JP4884606B2 - Heating method of steel sheet for thermoforming - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、高い機械強度と優れたプレス成形性を両立するための高温プレス成形に使用する加熱成形用鋼板の加熱方法に関する。
【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、例えば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となるが、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、鋼板を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（ホット）プレスによる方法が有望である。この高温プレスに使用する鋼板は、めっきを行っていない材料を用いた場合、鋼板を８００℃以上の高温に加熱するため、鋼板の表面に酸化物（スケール）が発生し、それを取り除くための工程が必要となる。また、耐食性を必要とする部材等では、表面に防錆処理や金属被覆を施す必要があり、表面清浄化工程、表面処理工程が必要となる。
そこで、これらの欠点を克服するため、特開２０００−３８６４０公報に開示されているように、Ａｌ系の金属のめっき皮膜（層）を施した加熱成形用鋼板が提案されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記した加熱成形用鋼板は、目的とする材料強度は得られるものの、プレス加工前の予備加熱条件によっては、めっき層が溶融し、鋼板表面から垂れるので、製品の外観を損ねると共に局所的にめっき層の厚みが薄くなる部分が発生し、十分な耐食性を発揮できないといった問題点があった。
本発明はかかる事情に鑑みてなされたもので、加熱時におけるめっき層と鋼板の合金化反応を制御することで、美麗な外観を有し、しかも優れた耐食性を備えた加熱成形用鋼板の加熱方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
前記目的に沿う第１の発明に係る加熱成形用鋼板の加熱方法は、９．５ｗｔ％以上１０ｗｔ％以下のＳｉを含有するＡｌ主体の金属のめっきをした鋼板を、めっきに使用した金属の融点以上に加熱して成形加工する加熱成形用鋼板の加熱方法において、
金属の融点より２００℃低い所定温度から金属の融点直下までの温度領域で、めっきした鋼板を５秒以上加熱して、成形加工する際のめっき層の溶融を防止する。このように、めっきした鋼板を成形加工するための加熱途中に、所定の加熱温度及び加熱時間を設定するので、めっき皮膜の表層部へ鋼板成分（Ｆｅ）が拡散するために必要な温度、及び拡散に要する時間を確保することができる。
前記目的に沿う第２の発明に係る加熱成形用鋼板の加熱方法は、９．５ｗｔ％以上１０ｗｔ％以下のＳｉを含有するＡｌ主体の金属のめっきをした鋼板を、めっきに使用した金属の融点以上に加熱して成形加工する加熱成形用鋼板の加熱方法において、
金属の融点より２００℃低い所定温度から金属の融点直下までの温度領域で、めっきした鋼板を５秒以上加熱し、めっきの表層部に、金属の融点より高く、しかも成形加工するためのめっきした鋼板の加熱温度より高い融点を備えた金属間化合物を形成して、成形加工する際のめっき層の溶融を防止する。このように、めっきした鋼板を成形加工するための加熱途中に、所定の加熱温度及び加熱時間を設定することで、めっき皮膜の表層部へ鋼板成分（Ｆｅ）が拡散するために必要な温度、及び拡散に要する時間を確保できるので、このめっき皮膜の表層部に、成形加工するための加熱温度より高い融点を有する金属間化合物を形成することができる。
【０００５】
ここで、第１、第２の発明に係る加熱成形用鋼板の加熱方法において、めっきの皮膜の厚みδμｍと、所定温度から金属の融点直下までの加熱時間ｔ秒とが、ｔ≧δの関係を満たすことが好ましい。このように、めっきした鋼板のそれぞれのめっき皮膜の厚みに応じて所定温度領域での加熱時間を設定するので、めっきに使用した金属への鋼板成分の拡散時間を確保でき、めっき皮膜の表層部に、確実に金属間化合物を形成することができる。
また、第１、第２の発明に係る加熱成形用鋼板の加熱方法において、めっきした鋼板の加熱温度が金属の融点に到達する前までに、めっきの表層部に鋼板の成分であるＦｅを、原子比で２５％以上拡散させることが好ましい。これにより、めっき皮膜の表層部に、Ａｌを主体とする金属より融点が高いＡｌとＦｅの金属間化合物を形成できるので、成形加工するためにめっきした鋼板を加熱しても、金属間化合物の存在によりめっき皮膜の垂れを防止できる。
【０００６】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
ここに、図１は本発明の一実施の形態に係る加熱成形用鋼板の加熱方法を使用した温度履歴の説明図、図２（Ａ）、（Ｂ）はそれぞれ同加熱成形用鋼板の加熱方法を使用した変形例に係る温度履歴の説明図、他の変形例に係る温度履歴の説明図、図３は実施例における加熱時間とめっき皮膜の厚みとの関係を示す説明図である。
【０００７】
本発明の一実施の形態に係る加熱成形用鋼板の加熱方法は、厚みが例えば１〜２ｍｍ程度で、例えば車の製造に使用するめっきした鋼板を、めっきに使用した金属の融点以上、例えば８００℃〜１０００℃程度に加熱し、プレス加工（成形加工）を行った後冷却するいわゆる高温（ホット）プレスを行う場合に適用する方法で、金属の融点より２００℃低い所定温度から金属の融点直下までの温度領域で、めっきした鋼板を５秒以上加熱する方法である。なお、本実施の形態では、図１に示すように、金属の融点より１００℃低い所定温度から金属の融点直下までの温度領域で、めっきした鋼板を１０秒以上加熱した。このめっきした鋼板は、例えば０．１５＜Ｃ＜０．５、０．５＜Ｍｎ＜３、０．１＜Ｓｉ＜０．５、０．０１＜Ｃｒ＜１、Ｔｉ＜０．２、Ａｌ＜０．１、Ｐ＜０．１、Ｓ＜０．０５、０．０００５＜Ｂ＜０．０８の成分を有し、残部がＦｅと不可避的不純物で構成されている。なお、単位はｗｔ％である。以下、詳しく説明する。
【０００８】
このめっきした鋼板を、前記温度領域で５秒以上加熱することで、めっき皮膜（この実施の形態では、５〜３０μｍ程度の厚み）の表層部に、金属の融点より高く、しかも成形加工するためのめっきした鋼板の加熱温度、即ち成形加工するための加熱時における最高加熱温度より高い融点を備えた金属間化合物を形成する。
めっきに使用する金属としては、Ａｌを主体とする金属として、例えば純Ａｌ、Ａｌ−１０％Ｓｉ、Ａｌ−Ｓｉ−Ｃｒ等を、また、Ｓｎを主体とする金属として、例えば純Ｓｎやその合金等を使用できる。
めっきにＡｌを主体とする金属を使用した場合、めっき皮膜の表層部には、めっきした鋼板の加熱温度、即ち鋼板温度が金属の融点に到達する前までに、めっきの表層部に鋼板の成分であるＦｅを、原子比で２５％以上拡散させた融点及び沸点が１０００℃以上の金属間化合物、例えばＦｅＡｌ3 を形成させる。
そして、めっきにＳｎを主体とする金属を使用した場合、めっき皮膜の表層部には、めっきした鋼板の加熱温度、即ち鋼板温度が金属の融点に到達する前までに、めっきの表層部に鋼板の成分であるＦｅを、原子比で３３．３％以上拡散させた融点及び沸点が１０００℃以上金属間化合物、例えばＦｅＳｎ2 を形成させる。
【０００９】
なお、めっき皮膜の表層部に例えばＦｅ−Ａｌ系合金を形成するためには、鋼板内部からのＦｅの拡散が必要である。このＦｅの拡散距離は、鋼板温度と加熱時間によって決まるため、めっきした鋼板の鋼板温度（温度領域）を金属の融点より２００℃低い所定温度から金属の融点直下までとし、その加熱時間を５秒以上と設定した。以下、その理由について説明する。
鋼板温度については、成形加工する際のめっき層の溶融防止を、めっきに使用した金属と鋼板成分との合金化反応によって行うため、鉄又はめっきする金属の拡散を行うことが可能な温度が必要である。従って、温度が高ければ高いほど短時間で合金化できるので、鋼板温度がめっきに使用した金属の融点より２００℃低い所定温度未満の場合、めっきに使用した金属と鋼板成分（鉄）との合金化反応（高融点の金属間化合物の形成）が進行しない。
なお、鋼板温度が低くても時間さえかければ合金化は進行するが、実際の生産性を考えると、鋼板温度の下限値をめっきに使用した金属の融点より１５０℃低い温度、更には１００℃低い温度とすることが好ましい。一方、鋼板温度が融点以上の場合、めっきに使用した金属が溶融し、金属間化合物の形成ができない。従って、上限をめっきに使用する金属の融点直下とした。
【００１０】
また、加熱時間については、融点直下のＦｅの拡散速度とめっき皮膜の厚み（＝必要な拡散距離）の関係を考慮すれば、加熱時間が１０秒以上必要である。
このため、加熱時間が５秒未満の場合、めっき皮膜の表層部へ鋼板成分が拡散せず、金属間化合物が形成されない。従って、めっきした鋼板を成形加工するため加熱するとき、めっきした金属が溶融すると共に鋼板表面から垂れ、製品（加熱成形用鋼板）の外観形状悪くなる。また、加熱時間が５秒以上１０秒未満の場合、めっき皮膜の表層部への鋼板成分の拡散が不十分であり、金属間化合物が十分に形成されない。しかし、めっきした鋼板を成形加工するために加熱するとき、めっきした金属の溶融は発生するものの、部分的に金属間化合物が形成されているため、めっきした金属の鋼板表面からの垂れを防止でき、製品の外観形状も良好となる。そして、加熱時間が１０秒以上の場合、前記した理由からめっきした金属の溶融を防止できると共に、鋼板表面からの垂れも防止できるため、製品の外観形状を非常に良好にできる。
上記したことから、めっきした鋼板の前記温度領域での加熱時間は、５秒以上、更には１０秒以上とすることが好ましい。一方、加熱時間の上限値については、めっき皮膜の表層部に金属間化合物が形成されるまで加熱すればよいため、特に限定していないが、生産性、経済性等を考慮すれば、例えば５分程度とすることが好ましい。
【００１１】
加熱時の温度制御は、前記した温度領域で徐々に昇温するように、１０秒以上加熱している。
なお、図２（Ａ）に示すように、前記した温度領域の途中まで、連続的に温度を上昇させた後、一定の温度に保持することや、また図２（Ｂ）に示すように、急速に融点直下まで加熱時の温度を上昇させた後、その後徐冷して前記温度領域で１０秒以上保持することも可能である。
【００１２】
また、めっきした金属の表層部に形成される金属間化合物は、めっきした金属の鋼板への拡散と、鋼板成分のめっき層への拡散によって起こるため、めっき皮膜の厚み（δμｍ）が厚くなればなるほど拡散距離がのびる。この場合、前記温度領域での加熱時間が５秒では、めっきした金属の鋼板表面からの垂れを防止できない場合が発生するが、この拡散距離は、加熱時間（ｔ秒）に対して１次比例なので、ｔ≧ａ×δが成立する。なお、ａは比例定数である。
ここで、めっき皮膜の厚みが、この実施の形態で最も薄い５μｍの場合、前記温度領域内で必要となる加熱時間は５秒である。この場合、ａ＝１なので、めっき皮膜の厚みδμｍと、所定温度からめっき成分の融点直下までの加熱時間ｔ秒とが、ｔ≧δの関係を満たす。しかし、めっき皮膜の厚みが５μｍの場合、更に好ましい条件としては、前記温度領域内で必要となる加熱時間が１０秒である。この場合、ａ＝２なので、ｔ≧２×δ、即ちｔ≧δ／０．５の関係を満たすことがより好ましい。
【００１３】
【実施例】
本発明に係る加熱成形用鋼板の加熱方法を適用し、試験を行った結果について説明する。なお、ここでは、めっきした鋼板を成形加工するための加熱途中に設定する温度領域として、最も好ましい条件、即ち金属の融点より１００℃低い所定温度から金属の融点直下までの領域を使用し試験を行った。
熱間圧延、冷間圧延を経て製造された板厚１．２ｍｍの冷延鋼板（Ｃ：０．２０、Ｓｉ：０．０２、Ｍｎ：０．１６、Ｐ：０．００９、Ｓ：０．０１０、Ａｌ：０．０５、Ｔｉ：０．１２、Ｃｒ：０．００３を有し、残部がＦｅと不可避的不純物からなる）を、無酸化炉−還元炉方式のラインを使用して７００〜８００℃程度で還元−焼鈍を行った後、表１に示すめっき浴に鋼板を浸漬して溶融めっきを行った。なお、鋼板中の各成分の単位はｗｔ％である。
【００１４】
【表１】
鋼板をめっきした後は、ガスワイピングで鋼板に対するめっき付着量を片面当り５〜３０μｍに調整した。このときのめっき組成は、表１中の元素以外に２ｗｔ％のＦｅが含まれていたが、Ｆｅは浴中の機器や鋼板（ストリップ）から供給される不可避のものである。
このＡｌを主体とする金属及びＳｎを主体とする金属でめっきした鋼板を、めっきに使用した金属の融点以上、即ち９５０℃に、交流による直接通電加熱を用いて、表２〜表４に示す加熱パターンで加熱し熱処理した。ここで、加熱時間ｔ秒とめっき皮膜の厚みδμｍとの関係を図示したものを図３に示す。
こうして製造しためっき鋼板について、熱処理後のめっきの溶融状態を評価した。なお、表２及び表３は本発明の実施例であり、表４は比較例である。また、表２〜表４中の金属の溶融とは、金属をめっきした鋼板の表面外観に変化がないもの、即ち良品を○、鋼板にめっきした金属が溶融するが、鋼板表面に金属の垂れ（タレ）が発生しないもの、即ちやや良品を△、鋼板表面に金属の垂れが発生したもの、即ち不良品を×とした。
【００１６】
【表２】
【表３】
【表４】
符号１〜１５は、めっきした金属の融点より１００℃低い温度（融点−１００℃）から融点直下までの温度範囲における鋼板の昇温（加熱）時間を１０秒以上とし、めっき皮膜の膜厚が厚いものについては、メタル（金属）の厚み（δ）、昇温時間（ｔ）がｔ≧δ／０．５を満足したものであり、いずれも良好な外観が得られている。即ち、前記温度範囲での加熱時間が重要であり、この温度範囲の前後の温度域の昇温時間を変更しても、また、最高加熱温度における保持時間を変化させても、良好な外観が得られている。
また、符号１６〜２４は、符号１〜１５よりやや条件が悪い場合、即ち前記温度範囲における鋼板の昇温時間を５秒以上とし、しかもｔ≧δを満足したものである。この場合、鋼板にめっきした金属が溶融するが、鋼板表面に金属の垂れ（タレ）が発生せず、符号１〜１５と比較すると品質は劣るが、品質に問題ない製品を製造できた。
【００２０】
一方、符号２７、２９、及び３２は、いずれも前記温度範囲での加熱時間が５秒未満と短く、鋼板表面でめっきした金属が垂れていた。また、符号２８、３０、及び３３は、いずれも前記温度範囲での加熱時間が５秒以上１０秒未満ではあるが、ｔ≧δの式を満足できておらず、やはり鋼板表面にめっきした金属が垂れていた。そして、符号２５、２６、及び３１は、いずれも前記温度範囲での加熱時間が１０秒以上ではあるが、ｔ≧δの式を満足できておらず、やはり鋼板表面にめっきした金属が垂れていた。
【００２１】
以上、本発明を、一実施の形態を参照して説明してきたが、本発明は何ら上記した実施の形態に記載の構成に限定されるものではなく、特許請求の範囲に記載されている事項の範囲内で考えられるその他の実施の形態や変形例も含むものである。
例えば、前記実施の形態においては、めっきに使用する金属として、Ａｌ及びＳｎをそれぞれ主体とした金属を使用した場合について説明したが、めっきに使用した金属の融点が、めっきした鋼板を成形加工するための加熱時における最高加熱温度（例えば、８００〜１０００℃程度）以下で、その金属から形成される金属間化合物が成形加工時の加熱温度、即ち前記最高加熱温度より高い融点を備えた金属であれば、適用可能である。
また、前記実施の形態においては、めっきした鋼板を成形加工するための加熱途中における温度の制御方法を３種類説明したが、めっきに使用した金属の融点より２００℃低い所定温度から金属の融点直下までの温度領域で、めっきした鋼板を５秒以上、好ましくは１０秒以上加熱することができれば、その時間中の温度の変遷は特に限定されない。
【００２２】
そして、前記実施の形態においては、Ａｌ及びＳｎをそれぞれ主体とする金属を鋼板にめっきし、めっき皮膜の表層部にＦｅＡｌ3 、ＦｅＳｎ2 の金属間化合物を形成した場合について説明した。しかし、金属間化合物の融点及び沸点が、成形加工するための加熱時における最高加熱温度、例えば８００〜１０００℃程度より高い融点及び沸点を有する他の合金が形成されてもよい。
更に、めっきした金属の加熱手段としては、特に限定されるものではなく、例えば直接通電加熱（直流、交流）、誘導加熱、赤外線加熱、炉（燃焼チューブからの輻射伝熱、燃焼排ガス）等を使用することが可能である。
【００２３】
【発明の効果】
請求項１及びこれに従属する請求項３、４記載の加熱成形用鋼板の加熱方法においては、めっきした鋼板を成形加工するための加熱途中に、所定の加熱温度及び加熱時間を設定するので、めっき皮膜の表層部へ鋼板成分が拡散するために必要な温度、及び拡散に要する時間を確保することができる。従って、めっき皮膜の表層部には、めっきに使用した金属より融点が高い金属間化合物が形成されるので、金属の融点以上にめっきした鋼板が加熱されても、めっき皮膜の垂れを防止することが可能となる。
請求項２及びこれに従属する請求項３、４記載の加熱成形用鋼板の加熱方法においては、めっきした鋼板を成形加工するための加熱途中に、所定の加熱温度及び加熱時間を設定することで、めっき皮膜の表層部へ鋼板成分が拡散するために必要な温度、及び拡散に要する時間を確保できるので、このめっき皮膜の表層部に、成形加工するための加熱温度より高い融点を有する金属間化合物を形成することができる。従って、加熱成形用鋼板を高温プレスする際の課題であっためっきに使用した金属の垂れを防止できるので、美麗な外観を有し、しかも優れた耐食性を備えた加熱成形用鋼板を製造できる。また、非めっき鋼板で問題となる高温プレス後のデスケーリング処理が不要なため、作業効率が良好となる。
【００２４】
特に、請求項３記載の加熱成形用鋼板の加熱方法においては、めっきした鋼板のそれぞれのめっき皮膜の厚みに応じて所定温度領域での加熱時間を設定するので、めっきに使用した金属への鋼板成分の拡散時間を確保でき、めっき皮膜の表層部に、確実に金属間化合物を形成することができる。従って、鋼板にめっきするめっきの厚みが変化しても、めっき皮膜の表層部に鋼板成分を確実に拡散させることができるので、美麗な外観を有し、しかも優れた耐食性を備えた加熱成形用鋼板を製造できる。
請求項４記載の加熱成形用鋼板の加熱方法においては、めっき皮膜の表層部に、Ａｌを主体とする金属より融点が高いＡｌとＦｅの金属間化合物を形成できるので、成形加工するためにめっきした鋼板を加熱しても、金属間化合物の存在によりめっき皮膜の垂れを防止できる。従って、めっきした鋼板を成形加工するための加熱時における最高加熱温度より融点が低い、Ａｌを主体とする金属をめっき皮膜として使用した加熱成形用鋼板でも高温プレスができるため、産業上の意義が大きい。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る加熱成形用鋼板の加熱方法を使用した温度履歴の説明図である。
【図２】（Ａ）、（Ｂ）はそれぞれ同加熱成形用鋼板の加熱方法を使用した変形例に係る温度履歴の説明図、他の変形例に係る温度履歴の説明図である。
【図３】実施例における加熱時間とめっき皮膜の厚みとの関係を示す説明図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for heating a steel sheet for hot forming used for high temperature press forming in order to achieve both high mechanical strength and excellent press formability.
[0002]
[Prior art]
In recent years, in order to protect the environment and prevent global warming, there has been an increasing movement to reduce the consumption of fossil fuels. For example, automobiles that are indispensable for our daily lives as a means of transportation are strongly required to be lighter. .
In order to achieve this weight reduction, it is necessary to use a material having a higher mechanical strength than in the past. Generally, a material having a higher strength has a lower shape freezing property in a molding process such as bending. It tends to be difficult to form a complicated shape.
As a method for solving these problems, a method using a so-called high-temperature (hot) press in which a steel plate is heated to a high temperature of 800 ° C. or higher, pressed and then cooled is promising. The steel plate used for this high-temperature press is a material for removing the oxide (scale) generated on the surface of the steel plate because the steel plate is heated to a high temperature of 800 ° C. or higher when a material not plated is used. A process is required. Moreover, in the member etc. which require corrosion resistance, it is necessary to give a rust prevention process and metal coating to the surface, and a surface cleaning process and a surface treatment process are needed.
Therefore, in order to overcome these drawbacks, as disclosed in JP 2000-38640 A, a steel sheet for heat forming having an Al-based metal plating film (layer) has been proposed.
[0003]
[Problems to be solved by the invention]
However, although the steel sheet for thermoforming described above can achieve the desired material strength, depending on the preheating conditions before press working, the plating layer melts and hangs down from the surface of the steel sheet. In other words, there is a problem that a portion where the thickness of the plating layer becomes thin is generated, and sufficient corrosion resistance cannot be exhibited.
The present invention has been made in view of such circumstances. By controlling the alloying reaction between the plating layer and the steel sheet during heating, the heating of the steel sheet for thermoforming having a beautiful appearance and excellent corrosion resistance is achieved. It aims to provide a method.
[0004]
[Means for Solving the Problems]
The heating method of the steel sheet for thermoforming according to the first invention in accordance with the above object is the melting point of the metal used for plating the steel sheet plated with Al-based metal containing 9.5 wt% or more and 10 wt% or less of Si. In the heating method of the steel sheet for thermoforming that is heated and formed as described above,
In a temperature range from a predetermined temperature 200 ° C. lower than the melting point of the metal to immediately below the melting point of the metal, the plated steel plate is heated for 5 seconds or more to prevent melting of the plating layer during forming . In this way, since a predetermined heating temperature and heating time are set during the heating for forming the plated steel sheet, the temperature necessary for the steel sheet component (Fe) to diffuse into the surface layer portion of the plating film, and The time required for diffusion can be ensured.
The method for heating a steel sheet for thermoforming according to the second invention in accordance with the above object is the melting point of the metal used for plating the steel sheet plated with Al-based metal containing 9.5 wt% or more and 10 wt% or less of Si. In the heating method of the steel sheet for thermoforming that is heated and formed as described above,
In a temperature range from a predetermined temperature 200 ° C. lower than the melting point of the metal to immediately below the melting point of the metal, the plated steel plate is heated for 5 seconds or more, and the surface layer of the plating is plated to be higher than the melting point of the metal and for forming. An intermetallic compound having a melting point higher than the heating temperature of the steel sheet is formed to prevent melting of the plating layer during forming . In this way, by setting a predetermined heating temperature and heating time during the heating for forming the plated steel sheet, the temperature necessary for the steel sheet component (Fe) to diffuse into the surface layer part of the plating film, And since the time required for diffusion can be secured, an intermetallic compound having a melting point higher than the heating temperature for forming can be formed on the surface layer portion of the plating film.
[0005]
Here, in the heating method of the steel sheet for thermoforming according to the first and second inventions, the relation of t ≧ δ between the thickness δ μm of the plating film and the heating time t seconds from the predetermined temperature to just below the melting point of the metal It is preferable to satisfy. Thus, since the heating time in the predetermined temperature range is set according to the thickness of each plating film of the plated steel sheet, the diffusion time of the steel sheet component to the metal used for plating can be secured, and the surface layer part of the plating film In addition, it is possible to reliably form an intermetallic compound.
Moreover, in the heating method of the steel sheet for thermoforming according to the first and second inventions, before the heating temperature of the plated steel sheet reaches the melting point of the metal, Fe which is a component of the steel sheet on the surface layer part of the plating, It is preferable to diffuse 25% or more in atomic ratio. As a result, an intermetallic compound of Al and Fe having a melting point higher than that of a metal mainly composed of Al can be formed on the surface layer portion of the plating film. Therefore, even if the plated steel sheet is heated for forming, the intermetallic compound is heated. The presence of the plating film can be prevented from sagging.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory diagram of a temperature history using the heating method of the steel sheet for thermoforming according to one embodiment of the present invention, and FIGS. 2A and 2B are heating methods of the steel sheet for thermoforming, respectively. FIG. 3 is an explanatory diagram showing the relationship between the heating time and the thickness of the plating film in the examples.
[0007]
The method for heating a steel sheet for thermoforming according to an embodiment of the present invention has a thickness of, for example, about 1 to 2 mm. For example, a plated steel sheet used for car manufacture is equal to or higher than the melting point of the metal used for plating, for example 800 This method is applied when performing so-called high-temperature (hot) pressing, in which the steel is heated to about 1000 to 1000 ° C., cooled after being pressed (molded), and immediately below the melting point of the metal from a predetermined temperature 200 ° C. below the melting point of the metal In this temperature range, the plated steel sheet is heated for 5 seconds or more. In the present embodiment, as shown in FIG. 1, the plated steel sheet was heated for 10 seconds or more in a temperature range from a predetermined temperature 100 ° C. lower than the melting point of the metal to immediately below the melting point of the metal. This plated steel sheet is, for example, 0.15 <C <0.5, 0.5 <Mn <3, 0.1 <Si <0.5, 0.01 <Cr <1, Ti <0.2, Al It has components of <0.1, P <0.1, S <0.05, 0.0005 <B <0.08, and the balance is composed of Fe and inevitable impurities. The unit is wt%. This will be described in detail below.
[0008]
By heating the plated steel sheet in the temperature range for 5 seconds or more, the surface layer of the plating film (in this embodiment, a thickness of about 5 to 30 μm) is higher than the melting point of the metal and is formed. An intermetallic compound having a melting point higher than the heating temperature of the plated steel plate, that is, the maximum heating temperature at the time of heating for forming is formed.
The metal used for plating is, for example, pure Al, Al-10% Si, Al-Si-Cr, etc., as a metal mainly composed of Al, and as a metal mainly composed of Sn, such as pure Sn or an alloy thereof. Etc. can be used.
When a metal mainly composed of Al is used for plating, the surface layer portion of the plating film has a steel plate component on the surface layer portion of the plating before the heating temperature of the plated steel plate, that is, before the steel plate temperature reaches the melting point of the metal. And an intermetallic compound having a melting point and a boiling point of 1000 ° C. or more, for example, FeAl 3 , in which Fe is diffused by 25% or more by atomic ratio.
When a metal mainly composed of Sn is used for plating, the surface layer portion of the plating film has a steel plate on the surface layer portion of the plating before the heating temperature of the plated steel plate, that is, the steel plate temperature reaches the melting point of the metal. An intermetallic compound having a melting point and a boiling point of 1000 ° C. or more, for example, FeSn 2, is formed by diffusing Fe, which is the above component, in an atomic ratio of 33.3% or more.
[0009]
In addition, in order to form, for example, an Fe—Al alloy in the surface layer portion of the plating film, it is necessary to diffuse Fe from the inside of the steel plate. Since the diffusion distance of Fe is determined by the steel plate temperature and the heating time, the steel plate temperature (temperature region) of the plated steel plate is set from a predetermined temperature 200 ° C. lower than the melting point of the metal to immediately below the melting point of the metal, and the heating time is 5 seconds. It was set as above. The reason will be described below.
Regarding the steel sheet temperature, the temperature at which diffusion of iron or the metal to be plated is required because the plating layer is prevented from being melted by the alloying reaction between the metal used for plating and the steel sheet components. It is. Therefore, the higher the temperature, the shorter the alloying time. Therefore, when the steel plate temperature is lower than a predetermined temperature 200 ° C. lower than the melting point of the metal used for plating, the alloy of the metal used for plating and the steel plate component (iron) Reaction (formation of a high melting intermetallic compound) does not proceed.
Although the alloying proceeds as long as the steel sheet temperature is low, if it takes a long time, considering the actual productivity, the lower limit value of the steel sheet temperature is 150 ° C. lower than the melting point of the metal used for plating, and further 100 ° C. A low temperature is preferable. On the other hand, when the steel plate temperature is equal to or higher than the melting point, the metal used for plating melts and an intermetallic compound cannot be formed. Therefore, the upper limit is set immediately below the melting point of the metal used for plating.
[0010]
Further, regarding the heating time, if the relationship between the diffusion rate of Fe immediately below the melting point and the thickness of the plating film (= necessary diffusion distance) is taken into consideration, the heating time needs to be 10 seconds or longer.
For this reason, when the heating time is less than 5 seconds, the steel plate component does not diffuse into the surface layer portion of the plating film, and no intermetallic compound is formed. Accordingly, when the plated steel sheet is heated for forming, the plated metal melts and hangs down from the surface of the steel sheet, which deteriorates the external shape of the product (heat-forming steel sheet). Moreover, when heating time is 5 second or more and less than 10 second, the diffusion of the steel plate component to the surface layer part of the plating film is insufficient, and the intermetallic compound is not sufficiently formed. However, when the plated steel sheet is heated to form it, the plated metal melts, but the intermetallic compound is partially formed, preventing the plated metal from sagging from the steel sheet surface. The appearance of the product is also good. When the heating time is 10 seconds or longer, the plated metal can be prevented from melting for the reasons described above, and the dripping from the steel sheet surface can be prevented, so that the appearance of the product can be made very good.
From the above, the heating time of the plated steel sheet in the temperature range is preferably 5 seconds or longer, and more preferably 10 seconds or longer. On the other hand, the upper limit of the heating time is not particularly limited because it may be heated until an intermetallic compound is formed on the surface layer portion of the plating film, but considering productivity, economy, etc., for example, 5 It is preferable to be about minutes.
[0011]
In the temperature control at the time of heating, heating is performed for 10 seconds or more so that the temperature is gradually raised in the above-described temperature range.
In addition, as shown in FIG. 2 (A), after raising the temperature continuously to the middle of the temperature range described above, it can be maintained at a constant temperature, or as shown in FIG. 2 (B), It is also possible to rapidly raise the temperature during heating to just below the melting point, and then gradually cool it and keep it in the temperature range for 10 seconds or more.
[0012]
Moreover, since the intermetallic compound formed in the surface layer portion of the plated metal is caused by diffusion of the plated metal into the steel plate and diffusion of the steel plate component into the plating layer, if the thickness of the plating film (δ μm) increases. The diffusion distance increases. In this case, when the heating time in the temperature range is 5 seconds, the plating metal may not be prevented from sagging from the surface of the steel sheet. This diffusion distance is linearly proportional to the heating time (t seconds). Therefore, t ≧ a × δ holds. A is a proportionality constant.
Here, when the thickness of the plating film is 5 μm, which is the thinnest in this embodiment, the heating time required in the temperature range is 5 seconds. In this case, since a = 1, the thickness δ μm of the plating film and the heating time t seconds from the predetermined temperature to immediately below the melting point of the plating component satisfy the relationship of t ≧ δ. However, when the thickness of the plating film is 5 μm, a more preferable condition is that the heating time required in the temperature range is 10 seconds. In this case, since a = 2, it is more preferable to satisfy the relationship of t ≧ 2 × δ, that is, t ≧ δ / 0.5.
[0013]
【Example】
The result of having applied the heating method of the steel sheet for thermoforming which concerns on this invention, and performed the test is demonstrated. Here, as a temperature region set during the heating for forming the plated steel sheet, the most preferable condition, that is, a region from a predetermined temperature 100 ° C. lower than the melting point of the metal to a point immediately below the melting point of the metal is used for the test. went.
Cold rolled steel sheet having a thickness of 1.2 mm manufactured through hot rolling and cold rolling (C: 0.20, Si: 0.02, Mn: 0.16, P: 0.009, S: 0.0. 010, Al: 0.05, Ti: 0.12, Cr: 0.003, with the balance being Fe and inevitable impurities) using a non-oxidation furnace-reduction furnace type line 700- After performing reduction-annealing at about 800 ° C., the steel sheet was immersed in the plating bath shown in Table 1 to perform hot dipping. In addition, the unit of each component in a steel plate is wt%.
[0014]
[Table 1]
After plating the steel plate, the amount of plating attached to the steel plate was adjusted to 5 to 30 μm per side by gas wiping. The plating composition at this time contained 2 wt% Fe in addition to the elements in Table 1, but Fe is inevitable supplied from equipment in the bath or a steel plate (strip).
Tables 2 to 4 show the steel plates plated with the metal mainly composed of Al and the metal composed mainly of Sn, using direct current heating by alternating current at a temperature equal to or higher than the melting point of the metal used for plating, that is, 950 ° C. Heating was performed with a heating pattern and heat treatment was performed. FIG. 3 shows the relationship between the heating time t seconds and the thickness δ μm of the plating film.
About the plated steel plate manufactured in this way, the molten state of the plating after heat processing was evaluated. Tables 2 and 3 are examples of the present invention, and Table 4 is a comparative example. In Tables 2 to 4, the melting of the metal means that there is no change in the surface appearance of the steel sheet plated with metal, that is, a non-defective product is melted, and the metal plated on the steel sheet melts. A sample in which no (sag) was generated, that is, a slightly non-defective product was evaluated as Δ, and a sample in which metal sagging occurred on the steel plate surface, that is, a defective product was evaluated as x.
[0016]
[Table 2]
[Table 3]
[Table 4]
Reference numerals 1 to 15 indicate that the heating (heating) time of the steel sheet in the temperature range from a temperature lower than the melting point of the plated metal (melting point−100 ° C.) to just below the melting point is 10 seconds or more, and the film thickness of the plating film is For thicker ones, the metal thickness (δ) and the temperature rise time (t) satisfy t ≧ δ / 0.5, and both have good appearance. That is, the heating time in the above temperature range is important, and even if the temperature rising time in the temperature range before and after this temperature range is changed or the holding time at the maximum heating temperature is changed, a good appearance is obtained. Has been obtained.
Reference numerals 16 to 24 indicate conditions where the conditions are slightly worse than those of reference numerals 1 to 15, that is, the heating time of the steel sheet in the temperature range is 5 seconds or more, and t ≧ δ is satisfied. In this case, the metal plated on the steel plate melts, but no metal dripping (sagging) occurs on the steel plate surface, and although the quality is inferior to those of reference numerals 1 to 15, a product with no problem in quality could be manufactured.
[0020]
On the other hand, as for the codes | symbols 27, 29, and 32, all the heating time in the said temperature range was short with less than 5 second, and the metal plated on the steel plate surface dripped. In addition,
[0021]
As described above, the present invention has been described with reference to one embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and is described in the claims. Other embodiments and modifications conceivable within the scope of the above are also included.
For example, in the above-described embodiment, the case where metals mainly composed of Al and Sn are used as the metal used for plating has been described. However, the melting point of the metal used for plating forms the plated steel sheet. A metal having a melting point higher than the maximum heating temperature at the time of molding, that is, an intermetallic compound formed from the metal at a maximum heating temperature (for example, about 800 to 1000 ° C.) or less during heating if there is applicable.
Moreover, in the said embodiment, although the three types of temperature control methods in the middle of the heating for shaping | molding the plated steel plate were demonstrated, from the predetermined temperature 200 degreeC lower than melting | fusing point of the metal used for plating, just below melting | fusing point of a metal If the plated steel plate can be heated for 5 seconds or more, preferably 10 seconds or more in the temperature range up to, the temperature transition during that time is not particularly limited.
[0022]
In the embodiment described above, the case where the metal mainly composed of Al and Sn is plated on the steel sheet and the intermetallic compound of FeAl 3 and FeSn 2 is formed on the surface layer portion of the plating film has been described. However, other alloys having a melting point and a boiling point higher than the maximum heating temperature, for example, about 800 to 1000 ° C., at the time of heating for forming the intermetallic compound may be formed.
Further, the heating means for the plated metal is not particularly limited, and for example, direct current heating (direct current, alternating current), induction heating, infrared heating, furnace (radiation heat transfer from combustion tube, combustion exhaust gas), etc. It is possible to use.
[0023]
【Effect of the invention】
In the heating method of the steel sheet for heat forming according to claim 1 and claims 3 and 4 dependent thereon, a predetermined heating temperature and heating time are set during heating for forming the plated steel sheet. The temperature required for the steel plate component to diffuse into the surface layer portion of the plating film and the time required for the diffusion can be ensured. Therefore, an intermetallic compound having a melting point higher than that of the metal used for plating is formed on the surface layer portion of the plating film, so that the plating film is prevented from sagging even when a steel plate plated to a temperature higher than the melting point of the metal is heated. Is possible.
In the heating method of the steel sheet for thermoforming according to claim 2 and claims 3 and 4 subordinate thereto, by setting a predetermined heating temperature and heating time during heating for forming the plated steel sheet. Since the temperature necessary for the steel plate component to diffuse into the surface layer part of the plating film and the time required for diffusion can be secured, the surface layer part of this plating film has a melting point higher than the heating temperature for forming. Compounds can be formed. Therefore, since the dripping of the metal used for plating, which was a problem in hot pressing the hot forming steel plate, can be prevented, a hot forming steel plate having a beautiful appearance and excellent corrosion resistance can be manufactured. Moreover, since the descaling process after the high temperature press which becomes a problem with a non-plated steel plate is unnecessary, work efficiency becomes favorable.
[0024]
In particular, in the method of heating a steel sheet for thermoforming according to claim 3, since the heating time in a predetermined temperature region is set according to the thickness of each plating film of the plated steel sheet, the steel sheet to the metal used for plating The component diffusion time can be secured, and an intermetallic compound can be reliably formed on the surface layer portion of the plating film. Therefore, even if the thickness of the plating plated on the steel sheet changes, the steel plate components can be reliably diffused to the surface layer part of the plating film, so that it has a beautiful appearance and has excellent corrosion resistance. Steel sheets can be manufactured.
In the heating method of the steel sheet for heat forming according to claim 4, since an intermetallic compound of Al and Fe having a melting point higher than that of a metal mainly composed of Al can be formed on the surface layer portion of the plating film, plating is performed for forming processing. Even if the heated steel sheet is heated, it is possible to prevent the plating film from sagging due to the presence of the intermetallic compound. Therefore, high-temperature pressing is possible even with a hot-forming steel plate using a metal mainly composed of Al as the plating film, which has a melting point lower than the maximum heating temperature during the heating for forming the plated steel plate. large.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a temperature history using a heating method of a steel sheet for heat forming according to an embodiment of the present invention.
FIGS. 2A and 2B are explanatory diagrams of a temperature history according to a modification using the heating method of the steel sheet for thermoforming, respectively, and explanatory diagrams of a temperature history according to another modification.
FIG. 3 is an explanatory diagram showing the relationship between the heating time and the thickness of the plating film in the examples.
Claims (4)
前記金属の融点より２００℃低い所定温度から前記金属の融点直下までの温度領域で、前記めっきした鋼板を５秒以上加熱して、成形加工する際のめっき層の溶融を防止することを特徴とする加熱成形用鋼板の加熱方法。 In a heating method of a steel sheet for thermoforming , in which a steel plate plated with an Al-based metal containing 9.5 wt% or more and 10 wt% or less of Si is heated to a temperature equal to or higher than the melting point of the metal used for the plating,
Heating the plated steel sheet for 5 seconds or more in a temperature range from a predetermined temperature 200 ° C. lower than the melting point of the metal to just below the melting point of the metal to prevent melting of the plating layer when forming. Heating method for heat forming steel sheet.
前記金属の融点より２００℃低い所定温度から前記金属の融点直下までの温度領域で、前記めっきした鋼板を５秒以上加熱し、前記めっきの表層部に、前記金属の融点より高く、しかも前記成形加工するための前記めっきした鋼板の加熱温度より高い融点を備えた金属間化合物を形成して、成形加工する際のめっき層の溶融を防止することを特徴とする加熱成形用鋼板の加熱方法。 In a heating method of a steel sheet for thermoforming , in which a steel plate plated with an Al-based metal containing 9.5 wt% or more and 10 wt% or less of Si is heated to a temperature equal to or higher than the melting point of the metal used for the plating,
The plated steel sheet is heated for 5 seconds or more in a temperature range from a predetermined temperature 200 ° C. lower than the melting point of the metal to immediately below the melting point of the metal, and the surface layer portion of the plating is higher than the melting point of the metal and the forming A method for heating a steel sheet for thermoforming, characterized in that an intermetallic compound having a melting point higher than the heating temperature of the plated steel sheet for processing is formed to prevent melting of a plating layer during forming.
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| DE102004007071B4 (en) * | 2004-02-13 | 2006-01-05 | Audi Ag | Method for producing a component by forming a circuit board and apparatus for carrying out the method |
| JP4830742B2 (en) * | 2006-09-13 | 2011-12-07 | 住友金属工業株式会社 | Al-plated heat-treated steel and method for producing the same |
| DE102008006771B3 (en) * | 2008-01-30 | 2009-09-10 | Thyssenkrupp Steel Ag | A method of manufacturing a component from a steel product provided with an Al-Si coating and an intermediate of such a method |
| JP5476676B2 (en) * | 2008-04-22 | 2014-04-23 | 新日鐵住金株式会社 | Hot-pressed member and manufacturing method thereof |
| JP4616900B2 (en) * | 2008-05-27 | 2011-01-19 | 新日本製鐵株式会社 | High-strength automotive parts with excellent corrosion resistance after painting |
| BRPI0915898B1 (en) | 2008-07-11 | 2017-07-18 | Nippon Steel & Sumitomo Metal Corporation | COATED ALUMINUM STEEL SHEET FOR QUICK HEATING PRESSURE HEATING METHOD, SAME PRODUCTION METHOD AND HOT STEMPING METHOD WITH QUICK HEATING USING THAT STEEL PLATE |
| JP5444650B2 (en) * | 2008-07-11 | 2014-03-19 | 新日鐵住金株式会社 | Plated steel sheet for hot press and method for producing the same |
| JP4837712B2 (en) * | 2008-09-18 | 2011-12-14 | 新日本製鐵株式会社 | Hot press molding method, molded products and automotive parts |
| KR101171450B1 (en) * | 2009-12-29 | 2012-08-06 | 주식회사 포스코 | Method for hot press forming of coated steel and hot press formed prodicts using the same |
| DE102010017905B4 (en) * | 2010-04-21 | 2014-08-21 | TRUMPF Hüttinger GmbH + Co. KG | Method and induction heating device for hot sheet metal forming |
| JP5625902B2 (en) * | 2010-12-28 | 2014-11-19 | Ｊｆｅスチール株式会社 | Stainless steel for polymer electrolyte fuel cell separator and method for producing the same |
| JP6493111B2 (en) * | 2015-09-11 | 2019-04-03 | 日産自動車株式会社 | Sequential forming method, sequential forming apparatus and sequential forming method tool |
| KR101720501B1 (en) * | 2016-05-09 | 2017-03-28 | 주식회사 엠에스 오토텍 | High-frequency heating method for hot stamping |
| JP7433972B2 (en) * | 2020-02-19 | 2024-02-20 | 日本製鉄株式会社 | Al-plated steel pipes and aluminum-plated steel pipe parts for STAF (registered trademark) construction method, and their manufacturing method |
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