JP4048675B2 - High carbon steel sheet for machining with low in-plane anisotropy with excellent hardenability and toughness and method for producing the same - Google Patents

Description

【００５５】
また、二次焼鈍温度により炭化物の粒径および粒径分布が変化するのは第１の方法の場合と同様であり、０．６μｍ以下の炭化物および１．５μｍ以上の炭化物を析出させるために、二次焼鈍温度Ｔ_２を６２０℃〜６８０℃の範囲に規定した。なお、焼鈍は連続焼鈍および箱焼鈍のいずれでもよい。
【００５６】
なお、本発明においては、鋼板を製造する際に、スラブを加熱した後に圧延する方法としては、連続鋳造後短時間の加熱処理を施す方法、またはこの加熱工程を省略して、直ちに圧延する方法のいずれの方法を採用してもよいが、特にスラブを室温まで冷却せずに再加熱する方法は、省エネルギーの観点からより好ましい。また、熱間圧延中において、均熱を目的として、バーヒーター等により加熱しても何ら問題はない。バーヒーターによる加熱は、コイルｂｏｘ等を用いた連続熱延プロセスに対しても効果的に使用することができる。この際、粗圧延バーの加熱は上記以外に、コイルｂｏｘの前後や粗圧延機の間または後に行ってもよい。また、コイルｂｏｘの後で溶接機の前後で粗圧延バーの加熱を行っても本発明の効果は十分に発揮される。さらに、このようにして製造された鋼板の表面に対し摺動性向上のため、亜鉛めっき後、りん酸塩処理を施してもよい。亜鉛めっきは、電気亜鉛めっき法、溶融亜鉛めっき法等によって施すことができる。
【００５７】
【実施例】
以下、本発明の具体的な実施例について、比較例と比較しつつ説明する。
（実施例１）
この実施例では第１の高炭素鋼板およびその製造方法の例について示す。
ＪＩＳ Ｇ４０５１のＳ３５Ｃ相当の成分系（質量％で、Ｃ：０．３５％、Ｓｉ：０．２０％、Ｍｎ：０．７６％、Ｐ：０．０１６％、Ｓ：０．００３％、Ａｌ：０．０２６％）のスラブを連続鋳造により製造し、このスラブを１１００℃に加熱した後、熱間圧延し、冷却した後、表２に示す条件で巻取り、一次焼鈍、冷間圧延、二次焼鈍を順次行い、その後、１．５％の調質圧延を施して、板厚１．０ｍｍの鋼板を作製した。なお、サンプルＮｏ．Ｈは従来材である。
【００５８】
【表２】

【００５９】
これらの試料について、以下のようにして炭化物粒径測定および粒度分布測定、引張試験、焼入れ試験、焼入れ後の旧オーステナイト粒径測定を行った。その結果を表３に示す。
【００６０】
（ａ）炭化物粒径測定および粒度分布測定
サンプルの板厚断面を研磨・腐食後、走査型電子顕微鏡にてミクロ組織を撮影し、２５００μｍ^２の範囲から炭化物の粒径および粒度分布の測定を行った。
【００６１】
（ｂ）引張強度
圧延方向に対し０°方向（Ｌ方向）、４５°方向（Ｓ方向）、９０°方向（Ｃ方向）に沿ってＪＩＳ５号試験片を採取し、引張速度１０ｍｍ／ｍｉｎで引張試験を行い、各方向の引張特性を測定し、面内異方性について評価した。なお、表３中の降伏強度、引張強度および全伸びの各欄に記載したΔ_ｍａｘとは、それぞれの引張特性値のＬ、Ｓ、Ｃ方向における最大格差を示している。また、表３中のｒ値の欄に記載したΔｒとは、Δｒ＝（ｒ０＋ｒ９０−２×ｒ４５）／４により規定される値である。ここで、前記ｒ０、ｒ４５、ｒ９０は、それぞれ圧延方向に対し、０°方向（Ｌ方向）、４５°方向（Ｓ方向）、９０°方向（Ｃ方向）におけるｒ値を示す。
【００６２】
（ｃ）焼入れ試験
上記鋼板を５０×１００ｍｍの大きさに切断後、加熱炉で８２０℃に昇温し、１０秒保持後に約２０℃の油中へ焼入れした。焼入れ後の試験片の表面における硬さをロックウェルＣスケール（ＨＲＣ）で１０点測定し、焼入れ性を評価した。評価は平均硬さで行った。硬さ（ＨＲＣ）５０以上を合格とした。
【００６３】
（ｄ）旧オーステナイト粒径の測定
上記焼入れ後のサンプルの板厚断面を研磨・腐食後、光学顕微鏡にてミクロ組織を撮影し、ＪＩＳＧ０５５１に従い、旧オーステナイト粒度番号を測定した。
【００６４】
【表３】

【００６５】
表３に示すように本発明例であるＮｏ．Ａ〜Ｎｏ．Ｃは、炭化物の粒径および粒度分布が適正であるため、焼入れ後の硬さおよび旧オーステナイト粒径の値が良好であり、焼入れ性および靱性に優れていることが確認された。また、これらは降伏強度および引張強度のΔ_ｍａｘが１０ＭＰａ以下、伸びのΔ_ｍａｘが１．５％以下、ｒ値のΔｒが−０．１５超〜０．１５未満であり、面内での引張特性の異方性が極めて小さいことが確認された。
【００６６】
一方、比較例では、引張特性のいずれかについてのΔ_ｍａｘ、あるいはΔｒが大きく、面内での引張特性の異方性に劣っているかことが確認された。例えば、巻取温度が低い場合（Ｎｏ．Ｄ）には、伸びのΔ_ｍａｘが１．７、ｒ値のΔｒが０．１６とそれぞれ大きくなっており、また、１．５μｍ以上の炭化物が少ないために旧オーステナイト粒径が粗大化し、靭性が損なわれる。また、一次焼鈍温度が高い場合（Ｎｏ．Ｅ）には、ｒ値のΔｒが０．１８と大きく、また、粗大炭化物が増加するため微細炭化物が減少し、焼き入れ性が著しく低下した。さらに、冷間圧延圧下率が４０％と低い場合（Ｎｏ．Ｆ）には、降伏強度のΔ_ｍａｘが１１、引張強度のΔ_ｍａｘが１４、伸びのΔ_ｍａｘが１．７、ｒ値のΔｒが０．２０とそれぞれ大きく、二次焼鈍温度が高い場合（Ｎｏ．Ｇ）には、粗大炭化物が増大し、焼き入れ後の硬さが大幅に低下するとともに、ｒ値のΔｒが０．２３となり、面内異方性が大きかった。また、従来材のＮｏ．Ｈは、降伏強度のΔ_ｍａｘが１７、引張強度のΔ_ｍａｘが１５、伸びのΔ_ｍａｘが１．９、ｒ値のΔｒが０．１６とそれぞれ高く、面内異方性が大きかった。
（実施例２）
この実施例では第２の高炭素鋼板の第１の製造方法の例について示す。
ＪＩＳ Ｇ４０５１のＳ３５Ｃ相当の成分系（質量で、Ｃ：０．３６％、Ｓｉ：０．２０％、Ｍｎ：０．７５％、Ｐ：０．０１１％、Ｓ：０．００２％、Ａｌ：０．０２０％）のスラブを連続鋳造により製造し、このスラブを１１００℃に加熱した後、表４に示す条件で熱間圧延、一次焼鈍、冷間圧延、二次焼鈍を順次行い、その後、１．５％の調質圧延を施して、板厚２．５ｍｍの１９種類の鋼板を作製した。
【００６７】
【表４】

【００６８】
これらの試料について、実施例１と同様にして炭化物粒径測定および粒度分布測定、引張試験、焼入れ試験、焼入れ後の旧オーステナイト粒径測定を行った。その結果を表５に示す。なお、サンプルＮｏ．１９は、従来材である。
【００６９】
【表５】

【００７０】
表５に示すように本発明例であるＮｏ．１〜Ｎｏ．７は、炭化物の粒径および粒度分布が適正であるため、焼入れ後の硬さおよび旧オーステナイト粒径の値が良好であり、焼入れ性および靱性に優れていることが確認された。また、これらは降伏強度および引張強度のΔ_ｍａｘが１０ＭＰａ以下、伸びのΔ_ｍａｘが１．５％以下、ｒ値のΔ_ｍａｘが０．２未満であり、引張特性の異方性が極めて小さいことが確認された。
【００７１】
一方、比較例では、引張特性のいずれかについてΔ_ｍａｘが大きく面内異方性に劣っているか、焼入れ性または靱性に劣っていることが確認された。例えば、一次焼鈍温度が高い場合（Ｎｏ．１１）には、ｒ値のΔ_ｍａｘが０．３０となり、冷延率が３０％と低い場合（Ｎｏ．１３）には、降伏強度、引張強度およびｒ値のΔ_ｍａｘがそれぞれ１８、１３および０．３８と大きくなり、いずれも面内異方性が大きかった。また、サンプルＮｏ．１６は二次焼鈍温度が高すぎるため、炭化物溶解が十分になされず焼入れ後の硬さが４３と低く、サンプルＮｏ．１７は二次焼鈍温度が低すぎるため粒径０．６μｍ以下の炭化物が多くなりすぎてしまい、旧オーステナイト粒径が粗大化しており靭性が損なわれる。また、比較のために示した従来材（Ｎｏ．１９）では、ｒ値のΔ_ｍａｘが０．４２と高く、面内異方性が大きかった。
【００７２】
（実施例３）
この実施例も第２の高炭素鋼板の第１の製造方法の例について示す。
ＪＩＳ Ｇ４８０２のＳ６５Ｃ−ＣＳＰ相当の成分系（質量で、Ｃ：０．６５％、Ｓｉ：０．１９％、Ｍｎ：０．７３％、Ｐ：０．０１１％、Ｓ：０．００２％、Ａｌ：０．０２０％）のスラブを連続鋳造により製造し、このスラブを１１００℃に加熱した後、表６に示す条件で熱間圧延、一次焼鈍、冷間圧延、二次焼鈍を順次行い、その後１．５％の調質圧延を施して、板厚２．５ｍｍの１９種類の鋼板を作製した。
【００７３】
【表６】

【００７４】
これらの試料について、実施例１と同様にして、炭化物粒径測定ならびに粒度分布測定、引張試験、焼入れ試験、焼入れ後の旧オーステナイト粒径測定を行った。その結果を表７に示す。なお、サンプルＮｏ．３８は、従来材である。
【００７５】
【表７】

【００７６】
表７に示すように本発明例であるＮｏ．２０〜Ｎｏ．２６は、炭化物の粒径および粒径分布が適正であるため、焼入れ後の硬さおよび旧オーステナイト粒径の値が良好であり、焼入れ性および靱性に優れていることが確認された。また、これらは降伏強度および引張強度のΔ_ｍａｘが１５ＭＰａ以下、伸びのΔ_ｍａｘが１．５％以下、ｒ値のΔ_ｍａｘが０．２未満であり、面内での引張特性の異方性が極めて小さいことが確認された。
【００７７】
一方、比較例では、引張特性のいずれかについてΔ_ｍａｘが大きく面内異方性に劣っているか、焼入れ性または靱性に劣っていることが確認された。例えば、一次焼鈍温度が高い場合（Ｎｏ．３０）には、ｒ値のΔ_ｍａｘが０．２６となり、冷延率が３０％と低い場合（Ｎｏ．３２）には、降伏強度、引張強度およびｒ値のΔ_ｍａｘがそれぞれ２０、１７および０．３９と大きくなり、いずれも面内異方性が大きかった。また、サンプルＮｏ．３５は二次焼鈍温度が高すぎるため、炭化物溶解が十分になされず焼入れ後の硬さが５１と低く、サンプルＮｏ．３６は二次焼鈍温度が低すぎるため粒径０．６μｍ以下の炭化物が多くなりすぎてしまい、旧オーステナイト粒径が粗大化しており靭性が損なわれる。また、比較のために示した従来材のＮｏ．３８も、ｒ値のΔ_ｍａｘが０．４６と高く、面内異方性が大きかった。
【００７８】
（実施例４）
この実施例では第２の高炭素鋼板の第２の製造方法の例について示す。
ＪＩＳ Ｇ４０５１のＳ３５Ｃ相当の成分系（質量で、Ｃ：０．３６％、Ｓｉ：０．２０％、Ｍｎ：０．７５％、Ｐ：０．０１１％、Ｓ：０．００２％、Ａｌ：０．０２０％）のスラブを連続鋳造により製造し、このスラブを１１００℃に加熱した後、表８に示す条件で熱間圧延、一次焼鈍、冷間圧延、二次焼鈍を順次行い、その後、１．５％の調質圧延を施して、板厚２．５ｍｍの２６種類の鋼板を作製した。
【００７９】
【表８】

【００８０】
これらの試料について、実施例１と同様に、炭化物粒径測定および粒度分布測定、引張試験、焼入れ試験、焼入れ後の旧オーステナイト粒径測定を行った。その結果を表９に示す。なお、サンプルＮｏ．６４は、従来材である。
【００８１】
【表９】

【００８２】
表９に示すように本発明例であるＮｏ．３９〜Ｎｏ．５２は、炭化物の粒径および粒径分布が適正であるため、焼入れ後の硬さおよび旧オーステナイト粒径の値が良好であり、焼入れ性および靱性に優れていることが確認された。また、これらは降伏強度および引張強度のΔ_ｍａｘが１０ＭＰａ以下、伸びのΔ_ｍａｘが１．５％以下、ｒ値のΔ_ｍａｘが０．２未満であり、面内での引張特性の異方性が極めて小さいことが確認された。さらに、粗圧延前に誘導加熱を施す方法は、引張特性の異方性の低減だけでなく板厚方向の組織の均一性の向上の観点からより好ましいことが確認された。
【００８３】
一方、比較例では、引張特性のいずれかについてΔ_ｍａｘが大きく面内異方性に劣っているか、焼入れ性または靱性に劣っていることが確認された。例えば、一次焼鈍温度が高い場合（Ｎｏ．５６）には、ｒ値のΔ_ｍａｘが０．３０となり、冷延率が３０％と低い場合（Ｎｏ．５８）には、降伏強度、引張強度およびｒ値のΔ_ｍａｘがそれぞれ１８、１３および０．３８と大きくなり、面内異方性が大きいことが確認された。また、サンプルＮｏ．６１は二次焼鈍温度が高すぎるため、炭化物溶解が十分になされず焼入れ後の硬さが４４と低く、サンプルＮｏ．６２は二次焼鈍温度が低すぎるため粒径０．６μｍ以下の炭化物が多くなりすぎてしまい、旧オーステナイト粒径が粗大化しており靭性が損なわれる。また、比較のために示した従来材のＮｏ．６４では、ｒ値のΔ_ｍａｘが０．４２と高く、面内異方性が大きいことが確認された。
【００８４】
（実施例４）
この実施例も第２の高炭素鋼板の第２の製造方法の例について示す。
ＪＩＳ Ｇ４８０２のＳ６５Ｃ−ＣＳＰ相当の成分系（質量で、Ｃ：０．６５％、Ｓｉ：０．１９％、Ｍｎ：０．７３％、Ｐ：０．０１１％、Ｓ：０．００２％、Ａｌ：０．０２０％）のスラブを連続鋳造により製造し、このスラブを１１００℃に加熱した後、表１０に示す条件で熱間圧延、一次焼鈍、冷間圧延、二次焼鈍を順次行い、その後１．５％の調質圧延を施して、板厚２．５ｍｍの２６種類の鋼板を作製した。
【００８５】
【表１０】

【００８６】
これらの試料について、実施例１と同様に、炭化物粒径測定ならびに粒度分布測定、引張試験、焼入れ試験、焼入れ後の旧オーステナイト粒径測定を行った。その結果を表１１に示す。なお、サンプルＮｏ．９０は、従来材である。
【００８７】
【表１１】

【００８８】
表１１に示すように本発明例であるＮｏ．６５〜Ｎｏ．７８は、炭化物の粒径および粒径分布が適正であるため、焼入れ後の硬さおよび旧オーステナイト粒径の値が良好であり、焼入れ性および靱性に優れていることが確認された。また、これらは降伏強度および引張強度のΔ_ｍａｘが１５ＭＰａ以下、伸びのΔ_ｍａｘが１．５％以下、ｒ値のΔ_ｍａｘが０．２未満であり、面内での引張特性の異方性が極めて小さいことが確認された。さらに粗圧延前に誘導加熱を施す方法は、引張特性の異方性の低減だけでなく、板厚方向の組織の均一性の向上の観点からより好ましいことが確認された。
【００８９】
一方、比較例では、引張特性のいずれかについてΔ_ｍａｘが大きく面内異方性に劣っているか、焼入れ性または靱性に劣っていることが確認された。例えば、一次焼鈍温度が高い場合（Ｎｏ．８２）には、ｒ値のΔ_ｍａｘが０．２７となり、冷延率が３０％と低い場合（Ｎｏ．８４）には、降伏強度、引張強度およびｒ値のΔ_ｍａｘがそれぞれ２０、１７および０．３９と大きくなり、面内異方性が大きいことが確認された。また、サンプルＮｏ．８７は二次焼鈍温度が高すぎるため、炭化物溶解が十分になされず焼入れ後の硬さが５２と低く、サンプルＮｏ．８８は二次焼鈍温度が低すぎるため粒径０．６μｍ以下の炭化物が多くなりすぎてしまい、旧オーステナイト粒径が粗大化しており靭性が損なわれる。また、比較のために示した従来材のＮｏ．９０では、ｒ値のΔ_ｍａｘが０．４６と高く、面内異方性が大きいことが確認された。
【００９０】
【発明の効果】
以上説明したように、本発明によれば、焼入れ性および靭性に優れ、かつ成形性に大きな影響を及ぼす引張特性に対する面内異方性の小さい高炭素鋼板を得ることができる。したがって、本発明によって得られた高炭素鋼板は、高い寸法精度が要求されるギア部品等に供することができる。また、本発明を適用することにより、ギア部品等を製造するに際して、鋼板の一体成形および焼入れ焼戻し処理により製造することができ、従来の鋳造鍛造プロセスに比べて、安価に製造することが可能となる。
【図面の簡単な説明】
【図１】Ｓ３５Ｃ鋼板に８２０℃×１０ｓ保持後油焼入れを施した場合の硬さに及ぼす焼入れ前の炭化物粒径の影響を説明する図。
【図２】Ｓ３５Ｃ鋼板に８２０℃×１０ｓ保持後油焼入れを施した場合の旧オーステナイト粒径に及ぼす焼入れ前の粒径１．５μｍ以上の炭化物数の影響を説明する図。
【図３】第２の高炭素鋼板を製造する第１の方法において、ｒ値の面内異方性および炭化物の分散形態に及ぼす、一次焼鈍温度および二次焼鈍温度の影響を示す図。
【図４】第２の高炭素鋼板を製造する第２の方法において、ｒ値の面内異方性および炭化物の分散形態に及ぼす、一次焼鈍温度および二次焼鈍温度の影響を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention is excellent in hardenability and toughness and has different in-plane tensile properties, for example, which is disk processing or cylindrical molding, and requires high dimensional accuracy, and is suitable for parts that are subsequently subjected to heat treatment such as quenching and tempering. The present invention relates to a high-carbon steel sheet for processing with a low degree of directivity and a method for producing the same.
[0002]
[Prior art]
Conventionally, high carbon steel sheets have been used for machine structural parts such as washers and chain parts. Such a high carbon steel sheet is required to have high hardenability, and recently, not only improvement of hardness after quenching but also quenching in a short time at low temperature is desired from the viewpoint of cost reduction of quenching work. Yes. In recent years, safety standards have been reviewed, and it is also important that parts after quenching have high toughness.
[0003]
On the other hand, high-carbon cold-rolled steel sheets are generally harder than low-carbon steels, so they are not only inferior in formability but also in-plane anisotropy of mechanical properties due to hot rolling, annealing, and cold rolling. Therefore, it has been difficult to apply to gear parts that are conventionally manufactured by casting and forging and requiring high dimensional accuracy.
[0004]
Therefore, it was a big subject to improve hardenability and toughness, and to reduce the in-plane anisotropy of mechanical properties with respect to moldability.
[0005]
Thus, the following techniques have been proposed so far in order to improve the hardenability and toughness of high carbon steel sheets or to reduce the in-plane anisotropy of mechanical properties.
[0006]
(1) Japanese Patent Application Laid-Open No. 5-9588 (hereinafter referred to as Prior Art 1)
In this publication, the steel strip after hot rolling is cooled to a temperature range of 20 to 500 ° C. at a cooling rate of 10 ° C./sec or more to form fine pearlite, and then reheated and wound up to spheroidize the carbide. Techniques that promote and enhance the hardenability of high carbon steel sheets are described.
[0007]
(2) Japanese Patent Laid-Open No. 5-98388 (hereinafter referred to as Conventional Technology 2)
In this publication, Nb and Ti are added to a high carbon steel sheet containing C: 0.30 to 0.70%, carbonitrides are formed to suppress austenite grain growth, and toughness of the high carbon steel sheet. Techniques for improving the performance are described.
[0008]
(3) Materials and Processes, Vol. 1 (1988), p. 1729 (hereinafter referred to as Conventional Technology 3)
In general, a steel sheet (S65C) containing a high concentration of 0.65% carbon and having a ferrite / cementite structure has a lower formability than a low-carbon steel sheet. In this document, after hot rolling, cold rolling (cold rolling rate 50%) and batch annealing at 650 ° C. for 24 hours are performed, and further, secondary cold rolling (cold rolling rate 65%) and 680 ° C. for 24 hours. It describes that a high carbon cold-rolled steel sheet excellent in workability is manufactured by performing batch annealing. For the purpose of graphitizing cementite, the chemical components in S65C are adjusted, and after hot rolling, cold rolling (cold rolling rate 50%) and batch annealing at 650 ° C. for 24 hours are performed, and further secondary Cold rolling (cold rolling ratio 65%) and secondary batch annealing at 680 ° C. for 24 hours reduces tensile strength, improves r-value and elongation, and lowers the in-plane anisotropy of r-value. A method for producing a high-carbon cold-rolled steel sheet that is equivalent to a carbon steel sheet is also disclosed.
[0009]
(4) Japanese Patent Application Laid-Open No. 10-152757 (hereinafter referred to as Prior Art 4)
In this publication, the cause of the anisotropy of the mechanical properties of the high carbon steel sheet is the presence of sulfide-based non-metallic inclusions elongated in the rolling direction, and C, Si, Mn, P, Cr, Ni , Mo, V, Ti, Al are regulated, S content is reduced to 0.002% or less by weight, the average length of inclusions in the rolling direction is 6 μm or less, and the length in the rolling direction is 4 μm or less. By setting the number of inclusions to 80% or more of the total number of inclusions, the ratio of the mechanical properties in the rolling direction to the mechanical properties in the direction perpendicular to the rolling direction with respect to the impact value and total elongation is 0.9 to 1. It describes that a high carbon steel sheet having a small in-plane anisotropy so as to be in a range of 0.0 is manufactured.
[0010]
(5) Japanese Patent Laid-Open No. 6-271935 (hereinafter referred to as Prior Art 5)
In this publication, when hot rolling a high carbon steel sheet that specifies C, Si, Mn, Cr, Mo, Ni, B, and Al, the hot finishing temperature is set to Ar.₃The temperature from the end of hot rolling to the winding is cooled at 30 ° C / sec or more, wound in the temperature range of 550 to 700 ° C, descaled, and then annealed at a temperature of 600 to 680 ° C. Cold rolling at a rolling reduction of 40% or more, further annealing at a temperature of 600 to 680 ° C., and then adjusting the pressure to obtain a high carbon cold-rolled steel sheet having a small dimensional change anisotropy during heat treatment such as quenching and tempering. Manufacturing is described.
[0011]
[Problems to be solved by the invention]
However, the above-described prior art has the following problems.
In prior art 1, since it winds and cools as it is, even if it reheats, the retention time for spheroidizing of a carbide | carbonized_material is very short compared with the normal spheroidizing annealing time, and the spheroidization rate of a carbide | carbonized_material is still low. Due to the level, sufficient hardenability may not be obtained. Moreover, the reheating after the rapid cooling requires an electric heating equipment, and the manufacturing cost becomes enormous.
[0012]
In prior art 2, since expensive Nb and Ti are added in order to suppress austenite grain growth, cost increases.
[0013]
In prior art 3, for S65C having a ferrite / cementite structure, the average r value is as high as about 1.3, but the 0 ° direction (L direction), 45 ° direction (S direction), 90 ° with respect to the rolling direction. An in-plane anisotropy index Δr having an r value defined by Δr = (r0 + r90−2 × r45) / 4 from r0, r45, and r90, which are r values in each direction of the ° direction (C direction), is −0. .47, and Δ which is the maximum difference between the r values._maxIs 1.17, and the in-plane anisotropy of the r value is very large. Moreover, since the cold rolling-annealing process is performed twice, there is a problem that the manufacturing cost increases. On the other hand, for the graphitized high carbon steel sheet, the r value is further improved, and Δr is 0.34, Δ_maxHowever, the in-plane anisotropy of the r value is still large. Moreover, since graphite has a slow dissolution rate in austenite, the hardenability is significantly reduced.
[0014]
In the prior art 4, only the in-plane anisotropy with respect to only the impact value and the total elongation is taken into consideration. Not considered.
[0015]
Prior art 5 describes a method for producing a high-carbon steel sheet having a small dimensional change during heat treatment such as quenching and tempering, but no in-plane anisotropy with respect to formability has been studied.
[0016]
The present invention is made in view of such circumstances, and provides a high-carbon steel sheet having excellent hardenability and toughness and small in-plane anisotropy with respect to tensile properties that have a large effect on formability, and a method for producing the same. For the purpose.
[0017]
[Means for Solving the Problems]
The inventors of the present invention have a C amount of 0.2% defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for springs). As a result of repeated investigations on the conditions for improving the in-plane anisotropy of the hardenability and toughness and tensile properties of the high carbon cold rolled steel sheet having the above component system, the coiling temperature after the hot finish rolling, the primary Appropriate control of annealing temperature, cold rolling rate, and secondary annealing temperature, or rough bar or rolled material after Ar hot rolling₃After induction heating at a temperature above the transformation point to improve the uniformity of the structure in the thickness direction, the coiling temperature, primary annealing temperature, cold rolling rate and secondary annealing temperature after hot rolling are controlled appropriately. And it has been found that it is effective to appropriately adjust the state of carbides in the steel sheet. In addition, as a result, Δr is more than −0.15 and less than 0.15, and further, the r value Δ_maxHas been confirmed to be a very small value of less than 0.2.
[0018]
The present invention has been made on the basis of the above knowledge, and the first invention is JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), JIS G 4802 (cold rolled steel for springs). A high-carbon steel sheet having a component system defined by
Carbide with a particle size of 1.5 μm or more is 2500 μm²It is characterized in that 50 or more of the carbides having a particle size of 0.6 μm or less occupy 80% or more, and that the in-plane anisotropy index Δr of the r value is more than −0.15 and less than 0.15. The present invention provides a high carbon steel sheet for processing that has excellent hardenability and toughness and small in-plane anisotropy.
However, (DELTA) r shows the value prescribed | regulated by (DELTA) r = (r0 + r90-2 * r45) / 4. Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction), respectively, with respect to the rolling direction.
[0019]
  The second invention isA method for producing a high-carbon steel sheet for processing that has excellent hardenability and toughness according to the first invention and has small in-plane anisotropy,
  A steel plate after hot finish rolling having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring) is 520. Winding at a temperature of ~ 600 ° C,
  Next, after descaling the steel sheet after winding, 640-690 ° C (Except 690 ° C)In the primary annealing for 20 hours or more,
  Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
  Then, the manufacturing method of the high carbon steel plate for a process with small in-plane anisotropy excellent in hardenability and toughness characterized by performing secondary annealing in the temperature range of 620-680 degreeC is provided.
[0020]
The third invention is a high carbon steel plate having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), JIS G 4802 (cold rolled steel strip for spring). There,
Carbide with a particle size of 1.5 μm or more is 2500 μm²Among them, carbides having a particle size of 0.6 μm or less occupy 80% or more, and an r value Δ_maxThe present invention provides a high-carbon steel sheet for processing having low in-plane anisotropy and excellent hardenability and toughness.
However, Δ_maxIndicates the maximum difference in values in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction) with respect to the rolling direction.
[0021]
  The fourth invention isA method for producing a high-carbon steel sheet for processing that has excellent hardenability and toughness according to the third invention and has small in-plane anisotropy,
  A steel plate after hot finish rolling having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring) is 520. Winding at a temperature of ~ 600 ° C,
  Next, after descaling the steel sheet after winding, 640-690 ° C (Except 690 ° C)In the primary annealing for 20 hours or more,
  Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
  Thereafter, the high carbon steel sheet for processing having low in-plane anisotropy and excellent hardenability and toughness, characterized by satisfying the following formula (1) and performing secondary annealing in a temperature range of 620 to 680 ° C. A manufacturing method is provided.
  1024-0.6 × T₁≦ T₂≦ 1202-0.80 × T₁      ... (1)
  T₁: Primary annealing temperature (° C), T₂: Secondary annealing temperature (℃)
[0022]
  The fifth inventionA method for producing a high-carbon steel sheet for processing that has excellent hardenability and toughness according to the third invention and has small in-plane anisotropy,
  A cast slab having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring) is continuously cast or cooled. After heating to a predetermined temperature after, rough rolling with a roughing mill to form a rough bar,
  Subsequently, when finishing and rolling by a continuous hot finish rolling mill, Ar or coarse material is removed between the entrance side of the finishing mill or between the stands of the finishing mill.₃Induction heating at a temperature above the transformation point,
  The steel plate after hot finish rolling is wound at a temperature of 500 to 650 ° C.,
  Next, after descaling the steel sheet after winding, primary annealing is performed at 630 to 700 ° C. for 20 hours or more,
  Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
  Then, the following high-carbon steel sheet for processing with low in-plane anisotropy excellent in hardenability and toughness, characterized by satisfying the following formula (2) and performing secondary annealing in a temperature range of 620 to 680 ° C. A manufacturing method is provided.
  1010-0.59 × T₁≦ T₂≦ 1210−0.80 × T₁      ... (2)
  T₁: Primary annealing temperature (° C), T₂: Secondary annealing temperature (℃)
[0023]
The in-plane anisotropy indicates the maximum difference in tensile properties in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction) with respect to the rolling direction.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described.
The first high carbon steel sheet of the present invention has a C content defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). Is a high carbon steel plate having a component system of 0.2% or more, and carbides having a particle size of 1.5 μm or more are 2500 μm.²It is characterized in that 50 or more of the carbides having a particle size of 0.6 μm or less occupy 80% or more, and that the in-plane anisotropy index Δr of the r value is more than −0.15 and less than 0.15. To do.
However, (DELTA) r shows the value prescribed | regulated by (DELTA) r = (r0 + r90-2 * r45) / 4. Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction), respectively, with respect to the rolling direction.
The reason for limitation is explained below
[0025]
(1) Carbide with a particle size of 1.5 μm or more is 2500 μm²80% or more of carbides having a particle size of 0.6 μm or less are present in 50 or more
The carbide particle size and particle size distribution have a great influence on the hardenability and toughness in low temperature and short time heating. Therefore, first, the influence of the carbide particle size on the hardenability of the carbide was investigated.
[0026]
After melting steel of C: 0.36%, Si: 0.20%, Mn: 0.75%, P: 0.011%, S: 0.002%, Al: 0.020% by weight% , Finishing temperature: 850 ° C., coiling temperature: 560 ° C., hot pickling, and after pickling, primary annealing is performed at 640-690 ° C. for 40 hours, cold rolling reduction is 60%, and secondary annealing is 610 40 hours at ~ 690 ° C. The obtained steel sheet was cut to a size of 50 × 100 mm, heated to 820 ° C. in a heating furnace, held for 10 seconds, and then quenched into oil at about 20 ° C. The hardenability was evaluated by measuring the hardness of the test piece after quenching at 10 points on the Rockwell C scale (HRc). Evaluation made the average hardness (HRc) 50 or more pass.
[0027]
1 shows 2500 μm²The relationship between the particle size and hardness at which the cumulative number of carbides from the minimum particle size becomes 80% for the carbides within the range is shown. When the particle size is 0.6 μm or less, a hardness (HRc) of 50 or more is secured. That is, when the carbide having a particle size of 0.6 μm or less occupies 80% or more of the total carbide, the carbide quickly dissolves in austenite during heating and holding, and the hardenability is improved. However, if the total carbide is as fine as 0.6 μm or less, all the carbide dissolves during heating for a short time, and the austenite grains become extremely coarse.
[0028]
2 shows 2500 μm²The relationship between the number of carbides having a particle size of 1.5 μm or more and the prior austenite particle size is shown. As the number of carbides decreases, the prior austenite grain size becomes coarser. In particular, when the number of carbides is less than 50, it rapidly becomes coarse. The prior austenite grain size greatly affects the toughness of steel, and the finer the toughness, the higher the toughness. That is, regarding toughness, it is necessary to moderately disperse carbides having a particle size of 1.5 μm or more, but at least 2500 μm.²If it is not 50 or more, the effect of refining austenite cannot be obtained.
[0029]
The method for measuring the particle size and particle size distribution of the carbide is not particularly limited, but after polishing and corroding the plate thickness section of the sample, take a scanning electron micrograph of 1500 to 5000 times, It is preferable to measure the carbide particle size and particle size distribution from the photograph. When actually measuring the carbide particle size in the sample, the average particle size taken in the photograph is taken as the average particle size. The particle size distribution is measured at least 2500 μm.²Otherwise, the number of measured carbides is small and an appropriate particle size distribution cannot be obtained. On the other hand, as for the upper limit of the measurement region, it is sufficient if the particle size distribution of the present invention is satisfied by measuring about 60% of the plate thickness cross section. Moreover, it is good to use picral corrosion liquid as corrosive liquid.
[0030]
(2) In-plane anisotropy index Δr of r value is more than −0.15 and less than 0.15
In this way, by setting the r value Δr to a value as extremely small as more than −0.15 to less than 0.15, gear parts that have been conventionally produced by casting and forging and that require high dimensional accuracy. Can be applied.
[0031]
In producing such a first high carbon steel sheet, after hot-rolling the steel sheet having the above component system at a temperature of 520 to 600 ° C., and then descaling the steel sheet after winding, Primary annealing is performed at 640 to 690 ° C. for 20 hours or more, and the annealed steel sheet is cold-rolled at a reduction rate of 50% or more, and then subjected to secondary annealing in a temperature range of 620 to 680 ° C. The reason for limitation will be described below.
[0032]
(1) Hot coiling temperature: 520-600 ° C
When the coiling temperature is less than 520 ° C., the pearlite structure becomes extremely fine, so that the carbide becomes extremely fine by the primary annealing, and carbides of 1.5 μm or more cannot be obtained after the secondary annealing. On the other hand, if the temperature becomes too high, coarse pearlite is generated, and carbides having a particle size of 0.6 μm or less cannot be obtained after secondary annealing, so the upper limit was set to 600 ° C.
[0033]
(2) Primary annealing conditions: 640-690 ° C., 20 hours or more
The hot-rolled sheet after winding is subjected to primary annealing for the purpose of spheroidizing the carbide after descaling such as pickling. When the primary annealing temperature is higher than 690 ° C., the spheroidization of the carbide proceeds too much, and a carbide of 0.6 μm or less cannot be obtained even after the secondary annealing. Therefore, 690 ° C. was set as the upper limit. On the other hand, when the temperature is less than 640 ° C., spheroidization of the carbide becomes difficult and a carbide of 1.5 μm or more cannot be obtained even after the secondary annealing. The annealing time was set to 20 hours or more in order to uniformly spheroidize.
[0034]
(3) Cold rolling rate: 50% or more
A texture is formed in which the in-plane anisotropy of the r value decreases as the cold rolling rate increases. However, in order to sufficiently reduce the in-plane anisotropy of the r value, at least 50% or more of cold rolling is performed. A rate is needed. In addition, although an upper limit is not specifically limited, Since a plate | board property will fall remarkably in the high cold rolling rate which exceeds 80%, it is preferable that it is 80% or less.
[0035]
(4) Secondary annealing conditions: 620-680 ° C
The cold-rolled sheet is subjected to secondary annealing for the purpose of recrystallization. When the secondary annealing temperature is higher than 680 ° C., the carbides are remarkably coarsened, and recrystallization and grain growth remarkably occur. The r value in the C direction becomes significantly larger than the r values in the L and S directions. The anisotropy of 680 ° C. was set as the upper limit. On the other hand, when the secondary annealing temperature is less than 620 ° C., all the carbides become fine, and recrystallization and grain growth become insufficient, and workability deteriorates. Therefore, 620 ° C. is set as the lower limit. The annealing may be either continuous annealing or box annealing.
[0036]
The second high-carbon steel sheet of the present invention has a C content defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for springs). Is a high carbon steel plate having a component system of 0.2% or more, and carbides having a particle size of 1.5 μm or more are 2500 μm.²Among them, carbides having a particle size of 0.6 μm or less occupy 80% or more, and an r value Δ_maxIs less than 0.2.
However, Δ_maxIndicates the maximum disparity in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction) with respect to the rolling direction. The reason for limitation will be described below.
[0037]
(1) Carbide with a particle size of 1.5 μm or more is 2500 μm²80% or more of carbides having a particle size of 0.6 μm or less are present in 50 or more
The carbide particle size and the particle size distribution are defined in this way as in the case of the first high-carbon steel plate, a carbide having a particle size of 1.5 μm or more is 2500 μm.²This is because the austenite is refined by improving the toughness by making 50 or more present therein, and the hardenability is improved by making the carbide having a particle size of 0.6 μm or less 80% or more of the total carbide.
[0038]
(2) r value Δ_maxIs less than 0.2
In this way, the r value Δ_maxBy setting the value to a very small value of less than 0.2, it is possible to apply to gear parts that are conventionally manufactured by casting and forging and requiring high dimensional accuracy.
[0039]
In manufacturing such a second high carbon steel sheet, the following first and second methods can be applied.
[0040]
First, the first method will be described.
In the first method, the hot-rolled steel sheet having the above component system is wound at a temperature of 520 to 600 ° C., and then the steel sheet after winding is descaled and then at 640 to 690 ° C. for 20 hours or more. Primary annealing is performed, and the annealed steel sheet is cold-rolled at a reduction rate of 50% or more, and then the following equation (1) is satisfied and secondary annealing is performed in a temperature range of 620 to 680 ° C.
1024-0.6 × T₁≦ T₂≦ 1202-0.80 × T₁      ... (1)
(However, T₁: Primary annealing temperature (° C), T₂: Secondary annealing temperature (° C). same as below. )
[0041]
(1) Hot coiling temperature: 520-600 ° C
Similarly to the method for producing the first high carbon steel sheet, when the coiling temperature is less than 520 ° C., carbide of 1.5 μm or more cannot be obtained after the secondary annealing, so 520 ° C. is set as the lower limit. On the other hand, if the coiling temperature becomes too high, carbides having a particle size of 0.6 μm or less cannot be obtained after secondary annealing. The upper limit was 600 ° C.
[0042]
(2) Primary annealing conditions: 640-690 ° C., 20 hours or more
Similar to the manufacturing method of the first high-carbon steel sheet, primary annealing for the purpose of spheroidizing the carbide is performed after descaling such as pickling. If the primary annealing temperature is higher than 690 ° C., a carbide of 0.6 μm or less cannot be obtained even after the secondary annealing. On the other hand, when the primary annealing temperature is less than 640 ° C., carbides of 1.5 μm or more cannot be obtained even after the secondary annealing. For this reason, the primary annealing temperature was set to 640-690 ° C. Also, the annealing time was set to 20 hours or more in order to uniformly spheroidize.
[0043]
(3) Cold rolling rate: 50% or more
Similar to the method for producing the first high carbon steel sheet, a cold rolling rate of at least 50% or more is required in order to sufficiently reduce the in-plane anisotropy of the r value. In addition, although the upper limit of a cold rolling rate is not prescribed | regulated in particular, it is preferable that it is 80% or less from a viewpoint of keeping plate | board property favorable.
[0044]
(4) Secondary annealing conditions: 1024-0.6 × T₁≦ T₂≦ 1202-0.80 × T₁And 620 ° C. ≦ T₂≦ 680 ℃
The secondary annealing condition is an essential condition that should be appropriately controlled with respect to the primary annealing temperature in order to reduce the in-plane anisotropy of the r value. Therefore, the effects of primary annealing conditions and secondary annealing conditions on in-plane anisotropy were investigated. The survey results will be described below.
[0045]
After melting steel of C: 0.36%, Si: 0.20%, Mn: 0.75%, P: 0.011%, S: 0.002%, Al: 0.020% by mass% , Finishing temperature: 850 ° C., coiling temperature: 560 ° C., hot pickling, and after pickling, primary annealing is performed at 640-690 ° C. for 40 hours, cold rolling reduction is 60%, and secondary annealing is 610 The in-plane anisotropy was examined by a tensile test for the steel plate subjected to 40 hours at ˜690 ° C. The result is shown in FIG. FIG. 3 shows the primary annealing temperature T related to the in-plane anisotropy of the r value.₁And secondary annealing temperature T₂It is a figure which shows the relationship. As shown in FIG. 3, the secondary annealing temperature T₂Is (1024-0.6 × T₁) Or more, (1202-0.80 × T₁) Δ of r value in the following range_max(Δr in FIG. 3_maxIt is clear that the in-plane anisotropy is small. Therefore, the secondary annealing temperature is set to 1024−0.6 × T.₁≦ T₂≦ 1202-0.80 × T₁The range. In addition, Δ of the r value_maxIndicates the maximum difference in r values in the L, S, and C directions.
[0046]
Further, the particle size and particle size distribution of the carbide change depending on the secondary annealing temperature. That is, when the secondary annealing temperature is higher than 680 ° C., the carbide is coarsened, and a carbide of 0.6 μm or less cannot be obtained. On the other hand, when the temperature is lower than 620 ° C., carbides of 1.5 μm or more cannot be obtained. For this reason, the secondary annealing temperature T₂Was specified in the range of 620 ° C to 680 ° C. The annealing may be either continuous annealing or box annealing.
[0047]
Next, the second method will be described.
In the second method, the cast slab having the above component system is continuously cast or heated to a predetermined temperature after cooling, and then roughly rolled into a rough bar by a roughing mill, followed by continuous hot finish rolling. When finishing rolling with a mill, rough bars or rolled material is put into Ar between the entrance of the finishing mill or between the stands of the finishing mill.₃Inductive heating at a temperature above the transformation point, winding the steel sheet after hot finish rolling at a temperature of 500 to 650 ° C., then descaling the steel sheet after winding, followed by primary annealing at 630 to 700 ° C. for 20 hours or more Then, the annealed steel sheet is cold-rolled at a reduction rate of 50% or more, and then the following equation (2) is satisfied and secondary annealing is performed in a temperature range of 620 to 680 ° C.
1010-0.59 × T₁≦ T₂≦ 1210−0.80 × T₁    ... (2)
The reason for limitation will be described below.
[0048]
(1) Induction heating
Induction heat treatment makes the dispersion of cementite dispersion after secondary annealing smaller in the plate thickness direction by making the γ grain size and structure of the steel plate uniform in the plate thickness direction during hot rolling, and the secondary A texture in which in-plane anisotropy with respect to tensile properties becomes small after annealing is uniformly formed in the thickness direction. Specifically, after rough rolling, when finishing rolling with a hot finish rolling mill, rolling between rough bars on the entry side of the finishing mill before finishing rolling, or between stands of the finishing mill during finish rolling For materials, Ar₃Induction heating at a temperature equal to or higher than the transformation point is performed at least once. Heating temperature is Ar₃The reason why the temperature is equal to or higher than the transformation point is to make the γ grain size and the structure uniform. The heating time is preferably at least 3 seconds. Note that the heat treatment includes temperature increase and temperature decrease holding.
[0049]
(2) Hot coiling temperature: 520-600 ° C
As in the first method, when the coiling temperature is less than 520 ° C., carbides of 1.5 μm or more cannot be obtained after secondary annealing, and when the coiling temperature is 600 ° C. or more, carbides having a particle size of 0.6 μm or less are obtained after secondary annealing. Since it cannot be obtained, the coiling temperature is set to a range of 520 to 600 ° C.
[0050]
  (3) Primary annealing conditions:630~700℃, 20hr or more
  Although the primary annealing for the purpose of spheroidizing the carbide is performed on the hot-rolled sheet after descaling, the primary annealing temperature is the same as in the first method.700If it becomes higher than ° C., a carbide of 0.6 μm or less cannot be obtained even after secondary annealing,630If it is less than ℃, carbide of 1.5μm or more cannot be obtained even after secondary annealing.630~700The annealing time is 20 hours or more from the viewpoint of promoting spheroidization.
[0051]
(4) Cold rolling rate: 50% or more
As in the case of the first method, the cold rolling rate is set to 50% or more in order to sufficiently reduce the in-plane anisotropy of the r value. Moreover, it is preferable that it is 80% or less from a viewpoint of maintaining plate | board property favorable like the 1st method.
[0052]
(5) Secondary annealing conditions: 1010-0.59 × T₁≦ T₂≦ 1210−0.80 × T₁And 620 ° C. ≦ T₂≦ 680 ℃
Similar to the first method, the secondary annealing condition is an essential requirement that should be appropriately controlled with respect to the primary annealing temperature in order to reduce the in-plane anisotropy of the r value. Therefore, the effects of primary annealing conditions and secondary annealing conditions on in-plane anisotropy were investigated. The survey results will be described below.
[0053]
After melting steel of C: 0.36%, Si: 0.20%, Mn: 0.75%, P: 0.011%, S: 0.002%, Al: 0.020% by mass% Before finishing rolling the slab, the rough bar is subjected to heat treatment at 1010 ° C. for 15 seconds by induction heating, finish rolling at a finishing temperature of 850 ° C., and after finishing rolling, winding at a winding temperature of 560 ° C. After washing, steel sheet subjected to primary annealing at 640 to 700 ° C. for 40 hr, cold rolling reduction ratio of 60%, and secondary annealing at 610 to 690 ° C. for 40 hr was measured for in-plane anisotropy in a tensile test. The integrated reflection intensity of the surface parallel to the rolling surface at each position of the steel sheet surface, the thickness 1/4 and the thickness 1/2 was examined by X-ray diffraction. Table 1 shows the measurement results of the integrated reflection intensity in the thickness direction. By performing induction heating of the coarse bar, the maximum difference in (222) integrated reflection intensity is reduced, and the structure is formed to be uniform in the plate thickness direction. FIG. 4 shows the primary annealing temperature T related to the in-plane anisotropy of the r value when the rough bar is induction-heated according to the present method.₁And secondary annealing temperature T₂Shows the relationship. When induction heating is not performed according to the first method, as shown in FIG. 3, the secondary annealing temperature is (1024−0.6 × T₁) And (1202-0.80 × T₁) Δ of r value within the following range_maxIs less than 0.2, but by performing induction heating of the coarse bar, the secondary annealing temperature T₂Is (1010-0.59 × T₁) And (1210-0.80 × T₁) Expands to the following range and r value Δ_max(In FIG. 4, Δr_maxAs shown. ) Decreased from less than 0.2 to less than 0.15, and it became clear that the in-plane anisotropy was further reduced over a wider range. For this reason, in the second method, the secondary annealing temperature T₂1010-0.59 × T₁≦ T₂≦ 1210−0.80 × T₁And in a wider range than the first method.
[0054]
[Table 1]

[0055]
In addition, the particle size and particle size distribution of the carbide change depending on the secondary annealing temperature, as in the case of the first method. In order to precipitate a carbide of 0.6 μm or less and a carbide of 1.5 μm or more, Secondary annealing temperature T₂Was specified in the range of 620 ° C to 680 ° C. The annealing may be either continuous annealing or box annealing.
[0056]
In the present invention, when manufacturing a steel sheet, as a method of rolling after heating the slab, a method of performing a heat treatment for a short time after continuous casting, or a method of omitting this heating step and immediately rolling Any of these methods may be adopted, but the method of reheating the slab without cooling to room temperature is more preferable from the viewpoint of energy saving. Further, during hot rolling, there is no problem even if heating with a bar heater or the like for the purpose of soaking. Heating by a bar heater can be effectively used for a continuous hot rolling process using a coil box or the like. At this time, the heating of the rough rolling bar may be performed before or after the coil box or between or after the roughing mill, in addition to the above. Even if the rough rolling bar is heated before and after the welding machine after the coil box, the effect of the present invention is sufficiently exhibited. Furthermore, in order to improve slidability with respect to the surface of the steel plate thus manufactured, a phosphating treatment may be performed after galvanization. Zinc plating can be performed by electrogalvanizing or hot dip galvanizing.
[0057]
【Example】
Hereinafter, specific examples of the present invention will be described in comparison with comparative examples.
Example 1
In this embodiment, an example of the first high carbon steel sheet and the manufacturing method thereof will be described.
Component system equivalent to S35C of JIS G4051 (mass%, C: 0.35%, Si: 0.20%, Mn: 0.76%, P: 0.016%, S: 0.003%, Al: 0.026%) slab was manufactured by continuous casting, this slab was heated to 1100 ° C., then hot-rolled and cooled, and then wound up under the conditions shown in Table 2, primary annealing, cold rolling, two Subsequent annealing was performed sequentially, and then 1.5% temper rolling was performed to produce a steel plate having a thickness of 1.0 mm. Sample No. H is a conventional material.
[0058]
[Table 2]

[0059]
For these samples, carbide particle size measurement and particle size distribution measurement, tensile test, quenching test, and prior austenite particle size measurement after quenching were performed as follows. The results are shown in Table 3.
[0060]
(A) Carbide particle size measurement and particle size distribution measurement
After polishing and corrosion of the plate thickness section of the sample, the microstructure was photographed with a scanning electron microscope, 2500 μm²From this range, the particle size and particle size distribution of the carbide were measured.
[0061]
(B) Tensile strength
JIS No. 5 specimens were sampled along the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction) with respect to the rolling direction, and subjected to a tensile test at a tensile speed of 10 mm / min. Directional tensile properties were measured and evaluated for in-plane anisotropy. In addition, Δ described in each column of yield strength, tensile strength and total elongation in Table 3_maxIndicates the maximum disparity in the L, S, and C directions of the respective tensile property values. Further, Δr described in the column of r value in Table 3 is a value defined by Δr = (r0 + r90−2 × r45) / 4. Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction), respectively, with respect to the rolling direction.
[0062]
(C) Quenching test
The steel sheet was cut into a size of 50 × 100 mm, heated to 820 ° C. in a heating furnace, and kept in oil at about 20 ° C. after holding for 10 seconds. The hardness on the surface of the test piece after quenching was measured at 10 points on the Rockwell C scale (HRC) to evaluate the hardenability. Evaluation was performed by average hardness. A hardness (HRC) of 50 or more was considered acceptable.
[0063]
(D) Measurement of prior austenite particle size
After polishing and corrosion of the plate thickness section of the sample after quenching, the microstructure was photographed with an optical microscope, and the prior austenite grain size number was measured in accordance with JISG0551.
[0064]
[Table 3]

[0065]
As shown in Table 3, No. 1 is an example of the present invention. A-No. Since C had an appropriate particle size and particle size distribution of carbide, it was confirmed that the hardness after quenching and the value of the prior austenite particle size were good, and the hardenability and toughness were excellent. In addition, these are Δ of yield strength and tensile strength._maxIs 10 MPa or less, elongation Δ_maxIs 1.5% or less and the r value Δr is more than −0.15 to less than 0.15, and it was confirmed that the anisotropy of the in-plane tensile properties was extremely small.
[0066]
On the other hand, in the comparative example, Δ for any of the tensile properties_maxOr Δr was large, and it was confirmed that the anisotropy of the in-plane tensile properties was inferior. For example, when the coiling temperature is low (No. D), the elongation Δ_max1.7, and the r value Δr is as large as 0.16, and since there are few carbides of 1.5 μm or more, the prior austenite grain size becomes coarse and the toughness is impaired. Further, when the primary annealing temperature was high (No. E), the r value Δr was as large as 0.18, and the coarse carbides increased, so that the fine carbides decreased and the hardenability was significantly lowered. Furthermore, when the cold rolling reduction is as low as 40% (No. F), the yield strength Δ_max11 and Δ of tensile strength_maxIs 14, Δ of elongation_maxIs 1.7, the r value Δr is as large as 0.20, and the secondary annealing temperature is high (No. G), the coarse carbides increase, and the hardness after quenching decreases significantly. The r value Δr was 0.23, and the in-plane anisotropy was large. In addition, the conventional material No. H is the yield strength Δ_max17 and Δ of tensile strength_maxIs 15 and elongation Δ_max1.9 and r value of Δr were as high as 0.16, respectively, and the in-plane anisotropy was large.
(Example 2)
In this embodiment, an example of the first manufacturing method of the second high carbon steel sheet will be described.
Component system equivalent to JIS G4051 S35C (by mass, C: 0.36%, Si: 0.20%, Mn: 0.75%, P: 0.011%, S: 0.002%, Al: 0 .020%) slab was manufactured by continuous casting, and the slab was heated to 1100 ° C., and then subjected to hot rolling, primary annealing, cold rolling, and secondary annealing sequentially under the conditions shown in Table 4, followed by 1 19% steel sheets with a thickness of 2.5 mm were prepared by temper rolling of 0.5%.
[0067]
[Table 4]

[0068]
These samples were subjected to carbide particle size measurement and particle size distribution measurement, tensile test, quenching test, and prior austenite particle size measurement after quenching in the same manner as in Example 1. The results are shown in Table 5. Sample No. 19 is a conventional material.
[0069]
[Table 5]

[0070]
As shown in Table 5, examples of the present invention are No. 1-No. In No. 7, since the particle size and particle size distribution of the carbide are appropriate, the hardness after quenching and the value of the prior austenite particle size are good, and it was confirmed that the hardenability and toughness are excellent. In addition, these are Δ of yield strength and tensile strength._maxIs 10 MPa or less, elongation Δ_maxIs 1.5% or less, r value Δ_maxIs less than 0.2, and it was confirmed that the anisotropy of the tensile properties was extremely small.
[0071]
On the other hand, in the comparative example, Δ_maxIs large, inferior in in-plane anisotropy, or inferior in hardenability or toughness. For example, when the primary annealing temperature is high (No. 11), the r value Δ_maxWhen the cold rolling rate is as low as 30% (No. 13), the yield strength, tensile strength, and r value Δ_maxRespectively increased to 18, 13 and 0.38, and all had large in-plane anisotropy. Sample No. No. 16 has a secondary annealing temperature that is too high, so that the carbide is not sufficiently dissolved and the hardness after quenching is as low as 43. In No. 17, the secondary annealing temperature is too low, so the amount of carbide having a particle size of 0.6 μm or less increases, the prior austenite particle size becomes coarse, and the toughness is impaired. Further, in the conventional material (No. 19) shown for comparison, the r value Δ_maxWas as high as 0.42, and the in-plane anisotropy was large.
[0072]
(Example 3)
This example also shows an example of the first manufacturing method of the second high carbon steel sheet.
Component system equivalent to JIS G4802 S65C-CSP (by mass, C: 0.65%, Si: 0.19%, Mn: 0.73%, P: 0.011%, S: 0.002%, Al : 0.020%) slab was manufactured by continuous casting, this slab was heated to 1100 ° C., and then hot rolling, primary annealing, cold rolling, and secondary annealing were sequentially performed under the conditions shown in Table 6. The temper rolling of 1.5% was performed, and 19 types of steel plates with a thickness of 2.5 mm were produced.
[0073]
[Table 6]

[0074]
These samples were subjected to carbide particle size measurement, particle size distribution measurement, tensile test, quenching test, and prior austenite particle size measurement after quenching in the same manner as in Example 1. The results are shown in Table 7. Sample No. 38 is a conventional material.
[0075]
[Table 7]

[0076]
As shown in Table 7, No. 20-No. Since No. 26 has an appropriate particle size and particle size distribution of carbide, the hardness after quenching and the value of prior austenite particle size are good, and it was confirmed that the hardenability and toughness are excellent. In addition, these are Δ of yield strength and tensile strength._maxIs 15 MPa or less, elongation Δ_maxIs 1.5% or less, r value Δ_maxWas less than 0.2, and it was confirmed that the in-plane tensile property anisotropy was extremely small.
[0077]
On the other hand, in the comparative example, Δ_maxIs large, inferior in in-plane anisotropy, or inferior in hardenability or toughness. For example, when the primary annealing temperature is high (No. 30), the r value Δ_maxIs 0.26 and the cold rolling rate is as low as 30% (No. 32), the yield strength, tensile strength and r value Δ_maxWere increased to 20, 17 and 0.39, respectively, and all had large in-plane anisotropy. Sample No. No. 35 has a secondary annealing temperature that is too high, so that the carbide is not sufficiently dissolved and the hardness after quenching is as low as 51. Since the secondary annealing temperature of 36 is too low, the amount of carbide having a particle size of 0.6 μm or less is increased, and the prior austenite particle size is coarsened and the toughness is impaired. In addition, the conventional material No. shown for comparison. 38 is also the Δ of the r value_maxWas as high as 0.46, and the in-plane anisotropy was large.
[0078]
Example 4
In this embodiment, an example of the second manufacturing method of the second high carbon steel sheet will be described.
Component system equivalent to JIS G4051 S35C (by mass, C: 0.36%, Si: 0.20%, Mn: 0.75%, P: 0.011%, S: 0.002%, Al: 0 .020%) slab was manufactured by continuous casting, and this slab was heated to 1100 ° C., and then subjected to hot rolling, primary annealing, cold rolling, and secondary annealing sequentially under the conditions shown in Table 8. A temper rolling of 5% was applied to produce 26 types of steel plates with a thickness of 2.5 mm.
[0079]
[Table 8]

[0080]
These samples were subjected to carbide particle size measurement and particle size distribution measurement, tensile test, quenching test, and prior austenite particle size measurement after quenching in the same manner as in Example 1. The results are shown in Table 9. Sample No. 64 is a conventional material.
[0081]
[Table 9]

[0082]
As shown in Table 9, No. 1 as an example of the present invention. 39-No. No. 52 had an appropriate particle size and particle size distribution of the carbide, so that the hardness after quenching and the prior austenite particle size were good, and it was confirmed that the hardenability and toughness were excellent. In addition, these are Δ of yield strength and tensile strength._maxIs 10 MPa or less, elongation Δ_maxIs 1.5% or less, r value Δ_maxWas less than 0.2, and it was confirmed that the in-plane tensile property anisotropy was extremely small. Furthermore, it was confirmed that the method of performing induction heating before rough rolling is more preferable from the viewpoint of not only reducing the anisotropy of tensile properties but also improving the uniformity of the structure in the thickness direction.
[0083]
On the other hand, in the comparative example, Δ_maxIs large, inferior in in-plane anisotropy, or inferior in hardenability or toughness. For example, when the primary annealing temperature is high (No. 56), the r value Δ_maxIs 0.30 and the cold rolling rate is as low as 30% (No. 58), the yield strength, tensile strength and r value Δ_maxRespectively increased to 18, 13 and 0.38, and it was confirmed that the in-plane anisotropy was large. Sample No. No. 61 has a secondary annealing temperature that is too high, so that the carbide is not sufficiently dissolved and the hardness after quenching is as low as 44. Since the secondary annealing temperature of 62 is too low, the amount of carbide having a particle size of 0.6 μm or less is increased, and the prior austenite particle size is coarsened and the toughness is impaired. In addition, the conventional material No. shown for comparison. 64, the r value Δ_maxWas as high as 0.42, and it was confirmed that the in-plane anisotropy was large.
[0084]
Example 4
This example also shows an example of the second manufacturing method of the second high carbon steel sheet.
Component system equivalent to JIS G4802 S65C-CSP (by mass, C: 0.65%, Si: 0.19%, Mn: 0.73%, P: 0.011%, S: 0.002%, Al : 0.020%) slab was manufactured by continuous casting, this slab was heated to 1100 ° C., and then hot rolling, primary annealing, cold rolling, and secondary annealing were sequentially performed under the conditions shown in Table 10. A temper rolling of 1.5% was applied to produce 26 types of steel plates with a thickness of 2.5 mm.
[0085]
[Table 10]

[0086]
These samples were subjected to carbide particle size measurement, particle size distribution measurement, tensile test, quenching test, and prior austenite particle size measurement after quenching in the same manner as in Example 1. The results are shown in Table 11. Sample No. 90 is a conventional material.
[0087]
[Table 11]

[0088]
As shown in Table 11, No. 1 as an example of the present invention. 65-No. No. 78 had an appropriate particle size and particle size distribution of the carbide, so that the hardness after quenching and the prior austenite particle size were good, and it was confirmed that the hardenability and toughness were excellent. In addition, these are Δ of yield strength and tensile strength._maxIs 15 MPa or less, elongation Δ_maxIs 1.5% or less, r value Δ_maxWas less than 0.2, and it was confirmed that the in-plane tensile property anisotropy was extremely small. Furthermore, it was confirmed that the method of performing induction heating before rough rolling is more preferable from the viewpoint of not only reducing the anisotropy of tensile properties but also improving the uniformity of the structure in the thickness direction.
[0089]
On the other hand, in the comparative example, Δ_maxIs large, inferior in in-plane anisotropy, or inferior in hardenability or toughness. For example, when the primary annealing temperature is high (No. 82), the r value Δ_maxIs 0.27 and the cold rolling rate is as low as 30% (No. 84), the yield strength, tensile strength and r value Δ_maxWere increased to 20, 17 and 0.39, respectively, and it was confirmed that the in-plane anisotropy was large. Sample No. No. 87 has a secondary annealing temperature that is too high, so that the carbide is not sufficiently dissolved and the hardness after quenching is as low as 52. Since the secondary annealing temperature of 88 is too low, the amount of carbide having a particle size of 0.6 μm or less is increased, and the prior austenite particle size is coarsened and the toughness is impaired. In addition, the conventional material No. shown for comparison. At 90, the r value Δ_maxWas as high as 0.46, and it was confirmed that the in-plane anisotropy was large.
[0090]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a high-carbon steel sheet that is excellent in hardenability and toughness and has small in-plane anisotropy with respect to tensile properties that greatly affect the formability. Therefore, the high carbon steel plate obtained by the present invention can be used for gear parts and the like that require high dimensional accuracy. In addition, by applying the present invention, when manufacturing gear parts and the like, it can be manufactured by integral forming and quenching and tempering of steel plates, and can be manufactured at a lower cost than conventional casting and forging processes. Become.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the influence of carbide grain size before quenching on the hardness when oil quenching is performed on an S35C steel sheet after holding at 820 ° C. × 10 s.
FIG. 2 is a diagram for explaining the influence of the number of carbides having a grain size of not less than 1.5 μm before quenching on the prior austenite grain size when oil quenching is performed on an S35C steel plate after holding at 820 ° C. × 10 s.
FIG. 3 is a diagram showing the influence of the primary annealing temperature and the secondary annealing temperature on the in-plane anisotropy of the r value and the dispersion form of carbides in the first method for producing the second high carbon steel sheet.
FIG. 4 is a diagram showing the influence of the primary annealing temperature and the secondary annealing temperature on the in-plane anisotropy of the r value and the dispersion form of carbides in the second method for producing the second high carbon steel sheet.

Claims (5)

JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), JIS G 4802 (cold rolled steel strip for spring), a high carbon steel plate having a component system defined by:
Carbides having a particle size of 1.5 μm or more are present in 50 or more in 2500 μm ² , and carbides having a particle size of 0.6 μm or less account for 80% or more, and the in-plane anisotropy index Δr of r value exceeds −0.15. A high-carbon steel sheet for processing having low in-plane anisotropy and excellent hardenability and toughness, characterized by being less than ˜0.15.
However, (DELTA) r shows the value prescribed | regulated by (DELTA) r = (r0 + r90-2 * r45) / 4. Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction), respectively, with respect to the rolling direction. A method for producing a high-carbon steel sheet for processing having low in-plane anisotropy and excellent hardenability and toughness according to claim 1,
A steel plate after hot finish rolling having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring) is 520. Winding at a temperature of ~ 600 ° C,
Then, after descaling the steel sheet after winding, primary annealing is performed at 640 to 690 ° C. ( excluding 690 ° C.) for 20 hours or more,
Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
Then, the secondary annealing is performed in a temperature range of 620 to 680 ° C., and a method for producing a high-carbon steel sheet for processing having excellent in-plane anisotropy and low in-plane anisotropy. JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), JIS G 4802 (cold rolled steel strip for spring), a high carbon steel plate having a component system defined by:
And wherein the particle size 1.5μm or more carbide is present ² in 50 or more 2500 [mu] m, and the particle size 0.6μm or less of carbides account for 80% or more, further r value of delta _max is less than 0.2 A high-carbon steel sheet for processing that has excellent hardenability and toughness and small in-plane anisotropy.
However, (DELTA) _max shows the maximum difference of the value of 0 degree direction (L direction), 45 degree direction (S direction), and 90 degree direction (C direction) with respect to a rolling direction. A method for producing a high-carbon steel sheet for processing having excellent in-hardenability and toughness according to claim 3 and having a small in-plane anisotropy,
A steel plate after hot finish rolling having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring) is 520. Winding at a temperature of ~ 600 ° C,
Then, after descaling the steel sheet after winding, primary annealing is performed at 640 to 690 ° C. ( excluding 690 ° C.) for 20 hours or more,
Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
Thereafter, the high carbon steel sheet for processing having low in-plane anisotropy and excellent hardenability and toughness, characterized by satisfying the following formula (1) and performing secondary annealing in a temperature range of 620 to 680 ° C. Manufacturing method.
1024-0.6 × T ₁ ≦ T ₂ ≦ 1202-0.80 × T ₁ (1)
However, T ₁ : Primary annealing temperature (° C.), T ₂ : Secondary annealing temperature (° C.) A method for producing a high-carbon steel sheet for processing having excellent in-hardenability and toughness according to claim 3 and having a small in-plane anisotropy,
Cast slabs having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for springs) are continuously cast or cooled. After heating to a predetermined temperature after, rough rolling with a roughing mill to form a rough bar,
Subsequently, during finish rolling by a continuous hot finish rolling mill, the rough bar or the rolled material is induction-heated at a temperature equal to or higher than the Ar ₃ transformation point on the entrance side of the finish mill or between the stands of the finish mill,
The steel plate after hot finish rolling is wound at a temperature of 500 to 650 ° C.,
Next, after descaling the steel sheet after winding, primary annealing is performed at 630 to 700 ° C. for 20 hours or more,
Cold-roll the annealed steel sheet at a reduction rate of 50% or more,
Then, the following high-carbon steel sheet for processing with low in-plane anisotropy excellent in hardenability and toughness, characterized by satisfying the following formula (2) and performing secondary annealing in a temperature range of 620 to 680 ° C. Manufacturing method.
1010−0.59 × T ₁ ≦ T ₂ ≦ 1210−0.80 × T ₁ (2)
However, T ₁ : Primary annealing temperature (° C.), T ₂ : Secondary annealing temperature (° C.)

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