JP4287974B2 - Method for processing molten steel with finely solidified structure characteristics - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、脱炭精練を行った後の溶鋼を造塊法や連続鋳造等を用いて鋳塊や鋳片を製造した際に、凝固組織を微細にして品質や加工性等を向上することができる微細凝固組織特性を有する溶鋼の処理方法に関する。
【０００２】
【従来の技術】
従来、溶鋼は、上底吹き転炉や電気炉等の精練炉を用いて脱炭精練を行い、炭素や燐、硫黄等を除去してから所望の機械特性が得られるように、合金鉄を添加して成分調整を行ない、造塊法や連続鋳造等により凝固させて、鋳塊や鋳片が製造されている。
そして、鋳塊や鋳片を加熱して圧延加工を施すことにより、鋼材が製造される。
しかし、溶鋼が凝固する際に、特に内部の凝固組織が粗大になると、鋳片の内部に割れや中心偏析、センターポロシティ等の内部欠陥が発生して屑化し、良鋳片歩留りの低下を招く。
更に、外観を重要視するステンレス鋼材においては、エッジシーム疵やローピング等の表面欠陥が発生し、外観不良、端部のトリム量の増加等から品質や良製品歩留りの低下を招く等の問題がある。
この対策として、特開昭５２−４７５２２号公報に記載されているように、連続鋳造中の鋳型内の湯面から１．５〜３．０ｍの位置に電磁攪拌装置を設けて、６０ｍｍＨｇの推力で攪拌を行うことにより、鋳片を製造している。あるいは特開昭５２−６０２３１号公報に記載されているように、溶鋼の過熱温度を１０〜５０℃とした低温鋳造を行い、しかも、鋳造中の鋳片の未凝固層に電磁攪拌を行って、鋳片の凝固組織を等軸晶からなる微細な組織にして、中心偏析やＵＳＴ欠陥の無い鋼材を製造することが行われている。
更に、特開平７−４８６１６号公報に記載されているように、取鍋等の容器内の溶鋼表面を覆うスラグの組成をＭｇＯを３〜１５質量％、ＦｅＯとＦｅ2Ｏ3及びＭｎＯを５質量％以下にしたＣａＯ・ＳｉＯ2・Ａｌ2Ｏ3系にしておき、このスラグを貫通してＭｇ合金を添加することにより、溶鋼中へのＭｇ歩留りを高め、しかも、微細なＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3の酸化物を生成して鋼材の品質を向上することが行われている。
【０００３】
【発明が解決しようとする課題】
しかしながら、特開昭５２−４７５２２号公報では、鋳型内で凝固しつつある溶鋼に電磁攪拌を行って、成長する柱状晶（デンドライト組織）を抑制するので、電磁攪拌を付与した部位近傍の凝固組織をある程度は微細にできる。しかし、鋳片の全体を微細にするには、多段の電磁攪拌装置が必要になり、設備費が増大し、設置スペースの観点からも極めて困難であり、鋳片の全体を微細化した鋳片を製造するのに限界が生じる。
更に、特開昭５２−６０２３１号公報では、低温鋳造を行うため、浸漬ノズルの内面に介在物が付着してノズル詰まりを生じたり、鋳型内溶鋼の温度が低下して湯面皮張りが生じ、場合によっては、鋳造中断をせざるを得ない等、操業が不安定になる。
また、特開平７−４８６１６号公報に記載された方法では、ＣａＯ・ＳｉＯ2・Ａｌ2Ｏ3系のスラグで溶鋼の表面を覆っているので、Ｍｇの蒸発を抑制して歩留りの向上を図る利点を有する。しかし、スラグ組成によっては、溶鋼が凝固する際に凝固核として有効なＭｇＯ、ＭｇＯ・Ａｌ2Ｏ3の酸化物を必ずしも安定して生成することができない場合がある。
即ち、スラグ中に含まれるＡｌ2Ｏ3やＣａＯ等によって、ＣａＯを含む低融点の酸化物や表面をＡｌ2Ｏ3が覆ったＭｇ酸化物が形成され、凝固初晶のδフェライトとの格子整合性が悪化して接種核（凝固核）として作用しなくなる。
その結果、溶鋼が、これ等の酸化物を起点にして凝固することができず、微細な組織の鋳片を製造することができない。
凝固組織が粗大化すると、鋳片の内部に割れや中心偏析、センターポロシティ等の欠陥が発生し、良鋳片歩留りの低下等を招く。
更に、この鋳片を用いて加工した鋼材にも粗大な凝固組織に起因した表面及び内部欠陥が発生し、歩留りや品質の低下を招く等の問題がある。
【０００４】
本発明はかかる事情に鑑みてなされたもので、有効な接種核を生成させて凝固組織を微細にし、鋳片や鋼材に発生する表面及び内部欠陥を防止して、品質を向上することができる微細凝固組織特性を有する溶鋼の処理方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
前記目的に沿う本発明の微細凝固組織特性を有する溶鋼の処理方法は、表面がスラグで覆われたフェライト系ステンレス溶鋼中に含まれるスラグ（Ａｌ2Ｏ3及びＣａＯを含む）及び脱酸生成物からなる酸化物の組成を求め、前記フェライト系ステンレス溶鋼にＭｇを添加した際に生成する酸化物が下記（１）、（２）式を満たすように歩留りを考慮して、金属Ｍｇの添加量を求めてＭｇを添加する。
１７．４（ｋＡｌ2Ｏ3）＋３．９（ｋＭｇＯ）＋０．３（ｋＭｇＡｌ2Ｏ4）＋１８．７（ｋＣａＯ）≦５００ ・・・・・（１）
（ｋＡｌ2Ｏ3）＋（ｋＭｇＯ）＋（ｋＭｇＡｌ2Ｏ4）＋（ｋＣａＯ）≧９５
・・・・・（２）
ここで、ｋは、酸化物のモル％を表す。
この方法により、δフェライトとの格子整合度が５％以下の接種核（凝固核）として有効な酸化物である図２の斜線で示す範囲にあるＣａＯ・Ａｌ2Ｏ3・ＭｇＯの３元系と、ＭｇＯ・Ａｌ2Ｏ3、ＭｇＯ等からなる複合Ｍｇ酸化物を生成することができ、溶鋼が凝固する際に、これ等の複合Ｍｇ酸化物を凝固核として作用させることで、等軸晶を生成させて鋳片の凝固組織を微細にすることができる。
【０００６】
ここで、前記溶鋼はフェライト系ステンレス溶鋼である。
凝固組織が粗大化し易いフェライト系ステンレス溶鋼の凝固組織を微細な凝固組織にすることができ、鋳片に発生する内部割れや中心偏析、センターポロシティ等を抑制し、また、この鋳片を加工した鋼材に発生する粗大な凝固組織に起因したローピング、エッジシーム疵が生じるのを防止することができる。
【０００７】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
Ｍｇを溶鋼に添加することにより酸化物を生成し、鋳片の凝固組織を微細化する場合、他の添加元素やスラグ組成等により、ＭｇＯ・Ａｌ2Ｏ3・ＣａＯ系の酸化物が形成されたり、ＭｇＯ・ＣａＯ系の高融点の酸化物等が形成されたりする。
しかし、ＭｇＯ・Ａｌ2Ｏ3・ＣａＯの酸化物は、低融点であるので、溶鋼が凝固する際に、凝固核として作用しない。一方、ＭｇＯ・ＣａＯの酸化物は、融点が高いので固相状態で存在するが、凝固初晶のδフェライトとの格子整合性が悪くなり、凝固核として作用しない。
そこで、本発明者は、これ等のＭｇＯ・Ａｌ2Ｏ3・ＣａＯ系及びＭｇＯ・ＣａＯ系の酸化物について、鋭意研究を重ねた結果、その酸化物の組成のモル分率を適正な範囲にすることにより、この酸化物の低融点化を抑制し、且つ、凝固初晶であるδフェライトとの格子整合度を改善することができることを知見し、本発明の完成に至ったものである。
【０００８】
ここで、図１は本発明の一実施の形態に係る微細凝固組織特性を有する溶鋼の処理方法に適用される溶鋼の処理装置の全体図、図２はＣａＯ−Ａｌ2Ｏ3−ＭｇＯ系の３元状態図、図３は鋳片の凝固組織の模式図である。
図１に示すように、本発明の一実施の形態に係る微細凝固組織特性を有する溶鋼の処理方法に用いる溶鋼の処理装置１０は、クロムを１０質量％以上含むフェライト系ステンレス溶鋼（以下溶鋼という）１１を入れた取鍋１２と、この取鍋１２の上方に設けられた金属Ａｌを貯蔵するホッパ１３及びホッパ１３から切り出された金属Ａｌを溶鋼１１に添加するためのシュート１４と、表面を薄鋼板で被覆した金属Ｍｇワイヤ１６をガイドパイプ１５により案内して、スラグ１７を貫通して溶鋼１１に添加する供給装置１８を備えている。
なお、符号１９は、取鍋１２内の溶鋼１１に不活性ガスの一例であるアルゴンガスを供給するためのポーラスプラグである。
【０００９】
次に、本実施の形態に係る微細凝固組織特性を有する溶鋼の処理方法について説明する。
上底吹き転炉や電気炉等の精練炉を用いて、脱炭及び燐、硫黄等の不純物を除去した溶鋼１１を取鍋１２に１５０トン受湯した。
その後、ポーラスプラグ１９から３０〜５０ＮＬ／分のアルゴンガスを吹き込みながら、ホッパ１３から金属Ａｌを５０〜１００ｋｇ添加して溶鋼１１を攪拌しながら均一に混合して脱酸を行った。
その後、溶鋼１１をサンプリングして、ＥＰＭＡ（Ｅｌｅｃｔｒｏｎ・Ｐｒｏｂｅ・Ｍｉｃｒｏ・Ａｎａｌｙｚｅｒ）により含まれる酸化物の組織を分析し、（３）式を用いて酸化物とδフェライトの格子整合度の指標であるα値を計算する。
α＝１７．４（ｋＡｌ2Ｏ3）＋３．９（ｋＭｇＯ）
＋０．３（ｋＭｇＡｌ2Ｏ4）＋１８．７（ｋＣａＯ） ・・・・・（３）
なお、ｋは酸化物のモル％を表す。
α値は、５００を超えると、酸化物が低融点化、あるいは高融点化したり、酸化物の表面を覆うＭｇＯが少なくなって凝固核として作用しなくなる。
更に、下記（４）式によりβ値を求める。このβ値は、９５未満になると、ＳｉＯ2、ＦｅＯ等の他の酸化物が増加して凝固核となる複合Ｍｇ酸化物の生成が阻害される。
β＝（ｋＡｌ2Ｏ3）＋（ｋＭｇＯ）＋（ｋＭｇＡｌ2Ｏ4）＋（ｋＣａＯ）
・・・・・（４）
なお、ｋは、酸化物のモル（％）を表す。
従って、α値が５００以下となり、β値が９５以上となるように、歩留りを考慮して、金属Ｍｇの添加量を求める。
このように求めた金属Ｍｇの値に相当する金属Ｍｇワイヤ１６をガイドパイプ１５で案内しながら供給装置１８を作動して溶鋼１１に添加する。
その結果、図２の斜線で示す範囲にあるＣａＯ・Ａｌ2Ｏ3・ＭｇＯの３元系と、一部がＡｌ2Ｏ3・ＭｇＯ、ＭｇＯ等からなる酸化物（複合Ｍｇ酸化物）を多数形成することができ、この複合Ｍｇ酸化物を溶鋼中に分散させ、温度が低下するにつれ、これ等の凝固核を起点にして溶鋼１１が凝固を開始し、等軸晶を生成し、微細な凝固組織を備えた鋳片を製造することができる。
【００１０】
このようにして、溶鋼１１が凝固した鋳片の凝固組織は、図３の（Ａ）に示すように微細組織となる。
凝固組織を微細にすることにより、鋳片の内部割れ、中心偏析、センターポロシティ等の内部欠陥を防止することができ、更に、凝固組織が微細な鋳片を加工した鋼材は、凝固組織が微細になるので、圧延等の加工性が良好になり、エッジシーム疵、ローピング等の表面欠陥等の発生も安定して防止することができる。
この金属Ｍｇの添加量としては、０．０００５〜０．０１０質量％の濃度に相当する範囲に調整することが好ましい。
Ｍｇ濃度が０．０００５質量％より低くなると、δフェライトとの格子整合度が５％以下の複合Ｍｇ酸化物を生成できず、鋳片の凝固組織を微細化することができない。一方、Ｍｇ濃度を０．０１０質量％より高くしても、凝固組織の微細化効果が飽和し、金属Ｍｇの合金コストが増大する。
【００１１】
【実施例】
次に、微細凝固組織特性を有する溶鋼の処理方法の実施例について説明する。
上底吹き転炉を用いて、クロムを１０〜２３質量％含む溶鋼を取鍋に１５０トン受湯し、ポーラスプラグから５０ＮＬ／分のアルゴンガスを吹き込みながら、ホッパから金属Ａｌを１００ｋｇ添加して溶鋼を攪拌しながら均一に混合して脱酸を行った。
その後、溶鋼をサンプリングして、ＥＰＭＡにより酸化物を測定し、前述した（１）、（２）式を満たすように、金属Ｍｇの添加量を調整し、複合Ｍｇ酸化物を生成させた。その後、溶鋼を連続鋳造して鋳片を製造した。
そして、鋳片の内部割れや中心偏析、センターポロシティ等の内部欠陥の有無、凝固組織の良否、加工後の鋼材の表面性状や加工性を含めた総合評価について調査した。その結果を表１に示す。
実施例１は、溶鋼に金属Ｍｇを１２５ｋｇ添加して溶鋼を攪拌し、溶鋼中に含まれる複合の酸化物のα値（（３）式で求めた酸化物とδフェライトとの格子整合度の指標）を３２６にした場合であり、鋳片に内部欠陥が発生しておらず、凝固組織が微細化されて良好であり、鋼材の表面性状や加工性も良く、総合評価として良好な結果が得られた。
実施例２は、金属Ｍｇを３０ｋｇ添加して溶鋼を攪拌し、溶鋼中に含まれる複合の酸化物のα値を４９７にした場合であり、鋳片の表面及び内部欠陥が発生しておらず、図３の（Ａ）に示すように凝固組織が微細化されて良好であり、鋼材の表面性状や加工性も良く、総合評価として良好な結果が得られた。
【００１２】
【表１】
これに対し、比較例１は、Ｍｇ添加前の溶鋼に含まれる酸化物の組成を何ら考慮せずに、金属Ｍｇを８５ｋｇ添加して溶鋼を攪拌した。その結果、溶鋼中に含まれる複合の酸化物のα値が５００を超え、鋳片の内部欠陥が発生し、図３の（Ｂ）に示すように凝固組織が粗大化して悪くなり、総合評価として悪い結果になった。
【００１４】
以上、本発明の実施の形態を説明したが、本発明は、上記した形態に限定されるものでなく、要旨を逸脱しない条件の変更等は全て本発明の適用範囲である。例えば、溶鋼中に含まれる酸化物の測定について、ＥＰＭＡの他に、スラグの組成や脱酸等の溶製条件をもとに、過去の実績から酸化物の組成を求めることもできる。
更に、添加するＭｇは、Ａｌ−Ｍｇ、Ｎｉ−Ｍｇ、Ｆｅ−Ｓｉ−Ｍｇ等の合金を用いることができる。
【００１５】
【発明の効果】
請求項１記載の微細凝固組織特性を有する溶鋼の処理方法は、溶鋼中に含まれるスラグ及び脱酸生成物からなる酸化物と溶鋼にＭｇを添加した際に生成する酸化物を所定範囲になるように、Ｍｇを添加するので、凝固核として作用し難いＣａＯやＡｌ2Ｏ3を改質して、凝固核として有効な複合Ｍｇ酸化物を多数生成して鋳片の凝固組織を微細にすることができ、鋳片の内部に発生する割れや中心偏析、センタポロシティ等の発生を抑制し、良鋳片及び鋼材の歩留りや品質を向上することができる。
【００１６】
特に、請求項１記載の微細凝固組織特性を有する溶鋼の処理方法は、フェライト系ステンレス溶鋼を用いるので、組織の微細化効果が著しく、良鋳片及び鋼材の歩留り、鋼材に発生するローピング、エッジシーム疵を安定して防止して品質を向上することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る微細凝固組織特性を有する溶鋼の処理方法に適用される溶鋼の処理装置の全体図である。
【図２】ＣａＯ−Ａｌ2Ｏ3−ＭｇＯ系の３元状態図である。
【図３】（Ａ）、（Ｂ）はそれぞれ鋳片の凝固組織の模式図である。
【符号の説明】
１０：溶鋼の処理装置、１１：溶鋼、１２：取鍋、１３：ホッパ、１４：シュート、１５：ガイドパイプ、１６：金属Ｍｇワイア、１７：スラグ、１８：供給装置、１９：ポーラスプラグ[0001]
BACKGROUND OF THE INVENTION
The present invention improves the quality, workability, etc. by making the solidified structure fine when producing ingots and cast pieces of molten steel after decarburizing and refining using the ingot forming method or continuous casting. The present invention relates to a method for treating molten steel having finely solidified structure characteristics.
[0002]
[Prior art]
Conventionally, molten steel is made of alloyed iron so that desired mechanical properties can be obtained after decarburization and refining using a refining furnace such as a top-bottom converter or electric furnace to remove carbon, phosphorus, sulfur, etc. Ingots and slabs are produced by adding components to adjust the ingredients and solidifying them by an ingot-making method or continuous casting.
And a steel material is manufactured by heating an ingot and a slab and performing a rolling process.
However, when the molten steel solidifies, especially when the internal solidification structure becomes coarse, internal defects such as cracks, center segregation, and center porosity are generated inside the slab, resulting in scrapping, resulting in a decrease in yield of good slab. .
In addition, stainless steel materials that emphasize the appearance have surface defects such as edge seam wrinkles and roping, resulting in problems such as poor appearance and increased trim amount at the end, leading to a decrease in quality and yield of good products. .
As a countermeasure against this, as described in JP-A-52-47522, an electromagnetic stirring device is provided at a position of 1.5 to 3.0 m from the molten metal surface in the mold during continuous casting, and a thrust of 60 mmHg. The slab is manufactured by stirring with. Alternatively, as described in JP-A-52-60231, low temperature casting is performed at a superheated temperature of the molten steel of 10 to 50 ° C., and electromagnetic stirring is performed on the unsolidified layer of the slab during casting. It has been practiced to produce a steel material free from center segregation and UST defects by making the solidified structure of the slab a fine structure consisting of equiaxed crystals.
Furthermore, as described in JP-A-7-48616, the composition of the slag covering the surface of the molten steel in a container such as a ladle is 3 to 15 % by mass of MgO, 5 of FeO, Fe 2 O 3 and MnO. By making the CaO.SiO 2 .Al 2 O 3 system less than mass% and adding an Mg alloy through this slag, the Mg yield in the molten steel is increased, and fine MgO, MgO. Production of oxides of Al 2 O 3 to improve the quality of steel materials has been performed.
[0003]
[Problems to be solved by the invention]
However, in Japanese Patent Laid-Open No. 52-47522, electromagnetic stirring is performed on molten steel that is solidifying in a mold to suppress growing columnar crystals (dendritic structure). Can be made fine to some extent. However, in order to make the entire slab finer, a multistage electromagnetic stirring device is required, which increases equipment costs and is extremely difficult from the viewpoint of installation space. There is a limit to the production.
Furthermore, in Japanese Patent Application Laid-Open No. 52-60231, since low temperature casting is performed, inclusions adhere to the inner surface of the immersion nozzle, resulting in nozzle clogging, or the temperature of the molten steel in the mold is lowered, resulting in hot water surface coating. In some cases, the operation becomes unstable, for example, casting must be interrupted.
Further, in the method described in JP-A-7-48616, the surface of the molten steel is covered with CaO · SiO 2 · Al 2 O 3 slag, so that the evaporation of Mg is suppressed and the yield is improved. Have advantages. However, depending on the slag composition, it may not always be possible to stably produce oxides of MgO and MgO.Al 2 O 3 effective as solidification nuclei when the molten steel solidifies.
That is, a low melting point oxide containing CaO or Mg oxide with the surface covered with Al 2 O 3 is formed by Al 2 O 3 or CaO contained in the slag, and a lattice with a solidified primary crystal δ ferrite. The consistency deteriorates and it does not act as an inoculum nucleus (coagulation nucleus).
As a result, the molten steel cannot be solidified starting from these oxides, and a slab having a fine structure cannot be produced.
When the solidified structure becomes coarse, defects such as cracks, center segregation, and center porosity occur inside the slab, leading to a decrease in the yield of good slabs.
Furthermore, the steel material processed using this slab also has problems such as surface and internal defects caused by a coarse solidified structure, resulting in a decrease in yield and quality.
[0004]
The present invention has been made in view of such circumstances, and it is possible to improve the quality by generating effective inoculation nuclei and making the solidified structure fine, preventing the surface and internal defects generated in slabs and steel materials. It aims at providing the processing method of the molten steel which has a fine solidification structure characteristic.
[0005]
[Means for Solving the Problems]
The processing method of the molten steel having the fine solidification structure characteristics of the present invention that meets the above-mentioned object is the slag (including Al 2 O 3 and CaO) and deoxidation product contained in the ferritic stainless molten steel whose surface is covered with slag. The amount of metal Mg added is determined in consideration of the yield so that the oxide produced when Mg is added to the ferritic stainless steel molten steel satisfies the following formulas (1) and (2): And Mg is added.
17.4 (kAl 2 O 3 ) +3.9 (kmMgO) +0.3 (kmMgAl 2 O 4 ) +18.7 (kCaO) ≦ 500 (1)
(KAl 2 O 3 ) + (kmgO) + (kmgAl 2 O 4 ) + (kCaO) ≧ 95
(2)
Here, k represents the mol% of the oxide.
By this method, a CaO.Al 2 O 3 .MgO ternary system in the range shown by the oblique lines in FIG. 2 is an effective oxide as an inoculation nucleus (solidification nucleus) having a lattice matching degree of 5% or less with δ ferrite. And a composite Mg oxide composed of MgO.Al 2 O 3 , MgO, etc., and when molten steel solidifies, these composite Mg oxides act as solidification nuclei, thereby producing equiaxed crystals. The solidified structure of the slab can be made finer.
[0006]
Here, the molten steel is Ru ferritic stainless molten steel der.
The solidification structure of ferritic stainless steel, which tends to coarsen the solidification structure, can be made into a fine solidification structure, suppressing internal cracks, center segregation, center porosity, etc. occurring in the slab, and processing this slab It is possible to prevent the occurrence of roping and edge seam wrinkles due to the coarse solidified structure generated in the steel material.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
When Mg is added to molten steel to produce an oxide and the solidification structure of the slab is refined, MgO / Al 2 O 3 / CaO-based oxides are formed by other additive elements and slag composition. Or a high melting point oxide such as MgO / CaO is formed.
However, oxides of MgO · Al 2 O 3 · Ca O is, since a low melting point, when the molten steel solidifies, does not act as solidification nuclei. On the other hand, the oxide of MgO · Ca 2 O exists in a solid state because of its high melting point, but the lattice matching with the solidification primary crystal δ ferrite is deteriorated and does not act as a solidification nucleus.
Therefore, as a result of intensive studies on these MgO.Al 2 O 3 .CaO-based and MgO.CaO-based oxides, the present inventors have set the molar fraction of the oxide composition within an appropriate range. As a result, it has been found that the lowering of the melting point of the oxide can be suppressed and the degree of lattice matching with δ ferrite, which is a solidified primary crystal, can be improved, and the present invention has been completed.
[0008]
Here, FIG. 1 is an overall view of a processing apparatus for molten steel applied to a processing method for molten steel having finely solidified structure characteristics according to an embodiment of the present invention, and FIG. 2 is a diagram of a CaO—Al 2 O 3 —MgO system. A ternary phase diagram, FIG. 3 is a schematic diagram of a solidified structure of a slab.
As shown in FIG. 1, the molten
In addition, the code |
[0009]
Next, the processing method of the molten steel which has the fine solidification structure characteristic based on this Embodiment is demonstrated.
Using a smelting furnace such as a top-bottom blowing converter or an electric furnace, 150 tons of
Then, while blowing argon gas of 30 to 50 NL / min from the
Thereafter, the
α = 17.4 (kAl 2 O 3 ) +3.9 (kmMgO)
+0.3 (kmMgAl 2 O 4 ) +18.7 (kCaO) (3)
Note that k represents the mol% of the oxide.
When the α value exceeds 500, the oxide has a low melting point or a high melting point, or the MgO covering the surface of the oxide is reduced and does not act as a solidification nucleus.
Further, the β value is obtained by the following equation (4). When this β value is less than 95, other oxides such as SiO 2 and FeO increase to inhibit the formation of composite Mg oxides that become solidification nuclei.
β = (kAl 2 O 3 ) + (kmMgO) + (kmMgAl 2 O 4 ) + (kCaO)
(4)
Note that k represents the mole (%) of the oxide.
Therefore, the additive amount of metal Mg is determined in consideration of the yield so that the α value is 500 or less and the β value is 95 or more.
The
As a result, there are many ternary systems of CaO.Al 2 O 3 .MgO in the range shown by the oblique lines in FIG. 2 and a large number of oxides (composite Mg oxides) partially made of Al 2 O 3 .MgO, MgO, etc. As this composite Mg oxide is dispersed in the molten steel and the temperature decreases, the
[0010]
In this way, the solidified structure of the slab solidified by the
By making the solidification structure fine, internal defects such as internal cracks, center segregation, and center porosity of the slab can be prevented, and the steel material processed from a slab with a fine solidification structure has a fine solidification structure. Therefore, workability such as rolling is improved, and surface defects such as edge seam wrinkling and roping can be stably prevented.
The addition amount of the metal Mg is preferably adjusted to a range corresponding to a concentration of 0.0005 to 0.010 mass% .
When the Mg concentration is lower than 0.0005 mass%, a composite Mg oxide having a lattice matching degree with δ ferrite of 5% or less cannot be generated, and the solidified structure of the slab cannot be refined. On the other hand, even if the Mg concentration is higher than 0.010 % by mass , the effect of refining the solidified structure is saturated, and the alloy cost of metallic Mg increases.
[0011]
【Example】
Next, an example of a processing method for molten steel having finely solidified structure characteristics will be described.
Using an upper-bottom blowing converter, 150 tons of molten steel containing 10 to 23 % by mass of chromium is received in a ladle, and 100 kg of metal Al is added from a hopper while argon gas is blown at 50 NL / min from a porous plug. The molten steel was uniformly mixed with stirring to perform deoxidation.
Thereafter, the molten steel was sampled, the oxide was measured by EPMA, and the amount of metal Mg added was adjusted so as to satisfy the above-described formulas (1) and (2), thereby generating a composite Mg oxide. Thereafter, the molten steel was continuously cast to produce a slab.
And the comprehensive evaluation including the presence or absence of internal defects, such as an internal crack of a slab, center segregation, a center porosity, the quality of a solidification structure, and the surface property and workability of the steel material after a process was investigated. The results are shown in Table 1.
In Example 1, 125 kg of metal Mg was added to molten steel and the molten steel was stirred, and the α value of the composite oxide contained in the molten steel (of the lattice matching degree of the oxide and δ ferrite determined by the equation (3)) The index) is set to 326. Internal defects are not generated in the slab, the solidified structure is refined and good, the surface properties and workability of the steel are good, and the overall evaluation is good. Obtained.
Example 2 is a case where 30 kg of metal Mg is added and the molten steel is stirred, and the α value of the composite oxide contained in the molten steel is set to 497, and the surface of the slab and internal defects are not generated. As shown in FIG. 3 (A), the solidified structure was refined and good, and the surface properties and workability of the steel were good, and good results were obtained as a comprehensive evaluation.
[0012]
[Table 1]
In contrast, Comparative Example 1, the composition of oxides contained in molten steel before Mg addition, without any consideration was stirred molten steel was 8 5k g added pressure to the metal Mg. As a result, the α value of the composite oxide contained in the molten steel exceeds 500, an internal defect of the slab is generated , and the solidified structure becomes coarse and deteriorates as shown in FIG. As a bad result.
[0014]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention. For example, regarding the measurement of oxides contained in molten steel, in addition to EPMA, based on melting conditions such as slag composition and deoxidation, the oxide composition can also be obtained from past results.
Furthermore, as the added Mg, an alloy such as Al—Mg, Ni—Mg, Fe—Si—Mg can be used.
[0015]
【The invention's effect】
The processing method of the molten steel which has the fine solidification structure characteristic of
[0016]
In particular, since the processing method for molten steel having finely solidified structure characteristics according to
[Brief description of the drawings]
FIG. 1 is an overall view of a molten steel processing apparatus applied to a method for processing molten steel having finely solidified structure characteristics according to an embodiment of the present invention.
FIG. 2 is a ternary phase diagram of a CaO—Al 2 O 3 —MgO system.
FIGS. 3A and 3B are schematic diagrams of solidification structures of slabs, respectively.
[Explanation of symbols]
10: Molten steel processing device, 11: Molten steel, 12: Ladle, 13: Hopper, 14: Chute, 15: Guide pipe, 16: Metal Mg wire, 17: Slag, 18: Feeder, 19: Porous plug
Claims (1)
１７．４（ｋＡｌ2Ｏ3）＋３．９（ｋＭｇＯ）＋０．３（ｋＭｇＡｌ2Ｏ4）＋１８．７（ｋＣａＯ）≦５００ ・・・・・（１）
（ｋＡｌ2Ｏ3）＋（ｋＭｇＯ）＋（ｋＭｇＡｌ2Ｏ4）＋（ｋＣａＯ）≧９５
・・・・・（２）
ここで、ｋは、酸化物のモル％を表す。The composition of oxides composed of slag (including Al 2 O 3 and CaO) and deoxidation products contained in the ferritic stainless steel with the surface covered with slag was determined, and Mg was added to the ferritic stainless steel In consideration of the yield so that the oxide produced at the time satisfies the following formulas (1) and (2), the amount of metal Mg is obtained and Mg is added to obtain molten steel having finely solidified structure characteristics Processing method.
17.4 (kAl 2 O 3 ) +3.9 (kmMgO) +0.3 (kmMgAl 2 O 4 ) +18.7 (kCaO) ≦ 500 (1)
(KAl 2 O 3 ) + (kmgO) + (kmgAl 2 O 4 ) + (kCaO) ≧ 95
(2)
Here, k represents the mol% of the oxide.
Priority Applications (15)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000086215A JP4287974B2 (en) | 2000-03-27 | 2000-03-27 | Method for processing molten steel with finely solidified structure characteristics |
| KR1020007013895A KR100550678B1 (en) | 1999-04-08 | 2000-04-07 | Method for treatment of molten steel for making solidification structure of cast steel piece fine |
| RU2001101464/02A RU2228235C2 (en) | 1999-04-08 | 2000-04-07 | Steel casting (variants) and steel material with improved workability, method for processing melt steel (variants) and method for making steel casting and steel material |
| CNB2005100068043A CN1321766C (en) | 1999-04-08 | 2000-04-07 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
| EP07005688.2A EP1803512B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel with excellent workability and method for manufacturing the cast steel |
| EP10186285.2A EP2308617B1 (en) | 1999-04-08 | 2000-04-07 | Method for processing molten steel |
| KR1020057018257A KR100706973B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece with fine solidification sturcture and excellent forming characteristics and steel product and seamless steel pipe produced by using the same |
| EP10186277.9A EP2308616B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
| CA002334352A CA2334352C (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel material with excellent workability, method for processing molten steel therefor and method for manufacutring the cast steel and steel material |
| EP00915437A EP1099498A4 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| EP10186292.8A EP2292352B1 (en) | 1999-04-08 | 2000-04-07 | Method for processing molten steel for cast steel and steel material with excellent workability |
| AU36746/00A AU753777B2 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| PCT/JP2000/002296 WO2000061322A1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| US09/719,206 US6585799B1 (en) | 1999-04-08 | 2000-04-07 | Cast steel piece and steel product excellent in forming characteristics and method for treatment of molted steel therefor and method for production thereof |
| US10/222,362 US6918969B2 (en) | 1999-04-08 | 2002-08-16 | Cast steel and steel material with excellent workability, method for processing molten steel therefor and method for manufacturing the cast steel and steel material |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000086215A JP4287974B2 (en) | 2000-03-27 | 2000-03-27 | Method for processing molten steel with finely solidified structure characteristics |
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| TWI464271B (en) * | 2011-12-20 | 2014-12-11 | Univ Nat Cheng Kung | A metallurgical method by adding mg-al to modify the inclusions and grain refinement of steel |
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