JP3757435B2 - Method for decarburizing and refining chromium-containing molten steel - Google Patents
Method for decarburizing and refining chromium-containing molten steel Download PDFInfo
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Description
【０００１】
【産業上の利用分野】
本発明は、溶鋼の脱炭精錬方法に関し、特に送酸機能及び底吹きガスによる溶鋼の撹拌機能を備えた減圧精錬容器での含Ｃｒ溶鋼の脱炭精錬方法に係わる。
【０００２】
【従来の技術】
現在、含クロム溶鋼の脱炭精錬は、前段の上底吹転炉、ＡＯＤ又は電気炉と、後段のＲＨ、ＶＯＤ等所謂減圧精錬容器とを組み合わせた複合脱炭工程によって行われるのが一般的である。そして、これらの複合脱炭工程においては、前後段の操業条件をそれぞれ最適化し、Ｃｒ歩留りを向上させつつ脱炭速度を向上させることが望まれている。
【０００３】
その具体的方法として、例えば、特開平３−２７１３１５号公報は、後段のＲＨ真空脱ガス容器において、ステンレス溶鋼中［％Ｓｉ］を０．３５重量％以下とし、且つ溶鋼中［Ｏ］の活量と前記脱ガス容器からの排ガス中のＣＯ濃度とに基づいて、酸素吹込みによる脱炭および酸素を吹込みを行わない自己脱炭とを繰り返しながら脱炭処理を行い、且つその酸素吹込み時の送酸速度を４００〜８００Ｎｍ3 ／ｈｒとするステンレス溶鋼のＲＨ真空脱炭方法を提唱している。また、特開平６−１００２４号公報は、減圧精錬容器を用いて含Ｃｒ溶鋼を精錬するにあたり、減圧精錬開始時における含Ｃｒ溶鋼中の［％Ｓｉ］を０．１０重量％以下として、減圧下において送酸脱炭を開始し、含Ｃｒ溶鋼中の［％Ｃ］が所定の濃度になるまで脱炭した後、精錬容器を減圧下に保持したまま、Ｓｉ以外の還元・脱酸剤及び脱硫フラックスを投入し、撹拌することにより。スラグ中Ｃｒ酸化物の還元及び溶鋼の脱酸、脱硫処理を行うことを特徴とする極低炭・脱硫処理を行う極低炭・極低硫含クロム溶鋼の精錬方法を開示している。
【０００４】
【発明が解決しようとする課題】
しかしながら、これらの方法は、以下の点で問題である。すなわち、特開平３−２７１３１５号公報記載のものは、鋼浴面下に送酸を行っても脱炭速度が遅く、また設備的にもＲＨ精錬容器の下部槽や浸漬管の寿命を著しく短くし、しかも送酸中に溶鋼中Ｃｒの損失が大きいという問題がある。また、特開平６−１００２４号公報記載のものは、減圧精錬開始時における含Ｃｒ溶鋼中の［％Ｓｉ］を０．１０重量％以下とするため、前段の転炉工程において溶鋼中Ｃｒの損失が大きいという問題があった。
【０００５】
そこで、本発明は、上記問題点を解決するため、減圧精錬前の送酸処理における溶鋼中Ｃｒの酸化損失を極力抑えると共に、該減圧精錬で溶鋼の脱炭速度を向上させる含クロム溶鋼の脱炭精錬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、従来技術の問題点を見直し、解決策を鋭意研究した。本発明は、その成果を具現化したもので、ＶＯＤ設備を用いて含クロム溶鋼を減圧下で脱炭精錬するに際して、出発溶鋼を、Ｓｉが０．１１〜０．２５重量％の含Ｃｒ溶鋼にすると共に、上吹ランスの高さを下記（１）及び（２）式を満たす高さにして送酸することを特徴とする含Ｃｒ溶鋼の脱炭精錬方法。
【０００７】
ここで、Ｙ：上吹ランスの高さ（ｍ），Ｘ：減圧脱炭開始時の溶鋼中Ｓｉ（％）である。
Ｙ≧−４×Ｘ＋２ …（１）
０．１１≦Ｘ≦０．２５ …（２）
なお、上吹ランスの高さは、ランス先端と湯面間の距離である。
【０００８】
【作用】
本発明では、ＶＯＤ設備を用いて含クロム溶鋼を減圧下で脱炭精錬するに際して、出発溶鋼を、Ｓｉが０．１１〜０．２５重量％の含Ｃｒ溶鋼にすると共に、上吹ランスの高さを上記（１）及び（２）式を満たす高さにして送酸するようにしたので、粗脱炭炉での精錬において生成した酸化物をその出鋼前に還元回収できるようになり、また、減圧下での脱炭速度が向上し、脱炭に要する時間が短縮され、従来法で生じていた生産性の低下を抑制できるようになる。
【０００９】
以下、発明者が本発明を検討するにあたり行った実験で得た図１〜図３に基づき、本発明の内容を補足する。
図１は、含Ｃｒ溶鋼を転炉で粗脱炭し、出鋼した溶鋼中［％Ｓｉ］と、該転炉に還元剤を投入して還元したスラグ中の酸化物量との関係を示したものである。図１から明らかなように、溶鋼中［％Ｓｉ］が０．１０重量％以下になると、極端に還元後スラグ中の酸化物量が増加し、必要成分の損失が大きくなるので、出発溶鋼中の［％Ｓｉ］を０．１１重量％以上とすることが必要である。また、図２は、減圧精錬の出発溶鋼中［％Ｓｉ］と脱炭速度との関係を示すものである。図２から明らかなように、出発溶鋼［％Ｓｉ］を０．２５重量％以上とすると、減圧脱炭中の脱炭速度が遅くなるので、本発明では、減圧脱炭の出発溶鋼中［％Ｓｉ］を０．２５重量％未満とする必要がある。さらに、図３には、減圧脱炭で上吹ランスの高さを１．０、１．３及び１．６ｍと変更した場合における溶鋼［％Ｓｉ］とクロム酸化損失を示す。図３から明らかなように、上吹ランス高さを１．０ｍ以下及び底吹送酸では、送酸脱炭中のクロムの酸化損失が増加していることがわかる。これは、ある程度の高さ以下で溶鋼に酸素を吹きつけると、クロムの酸化損失が増加することを示している。この結果から、出鋼［％Ｓｉ］によりある程度のランス高さを確保して、送酸することがクロムの酸化損失低減に必要であり、出発溶鋼の［％Ｓｉ］に応じた以下の式を導出したのである。
【００１０】
Ｙ≧−４×Ｘ＋２ …（１）
０．１１≦Ｘ≦０．２５ …（２）
ここで、上吹ランスの高さはＹ（ｍ）、減圧脱炭開始時の溶鋼中［％Ｓｉ］はＸ（％）で表わされている。
【００１１】
【実施例】
まず、ガスの上底吹き機能を有する１６０ｔ転炉に、脱Ｐ溶銑を１００ｔ装入し、送酸によって粗脱炭を行いつつ、Ｆｅ−Ｃｒ合金を投入した。該粗脱炭の終了後、溶鋼に１３．１ｋｇ／ｔのＦｅ−Ｓｉ合金を投入し、脱炭中に生成したスラグ中の酸化物を還元すると共に、溶鋼の脱硫を行った。表１及び表２は、この粗脱炭後の溶鋼組成及びスラグ還元後のスラグ組成である。
【００１２】
次に、上記転炉から溶鋼を減圧設備としてのＶＯＤ装置に移し、該ＶＯＤ設備内で送酸を行った。その際、送酸は、上吹きランスを用い、その高さは、先端が湯面から１．６ｍの距離になるようにした。また、該設備内は、３５ Ｔｏｒｒの減圧として、溶鋼は［％Ｃ］＝０．０８％まで送酸脱炭した後、さらに４．５Ｔｏｒｒまで減圧され、同時に底吹きガスによる撹拌も行った。
【００１３】
なお、この場合の送酸量は、如何なる量であっても良いが、好ましくは本実施例の程度で上吹酸素量が６００〜２４００Ｎｍ3 ／ｈｒの範囲である。
比較例１としては、同じ転炉に、脱Ｐ溶銑を１００ｔ装入し、粗脱炭を行いつつ、Ｆｅ−Ｃｒ合金鉄を投入し、該粗脱炭の終了後、溶鋼に１１．９ｋｇ／ｔのＦｅ−Ｓｉを投入して、脱炭中に生成したスラグ中の酸化物を還元したり、溶鋼の脱硫を行った。粗脱炭後の溶鋼組成及びスラグ還元後のスラグ組成は、前記表１及び表２に示してある。比較例１は、前記実施例と減圧脱炭開始前の溶鋼中Ｓｉが低い値であり、明確に異なっている。その後、該溶鋼をＶＯＤ設備にて３５Ｔｏｒｒの減圧下で［％Ｃ］＝０．０８％まで送酸脱炭し、その後さらに４．５Ｔｏｒｒまで減圧し、ガス撹拌により真空脱炭を実施した。
【００１４】
比較例２としては、比較例１と同様に粗脱炭を行い、粗脱炭の終了後、溶鋼には１５．４ｋｇ／ｔのＦｅ−Ｓｉを投入し、脱炭中に生成したスラグ中の酸化物の還元や溶鋼の脱硫を行った。表１より、比較例２の溶鋼中Ｓｉは、本発明の実施例より溶鋼中のＳｉが高い値になっている。この溶鋼のＶＯＤ設備での減圧送酸は、３５Ｔｏｒｒの減圧下で［％Ｃ］＝０．０８％まで送酸脱炭し、さらに、４．５Ｔｏｒｒまで減圧してガス撹拌により真空脱炭を行った。
【００１５】
【表１】
【表２】
実施成績は、表３に、Ｃｒ歩留り、脱炭速度定数、ＶＯＤ処理時間として一括して示す。表３より明らかなように、比較例１と本発明の実施例では、本発明の方がＣｒ歩留り７．２％高く、比較例２と実施例では、脱炭速度の向上効果として、処理時間が１５．４分も短縮できるという良好な結果を得た。
。
【００１８】
【表３】
【発明の効果】
以上述べたように、本発明により、ＶＯＤ設備を用いた含Ｃｒ溶鋼の脱炭精錬において、減圧精錬前の送酸処理におけるＣｒの酸化損失を極力抑え、減圧脱炭で脱炭速度を向上させることができた。
【図面の簡単な説明】
【図１】粗脱炭炉からの出鋼した溶鋼中の［％Ｓｉ］と還元後のスラグ中酸化物量との関係を示した図である。
【図２】出発溶鋼中の［％Ｓｉ］と減圧脱炭での脱炭速度定数との関係を示した図である。
【図３】減圧脱炭で上吹ランスの高さを変更した場合の溶鋼中［％Ｓｉ］とＣｒの酸化損失との関係を示す図である。[0001]
[Industrial application fields]
The present invention relates to a method for decarburizing and refining molten steel, and in particular, to a method for decarburizing and refining Cr-containing molten steel in a vacuum refining vessel equipped with an acid feeding function and a stirring function of molten steel by bottom blowing gas.
[0002]
[Prior art]
Currently, decarburization and refining of chromium-containing molten steel is generally performed by a combined decarburization process in which a top-stage blown converter, AOD, or electric furnace in the previous stage is combined with a so-called reduced-pressure refining vessel such as RH and VOD in the subsequent stage It is. In these combined decarburization processes, it is desired to optimize the operating conditions at the front and rear stages, and improve the decarburization speed while improving the Cr yield.
[0003]
As a specific method thereof, for example, Japanese Patent Laid-Open No. 3-271315 discloses that in a subsequent RH vacuum degassing vessel, [% Si] in molten stainless steel is 0.35 wt% or less and [O] in molten steel is activated. The decarburization treatment is performed while repeating the decarburization by blowing oxygen and the self-decarburization without blowing oxygen based on the amount and the CO concentration in the exhaust gas from the degassing vessel. It proposes an RH vacuum decarburization method for molten stainless steel with an acid feed rate of 400 to 800 Nm 3 / hr. Japanese Patent Laid-Open No. 6-10024 discloses that when refining Cr-containing molten steel using a reduced-pressure refining vessel, [% Si] in the Cr-containing molten steel at the start of reduced-pressure refining is set to 0.10% by weight or less under reduced pressure. And decarburization until [% C] in the Cr-containing molten steel reaches a predetermined concentration, and then the reducing / deoxidizing agent and desulfurization other than Si while keeping the smelting vessel under reduced pressure By adding flux and stirring. The present invention discloses a method for refining ultra-low carbon / ultra-low sulfur chromium-containing molten steel that performs ultra-low carbon / desulfurization, characterized by reducing Cr oxide in slag and deoxidizing and desulfurizing the molten steel.
[0004]
[Problems to be solved by the invention]
However, these methods are problematic in the following points. That is, the one described in JP-A-3-271315 has a slow decarburization rate even when acid is fed under the steel bath surface, and the life of the lower tank and dip pipe of the RH refining vessel is also significantly shortened in terms of equipment. In addition, there is a problem that the loss of Cr in the molten steel is large during acid feeding. Moreover, in the thing of Unexamined-Japanese-Patent No. 6-10024, in order to make [% Si] in Cr containing molten steel at the time of a vacuum refining start into 0.10 weight% or less, it is the loss of Cr in molten steel in the previous converter process. There was a problem that was large.
[0005]
Therefore, in order to solve the above problems, the present invention suppresses the oxidization loss of Cr in molten steel as much as possible in the acid feeding treatment before the vacuum refining, and improves the decarburization rate of the molten steel by the vacuum refining. The purpose is to provide a method for refining charcoal.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the inventor reviewed the problems of the prior art and intensively studied solutions. The present invention embodies the results, and when decarburizing and refining chromium-containing molten steel under reduced pressure using a VOD facility , the starting molten steel is Cr-containing molten steel having a Si content of 0.11 to 0.25% by weight. In addition, a method for decarburizing and refining Cr-containing molten steel is characterized in that the upper blow lance is fed at a height that satisfies the following formulas (1) and (2).
[0007]
Here, Y: height of upper blowing lance (m), X: Si (%) in molten steel at the start of vacuum decarburization.
Y ≧ −4 × X + 2 (1)
0.11 ≦ X ≦ 0.25 (2)
The height of the upper blowing lance is the distance between the tip of the lance and the hot water surface.
[0008]
[Action]
In the present invention, when a chrome-containing molten steel decarburized refining under reduced pressure using a VOD equipment, starting molten steel, the Si is a free Cr molten steel from 0.11 to 0.25 wt%, the upper blowing lance height the since so as to oxygen-flow in the height satisfies the above (1) and (2) is made a rough oxide formed in refining decarburization furnace to be reduced recovery before the tapping, In addition, the decarburization speed under reduced pressure is improved, the time required for decarburization is shortened, and the decrease in productivity caused by the conventional method can be suppressed.
[0009]
Hereinafter, the content of the present invention will be supplemented on the basis of FIGS. 1 to 3 obtained by experiments conducted by the inventor to study the present invention.
FIG. 1 shows the relationship between [% Si] in the molten steel that is roughly decarburized from the Cr-containing molten steel in a converter and the amount of oxide in the slag reduced by introducing a reducing agent into the converter. Is. As is clear from FIG. 1, when [% Si] in the molten steel is 0.10% by weight or less, the amount of oxide in the slag after the reduction is extremely increased and the loss of necessary components is increased. [% Si] needs to be 0.11% by weight or more. FIG. 2 shows the relationship between [% Si] in the starting molten steel for vacuum refining and the decarburization rate. As apparent from FIG. 2, when the starting molten steel [% Si] is 0.25% by weight or more, the decarburization rate during the vacuum decarburization becomes slow. Therefore, in the present invention, [% Si] needs to be less than 0.25% by weight. Further, FIG. 3 shows molten steel [% Si] and chromium oxidation loss when the height of the top blowing lance is changed to 1.0, 1.3, and 1.6 m by vacuum decarburization. As is apparent from FIG. 3, it can be seen that, when the top blowing lance height is 1.0 m or less and the bottom blowing acid, the oxidation loss of chromium during acid feeding decarburization increases. This shows that the oxidation loss of chromium increases when oxygen is blown to molten steel below a certain height. From this result, it is necessary to secure a certain lance height with the steel output [% Si] and to send the acid to reduce the oxidation loss of chromium, and the following equation corresponding to the [% Si] of the starting molten steel is It was derived.
[0010]
Y ≧ −4 × X + 2 (1)
0.11 ≦ X ≦ 0.25 (2)
Here, the height of the top blowing lance is represented by Y (m), and [% Si] in the molten steel at the start of vacuum decarburization is represented by X (%).
[0011]
【Example】
First, 100 t of de-P molten iron was charged into a 160 t converter having a gas top-bottom blowing function, and an Fe—Cr alloy was charged while performing rough decarburization by acid feeding. After the completion of the rough decarburization, 13.1 kg / t Fe—Si alloy was added to the molten steel to reduce oxides in the slag generated during the decarburization and to desulfurize the molten steel. Tables 1 and 2 show the molten steel composition after rough decarburization and the slag composition after slag reduction.
[0012]
Next, the molten steel was transferred from the converter to a VOD device as a decompression facility, and acid was sent in the VOD facility. At that time, the acid feed was carried out using a top blowing lance, and the height was adjusted so that the tip was 1.6 m from the molten metal surface. In addition, the inside of the equipment was reduced to 35 Torr, and the molten steel was acid-decarburized to [% C] = 0.08%, then further depressurized to 4.5 Torr, and simultaneously stirred by bottom blowing gas.
[0013]
In this case, the amount of acid sent may be any amount, but preferably the amount of oxygen blown up is in the range of 600 to 2400 Nm 3 / hr as in this embodiment.
As Comparative Example 1, 100 tons of de-P molten iron was charged into the same converter, and Fe—Cr alloy iron was introduced while performing rough decarburization. After the rough decarburization, 11.9 kg / t-Fe-Si was added to reduce oxides in the slag produced during decarburization or to desulfurize molten steel. The molten steel composition after rough decarburization and the slag composition after slag reduction are shown in Tables 1 and 2 above. In Comparative Example 1, the Si in the molten steel before the start of vacuum decarburization is a low value and is clearly different. Thereafter, the molten steel was acid-decarburized to [% C] = 0.08% under a reduced pressure of 35 Torr in a VOD facility, and then further depressurized to 4.5 Torr, and vacuum decarburization was performed by gas stirring.
[0014]
As Comparative Example 2, rough decarburization was performed in the same manner as in Comparative Example 1, and after the completion of rough decarburization, 15.4 kg / t of Fe—Si was introduced into the molten steel, and the slag produced during decarburization Oxide reduction and molten steel desulfurization were performed. From Table 1, Si in the molten steel of Comparative Example 2 has a higher value of Si in the molten steel than the examples of the present invention. The reduced pressure acid feeding in the VOD equipment of this molten steel is deacidified by 35% torr [% C] = 0.08%, further depressurized to 4.5 Torr and vacuum decarburized by gas stirring. It was.
[0015]
[Table 1]
[Table 2]
The implementation results are collectively shown in Table 3 as Cr yield, decarburization rate constant, and VOD treatment time. As is clear from Table 3, in Comparative Example 1 and the examples of the present invention, the Cr yield of the present invention is 7.2% higher. In Comparative Examples 2 and Examples, the treatment time is improved as an effect of improving the decarburization rate. Obtained a good result that can be shortened by 15.4 minutes.
.
[0018]
[Table 3]
【The invention's effect】
As described above, according to the present invention, in the decarburization and refining of Cr-containing molten steel using VOD equipment, the oxidation loss of Cr in the acid feeding treatment before the vacuum refining is suppressed as much as possible, and the decarburization speed is improved by the vacuum decarburization. I was able to.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between [% Si] in molten steel produced from a rough decarburization furnace and the amount of oxide in slag after reduction.
FIG. 2 is a graph showing a relationship between [% Si] in the starting molten steel and a decarburization rate constant in vacuum decarburization.
FIG. 3 is a diagram showing a relationship between [% Si] in molten steel and oxidation loss of Cr when the height of the top blowing lance is changed by vacuum decarburization.
Claims (1)
出発溶鋼を、Ｓｉが０．１１〜０．２５重量％の含Ｃｒ溶鋼にすると共に、上吹ランスを下記（１）及び（２）式を満たす高さにして送酸することを特徴とする含Ｃｒ溶鋼の脱炭精錬方法。
ここで、Ｙ：上吹ランスの高さ（ｍ），Ｘ：減圧脱炭開始時の溶鋼中Ｓｉ（％）である。
Ｙ≧−４×Ｘ＋２ …（１）
０．１１≦Ｘ≦０．２５ …（２） When decarburizing and refining chromium-containing molten steel under reduced pressure using VOD equipment ,
The starting molten steel is made of a Cr-containing molten steel having a Si content of 0.11 to 0.25% by weight, and the upper blowing lance is sent to a height that satisfies the following formulas (1) and (2). Decarburization refining method for Cr-containing molten steel.
Here, Y: height of upper blowing lance (m), X: Si (%) in molten steel at the start of vacuum decarburization.
Y ≧ −4 × X + 2 (1)
0.11 ≦ X ≦ 0.25 (2)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14903595A JP3757435B2 (en) | 1995-06-15 | 1995-06-15 | Method for decarburizing and refining chromium-containing molten steel |
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| Application Number | Priority Date | Filing Date | Title |
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| JP14903595A JP3757435B2 (en) | 1995-06-15 | 1995-06-15 | Method for decarburizing and refining chromium-containing molten steel |
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| Publication Number | Publication Date |
|---|---|
| JPH093525A JPH093525A (en) | 1997-01-07 |
| JP3757435B2 true JP3757435B2 (en) | 2006-03-22 |
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| Application Number | Title | Priority Date | Filing Date |
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| JP14903595A Expired - Fee Related JP3757435B2 (en) | 1995-06-15 | 1995-06-15 | Method for decarburizing and refining chromium-containing molten steel |
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| Country | Link |
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| JP (1) | JP3757435B2 (en) |
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| Publication number | Publication date |
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| JPH093525A (en) | 1997-01-07 |
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