JP3608383B2 - Ferritic stainless steel with excellent surface properties and press formability - Google Patents
Ferritic stainless steel with excellent surface properties and press formability Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
この発明は、表面性状およびプレス成形性に優れたフェライト系ステンレス鋼に関し、特にフェライト系ステンレス鋼における酸化物系介在物の組成状態を適切に制御すると共に、Ｖを適量添加することによって、表面性状の劣化を招くことなしにプレス成形性の有利な改善を図ろうとするものである。
【０００２】
【従来の技術】
ＳＵＳ ４３０ で代表されるフェライト系ステンレス鋼は、高価なＮｉを殆ど含まないため、オーステナイト系ステンレス鋼に比べると安価なだけでなく、耐応力腐食割れ性に優れることから、各種厨房器具、自動車排気系部品などの分野で幅広く使用されている。
【０００３】
このフェライト系ステンレス鋼のプレス成形性に関しては、絞り、張り出し、深絞り加工性などが要求され、これらの特性を改善するために、これまで数多くの試みがなされている。
例えば、特開平１−２０１４４５号公報には、低Ｐ，Ｓ化と共に、Ｎｂ，Ｔｉ等の炭窒化物生成元素の添加による深絞り性の改善技術が提唱されている。しかしながら、この技術は、低Ｐ，Ｓ化が不可欠であるため、製鋼工程での負荷が大きいという問題があった。
【０００４】
また、特開昭５８−７１３５６号公報には、熱間圧延前におけるスラブ加熱温度を１１３０℃を超えないように制御することによって、平均ｒ値を向上する製造方法が提唱されている。しかしながら、スラブ加熱温度を下げると、熱間加工性が低下し、コイル表面にヘゲ疵などの表面欠陥が発生する危険性が高く、その後のグラインダー手入れや酸洗によるコスト増を招くという問題があった。
【０００５】
さらに、特開平１−１３６９３０号公報には、熱間圧延における仕上げ圧延条件を規定することによって平均ｒ値を向上させる方法が提唱されている。
しかしながら、この方法は、熱延工程における制御圧延であり、仕上げ温度が低い上にロール潤滑を行わなければならないなど、工程的な負荷が大きいという問題があった。
【０００６】
【発明が解決しようとする課題】
上述したとおり、従来の技術は、たとえｒ値の改善がなされても、製造コストの増加や工程的な負荷が大きい、あるいは鋼板の表面性状を大きく損なうといった各種の問題を残していた。
この発明は、上記の実情に鑑み開発されたもので、ｒ値に優れるのはいうまでもなく、従来技術が抱えている工程負荷およびヘゲ発生等の問題を有利に解決したフェライト系ステンレス鋼を提案することを目的とする。
【０００７】
【課題を解決するための手段】
さて、発明者らは、上記の目的を達成すべく鋭意研究を行った結果、ｒ値は、フェライト系ステンレス鋼における酸化物系介在物の組成状態に強く依存し、従ってかかる酸化物系介在物の組成を適切に制御すると共に、Ｖを適量添加することが、所期した目的の達成に極めて有効であるとの知見を得た。
この発明は、上記の知見に立脚するものである。
【０００８】
すなわち、この発明は、Ｃｒ：１５〜２０ｗｔ％を含有するフェライト系ステンレス鋼において、Ｖを ０．００５〜１．０ ｗｔ％の範囲で含有させると共に、Ａｌを ０．００５ｗｔ％以下、Ｏを ０．００１〜０．００７ ｗｔ％の範囲とし、かつ鋼中の酸化物系介在物の成分中、 Ａｌ２Ｏ３およびＣｒ２Ｏ３ をそれぞれ、 Ａｌ２Ｏ３：５ｗｔ％以下、 Ｃｒ２Ｏ３：１０〜５０ｗｔ％の範囲としたことを特徴とする、表面性状およびプレス成形性に優れたフェライト系ステンレス鋼である。
【０００９】
この発明において、鋼中の酸化物系介在物については、上記したとおり、 Ａｌ２Ｏ３およびＣｒ２Ｏ３ をそれぞれ Ａｌ２Ｏ３：５ｗｔ％以下、 Ｃｒ２Ｏ３：１０〜５０ｗｔ％にすると共に、ＭｎＯ を１０〜５０ｗｔ％およびＳｉＯ２を２０ｗｔ％以下とすることがより好ましい。
【００１０】
なお、この発明において、酸化物系介在物とは、製鋼工程で生成する脱酸生成物と原料から混入する酸化物の両者を含む。また、製鋼工程で生成する脱酸生成物とは、単なる酸化物だけでなく、硫化物等が混在した複合形態を含む。ここに、酸化物系介在物としては、上記した Ａｌ２Ｏ３やＣｒ２Ｏ３， ＭｎＯ， ＳｉＯ２の他、 ＭｇＯおよびＦｅＯ 等が挙げられる。
【００１１】
【発明実施の形態】
以下、この発明を導くに至った実験結果について説明する。
Ｃ：０．０６ｗｔ％、Ｃｒ：１６．４ｗｔ％、Ｏ：４０ ｐｐｍに固定し、ＡｌおよびＶをそれぞれ、Ａｌ：０．０００６〜０．０５ｗｔ％、Ｖ：０．００１ 〜３．０ ｗｔ％の範囲で変化させた組成の鋼を、真空溶解炉で溶製し、小型鋼塊（５０ｋｇ）とした。その際、酸化物系介在物の組成状態を、溶製条件を変更することによって種々に変化させた。
ついで、１１８０℃に加熱後、熱間圧延により４．０ ｍｍ厚の熱延板とし、ついでこれらの熱延板に ８６０℃， ８ｈの焼鈍を行い、１５℃／ｈ程度の冷却速度で徐冷処理を施した後、冷間圧延により０．５ ｍｍ厚の冷延板とした。その後、冷延板に ８１０℃， ３０ｓの仕上げ焼鈍を施して製品板とした。
【００１２】
かくして得られた製品板から、圧延方向（Ｌ方向）、圧延方向と４５°をなす方向（Ｘ方向）および圧延方向と直角な方向（Ｃ方向）からＪＩＳ １３号Ｂ試験片を採取し、引張試験を実施して、各方向のｒ値（ｒＬ，ｒＸ，ｒＣ ）を測定し、平均ｒ値を求めた。ここで、平均ｒ値は次式で定義するものとする。
平均ｒ値＝（ｒＬ ＋２ｒＸ ＋ｒＣ ）／４
【００１３】
図１に、Ｖ添加量と平均ｒ値との関係について調査した結果を示す。
同図に示したとおり、Ｖ量を ０．００５ｗｔ％以上添加した場合には良好な平均ｒ値が得られることが分かる。
なお、Ｖ量の上限は、製造コストおよび過剰添加による硬質化の面から１．０ ｗｔ％とする必要がある。
【００１４】
次に、図２に、酸化物系介在物中の Ａｌ２Ｏ３濃度と平均ｒ値との関係について調べた結果を、また図３には、酸化物系介在物中の Ｃｒ２Ｏ３濃度と平均ｒ値との関係について調べた結果を、それぞれ示す。
図２に示したとおり、酸化物系介在物中の Ａｌ２Ｏ３濃度が５ｗｔ％以下であれば平均ｒ値の改善が見込まれることが分かる。
また、図３に示したとおり、酸化物系介在物中の Ｃｒ２Ｏ３濃度が１０〜５０ｗｔ％の範囲を満足する場合に、平均ｒ値が著しく改善されることが分かる。
【００１５】
そこで、この発明では、フェライト系ステンレス鋼に、 ０．００５〜１．０ ｗｔ％の範囲でＶを添加すると共に、酸化物系介在物の成分中、特に Ａｌ２Ｏ３およびＣｒ２Ｏ３ について、それぞれ Ａｌ２Ｏ３≦５ｗｔ％、 Ｃｒ２Ｏ３：１０〜５０ｗｔ％の範囲に制限することにしたのである。
【００１６】
上述したとおり、酸化物系介在物の成分中、ｒ値に特に影響を及ぼす成分は、 Ａｌ２Ｏ３およびＣｒ２Ｏ３ であるが、その他にも、ＭｎＯ などもｒ値に影響を及ぼすことが判明した。
図４に、酸化物系介在物中の ＭｎＯ濃度と平均ｒ値との関係について調べた結果を示す。
同図に示したとおり、満足できる平均ｒ値が得るためには、酸化物系介在物中の ＭｎＯ濃度を１０〜５０ｗｔ％程度とするのが好ましいことが判る。
【００１７】
さらに、酸化物系介在物のうち、ＳｉＯ２も加工性に影響を及ぼし、この加工性の面からはＳｉＯ２濃度を２０ｗｔ％以下に制限するのが有利であることが判明した。
従って、良好な加工性を得るためには、鋼中の酸化物系介在物の各成分につき、 Ａｌ２Ｏ３およびＣｒ２Ｏ３ をそれぞれ Ａｌ２Ｏ３：５ｗｔ％以下、 Ｃｒ２Ｏ３：１０〜５０ｗｔ％にすると共に、 ＭｎＯを１０〜５０ｗｔ％およびＳｉＯ２を２０ｗｔ％以下とすることが好ましい。
【００１８】
次に、この発明の素材成分について説明する。
この発明は、Ｃｒを１５〜２０ｗｔ％の範囲で含有し、Ａｌを ０．００５ｗｔ％以下かつＯ量を ０．００１〜０．００７ ｗｔ％の範囲に制限したものであれば、いわゆるフェライト系ステンレス鋼全般に適用することができる。
ここに、Ｃｒ， ＡｌおよびＯ含有量を上記の範囲に限定した理由を、Ｖ含有量の限定理由と共に説明する。
Ｃｒ：１５〜２０ｗｔ％
Ｃｒは、ステンレス鋼としての耐食性を確保するために不可欠な元素である。しかしながら、その量が１５ｗｔ％未満では耐食性が不足し、一方２０ｗｔ％を超えると冷間加工性の低下や靱性の劣化を招くので、含有量は１５〜２０ｗｔ％の範囲に限定した。より好適には１６〜１８ｗｔ％の範囲である。
【００１９】
Ａｌ：０．００５ ｗｔ％以下
Ａｌを添加すると、酸化物系介在物中の Ａｌ２Ｏ３濃度が上昇し、耐食性を劣化させるばかりでなく、コイルの表面品質を劣化させる原因となる。また、酸化物系介在物中のＡｌ２Ｏ３ 濃度が上昇すると、酸化物系介在物中の Ｃｒ２Ｏ３濃度が減少し、Ｖ炭窒化物が周りに析出しにくくなり、仕上げ焼鈍時に固溶Ｃ，Ｎ量の低減が期待できない。従って、Ａｌは意図的な添加を避け、上限を ０．００５ｗｔ％とした。より好適には０．００３ ｗｔ％以下である。
【００２０】
Ｏ：０．００１ 〜０．００７ ｗｔ％
Ｏは、溶鋼中でＡｌやＭｎと結合し酸化物系介在物を生成する。その結果、耐食性の劣化や鋼板表面の傷の原因となるため、Ｏの上限は ０．００７ｗｔ％とした。一方、この発明において、酸化物系介在物、ＶやＣｒ等の炭窒化物の析出サイトとして作用するため、０．００１ ｗｔ％に満たないと固溶Ｃ，Ｎの低減に寄与しない。従って、この発明では、Ｏ量について ０．００１〜０．００７ ｗｔ％の範囲に限定した。より好適には０．００１５〜０．００６ ｗｔ％の範囲である。
【００２１】
Ｖ：０．００５ 〜１．０ ｗｔ％
Ｖは、炭窒化物として酸化物系介在物の周りに析出し、プレス成形性に有害なＣ，Ｎを固定するためのサイトとして有効に作用し、軟質化およびｒ値向上に極めて有用な元素である。しかしながら、含有量が ０．００５ｗｔ％未満ではこれらの効果が期待できず、一方 １．０ｗｔ％を超える添加は効果が飽和するばかりか、製造性の低下やコストの上昇を招く。従って、Ｖの添加量は ０．００５〜１．０ ｗｔ％の範囲に限定した。より好適には０．０１〜０．５ ｗｔ％の範囲である。
【００２２】
その他の成分については、特に限定されることはないが、特に好ましい成分組成範囲は次のとおりである。
Ｃ：０．１ ｗｔ％以下
Ｃは、ｒ値および伸び特性を低下させる元素である。とくに、０．１ ｗｔ％を超えるとその影響が顕著になるので、Ｃは ０．１ｗｔ％以下とすることが望ましい。より好適には０．０７ｗｔ％以下である。
【００２３】
Ｓｉ：１．０ ｗｔ％以下
Ｓｉは、脱酸のために有効な元素であるが、過剰の添加は硬質化を招くので、その添加量は １．０ｗｔ％以下とすることが望ましい。より好適には ０．５ｗｔ％以下である。
【００２４】
Ｍｎ：１．０ ｗｔ％以下
Ｍｎは、鋼中に存在するＳを析出固定し、熱間圧延性を保つために有効な元素であるが、過剰の添加は冷間加工性の低下を招くので、その添加量は １．０ｗｔ％以下とすることが望ましい。より好適には ０．８ｗｔ％以下である。
【００２５】
Ｎ：０．１ ｗｔ％以下
Ｎは、Ｃと同様、ｒ値および伸び特性を低下させる元素である。特に、０．１ ｗｔ％を超えるとその影響が顕著になるので、Ｎは ０．１ｗｔ％以下とすることが望ましい。より好適には０．０７ｗｔ％以下である。
【００２６】
なお、この発明では、ＰおよびＳ等については、特に厳しく制限しなくても、十分に所定の材質を得ることができる。
【００２７】
この発明に従い、Ｖ添加量ならびに酸化物系介在物中の Ｃｒ２Ｏ３濃度および Ａｌ２Ｏ３濃度を所定の範囲に制限することによってｒ値が改善される理由は、まだ明確に解明されたわけではないが、冷延板焼鈍中の再結晶挙動が関与しているものと思われる。
すなわち、酸化物系介在物中の Ａｌ２Ｏ３濃度が５ｗｔ％以下、Ｃｒ２Ｏ３ 濃度が１０〜５０ｗｔ％、さらに好ましくは ＭｎＯ濃度が１０〜５０ｗｔ％の範囲を満足していると、Ｖ添加により酸化物系介在物の周りに析出したＶ炭窒化物が析出サイトとして作用し、さらにその周りにＣｒの炭窒化物が析出し、仕上げ焼鈍時に固溶Ｃ，Ｎの低減が図られる。その結果、引き続く再結晶において、ｒ値の向上に有効な（１１１）集合組織を優先的に発達させることができる。
一方、 Ａｌ２Ｏ３濃度が５ｗｔ％を上回るか、 Ｃｒ２Ｏ３濃度が１０ｗｔ％未満または５０ｗｔ％超の場合には、前述したＶ炭窒化物の析出サイトとしての効果が小さく、仕上げ焼鈍時に固溶Ｃ，Ｎの低減が望めないことから、（１１１）集合組織の発達が抑制されてしまうためと考えられる。
【００２８】
この発明において、上記したような酸化物系介在物の組成状態は、次のようにして制御することができる。
まず、溶製時におけるスラグとして、 ＣａＯ−ＳｉＯ２−Ａｌ２Ｏ３ 三元系のものを用いる。そして、このスラグ中における Ａｌ２Ｏ３濃度を５ｗｔ％以下に制御すると共に、塩基度（ＣａＯ ／ＳｉＯ２）を１．５ 以下に調整する。なお、溶鋼中のＡｌ量は ０．００５ｗｔ％以下に抑制しておく必要があり、またＯ量については７０ ｐｐｍ以下まで低減することが望ましい。
上記の処理によって、酸化物系介在物における Ａｌ２Ｏ３濃度および Ｃｒ２Ｏ３濃度を所定の範囲に制御することができる。
なお、連続鋳造スラブの冷却速度を３０℃／ｓ以下とすることも有利である。
【００２９】
その後の処理については、常法に従って行えば良く、例えば１３００〜７００ ℃で熱間圧延したのち、圧下率：５０〜９０％程度で冷間圧延し、ついで ７００〜１０００℃程度の温度で仕上げ焼鈍を施せば良い。
なお、この発明鋼は、熱延焼鈍薄鋼板、タンデム圧延−達続焼鈍を行った冷延鋼板、光輝焼鈍板等にも適用可能である。
【００３０】
【実施例】
表１に示す成分組成の鋼を溶製し、連続鋳造により２００ ｍｍ厚のスラブとした。その際、脱酸方法、鋳造条件を変えることによって、スラブ中における酸化物系介在物の組成状態を変化させた。
このとき ＭｎＯ−ＳｉＯ２系介在物とする場合には、スラグの塩基度を１．４ とし、スラグ中の Ａｌ２Ｏ３濃度を５ｗｔ％以下まで低減した。一方、 Ａｌ２Ｏ３系介在物とする場合には、塩基度を２．０ 以上とし、スラグ中の Ａｌ２Ｏ３濃度を２０％以上とした。
この実験において、脱酸に要した時間は３０分であり、Ｏ量を４０ ｐｐｍまで低減させた。なお、鋳造に先立って鋳型内に不活性ガスを吹き込み、溶鋼の温度制御ならびに介在物の浮上除去を促進させた。
【００３１】
鋳造に際しては、ＳｉＯ２， ＣａＯ を主成分とするモールドパウダーを鋳型内で鋳片表面に投入し、鋳片と鋳型の間を潤滑すると同時に、鋳造中に鋳片内部から浮上してくる介在物を捕捉除去した。
ついで、この連続鋳造スラブを、通常の熱間圧延により熱延板とし、熱延板焼鈍後、酸洗したのち、冷間圧延により０．５ ｍｍ厚の冷延板とし、ついで仕上げ焼鈍を施して製品板とした。
【００３２】
かくして得られた製品板について、前述の方法で、平均ｒ値を求めた。
また、各製品板の組織を走査型電子顕微鏡で ２００視野について観察ならびに同定を行い、さらに抽出分析により酸化物系介在物の組成を調査した。
さらに、重量：約２０ｔのコイル全長にわたって表面性状を観察し、ヘゲ疵の定量を行った。ここに、ヘゲ疵の量は、１個／コイル以下を良好と判断した。
これらの結果を表２に示す。
【００３３】
【表１】
【表２】
表２に示したとおり、この発明に従い、所定量のＶを添加すると共に、Ａｌ２Ｏ３ およびＣｒ２Ｏ３ をそれぞれ、 Ａｌ２Ｏ３≦５ｗｔ％、 Ｃｒ２Ｏ３：１０〜５０ｗｔ％の範囲に制限したものはいずれも、優れたｒ値が得られ、またヘゲ疵の発生もほとんど認められなかった。
【００３６】
【発明の効果】
かくして、この発明によれば、表面性状の劣化なしに、プレス成形性に優れたフェライト系ステンレス鋼を安価に得ることができ、産業上極めて有用であるといえる。
【図面の簡単な説明】
【図１】Ｖ添加量と平均ｒ値との関係を示すグラフである。
【図２】酸化物系介在物中の Ａｌ２Ｏ３濃度と平均ｒ値との関係を示すグラフである。
【図３】酸化物系介在物中の Ｃｒ２Ｏ３濃度と平均ｒ値との関係を示すグラフである。
【図４】酸化物系介在物中の ＭｎＯ濃度と平均ｒ値との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ferritic stainless steel excellent in surface properties and press formability, and in particular, by appropriately controlling the composition state of oxide inclusions in ferritic stainless steel and adding an appropriate amount of V, the surface properties. Thus, it is intended to advantageously improve the press formability without incurring deterioration.
[0002]
[Prior art]
Since ferritic stainless steel represented by SUS 430 contains almost no expensive Ni, it is not only cheaper than austenitic stainless steel, but also has excellent resistance to stress corrosion cracking. Widely used in fields such as system parts.
[0003]
With respect to the press formability of this ferritic stainless steel, drawing, overhanging, deep drawing workability, etc. are required, and many attempts have been made so far to improve these properties.
For example, Japanese Patent Laid-Open No. 1-201445 proposes a technique for improving deep drawability by adding carbonitride-generating elements such as Nb and Ti as well as reducing P and S. However, this technique has a problem that the load in the steel making process is large because low P and S are indispensable.
[0004]
Japanese Patent Laid-Open No. 58-71356 proposes a manufacturing method for improving the average r value by controlling the slab heating temperature before hot rolling so as not to exceed 1130 ° C. However, when the slab heating temperature is lowered, hot workability is reduced, and there is a high risk that surface defects such as lashes will be generated on the coil surface, resulting in increased costs due to subsequent grinder care and pickling. there were.
[0005]
Furthermore, Japanese Patent Application Laid-Open No. 1-136930 proposes a method for improving the average r value by defining finish rolling conditions in hot rolling.
However, this method is controlled rolling in the hot rolling process, and there is a problem that the process load is large, for example, the finishing temperature is low and roll lubrication must be performed.
[0006]
[Problems to be solved by the invention]
As described above, even if the r value is improved, the conventional technique has left various problems such as an increase in manufacturing cost, a large process load, or a large deterioration in the surface properties of the steel sheet.
The present invention was developed in view of the above circumstances, and it goes without saying that the r-value is excellent, and the ferritic stainless steel that advantageously solves the problems such as process load and generation of baldness that the prior art has. The purpose is to propose.
[0007]
[Means for Solving the Problems]
Now, as a result of intensive studies to achieve the above object, the inventors have determined that the r value strongly depends on the composition state of oxide inclusions in the ferritic stainless steel, and accordingly, such oxide inclusions. The present inventors have found that it is extremely effective to appropriately control the composition and to add an appropriate amount of V to achieve the intended purpose.
The present invention is based on the above findings.
[0008]
That is, according to the present invention, in a ferritic stainless steel containing Cr: 15 to 20 wt%, V is contained in a range of 0.005 to 1.0 wt%, Al is 0.005 wt% or less, and O is 0. In the components of oxide inclusions in steel, Al 2 O 3 and Cr 2 O 3 are each in the range of 0.001 to 0.007 wt%, Al 2 O 3 : 5 wt% or less, Cr 2 O 3 : Ferritic stainless steel excellent in surface properties and press formability, characterized by being in the range of 10 to 50 wt%.
[0009]
In the present invention, for oxide inclusions in the steel, as described above, Al 2 O 3 and Cr 2 O 3, respectively Al 2 O 3: 5wt% or less, Cr 2 O 3: To range of 10 to 50 wt% In addition, it is more preferable that MnO 2 is 10 to 50 wt% and SiO 2 is 20 wt% or less.
[0010]
In addition, in this invention, an oxide inclusion includes both the deoxidation product produced | generated at a steelmaking process, and the oxide mixed from a raw material. Moreover, the deoxidation product produced | generated by a steelmaking process includes the composite form with which not only a simple oxide but sulfide etc. were mixed. Here, examples of the oxide-based inclusion include MgO and FeO 2 in addition to the above-described Al 2 O 3 , Cr 2 O 3 , MnO, and SiO 2 .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The experimental results that led to this invention will be described below.
C: 0.06 wt%, Cr: 16.4 wt%, O: 40 ppm fixed, Al and V are respectively Al: 0.0006-0.05 wt%, V: 0.001-3.0 wt% The steel having the composition changed in the range was melted in a vacuum melting furnace to obtain a small steel ingot (50 kg). At that time, the composition state of the oxide inclusions was variously changed by changing the melting conditions.
Next, after heating to 1180 ° C., hot-rolled sheets having a thickness of 4.0 mm are formed by hot rolling. Then, these hot-rolled sheets are annealed at 860 ° C. for 8 hours, and gradually cooled at a cooling rate of about 15 ° C./h. After the treatment, a cold-rolled sheet having a thickness of 0.5 mm was formed by cold rolling. Thereafter, the cold-rolled sheet was subjected to finish annealing at 810 ° C. for 30 seconds to obtain a product sheet.
[0012]
From the product plate thus obtained, JIS No. 13 B specimens were collected from the rolling direction (L direction), the direction forming 45 ° with the rolling direction (X direction), and the direction perpendicular to the rolling direction (C direction). The test was carried out to measure the r value (r L, r X, r C ) in each direction, and the average r value was obtained. Here, the average r value is defined by the following equation.
Average r value = (r L + 2r X + r C ) / 4
[0013]
FIG. 1 shows the results of investigation on the relationship between the V addition amount and the average r value.
As shown in the figure, it can be seen that a good average r value can be obtained when the amount of V is 0.005 wt% or more.
In addition, the upper limit of V amount needs to be 1.0 wt% from the viewpoint of manufacturing cost and hardening due to excessive addition.
[0014]
Next, FIG. 2 shows the results of investigating the relationship between the Al 2 O 3 concentration in the oxide inclusions and the average r value, and FIG. 3 shows the Cr 2 O 3 concentration in the oxide inclusions. The results of examining the relationship between the average r value and the average r value are shown below.
As shown in FIG. 2, it can be seen that if the Al 2 O 3 concentration in the oxide inclusions is 5 wt% or less, improvement of the average r value is expected.
In addition, as shown in FIG. 3, it can be seen that the average r value is remarkably improved when the Cr 2 O 3 concentration in the oxide inclusions satisfies the range of 10 to 50 wt%.
[0015]
Therefore, in the present invention, V is added to the ferritic stainless steel in the range of 0.005 to 1.0 wt%, and among the components of the oxide inclusions, particularly Al 2 O 3 and Cr 2 O 3 . These are limited to the ranges of Al 2 O 3 ≦ 5 wt% and Cr 2 O 3 : 10 to 50 wt%, respectively.
[0016]
As described above, among the components of oxide inclusions, the components that particularly affect the r value are Al 2 O 3 and Cr 2 O 3 , but in addition, MnO and the like also affect the r value. There was found.
FIG. 4 shows the results of examining the relationship between the MnO concentration in the oxide inclusions and the average r value.
As shown in the figure, it is understood that the MnO concentration in the oxide inclusions is preferably about 10 to 50 wt% in order to obtain a satisfactory average r value.
[0017]
Further, among oxide inclusions, SiO 2 also affects workability, and it has been found that it is advantageous to limit the SiO 2 concentration to 20 wt% or less from the viewpoint of workability.
Therefore, in order to obtain good workability, Al 2 O 3 and Cr 2 O 3 are contained in each component of the oxide inclusions in the steel, and Al 2 O 3 is 5 wt% or less, Cr 2 O 3 : It is preferable that the content is 10 to 50 wt%, MnO is 10 to 50 wt%, and SiO 2 is 20 wt% or less.
[0018]
Next, the raw material component of this invention is demonstrated.
If this invention contains Cr in the range of 15 to 20 wt%, Al is 0.005 wt% or less and the amount of O is limited to the range of 0.001 to 0.007 wt%, so-called ferritic stainless steel It can be applied to all types of steel.
Here, the reason why the Cr, Al and O contents are limited to the above range will be described together with the reason for limiting the V content.
Cr: 15-20 wt%
Cr is an indispensable element for ensuring the corrosion resistance as stainless steel. However, if the amount is less than 15 wt%, the corrosion resistance is insufficient. On the other hand, if it exceeds 20 wt%, the cold workability is deteriorated and the toughness is deteriorated, so the content is limited to the range of 15 to 20 wt%. More preferably, it is the range of 16-18 wt%.
[0019]
Al: 0.005 wt% or less When Al is added, the concentration of Al 2 O 3 in the oxide inclusions increases, which not only deteriorates the corrosion resistance but also causes the surface quality of the coil to deteriorate. In addition, when the Al 2 O 3 concentration in the oxide inclusions increases, the Cr 2 O 3 concentration in the oxide inclusions decreases, making it difficult for V carbonitrides to precipitate around and solidifying during finish annealing. Reduction of the amount of dissolved C and N cannot be expected. Accordingly, intentional addition of Al was avoided, and the upper limit was made 0.005 wt%. More preferably, it is 0.003 wt% or less.
[0020]
O: 0.001 to 0.007 wt%
O couple | bonds with Al and Mn in molten steel, and produces | generates an oxide type inclusion. As a result, the corrosion resistance is deteriorated and the surface of the steel sheet is damaged, so the upper limit of O is set to 0.007 wt%. On the other hand, in this invention, since it acts as a precipitation site for oxide inclusions and carbonitrides such as V and Cr, it does not contribute to the reduction of dissolved C and N unless it is less than 0.001 wt%. Therefore, in the present invention, the amount of O is limited to a range of 0.001 to 0.007 wt%. More preferably, it is in the range of 0.0015 to 0.006 wt%.
[0021]
V: 0.005 to 1.0 wt%
V precipitates around oxide inclusions as carbonitrides, effectively acts as a site for fixing C and N harmful to press formability, and is an extremely useful element for softening and improving the r value. It is. However, if the content is less than 0.005 wt%, these effects cannot be expected. On the other hand, the addition exceeding 1.0 wt% not only saturates the effect, but also causes a decrease in manufacturability and an increase in cost. Therefore, the addition amount of V is limited to the range of 0.005 to 1.0 wt%. More preferably, it is in the range of 0.01 to 0.5 wt%.
[0022]
Other components are not particularly limited, but particularly preferable component composition ranges are as follows.
C: 0.1 wt% or less C is an element that lowers the r value and elongation characteristics. In particular, when the amount exceeds 0.1 wt%, the effect becomes significant. Therefore, C is preferably set to 0.1 wt% or less. More preferably, it is 0.07 wt% or less.
[0023]
Si: 1.0 wt% or less Si is an effective element for deoxidation, but excessive addition causes hardening, so the addition amount is preferably 1.0 wt% or less. More preferably, it is 0.5 wt% or less.
[0024]
Mn: 1.0 wt% or less Mn is an element effective for precipitating and fixing S present in steel and maintaining hot rollability, but excessive addition causes a decrease in cold workability. The added amount is desirably 1.0 wt% or less. More preferably, it is 0.8 wt% or less.
[0025]
N: 0.1 wt% or less N, like C, is an element that decreases the r value and elongation characteristics. In particular, when the amount exceeds 0.1 wt%, the influence becomes significant. Therefore, N is preferably 0.1 wt% or less. More preferably, it is 0.07 wt% or less.
[0026]
In the present invention, it is possible to sufficiently obtain a predetermined material without particularly restricting P and S.
[0027]
The reason why the r value is improved by limiting the V addition amount and the Cr 2 O 3 concentration and the Al 2 O 3 concentration in the oxide inclusions to a predetermined range according to the present invention is still clearly elucidated. However, it seems that recrystallization behavior during cold-rolled sheet annealing is involved.
That is, if the Al 2 O 3 concentration in the oxide inclusions is 5 wt% or less, the Cr 2 O 3 concentration is 10 to 50 wt%, more preferably the MnO concentration is in the range of 10 to 50 wt%, V carbonitride precipitated around oxide inclusions by addition acts as a precipitation site, and Cr carbonitride precipitates around it, so that solid solution C and N can be reduced during finish annealing. As a result, in the subsequent recrystallization, the (111) texture effective for improving the r value can be preferentially developed.
On the other hand, when the Al 2 O 3 concentration exceeds 5 wt%, or the Cr 2 O 3 concentration is less than 10 wt% or more than 50 wt%, the effect as a precipitation site of the V carbonitride described above is small, and during finish annealing It is considered that the development of the (111) texture is suppressed because the reduction of the solid solution C and N cannot be expected.
[0028]
In the present invention, the composition state of the oxide inclusions as described above can be controlled as follows.
First, as a slag at the time of melting, a CaO—SiO 2 —Al 2 O 3 ternary system is used. Then, to control the concentration of Al 2 O 3 in the slag below 5 wt%, adjusted basicity (CaO / SiO 2) to 1.5 or less. In addition, it is necessary to suppress the amount of Al in molten steel to 0.005 wt% or less, and it is desirable to reduce the amount of O to 70 ppm or less.
By the above treatment, the Al 2 O 3 concentration and the Cr 2 O 3 concentration in the oxide inclusions can be controlled within a predetermined range.
It is also advantageous to set the cooling rate of the continuously cast slab to 30 ° C./s or less.
[0029]
The subsequent treatment may be performed according to a conventional method, for example, hot rolling at 1300 to 700 ° C., then cold rolling at a reduction ratio of about 50 to 90%, and then finish annealing at a temperature of about 700 to 1000 ° C. Should be applied.
In addition, this invention steel is applicable also to the hot rolled annealing thin steel plate, the cold rolled steel plate which performed the tandem rolling-sequential annealing, the bright annealing plate, etc.
[0030]
【Example】
Steels having the composition shown in Table 1 were melted and slabs having a thickness of 200 mm were obtained by continuous casting. At that time, the composition state of the oxide inclusions in the slab was changed by changing the deoxidation method and casting conditions.
At this time, when using MnO—SiO 2 inclusions, the basicity of the slag was set to 1.4, and the Al 2 O 3 concentration in the slag was reduced to 5 wt% or less. On the other hand, when Al 2 O 3 inclusions were used, the basicity was set to 2.0 or more, and the Al 2 O 3 concentration in the slag was set to 20% or more.
In this experiment, the time required for deoxidation was 30 minutes, and the amount of O was reduced to 40 ppm. Prior to casting, an inert gas was blown into the mold to promote the temperature control of molten steel and the floating removal of inclusions.
[0031]
At the time of casting, mold powder containing SiO 2 and CaO as main components is put on the surface of the slab in the mold and lubricated between the slab and the mold, and at the same time, inclusions floating from the inside of the slab during casting Was trapped and removed.
Next, this continuous cast slab is made into a hot-rolled sheet by ordinary hot rolling, and after hot-rolled sheet annealing, pickled, then cold-rolled to a 0.5 mm thick cold-rolled sheet, and then subjected to finish annealing. The product board.
[0032]
For the product plate thus obtained, the average r value was determined by the method described above.
In addition, the structure of each product plate was observed and identified for 200 fields of view with a scanning electron microscope, and the composition of oxide inclusions was investigated by extraction analysis.
Furthermore, the surface properties were observed over the entire length of the coil having a weight of about 20 t, and the balance was determined. Here, it was judged that the amount of lashes was 1 / coil or less.
These results are shown in Table 2.
[0033]
[Table 1]
[Table 2]
As shown in Table 2, according to the present invention, a predetermined amount of V is added, and Al 2 O 3 and Cr 2 O 3 are added to each of Al 2 O 3 ≦ 5 wt% and Cr 2 O 3 : 10 to 50 wt%. In all cases, the r value was excellent and almost no occurrence of baldness was observed.
[0036]
【The invention's effect】
Thus, according to the present invention, it is possible to obtain a ferritic stainless steel excellent in press formability at low cost without deterioration of the surface properties, and it can be said that it is extremely useful industrially.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the V addition amount and the average r value.
FIG. 2 is a graph showing the relationship between the Al 2 O 3 concentration in oxide inclusions and the average r value.
FIG. 3 is a graph showing the relationship between the Cr 2 O 3 concentration in oxide inclusions and the average r value.
FIG. 4 is a graph showing the relationship between the MnO concentration in oxide inclusions and the average r value.
Claims (2)
Priority Applications (1)
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| JP15466098A JP3608383B2 (en) | 1998-06-03 | 1998-06-03 | Ferritic stainless steel with excellent surface properties and press formability |
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|---|---|---|---|
| JP15466098A JP3608383B2 (en) | 1998-06-03 | 1998-06-03 | Ferritic stainless steel with excellent surface properties and press formability |
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| JP3608383B2 true JP3608383B2 (en) | 2005-01-12 |
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| CN106536777A (en) * | 2014-07-22 | 2017-03-22 | 新日铁住金不锈钢株式会社 | Ferritic stainless steel and method for producing same, and heat exchanger equipped with ferritic stainless steel as member |
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| JP6530923B2 (en) * | 2015-02-17 | 2019-06-12 | 日鉄日新製鋼株式会社 | Stainless steel sheet excellent in corrosion resistance and method of manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106536777A (en) * | 2014-07-22 | 2017-03-22 | 新日铁住金不锈钢株式会社 | Ferritic stainless steel and method for producing same, and heat exchanger equipped with ferritic stainless steel as member |
| CN106536777B (en) * | 2014-07-22 | 2018-10-30 | 新日铁住金不锈钢株式会社 | Ferrite-group stainless steel and its manufacturing method and using ferrite-group stainless steel as the heat exchanger of component |
| US11091824B2 (en) | 2014-07-22 | 2021-08-17 | Nippon Steel & Sumikin Stainless Steel Corporation | Ferritic stainless steel and method for producing same, and heat exchanger equipped with ferritic stainless steel as member |
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