JP4111352B2 - High-cleaning refining method for stainless steel - Google Patents
High-cleaning refining method for stainless steel Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、ステンレス鋼の精錬法において、Ｃａの添加方法およびスラグの組成を制御することにより、溶鋼中の非金属介在物（以下、単に介在物という）の無害化をはかる高清浄度ステンレス鋼の製造方法に関するものである。
【０００２】
【従来の技術】
ステンレス鋼の介在物は、その量が多すぎたり融点が高く硬質の場合には、製品の表面疵や加工時の割れ発生の原因となる。一般に介在物を除去したり、介在物の融点を下げ軟質化する方法はステンレス鋼の精錬ではＡＯＤ，ＶＯＤ等の二次精錬炉で実施している。
【０００３】
すなわち、酸素ガスを吹込み、脱炭等の処理を行う酸化精錬の終了後、酸化精錬時に生成したクロム酸化物を含むスラグを還元するために、ＣａＯを主体とする塩基性フラックスと共に、ＳｉやＡｌ等の還元剤を添加し、Ａｒガスや窒素ガス等の不活性ガスを吹込むことにより攪拌し、脱酸および介在物の除去を促進させている。特に低硫・低酸素化の要求される材料に対しては還元剤としてＡｌを用いる方法が採用されている。
【０００４】
これはＡｌは脱酸力が強く、脱硫能の高いスラグを形成させることができるためである。また、この方法では通常、還元時に生成した高融点のＡｌ2 Ｏ3 を改質して、介在物の組成を抑制し、かつ鋳造時のノズル閉塞を防止するためにＣａが添加されている。
【０００５】
ステンレス鋼中の介在物の低減および軟質化をはかるためにＣａやＡｌを添加する例としては、特公昭６０−３０６８６号公報および特開平６０−３０６４３９号公報に記載の方法が知られている。
特公昭６０−３２６８６号公報に記載の方法は、酸素濃度に対応してＣａまたはＡｌの添加量を制御することにより、介在物を低融点のＣａＯ−Ａｌ2 Ｏ3 とすることで、浮上分離を促進させて大型介在物量を低減できることが述べられている。
しかし、該方法では硬質の介在物（ＭｇＯ−Ａｌ2 Ｏ3 ，ＭｇＯ）が皆無になっておらず、介在物の無害化の点では問題が残っている。
【０００６】
さらに、特開平６−３０６４３９号公報に記載の方法は、Ａｌ中の〔Ｍｇ〕濃度を１．０ｍａｓｓ％以下とし、スラグ中の（ＭｇＯ）濃度を８ｍａｓｓ％以下とし、かつ〔Ｃａ〕と〔Ａｌ〕濃度を調整することで硬質のＭｇＯ−Ａｌ2 Ｏ3 介在物を低減できることが述べられている。
しかし、この方法ではＡｌ2 Ｏ3 濃度の高い高融点のＣａＯ−Ａｌ2 Ｏ3 介在物（一般には６０ｍａｓｓ％以上のＡｌ2 Ｏ3 を含む）およびＭｇＯ介在物が残存しており、一部にはＭｇＯ−Ａｌ2 Ｏ3 介在物が存在するために介在物の無害化は完全に達成されていない。
【０００７】
【発明が解決しようとする課題】
本発明はステンレス鋼の精錬法において、還元剤にＡｌを用い、その後に添加するＣａ量、Ｃａ添加後の不活性ガス吹込み量およびスラグ組成を制御することにより、還元時に生成した硬質のＡｌ2 Ｏ3 を軟質化し、かつ硬質の介在物の生成を抑えることで、介在物の完全無害化を達成し、これにより製品の表面疵や加工時の割れを防止することを目的とするものである。
【０００８】
【課題を解決するための手段】
本発明は、上記目的を達成するために下記手段を採用するものである。
すなわち、ステンレス鋼の精錬において、酸化精錬時に生成したクロム酸化物を含むスラグの還元剤としてＡｌを用い、かつ出鋼後の取鍋内の溶鋼にＣａまたはＣａ合金あるいはこれらの両者を添加する工程において、ＣａまたはＣａ合金あるいはこれらの両者を添加する量をＣａの純分で溶鋼トン当り５０ｇ以上かつ１２０ｇ以下とし、かつ該Ｃａの添加後に溶鋼内に下記（１）式を満足する量の不活性ガスを吹込んで溶鋼の攪拌を行うことを特徴とするステンレス鋼の高清浄化精錬法にある。
１．５≦Ｗ Ｃａ ／Ｑ ｄ ≦４．２ ・・・（１）
Ｑｄ ：不活性ガスの吹込み流量（Ｎｍ３ ）
ＷＣａ：添加したＣａまたはＣａ合金中のＣａ純分量の合計（ｋｇ）
【０００９】
さらに、前記精錬後のスラグ中の（ＭｇＯ）濃度を１５ｍａｓｓ％以下とし、かつスラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）の濃度比を１．０以上、２．５以下とすることを特徴とするステンレス鋼の高清浄化精錬法にある。
【００１０】
【発明の実施の形態】
本発明者らはステンレス鋼の製品の表面疵や加工時の割れの原因として、硬質の介在物であるＡｌ2 Ｏ3 ，ＭｇＯ，ＭｇＯ−Ａｌ2 Ｏ3 ，ＣａＯおよびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 の影響が極めて大きいことを見出し、かつこれらの介在物の硬質、軟質の区別は介在物組成より求められる介在物の融点で評価できることを見出した。
さらに、Ａｌを還元剤として用い、精錬炉から出鋼後、取鍋内でＣａまたはＣａ合金あるいはこれらの両者を添加した場合の介在物の組成推移について種々の調査を重ねた結果、下記の知見を得た。
【００１１】
▲１▼還元剤としてＡｌを添加した場合は、溶鋼中に介在物として硬質のＡｌ2 Ｏ3 ，ＭｇＯ−Ａｌ2 Ｏ3 ，ＭｇＯおよびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 が生成し、これが後工程まで残存することがある。
▲２▼取鍋内で、ＣａまたはＣａ合金あるいはこれらの両者を添加し、溶鋼の攪拌を十分に行うことによって、上記介在物の軟質化反応が進行し、介在物の主体は一部にＳｉＯ2 およびＭｇＯを含んだ比較的Ａｌ2 Ｏ3 濃度の低いＣａＯ−Ａｌ2 Ｏ3 となる。
【００１２】
▲３▼ＣａまたはＣａ合金あるいはこれらの両者を添加した後の溶鋼の攪拌が不十分な場合には、硬質のＡｌ2 Ｏ3 ，ＭｇＯ−Ａｌ2 Ｏ3 ，ＭｇＯおよびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 が残存すると共に、Ｃａ添加によって生成したＣａＯが介在物として残存することがある。
▲４▼スラグ中の（ＭｇＯ）濃度が極端に高い場合およびスラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）濃度比が極端に高かったり、低かったりした場合には、上記の硬質の介在物が残存することがある。
【００１３】
したがって、硬質の介在物であるＡｌ2 Ｏ3 ，ＭｇＯ−Ａｌ2 Ｏ3 ，ＭｇＯ，ＣａＯおよびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 の生成を抑制するには、Ｃａの添加量、Ｃａ添加後の不活性ガス吹込みによる溶鋼の攪拌量およびスラグの組成を適切に制御することが非常に重要であることがわかった。
また、前記の特開平６−３０６４３９号公報に記載されている、還元剤として添加するＡｌ中のＭｇ濃度の規制、あるいは溶鋼中〔Ｃａ〕，〔Ａｌ〕の規制は、Ｃａ添加後の溶鋼への不活性ガス吹込み量が十分であれば緩和できることを確認した。
【００１４】
さらに、介在物には多種類の硬質の介在物が存在することから、これらを一律に評価する指標として、介在物の組成より求められる介在物の融点を用いることが有効であり、介在物の融点が１６００℃を超える介在物を高融点介在物とし、この高融点介在物の全介在物に占める存在率を高融点介在物の発生率として定義して、介在物の無害化を評価すればよいことがわかった。
なお、高融点介在物の発生率が高いほど、介在物の絶対量が多くなる傾向になることが確認された。
【００１５】
上記の結果に基づき、Ｃａ添加量、Ｃａ添加後の溶鋼への不活性ガス吹込み量およびスラグ組成を制御することに着目して、高融点介在物の発生率を抑える条件について検討した。
なお、還元剤としてＡｌを用いる場合、スラグの還元反応の促進をはかり、かつ低硫・低酸素化を円滑に達成するためには、精錬中における溶鋼中の〔Ａｌ〕濃度は１００〜１５００ｐｐｍの範囲であり、本発明においてもこの範囲内に調整している。
【００１６】
図１は、酸化精錬後のステンレス鋼にＡｌを添加して還元精錬を行い、この溶鋼を取鍋に出鋼し、取鍋内にＣａあるいはＣａ合金を添加し、不活性ガスを吹込んで精錬を行った場合の、取鍋で添加する溶鋼トン当りのＣａ添加量と高融点介在物の発生率の関係を示す。なお、Ｃａ源としてＣａ合金を添加する場合のＣａ添加量はＣａ合金中に含まれるＣａ量であり、Ｃａ添加量／ガス吹込み流量は４．０ｋｇ／Ｎｍ3 以下とした。
図１より、溶鋼トン当りのＣａ添加量が５０ｇより小さい場合には、ＭｇＯ，ＭｇＯ−Ａｌ2 Ｏ3 およびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 の高融点介在物の発生率が急激に増大するために、溶鋼トン当りのＣａ添加量は５０ｇ以上が必要である。
【００１７】
図２は、図１と同様な精錬において、Ｃａ添加量／ガス吹込み流量を１．３〜８．２ｋｇ／Ｎｍ3 とした場合のＣａ添加量／ガス吹込み流量と高融点介在物の発生率の関係を示す。なお、Ｃａの溶鋼トン当りの添加量は、いずれも５０ｇ以上とした場合の値である。
図２より、Ｃａ添加量／ガス吹込み流量の値が４．２を超えると高融点介在物の発生率が急激に増大するために、Ｃａ添加量／ガス吹込み流量は４．２以下とする必要がある。
【００１８】
これより、前記（１）式の関係が求められる。なお、Ｃａ添加量およびガス吹込み流量が多くなると、取鍋での溶鋼温度の低下が大きく、制御が難しくなるために、溶鋼トン当りのＣａ添加量としては１２０ｇ以下、Ｃａ添加量／ガス吹込み流量の比は１．５ｋｇ／Ｎｍ3 以上が望ましい。
【００１９】
図３には前記精錬後のスラグ中の（ＭｇＯ）濃度と高融点介在物の発生率の関係を示す。なお、Ｃａの添加量およびＣａ添加後の溶鋼への不活性ガス吹込み流量は本発明の条件内で行った場合である。
図３より、スラグ中の（ＭｇＯ）濃度が１５ｍａｓｓ％を超えると徐々に高融点介在物の発生率が増大しており、スラグ中の（ＭｇＯ）濃度は１５ｍａｓｓ％以下とする必要がある。
【００２０】
図４には前記精錬後のスラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）の濃度比と高融点介在物の発生率の関係を示す。なお、Ｃａの添加量およびＣａ添加後の溶鋼への不活性ガス吹込み流量は本発明の条件内で行った場合である。
図４より、スラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）の濃度比が１．０未満および２．５を超えると高融点介在物の発生率が増大しており、スラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）の濃度比は１．０以上、２．５以下にする必要がある。
【００２１】
以上のように、Ａｌ2 Ｏ3 ，ＭｇＯ，ＭｇＯ−Ａｌ2 Ｏ3 ，ＣａＯおよびＡｌ2 Ｏ3 濃度の高いＣａＯ−Ａｌ2 Ｏ3 の高融点介在物の発生率を抑制するためには、取鍋内で添加するＣａ量、Ｃａの添加後の溶鋼内への不活性ガスの吹込み流量および精錬後のスラグ中の（ＭｇＯ）濃度、（ＣａＯ）／（Ａｌ2 Ｏ3 ）濃度比を適正な範囲に制御することが重要である。
【００２２】
【実施例】
ＳＵＳ３０４ステンレス鋼（１８ｍａｓｓ％Ｃｒ−８ｍａｓｓ％Ｎｉ）を６０ｔ電気炉にて溶解し、ＡＯＤ炉にてＯ2 −Ａｒ混合ガスによる脱炭精錬を行った後に、Ａｒガス吹込み下で還元剤としてＡｌを添加して、還元精錬を行った後に取鍋に出鋼した。
取鍋内ではＣａおよびＣａ合金を添加し、その後、取鍋底部よりＡｒガスを吹込み攪拌処理を行った。なお、精錬中における溶鋼中の〔Ａｌ〕濃度は１００〜１０００ｐｐｍの範囲にあり、スラグ量は溶鋼トン当り４０〜１００ｋｇの範囲にあった。
【００２３】
得られた鋼は連続鋳造により、断面サイズ１７８ｍｍφのビレットとし、次いで線材圧延により５．５ｍｍφの線材とし、この線材を０．５ｍｍφに冷間伸線加工した。表１にＡＯＤ精錬後のスラグ組成、Ｃａ添加条件および線材品質をまとめて示す。なお、Ｎｏ．１〜６の例は本発明例、Ｎｏ．７〜１０は本発明の条件外の比較例を示す。
【００２４】
【表１】
介在物の調査は、線材横断面１０ｃｍ2 を光学顕微鏡により観察し、５μｍ以上の介在物個数を測定すると共に、Ｘ線マイクロアナライザーによる組成分析を行った。組成分析結果より各介在物毎の融点を換算し、融点が１６００℃以上の介在物個数を求め、高融点介在物の発生率を算出した。
【００２６】
本発明の例では高融点介在物の発生率が低位に安定しており、かつ線材中の５μｍ以上の介在物個数も著しく低減しており、介在物の無害化を達成できた。
【００２７】
【発明の効果】
本発明では、ステンレス鋼の精錬において、精錬後のスラグ組成、取鍋内で添加するＣａの量およびＣａ添加後の不活性ガスの吹込み流量を制御することにより、硬質の高融点介在物の発生率を低位に安定させることができるので、介在物の無害化を達成できる。このため、製品の表面疵や加工時の割れのない材料を製造でき、冷間加工性の優れた細線、極細線などの製造が可能になった。
【図面の簡単な説明】
【図１】取鍋内で添加するＣａまたはＣａ合金あるいはこれらの両者の溶鋼トン当りのＣａ添加量と高融点介在物の発生率の関係を示す図
【図２】取鍋内で添加するＣａ量とＣａ添加後の不活性ガスの吹込み流量の比と高融点介在物の発生率の関係を示す図
【図３】精錬後のスラグ中の（ＭｇＯ）濃度と高融点介在物の発生率の関係を示す図
【図４】精錬後のスラグ中の（ＣａＯ）／（Ａｌ2 Ｏ3 ）の濃度比と高融点介在物の発生率の関係を示す図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high cleanliness stainless steel for detoxifying non-metallic inclusions (hereinafter simply referred to as inclusions) in molten steel by controlling the addition method of Ca and the composition of slag in the refining method of stainless steel. It is related with the manufacturing method.
[0002]
[Prior art]
If the amount of stainless steel inclusions is too large or has a high melting point and is hard, it can cause surface defects on the product and cracks during processing. In general, a method of removing inclusions or lowering the melting point of the inclusions to make them softer is performed in a secondary refining furnace such as AOD or VOD in the refining of stainless steel.
[0003]
That is, after the completion of oxidation refining in which oxygen gas is blown and decarburization is performed, in order to reduce slag containing chromium oxide generated during oxidation refining, together with basic flux mainly composed of CaO, Si and A reducing agent such as Al is added, and stirring is performed by blowing an inert gas such as Ar gas or nitrogen gas to promote deoxidation and removal of inclusions. In particular, a method using Al as a reducing agent is employed for materials that require low sulfur and low oxygen.
[0004]
This is because Al has a strong deoxidizing power and can form a slag having a high desulfurization ability. Also, in this method, Ca is usually added in order to modify the high melting point Al 2 O 3 produced at the time of reduction to suppress the composition of inclusions and prevent nozzle clogging during casting.
[0005]
As examples of adding Ca and Al in order to reduce inclusions and soften the inclusions in stainless steel, methods described in JP-B-60-30686 and JP-A-60-306439 are known.
In the method described in Japanese Patent Publication No. 60-32686, the inclusion is changed to CaO—Al 2 O 3 having a low melting point by controlling the amount of Ca or Al added in accordance with the oxygen concentration. It is stated that the amount of large inclusions can be reduced by promoting the above.
However, this method does not eliminate hard inclusions (MgO—Al 2 O 3 , MgO), and there remains a problem in terms of detoxification of the inclusions.
[0006]
Furthermore, in the method described in JP-A-6-306439, the [Mg] concentration in Al is set to 1.0 mass% or less, the (MgO) concentration in slag is set to 8 mass% or less, and [Ca] and [Al It is stated that hard MgO—Al 2 O 3 inclusions can be reduced by adjusting the concentration.
However, in this method, high melting point CaO—Al 2 O 3 inclusions (generally containing 60 mass% or more of Al 2 O 3 ) and MgO inclusions with a high Al 2 O 3 concentration remain, and some of them Since MgO—Al 2 O 3 inclusions exist, the inclusions are not completely detoxified.
[0007]
[Problems to be solved by the invention]
In the refining method of the stainless steel, the present invention uses hard Al produced during reduction by using Al as a reducing agent and controlling the amount of Ca added thereafter, the amount of inert gas blown after Ca addition, and the slag composition. It is intended to soften 2 O 3 and suppress the formation of hard inclusions, thereby making the inclusions completely harmless, thereby preventing product surface flaws and cracks during processing. is there.
[0008]
[Means for Solving the Problems]
The present invention employs the following means to achieve the above object.
That is, in the refining of stainless steel, a process of using Al as a reducing agent for slag containing chromium oxide generated during oxidative refining, and adding Ca or Ca alloy or both of them to the molten steel in the ladle after steel is removed In this case, the amount of Ca or Ca alloy or both of them added is not less than 50 g and 120 g or less per ton of molten steel in terms of pure Ca, and the amount satisfying the following formula (1) in the molten steel after the addition of Ca The present invention resides in a highly purified refining method for stainless steel, characterized in that molten steel is stirred by blowing active gas.
1.5 ≦ W Ca / Q d ≦ 4.2 (1)
Q d : Blowing flow rate of inert gas (Nm 3 )
W Ca : Total amount of pure Ca in the added Ca or Ca alloy (kg)
[0009]
Furthermore, the (MgO) concentration in the slag after the refining is 15 mass% or less, and the concentration ratio of (CaO) / (Al 2 O 3 ) in the slag is 1.0 or more and 2.5 or less. It is in the high cleaning and refining method of stainless steel, which is a feature.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have high concentrations of Al 2 O 3 , MgO, MgO—Al 2 O 3 , CaO and Al 2 O 3 which are hard inclusions as the cause of surface defects and cracks during processing of stainless steel products. It has been found that the influence of CaO—Al 2 O 3 is extremely large, and the distinction between hard and soft inclusions can be evaluated by the melting point of the inclusions determined from the inclusion composition.
Furthermore, as a result of repeated investigations on the composition transition of inclusions when Al was used as a reducing agent and Ca or Ca alloy or both of them were added in the ladle after steel removal from the refining furnace, the following findings Got.
[0011]
▲ 1 ▼ the case of adding Al as a reducing agent, hard Al 2 O 3, MgO-Al 2
(2) In the ladle, Ca or Ca alloy or both of them are added, and the molten steel is sufficiently stirred to advance the softening reaction of the inclusions. CaO—Al 2 O 3 having a relatively low Al 2 O 3 concentration containing 2 and MgO.
[0012]
(3) When stirring of molten steel after addition of Ca or Ca alloy or both of them is insufficient, hard Al 2 O 3 , MgO-Al 2 O 3 , MgO and Al 2 O 3 concentrations are high. While CaO—Al 2 O 3 remains, CaO produced by addition of Ca may remain as inclusions.
(4) When the (MgO) concentration in the slag is extremely high and the (CaO) / (Al 2 O 3 ) concentration ratio in the slag is extremely high or low, the above hard inclusions May remain.
[0013]
Therefore, in order to suppress the formation of hard inclusions Al 2 O 3 , MgO—Al 2 O 3 , MgO, CaO and CaO—Al 2 O 3 having a high Al 2 O 3 concentration, the amount of Ca added, It was found that it is very important to appropriately control the amount of stirring of the molten steel and the composition of the slag by injecting inert gas after adding Ca.
Further, the regulation of Mg concentration in Al added as a reducing agent or regulation of [Ca] and [Al] in molten steel described in JP-A-6-306439 is applied to molten steel after addition of Ca. It was confirmed that if the inert gas blowing amount of was sufficient, it could be relaxed.
[0014]
Furthermore, since there are many kinds of inclusions in the inclusion, it is effective to use the melting point of the inclusion determined from the composition of the inclusion as an index for uniformly evaluating these inclusions. If the inclusion having a melting point exceeding 1600 ° C. is defined as a high melting point inclusion, the abundance ratio of the high melting point inclusion in all the inclusions is defined as the occurrence rate of the high melting point inclusion, and the detoxification of the inclusion is evaluated. I found it good.
It was confirmed that the higher the incidence of high melting point inclusions, the greater the absolute amount of inclusions.
[0015]
Based on the above results, focusing on controlling the amount of Ca added, the amount of inert gas blown into the molten steel after addition of Ca, and the slag composition, the conditions for suppressing the incidence of high melting point inclusions were examined.
When Al is used as the reducing agent, the [Al] concentration in the molten steel during refining is 100 to 1500 ppm in order to promote the reduction reaction of slag and smoothly achieve low sulfur and low oxygen. This range is also adjusted in the present invention.
[0016]
Fig. 1 shows reduction refining by adding Al to stainless steel after oxidation refining, removing this molten steel into a ladle, adding Ca or Ca alloy into the ladle, and blowing in an inert gas to refining Shows the relationship between the amount of Ca added per ton of molten steel added in the ladle and the incidence of high melting point inclusions. In addition, the Ca addition amount in the case of adding a Ca alloy as a Ca source is the amount of Ca contained in the Ca alloy, and the Ca addition amount / gas blowing flow rate was 4.0 kg / Nm 3 or less.
From FIG. 1, when the amount of Ca addition per ton of the molten steel is 50g less than, MgO, incidence of high-melting inclusions MgO-Al 2 O 3 and Al 2 O 3 higher concentrations CaO-Al 2 O 3 In order to increase rapidly, the amount of Ca added per ton of molten steel is required to be 50 g or more.
[0017]
FIG. 2 shows the generation of high melting point inclusions and Ca addition amount / gas injection flow rate when the Ca addition amount / gas injection flow rate is 1.3 to 8.2 kg / Nm 3 in the same refining as in FIG. The relationship of rate is shown. In addition, the addition amount per ton of molten steel of Ca is a value when all are 50 g or more.
From FIG. 2, when the value of Ca addition amount / gas injection flow rate exceeds 4.2, the incidence of high melting point inclusions increases rapidly, so the Ca addition amount / gas injection flow rate is 4.2 or less. There is a need to.
[0018]
From this, the relationship of said (1) Formula is calculated | required. As the Ca addition amount and the gas blowing flow rate increase, the temperature of the molten steel in the ladle decreases greatly, and control becomes difficult. Therefore, the Ca addition amount per ton of molten steel is 120 g or less, and the Ca addition amount / gas blowing rate. The flow rate ratio is preferably 1.5 kg / Nm 3 or more.
[0019]
FIG. 3 shows the relationship between the (MgO) concentration in the slag after refining and the occurrence rate of high melting point inclusions. In addition, the addition amount of Ca and the flow rate of the inert gas blown into the molten steel after the addition of Ca are performed within the conditions of the present invention.
As shown in FIG. 3, when the (MgO) concentration in the slag exceeds 15 mass%, the generation rate of high melting point inclusions gradually increases, and the (MgO) concentration in the slag needs to be 15 mass% or less.
[0020]
FIG. 4 shows the relationship between the concentration ratio of (CaO) / (Al 2 O 3 ) in the slag after refining and the incidence of high melting point inclusions. In addition, the addition amount of Ca and the inert gas blowing flow rate to the molten steel after the addition of Ca are performed under the conditions of the present invention.
From FIG. 4, when the concentration ratio of (CaO) / (Al 2 O 3 ) in the slag is less than 1.0 and exceeds 2.5, the incidence of high melting point inclusions increases, and (CaO in the slag increases. ) / (Al 2 O 3 ) concentration ratio must be 1.0 or more and 2.5 or less.
[0021]
As described above, in order to suppress the incidence of high melting point inclusions of Al 2 O 3 , MgO, MgO—Al 2 O 3 , CaO, and CaO—Al 2 O 3 having a high Al 2 O 3 concentration, Appropriate amount of Ca added in the pan, flow rate of inert gas into the molten steel after addition of Ca, (MgO) concentration in the slag after refining, (CaO) / (Al 2 O 3 ) concentration ratio It is important to control within a proper range.
[0022]
【Example】
SUS304 stainless steel (18 mass% Cr-8 mass% Ni) was melted in a 60-ton electric furnace, decarburized and refined with an O 2 -Ar mixed gas in an AOD furnace, and then Al was added as a reducing agent under Ar gas blowing. Was added to the ladle after reduction refining.
Ca and Ca alloy were added in the ladle, and then Ar gas was blown from the bottom of the ladle to perform stirring. In addition, the [Al] concentration in the molten steel during refining was in the range of 100 to 1000 ppm, and the amount of slag was in the range of 40 to 100 kg per ton of molten steel.
[0023]
The obtained steel was formed into a billet with a cross-sectional size of 178 mmφ by continuous casting, and then into a wire rod of 5.5 mmφ by wire rolling, and this wire was cold drawn to 0.5 mmφ. Table 1 summarizes the slag composition, Ca addition conditions and wire quality after AOD refining. In addition, No. Examples 1 to 6 are examples of the present invention, No. 7-10 show comparative examples outside the conditions of the present invention.
[0024]
[Table 1]
The inclusions were examined by observing a cross section of 10 cm 2 of the wire rod with an optical microscope, measuring the number of inclusions of 5 μm or more, and conducting composition analysis with an X-ray microanalyzer. The melting point of each inclusion was converted from the composition analysis result, the number of inclusions having a melting point of 1600 ° C. or higher was determined, and the incidence of high melting point inclusions was calculated.
[0026]
In the example of the present invention, the incidence of high melting point inclusions is stable at a low level, and the number of inclusions of 5 μm or more in the wire is remarkably reduced, and the inclusions can be made harmless.
[0027]
【The invention's effect】
In the present invention, in the refining of stainless steel, by controlling the slag composition after refining, the amount of Ca added in the ladle and the flow rate of the inert gas after the addition of Ca, Since the incidence can be stabilized at a low level, inclusions can be rendered harmless. For this reason, it is possible to produce a material that is free from surface defects and cracks during processing, and it has become possible to produce fine wires and ultra fine wires with excellent cold workability.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of Ca added per ton of molten steel and the rate of occurrence of high melting point inclusions in a ladle. Fig. 3 shows the relationship between the ratio of the flow rate of the inert gas after addition of Ca and the flow rate of inert gas and the occurrence rate of high melting point inclusions. FIG. 4 is a diagram showing the relationship between the concentration ratio of (CaO) / (Al 2 O 3 ) in the slag after refining and the incidence of high melting point inclusions.
Claims (2)
１．５≦Ｗ Ｃａ ／Ｑ ｄ ≦４．２ ・・・（１）
Ｑｄ ：不活性ガスの吹込み流量（Ｎｍ３ ）
ＷＣａ：添加したＣａまたはＣａ合金中のＣａ純分量の合計（ｋｇ）In the refining of stainless steel, in the step of using Al as a reducing agent for slag containing chromium oxide generated during oxidative refining, and adding Ca or Ca alloy or both of them to the molten steel in the ladle after the steel is tapped, The amount of Ca or Ca alloy, or both of them added is 50 g or more and 120 g or less per ton of molten steel in terms of pure Ca, and after the addition of Ca, an inert gas in an amount that satisfies the following formula (1) A high-cleaning refining method for stainless steel, characterized by stirring molten steel by blowing
1.5 ≦ W Ca / Q d ≦ 4.2 (1)
Q d : Blowing flow rate of inert gas (Nm 3 )
W Ca : Total amount of pure Ca in the added Ca or Ca alloy (kg)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14855096A JP4111352B2 (en) | 1996-05-21 | 1996-05-21 | High-cleaning refining method for stainless steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14855096A JP4111352B2 (en) | 1996-05-21 | 1996-05-21 | High-cleaning refining method for stainless steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09310113A JPH09310113A (en) | 1997-12-02 |
| JP4111352B2 true JP4111352B2 (en) | 2008-07-02 |
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| Application Number | Title | Priority Date | Filing Date |
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| JP14855096A Expired - Lifetime JP4111352B2 (en) | 1996-05-21 | 1996-05-21 | High-cleaning refining method for stainless steel |
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| US6489355B2 (en) | 1993-12-01 | 2002-12-03 | Eli Lilly And Company | Methods of inhibiting the effects of amyloidogenic proteins |
| US5521198A (en) | 1993-12-21 | 1996-05-28 | Eli Lilly And Company | Methods of inhibiting autoimmune diseases |
| US6417198B1 (en) | 1993-12-21 | 2002-07-09 | Eli Lilly And Company | Methods of inhibiting CNS problems in post-menopausal women |
| US6703407B1 (en) | 1994-09-20 | 2004-03-09 | Eli Lilly And Company | Benzofuran compounds, compositions, and methods |
| WO1997001549A1 (en) | 1995-06-26 | 1997-01-16 | Eli Lilly And Company | Benzothiophene compounds |
| US6353003B1 (en) | 1998-06-17 | 2002-03-05 | Eli Lilly And Company | Method for reducing levels of homocysteine and C-reactive protein |
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