JP2004011017A - Hot rolled steel sheet for rotary ironing, method for producing the same and automobile parts - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、自動車、産業機械等の軸対称形状の部品に適用可能な回転しごき加工用熱延鋼板およびその製造方法に関する。
【０００２】
【従来の技術】
一般に、自動車等の駆動系部品の中で、クラッチ、ハブ、キャリア等の軸対称形状の部品は、極めて複雑な形状を有している。従来、これらの部品は、鋳造、鍛造、もしくはプレス等により成形した部品、又は棒鋼を切削加工した部品等を、個別成形して電子ビーム溶接で接合することにより製造されていた。そのため、部品点数および製造工程が多くなり、膨大な在庫管理コストおよび製造コストを要していた。
【０００３】
近年、このような軸対称形状の部品に対し、製造コストの低減を狙って、鋼板からの一体成形が行われるようになって来ている。特に、ドライブプレート一体型リングギア等、比較的簡単な形状の部品においては、プレス成形による製造が積極的に行われている。
【０００４】
例えば、特開平０９−１３７２４８号公報には、鋼板としての機械的性質の低下を招くことなく、摺動性を向上させた、成形性に優れる熱延鋼板とその製造方法が提案されている。これは、鋼板の組織が再結晶フェライト相であって、かつ鋼板表層部におけるフェライト相の平均結晶粒径を１０μｍ未満、鋼板内部のフェライト相の平均結晶粒径を１０μｍ以上とする。また、この熱延鋼板を、粗圧延で得られたシートバーを表面温度（Ａｒ３点＋５０〜２００℃）から（Ａｒ３点−２０〜３００℃）まで、０．１ 秒以内で強制冷却し、引き続き仕上げ圧延を５秒以内に開始し、圧延終了温度：Ａｒ３点〜（Ａｒ３点＋１００℃）の４５０〜６００℃で巻き取ることにより製造するというものである。
【０００５】
特開平０９−１２５１９５号公報には、低炭素鋼における加工性の優れた熱延鋼板とその製造方法が提案されている。これは、低炭素鋼をＡｒ３ 点以下７５０℃の温度域で仕上圧延を終了した後、６００〜７５０℃の温度域で巻き取り、中心層と表層における（２２２）面強度の比を２以内とすることを特徴とする加工性の優れた熱延鋼板とその製造方法というものである。
【０００６】
また、特開平０７−２４２９８８号公報には、平均ランクフォード値（平均ｒ値）が１．１以上で、各方向のｒ値の異方性を示すΔｒが０．１以下の深絞り性に優れた加工用熱延鋼板が提案されている。これは、３次元集合組織解析を行った場合、板厚中心部のＸ線相対強度の最大値が３以下であり、表層部において｛１１２｝〈１１１〉および｛１１０｝〈１００〉のＸ線相対強度が２以上であり両者の差が３以下であることを特徴とする深絞り性に優れ異方性の小さい加工用熱延鋼板というものである。
【０００７】
特開平０９−１７６７４２号公報には、熱延時に集合組織を制御して熱延鋼板の異方性ならびに強度−延性バランスを向上させる製造方法が提案されている。これは、スラブを熱延する際に、必要に応じ、粗圧延後、先行の粗圧延材に接合して、Ａｒ３変態点＋１００℃以下、Ａｒ３変態点以上の温度で合計圧下率が５０％以上の圧延を、潤滑を施して行うことを特徴とする成形性の面内異方性の小さい加工用熱延鋼板の製造方法というものである。
【０００８】
【発明が解決しようとする課題】
最近では、回転しごき加工技術の進歩により、従来は成形困難であった、板厚を部分的に厚く、又は薄くする成形、またそれらを複数施すような極めて複雑な部品に対して、一体成形化が可能となりつつある。このような加工においては、極めて加工度が高く、極限に近い変形能が要求される。また、軸対称の形状、即ち回転体の部品では、真円度等について高い寸法精度が要求される。
【０００９】
しかしながら、上記の従来技術はこれらの要求に対して答えることが困難である。特に、回転しごき加工のように強度の加工における局部延性が求められ、さらに、かじりを防止し、製品の真円度等の寸法精度の厳しい用途に対しては、十分満足できる従来技術はなかった。
【００１０】
例えば、特開平０９−１３７２４８号公報記載の技術は、プレス加工におけるプレス型と材料の摺動性の向上については記載されているが、しごき加工については記載されていない。
【００１１】
特開平０９−１２５１９５号公報記載の技術は、均一伸びの向上について記載されているが、そのためには熱延の仕上温度をＡｒ３以下とする必要がある。しかし、このような変態点以下の圧延は、強い集合組織を形成するため、面内異方性の増加が避けられないという問題がある。
【００１２】
特開平０７−２４２９８８号公報記載の技術は、３次元集合組織解析による個々の結晶方位の集積度について規定しているが、いずれも深絞り性（ｒ値）とその面内異方性に関するものであり、しごき加工については記載されていない。
【００１３】
特開平０９−１７６７４２号公報記載の技術は、熱延において潤滑を施す圧延を、合計圧下率が５０％以上となるよう行うというもので、このような潤滑圧延は、潤滑用の特別な設備を必要とし、また、操業上も潤滑条件の調整を必要とする。従って、通常の熱延の設備および操業では実施困難である。
【００１４】
本発明は以上の問題点を解決し、優れた回転しごき加工特性を有し、自動車、産業機械等の軸対称形状の部品の寸法精度を向上させることが可能な、回転しごき加工用熱延鋼板およびその製造方法を提供することを目的とする。
【００１５】
【課題を解決するための手段】
上記の課題は次の発明により解決される。その発明は、質量％で、Ｃ：０．０２〜０．１０％、Ｓｉ：１．０％以下、Ｍｎ：０．１〜２．５％、Ｐ：０．０５％以下、Ｓ：０．０１％以下、ｓｏｌ．Ａｌ：０．０１〜０．１０％、Ｎ：０．００６％以下で、残部が実質的に鉄からなり、ミクロ組織が、フェライト相と、パーライト、ベイナイト、およびマルテンサイトの内１種以上の第２相とからなり、フェライト相の平均粒径ｄ（μｍ）およびＣ量 ［Ｃ］（％）が下記の式を満たし、第２相の平均粒径が５μｍ以下、第２相の体積率が３〜３０％、かつｎ値の面内異方性Δｎが｜Δｎ｜≦０．０１５であることを特徴とする回転しごき加工用熱延鋼板である。
【００１６】
ｄ≦２１．５−１５０［Ｃ］ （１）
この発明は、ｎ値の面内異方性が小さい熱延鋼板を製造するため、特に化学成分および組織に着目して詳細な検討を行った結果なされた。検討の過程で、フェライト相と分散した第２相からなる組織とすることにより、分散した第２相がフェライト相の塑性変形に影響を及ぼし、加工硬化指数ｎ値の面内異方性｜Δｎ｜が低減されることを見出した。この知見に基づき、フェライト相および第２相の平均粒径および第２相体積率を規定することにより、優れた回転しごき加工特性、および優れた寸法精度を同時に達成することに成功した。
【００１７】
以下、発明の個々の限定理由について説明する。
【００１８】
Ｃ：０．０２〜０．１０％
Ｃは、パーライト、ベイナイト、およびマルテンサイトの内１種以上の第２相を形成し、しごき加工時の型への凝着（型かじり）を抑制するための重要な元素である。Ｃ量が０．０２％未満では、第２相の体積率が３％未満となり、上記の効果が得られない。一方、Ｃ量が０．１０％を超えると、第２相の体積率が３０％を超えるとともに、第２相が互いに連結して第２相の平均粒径を増加させる。そのため、しごき加工時に割れが生じやすくなり、加工性を損なう。従って、Ｃ量を０．０２〜０．１０％とする。
【００１９】
Ｓｉ： １．０％以下
Ｓｉは、フェライト相の生成を促進し、第２相の体積率を低減するとともに、第２相の平均粒径を減少させる。一方、Ｓｉ量が１．０％を超えると、過度の強度上昇により延性が劣化し、しごき加工性も劣化する。従って、Ｓｉ量を１．０％以下とする。
【００２０】
Ｍｎ： ０．１〜２．５％
Ｍｎは、熱延時の延性を阻害するＳをＭｎＳとして固定して、無害化する元素である。この効果は、Ｍｎ量が０．１％以下では得られない。一方、Ｍｎ量が２．５％を超えるような大量添加は、バンド組織を形成するとともに、強度の著しい上昇により延性が低下し、しごき加工性が劣化する。従って、Ｍｎ量は０．１〜２．５％とする。
【００２１】
Ｐ： ０．０５％以下
Ｐは、Ｓｉと同様に、フェライト相の生成を促進し、第２相の体積率を低減するとともに、第２相の平均粒径も減少させる元素である。しかし、Ｐ量が０．０５％を超えると、Ｐの偏析に起因したバンド組織が顕著となり、延性が低下するためしごき加工性が劣化する。従って、Ｐ量を０．０５％以下とする。
【００２２】
Ｓ： ０．０１％以下
Ｓは、微細なＭｎＳを析出することにより局部延性を低下させる。そのためＳ量が０．０１％を超えると、しごき加工性を大幅に劣化させる。従って、Ｓ量を０．０１％以下とする。
【００２３】
ｓｏｌ．Ａｌ： ０．０１〜０．１０％
Ａｌは脱酸剤として酸化物系の介在物を低減し、局部延性を向上させる重要な元素である。ｓｏｌ．Ａｌが０．０１％未満ではその効果が得られず、一方、０．１０％を超えると効果が飽和する。従って、ｓｏｌ．Ａｌ量を０．０１〜０．１０％の範囲内とする。
【００２４】
Ｎ： ０．００６％以下
Ｎは、不純物として含有され、ＡｌとＡｌ Ｎを形成して局部延性を低下させる。Ｎ量が０．００６％を超えると、Ａｌ Ｎの生成が顕著となり、しごき加工性を大幅に劣化させる。従って、Ｎ量を０．００６％以下とする。
【００２５】
なお、以上の説明において「残部が実質的に鉄」とは、発明の作用・効果を損なわない限り、不可避的不純物をはじめ、他の微量元素を含有するものが本発明の範囲に含まれることを意味する。
【００２６】
次に、ミクロ組織について説明する。
【００２７】
フェライト相の平均粒径ｄ： 式（１） ｄ≦２１．５−１５０［Ｃ］
フェライト相の平均粒径は、第２相の分散状況に大きく影響する。Ｃ量の増加に伴い、第２相の粒径および体積率も増加する。そのため、第２相同士の間隔が狭くなり、場合によっては相互に連結して第２相の粒径の増加を招く。そこで、Ｃ量の増加に伴い、第２相を均一微細に分散させるため、フェライト粒界の面積を増加させる必要がある。それは、第２相の生成サイトを増やすこと、即ちフェライト粒の細粒化により可能であり、検討の結果、フェライト相の平均粒径が満たすべき条件として、上記の不等式が得られた。従って、フェライト相の平均粒径ｄ（μｍ）とＣ量［Ｃ］（％）を上記式（１）を満たす範囲内とする。
【００２８】
第２相の平均粒径：５μｍ以下
第２相の平均粒径は、しごき加工の際のボイドの生成に大きく影響する。平均粒径が５μｍを超えると、第２相とフェライト相の界面における応力集中が著しくなり、しごき加工の際にボイドを生成し、割れの原因となる。従って、第２相の平均粒径を５μｍ以下とする。
【００２９】
第２相の体積率：３〜３０％
第２相は、しごき加工の際の型への凝着を抑制するという重要な役割を有するが、体積率が３％未満では、その効果が十分得られない。一方、第２相の体積率が３０％を超えると、第２相同士が連結して粒径が増加するため、しごき加工の際、ボイドが生成しやすくなる。また、分散した第２相についても相互の間隔が狭くなっており、生成したボイド同士が連結しやすくなるので、やはり割れの原因となる。従って、第２相の体積率を３〜３０％の範囲内とする。
【００３０】
加工硬化指数ｎ値の面内異方性については、次のようになる。
【００３１】
ｎ値の面内異方性Δｎ：｜Δｎ｜≦０．０１５
ｎ値の面内異方性Δｎの絶対値｜Δｎ｜を小さくすることにより、回転対称形状の部品を、周方向に均一に成形することができる。軸対称の部品では、高い真円度が要求される場合が多いが、しごき加工においては、加工硬化挙動の周方向での差異により加工量が変動するので、寸法精度が低下する。検討の結果、加工硬化指数の面内異方性の絶対値｜Δｎ｜が０．０１５以上となると、真円度の劣化が顕著となる。従って、｜Δｎ｜を０．０１５未満とする。
【００３２】
なお、ｎ値の面内異方性Δｎは次の式で表される。
【００３３】
Δｎ＝（ｎ０＋ｎ９０）−２ｎ４５ （２）
ここで、ｎ０、ｎ４５、ｎ９０は、圧延方向に対しそれぞれ０゜、４５°、９０°方向のｎ値を表す。また、各方向のｎ値は、測定歪み５％および１０％の２点法により測定すればよい。
【００３４】
上述の熱延鋼板を得ることが可能な製造方法の発明は、次のようになる。その発明は、上述の発明の化学成分からなる鋼を仕上圧延温度（Ａｒ３−１０℃）以上で熱間圧延後、２０℃／秒を超える冷却速度で６３０℃以下の温度まで一次冷却を行い、その後二次冷却を行い、６００℃以下で巻取ることにより、ミクロ組織を請求項１記載のミクロ組織に制御することを特徴とする回転しごき加工用熱延鋼板の製造方法である。
【００３５】
この発明は、上記の発明の熱延鋼板を得ることが可能な製造条件について検討した結果なされたものであり、以下、その詳細について説明する。
【００３６】
仕上圧延温度：（Ａｒ３−１０℃）以上
仕上圧延においては、仕上温度が低いほど圧延後のフェライト相の生成が促進され、第２相が細粒化する。しかし、仕上温度が（Ａｒ３−１０）℃未満に低下すると、圧延中にフェライト変態が進行する。そのため、フェライト相が加工組織となり、局部延性が低下するとともに、ｎ値の異方性が増加する。従って、仕上圧延温度を（Ａｒ３−１０℃）以上とする。
【００３７】
熱間圧延後の冷却速度：２０℃／秒超
熱間圧延後は、微細に分散した第２相を得るため、急速冷却を行う。冷却速度が２０℃／秒以下であると、オーステナイトの過冷度が小さいため、初析フェライトがＭｎおよびＰの偏析に対応して析出する。ＭｎおよびＰの偏析は圧延により層状となっており、第２相のパーライトも初析フェライトの間に層状に生成する。そのため、第２相の粒径が大幅に増加することになり、しごき加工の際は、フェライト界面のボイドの生成を助長し、しごき加工特性を著しく劣化させる。従って、熱間圧延後の冷却速度を２０℃／秒超とする。
【００３８】
また、熱間圧延後の冷却速度を１２０℃／秒以上とすることにより、フェライト粒がさらに微細化し、第２相もさらに微細に分散するので、極めて優れたしごき加工特性が得られる。なお、冷却速度の上限は特に規定しないが、工業的には２０００℃／秒程度が限度である。また、熱間圧延後の冷却を仕上げ圧延後０．１秒を超え１．０秒未満に開始することにより結晶粒が微細化するため、しごき加工特性の向上に効果的である。
【００３９】
一次冷却終了温度：６３０℃以下
一次冷却は巻取温度まで行ってもよいが、巻取温度制御のためには少し高めの温度で急冷を終了し、冷却速度の比較的遅い二次冷却を行うことができる。この一次冷却終了温度が６３０℃より高いと、その後の徐冷中に前述と同様、フェライト相と第２相パーライトが層状に生成し、しごき加工特性を著しく劣化させる。従って、一次冷却終了温度は６３０℃以下とする。なお、二次冷却は、巻取温度の制御が可能である限り、冷却速度については特に制限はなく、徐冷でも急冷でもよい。
【００４０】
巻取温度：６００℃以下
巻取温度は、第２相の種類および形態に大きく影響を与える。巻取温度が６００℃を超えると、第２相として生成するパーライトが、微細に分散せずに粗大化するため、しごき加工時にボイドを生成し、割れの原因となる。それと同時に、パーライトのラメラー間隔が広くなることも、ボイドの生成を助長し、割れの原因となる。一方、巻取温度を５００℃以下とすることにより、第２相の分散がさらに均一化し、極めて優れたしごき加工特性が得られる。従って、巻取温度を６００℃以下、好ましくは５００℃以下とする。なお、巻取温度の下限は、特に規定しないが、あまり低温になると熱延コイルの形状が劣化するので、２００℃以上とすることが好ましい。
【００４１】
また、これらの熱延鋼板からなる自動車用部品の発明は、上述の回転しごき加工用熱延鋼板により製造された軸対称形状を有する自動車用部品である。上述の発明に係る熱延鋼板またはその製造方法により製造された熱延鋼板は、優れた回転しごき加工性を有するため、自動車、産業機械等の軸対称形状の部品に適しており、とくにクラッチ、ハブ、キャリア等の自動車等の駆動系部品に好適である。
【００４２】
本発明に係る自動車部品は、前述の回転しごき加工用熱延鋼板により製造されるので、回転しごき加工による一体成形化が可能となることから、製造コストの低廉化が図られるとともに、高い真円度等の優れた寸法精度を有している。
【００４３】
【発明の実施の形態】
本発明に係る熱延鋼板の好ましい製造条件について説明する。
【００４４】
この発明に用いる鋼は、上述の成分および機械的特性とする他は、金属組織が前述の第２相体積率および平均粒径の分散状態となり得るものであればよい。その他の化学成分については、目的に応じて、通常添加される範囲内でＢ，Ｃｒ，Ｃｕ，Ｎｉ，Ｍｏ，Ｔｉ，Ｎｂ，Ｗ，Ｖ，Ｚｒ等の各種元素を添加してもよい。また、製造過程でＳｎ，Ｐｂ等の各種元素が不純物として混入する場合があるが、このような不純物も本発明の効果に特に影響を及ぼすものではない。なお、本発明の熱延鋼板の成分調製には、転炉あるいは電気炉のどちらでも使用可能である。
【００４５】
上記のように成分調製された鋼を、造塊−分塊圧延または連続鋳造によりスラブとする。このスラブについて熱間圧延を行うが、その際、スラブ加熱温度は、スケール発生による表面状態の劣化を避けるためには１２８０℃以下とすることが好ましい。また、熱間圧延時に粗圧延を省略して仕上圧延を行ってもよく、連続鋳造スラブをそのまま又は温度低下を抑制する目的で保熱しつつ圧延する直送圧延を行ってもよい。
【００４６】
なお、仕上圧延においては、仕上温度確保のため、熱間圧延中にバーヒータ等の加熱手段により圧延材の加熱を行ってもよい。さらに、第２相の球状化あるいは硬度低減のため、巻取後にコイルを徐冷カバー等の手段で保温してもよい。
【００４７】
熱間圧延後に必要に応じて焼鈍を行ってもよく、その場合、箱焼鈍、連続焼鈍のいずれでもよい。その後、必要に応じて調質圧延を行う。この調質圧延については焼入れには影響を及ぼさないことから、その条件に対して特に制限はない。
【００４８】
【実施例】
［実施例１］
表１に示す化学成分を有する鋼Ａ〜Ｇの連続鋳造スラブを１２５０℃に加熱し、仕上温度８７０℃で熱間圧延を終了し、３０℃／秒で即急冷後、一次冷却終了温度５８０℃、巻取温度：５５０℃として、その後、酸洗−調質圧延を施し６．０ｍｍの鋼板を製造した。
【００４９】
【表１】
これらの鋼板からサンプルを採取し、引張試験およびフェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）ならびに第２相の平均粒径（ｄｓ）の測定および回転しごき加工を実施した。それぞれの試験・測定の方法および条件について以下に示す。
【００５１】
▲１▼ 引張試験
ＪＩＳ５号サイズの引張試験片を圧延方向に対し９０°の方向から採取し、試験を行った。また、ｎ値の異方性（△ｎ）については、圧延方向に対し、０°、４５°、９０°の３方向から引張試験片を採取し、５％−１０％歪みでの２点法によるｎ値測定を行い調査した。
【００５２】
▲２▼ フェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）と平均粒径（ｄｓ）
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、０．０１ｍｍ２の範囲でフェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）および第２相の平均粒径（ｄｓ）の測定を行った。
【００５３】
▲２▼ 回転しごき加工
図１に示すように、ブランク径２００ｍｍφのサンプルを成形型に取り付け、主軸を回転させ、ロールを押し付けて成形型に沿って成形を行った。成形体の内径は、１００ｍｍφとした。初期板厚は６．０ｍｍであるが、しごき成形により４．０ｍｍまで減少する条件にて実施した。潤滑は、マシン油を用いた。ロール先端Ｒ＝２ｍｍとし、ロール送り速度＝２００ｍｍ／ｍｉｎとした。評価は、加工面の割れとかじりの有無、および寸法精度として真円度（７／１００以下を良好とする）で行った。
【００５４】
以上の測定結果より得られた、引張特性、フェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）、第２相の平均粒径（ｄｓ）および回転しごき加工性の結果を表２に示す。
【００５５】
【表２】
表２では、鋼板Ａ〜Ｃは発明例であり、本発明範囲である、フェライト平均粒径ｄｆ≦２１．５−１５０Ｃ、第２相の体積率が３％〜３０％、第２相の平均粒径５μｍ以下、△ｎ≦±０．０１５を満足する。鋼板Ｄ〜Ｇは比較例で、鋼板ＤはＣが低く、鋼ＥはＣとＳが高く第２相の体積率も３０％を超えている。鋼ＦはＳｉとＰが高く、鋼ＧはＭｎとＮが高く第２相平均粒径も５μｍを超えており、いずれも本発明の範囲外である。
【００５７】
この表２より、発明例Ａ〜Ｃでは、しごき加工試験において、いずれもクラック、かじり等の発生が無く、かつ、寸法精度にも優れ、良好な加工性が得られることが確認できた。また、発明例Ａ〜Ｃは、比較例Ｄ〜Ｇに比べて同じ強度レベルの場合、局部伸び（Ｌ．ＥＬ）において約５％向上しており、優れた極限変形能を有することが確認された。
【００５８】
［実施例２］
前記表１に示す鋼Ａ，Ｃの連続鋳造スラブを１２５０℃に加熱し、表３に示す条件にて板厚６．０ｍｍの熱延鋼板とし、その後、酸洗−調質圧延を施した。
【００５９】
【表３】
これらの鋼板からサンプルを採取し、引張試験およびフェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）ならびに第２相の平均粒径（ｄｓ）の測定および回転しごき加工を実施した。それぞれの試験・測定の方法および条件について以下に示す。
【００６１】
▲１▼ 引張試験
ＪＩＳ５号サイズの引張試験片を圧延方向に対し９０°の方向から採取し、試験を行った。また、ｎ値の異方性（△ｎ）については、圧延方向に対し、０°、４５°、９０°の３方向から引張試験片を採取し、５％−１０％歪みでのｎ値測定を行い調査した。
【００６２】
▲２▼ フェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）および第２相の平均粒径（ｄｓ）
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、０．０１ｍｍ２の範囲でフェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）および第２相の平均粒径（ｄｓ）の測定を行った。
【００６３】
▲２▼ 回転しごき加工
図１に示すように、ブランク径２００ｍｍφのサンプルを成形型に取り付け、主軸を回転させ、ロールを押し付けて成形型に沿って成形を行った。成形体の内径は、１００ｍｍφとした。初期板厚は６．０ｍｍであるが、しごき成形により４．０ｍｍまで減少する条件にて実施した。潤滑は、マシン油を用いた。ロール先端Ｒ＝２とし、ロール送り速度は、１）通常：２００ｍｍ／ｍｉｎ、２）高速：４００ｍｍ／ｍｉｎの２条件とした。評価は、加工面の割れとかじりの有無、および寸法精度として真円度（７／１００以下）で行った。
【００６４】
以上の測定結果より得られた、引張特性、△ｎ値、フェライト平均粒径（ｄｆ）、第２相体積率（Ｖｆ）、第２相の平均粒径（ｄｓ）および回転しごき加工性の結果を表３に併せて示す。
【００６５】
表３より、Ｎｏ．１，２，５，６は本発明範囲内で、フェライト平均粒径がｄｆ≦２１．５−１５０Ｃを満足し、第２相の体積率が３％〜３０％で、第２相の平均粒径が５μｍ以下、△ｎ≦±０．０１５の発明例であり、良好なしごき加工性および優れた寸法精度が得られることが確認された。
【００６６】
一方、Ｎｏ．３，４，７，８は比較例で、Ｎｏ．３は局部伸び（Ｌ．ＥＬ）が低く、フェライト平均粒径が大きいため、しごき加工表面で割れが発生した。また、△ｎが大きく、真円度が劣り、寸法精度不良となった。Ｎｏ．４は、フェライト平均粒径および第２相粒径が大きくなり、しごき加工表面で割れが発生した。Ｎｏ．７は、局部伸び（Ｌ．ＥＬ）が低く、フェライト平均粒径および第２相の平均粒径が大きくなり、しごき加工表面で割れが発生した。また、Ｎｏ．７は、△ｎが大きく、真円度が劣り、寸法精度不良となった。Ｎｏ．８は、局部伸び（Ｌ．ＥＬ）が低く、フェライト平均粒径が大きく、また、第２相の体積率が３０％を超えると同時に第２相の平均粒径が５μｍを超えている。そのため、しごき加工面から割れが発生した。
【００６７】
【発明の効果】
この発明は、しごき加工性および加工後の寸法精度の向上を図るに当たって、化学成分の制御および製造条件の制御により、フェライト平均粒径、第２相の体積率、第２相の平均粒径を制御することで、強加工時のボイドの発生を抑制し、また、ｎ値の異方性を低減することで、周方向での加工の変動が抑制することができる。その結果、極めて優れた回転しごき加工性と優れた寸法精度を有する熱延鋼板の提供が可能となる。このような熱延鋼板を用いることにより、キャリアやハブに代表される軸対称回転体の複雑形状部品を一体成形することができ、その結果、製造工程を省略して低コストで部品等を製造することが可能となる。
【図面の簡単な説明】
【図１】回転しごき加工の例を示す図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot-rolled steel sheet for rotary ironing that can be applied to axially symmetric parts such as automobiles and industrial machines, and a method of manufacturing the same.
[0002]
[Prior art]
2. Description of the Related Art Generally, among drive system components such as automobiles, axially symmetric components such as clutches, hubs, and carriers have extremely complicated shapes. Conventionally, these parts have been manufactured by individually forming parts formed by casting, forging, pressing, or the like, or parts obtained by cutting steel bars, and joining them by electron beam welding. Therefore, the number of parts and the number of manufacturing steps are increased, and enormous inventory management costs and manufacturing costs are required.
[0003]
In recent years, such axially symmetric parts have been integrally formed from steel plates with the aim of reducing manufacturing costs. In particular, for parts having a relatively simple shape such as a ring gear integrated with a drive plate, production by press molding is actively performed.
[0004]
For example, Japanese Unexamined Patent Publication No. 09-137248 proposes a hot-rolled steel sheet having improved formability and improved formability without deteriorating the mechanical properties of the steel sheet, and a method for producing the same. This means that the structure of the steel sheet is a recrystallized ferrite phase, the average crystal grain size of the ferrite phase in the surface layer portion of the steel sheet is less than 10 μm, and the average crystal grain size of the ferrite phase inside the steel sheet is 10 μm or more. The sheet bar obtained by the rough rolling of the hot-rolled steel sheet is forcibly cooled within 0.1 second from the surface temperature (Ar 3 points +50 to 200 ° C.) to (Ar 3 points −20 to 300 ° C.). Then, finish rolling is started within 5 seconds, and rolling is completed at 450 to 600 ° C. at a rolling end temperature of Ar 3 points to (Ar 3 points + 100 ° C.).
[0005]
Japanese Patent Application Laid-Open No. 09-125195 proposes a hot-rolled steel sheet having excellent workability in a low-carbon steel and a method for producing the same. This means that after finishing the low-carbon steel in the temperature range of 750 ° C. below the Ar 3 point, it is wound up in the temperature range of 600 to 750 ° C. and the ratio of the (222) plane strength between the center layer and the surface layer is within 2 A hot-rolled steel sheet having excellent workability and a method for producing the same.
[0006]
JP-A-07-242988 discloses a deep drawability in which the average Rankford value (average r value) is 1.1 or more, and Δr indicating the anisotropy of the r value in each direction is 0.1 or less. Excellent hot-rolled steel sheets for processing have been proposed. This is because, when a three-dimensional texture analysis is performed, the maximum value of the X-ray relative intensity at the center of the sheet thickness is 3 or less, and the X-rays of {112} <111> and {110} <100> A hot-rolled steel sheet for processing having excellent deep drawability and low anisotropy, characterized in that the relative strength is 2 or more and the difference between them is 3 or less.
[0007]
Japanese Patent Application Laid-Open No. 09-176742 proposes a manufacturing method for controlling the texture during hot rolling to improve the anisotropy and the strength-ductility balance of the hot-rolled steel sheet. This is because when the slab is hot-rolled, if necessary, after the rough rolling, it is joined to the preceding rough rolled material, and the total draft is 50 at the Ar 3 transformation point + 100 ° C. or lower and the Ar 3 transformation point or higher. % Is a method for producing a hot-rolled steel sheet for processing having a small in-plane anisotropy of formability, characterized in that rolling at a ratio of at least% is performed with lubrication.
[0008]
[Problems to be solved by the invention]
In recent years, due to the advancement of rotary ironing technology, molding has been difficult to form in the past. Is becoming possible. In such processing, the degree of processing is extremely high and deformability close to the limit is required. Also, in the case of an axially symmetric shape, that is, a rotating body part, high dimensional accuracy is required for roundness and the like.
[0009]
However, it is difficult for the above-mentioned prior art to respond to these demands. In particular, there is no conventional technology that is sufficiently satisfactory for applications that require local ductility in high-strength processing such as rotary ironing, prevent galling, and have severe dimensional accuracy such as roundness of products. .
[0010]
For example, the technology described in Japanese Patent Application Laid-Open No. 09-137248 describes improvement of the slidability between a press die and a material in press working, but does not describe ironing.
[0011]
The technique described in Japanese Patent Application Laid-Open No. 09-125195 describes improvement of uniform elongation. For that purpose, the finishing temperature of hot rolling must be Ar 3 or less. However, rolling at a temperature lower than the transformation point has a problem that an in-plane anisotropy cannot be avoided because a strong texture is formed.
[0012]
The technique described in Japanese Patent Application Laid-Open No. 07-242988 specifies the degree of integration of individual crystal orientations by three-dimensional texture analysis, but all of them relate to deep drawability (r value) and its in-plane anisotropy. No ironing process is described.
[0013]
Japanese Patent Application Laid-Open No. 09-176742 discloses a technique in which rolling for lubricating in hot rolling is performed so that the total draft becomes 50% or more. Such lubricating rolling requires special equipment for lubrication. In addition, lubrication conditions must be adjusted during operation. Therefore, it is difficult to implement with ordinary hot rolling equipment and operation.
[0014]
The present invention solves the above problems, has excellent rotary ironing properties, and can improve the dimensional accuracy of axially symmetric parts such as automobiles and industrial machines, and is capable of improving the dimensional accuracy of rotary ironing hot rolled steel sheets. And a method for producing the same.
[0015]
[Means for Solving the Problems]
The above problem is solved by the following invention. In the invention, C: 0.02 to 0.10%, Si: 1.0% or less, Mn: 0.1 to 2.5%, P: 0.05% or less, S: 0. 01% or less, sol. Al: 0.01 to 0.10%, N: 0.006% or less, the balance substantially consisting of iron, and the microstructure is at least one of ferrite phase, pearlite, bainite, and martensite. The ferrite phase has an average particle diameter d (μm) and a C content [C] (%) satisfying the following equation, the average particle diameter of the second phase is 5 μm or less, and the volume fraction of the second phase. Is 3 to 30%, and the in-plane anisotropy Δn of the n value is | Δn | ≦ 0.015.
[0016]
d ≦ 21.5-150 [C] (1)
The present invention has been made as a result of a detailed study focusing on a chemical composition and a structure in order to produce a hot-rolled steel sheet having a small n-value in-plane anisotropy. In the course of the study, by forming a structure composed of a ferrite phase and a dispersed second phase, the dispersed second phase affects the plastic deformation of the ferrite phase, and the in-plane anisotropy | Δn of the work hardening index n value. | Was reduced. Based on this finding, by defining the average grain size and the volume ratio of the second phase of the ferrite phase and the second phase, it was possible to simultaneously achieve excellent rotary ironing properties and excellent dimensional accuracy.
[0017]
Hereinafter, individual reasons for limitation of the invention will be described.
[0018]
C: 0.02 to 0.10%
C is an important element for forming one or more second phases out of pearlite, bainite, and martensite, and for suppressing adhesion to a mold (mold seizure) during ironing. When the amount of C is less than 0.02%, the volume ratio of the second phase is less than 3%, and the above effects cannot be obtained. On the other hand, when the C content exceeds 0.10%, the volume fraction of the second phase exceeds 30%, and the second phases are connected to each other to increase the average particle size of the second phase. For this reason, cracks are likely to occur during ironing, thereby impairing workability. Therefore, the C content is set to 0.02 to 0.10%.
[0019]
Si: 1.0% or less Si promotes the formation of a ferrite phase, reduces the volume ratio of the second phase, and reduces the average particle size of the second phase. On the other hand, when the amount of Si exceeds 1.0%, ductility is deteriorated due to an excessive increase in strength, and ironing workability is also deteriorated. Therefore, the amount of Si is set to 1.0% or less.
[0020]
Mn: 0.1-2.5%
Mn is an element that fixes S, which inhibits ductility during hot rolling, as MnS and renders it harmless. This effect cannot be obtained if the Mn content is 0.1% or less. On the other hand, when a large amount is added such that the Mn content exceeds 2.5%, a band structure is formed and ductility is reduced due to a remarkable increase in strength, and ironing workability is deteriorated. Therefore, the amount of Mn is set to 0.1 to 2.5%.
[0021]
P: 0.05% or less P is an element that promotes the formation of a ferrite phase, reduces the volume fraction of the second phase, and also reduces the average grain size of the second phase, like Si. However, when the P content exceeds 0.05%, the band structure caused by the segregation of P becomes remarkable, and the ductility is reduced, so that the ironing workability is deteriorated. Therefore, the P content is set to 0.05% or less.
[0022]
S: 0.01% or less S lowers local ductility by precipitating fine MnS. Therefore, when the amount of S exceeds 0.01%, ironing workability is significantly deteriorated. Therefore, the S content is set to 0.01% or less.
[0023]
sol. Al: 0.01 to 0.10%
Al is an important element that reduces oxide inclusions as a deoxidizing agent and improves local ductility. sol. If Al is less than 0.01%, the effect cannot be obtained, while if Al exceeds 0.10%, the effect is saturated. Therefore, sol. The Al content is in the range of 0.01 to 0.10%.
[0024]
N: 0.006% or less N is contained as an impurity and forms Al and AlN to lower the local ductility. If the amount of N exceeds 0.006%, generation of AlN becomes remarkable, and ironing workability is significantly deteriorated. Therefore, the N content is set to 0.006% or less.
[0025]
In the above description, "the balance is substantially iron" means that those containing other trace elements, including unavoidable impurities, are included in the scope of the present invention, as long as the functions and effects of the invention are not impaired. Means
[0026]
Next, the microstructure will be described.
[0027]
Average particle size d of ferrite phase: Equation (1) d ≦ 21.5-150 [C]
The average particle size of the ferrite phase greatly affects the dispersion state of the second phase. As the amount of C increases, the particle size and volume fraction of the second phase also increase. For this reason, the interval between the second phases becomes narrower, and in some cases, they are connected to each other, causing an increase in the particle size of the second phase. Therefore, in order to uniformly and finely disperse the second phase with an increase in the amount of C, it is necessary to increase the area of the ferrite grain boundary. This can be achieved by increasing the number of sites for forming the second phase, that is, by making the ferrite grains finer. As a result of the study, the above inequality was obtained as a condition that the average grain size of the ferrite phase should satisfy. Therefore, the average particle diameter d (μm) and the C content [C] (%) of the ferrite phase are set to be within the range satisfying the above-described formula (1).
[0028]
Average particle size of the second phase: 5 μm or less The average particle size of the second phase greatly affects the generation of voids during ironing. If the average particle size exceeds 5 μm, stress concentration at the interface between the second phase and the ferrite phase becomes remarkable, and voids are generated during ironing, which causes cracking. Therefore, the average particle size of the second phase is set to 5 μm or less.
[0029]
Volume ratio of the second phase: 3 to 30%
The second phase has an important role of suppressing adhesion to the mold during ironing, but if the volume ratio is less than 3%, the effect cannot be sufficiently obtained. On the other hand, when the volume ratio of the second phase exceeds 30%, the second phases are connected to each other to increase the particle size, and thus, during ironing, voids are easily generated. In addition, the distance between the dispersed second phases is also small, and the generated voids are easily connected to each other, which also causes a crack. Therefore, the volume ratio of the second phase is set in the range of 3 to 30%.
[0030]
The in-plane anisotropy of the work hardening index n value is as follows.
[0031]
In-plane anisotropy Δn of n value: | Δn | ≦ 0.015
By reducing the absolute value | Δn | of the in-plane anisotropy Δn of the n-value, a rotationally symmetric part can be uniformly formed in the circumferential direction. Axisymmetric parts often require high roundness, but in ironing, the dimensional accuracy is reduced because the amount of processing varies due to differences in the work hardening behavior in the circumferential direction. As a result of the study, when the absolute value | Δn | of the in-plane anisotropy of the work hardening index is 0.015 or more, the deterioration of roundness becomes remarkable. Therefore, | Δn | is less than 0.015.
[0032]
The n-value in-plane anisotropy Δn is represented by the following equation.
[0033]
Δn = (n 0 + n 90 ) −2n 45 (2)
Here, n 0 , n 45 , and n 90 represent n values in directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, respectively. Further, the n value in each direction may be measured by a two-point method of measuring distortion of 5% and 10%.
[0034]
The invention of a manufacturing method capable of obtaining the above-described hot-rolled steel sheet is as follows. According to the invention, a steel comprising the chemical component of the above-described invention is hot-rolled at a finish rolling temperature (Ar 3 −10 ° C.) or higher, and then primary cooled to a temperature of 630 ° C. or lower at a cooling rate exceeding 20 ° C./sec. Then, secondary cooling is performed, and the microstructure is controlled to the microstructure according to claim 1 by winding at a temperature of 600 ° C. or less, thereby producing a hot-rolled steel sheet for rotary ironing.
[0035]
The present invention has been made as a result of studying the manufacturing conditions under which the hot-rolled steel sheet of the above invention can be obtained, and the details thereof will be described below.
[0036]
Finish rolling temperature: (Ar 3 -10 ° C.) or more In finish rolling, the lower the finishing temperature, the more the formation of a ferrite phase after rolling is promoted, and the second phase is refined. However, when the finishing temperature drops below (Ar 3 -10) ℃, ferrite transformation proceeds during rolling. Therefore, the ferrite phase becomes a processed structure, the local ductility decreases, and the anisotropy of the n value increases. Accordingly, the finish rolling temperature (Ar 3 -10 ℃) or higher.
[0037]
Cooling rate after hot rolling: 20 ° C./sec After super hot rolling, rapid cooling is performed to obtain a finely dispersed second phase. When the cooling rate is 20 ° C./second or less, the degree of supercooling of austenite is small, so that pro-eutectoid ferrite is precipitated corresponding to segregation of Mn and P. The segregation of Mn and P is layered by rolling, and the second phase pearlite is also formed in layers between pro-eutectoid ferrites. For this reason, the particle size of the second phase is greatly increased, and during ironing, the formation of voids at the ferrite interface is promoted, and ironing characteristics are significantly deteriorated. Therefore, the cooling rate after hot rolling is set to more than 20 ° C./sec.
[0038]
By setting the cooling rate after hot rolling to 120 ° C./second or more, the ferrite grains are further refined and the second phase is further finely dispersed, so that extremely excellent ironing characteristics can be obtained. The upper limit of the cooling rate is not particularly specified, but is industrially limited to about 2000 ° C./sec. In addition, by starting cooling after hot rolling more than 0.1 second and less than 1.0 second after finish rolling, crystal grains are refined, which is effective in improving ironing characteristics.
[0039]
Primary cooling end temperature: 630 ° C. or less Primary cooling may be performed up to the winding temperature. However, for winding temperature control, rapid cooling is terminated at a slightly higher temperature, and secondary cooling with a relatively slow cooling rate is performed. be able to. When the primary cooling end temperature is higher than 630 ° C., the ferrite phase and the second phase pearlite are formed in layers during the subsequent slow cooling as described above, and the ironing properties are significantly deteriorated. Therefore, the primary cooling end temperature is set to 630 ° C. or less. In the secondary cooling, the cooling rate is not particularly limited as long as the winding temperature can be controlled, and may be slow cooling or rapid cooling.
[0040]
Winding temperature: 600 ° C. or less The winding temperature greatly affects the type and form of the second phase. If the winding temperature exceeds 600 ° C., the pearlite generated as the second phase becomes coarse without being finely dispersed, so that voids are generated during ironing and cause cracks. At the same time, an increase in the pearlite lamellar spacing also promotes the formation of voids and causes cracks. On the other hand, by setting the winding temperature to 500 ° C. or lower, the dispersion of the second phase is further uniformed, and extremely excellent ironing characteristics can be obtained. Therefore, the winding temperature is set to 600 ° C. or lower, preferably 500 ° C. or lower. The lower limit of the winding temperature is not particularly defined, but is preferably set to 200 ° C. or higher, because if the temperature is too low, the shape of the hot-rolled coil deteriorates.
[0041]
In addition, the invention of an automobile part made of such a hot-rolled steel sheet is an automobile part having an axially symmetric shape manufactured by the above-mentioned hot-rolled steel sheet for rotary ironing. The hot-rolled steel sheet according to the above-described invention or the hot-rolled steel sheet manufactured by the method for manufacturing the same has excellent rotary ironability, so that it is suitable for parts having an axially symmetric shape such as automobiles and industrial machines. It is suitable for a drive system component such as an automobile such as a hub and a carrier.
[0042]
Since the automobile part according to the present invention is manufactured from the hot-rolled steel sheet for rotary ironing described above, it can be integrally formed by rotary ironing, so that the manufacturing cost can be reduced and the roundness is high. It has excellent dimensional accuracy such as degrees.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred manufacturing conditions for the hot-rolled steel sheet according to the present invention will be described.
[0044]
The steel used in the present invention may be any steel as long as the metal structure can be in a dispersed state of the above-mentioned second phase volume fraction and average particle size, except for the above-mentioned components and mechanical properties. As for other chemical components, various elements such as B, Cr, Cu, Ni, Mo, Ti, Nb, W, V, and Zr may be added within a range that is usually added. Further, various elements such as Sn and Pb may be mixed as impurities in the manufacturing process, but such impurities do not particularly affect the effects of the present invention. The components of the hot-rolled steel sheet of the present invention can be prepared using either a converter or an electric furnace.
[0045]
The steel prepared as described above is made into a slab by ingot-bulking rolling or continuous casting. Hot rolling is performed on this slab, and at this time, the slab heating temperature is preferably set to 1280 ° C. or lower in order to avoid deterioration of the surface state due to scale generation. In addition, rough rolling may be omitted during hot rolling and finish rolling may be performed, or direct-convey rolling may be performed in which a continuously cast slab is rolled as it is or while keeping heat for the purpose of suppressing a temperature decrease.
[0046]
In the finish rolling, the rolled material may be heated by a heating means such as a bar heater during hot rolling in order to secure the finishing temperature. Further, in order to make the second phase spheroidized or to reduce the hardness, the coil may be kept warm by means such as a slow cooling cover after winding.
[0047]
Annealing may be performed as necessary after hot rolling, and in that case, any of box annealing and continuous annealing may be used. Thereafter, temper rolling is performed if necessary. Since the temper rolling does not affect quenching, the conditions are not particularly limited.
[0048]
【Example】
[Example 1]
A continuous cast slab of steels A to G having the chemical components shown in Table 1 was heated to 1250 ° C., hot rolling was completed at a finishing temperature of 870 ° C., immediately cooled at a rate of 30 ° C./sec, and a primary cooling end temperature of 580 ° C. The temperature was adjusted to 550 ° C., and then pickling and temper rolling were performed to produce a 6.0 mm steel sheet.
[0049]
[Table 1]
Samples were taken from these steel sheets and subjected to a tensile test, measurement of ferrite average particle size (df), second phase volume fraction (Vf), and average particle size (ds) of the second phase, and rotary ironing. The methods and conditions for each test and measurement are described below.
[0051]
{Circle around (1)} Tensile test A JIS No. 5 size tensile test piece was sampled from a direction at 90 ° to the rolling direction and tested. For the anisotropy of the n value (△ n), tensile test pieces were sampled from three directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and a two-point method with 5% to 10% strain was used. The n-value measurement was performed and investigated.
[0052]
{Circle around (2)} Ferrite average particle size (df), second phase volume fraction (Vf) and average particle size (ds)
After polishing and corroding the thickness section of the sample, the microstructure was photographed with a scanning electron microscope, and the average ferrite particle size (df), the volume fraction of the second phase (Vf), and the second phase were measured within a range of 0.01 mm 2. Was measured for the average particle size (ds).
[0053]
{Circle over (2)} Rotating and ironing As shown in FIG. 1, a sample having a blank diameter of 200 mmφ was attached to a mold, the main shaft was rotated, and a roll was pressed to mold along the mold. The inner diameter of the molded body was 100 mmφ. The initial plate thickness was 6.0 mm, but the condition was reduced to 4.0 mm by ironing. For lubrication, machine oil was used. The roll tip R was set to 2 mm, and the roll feed speed was set to 200 mm / min. The evaluation was made based on the presence or absence of cracks and galling on the machined surface, and the roundness as dimensional accuracy (7/100 or less is considered good).
[0054]
Table 2 shows the results of the tensile properties, ferrite average particle size (df), second phase volume fraction (Vf), second phase average particle size (ds), and ironing properties obtained from the above measurement results. Show.
[0055]
[Table 2]
In Table 2, the steel sheets A to C are examples of the present invention, and the ferrite average particle diameter df ≦ 21.5-150C, the volume ratio of the second phase is 3% to 30%, and the average of the second phase is the range of the present invention. The particle size is 5 μm or less, and Δn ≦ ± 0.015 is satisfied. Steel sheets D to G are comparative examples, and steel sheet D has low C, steel E has high C and S, and the volume fraction of the second phase also exceeds 30%. Steel F has high Si and P, steel G has high Mn and N, and the second phase average particle size exceeds 5 μm, all of which are outside the scope of the present invention.
[0057]
From Table 2, it can be confirmed that in Examples A to C, in the ironing test, cracks, galling and the like were not generated, and the dimensional accuracy was excellent and good workability was obtained. In addition, the invention examples A to C show about 5% improvement in local elongation (L.EL) at the same strength level as compared with the comparative examples D to G, confirming that they have excellent ultimate deformability. Was.
[0058]
[Example 2]
The continuously cast slabs of steels A and C shown in Table 1 were heated to 1250 ° C. to form a hot-rolled steel sheet having a thickness of 6.0 mm under the conditions shown in Table 3, and then subjected to pickling and temper rolling.
[0059]
[Table 3]
Samples were taken from these steel sheets and subjected to a tensile test, measurement of ferrite average particle size (df), second phase volume fraction (Vf), and average particle size (ds) of the second phase, and rotary ironing. The methods and conditions for each test and measurement are described below.
[0061]
{Circle around (1)} Tensile test A JIS No. 5 size tensile test piece was sampled from a direction at 90 ° to the rolling direction and tested. For the anisotropy of the n value (Δn), tensile test pieces were sampled from three directions of 0 °, 45 °, and 90 ° with respect to the rolling direction, and the n value was measured at a strain of 5% to 10%. And conducted a survey.
[0062]
{Circle around (2)} Ferrite average particle size (df), second phase volume fraction (Vf), and second phase average particle size (ds)
After polishing and corrosion plate thickness cross-section of the sample, a scanning electron microscope photograph the microstructures at average ferrite grain diameter in the range of 0.01 mm 2 (df), the second phase volume fraction (Vf) and a second phase Was measured for the average particle size (ds).
[0063]
{Circle over (2)} Rotating and ironing As shown in FIG. 1, a sample having a blank diameter of 200 mmφ was attached to a mold, the main shaft was rotated, and a roll was pressed to mold along the mold. The inner diameter of the molded body was 100 mmφ. The initial plate thickness was 6.0 mm, but the condition was reduced to 4.0 mm by ironing. For lubrication, machine oil was used. The roll tip R was set to 2, and the roll feed speed was set to 2 conditions of 1) normal: 200 mm / min and 2) high speed: 400 mm / min. The evaluation was made based on the presence or absence of cracks and galling on the processed surface and the roundness (7/100 or less) as the dimensional accuracy.
[0064]
Tensile properties, Δn value, ferrite average particle size (df), second phase volume fraction (Vf), second phase average particle size (ds), and results of rotary ironing obtained from the above measurement results Are also shown in Table 3.
[0065]
From Table 3, No. 1, 2, 5, and 6 are within the scope of the present invention, and have an average ferrite particle diameter satisfying df ≦ 21.5-150C, a volume fraction of the second phase of 3% to 30%, and This is an invention example having a diameter of 5 μm or less and Δn ≦ ± 0.015, and it was confirmed that good ironing workability and excellent dimensional accuracy were obtained.
[0066]
On the other hand, No. Nos. 3, 4, 7, and 8 are comparative examples. Sample No. 3 had a low local elongation (L.EL) and a large average ferrite grain size, so that cracks occurred on the ironed surface. Also, Δn was large, the roundness was poor, and the dimensional accuracy was poor. No. In No. 4, the average ferrite grain size and the second phase grain size were large, and cracks occurred on the ironed surface. No. In No. 7, the local elongation (L.EL) was low, the average ferrite grain size and the average grain size of the second phase were large, and cracks occurred on the ironed surface. No. In No. 7, Δn was large, roundness was poor, and dimensional accuracy was poor. No. No. 8 has a low local elongation (L.EL), a large average ferrite grain size, and a volume fraction of the second phase of more than 30% and an average grain size of the second phase of more than 5 μm. Therefore, cracks occurred from the ironed surface.
[0067]
【The invention's effect】
In order to improve ironing workability and dimensional accuracy after processing, the present invention controls the chemical composition and the manufacturing conditions to control the average particle diameter of ferrite, the volume fraction of the second phase, and the average particle diameter of the second phase. By controlling, it is possible to suppress the generation of voids during heavy working, and to reduce the anisotropy of the n value, thereby suppressing the fluctuation of working in the circumferential direction. As a result, it becomes possible to provide a hot-rolled steel sheet having extremely excellent rotary ironing workability and excellent dimensional accuracy. By using such a hot-rolled steel sheet, it is possible to integrally mold a complicatedly shaped part of an axisymmetric rotating body typified by a carrier and a hub. It is possible to do.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of rotary ironing.
Claims (4)
ｄ≦２１．５−１５０［Ｃ］Chemical components in mass%: C: 0.02 to 0.10%, Si: 1.0% or less, Mn: 0.1 to 2.5%, P: 0.05% or less, S: 0. 01% or less, sol. Al: 0.01 to 0.10%, N: 0.006% or less, the balance substantially consisting of iron, and the microstructure is at least one of ferrite phase, pearlite, bainite, and martensite. The ferrite phase has an average particle diameter d (μm) and a C content [C] (%) satisfying the following equation, the average particle diameter of the second phase is 5 μm or less, and the volume fraction of the second phase. Wherein the in-plane anisotropy Δn of n value is | Δn | ≦ 0.015.
d ≦ 21.5-150 [C]
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102959116A (en) * | 2010-06-29 | 2013-03-06 | 杰富意钢铁株式会社 | High-strength hot-dip galvanized steel sheet with excellent processability and process for producing same |
| CN102971443A (en) * | 2010-06-29 | 2013-03-13 | 杰富意钢铁株式会社 | High-strength steel sheet with excellent processability and process for producing same |
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| CN116920180A (en) * | 2023-09-14 | 2023-10-24 | 乐普（北京）医疗器械股份有限公司 | Degradable metal material and preparation method and application thereof |
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| CN110711825B (en) * | 2019-09-19 | 2021-05-25 | 上海航天精密机械研究所 | Pear-shaped member forming device and method |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102959116A (en) * | 2010-06-29 | 2013-03-06 | 杰富意钢铁株式会社 | High-strength hot-dip galvanized steel sheet with excellent processability and process for producing same |
| CN102971443A (en) * | 2010-06-29 | 2013-03-13 | 杰富意钢铁株式会社 | High-strength steel sheet with excellent processability and process for producing same |
| CN102971443B (en) * | 2010-06-29 | 2015-03-25 | 杰富意钢铁株式会社 | High-strength steel sheet with excellent processability and process for producing same |
| CN110405040A (en) * | 2019-08-10 | 2019-11-05 | 西安长峰机电研究所 | A kind of reversed spin-on process of unimach outer step thin-wall barrel |
| CN116920180A (en) * | 2023-09-14 | 2023-10-24 | 乐普（北京）医疗器械股份有限公司 | Degradable metal material and preparation method and application thereof |
| CN116920180B (en) * | 2023-09-14 | 2023-12-15 | 乐普（北京）医疗器械股份有限公司 | Degradable metal material and preparation method and application thereof |
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