観を損ねるとともに、耐食性が低下するおそれがある、という欠点がある。
【０００４】
【特許文献１】
特開２０００−３８６４０号公報
【０００５】
【発明が解決しようとする課題】
本発明は、プレス成型時における上記の加工傷発生を制御することで、美麗な外観を有し、かつ優れた耐食性を有した高強度成形品を可能とする高温プレス成形性用Ａｌ系めっき鋼板を提供するものである。
【０００６】
【課題を解決するための手段】
本発明者等は、鋼板成分、めっき浴組成及びめっき表面性状が、高温プレス成形性に及ぼす諸因子を詳細に検討した結果、特定の元素を含有する鋼板を使用することで、合金層の成長を制御でき、かつ、その表面に無機化合物皮膜、有機化合物皮膜、無機と有機の複合化合物皮膜のいずれかの皮膜を施すこと、また、更にこれらの皮膜中固体潤滑剤、粒状金属酸化物の少なくとも一方を含有させるとすることで、高い強度を有する外観良好な成形品を得ることができることを見出した。すなわち、鋼板の高強度化には、Ｃ、Ｍｎ、Ｓｉ、Ｂ、Ｔｉ、Ｃｒの添加が有効であり、冷却時に十分な焼入れ効果が得られ、１０００〜２０００ＭＰａの高い強度が得られること、かつ、成型後に美麗な外観を得るためには、高温に加熱されても表面に残留し、良好な潤滑作用を有する皮膜を施すことが有効であり、その皮膜中に固体潤滑剤、粒状金属酸化物を含有させれば、更に効果が大きいことを見出した。
【０００７】
本発明の特徴とするところは、
（１）質量％で、Ｃ：０．１％以上０．６％以下、Ｍｎ：０．１％以上３．０％以下、Ｐ：０．１％以下、Ｓ：０．０２％以下、Ａｌ：０．００５％以上０．１％以下を含み、Ｓｉ：０．０１％以上０．５％以下、Ｂ：０．０００２％以上０．０１％以下、Ｔｉ：０．００５％以上０．２％以下、Ｃｒ：０．００５％以上１．０％以下、の少なくとも一つ以上を含み、残部Ｆｅ及び不可避的不純物からなる鋼板に、Ｓｉ：３％以上１５％以下を含有し，残部Ａｌ及び不可避的不純物からなるアルミめっき被覆を施し、さらにその上に、無機化合物皮膜、有機化合物皮膜、又は、無機と有機の複合化合物皮膜のいずれか一つの皮膜を有することを特徴とする潤滑性に優れた高温プレス成形用Ａｌ系めっき鋼板、
（２）前記無機化合物皮膜又は複合化合物皮膜が、Ｓｉ、Ｚｒ、Ｔｉ、又は、Ｐの少なくとも一つを含有する（１）記載の潤滑性に優れた高温プレス成形性用Ａｌ系めっき鋼板、
（３）前記有機化合物皮膜又は複合化合物皮膜が、Ｆ、Ｓｉ、Ｃ、又は、Ｎの少なくとも一つを含有する（１）記載の潤滑性に優れた高温プレス成形性用Ａｌ系めっき鋼板、
（４）前記皮膜が、さらに固体潤滑剤又は粒状金属酸化物の何れか一方又は両方を含有する（１）〜（３）のいずれかに記載の潤滑性に優れた高温プレス成形用Ａｌ系めっき鋼板、
（５）前記固体潤滑剤の含有量が、皮膜中に１体積％以上５０体積％以下である（４）記載の潤滑性に優れた高温プレス成形性用Ａｌ系めっき鋼板、
（６）前記固体潤滑剤がフッ素系樹脂である（４）又は（５）に記載の潤滑性に優れた高温プレス成形性用Ａｌ系めっき鋼板、
（７）前記粒状金属酸化物の粒径が０．１μｍ以上、皮膜厚みの２．５倍以下であり、添加量が皮膜中に１体積％以上４０体積％以下である（４）記載の潤滑性に優れた高温プレス成形用Ａｌ系めっき鋼板、
（８）前記粒状金属酸化物がＡｌ系酸化物、Ｓｉ系酸化物、Ｔｉ系酸化物、又は、Ｚｒ系酸化物から選ばれる１種以上である（４）又は（７）に記載の潤滑性に優れた高温プレス成形性用Ａｌ系めっき鋼板、
である。
【０００８】
【発明の実施の形態】
まず、本発明に用いる鋼板の成分及び含有量の限定理由を述べる。
【０００９】
Ｃは、目的とする強度を確保するために添加する。Ｃが０．１％未満だと、十分な強度が得られず、効果に乏しい。一方、０．６％を超えると、さらに高強度化するものの、溶接割れが生じやすくなるため、上限を０．６％以下とした。
【００１０】
Ｍｎは、強化元素であり、焼入れ性を高める元素でもある。かつ、不純物であるＳによる熱間脆性を防止するのに有効である。Ｍｎが０．１％以上において、それらの効果が発現する。一方、３．０％を超えると、残留γ相が多くなりすぎ、強度が低下する。そのため、Ｍｎ濃度は０．１％以上３．０％以下とした。
【００１１】
Ｓｉは、強度向上元素として有効であり、０．０１％以上で効果を発現するが、易酸化性元素でもあり、溶融アルミめっきを行う際、鋼中のＳｉ濃度が０．５％を超えると、濡れ性が低下し、不めっきが生じる。したがって、Ｓｉは０．０１％以上０．５％以下とする。
【００１２】
Ｂは、焼入れ時に作用し、強度を向上させる効果をもつ。０．０００２％以上の添加で作用するが、０．０１％超では、介在物を形成して脆化し、疲労強度を低下させるため、０．０００２％以上０．０１％以下とする。
【００１３】
Ｔｉは、強度強化元素であり、また、アルミめっきの耐熱性を向上させる元素でもあるが、あまり添加しすぎると、炭化物、窒化物を形成して、軟質化してしまう恐れがある。０．００５％以上の添加で、強度向上効果、耐酸化性向上効果が現れるが、０．２％より多く添加すると、目的とする強度が得られない可能性がある。したがって、Ｔｉは０．００５％以上０．２％以下とする。
【００１４】
Ｃｒは、強度強化元素であり、かつ、耐食性も向上するが、その効果を得るには、０．００５％以上添加する必要がある。１．０％より多量に添加しても、強度の向上効果は少なく、コストが増大するため、上限値を１．０％とした。したがって、Ｃｒは０．００５％以上１．０％以下とした。
【００１５】
Ｐは、強度強化元素であるが、０．１％を超える添加は靭性を低下させる。したがって、０．１％以下とする。
【００１６】
Ｓは、硫化物系介在物による成形性低下のため、少ないほど好ましいが、０．０２％まで許容できる。したがって、Ｓは０．０２％以下とする。
【００１７】
Ａｌは、脱酸剤として作用する。この目的のためには、０．００５％以上が必要であるが、０．１％を超えると効果は飽和し、かえって介在物を形成して、脆化させるため、上限値を０．１％とした。したがって、Ａｌは０．００５％以上０．１％以下とする。
【００１８】
次に、アルミめっき層成分及び含有量の限定理由について述べる。
【００１９】
Ｓｉは、溶融めっき金属被覆時に生成する合金層の制御が目的で添加する。このＳｉの含有量は、３％以上１５％以下が好適である。３％未満だと、Ｆｅ−Ａｌ合金層がめっき段階で厚く成長し、加工時にめっき層割れを助長して、耐食性に悪影響を及ぼす。一方、１５％超では、めっき層の加工性、耐食性が低下するため、Ｓｉ含有量は３％以上１５％以下とした。
【００２０】
めっき層の厚みについては、本発明では特に制限を設けない。実使用上は、片側あたり合金層まで含めて、厚み８μｍ〜４０μｍで何ら問題なく使用可能である。
【００２１】
本発明では、プレス成型時の加工傷抑制を目的として、めっき層の表面に、無機化合物皮膜、有機化合物皮膜、又は、無機と有機の複合化合物皮膜のいずれかの皮膜を施すことを特徴とする。無機化合物皮膜は、一般的に耐熱性を有しているため、８００℃程度の高温においても、皮膜として存在し、被加工物と金型との接触を抑制することにより、加工傷の発生が抑制できる。これら無機化合物皮膜としては、その皮膜形成能から、Ｓｉ、Ｚｒ、Ｔｉ、Ｐの一つ以上の化合物もしくは化合物群から構成された皮膜が、好適である。これらは、例えば、Ｎａ_２ＳｉＯ_３、Ｋ_２ＳｉＯ_３、Ｌｉ_２ＳｉＯ_３等のケイ酸塩化合物、コロイダルシリカ（ＳｉＯ_２）、Ｋ_２ＺｒＦ_６，Ｋ_２ＴｉＦ_６等のフッ化物塩系化合物、リン酸（Ｈ_３ＰＯ_４）、及び、リン酸塩系化合物の皮膜等が挙げられる。
【００２２】
また、有機化合物皮膜は、無機化合物皮膜に比べ、潤滑性は優れるものの、耐熱性が低い傾向があるが、耐熱温度の比較的高い化合物を使用することにより、成形に要する加熱時間内においても分解飛散せず、十分に皮膜としての機能を発揮するし、また、炭化水素を基調とした比較的耐熱温度の低い樹脂系においても、他に耐熱温度の高い樹脂との併用、あるいは、無機化合物、粒状金属酸化物との併用により、良好な特性が得られる。これら有機化合物皮膜としては、Ｆ、Ｓｉ、Ｃ、Ｎの一つ以上の化合物もしくは化合物群を含有する皮膜が好適である。例えば、耐熱性の高い樹脂系では、ＰＴＦＥ（四フッ化エチレン樹脂）、ＦＥＰ（四フッ化エチレン・六フッ化プロピレン共重合樹脂）、ＥＴＦＥ（四フッ化エチレン・エチレン共重合樹脂）等のフッ素系樹脂皮膜や、純シリコン樹脂、ポリエステル変性シリコン樹脂等のシリコン系樹脂皮膜や、ＰＥＳ（ポリエーテルスルホン）樹脂、ＰＰＳ（ポリフェニレンスルフィド）樹脂等の芳香族樹脂系皮膜や、ポリアミドイミド樹脂、ポリエステルイミド樹脂等のポリイミド系樹脂皮膜、等が好適である。また、比較的耐熱温度の低い樹脂として、例えば、エポキシ樹脂、アクリル樹脂、ポリエステル樹脂、ウレタン樹脂等の樹脂が使用可能である。
【００２３】
また、無機化合物と有機化合物の複合皮膜を用いる場合、上述のそれぞれの皮膜成分を混合することで、両者の特徴を引き出せる。無機成分と有機成分の比率として、質量比で１０：９０〜８０：２０が好ましい。また、その他に、例えば、Ｓｉ（ＯＣ_２Ｈ_５）_４等の有機シリケート系化合物、Ｔｉ（ＯＣ_２Ｈ_５）_４等の有機チタネート系化合物とＳｉＯ_２，ＴｉＯ_２等の無機化合物を用いたゾル−ゲル法によって、皮膜を形成することも可能である。
【００２４】
また、これらの皮膜に、固体潤滑剤、粒状金属酸化物を加えることは、更に効果的である。固体潤滑剤としては、グラファイト、ＣａＦ_２、ＮａＦ、ＢａＦ_２、ＬａＦ_３等のフッ化物、ＭｏＳ_２、ＷＳ_２、ＦｅＳ等の硫化物、ＢＮ等の窒化物、Ａｌ_２Ｏ_３、ＭｏＯ_３、ＷＯ_３、Ｆｅ_２Ｏ_３等の酸化物、ＰＴＦＥ樹脂等のフッ素系樹脂、ポリイミド樹脂、シリコン樹脂等の高分子化合物が好適である。中でも、特にフッ素系樹脂を使用した場合に、良好な特性を示す。これら固体潤滑剤の含有量は、皮膜中に１体積％以上５０体積％以下であることが望ましい。１体積％未満ではその効果が乏しく、５０体積％以上では効果が飽和するとともに、皮膜系によっては皮膜形成能を阻害する恐れがある。
【００２５】
また、粒状金属酸化物としては、例えば、アルミナ等のＡｌ系酸化物、気相シリカ、コロイダルシリカ等のＳｉ系酸化物、チタニア等のＴｉ系酸化物、ジルコニア等のＺｒ系酸化物から選ばれる１種以上の酸化物が好適である。粒状金属酸化物は、粒径が０．１μｍ以上、皮膜厚みの２．５倍以下であり、添加量が皮膜中に１体積％以上４０体積％以下であることが望ましい。粒径が０．１μｍ未満では、本来の添加目的である接触面積の低下効果が乏しく、皮膜厚みの２．５倍以上になると、皮膜の粒子保持能力が低下する恐れがある。添加量は、１体積％未満ではその効果が乏しく、３０体積％以上では効果が飽和するとともに、皮膜系によっては皮膜形成能を阻害する恐れがある。
【００２６】
上記の皮膜の同定は、公知の分析手法を用いて可能である。例えば、皮膜断面からのＥＰＭＡ（（ＥｌｅｃｔｒｏｎＰｒｏｂｅＭｉｃｒｏＡｎａｌｙｚｅｒ）と蛍光Ｘ線分析を用いて、皮膜の組成と成分の含有率を同定する手法等である。皮膜成分の中には、処理液塗布後の焼付け乾燥時に反応して生成するものもあるが、そのような途中で形成される物質も、ＸＲＤ（Ｘ−ｒａｙＤｉｆｆｒａｃｔｉｏｎ）、ＥＳＣＡ（ＥｌｅｃｔｒｏｎＳｐｅｃｔｒｏｓｃｏｐｙｆｏｒＣｈｅｍｉｃａｌＡｎａｌｙｓｉｓ）、ＮＭＲ（ＮｕｃｌｅａｒＭａｇｎｅｔｉｃＲｅｓｏｎａｎｃｅ）、ＳＩＭＳ（ＳｅｃｏｎｄａｒｙＩｏｎＭａｓｓｓｐｅｃｔｒｏｓｃｏｐｙ）等の公知の分析手法を用いて、同定、定量することが可能である。
【００２７】
上記の皮膜は、水性塗料、油性塗料、ゾル−ゲル塗料からの塗布、焼付け・乾燥により、形成することが可能である。塗布方法も、特に限定はせず、ロール塗装、スプレー塗装、浸漬等の公知の方法が適用可能である。塗布後の焼付け・乾燥は、熱風炉、誘導加熱炉、近赤外線炉等の公知の方法あるいはこれを組み合わせた方法で行えばよい。また、使用する樹脂の種類によっては、紫外線や電子線等によって硬化させることができる。
【００２８】
また、溶融めっき後の後処理として、前記無機化合物皮膜、有機化合物皮膜、又は、無機と有機の複合化合物皮膜のいずれか一つの皮膜を施す前に、クロメート処理皮膜、もしくは、Ｃｒ化合物、Ｓｉ化合物、Ｐ化合物、Ｚｎの化合物、アクリル樹脂の少なくとも１種以上よりなる皮膜を施すことも可能である。その他、溶融めっき後の外観均一化処理であるゼロスパングル処理（ｍｉｎｉｍｉｚｅｄｓｐａｎｇｌｉｎｇ）、めっき層の加工性改善処理である焼鈍処理、組織制御の急冷処理等があり得るが、本発明においては、特にこれらを限定せず、適用することも可能である。
【００２９】
溶融アルミめっき鋼板の製造工程についても、何ら限定するものではなく、通常の製鋼、熱延、冷延、焼鈍条件が適用可能である。また、Ｎｉ、Ｆｅのプレめっき等もありうるが、これも適用可能である。
【００３０】
【実施例】
次に、実施例により、本発明を更に詳細に説明する。
【００３１】
表１に示す成分の鋼を、転炉−真空脱ガス処理により溶製し、鋼片とした後、熱間圧延して、板厚１．８ｍｍの酸洗後の熱延鋼板を得るとともに、冷間圧延を経て、板厚１．２ｍｍの冷延鋼板を得た。符号Ａ〜Ｅ、Ｇ〜Ｋが冷延鋼板、符号Ｆが熱延鋼板である。これらの鋼板に、無酸化炉−還元炉方式のラインを使用して、還元−焼鈍を行った後、９．２％Ｓｉ、及び１７．２％Ｓｉを含有するＡｌ−Ｓｉ合金めっき浴に浸漬して、溶融めっきを行った。めっき後、ガスワイピングで、めっき付着量を片面あたり２５μｍに調節した。このときのめっき組成は、Ａｌ、Ｓｉ以外に２．０％のＦｅが含まれていたが、Ｆｅは、浴中の機器やストリップから供給される不可避のものである。
【００３２】
【表１】

【００３３】
こうして製造しためっき鋼板について、表２に示す各種処理皮膜を、ロール塗装により所定の膜厚になるよう、塗布した後、熱風乾燥炉にて、焼付け乾燥した。
【００３４】
【表２】

【００３５】
そのようにして得られた供試材につき、熱処理後の強度とプレス成形性を評価した。評価結果を表３に示す。
【００３６】
評価方法は、以下によった。
（１）熱処理後の強度
９００℃の温度で５分間熱処理し、鋼板にはさんで冷却した後、ＪＩＳ５号引張り試験片にて引張り試験を実施し、引張り強度を測定した。
（２）高温プレス成形性評価
９００℃の温度で５分間加熱した後、５０ｍｍφの円筒プレス試験を実施した後、表面の外観を観察した。
【００３７】
◎：成形可能で、表面外観に変化なし
○：成形可能で、表面外観わずかに傷、黒化発生
△：成形可能で、かじり傷発生、もしくは黒化、スケール発生
×：成形可能で、全面かじり傷発生大、もしくは割れ発生
【００３８】
【表３】

【００３９】
比較例のＮｏ．１３は、目的とする高強度は得られたものの、表面の皮膜が無かったため、プレス成形後の外観が良くなかった。Ｎｏ．１４、１５も、目的とする高強度は得られたものの、めっき層中のＳｉが高すぎたため、プレス成形後の外観が良くなかった。また、Ｎｏ．１６、１７、１９は、Ｃ、Ｓｉ、Ｍｎ、Ｂの量が少なく、必要な焼き入れ性が得られずに、目的とする高強度が得られなかった。Ｎｏ．１８では、Ｍｎの量が高すぎ、目的の強度が得られなかった。本発明の実施例Ｎｏ．１〜１２については、鋼成分構成と皮膜の効果で、強度、外観とも、良好な特性が得られた。特に、固体潤滑剤、粒径０．１μｍ以上の粒状金属酸化物を添加したＮｏ．２〜６、Ｎｏ．８〜９、Ｎｏ．１１〜１２が良好である。
【００４０】
【発明の効果】
本発明により、高温プレス時の課題であったプレス成型後の外観を改善し、かつ、必要な強度を兼備した高強度プレス品用溶融アルミめっき鋼板が提供でき、この鋼板を用いれば、自動車車体等の軽量化を推進できるので、産業上の寄与も大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hot-dip aluminized steel sheet having excellent press formability at high temperatures, having extremely high mechanical strength, and having good corrosion resistance and appearance.
[0002]
[Prior art]
In recent years, there has been an increasing movement to reduce the consumption of fossil fuels in order to protect the environment and prevent global warming, and there is a strong demand for lighter bodies in vehicles that are indispensable for our lives as a means of transportation. . In order to achieve this weight reduction, it is necessary to use a material having a higher mechanical strength than in the past, but generally, a material having a high strength has a shape freezing property in a forming process such as a bending process. And the molding itself is difficult for those having complicated shapes. As a method for solving these problems, a method using a so-called high-temperature press, in which heating is performed to a high temperature of 800 ° C. or higher, press working is performed, and then cooling is promising. According to this method, once the material is once heated to a high temperature and brought into a softened state, it can be easily press-formed, and furthermore, by the quenching effect at the time of cooling after the molding, the strength can be increased, A molded article having good shape freezing property and high strength is obtained. However, when a steel plate is used as a material, since heating is performed at a high temperature of about 800 ° C., an oxide (scale) is generated on the surface, and a process for removing the oxide occurs. Further, in the case of a member or the like that requires corrosion resistance, it is necessary to perform rust prevention treatment or metal coating on the surface after processing, which requires a surface cleaning step and a surface treatment step.
[0003]
As a method of overcoming these drawbacks, there is disclosed a method of using a steel sheet having a predetermined steel component and applying an Al-based metal coating to the steel (for example, see Patent Document 1). However, in this method, although the desired material strength is obtained, depending on the preheating conditions before pressing, the alloy layer of Fe of the steel sheet and the Al of the plating layer grows too much, the surface is roughened, and the metal during molding is roughened. There is a drawback that a processing flaw is formed on the surface due to contact with the mold, and the appearance is impaired, and the corrosion resistance may be reduced.
[0004]
[Patent Document 1]
JP 2000-38640 A
[Problems to be solved by the invention]
The present invention is an Al-based plated steel sheet for high-temperature press formability by controlling the occurrence of the above processing scratches during press forming, thereby enabling a high-strength formed product having a beautiful appearance and excellent corrosion resistance. Is provided.
[0006]
[Means for Solving the Problems]
The present inventors have studied in detail the factors that affect the high-temperature press formability of the steel sheet components, the plating bath composition and the plating surface properties, and as a result, by using a steel sheet containing a specific element, the growth of the alloy layer Can be controlled, and, on the surface thereof, an inorganic compound film, an organic compound film, or any of inorganic and organic composite compound films, and further, a solid lubricant in these films, and at least a particulate metal oxide. It has been found that by including one of them, a molded article having high strength and good appearance can be obtained. That is, the addition of C, Mn, Si, B, Ti, and Cr is effective for increasing the strength of the steel sheet, a sufficient quenching effect is obtained during cooling, and a high strength of 1000 to 2000 MPa is obtained, and In order to obtain a beautiful appearance after molding, it is effective to apply a film which remains on the surface even when heated to a high temperature and has a good lubricating effect, and includes a solid lubricant and a particulate metal oxide in the film. Was found to be even more effective if contained.
[0007]
The features of the present invention include:
(1) In mass%, C: 0.1% or more and 0.6% or less, Mn: 0.1% or more and 3.0% or less, P: 0.1% or less, S: 0.02% or less, Al : 0.005% to 0.1%, Si: 0.01% to 0.5%, B: 0.0002% to 0.01%, Ti: 0.005% to 0.2 % Or less, Cr: 0.005% or more and 1.0% or less, and a steel sheet composed of the balance Fe and unavoidable impurities contains Si: 3% to 15% and a balance of Al and Excellent lubricity characterized by having an aluminum plating coating consisting of unavoidable impurities, and further having any one of an inorganic compound film, an organic compound film, and an inorganic and organic compound compound film thereon Al-plated steel sheet for hot press forming
(2) The Al-based coated steel sheet for high temperature press formability excellent in lubricity according to (1), wherein the inorganic compound film or the composite compound film contains at least one of Si, Zr, Ti, and P.
(3) The Al-plated steel sheet for high-temperature press-formability excellent in lubricity according to (1), wherein the organic compound film or the composite compound film contains at least one of F, Si, C, and N.
(4) The Al-based plating for high-temperature press molding excellent in lubricity according to any one of (1) to (3), wherein the coating further contains one or both of a solid lubricant and a granular metal oxide. steel sheet,
(5) The Al-based coated steel sheet for high-temperature press-formability excellent in lubricity according to (4), wherein the content of the solid lubricant is 1% by volume or more and 50% by volume or less in the film.
(6) The Al-based plated steel sheet for high-temperature press-formability excellent in lubricity according to (4) or (5), wherein the solid lubricant is a fluororesin.
(7) The lubrication according to (4), wherein the particle size of the particulate metal oxide is 0.1 μm or more, 2.5 times or less the thickness of the film, and the amount of addition is 1% by volume to 40% by volume in the film. Al-based plated steel sheet for high temperature press forming with excellent heat resistance,
(8) The lubricity according to (4) or (7), wherein the granular metal oxide is at least one selected from an Al-based oxide, a Si-based oxide, a Ti-based oxide, and a Zr-based oxide. Al-plated steel sheet for high-temperature press formability,
It is.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the components and contents of the steel sheet used in the present invention will be described.
[0009]
C is added to secure the desired strength. If C is less than 0.1%, sufficient strength cannot be obtained and the effect is poor. On the other hand, if it exceeds 0.6%, although the strength is further increased, welding cracks are likely to occur, so the upper limit was made 0.6% or less.
[0010]
Mn is a strengthening element and an element that enhances hardenability. Further, it is effective for preventing hot brittleness due to S as an impurity. When Mn is 0.1% or more, these effects are exhibited. On the other hand, if it exceeds 3.0%, the residual γ phase becomes too large, and the strength is reduced. Therefore, the Mn concentration is set to 0.1% or more and 3.0% or less.
[0011]
Si is effective as a strength improving element and exerts its effect at 0.01% or more. However, it is also an easily oxidizable element, and when hot-dip aluminum plating is performed, when the Si concentration in steel exceeds 0.5%. , The wettability is reduced, and non-plating occurs. Therefore, Si is set to 0.01% or more and 0.5% or less.
[0012]
B acts during quenching and has the effect of improving strength. The addition of 0.0002% or more acts, but if it exceeds 0.01%, inclusions are formed and become brittle, and the fatigue strength is reduced. Therefore, the content is made 0.0002% or more and 0.01% or less.
[0013]
Ti is an element that strengthens the strength and is also an element that improves the heat resistance of the aluminum plating. However, if too much is added, carbides and nitrides may be formed and become soft. When the content is 0.005% or more, the effect of improving the strength and the effect of improving the oxidation resistance appear. However, when the content is more than 0.2%, the intended strength may not be obtained. Therefore, Ti is set to 0.005% or more and 0.2% or less.
[0014]
Cr is a strength strengthening element and also improves corrosion resistance, but it is necessary to add 0.005% or more to obtain the effect. Even if added in a larger amount than 1.0%, the effect of improving the strength is small and the cost increases, so the upper limit was made 1.0%. Therefore, Cr is set to 0.005% or more and 1.0% or less.
[0015]
P is a strength strengthening element, but adding more than 0.1% decreases toughness. Therefore, it is set to 0.1% or less.
[0016]
S is preferably as small as possible because of a reduction in formability due to sulfide-based inclusions, but is acceptable up to 0.02%. Therefore, S is set to 0.02% or less.
[0017]
Al acts as a deoxidizing agent. For this purpose, 0.005% or more is necessary. However, if it exceeds 0.1%, the effect is saturated, and rather, inclusions are formed and embrittlement occurs. And Therefore, Al is set to 0.005% or more and 0.1% or less.
[0018]
Next, the reasons for limiting the components and contents of the aluminum plating layer will be described.
[0019]
Si is added for the purpose of controlling an alloy layer generated at the time of hot-dip metal coating. The content of Si is preferably 3% or more and 15% or less. If it is less than 3%, the Fe-Al alloy layer grows thick at the plating stage, and promotes cracking of the plated layer during processing, which adversely affects the corrosion resistance. On the other hand, if it exceeds 15%, the workability and corrosion resistance of the plating layer deteriorate, so the Si content is set to 3% or more and 15% or less.
[0020]
The thickness of the plating layer is not particularly limited in the present invention. In practical use, it can be used without any problem at a thickness of 8 μm to 40 μm including the alloy layer per side.
[0021]
In the present invention, for the purpose of suppressing processing scratches during press molding, on the surface of the plating layer, an inorganic compound film, an organic compound film, or an inorganic and organic composite compound film is applied. . Since the inorganic compound film generally has heat resistance, it exists as a film even at a high temperature of about 800 ° C., and by suppressing contact between the workpiece and the mold, the occurrence of processing scratches is reduced. Can be suppressed. As the inorganic compound film, a film composed of one or more compounds or compound groups of Si, Zr, Ti, and P is preferable in view of its film forming ability. These include, for example, silicate compounds such as Na ₂ SiO ₃ , K ₂ SiO ₃ and Li ₂ SiO ₃ , colloidal silica (SiO ₂ ), fluoride salt compounds such as K ₂ ZrF ₆ and K ₂ TiF ₆ , Phosphoric acid (H ₃ PO ₄ ) and a film of a phosphate compound, etc. may be mentioned.
[0022]
Organic compound films have better lubricity than inorganic compound films, but tend to have low heat resistance.However, by using a compound with a relatively high heat resistance temperature, it can be decomposed even during the heating time required for molding. It does not scatter and sufficiently exhibits its function as a film.Also, even in a resin system with a relatively low heat resistance based on hydrocarbons, it can be used in combination with a resin having a high heat resistance, or an inorganic compound, Good characteristics can be obtained by using in combination with the particulate metal oxide. As these organic compound films, films containing one or more compounds or compounds of F, Si, C and N are suitable. For example, in a resin system having high heat resistance, fluorine such as PTFE (ethylene tetrafluoride resin), FEP (ethylene tetrafluoride / hexafluoropropylene copolymer resin), and ETFE (ethylene tetrafluoride / ethylene copolymer resin) can be used. -Based resin film, silicon-based resin film such as pure silicon resin and polyester-modified silicone resin, aromatic resin-based film such as PES (polyether sulfone) resin, PPS (polyphenylene sulfide) resin, polyamide-imide resin, polyester-imide A polyimide resin film such as a resin is suitable. Further, as the resin having a relatively low heat resistance temperature, for example, a resin such as an epoxy resin, an acrylic resin, a polyester resin, and a urethane resin can be used.
[0023]
When a composite film of an inorganic compound and an organic compound is used, the characteristics of both can be brought out by mixing the respective film components described above. The mass ratio of the inorganic component to the organic component is preferably from 10:90 to 80:20. In addition, for example, a sol using an organic silicate-based compound such as Si (OC ₂ H ₅ ) ₄ , an organic titanate-based compound such as Ti (OC ₂ H ₅ ) ₄ and an inorganic compound such as SiO ₂ and TiO _2. -It is also possible to form a film by a gel method.
[0024]
It is more effective to add a solid lubricant and a particulate metal oxide to these films. Examples of the solid lubricant include graphite, fluorides such as CaF ₂ , NaF, BaF ₂ and LaF ₃ , sulfides such as MoS ₂ , WS ₂ , FeS, nitrides such as BN, Al ₂ O ₃ , MoO ₃ , WO ₃ , oxides such as Fe ₂ O ₃ , fluorine-based resins such as PTFE resin, and high molecular compounds such as polyimide resin and silicon resin are preferable. Among them, particularly when a fluorine-based resin is used, good characteristics are exhibited. The content of these solid lubricants is desirably from 1% by volume to 50% by volume in the coating. If the amount is less than 1% by volume, the effect is poor. If the amount is more than 50% by volume, the effect is saturated and, depending on the film system, the film-forming ability may be impaired.
[0025]
The particulate metal oxide is selected from, for example, Al-based oxides such as alumina, Si-based oxides such as gas-phase silica and colloidal silica, Ti-based oxides such as titania, and Zr-based oxides such as zirconia. One or more oxides are preferred. The particulate metal oxide preferably has a particle size of 0.1 μm or more and 2.5 times or less the thickness of the film, and the amount added is preferably 1% by volume or more and 40% by volume or less in the film. If the particle size is less than 0.1 μm, the effect of lowering the contact area, which is the original purpose of addition, is poor. If the particle size is 2.5 times or more the film thickness, the particle holding ability of the film may be reduced. When the amount is less than 1% by volume, the effect is poor, and when the amount is 30% by volume or more, the effect is saturated and, depending on the film system, the film-forming ability may be impaired.
[0026]
The above-mentioned film can be identified by using a known analysis technique. For example, there is a method of identifying the composition of the film and the content of the component using EPMA (Electron Probe Micro Analyzer) and X-ray fluorescence analysis from the cross section of the film. Some substances are formed by a reaction during baking and drying of the material, but the substances formed during such a process are also XRD (X-ray Diffraction), ESCA (Electron Spectroscopy for Chemical Analysis), NMR (Nuclear Magnetic Science, NMR). (Secondary Ion Mass spectroscopy) can be used for identification and quantification.
[0027]
The above-mentioned film can be formed by application from an aqueous paint, an oil paint, or a sol-gel paint, baking and drying. The application method is also not particularly limited, and a known method such as roll coating, spray coating, and dipping can be applied. Baking and drying after the application may be performed by a known method such as a hot blast furnace, an induction heating furnace, or a near-infrared furnace, or a combination thereof. Depending on the type of resin used, the resin can be cured by ultraviolet rays, electron beams, or the like.
[0028]
In addition, as a post-treatment after hot-dip plating, before applying any one of the inorganic compound film, the organic compound film, and the inorganic and organic composite compound film, a chromate treatment film, or a Cr compound, a Si compound. , A P compound, a Zn compound, and an acrylic resin. In addition, zero spangle processing (minimized spanling) as a process for uniforming the appearance after hot-dip plating, annealing treatment as a process for improving the workability of a plating layer, quenching process for controlling the structure, and the like are possible. It is also possible to apply without limiting.
[0029]
The manufacturing process of the hot-dip aluminized steel sheet is not limited at all, and ordinary steel making, hot rolling, cold rolling and annealing conditions can be applied. Further, there may be a pre-plating of Ni, Fe, etc., but this is also applicable.
[0030]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0031]
A steel having the components shown in Table 1 was melted by a converter-vacuum degassing process, turned into a billet, and then hot-rolled to obtain a pickled hot-rolled steel sheet having a thickness of 1.8 mm. After cold rolling, a cold-rolled steel sheet having a thickness of 1.2 mm was obtained. Symbols A to E and G to K indicate cold-rolled steel sheets, and symbol F indicates a hot-rolled steel sheet. These steel sheets were subjected to reduction-annealing using a non-oxidizing furnace-reduction furnace system line, and then immersed in an Al-Si alloy plating bath containing 9.2% Si and 17.2% Si. Then, hot-dip plating was performed. After plating, the amount of plating was adjusted to 25 μm per side by gas wiping. At this time, the plating composition contained 2.0% Fe in addition to Al and Si, but Fe is inevitable supplied from equipment or strip in the bath.
[0032]
[Table 1]

[0033]
With respect to the plated steel sheet thus manufactured, various treatment films shown in Table 2 were applied by roll coating so as to have a predetermined film thickness, and then baked and dried in a hot air drying furnace.
[0034]
[Table 2]

[0035]
The test material thus obtained was evaluated for strength after heat treatment and press formability. Table 3 shows the evaluation results.
[0036]
The evaluation method was as follows.
(1) Strength after heat treatment Heat treatment was performed at a temperature of 900 ° C for 5 minutes, and after cooling between steel plates, a tensile test was performed using a JIS No. 5 tensile test piece to measure tensile strength.
(2) Evaluation of high-temperature press formability After heating at a temperature of 900 ° C. for 5 minutes, a cylindrical press test of 50 mmφ was performed, and the appearance of the surface was observed.
[0037]
◎: Formable, no change in surface appearance ○: Formable, slightly scratched surface, blackening △: Formable, scratched or blackened, scale generated ×: Formable, whole surface galling Large scratches or cracks
[Table 3]

[0039]
No. of the comparative example. In No. 13, although the desired high strength was obtained, the appearance after press molding was not good because there was no film on the surface. No. In Nos. 14 and 15, although the desired high strength was obtained, the appearance after press molding was not good because Si in the plating layer was too high. No. In Nos. 16, 17, and 19, the amounts of C, Si, Mn, and B were small, the required hardenability was not obtained, and the desired high strength was not obtained. No. In No. 18, the amount of Mn was too high, and the desired strength could not be obtained. Example No. 1 of the present invention. With respect to Nos. 1 to 12, good properties were obtained in both strength and appearance due to the effects of the composition of the steel and the film. In particular, the solid lubricant and No. 3 containing a particulate metal oxide having a particle size of 0.1 μm or more were added. Nos. 2 to 6; 8-9, No. 11 to 12 are good.
[0040]
【The invention's effect】
According to the present invention, it is possible to provide a high-strength hot-dip aluminized steel sheet for a high-strength pressed product that improves the appearance after press molding, which has been a problem at the time of high-temperature pressing, and has the necessary strength. And so on, which contributes greatly to the industry.

Claims

In mass%, C: 0.1% or more and 0.6% or less, Mn: 0.1% or more and 3.0% or less, P: 0.1% or less, S: 0.02% or less, Al: 0. 005% to 0.1%, Si: 0.01% to 0.5%, B: 0.0002% to 0.01%, Ti: 0.005% to 0.2%, Cr: a steel sheet containing at least one of 0.005% or more and 1.0% or less, the balance being Fe and unavoidable impurities, a steel sheet containing Si: 3% or more and 15% or less, and a balance of Al and unavoidable impurities. A high-temperature press with excellent lubricity characterized by having an aluminum plating coating consisting of an inorganic compound film, an organic compound film, or a composite compound film of an inorganic and an organic material. Al-based plated steel sheet for forming.

The Al-plated steel sheet for high-temperature press-formability excellent in lubricity according to claim 1, wherein the inorganic compound film or the composite compound film contains at least one of Si, Zr, Ti, and P.

The Al-plated steel sheet for high-temperature press-formability excellent in lubricity according to claim 1, wherein the organic compound film or the composite compound film contains at least one of F, Si, C, and N.

The Al-coated steel sheet for high-temperature press forming excellent in lubricity according to any one of claims 1 to 3, wherein the coating further contains one or both of a solid lubricant and a granular metal oxide.

The Al-based plated steel sheet for high-temperature press-formability excellent in lubricity according to claim 4, wherein the content of the solid lubricant is 1% by volume or more and 50% by volume or less in the film.

The Al-plated steel sheet for high temperature press formability according to claim 4 or 5, wherein the solid lubricant is a fluororesin.

5. The lubricating property according to claim 4, wherein the particle size of the particulate metal oxide is 0.1 μm or more, 2.5 times or less of the film thickness, and the amount of addition is 1% by volume to 40% by volume in the film. Al-plated steel sheet for hot press forming.

The high temperature having excellent lubricity according to claim 4 or 7, wherein the granular metal oxide is at least one selected from an Al-based oxide, a Si-based oxide, a Ti-based oxide, and a Zr-based oxide. Al-based plated steel sheet for press formability.