JP3726599B2 - Method for refining molten steel using refractory scrap containing carbon - Google Patents
Method for refining molten steel using refractory scrap containing carbon Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、炭素含有量0.10質量％以下の鋼種を溶製するために取鍋精錬設備を用いて溶鋼の二次脱炭精錬を行なうに際して、二次脱炭精錬を阻害することなく炭素含有耐火物屑をスラグ成分の調整材として有効に利用し得る精錬方法に関する。
【０００２】
【従来の技術】
一般に転炉等の精錬炉や取鍋精錬設備を用いて溶鋼の精錬を行なうと、これらの精錬容器に用いられる耐火物は徐々に損耗していく。耐火物の損耗量が大きくなると炉体に種々の損傷を与えることになるので、定期的に耐火物を施工し直す必要がある。耐火物を施工し直す作業の際に回収された耐火物は、耐火物屑となる。
【０００３】
従来、耐火物屑は廃棄処分にされたり、埋め立て等に使用されており、資源の有効活用の観点から好ましい状況ではなかった。また特開平5-339615号公報には、MgＯ−Ｃ系あるいは Al2Ｏ3 −MgＯ−Ｃ系等の炭素を含有する耐火れんがのれんが屑を取鍋精錬の造滓材として利用する方法が開示されている。しかしながら取鍋精錬を行なう際に炭素含有れんが屑を添加すると、れんが屑が滓化することによって、れんが屑に含有される炭素が溶鋼中に溶け込み、炭素のピックアップが生じるという問題がある。
【０００４】
そのため特開平5-339615号公報に開示された方法では、ピックアップの問題が生じない炭素含有量が0.10質量％を超える鋼種（すなわちＪＩＳ SCM418 ）で炭素含有耐火物屑を使用している。
ところで、取鍋精錬設備において二次脱炭精錬する際には、溶鋼中の炭素含有量が成品の目標炭素含有量の範囲まで脱炭するのが通常である。これよりも低いレベルまで脱炭してから目標成分値まで加炭することも可能ではあるが、取鍋精錬炉における二次脱炭精錬は減圧下で行なうために、過度の脱炭は処理コスト（主に用役費）がかさむこと、また加炭材が余分に必要となるため、その分のコスト上昇も伴うので好ましくない。
【０００５】
しかしながら、成品の目標炭素含有量が0.10質量％以下の鋼種の場合には、上記のような通常の二次脱炭精錬を行なう際に単にスラグ成分調整剤としての炭素含有耐火物屑をスラグ中に添加したのでは、その後に溶鋼中に加炭が生じてしまい、鋳造時の溶鋼が目標炭素濃度範囲を超えてしまう問題があった。
【０００６】
【発明が解決しようとする課題】
本発明は上記のような問題を解消するべく、炭素含有耐火物屑を使用して資源の有効活用を図ると同時に、ピックアップを生じることなく炭素含有量0.10質量％以下の鋼種を溶製する方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、一次脱炭精錬した溶鋼を取鍋に出鋼し、次いで取鍋精錬設備において二次脱炭精錬を行ない炭素含有量0.10質量％以下の溶鋼を溶製する溶鋼の精錬方法において、二次脱炭精錬中の溶鋼中の炭素含有量が0.01質量％以上にある時期に取鍋内の溶鋼上のスラグに炭素含有耐火物屑を添加する溶鋼の精錬方法である。
【０００８】
前記した発明においては、第１の好適態様として、二次脱炭精錬において、溶鋼中の炭素含有量を成品の目標炭素含有量の範囲まで脱炭することが好ましい。
また第２の好適態様として、一次脱炭精錬を、転炉、ＡＯＤ炉または電気炉で行なうことが好ましい。
また第３の好適態様として、取鍋精錬設備が減圧精錬設備であることが好ましい。
【０００９】
また第４の好適態様として、溶鋼がCrを５質量％以上含有する含クロム溶鋼であることが好ましい。
【００１０】
【発明の実施の形態】
一般に、転炉、ＡＯＤ炉、電気炉などにおいて一次脱炭精錬を行なった溶鋼を、さらに取鍋を用いて二次脱炭精錬を行なう方法には、ＶＯＤ法，ＶＡＤ法，ＡＳＥＡ−ＳＫＦ法等がある。ここではＶＯＤ法を用い、MgＯ−Ｃ系耐火物屑を使用して二次精錬を行なう場合について、本発明をなすに至った知見と本発明の好ましい実施形態について説明する。
【００１１】
炭素含有量の上限が 0.015質量％のＪＩＳ規格のSUS409鋼を溶製するために、まずヒートサイズ 180ｔの転炉を用いて脱炭処理を行ない、溶鋼中の炭素含有量を0.10質量％とした。次いでＶＯＤ法によって二次脱炭精錬を行なうにあたって、溶鋼中の炭素濃度が0.08〜0.09質量％の範囲にある時期に炭素を20質量％含有するMgＯ−Ｃ系耐火物屑 500kgをスラグ組成の調整材としてスラグ中に添加してＶＯＤ処理を行なった。その結果、ＶＯＤ処理の後の鋼中の炭素含有量は 0.011質量％であり、規格で許容される上限である 0.015質量％以内に収まった。
【００１２】
またスラグ中には、スラグ組成調整材としてスラグ中に添加したMgＯ−Ｃ系耐火物屑に含まれていたMgＯが、濃化（８質量％）しており、これによって取鍋のスラグラインのMgＯ−Ｃ系耐火物の溶損を防止する効果を有することが分かった。
したがって取鍋を用いた２次精錬における造滓材として、一般に軽焼ドロマイトが使用されているが、本発明の方法によれば炭素含有量0.10質量％以下の鋼種においても造滓材の代替品としてMgＯ−Ｃ系耐火物屑が十分使用できることが分かった。
【００１３】
一方、炭素含有量の上限が 0.015質量％のSUS409鋼を溶製するために、転炉を用いて炭素含有量0.10質量％に脱炭し、その後ＶＯＤ法によって二次脱炭精錬を行ない、鋼中の炭素濃度を 0.009質量％とした後、炭素を20質量％含有するMgＯ−Ｃ系耐火物屑 500kgをスラグ成分調整材としてスラグ中に添加し、引き続きスラグ還元処理を行なった。この場合は、ＶＯＤ処理の後の鋼中の炭素含有量は 0.016質量％となり、炭素含有量の上限値（すなわち 0.015質量％）を外れることになった。
【００１４】
上記の鋼種の他に、種々の鋼種について転炉を用いて脱炭処理を行なった後、ＶＯＤ処理での脱炭前、脱炭中、脱炭後の種々の溶鋼中炭素濃度の時期に、取鍋スラグ中に炭素含有耐火物屑を造滓材として添加して精錬を行ない、炭素含有量の上限値外れの発生率を調査した。その結果を表１に示す。
なお表１中の炭素含有量の上限値外れ発生率は、下記のようにして調査した。それぞれ表１左欄の条件でスラグ中に炭素含有耐火物屑を投入する実験を20ヒートずつ行ない、各ヒートについて二次脱炭精錬終了時に成品として要求される炭素含有量上限値以下まで脱炭されたことを確認した上で、この溶鋼を連続鋳造した。連続鋳造時のタンディッシュでの代表炭素濃度を測定し、その値が成品として要求される炭素含有量上限値を超えたヒートを炭素含有量の上限値外れと定義し、その発生ヒート数の比率（％）を炭素含有量の上限外れ率とした。
【００１５】
【表１】
炭素含有耐火物屑添加時の溶鋼中の炭素含有量が0.05質量％以上では上限値外れは発生せず、炭素含有量が0.01質量％以上かつ0.05質量％未満の範囲では上限値外れの発生率は１％であった。一方、炭素含有量が0.01質量％未満では上限値外れの発生率は20％であった。よって、炭素含有耐火物屑を添加する時期は、溶鋼中の炭素含有量は、0.01質量％以上のときであることが望ましい。
【００１７】
次に、本発明の好ましい実施形態について説明する。まず、本発明では予め一次脱炭精錬した溶鋼を用いる。一次脱炭精錬を行なう精錬設備としては、上述した予備実験において使用した転炉が一般的であるが、転炉と同様に溶鋼に酸素を供給して脱炭するＡＯＤ炉も使用できる。また近年にといてはアーク式電気炉（ＡＣアーク炉、ＤＣアーク炉を問わない）でも、スクラップの早期溶解と脱炭を行なうために酸素吹錬設備が設けられているのが通常であり、したがってこのような電気炉によっても一次脱炭精錬は可能である。
【００１８】
また二次脱炭精錬を行なう目的は、下記の通りである。一次脱炭精錬炉において極端に溶鋼中の炭素含有量を低下すると、溶鋼の温度が高くなったり、スラグ中のFeＯ含有量が増大して、一次脱炭精錬炉の内張り耐火物を溶損してしまうこと、またCrを５質量％以上含有する溶鋼の場合は炭素濃度が 0.1質量％以下では炭素よりもCrの酸化が優先して実質上それ以上の脱炭が不可能となる。したがって、溶鋼を減圧下に保持して、一次脱炭精錬炉よりも脱炭に有利な条件を作り出すことの可能な、取鍋精錬設備を用いて二次脱炭精錬を行なうのである。
【００１９】
このような取鍋精錬設備としては、ＶＯＤ，ＶＡＤ，ＡＳＥＡ−ＳＫＦ，ＲＨ，ＤＨあるいは特開平11-140534 号公報等に開示されている直胴型の減圧可能な浸漬槽を用いる取鍋精錬設備等が挙げられる。本発明は、これらの設備において溶鋼表面上のスラグ成分を調整し、精錬反応に好適なものとしたり、取鍋，浸漬槽，浸漬管等の耐火物に対する溶損性を低下させるものである。
【００２０】
したがって精錬反応時にスラグの攪拌が激しく、スラグ−メタル間反応の生じやすく、かつ耐火物に対しても負荷の大きいＶＯＤ，ＶＡＤ，ＡＳＥＡ−ＳＫＦ，直胴式取鍋精錬設備等において、特に本発明を適用する効果が著しい。
このような取鍋精錬設備を用いて二次脱炭精錬する場合、減圧状態で溶鋼中に酸素を吹き込んだり、あるいは溶鋼表面に酸素を吹き付ける、いわゆる酸素吹錬脱炭法と、溶鋼を減圧することによってスラグ中のFeＯ，MnＯ， Cr2Ｏ3 や溶鋼中の溶存酸素によって脱炭反応を生じさせる真空脱炭法があるが、本発明の適用は、これらのいずれの方法を用いる場合にも適用が可能である。
【００２１】
上記の二次脱炭精錬の際に、溶鋼中の炭素濃度が0.01質量％以上にある時期（二次脱炭精錬を開始する前、二次脱炭精錬の途中のいずれでも良い）に、スラグ中に炭素含有耐火物屑を添加する。炭素濃度範囲の限定理由は、上述した通りである。
炭素含有耐火物屑としては、代表的なものとしては、転炉，電気炉，ＡＯＤ炉あるいは取鍋のスラグライン等に使用されたMgＯ−Ｃ系耐火物、溶鋼の連続鋳造に使用された Al2Ｏ3 −Ｃ系浸漬ノズル、混銑車の内張りに使用された Al2Ｏ3 −Ｃ系耐火物の屑等が挙げられるが、特にそれらに限定されるものではない。それぞれ調整すべきスラグ成分および目的に応じて、主成分としてどのような酸化物を含有する耐火物を、どの程度の量使用するかを決定すれば良い。
【００２２】
なお耐火物屑は、元々それがレンガ等の定形の耐火物であったか、流し込み等の不定形耐火物であったかは問題とならないが、スラグ中に添加した場合は迅速にスラグ中に分散ないし溶解することが望ましいので、予め 100mm以下程度の大きさまで粉砕しておくことが好ましく、取鍋精錬設備の合金材添加装置を用いて投入する場合は、ロータリーフィーダー等の切り出し設備の制約上約30mm以下程度の粒度とするのが良い。
【００２３】
【実施例】
180ｔの９質量％Crの溶鋼を上底吹き転炉によって一次脱炭精錬し、炭素濃度を0.15質量％で吹き止めて取鍋に出鋼した。この溶鋼をＶＯＤ設備において二次脱炭精錬し、成品の目標鋼中炭素濃度を 0.008〜0.015 質量％まで低下する処理の際に、二次脱炭精錬前のスラグにMgＯ−Ｃ耐火物屑（粒度 100mm以下）を 500kg添加した例（発明例１）、二次脱炭精錬の途中で溶鋼中炭素濃度が0.05質量％の時期にスラグ中にMgＯ−Ｃ耐火物屑（粒度20mm以下）を 500kg添加した例（発明例２）、および二次脱炭精錬末期の溶鋼中炭素濃度が 0.008質量％まで低下してからスラグ中にMgＯ−Ｃ耐火物屑（粒度20mm以下）を 500kg添加した例（比較例）の２種類の操業を行なった。
【００２４】
その結果、発明例１では二次脱炭精錬終了時の炭素濃度は 0.009質量％であり、その後この溶鋼を連続鋳造した際のタンディッシュでの代表炭素濃度も 0.009質量％で、目標成分範囲を満足した。
発明例２では、二次脱炭精錬終了時の炭素濃度は 0.008質量％であり、その後この溶鋼を連続鋳造した際のタンディッシュでの代表炭素濃度も 0.008質量％で、目標成分範囲を満足した。
【００２５】
一方、比較例では二次脱炭精錬終了時の炭素濃度は 0.008質量％であったが、その後、この溶鋼を連続鋳造した際のタンディッシュでの代表炭素濃度は 0.017質量％で、目標成分範囲の上限を超える結果となった。
【００２６】
【発明の効果】
本発明では、取鍋精錬設備を用いて二次脱炭精錬を行なう際に炭素含有耐火物屑を造滓材として使用することによって、資源を有効に活用でき、比較的高価な軽焼ドロマイト等の造滓材の使用量を削減できる。しかも取鍋のスラグラインの耐火物の寿命を延長できる。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a carbon-containing refractory without obstructing secondary decarburization refining when performing secondary decarburization refining of molten steel using a ladle refining facility in order to melt a steel type having a carbon content of 0.10 mass% or less. The present invention relates to a refining method that can effectively use waste as a slag component adjusting material.
[0002]
[Prior art]
In general, when molten steel is refined using a refining furnace such as a converter or a ladle refining facility, the refractories used in these refining vessels gradually wear out. If the amount of wear of the refractory increases, the furnace body will be damaged in various ways. Therefore, it is necessary to reconstruct the refractory periodically. The refractory collected at the time of reworking the refractory becomes refractory waste.
[0003]
Conventionally, refractory debris has been disposed of or used for land reclamation and the like, which is not a preferable situation from the viewpoint of effective utilization of resources. Also JP-A-5-339615, a method utilizing the disclosed brick debris refractory brick containing carbon of MgO-C-based or Al 2 O 3 -MgO-C type or the like as the slag forming a ladle refining Has been. However, when carbon-containing brick scraps are added during ladle refining, the brick scraps are hatched, so that the carbon contained in the brick scraps dissolves in the molten steel, and there is a problem that carbon pickup occurs.
[0004]
Therefore, in the method disclosed in Japanese Patent Laid-Open No. 5-339615, carbon-containing refractory waste is used with a steel type (ie, JIS SCM418) having a carbon content exceeding 0.10% by mass that does not cause a pickup problem.
By the way, when secondary decarburization refining is performed in a ladle refining facility, the carbon content in molten steel is usually decarburized to the range of the target carbon content of the product. Although it is possible to decarburize to a level lower than this and then to the target component value, secondary decarburization refining in the ladle refining furnace is performed under reduced pressure, so excessive decarburization is a processing cost. (Mainly utility costs) is bulky, and extra carburizing material is required, which is not preferable because of the corresponding increase in cost.
[0005]
However, when the target carbon content of the product is a steel grade of 0.10 mass% or less, the carbon-containing refractory waste as a slag component modifier is simply added to the slag when performing the above-described normal secondary decarburization refining. If added to, then carburization occurred in the molten steel, and there was a problem that the molten steel at the time of casting exceeded the target carbon concentration range.
[0006]
[Problems to be solved by the invention]
In order to solve the above problems, the present invention aims to effectively utilize resources by using carbon-containing refractory waste, and at the same time, a method of melting a steel type having a carbon content of 0.10% by mass or less without causing pickup. The purpose is to provide.
[0007]
[Means for Solving the Problems]
The present invention is a method for refining molten steel in which molten steel that has undergone primary decarburization refining is put into a ladle and then subjected to secondary decarburization refining in a ladle refining facility to melt molten steel having a carbon content of 0.10 mass% or less. This is a method for refining molten steel in which carbon-containing refractory waste is added to the slag on the molten steel in the ladle when the carbon content in the molten steel during secondary decarburization refining is 0.01% by mass or more.
[0008]
In the above-described invention, as the first preferred embodiment, in the secondary decarburization refining, it is preferable to decarburize the carbon content in the molten steel to the range of the target carbon content of the product.
As a second preferred embodiment, primary decarburization refining is preferably performed in a converter, an AOD furnace, or an electric furnace.
Moreover, as a 3rd suitable aspect, it is preferable that the ladle refining equipment is a reduced pressure refining equipment.
[0009]
As a fourth preferred embodiment, the molten steel is preferably a chromium-containing molten steel containing 5% by mass or more of Cr.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In general, methods for performing secondary decarburization refining using molten ladle that has undergone primary decarburization refining in converters, AOD furnaces, electric furnaces, etc. include VOD, VAD, ASEA-SKF, etc. There is. Here, the knowledge that has led to the present invention and preferred embodiments of the present invention will be described for the case where secondary refining is performed using MgO-C refractory waste using the VOD method.
[0011]
In order to melt JIS SUS409 steel with an upper limit of carbon content of 0.015 mass%, first, decarburization treatment was performed using a converter with a heat size of 180 t, so that the carbon content in the molten steel was 0.10 mass%. . Next, when performing secondary decarburization refining by the VOD method, adjusting the slag composition of 500 kg of MgO-C refractory waste containing 20% by mass of carbon when the carbon concentration in the molten steel is in the range of 0.08 to 0.09% by mass It added to slag as a material and performed the VOD process. As a result, the carbon content in the steel after VOD treatment was 0.011% by mass, which was within 0.015% by mass, which is the upper limit allowed by the standard.
[0012]
In addition, MgO contained in the MgO-C refractory waste added to the slag as a slag composition adjusting material is concentrated (8% by mass) in the slag. It has been found that the MgO—C refractory has an effect of preventing melting damage.
Therefore, light burned dolomite is generally used as a slagging material in secondary refining using a ladle, but according to the method of the present invention, a substitute for a slagging material even in a steel type having a carbon content of 0.10 mass% or less. As a result, it was found that MgO-C refractory waste can be used sufficiently.
[0013]
On the other hand, in order to melt SUS409 steel having an upper limit of carbon content of 0.015% by mass, decarburization to a carbon content of 0.10% by mass using a converter, followed by secondary decarburization refining by the VOD method, After the carbon concentration in the steel was 0.009% by mass, 500 kg of MgO-C refractory waste containing 20% by mass of carbon was added to the slag as a slag component adjusting material, followed by slag reduction treatment. In this case, the carbon content in the steel after the VOD treatment was 0.016% by mass, which deviated from the upper limit of the carbon content (ie 0.015% by mass).
[0014]
In addition to the above steel types, after performing decarburization treatment using a converter for various steel types, before the decarburization in the VOD treatment, during decarburization, at the time of various carbon concentrations in the molten steel, The refractory scrap containing carbon was added to the ladle slag as a slagging material and refined, and the occurrence rate of the carbon content exceeding the upper limit was investigated. The results are shown in Table 1.
In addition, the occurrence rate of deviation from the upper limit of the carbon content in Table 1 was investigated as follows. Each experiment was conducted to add carbon-containing refractory debris into slag under the conditions in the left column of Table 1, and each heat was decarburized to less than the upper limit of carbon content required as a product at the end of secondary decarburization refining. After confirming this, the molten steel was continuously cast. Measure the representative carbon concentration in the tundish during continuous casting, and define the heat that exceeds the upper limit of carbon content required for the product as being out of the upper limit of the carbon content, and the ratio of the number of generated heat (%) Was defined as the off-limit of the carbon content.
[0015]
[Table 1]
When the carbon content in molten steel when adding carbon-containing refractory scraps is 0.05% by mass or more, the upper limit is not deviated, and when the carbon content is 0.01% by mass or more and less than 0.05% by mass, the occurrence rate of deviating upper limit is not observed. Was 1%. On the other hand, when the carbon content was less than 0.01% by mass, the incidence of deviation from the upper limit was 20%. Therefore, it is desirable that the carbon-containing refractory scrap is added when the carbon content in the molten steel is 0.01% by mass or more.
[0017]
Next, a preferred embodiment of the present invention will be described. First, in the present invention, molten steel that has been subjected to primary decarburization refining in advance is used. As the refining equipment for performing the primary decarburization refining, the converter used in the preliminary experiment described above is generally used, but an AOD furnace for decarburizing by supplying oxygen to the molten steel can also be used similarly to the converter. Further, in recent years, even in an arc electric furnace (regardless of an AC arc furnace or a DC arc furnace), an oxygen blowing facility is usually provided to perform early melting and decarburization of scrap, Therefore, primary decarburization refining is also possible with such an electric furnace.
[0018]
The purpose of secondary decarburization refining is as follows. If the carbon content in the molten steel is drastically reduced in the primary decarburization refining furnace, the temperature of the molten steel increases, the FeO content in the slag increases, and the refractory lining the primary decarburization refining furnace is melted down. In addition, in the case of molten steel containing 5% by mass or more of Cr, if the carbon concentration is 0.1% by mass or less, the oxidation of Cr is prioritized over carbon and substantially no further decarburization is possible. Therefore, secondary decarburization refining is performed using a ladle refining facility that can hold the molten steel under reduced pressure and create conditions more advantageous for decarburization than the primary decarburization refining furnace.
[0019]
As such ladle refining equipment, ladle refining equipment using a straight body type depressurized immersion tank disclosed in VOD, VAD, ASEA-SKF, RH, DH or Japanese Patent Laid-Open No. 11-140534 Etc. The present invention adjusts the slag component on the surface of molten steel in these facilities to make it suitable for a refining reaction, or to reduce the erosion resistance to refractories such as ladle, dip tank, dip tube and the like.
[0020]
Therefore, in the VOD, VAD, ASEA-SKF, straight barrel ladle refining equipment, etc. that are particularly slag-stirring during the refining reaction, and that the reaction between the slag and the metal is likely to occur and the load to the refractory is large. The effect of applying is remarkable.
When secondary decarburization refining using such ladle refining equipment, the so-called oxygen blowing decarburization method, in which oxygen is blown into molten steel in a reduced pressure state or oxygen is blown onto the molten steel surface, and the molten steel is depressurized. There is a vacuum decarburization method in which a decarburization reaction is caused by FeO, MnO, Cr 2 O 3 in slag and dissolved oxygen in molten steel, but the application of the present invention can be applied to any of these methods. Applicable.
[0021]
During the above-mentioned secondary decarburization refining, slag is added at the time when the carbon concentration in the molten steel is 0.01 mass% or more (either before the start of secondary decarburization refining or in the middle of secondary decarburization refining). Add carbon-containing refractory waste. The reason for limiting the carbon concentration range is as described above.
Typical carbon-containing refractory scraps include MgO-C refractories used in converters, electric furnaces, AOD furnaces or ladle slag lines, and Al used in continuous casting of molten steel. Examples include 2 O 3 -C immersion nozzles, scraps of Al 2 O 3 -C refractories used for linings of kneading vehicles, but are not particularly limited thereto. Depending on the slag component to be adjusted and the purpose, what amount of refractory containing an oxide as a main component should be determined.
[0022]
It does not matter whether the refractory waste was originally a regular refractory such as brick or an irregular refractory such as pouring, but when added to the slag, it quickly disperses or dissolves in the slag. Therefore, it is preferable to pulverize to a size of about 100 mm or less in advance, and when charging using the alloy material addition device of the ladle refining equipment, it is about 30 mm or less due to restrictions on cutting equipment such as a rotary feeder. The grain size should be good.
[0023]
【Example】
180t of 9 mass% Cr molten steel was primary decarburized and refined by an upper bottom blowing converter, and the steel was blown to a ladle with a carbon concentration of 0.15 mass%. When this molten steel is subjected to secondary decarburization refining in a VOD facility and the carbon concentration in the target steel of the product is reduced to 0.008 to 0.015 mass%, MgO-C refractory waste ( Example of adding 500 kg of particle size 100 mm or less (Invention example 1), 500 kg of MgO-C refractory waste (particle size 20 mm or less) in the slag when the carbon concentration in the molten steel is 0.05 mass% during the secondary decarburization refining Added example (Invention example 2), and an example in which 500 kg of MgO-C refractory waste (particle size of 20 mm or less) was added to the slag after the carbon concentration in the molten steel at the end of secondary decarburization refining decreased to 0.008% by mass ( The two types of operations of Comparative Example) were performed.
[0024]
As a result, in Invention Example 1, the carbon concentration at the end of the secondary decarburization refining is 0.009% by mass, and then the typical carbon concentration in the tundish when continuously casting this molten steel is also 0.009% by mass, which is the target component range. Satisfied.
In Invention Example 2, the carbon concentration at the end of the secondary decarburization refining was 0.008% by mass, and then the typical carbon concentration in the tundish when this molten steel was continuously cast was also 0.008% by mass, satisfying the target component range. .
[0025]
On the other hand, in the comparative example, the carbon concentration at the end of the secondary decarburization refining was 0.008% by mass, but after that, the typical carbon concentration in the tundish when continuously casting this molten steel was 0.017% by mass, and the target component range The result exceeded the upper limit.
[0026]
【The invention's effect】
In the present invention, when performing secondary decarburization refining using the ladle refining equipment, by using the carbon-containing refractory scrap as a slagging material, resources can be effectively utilized, relatively expensive light-burning dolomite, etc. Can reduce the amount of iron making materials used. Moreover, the life of the refractory in the ladle slag line can be extended.
Claims (5)
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| Application Number | Priority Date | Filing Date | Title |
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| JP33283799A JP3726599B2 (en) | 1999-11-24 | 1999-11-24 | Method for refining molten steel using refractory scrap containing carbon |
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| JP33283799A JP3726599B2 (en) | 1999-11-24 | 1999-11-24 | Method for refining molten steel using refractory scrap containing carbon |
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| JP3726599B2 true JP3726599B2 (en) | 2005-12-14 |
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| JPS591610A (en) * | 1982-05-28 | 1984-01-07 | Shinagawa Rozai Kk | Composite slag forming agent for basic steel making furnace |
| JPS60234916A (en) * | 1984-05-08 | 1985-11-21 | Nisshin Steel Co Ltd | Manufacture of stainless steel containing low nitrogen |
| JPH05179333A (en) * | 1991-12-27 | 1993-07-20 | Daido Steel Co Ltd | Slag forming material |
| JPH05339615A (en) * | 1992-06-10 | 1993-12-21 | Daido Steel Co Ltd | Effective utilization method of waste brick for steel making |
| JPH0741840A (en) * | 1993-06-28 | 1995-02-10 | Nippon Steel Corp | Method for melting extra-low carbon steel |
| JP3607767B2 (en) * | 1995-12-05 | 2005-01-05 | 新日本製鐵株式会社 | Molten steel desulfurization and dehydrogenation method with small refractory melting loss |
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