JP3752801B2 - Method for melting ultra-low carbon and ultra-low nitrogen stainless steel - Google Patents
Method for melting ultra-low carbon and ultra-low nitrogen stainless steel Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、極低炭素・極低窒素ステンレス鋼の溶製方法に関し、詳しくは、含クロム溶鋼を、ＶＯＤ等の真空精錬装置内でクロムの酸化ロスを極力抑えて、効率良く、且つ迅速に、極低炭素及び窒素領域（現在では、一般に１００ｐｐｍ以下をいう）まで脱炭、脱窒する技術である。
【０００２】
【従来の技術】
現在、極低炭素ステンレス鋼を減圧下で脱炭して溶製するには、以下のようにしている。転炉等から出鋼した含Ｃｒ溶鋼を、まず、減圧下での上吹き送酸によって、［Ｃ］濃度が０．０１〜０．０２重量％程度に低下させ、その後、該溶鋼中［Ｃｒ］の酸化ロスを抑えるために、上吹き酸素を停止し，減圧のまま溶鋼を撹拌する。この撹拌によって、溶鋼中及びスラグ中の酸素と溶鋼中炭素とが反応し、ＣＯガスとして脱炭するので、溶鋼中［Ｃ］濃度が０．０１重量％以下の所謂極低炭素濃度領域になるのである。しかしながら、上記した上吹き酸素停止後の減圧下脱炭（以下、真空脱炭という）では、脱炭速度が送酸脱炭時に比べて著しく低下するので、かかる従来法ではトータルの製錬時間が長いという問題があった。
【０００３】
そこで、かかる減圧下での脱炭速度を向上させるため、特公昭５６−３３４４５号公報及び特公昭５９−５２２０３号公報は、「アルゴン・ガス等の不活性ガスと酸素ガスとの混合ガスを、溶鋼に上吹きするか、あるいは浸漬ランスを介して吹き込み、送酸の酸素ポテンシアルを低下させてクロムの酸化ロスを抑制しつつ、脱炭速度を向上させる」方法を開示した。しかしながら、これらの方法を採用すると、上吹き酸素停止後の脱炭速度は向上するが、使用されるアルゴン・ガスの原単位量が増大するので、精練コストが従来より大幅に増大するという問題が生じていた。
【０００４】
また、ＶＯＤでの脱窒素を強化するには、減圧下脱炭に伴うＣＯボイリングを活発にしなければならない。しかしながら、そのためには、減圧脱炭開始時の溶鋼中［Ｃ］濃度を高くする必要があり、このことも精練時間の延長に寄与していた。
【０００５】
【発明が解決しようとする課題】
本発明は、かかる事情を鑑み、減圧下で脱炭するに際し、従来より溶鋼中に含まれるクロムの酸化ロス量を極力抑え、真空脱炭工程を短縮又は省略して効率良く、且つ安価に極低炭素及び窒素のステンレス鋼を溶製する方法を提供することを目的としている。
【０００６】
【課題を解決するための手段】
発明者は、上記目的を達成するため、減圧下での送酸脱炭を、クロムの酸化ロスを極力抑えて迅速に行う方法の発見に鋭意努力し、その成果として本発明を完成させた。
すなわち、本発明は、含Cr溶鋼を一定の[C]濃度まで送酸脱炭し、未脱酸状態で取鍋に出鋼し、その後、さらに減圧下で送酸脱炭、真聖脱炭、及び還元処理を行う極低炭素及び極低窒素ステンレス鋼の溶製方法において、まず、最初の送酸脱炭を、上記［C]濃度が0.15〜0.10重量%の領域になるまで行って取鍋に出鋼し，その後の減圧下での送酸脱炭を、底吹き不活性ガスの流量5Nリットル/min/t以上及び，減圧精錬前に取鍋内の浴面上に添加する CaO 又は MgO 系フラックスの添加量を調整することで生成するスラグの重量15kg/t以下の条件で行うことを特徴とする極低炭素及び極低窒素ステンレス鋼の溶製方法である。
【０００７】
また、本発明は、減圧下での送酸脱炭から真空脱炭への切り換えを、上記溶鋼中[C]濃度が60ppm以下で行うか、あるいは真空脱炭を省略することを特徴とする極低炭素及び極低窒素ステンレス鋼の溶製方法である。
さらに、本発明は、減圧下の送酸脱炭期である上記溶鋼中[C]濃度が200ppm以上である期間内に、合金鉄を予め添加することを特徴とする極低炭素及び極低窒素ステンレス鋼の溶製方法でもある。
【０００８】
本発明では、極低炭素及び極低窒素ステンレス鋼を、上記のような方法で溶製するようにしたので、減圧下での送酸脱炭に際して溶鋼中クロムの酸化ロスが抑えられ、極低炭素の濃度領域まで高速で送酸脱炭できるようになる。その結果、その後の送酸無しによる真空脱炭を短縮、あるいは省略しても極低炭素および極低窒素領域にあるので、精錬時間が従来より短縮でき、あわせて使用還元剤の原単位が低減できるようになる。
【０００９】
本発明の内容を、発明に至る経緯も含めて、以下に説明する。発明者の研究によれば、転炉あるいはAOD等の精錬炉で送酸脱炭した溶鋼を未脱酸で出鋼すると、出鋼中に溶鋼表面からCOガスが発生したり、表面活性元素である酸素が溶鋼表面を覆うので、大気からの窒素の吸収が防止され、真空精錬を開始するまでの溶鋼中[N]濃度を100ｐｐｍ以下に抑えることができる。そこで、発明者は、VOD等の真空精錬装置で、長時間の脱窒処理を行わないでも、脱炭だけに専念すれば、極低炭素及び極低窒素ステンレス鋼に要求される[N]濃度にすることができると考えた。
【００１０】
一方、発明者は、脱炭反応速度と操業条件との関係を多くの実験データ用いて解析し、以下の新規な知見を見いだした。すなわち、図１及び図２に示すように。減圧下での送酸脱炭において、生成されるスラグ重量及び減圧精錬前に取鍋内の浴面上に添加するCaO又はMgO系フラックスの添加量を調整することで15Kg/ｔ以下に抑え、且つ底吹きするアルゴン・ガスの流量を5Nリットル/min/t以上にして送酸すると、脱炭速度が向上すること(高速化の可能性)を知った。さらに、図３に示すように、上記スラグ及びアルゴン・ガスの条件下で送酸脱炭を［C］＜60ppmまで継続しても、溶鋼中クロムの酸化ロス(△Cr=(取鍋出鋼時の溶鋼中[Cr]―減圧下での送酸脱炭後の溶鋼中[Cr]で定義する)は,殆ど増大しないことをも見いだした。これらの知見より、従来は、「溶鋼中［C]濃度が100〜150ppmの時点から送酸を停止し，目標とする極低炭素値までは送酸無しによる真空脱炭していた］が、かかる真空脱炭の時間を短縮したり、あるいは省略しても良いことがわかる。さらに、図４に示すように、前記条件下では、溶鋼の成分調整のために添加する合金鉄を、まだ減圧下の送酸脱炭期である溶鋼中[C]濃度が200ppm以上で添加すると、クロムの前記酸化ロスが一層低減できることをも見出したのである。
【００１１】
そこで、発明者は、これらの知見を上記した本発明として整理したのである。
【００１２】
【実施例】
16重量%Crの溶鋼を180トンを、転炉及び真空精錬装置(VOD)を用いて、本発明に係る図５に示す条件で脱炭し、目標炭素50ppm以下及び窒素100ppm以下の極低炭素及び極低窒素ステンレス鋼を溶製した。その際、スラグ重量を15kg以下に抑えるため、Al203生成の原因となり、且つスラグ量を増大させるAlの投入(昇熱)を行わずに、減圧下で送酸脱炭し、溶鋼中[C]濃度が40〜50ppmになった時点で上吹き送酸を停止した。そのため、莫空脱炭を省略して直ちに還元処理を行い、目標とする極低炭素及び極低窒素ステンレス鋼を得た。なお、本発明の効果を評価するため、同一鋼種で従来の溶製方法による比較溶製も行った。その際の脱炭状況を図６に示す。図６より、本発明の適用で、脱炭処理時間が従来法より40分も短縮できたことが明らかである。
【００１３】
また、減圧前の精練で、溶鋼を未脱酸で出鋼した結果、減圧処理開始時の溶鋼中［Ｎ］濃度は１００ｐｐｍ以下を維持でき、さらに、図７に示すように、減圧下では溶鋼が吸窒しないため、脱窒処理の必要性がないことがわかった。加えて、図８に示すように、クロムの酸化ロスが減少し、溶鋼還元用のＡｌ原単位量を大幅に削減することができた。
【００１４】
【発明の効果】
以上述べたように、本発明により、極低炭素及び極低窒素ステンレス鋼の溶製に際し、従来より脱炭速度が大幅に向上し、精錬時間を大幅に短縮できると共に、溶鋼中のCr酸化ロスが減少するので、脱炭後の溶鋼還元に使用するAl,あるいはSiの原単位が大幅に削減できた。つまり、極低炭素及び極低窒素ステンレス鋼の精錬コストの低減および生産量の向上が図れたのである。
【図面の簡単な説明】
【図1】 減圧下での送酸脱炭期におけるスラグ重量と脱炭速度定数との関係を示す図である。
【図2】 減圧での送酸脱炭期における底吹きアルゴン・ガス流量と脱炭速度定数との関係を示す図である。
【図3】 減圧下での上吹き送酸停止時における溶鋼中 [C] 濃度と送酸中での Cr 酸化ロス量との関係を示す図である。
【図4】 減圧下での送酸中のスラグ重量とクロム酸化ロス量との関係を示す図である。
【図5】 本発明に係る極低炭素及び極低窒素ステンレス鋼の溶製条件を示す図である。
【図6】 本発明に係る方法と比較例の減圧下での脱炭挙動を示す図である。
【図7】 本発明に係る方法と比較例の減圧下での脱窒の挙動を示す図である。
【図8】 本発明に係る方法と比較例の還元用Al原単位量を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for melting ultra-low carbon / ultra-low nitrogen stainless steel. More specifically, chromium-containing molten steel can be efficiently and rapidly reduced in chromium refining equipment such as VOD with minimal oxidation loss of chromium. This is a technology for decarburizing and denitrifying to the extremely low carbon and nitrogen range (currently generally referred to as 100 ppm or less).
[0002]
[Prior art]
Currently, ultra-low carbon stainless steel is decarburized and melted under reduced pressure as follows. The Cr-containing molten steel produced from a converter or the like is first reduced to about 0.01 to 0.02% by weight by [C] concentration by top blowing acid under reduced pressure, and then [Cr] In order to suppress the oxidation loss, the top blown oxygen is stopped and the molten steel is agitated while the pressure is reduced. By this stirring, oxygen in the molten steel and slag reacts with carbon in the molten steel and decarburizes as CO gas, so that the [C] concentration in the molten steel becomes a so-called extremely low carbon concentration region of 0.01% by weight or less. It is. However, in the decarburization under reduced pressure (hereinafter referred to as vacuum decarburization) after stopping the above-mentioned top blowing oxygen, the decarburization rate is remarkably reduced as compared with the time of acid decarburization. There was a problem of being long.
[0003]
Therefore, in order to improve the decarburization speed under such reduced pressure, Japanese Patent Publication No. 56-33445 and Japanese Patent Publication No. 59-52203 disclose that a mixed gas of an inert gas such as argon gas and oxygen gas is used. A method of improving the decarburization rate while suppressing the oxidation loss of chromium by lowering the oxygen potential of the acid supplied by blowing up the molten steel or through an immersion lance is disclosed. However, if these methods are adopted, the decarburization rate after stopping the top blowing oxygen is improved, but the basic unit amount of argon gas used is increased, so that there is a problem that the scouring cost is significantly increased as compared with the conventional method. It was happening.
[0004]
Moreover, in order to strengthen the denitrification at VOD, it is necessary to activate the CO boiler accompanying decarburization under reduced pressure. However, for that purpose, it is necessary to increase the [C] concentration in the molten steel at the start of vacuum decarburization, which also contributes to the extension of the scouring time.
[0005]
[Problems to be solved by the invention]
In view of such circumstances, the present invention suppresses the oxidation loss amount of chromium contained in molten steel as much as possible when decarburizing under reduced pressure, and shortens or omits the vacuum decarburization step to achieve efficiency and low cost. It aims at providing the method of melting low carbon and nitrogen stainless steel.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor diligently made efforts to discover a method for carrying out acid feeding decarburization under reduced pressure quickly while suppressing the oxidation loss of chromium as much as possible, and completed the present invention as a result.
That is, the present invention feeds and decarburizes the Cr-containing molten steel to a certain [C] concentration, steels in a ladle in an undeoxidized state, and then further feeds and decarburizes under reduced pressure. and in melting process of ultra low carbon and ultra-low nitrogen stainless steel which performs reduction processing, first, the first oxygen-flow decarburization, conducted until the [C] concentration of 0.15 to 0.10 wt% of area CaO added to the ladle and then added to the surface of the bath in the ladle before depressurizing and refining the acid decarburization under reduced pressure by adding a bottom blowing inert gas flow of 5 N liters / min / t or more. Alternatively, it is a melting method of ultra-low carbon and ultra-low nitrogen stainless steel characterized in that it is performed under the condition that the weight of slag produced by adjusting the amount of MgO- based flux added is 15 kg / t or less.
[0007]
Further, the present invention is characterized in that switching from acid feed decarburization to vacuum decarburization under reduced pressure is performed at a [C] concentration of 60 ppm or less in the molten steel, or vacuum decarburization is omitted. This is a method for melting low carbon and extremely low nitrogen stainless steel.
Furthermore, the present invention is an oxygen-flow decarburization period of reduced pressure within a period during the molten steel [C] concentration is 200ppm or more, very low carbon and extremely low, which comprises adding a slip KimuTetsu advance It is also a method for melting nitrogen stainless steel.
[0008]
In the present invention, since ultra-low carbon and ultra-low nitrogen stainless steel is melted by the above-described method, the oxidation loss of chromium in the molten steel is suppressed at the time of acid feeding decarburization under reduced pressure, and extremely low It will be possible to feed and decarburize at high speed up to the carbon concentration range. As a result, even if the vacuum decarburization without subsequent acid feeding is shortened or omitted, it is in the ultra-low carbon and ultra-low nitrogen region, so the refining time can be shortened compared to the conventional, and the basic unit of reducing agent used is also reduced. become able to.
[0009]
The contents of the present invention will be described below including the background to the invention. According to the inventor's research, when molten steel that has been acid decarburized in a refining furnace such as a converter or AOD is removed without deoxidation, CO gas is generated from the surface of the molten steel during steel output, Since some oxygen covers the surface of the molten steel, absorption of nitrogen from the atmosphere is prevented, and the [N] concentration in the molten steel until the start of vacuum refining can be suppressed to 100 ppm or less. Therefore, the inventor does not perform a denitrification process for a long time in a vacuum refining apparatus such as VOD, but if he concentrates on decarburization, [N] concentration required for ultra-low carbon and ultra-low nitrogen stainless steel I thought it could be.
[0010]
On the other hand, the inventor analyzed the relationship between the decarburization reaction rate and the operating conditions using a lot of experimental data, and found the following new knowledge. That is, as shown in FIGS. In acid decarburization under reduced pressure, the weight of slag produced and the amount of CaO or MgO flux added to the bath surface in the ladle before vacuum refining are adjusted to 15 kg / t or less, We also learned that the decarburization rate was improved (possibility of speeding up) by sending oxygen at a flow rate of 5 N liters / min / t or more at the bottom blowing argon gas. Furthermore, as shown in FIG. 3 , even when acid decarburization is continued up to [C] <60 ppm under the above slag and argon gas conditions, the chromium oxidation loss in the molten steel (ΔCr = (Ladle steel) It was also found that [Cr] in molten steel [defined by [Cr] in molten steel after acid decarburization under reduced pressure) hardly increases. C] Acid delivery was stopped when the concentration was 100 to 150 ppm, and vacuum decarburization without acid delivery was performed up to the target extremely low carbon value]. Furthermore, as shown in Fig. 4 , under the above conditions, the iron alloy added for adjusting the components of the molten steel is added to the molten steel that is still in the acid feeding decarburization period under reduced pressure [ It has also been found that when the C] concentration is added at 200 ppm or more, the oxidation loss of chromium can be further reduced.
[0011]
Therefore, the inventor arranged these findings as the present invention described above.
[0012]
【Example】
180 tons of molten steel of 16 wt% Cr was decarburized using a converter and vacuum refining equipment (VOD) under the conditions shown in FIG. 5 according to the present invention, and extremely low carbon with a target carbon of 50 ppm or less and nitrogen of 100 ppm or less. And very low nitrogen stainless steel was melted. At that time, in order to suppress the slag weight to 15 kg or less, it does not cause Al 2 O 3 generation and does not perform Al injection (heating) that increases the amount of slag, but it performs acid decarburization under reduced pressure in the molten steel When the concentration of [C] reached 40-50 ppm, the top blowing acid was stopped. For this reason, the reduction treatment was performed immediately without the enormous air decarburization, and target ultra-low carbon and ultra-low nitrogen stainless steel was obtained. In addition, in order to evaluate the effect of this invention, the comparative melting by the conventional melting method was also performed with the same steel type. Decarburization situation at that time is shown in FIG. From FIG. 6 , it is clear that the decarburization treatment time can be shortened by 40 minutes compared with the conventional method by applying the present invention.
[0013]
Further, as a result of smelting before depressurization, the molten steel was undeoxidized, and as a result, the [N] concentration in the molten steel at the start of the depressurization treatment can be maintained at 100 ppm or less. Further, as shown in FIG. It was found that there is no need for denitrification because no nitrogen is absorbed. In addition, as shown in FIG. 8, the oxidation loss of chromium decreased, and the amount of Al basic unit for molten steel reduction could be greatly reduced.
[0014]
【The invention's effect】
As described above, according to the present invention, when ultra-low carbon and ultra-low nitrogen stainless steel is melted, the decarburization speed is greatly improved compared to the conventional method, and the refining time can be greatly shortened, and Cr oxidation loss in the molten steel can be greatly reduced. Therefore, the basic unit of Al or Si used for reduction of molten steel after decarburization could be greatly reduced. That is, the refining cost and the production amount of ultra-low carbon and ultra-low nitrogen stainless steel can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between slag weight and decarburization rate constant during an acid feed decarburization period under reduced pressure.
FIG. 2 is a diagram showing a relationship between a bottom blown argon gas flow rate and a decarburization rate constant in a feed acid decarburization period under reduced pressure.
FIG. 3 is a graph showing the relationship between the [C] concentration in molten steel and the amount of Cr oxidation loss during acid feeding when top blowing acid feeding is stopped under reduced pressure .
FIG. 4 is a graph showing the relationship between the slag weight during acid delivery under reduced pressure and the chromium oxidation loss amount.
FIG. 5 is a diagram showing melting conditions for ultra-low carbon and ultra-low nitrogen stainless steel according to the present invention.
FIG. 6 is a diagram showing the decarburization behavior under reduced pressure of the method according to the present invention and a comparative example.
FIG. 7 is a diagram showing denitrification behavior under reduced pressure in the method according to the present invention and a comparative example.
FIG. 8 is a diagram showing the amount of Al basic unit for reduction in the method according to the present invention and a comparative example.
Claims (3)
まず、最初の送酸脱炭を、上記［C]濃度が0.15〜0.10重量%の領域になるまで行って取鍋に出鋼し，その後の減圧下での送酸脱炭を、底吹き不活性ガスの流量5Nリットル/min/t以上及び，減圧精錬前に取鍋内の浴面上に添加する CaO 又は MgO 系フラックスの添加量を調整することで生成するスラグの重量15kg/t以下の条件で行うことを特徴とする極低炭素及び極低窒素ステンレス鋼の溶製方法。And oxygen-flow decarburization-containing Cr molten steel to a certain [C] concentration, then tapped into a ladle in a non-deoxidized state, then, further oxygen-flow decarburization under vacuum, Masataka decarburization, and pole for performing reduction treatment In the melting method of low carbon and ultra low nitrogen stainless steel,
First, the first oxygen-flow decarburization, the [C] concentration went until the region of 0.15 to 0.10 wt% and tapped into a ladle, the oxygen-flow-decarburization in the subsequent reduced pressure, the bottom The flow rate of blowing inert gas is 5N liter / min / t or more, and the weight of slag generated by adjusting the amount of CaO or MgO flux added to the bath surface in the ladle before vacuum refining is 15kg / t. A method for melting ultra-low carbon and ultra-low nitrogen stainless steel, characterized by being performed under the following conditions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP27118197A JP3752801B2 (en) | 1997-10-03 | 1997-10-03 | Method for melting ultra-low carbon and ultra-low nitrogen stainless steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP27118197A JP3752801B2 (en) | 1997-10-03 | 1997-10-03 | Method for melting ultra-low carbon and ultra-low nitrogen stainless steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11106823A JPH11106823A (en) | 1999-04-20 |
| JP3752801B2 true JP3752801B2 (en) | 2006-03-08 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP27118197A Expired - Fee Related JP3752801B2 (en) | 1997-10-03 | 1997-10-03 | Method for melting ultra-low carbon and ultra-low nitrogen stainless steel |
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| Country | Link |
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| JP (1) | JP3752801B2 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100491007B1 (en) * | 2001-10-30 | 2005-05-24 | 주식회사 포스코 | A method for refining a molten steel in use for the manufacture of a stainles steel having low carbon |
| KR100523106B1 (en) * | 2001-12-17 | 2005-10-19 | 주식회사 포스코 | method for refining a stainless steel sheet with low nitrogen |
| JP5131727B2 (en) * | 2006-12-26 | 2013-01-30 | 日新製鋼株式会社 | Stainless steel melting method |
| KR100922061B1 (en) * | 2007-12-12 | 2009-10-16 | 주식회사 포스코 | Ultra low carbon ferritic stainless steel manufacturing method |
| CN105734203B (en) * | 2016-03-16 | 2017-10-03 | 甘肃酒钢集团宏兴钢铁股份有限公司 | A kind of double-position vacuum oxygen decarburization smelting process of super-purity ferrite stainless steel |
| CN105908056B (en) * | 2016-06-17 | 2017-11-07 | 辽宁科技大学 | A kind of smelting process of low carbon, low nitrogen high chrome |
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1997
- 1997-10-03 JP JP27118197A patent/JP3752801B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
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| JPH11106823A (en) | 1999-04-20 |
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