JP3619414B2

JP3619414B2 - Method for decarburizing and refining molten stainless steel

Info

Publication number: JP3619414B2
Application number: JP2000025604A
Authority: JP
Inventors: 勝彦加藤; 昭男新飼
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1999-02-08
Filing date: 2000-02-02
Publication date: 2005-02-09
Anticipated expiration: 2020-02-02
Also published as: JP2000297315A

Description

【０００１】
【発明の属する技術分野】
本発明は、ステンレス溶鋼の脱炭精錬を行う際に、スプラッシュにより発生した地金の細粒化を抑制し、細粒地金が排気系に付着や堆積するのを防止するステンレス溶鋼の脱炭精錬方法に関する。
【０００２】
【従来の技術】
ステンレス溶鋼の脱炭精錬においては、容器内を減圧して吹酸することによりクロムの酸化を抑制した脱炭が行われており、この代表的な方法としてＲＨ−ＯＢ法が広く知られている。
このＲＨ−ＯＢ法は、取鍋内の溶鋼に上昇管と下降管の両方を浸漬し、上昇管から供給するガスのガスリフト作用により溶鋼を吸い上げ、下降管から吐出して取鍋内の溶鋼を循環させながら、上昇管に設けたノズルから酸素含有ガスの吹き込みを行って脱炭する。
また、特開平８−１０９４１０号公報には、取鍋内の溶鋼に浸漬管を浸漬して、浸漬管の内部を排気して減圧し、取鍋の底部から０．６〜１５．０Ｎリットル／（分・溶鋼トン）の不活性ガスを供給しながら、浸漬管の上方より酸素含有ガスを吹き付けて脱炭を行うステンレス溶鋼の脱炭精錬方法が提案されている。
この方法は、Ｃｒ₂ Ｏ₃ （以下、クロム酸化物という）の生成とクロムのロスを少なくして迅速に脱炭を行うことができることから実用化が図られている。
【０００３】
【発明が解決しようとする課題】
しかしながら、前述のＲＨ−ＯＢ法では、浸漬管が上昇管と下降管に分離されており上昇管から吸い上げたステンレス溶鋼が下降管を経て取鍋に戻るまでの時間が短いので、ステンレス溶鋼の吹酸脱炭精錬を行う場合には、真空槽内で一旦生成したクロム酸化物が、瞬時に真空槽内から流出して、攪拌の影響が及ばない取鍋の上部に浮上する。
取鍋の上部に浮上したクロム酸化物は、ステンレス溶鋼中の炭素と殆ど反応しないので、脱炭の効率が悪く、クロム酸化物の増大を招き、このクロム酸化物を還元する還元剤の増加やクロムのロスが生じる等の問題がある。
更に、上昇管に供給する不活性ガスのガスリフトの作用により溶鋼を循環するため、上昇管から吹き込まれる気体の絶対量が増加し、吹き込まれた酸素含有ガスの脱炭酸素効率が低下するので、スプラッシュの発生と二次バースト（スプラッシュにより生じた地金が再酸化して細粒化する）が激しくなる。
また、特開平８−１０９４１０号公報では、取鍋の底部から不活性ガスを吹き込んで取鍋内の溶鋼を強く攪拌しながら、上方から酸素を溶鋼に吹き付けて脱炭するので、酸素を吹き付ける溶鋼表面にクロム酸化物が多量に生成する。
このクロム酸化物は、炭素と急激に反応し、その際に生成するＣＯガスの溶鋼表面での破泡によりスプラッシュが発生して地金が飛散する。
この地金が二次バーストを生じて細粒化し、排ガスに随伴して飛散して浸漬管内あるいは排気系に付着、堆積する。
また、酸素を溶鋼表面に吹き付けて脱炭するので、脱炭に有効に働く酸素効率が４０〜５５％と低くなり、脱炭に作用しない酸素が浸漬管内で二次燃焼し、飛散した地金の二次バーストを助長するので、排気系等に付着、堆積する細粒地金が増大する。
特に、クロムを５重量％以上含有するステンレス溶鋼では、排気系に生じた細粒地金の付着や堆積により、エゼクターの排気抵抗が増加して高真空度が得られない。
その結果、ステンレス溶鋼中のクロムの酸化が進行して、クロム酸化物の増加に起因するクロムのロスあるいはクロム酸化物を還元するためのＡｌ等の還元剤が増加する等の問題がある。
【０００４】
本発明はかかる事情に鑑みてなされたもので、ステンレス溶鋼の脱炭精錬の際に、スプラッシュにより地金が飛散し、その地金が二次バーストを生じて細粒になるのを抑制し、細粒地金が排気系に付着、堆積するのを防止し、安定した脱炭精錬を行うことができるステンレス溶鋼の脱炭精錬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】
前記目的に沿う第１の発明に係るステンレス溶鋼の脱炭精錬方法は、取鍋内のステンレス溶鋼に、排気ダクトが設けられた浸漬管を浸漬し、該浸漬管の内部を減圧すると共に、前記取鍋の底部から０．６〜１５．０Ｎリットル／（分・溶鋼トン）の不活性ガスを供給しつつ、前記浸漬管内の湯面の上方より酸素含有ガスを吹き付けて脱炭精錬を行うステンレス溶鋼の脱炭精錬方法において、前記排気ダクトに設けた排ガス流量計で測定された排ガス流量から下式により求められる前記浸漬管内の排ガス流速Ｖを５〜２０ｍ／秒にする。
Ｖ＝Ｑ÷Ｓ×（Ｐ ₀ ／Ｐ）×（Ｔ／Ｔ ₀ ）
ここで、Ｑは排ガス流量（Ｎｍ ³ ／ｈｒ）、Ｓは浸漬管の直径方向の面積（ｍ ² ）、Ｐ ₀ は標準大気圧（１０１３２５Ｐａ）、Ｐは浸漬管の内圧（Ｐａ）、Ｔは排ガス温度（Ｋ）、Ｔ ₀ は標準温度（Ｋ）である。
この方法により、スプラッシュにより飛散する地金が排ガスに随伴して飛散するのを抑制して、細粒地金が排気系に付着や堆積するのを防止し、排気抵抗をなくして高真空度による安定した脱炭精錬を行うことができる。
浸漬管内の排ガス流速が５ｍ／秒未満では、酸素含有ガスの吹き付け量を減少したり、真空度を極端な低真空にするので、脱炭精錬により生成する排ガス量の低減と共に十分な脱炭反応を行うことができず、精錬時間の延長やクロムロスを招く。一方、浸漬管内の排ガス流速が２０ｍ／秒を超えると、スプラッシュにより飛散する地金が排ガスに随伴して、雰囲気中に残存する酸素により二次燃焼して二次バーストを生じて、細粒化した地金が排気系に付着、堆積する。
この理由から、浸漬管内の排ガス流速は、５〜１５ｍ／秒にすると、脱炭精錬時間の延長、排気系への細粒地金の付着や堆積の防止等により好ましい結果が得られる。
また、取鍋の底部から供給する不活性ガスの量が０．６Ｎリットル／（分・溶鋼トン）未満では、浸漬管内の湯面に形成する気泡活性面が小さくなり、ステンレス溶鋼の全体の攪拌が弱くなって脱炭精錬の時間が延長する。不活性ガスの量が１５．０Ｎリットル／（分・溶鋼トン）を超えると、ステンレス溶鋼の全体の攪拌が強くなり過ぎて、浸漬管内の湯面で不活性ガスの気泡の破泡及び吹酸により地金の飛散が増加する。
【０００６】
ここで、前記排ガス流速を前記浸漬管内の湯面の上方より吹き付ける酸素含有ガス量により調整することができる。
これにより、溶鋼の湯面に吹き付ける酸素含有ガス中の酸素の脱炭酸素効率を高めて、クロム酸化物の生成を抑制し、浸漬管内の二次燃焼を少なくして飛散する地金の二次バーストを抑制することで地金の細粒化を防止できる。
【０００７】
更に、前記排ガス流速を前記浸漬管内の真空度により調整することができる。
これにより、浸漬管内の排ガス流速を迅速に低減できるので、二次バーストにより生成した細粒地金が排気系に飛散するのを的確に防止できる。
【０００８】
また、前記浸漬管の溶鋼浸漬部の内表面積を前記取鍋内の全溶鋼表面積の０．１〜０．７にすることができる。
これにより、脱炭に有効な気泡活性面（不活性ガスの気泡が膨張し、破泡して湯面が波立つ状態）を大きくし、脱炭に寄与する酸素効率を高くし、二次バーストを抑制しながら短時間で低い炭素濃度にできる。
浸漬管の溶鋼浸漬部の内表面積が取鍋内の全溶鋼表面積の０．１より小さいと、ステンレス溶鋼の攪拌力が不足して気泡活性面が狭くなり、脱炭反応が遅くなって到達炭素濃度を低くできない。一方、０．７より大きくなると、取鍋の内側と浸漬管の外周面との隙間が狭くなり、サンプリングの支障や浸漬管外に流出したクロム酸化物等の付着により、取鍋への浸漬管の浸漬が困難になる。
【０００９】
前記目的に沿う第２の発明に係るステンレス溶鋼の脱炭精錬方法は、取鍋内のステンレス溶鋼に浸漬管を浸漬し、該浸漬管の内部を減圧すると共に、前記取鍋の底部から０．６〜１５．０Ｎリットル／（分・溶鋼トン）の不活性ガスを供給しつつ、前記浸漬管内の湯面の上方に配置したランスから該湯面に向けて酸素含有ガスを吹き付けて脱炭精錬を行うステンレス溶鋼の脱炭精錬方法において、前記酸素含有ガスは、下記（１）、（２）式により求まるキャビティー深さＬが２１０〜５００ｍｍとなるようにして吹き付ける。
Ｌ＝Ｌｈ×１０^(-780H/Lh) ・・・・・（１）
Ｌｈ＝０．８９４×（Ｑ² ／Ｓ×ｎ）^1/3 ・・・・・（２）
ここで、Ｌはキャビティー深さ（ｍｍ）、Ｈはランスの先端位置から静止湯面までの距離（ｍ）、ＬｈはＨ＝０の時のキャビティー深さ（ｍｍ）、Ｑは酸素含有ガスの流量（Ｎｍ³ ）、Ｓはランス吐出口の最狭部の断面積（ｍ² ）、ｎはランス吐出口数である。
溶鋼の湯面に吹き付ける酸素含有ガスによるキャビティー深さＬが２１０〜５００ｍｍとなるように、吹酸をハードブローにするので、吹酸の火点及びその近傍における脱炭反応と、生成したＣｒ₂ Ｏ₃ の溶鋼中の炭素との反応を促進し、脱炭及び生成したＣＯガスの湯面上方での燃焼（二次燃焼）に消費される酸素を含めた脱炭酸素効率を向上でき、吹酸によって飛散する地金の粒を大きくし、しかも、この地金が酸素の噴流に暴露されるのを抑制して二次バーストを防止することができる。
【００１０】
【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。
図１は本発明の一実施の形態に係るステンレス溶鋼の脱炭精錬方法に適用される脱炭精錬装置の概念図、図２は同脱炭精錬装置を用いた吹酸脱炭精錬中の排ガス流速、送酸量、排ガス流量及び真空度の変化を示すグラフ、図３はランスの種類と排気ダクトへの地金付着速度の関係を示すグラフ、図４は吹酸時の火点近傍の部分拡大図である。
図１に示すように、本発明の一実施の形態に係るステンレス溶鋼の脱炭精錬方法に適用される脱炭精錬装置１０は、取鍋１１及び取鍋１１に受湯されたステンレス溶鋼１２内に図示しない昇降装置により浸漬する直胴型の浸漬管１３を有し、ステンレス溶鋼１２に不活性ガスを吹き込んで攪拌するためのポーラスプラグ１４を取鍋１１の底部に、浸漬管１３内のステンレス溶鋼１２の湯面１２ａに吹酸する酸素含有ガスの流量を設定する流量調整弁１５を設けたランス１６を浸漬管１３の上部に備えている。
また、浸漬管１３には、内部を減圧する図示しないエゼクターに連通した排気ダクト１７を設けている。
この排気ダクト１７には、浸漬管１３内部の真空度を測定する真空度計１８と排ガス流量計１９を設けている。
更に、浸漬管１３の溶鋼浸漬部の内表面積は、取鍋１１内のステンレス溶鋼１２の全溶鋼表面積に対して０．１〜０．７となるようにしている。
なお、図中、符号２０は浸漬管１３内に合金鉄や生石灰等の副原料を添加するシュートであり、２１は合金鉄や生石灰等の副原料の貯蔵ホッパーである。
【００１１】
次に、この脱炭精錬装置１０を用いた本実施の形態に係るステンレス溶鋼の脱炭精錬方法について説明する。
まず、取鍋１１にクロムを５重量％以上含有した１５０トンのステンレス溶鋼１２を受湯し、この取鍋１１内に浸漬管１３をその先端が取鍋１１内ステンレス溶鋼１２の表面から深さ６００ｍｍの位置に来るように浸漬し、浸漬管１３の内部を図示しないエゼクターにより排気ダクト１７から排気して減圧した。
浸漬管１３内の湯面１２ａには、取鍋１１のポーラスプラグ１４から不活性ガスの一例であるアルゴンガスを０．６〜１５．０Ｎリットル／（分・溶鋼トン）供給することにより気泡活性面を形成し、浸漬管１３内の真空度が２００ｔｏｒｒに到達してから、この湯面１２ａにランス１６を介して２８００ｍｍの高さから３０００Ｎｍ³ ／ｈｒの酸素含有ガスの一例である酸素を吹き付けて（吹酸）脱炭精錬を行った。
脱炭精錬の初期、すなわち吹酸を開始した直後は、浸漬管１３内に昇熱用の金属Ａｌを添加しているので、酸素が金属Ａｌの燃焼に消費され、発生する排ガス量が少ない。
金属Ａｌの燃焼が終わると、積極的に酸素とステンレス溶鋼１２中のクロムが（３）式の反応によりＣｒ₂ Ｏ₃ を生成し、このＣｒ₂ Ｏ₃ がステンレス溶鋼１２中の炭素と（４）式のように反応して脱炭が行われる。
２Ｃｒ＋３／２Ｏ₂ →Ｃｒ₂ Ｏ₃ ・・・・・（３）
Ｃｒ₂ Ｏ₃ ＋３Ｃ→２Ｃｒ＋３ＣＯ↑ ・・・・・（４）
この際に真空度が低いと、ステンレス溶鋼１２中のクロムの酸化が急激に起こり、過剰のＣｒ₂ Ｏ₃ が生成し、突沸等の異常反応やクロムの酸化ロスを招くことになる。
【００１２】
従って、図２に示すように、Ｃｒ₂ Ｏ₃ の過剰生成を抑制するために、吹酸初期には真空度計１８の値が１００ｔｏｒｒ程度の高真空度になるように図示しないエゼクターの排気量を調整して操業する。
そして、生成したＣＯガスや二次燃焼したＣＯ₂ ガス等を含む排ガスの流量（図中二点鎖線で示す）は、排気ダクト１７に設けた排ガス流量計１９で測定され、この排ガス流量は、脱炭反応の開始と共に急激に増加し、排ガス流速（図中太実線で示す）も排ガス流量の増加に追随して上昇する。
そこで、真空度（図中破線で示す）を１００ｔｏｒｒの高真空から図示しないエゼクターの排気量を調整して１５０ｔｏｒｒの低真空に調整し、排ガス流速を８〜１２ｍ／秒の範囲になるようにする。
この排ガス流速（ｍ／秒）をＶとすると、Ｖは（５）式により求めることができる。
Ｖ＝Ｑ÷Ｓ×（Ｐ₀ ／Ｐ）×（Ｔ／Ｔ₀ ）・・・・・（５）
ここで、Ｑは排ガス流量（Ｎｍ³ ／ｈｒ）、Ｓは浸漬管の直径方向の面積（ｍ² ）、Ｐ₀ は標準大気圧（１０１３２５Ｐａ）、Ｐは浸漬管の内圧（Ｐａ）、Ｔは排ガス温度（Ｋ）、Ｔ₀ は標準温度（Ｋ）である。
【００１３】
更に、ステンレス溶鋼１２の脱炭反応が進む中期では、排ガス流量がさらに増加し、排ガス流量計１９の指示が約３５００Ｎｍ³ ／ｈｒになり、排ガス流速が１２ｍ／秒を超える状態になったので、真空度を１５０ｔｏｒｒに維持した状態で、流量調整弁１５の開度を調整して、吹酸の酸素量すなわち送酸量（図中実線で示す）を２５００Ｎｍ³ ／ｈｒに減少し、排ガス流速を８〜１２ｍ／秒の範囲にした。
脱炭精錬の末期では、ステンレス溶鋼１２中の炭素濃度の低下により排ガス流量が減少するので、排ガス流量の減少に合わせて、浸漬管１３内を１５０ｔｏｒｒの低真空から５〜２ｔｏｒｒの高真空にして脱炭精錬を行う。
このように、送酸量と真空度を調整して浸漬管１３内を上昇する排ガスの流速を低くしているので、スプラッシュにより発生した地金の二次バーストにより生成する細粒な地金が排ガスの流れに随伴して飛散し、排気ダクト１７に付着したり、堆積するのを防止でき、排気抵抗の増加や堆積した地金の処理等の手間を解消することができる。
【００１４】
また、図３に示すように、吹酸に用いるランス１６は、吐出口の形状が一般に用いられてるストレートノズルの場合では、ガスの噴流が広がってソフトブローになり、脱炭の酸素効率が低下してスプラッシュにより発生した地金が雰囲気中に存在する酸素と二次燃焼を生じて二次バーストが発生する。
しかし、吐出口から音速以上の速さで吹き出すラバールノズルを用いてハードブローする場合では、脱炭の酸素効率が高くなり、スプラッシュにより発生した地金の二次バーストを抑制できる。
この傾向は３孔ラバールよりも単孔ラバールを用いると、よりハードブローにすることができるので、二次バーストの抑制に有効である。
即ち、図４に示すように、単孔ラバールを用いたハードブローの条件を一般的に用いられている前述した（１）、（２）式から求めた湯面１２ａのキャビティー深さ（へこみ深さ）Ｌ値を２１０〜５００ｍｍにすることにより、火点Ａの近傍では、酸素と溶鋼１２中の炭素の反応により脱炭が行われると共に、酸素とクロム（Ｃｒ）が反応してＣｒ₂ Ｏ₃ を生成する。
しかも、キャビティー深さＬを所定の範囲にしているので、生成したＣｒ₂ Ｏ₃ が浮上する際に、浸漬管１３内のステンレス溶鋼１２の上層部で炭素により還元され、脱炭に寄与する酸素効率を向上することができる。
また、キャビティー深さＬを前記の範囲のように深くするために、吹酸を行う際の吹き付け力を大きくすると、湯面１２ａから飛散する地金の量が増加し、その地金の粒が比較的大きくなる。
しかし、吹酸をハードブローにすることにより、酸素噴流の広がりは小さくなり、酸素の噴流に暴露される地金を少なくできるので、二次バースト（図中に点線で示す細粒）による微細化を抑制することができる。
そして、火点近傍のＣｒ₂ Ｏ₃ の還元を含めた脱炭酸素効率の向上、地金の粗大化、酸素の噴流の広がりの抑制等の相乗した働きにより、微細地金が排気系ダクト等に堆積するのを防止して、安定した操業を行うことができる。
吹酸をソフトブローにして、キャビティー深さＬが２１０ｍｍより小さくなると、地金の二次バーストが発生し、排気系ダクト等への地金付着が発生する。
吹酸時の吹き付け力が強過ぎて、キャビティー深さＬが５００ｍｍより大きくなると、地金の飛散が極端に増加したり、火点近傍の耐火物が損耗する。
従って、キャビティー深さＬ値は、３００〜４５０ｍｍにすると、より好ましい結果が得られる。
【００１５】
【実施例】
次に、本発明に係るステンレス溶鋼の脱炭精錬方法を適用した実施例について説明する。
転炉によりクロムを１３重量％含有するステンレス溶鋼を１５０トン溶製して取鍋に受湯してから、溶鋼浸漬部が取鍋内の全溶鋼表面積の０．３の内表面積を有する浸漬管の先端を取鍋のステンレス溶鋼の表面から深さ６００ｍｍに浸漬し、浸漬管内部を減圧して浸漬管内の真空度が１００ｔｏｒｒに到達した後、浸漬管上方からランスを介して吹酸して脱炭精錬を行い、排ガス流速、排気ダクト地金堆積の有無、操業時真空度の変動の有無等を調査した。
表１に示すように、実施例１は、吹酸時のキャビティー深さを３００ｍｍにし、吹酸脱炭精錬の初期に単孔ラバールを用いて３０００Ｎｍ³ ／ｈｒの酸素を湯面に吹き付け、中期には、真空度を１５０ｔｏｒｒの低真空にして酸素を２５００Ｎｍ³ ／ｈｒに減少し、吹酸脱炭精錬の末期では、中期と同じ酸素量にして真空度のみを１５０ｔｏｒｒから順次５０ｔｏｒｒの高真空にした場合であり、排ガス流速を平均で８ｍ／秒にでき、排気ダクト地金堆積が無く、操業時の真空度の変動が全く生じず安定した脱炭精錬を行うことができ、総合評価として良好（◎）であった。
更に、実施例２は、吹酸時のキャビティー深さを４５０ｍｍにし、吹酸脱炭精錬の初期に単孔ラバールを用いて３０００Ｎｍ³ ／ｈｒの酸素を湯面に吹き付けを行い、中期では、真空度を１２０ｔｏｒｒの低真空にして酸素を２５００Ｎｍ³ ／ｈｒに減少し、吹酸脱炭精錬の末期で、吹酸量を変えずに真空度を１２０ｔｏｒｒから順次５０ｔｏｒｒの高真空にした場合であり、排ガス流速を平均で１０ｍ／秒にでき、排気ダクト地金堆積が無く、操業時の真空度の変動が全く生じず安定した脱炭精錬をすることができ、総合評価として良好（◎）であった。
実施例３は、吹酸時のキャビティー深さを２１０ｍｍにし、吹酸脱炭精錬の初期に単孔ラバールを用いて３０００Ｎｍ³ ／ｈｒの酸素を湯面に吹き付け、中期には、真空度を１５０ｔｏｒｒの低真空にして酸素を２５００Ｎｍ³ ／ｈｒに減少し、吹酸脱炭精錬の末期では、中期と同じ酸素量にして真空度のみを１５０ｔｏｒｒから順次５０ｔｏｒｒの高真空にした場合であり、排ガス流速を平均で８ｍ／秒にでき、排気ダクト地金堆積が極微量であり、操業時の真空度の変動が全く生じず安定した脱炭精錬を行うことができ、総合評価として良い（○）結果が得られた。
【００１６】
【表１】

【００１７】
これに対し比較例は、吹酸時のキャビティー深さを１５０ｍｍにし、吹酸脱炭精錬の全期間中３孔ラバールのランスを用いて３０００Ｎｍ³ ／ｈｒの酸素を湯面に吹き付け、真空度を初期の１００ｔｏｒｒから中期に６０ｔｏｒｒ、末期に５０ｔｏｒｒの高真空度にした場合であり、排ガス流速が２７ｍ／秒と速くなり、排気ダクトに地金堆積が発生し、操業時の真空度が変動して不安定な脱炭精錬になり、総合評価としては悪い結果（×）となった。
【００１８】
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、前記実施の形態では、ステンレス溶鋼の脱炭精錬について説明したが、炭素を含有した一般の溶鋼の脱炭精錬に適用することもできる。
更に、浸漬管の形状は、直胴型の他に酸素含有ガスが吹き付けられる湯面の上部に相当する中間部の直径を大きくしたものを用いることができる。
また、酸素含有ガスも酸素にアルゴンガスあるいは炭酸ガス等を混合したガスを用いて脱炭精錬を行うことができる。
【００１９】
【発明の効果】
請求項１〜４記載のステンレス溶鋼の脱炭精錬方法は、取鍋内のステンレス溶鋼に浸漬管を浸漬し、浸漬管の内部を減圧すると共に、取鍋の底部から０．６〜１５．０Ｎリットル／（分・溶鋼トン）の不活性ガスを供給しつつ、浸漬管の上方より酸素含有ガスを吹き付けて脱炭精錬を行うステンレス溶鋼の脱炭精錬方法において、排ガス流速を５〜２０ｍ／秒にするので、スプラッシュや突沸等により発生した地金の二次バーストによって生成する細粒地金の飛散を抑制し、排気系ダクト等への付着や堆積を防止でき、安定した操業を行うことができる。
【００２０】
特に、請求項２記載のステンレス溶鋼の脱炭精錬方法は、排ガス流速を浸漬管の上方より吹き付ける酸素含有ガス量により調整するので、脱炭反応により生成したＣＯガスの二次燃焼を抑制し、スプラッシュや突沸等により発生した地金の二次バーストを効率良く抑制できる。
【００２１】
請求項３記載のステンレス溶鋼の脱炭精錬方法は、排ガス流速を浸漬管内の真空度により調整するので、排ガス流速を迅速に低下することができ、細粒地金が排ガスの流れに随伴して飛散するのを防止できる。
【００２２】
請求項４記載のステンレス溶鋼の脱炭精錬方法は、浸漬管の溶鋼浸漬部の内表面積を取鍋内の全溶鋼表面積の０．１〜０．７にしているので、排ガス流速を低減でき、脱炭に寄与する酸素効率を高くして二次バーストを抑制し、短時間で炭素濃度を低減できる。
【００２３】
請求項５記載のステンレス溶鋼の脱炭精錬方法は、取鍋内のステンレス溶鋼に浸漬管を浸漬し、浸漬管の内部を減圧すると共に、取鍋の底部から０．６〜１５．０Ｎリットル／（分・溶鋼トン）の不活性ガスを供給しつつ、浸漬管内の湯面の上方より酸素含有ガスを吹き付けて脱炭精錬を行うステンレス溶鋼の脱炭精錬方法において、酸素含有ガスを、キャビティー深さＬが所定の範囲になるようにして吹き付けるので、吹酸の火点近傍の脱炭反応とＣｒ₂ Ｏ₃ と炭素との反応が促進されて酸素効率を向上することができ、吹酸によって飛散する地金が二次バーストして微細化するのを抑制し、排気系ダクトへの地金堆積を防止して安定した操業が可能になる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係るステンレス溶鋼の脱炭精錬方法を適用した脱炭精錬装置の概念図である。
【図２】同脱炭精錬装置を用いた吹酸脱炭精錬中の排ガス流速、送酸量、排ガス流量及び真空度の変化を示すグラフである。
【図３】ランスの種類と排気ダクトへの地金の付着速度の関係を示すグラフである。
【図４】吹酸時の火点近傍の部分拡大図である。
【符号の説明】
１０：脱炭精錬装置、１１：取鍋、１２：ステンレス溶鋼、１２ａ：湯面、１３：浸漬管、１４：ポーラスプラグ、１５：流量調整弁、１６：ランス、１７：排気ダクト、１８：真空度計、１９：排ガス流量計、２０：シュート、２１：貯蔵ホッパー[0001]
BACKGROUND OF THE INVENTION
The present invention provides a stainless steel decarburization that suppresses fine metal ingots caused by splash and prevents fine metal from adhering to and depositing in an exhaust system when decarburizing and refining stainless steel. Refining method.
[0002]
[Prior art]
In the decarburization refining of molten stainless steel, decarburization is carried out by suppressing the oxidation of chromium by reducing the pressure inside the vessel and blowing acid, and the RH-OB method is widely known as this representative method. .
In this RH-OB method, both the riser and the downcomer are immersed in the molten steel in the ladle, the molten steel is sucked up by the gas lift action of the gas supplied from the riser, and discharged from the downcomer to remove the molten steel in the ladle. While circulating, decarburization is performed by blowing an oxygen-containing gas from a nozzle provided in the riser pipe.
JP-A-8-109410 discloses that a dip tube is immersed in molten steel in a ladle, the inside of the dip tube is evacuated and decompressed, and 0.6-15.0 Nl / There has been proposed a decarburizing and refining method for molten stainless steel in which decarburization is performed by blowing an oxygen-containing gas from above the dip pipe while supplying an inert gas of (minute / molten steel ton).
This method has been put to practical use because it can rapidly decarburize by reducing the generation of Cr ₂ O ₃ (hereinafter referred to as chromium oxide) and loss of chromium.
[0003]
[Problems to be solved by the invention]
However, in the above-described RH-OB method, the dip tube is separated into the riser and the downcomer, and the time taken for the molten stainless steel sucked up from the riser to return to the ladle through the downcomer is short. When acid decarburization refining is performed, the chromium oxide once generated in the vacuum chamber flows out of the vacuum chamber instantaneously, and floats on the upper portion of the ladle that is not affected by stirring.
The chromium oxide that floats on the top of the ladle hardly reacts with the carbon in the molten stainless steel, so the efficiency of decarburization is poor, leading to an increase in chromium oxide, an increase in reducing agents that reduce this chromium oxide, There are problems such as loss of chromium.
Furthermore, since the molten steel is circulated by the action of the gas lift of the inert gas supplied to the riser pipe, the absolute amount of gas blown from the riser pipe is increased, and the decarbonation efficiency of the blown oxygen-containing gas is reduced. Splash generation and secondary bursts (bullion generated by splashing reoxidizes and becomes finer) are intensified.
In JP-A-8-109410, since an inert gas is blown from the bottom of the ladle and the molten steel in the ladle is vigorously stirred, oxygen is blown onto the molten steel from above so that the molten steel blows oxygen. A large amount of chromium oxide is formed on the surface.
This chromium oxide reacts abruptly with carbon, and splash occurs due to bubble breakage on the molten steel surface of the CO gas generated at that time, and the metal is scattered.
The metal bulges into secondary bursts, which are finely divided and scattered along with the exhaust gas and adhere to and accumulate in the dip tube or exhaust system.
In addition, since oxygen is blown onto the surface of molten steel to decarburize, the oxygen efficiency that works effectively for decarburization is reduced to 40 to 55%, and oxygen that does not act on decarburization is secondary burned in the dip tube and scattered metal Because of this, the fine bullion that adheres to and accumulates in the exhaust system and the like increases.
In particular, in molten stainless steel containing 5% by weight or more of chromium, the exhaust resistance of the ejector increases due to the adhesion and deposition of fine-grain metal in the exhaust system, and a high degree of vacuum cannot be obtained.
As a result, the oxidation of chromium in the molten stainless steel proceeds, and there is a problem that the loss of chromium due to an increase in chromium oxide or a reducing agent such as Al for reducing the chromium oxide increases.
[0004]
The present invention has been made in view of such circumstances, and during the decarburization refining of the molten stainless steel, the bullion is scattered by the splash, the bullion suppresses the secondary burst to become fine particles, An object of the present invention is to provide a method for decarburizing and refining molten stainless steel that can prevent fine-grain metal from adhering to and accumulating in an exhaust system and perform stable decarburization and refining.
[0005]
[Means for Solving the Problems]
In the decarburizing and refining method for molten stainless steel according to the first aspect of the present invention, the dip tube provided with the exhaust duct is immersed in the molten stainless steel in the ladle, and the inside of the dip tube is decompressed, Stainless steel decarburizing and refining by supplying an oxygen-containing gas from above the molten metal surface in the dip tube while supplying an inert gas of 0.6 to 15.0 Nl / (min / ton of molten steel) from the bottom of the ladle. In the method for decarburizing and refining molten steel, the exhaust gas flow velocity V in the dip pipe determined from the following equation from the exhaust gas flow rate measured by the exhaust gas flow meter provided in the exhaust duct is set to 5 to 20 m / sec.
V = Q ÷ S × (P ₀ / P) × (T / T ₀ )
Where Q is the exhaust gas flow rate (Nm ³ / Hr), S is the area of the dip tube in the diameter direction (m ² ), P ₀ Is the standard atmospheric pressure (101325 Pa), P is the internal pressure (Pa) of the dip tube, T is the exhaust gas temperature (K), T ₀ Is the standard temperature (K).
By this method, the metal splattered by the splash is prevented from splattering with the exhaust gas, the fine metal slab is prevented from adhering to and accumulating in the exhaust system, and the exhaust resistance is eliminated, resulting in high vacuum. Stable decarburization and refining can be performed.
When the exhaust gas flow rate in the dip tube is less than 5 m / sec, the amount of oxygen-containing gas sprayed is reduced or the degree of vacuum is reduced to an extremely low vacuum, thus reducing the amount of exhaust gas generated by decarburization refining and sufficient decarburization reaction. Can not be performed, leading to extended refining time and chrome loss. On the other hand, when the exhaust gas flow velocity in the dip tube exceeds 20 m / sec, the metal splattered by the splash accompanies the exhaust gas, and secondary combustion is caused by oxygen remaining in the atmosphere to produce secondary bursts, resulting in finer particles. The deposited metal adheres to and accumulates in the exhaust system.
For this reason, when the exhaust gas flow rate in the dip tube is set to 5 to 15 m / second, a preferable result can be obtained by extending the decarburization refining time, preventing adhesion of fine-grain metal to the exhaust system, prevention of deposition, and the like.
In addition, if the amount of inert gas supplied from the bottom of the ladle is less than 0.6 N liters / (min / mol steel ton), the bubble active surface formed on the molten metal surface in the dip tube becomes small, and the entire stainless steel melt is stirred. Will become weaker and the decarburization refining time will be extended. When the amount of the inert gas exceeds 15.0 N liters / (minute / toned steel ton), the stirring of the entire stainless steel melt becomes too strong, and bubbles in the inert gas bubbles and blowing acid on the molten metal surface in the dip tube This increases the scattering of bullion.
[0006]
Here, the exhaust gas flow rate can be adjusted by the amount of oxygen-containing gas sprayed from above the hot water surface in the dip tube.
This increases the decarbonation efficiency of oxygen in the oxygen-containing gas sprayed on the molten steel surface, suppresses the formation of chromium oxides, reduces secondary combustion in the dip tube, and disperses secondary metal By suppressing the burst, it is possible to prevent the metal from becoming finer.
[0007]
Furthermore, the exhaust gas flow rate can be adjusted by the degree of vacuum in the dip tube.
Thereby, since the exhaust gas flow velocity in a dip tube can be reduced rapidly, it can prevent exactly that the fine-grain metal | gum produced | generated by the secondary burst is scattered to an exhaust system.
[0008]
Moreover, the internal surface area of the molten steel immersion part of the said dip tube can be 0.1-0.7 of the total molten steel surface area in the said ladle.
As a result, the bubble active surface effective for decarburization (inactive gas bubbles expand, bubble breaks and the molten metal surface undulates) is increased, the oxygen efficiency contributing to decarburization is increased, and the secondary burst is achieved. A low carbon concentration can be achieved in a short time while suppressing the above.
When the inner surface area of the molten steel immersion part of the dip tube is less than 0.1 of the total molten steel surface area in the ladle, the stirring force of the molten stainless steel becomes insufficient, the bubble active surface becomes narrow, the decarburization reaction becomes slow, and the carbon reached The concentration cannot be lowered. On the other hand, when it becomes larger than 0.7, the gap between the inner side of the ladle and the outer peripheral surface of the dip tube becomes narrow, and the dip tube to the ladle is caused by troubles in sampling or adhesion of chromium oxide flowing out of the dip tube. Soaking becomes difficult.
[0009]
In the method for decarburizing and refining molten stainless steel according to the second aspect of the present invention, the dip tube is immersed in the molten stainless steel in the ladle, the inside of the dip tube is depressurized, and 0. 0 from the bottom of the ladle. While supplying an inert gas of 6 to 15.0 N liters / (min / mol steel ton), decarburization and refining by blowing an oxygen-containing gas from the lance placed above the hot water surface in the dip tube toward the hot water surface In the method for decarburizing and refining molten stainless steel, the oxygen-containing gas is sprayed so that the cavity depth L determined by the following formulas (1) and (2) is 210 to 500 mm.
L = Lh × 10 ^{(-780H / Lh)} (1)
Lh = 0.894 × (Q ² / S × n) ^1/3 (2)
Here, L is the cavity depth (mm), H is the distance (m) from the tip position of the lance to the stationary hot water surface, Lh is the cavity depth (mm) when H = 0, and Q is oxygen-containing The gas flow rate (Nm ³ ), S is the cross-sectional area (m ² ) of the narrowest portion of the lance discharge port, and n is the number of lance discharge ports.
Since the blown acid is hard blown so that the cavity depth L by the oxygen-containing gas blown to the molten steel surface is 210 to 500 mm, the decarburization reaction at the fire point of the blown acid and its vicinity, and the generated Cr Promotes reaction with carbon in molten steel of ₂ O ₃ , improves decarbonation efficiency including oxygen consumed for decarburization and combustion above molten metal (secondary combustion), It is possible to increase the size of the metal particles scattered by the sprayed acid and to prevent the secondary metal from being exposed to the oxygen jet, thereby preventing secondary burst.
[0010]
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.
FIG. 1 is a conceptual diagram of a decarburizing and refining apparatus applied to a decarburizing and refining method for molten stainless steel according to an embodiment of the present invention, and FIG. 2 is an exhaust gas during blowing acid decarburizing and refining using the decarburizing and refining apparatus. FIG. 3 is a graph showing the relationship between the lance type and the rate of adhesion of the metal to the exhaust duct, and FIG. It is an enlarged view.
As shown in FIG. 1, a decarburizing and refining apparatus 10 applied to a method for decarburizing and refining stainless molten steel according to an embodiment of the present invention includes a ladle 11 and a stainless molten steel 12 received by a ladle 11. 1 has a straight barrel type dip tube 13 that is immersed in a lifting device (not shown), and a stainless steel tube in the dip tube 13 is placed at the bottom of the ladle 11 with a porous plug 14 for injecting and stirring an inert gas into the molten stainless steel 12. A lance 16 provided with a flow rate adjusting valve 15 for setting the flow rate of the oxygen-containing gas blown into the molten metal surface 12 a of the molten steel 12 is provided at the top of the dip tube 13.
Further, the dip tube 13 is provided with an exhaust duct 17 that communicates with an ejector (not shown) that decompresses the inside.
The exhaust duct 17 is provided with a vacuum meter 18 and an exhaust gas flow meter 19 for measuring the degree of vacuum inside the dip tube 13.
Furthermore, the inner surface area of the molten steel immersion portion of the dip tube 13 is set to 0.1 to 0.7 relative to the total molten steel surface area of the molten stainless steel 12 in the ladle 11.
In the figure, reference numeral 20 denotes a chute for adding auxiliary materials such as alloy iron and quicklime into the

dip tube

13, and 21 denotes a storage hopper for auxiliary materials such as alloy iron and quicklime.
[0011]
Next, a method for decarburizing and refining molten stainless steel according to the present embodiment using the decarburizing and refining apparatus 10 will be described.
First, 150 tons of molten stainless steel 12 containing 5% by weight or more of chromium is received in the ladle 11, and the tip of the dip tube 13 is deep in the ladle 11 from the surface of the molten stainless steel 12 in the ladle 11. It was immersed so as to come to a position of 600 mm, and the inside of the dip tube 13 was exhausted from the exhaust duct 17 by an ejector (not shown) and decompressed.
The molten metal surface 12a in the dip tube 13 is supplied with argon gas, which is an example of an inert gas, from a porous plug 14 of the ladle 11 by supplying 0.6 to 15.0 N liters / (min / ton of molten steel) to activate the bubble. After the surface is formed and the degree of vacuum in the dip tube 13 reaches 200 torr, oxygen, which is an example of an oxygen-containing gas of 3000 Nm ³ / hr from a height of 2800 mm, is sprayed onto the molten metal surface 12 a through the lance 16. (Blown acid) decarburization refining.
In the initial stage of decarburization refining, that is, immediately after the start of blowing acid, since the metal Al for heating is added into the dip tube 13, oxygen is consumed for the combustion of the metal Al, and the amount of generated exhaust gas is small.
When the combustion of the metal Al is finished, oxygen and chromium in the stainless molten steel 12 positively generate Cr ₂ O ₃ by the reaction of the formula (3), and this Cr ₂ O ₃ is combined with the carbon in the molten stainless steel 12 (4 Decarburization is carried out by reaction as shown in the formula.
2Cr + 3 / 2O ₂ → Cr ₂ O ₃ (3)
Cr ₂ O ₃ + 3C → 2Cr + 3CO ↑ (4)
At this time, if the degree of vacuum is low, oxidation of chromium in the molten stainless steel 12 occurs abruptly and excessive Cr ₂ O ₃ is generated, leading to abnormal reactions such as bumping and loss of chromium oxidation.
[0012]
Therefore, as shown in FIG. 2, in order to suppress the excessive production of Cr ₂ O ₃ , the exhaust amount of an ejector (not shown) is set so that the value of the vacuum gauge 18 becomes a high vacuum level of about 100 torr at the beginning of the blowing acid. Adjust the operation.
The flow rate of the exhaust gas including the generated CO gas and the CO ₂ gas that has been subjected to secondary combustion (indicated by a two-dot chain line in the figure) is measured by an exhaust gas flow meter 19 provided in the exhaust duct 17. As the decarburization reaction starts, it rapidly increases, and the exhaust gas flow velocity (shown by a thick solid line in the figure) also increases following the increase in the exhaust gas flow rate.
Therefore, the degree of vacuum (indicated by a broken line in the figure) is adjusted from a high vacuum of 100 torr to a low vacuum of 150 torr by adjusting the exhaust amount of an ejector (not shown) so that the exhaust gas flow velocity is in the range of 8 to 12 m / sec. .
When this exhaust gas flow velocity (m / sec) is V, V can be obtained by equation (5).
V = Q ÷ S × (P ₀ / P) × (T / T ₀ ) (5)
Where Q is the exhaust gas flow rate (Nm ³ / hr), S is the diameter direction area (m ² ) of the dip tube, P ₀ is the standard atmospheric pressure (101325 Pa), P is the internal pressure (Pa) of the dip tube, and T is The exhaust gas temperature (K), T ₀ is the standard temperature (K).
[0013]
Further, in the middle period when the decarburization reaction of the molten stainless steel 12 proceeds, the exhaust gas flow rate further increases, the instruction of the exhaust gas flow meter 19 becomes about 3500 Nm ³ / hr, and the exhaust gas flow rate exceeds 12 m / second. With the degree of vacuum maintained at 150 torr, the opening degree of the flow rate adjusting valve 15 is adjusted to reduce the oxygen amount of blown acid, that is, the amount of oxygen sent (shown by the solid line in the figure) to 2500 Nm ³ / hr, and the exhaust gas flow rate The range was 8-12 m / sec.
At the final stage of decarburization refining, the exhaust gas flow rate decreases due to the decrease in the carbon concentration in the molten stainless steel 12, so that the dip tube 13 is changed from a low vacuum of 150 torr to a high vacuum of 5 to 2 torr in accordance with the decrease of the exhaust gas flow rate. Perform decarburization refining.
In this way, the flow rate of the exhaust gas rising in the dip tube 13 is adjusted by adjusting the amount of acid sent and the degree of vacuum, so that the fine bullion generated by the secondary burst of bullion generated by the splash It is possible to prevent the exhaust gas from being scattered along with the flow of exhaust gas and adhering to or accumulating in the exhaust duct 17, thereby eliminating troubles such as an increase in exhaust resistance and processing of the deposited metal.
[0014]
In addition, as shown in FIG. 3, the lance 16 used for the blowing acid is a straight nozzle in which the shape of the discharge port is generally used, the gas jet spreads and becomes soft blow, and the oxygen efficiency of decarburization decreases. Then, the bullion generated by the splash causes secondary combustion with oxygen present in the atmosphere, and a secondary burst is generated.
However, in the case where hard blow is performed using a Laval nozzle that blows out from the discharge port at a speed higher than the speed of sound, the oxygen efficiency of decarburization increases, and secondary bursts of bullion generated by splash can be suppressed.
This tendency is effective in suppressing the secondary burst because a single-hole laval can be used for hard blow rather than a 3-hole laval.
That is, as shown in FIG. 4, the cavity depth (dent) of the molten metal surface 12a obtained from the above-mentioned formulas (1) and (2), which is generally used for hard blow conditions using single-hole rubber. Depth) By setting the L value to 210 to 500 mm, in the vicinity of the fire point A, decarburization is performed by the reaction of oxygen and carbon in the molten steel 12, and oxygen and chromium (Cr) react to produce Cr _2. O ₃ is produced.
Moreover, since the cavity depth L is in a predetermined range, when the generated Cr ₂ O ₃ floats, it is reduced by carbon at the upper layer portion of the molten stainless steel 12 in the dip tube 13 and contributes to decarburization. Oxygen efficiency can be improved.
In addition, in order to increase the cavity depth L as in the above range, increasing the spraying force when performing spraying acid increases the amount of bullion that scatters from the molten metal surface 12a. Is relatively large.
However, by making the blown acid hard blow, the spread of the oxygen jet becomes smaller, and the bare metal exposed to the oxygen jet can be reduced, so the secondary burst (fine particles shown by dotted lines in the figure) makes it finer Can be suppressed.
And, the fine bullion has an exhaust system duct etc. by the synergistic actions such as improvement of decarbonation efficiency including reduction of Cr ₂ O _{3 in} the vicinity of the fire point, coarsening of the bullion, and suppression of the spread of oxygen jet. Therefore, stable operation can be performed.
When the blown acid is soft blown and the cavity depth L is less than 210 mm, a secondary burst of metal occurs, and metal adhesion to the exhaust system duct or the like occurs.
When the spraying force at the time of spraying acid is too strong and the cavity depth L becomes larger than 500 mm, the scattering of the metal is extremely increased or the refractory near the fire point is worn out.
Therefore, a more preferable result is obtained when the cavity depth L value is 300 to 450 mm.
[0015]
【Example】
Next, the Example which applied the decarburization refining method of the molten stainless steel which concerns on this invention is described.
A dip tube in which a molten steel immersion part has an inner surface area of 0.3 of the total molten steel surface area in the ladle after 150 tons of molten stainless steel containing 13 wt% chromium is melted by a converter and received in a ladle. After immersing the tip of the steel plate to a depth of 600 mm from the surface of the molten steel in the pan, the inside of the dip tube is depressurized and the degree of vacuum in the dip tube reaches 100 torr. We performed charcoal refining and investigated the exhaust gas flow velocity, the presence of exhaust duct metal deposits, the fluctuation of vacuum during operation, and so on.
As shown in Table 1, in Example 1, the cavity depth at the time of blowing acid was set to 300 mm, and 3000 Nm ³ / hr of oxygen was sprayed on the molten metal surface using single-hole laval at the initial stage of blowing acid decarburization refining, In the middle period, the degree of vacuum is reduced to 150 Torr and oxygen is reduced to 2500 Nm ³ / hr. At the end of the blown acid decarburization refining process, only the degree of vacuum is increased from 150 torr to 50 torr. As a comprehensive evaluation, the exhaust gas flow rate can be set to 8 m / sec on average, there is no accumulation of metal in the exhaust duct, and there is no fluctuation in the degree of vacuum during operation, so that stable decarburization can be performed. It was good (◎).
Furthermore, in Example 2, the cavity depth at the time of blowing acid was set to 450 mm, and 3000 Nm ³ / hr of oxygen was sprayed onto the molten metal surface using single-hole laval at the initial stage of blowing acid decarburization refining. This is a case where the degree of vacuum is reduced to 120 Torr, oxygen is reduced to 2500 Nm ³ / hr, and at the end of blowing acid decarburization refining, the degree of vacuum is changed from 120 torr to 50 torr in order without changing the amount of blowing acid. The exhaust gas flow rate can be averaged to 10m / sec, there is no deposit of metal in the exhaust duct, and there is no fluctuation of the vacuum level during operation, and stable decarburization and refining can be performed. there were.
In Example 3, the cavity depth at the time of blowing acid was set to 210 mm, and 3000 Nm ³ / hr of oxygen was sprayed on the molten metal surface using single-hole laval at the initial stage of blowing acid decarburization refining, and in the middle period, the degree of vacuum was increased. The oxygen is reduced to 2500 Nm ³ / hr by reducing the vacuum to 150 torr, and at the final stage of the blown acid decarburization refining, the oxygen amount is the same as in the middle period and only the degree of vacuum is increased from 150 torr to a high vacuum of 50 torr. The flow velocity can be averaged to 8 m / sec, the exhaust duct metal deposit is extremely small, the fluctuation of the vacuum during operation does not occur at all, and stable decarburization refining can be performed. Results were obtained.
[0016]
[Table 1]

[0017]
In contrast, in the comparative example, the cavity depth at the time of blowing acid was set to 150 mm, and 3000 Nm ³ / hr of oxygen was sprayed onto the molten metal surface using a 3-hole rubber lance during the entire period of blowing acid decarburization and refining. Is a high vacuum level of 100 torr to 60 torr in the middle and 50 torr in the final period, the exhaust gas flow velocity becomes 27m / sec, metal deposits occur in the exhaust duct, and the vacuum level during operation fluctuates. The result was an unstable decarburization refining, and the overall evaluation was bad (×).
[0018]
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, in the above-described embodiment, the decarburization refining of molten stainless steel has been described. However, the present invention can be applied to the general decarburization refining of molten steel containing carbon.
Further, the shape of the dip tube may be a straight barrel type with a larger intermediate portion corresponding to the upper part of the hot water surface to which the oxygen-containing gas is blown.
The oxygen-containing gas can also be decarburized and refined using a gas in which argon gas or carbon dioxide gas is mixed with oxygen.
[0019]
【The invention's effect】
The decarburizing and refining method for molten stainless steel according to claims 1 to 4, wherein the dip tube is immersed in the molten stainless steel in the ladle, the pressure inside the dip tube is reduced, and 0.6-15.0 N from the bottom of the ladle. In a decarburizing and refining method for molten stainless steel in which oxygen-containing gas is blown from above the dip tube while supplying an inert gas of liter / (min / ton of molten steel), the exhaust gas flow rate is 5 to 20 m / sec. Therefore, it is possible to suppress the scattering of fine-grained bullion generated by secondary bursts of bullion generated by splash or bumping, prevent adhesion and accumulation on exhaust system ducts, etc., and perform stable operation it can.
[0020]
In particular, the decarburizing and refining method for molten stainless steel according to claim 2 adjusts the exhaust gas flow rate by the amount of oxygen-containing gas blown from above the dip pipe, so that secondary combustion of the CO gas generated by the decarburization reaction is suppressed, Secondary burst of bullion generated by splash or bumping can be efficiently suppressed.
[0021]
The method for decarburizing and refining molten stainless steel according to claim 3 adjusts the exhaust gas flow rate according to the degree of vacuum in the dip tube, so that the exhaust gas flow rate can be quickly reduced, and the fine bullion is accompanied by the flow of exhaust gas. It can be prevented from scattering.
[0022]
The decarburizing and refining method for molten stainless steel according to claim 4 is such that the inner surface area of the molten steel immersion portion of the dip tube is 0.1 to 0.7 of the total molten steel surface area in the pan, so that the exhaust gas flow rate can be reduced, The oxygen efficiency contributing to decarburization can be increased to suppress secondary bursts, and the carbon concentration can be reduced in a short time.
[0023]
The method for decarburizing and refining molten stainless steel according to claim 5 includes immersing the dip tube in the molten stainless steel in the ladle, depressurizing the inside of the dip tube, and 0.6 to 15.0 Nl / In a decarburizing and refining method for molten stainless steel in which decarburization and refining is performed by blowing an oxygen-containing gas from above the molten metal surface in the dip pipe while supplying an inert gas (min / mol steel ton), Since the spraying is performed so that the depth L is within a predetermined range, the decarburization reaction near the fire point of the blowing acid and the reaction between Cr ₂ O ₃ and carbon can be promoted to improve the oxygen efficiency. Suppresses secondary metal bursting and miniaturization, and prevents metal deposits in the exhaust system duct and enables stable operation.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a decarburizing and refining apparatus to which a method for decarburizing and refining molten stainless steel according to an embodiment of the present invention is applied.
FIG. 2 is a graph showing changes in exhaust gas flow velocity, acid feed amount, exhaust gas flow rate, and degree of vacuum during blown acid decarburization refining using the same decarburization refining apparatus.
FIG. 3 is a graph showing the relationship between the type of lance and the adhesion rate of the metal to the exhaust duct.
FIG. 4 is a partially enlarged view of the vicinity of a fire point during blowing acid.
[Explanation of symbols]
10: Decarburization refining equipment, 11: Ladle, 12: Molten stainless steel, 12a: Hot water surface, 13: Dip pipe, 14: Porous plug, 15: Flow control valve, 16: Lance, 17: Exhaust duct, 18: Vacuum Meter: 19: exhaust gas flow meter, 20: chute, 21: storage hopper

Claims

A dip tube provided with an exhaust duct is immersed in the molten stainless steel in the ladle, the inside of the dip tube is depressurized, and 0.6-15.0 N liter / (min / mol steel ton from the bottom of the ladle. ) In the decarburization and refining method of molten stainless steel in which decarburization and refining is performed by blowing an oxygen-containing gas from above the molten metal surface in the dip tube while supplying an inert gas), and measuring with an exhaust gas flow meter provided in the exhaust duct A method for decarburizing and refining molten stainless steel, characterized in that the exhaust gas flow velocity V in the dip tube obtained from the exhaust gas flow rate obtained by the following equation is 5 to 20 m / sec.
V = Q ÷ S × (P ₀ / P) × (T / T ₀ )
Where Q is the exhaust gas flow rate (Nm ³ / Hr), S is the area of the dip tube in the diameter direction (m ² ), P ₀ Is the standard atmospheric pressure (101325 Pa), P is the internal pressure (Pa) of the dip tube, T is the exhaust gas temperature (K), T ₀ Is the standard temperature (K).

The method for decarburizing and refining molten stainless steel according to claim 1, wherein the exhaust gas flow rate is adjusted by the amount of oxygen-containing gas sprayed from above the molten metal surface in the dip tube.

The method for decarburizing and refining molten stainless steel according to claim 1 or 2, wherein the exhaust gas flow rate is adjusted by the degree of vacuum in the dip tube.

The method for decarburizing and refining molten stainless steel according to any one of claims 1 to 3, wherein the inner surface area of the molten steel immersion portion of the dip tube is 0.1 to 0.7 of the total molten steel surface area in the ladle. A method for decarburizing and refining stainless steel.

A dip tube is immersed in the molten stainless steel in the ladle, the inside of the dip tube is depressurized, and an inert gas of 0.6 to 15.0 Nl / (min / ton of molten steel) is supplied from the bottom of the ladle. However, in the decarburizing and refining method for molten stainless steel in which decarburization refining is performed by blowing an oxygen-containing gas toward the molten metal surface from a lance arranged above the molten metal surface in the dip tube, the oxygen-containing gas is represented by the following formula: A decarburizing and refining method for molten stainless steel, characterized in that spraying is performed such that the cavity depth L determined by the above is 210 to 500 mm.
L = Lh × 10 ^{(-780H / Lh)}
Lh = 0.894 × (Q ² / S × n) ^1/3
Here, L is the cavity depth (mm), H is the distance (m) from the tip position of the lance to the stationary hot water surface, Lh is the cavity depth (mm) when H = 0, and Q is oxygen-containing The gas flow rate (Nm ³ ), S is the cross-sectional area (m ² ) of the narrowest portion of the lance discharge port, and n is the number of lance discharge ports.