JP4312068B2 - Method of melting ultra-low carbon steel - Google Patents
Method of melting ultra-low carbon steel Download PDFInfo
- Publication number
- JP4312068B2 JP4312068B2 JP2004027862A JP2004027862A JP4312068B2 JP 4312068 B2 JP4312068 B2 JP 4312068B2 JP 2004027862 A JP2004027862 A JP 2004027862A JP 2004027862 A JP2004027862 A JP 2004027862A JP 4312068 B2 JP4312068 B2 JP 4312068B2
- Authority
- JP
- Japan
- Prior art keywords
- decarburization
- molten steel
- ladle slag
- ladle
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Images
Landscapes
- Treatment Of Steel In Its Molten State (AREA)
Description
本発明は、極低炭素鋼の溶製方法に関するものであり、詳細には、介在物の抑制された極低炭素鋼（炭素濃度：０．０２％以下）を、効率良く脱炭処理を行って溶製する方法に関するものである。 The present invention relates to a method for melting ultra-low carbon steel. Specifically, ultra-low carbon steel with suppressed inclusions (carbon concentration: 0.02% or less) is efficiently decarburized. It is related with the method of melting.
極低炭素鋼の溶製では、転炉や電気炉等で、溶銑中または溶鋼中に酸素を吹き込んで溶鋼中の炭素濃度を約０．０３〜０．０７％まで低減する。しかしこの段階では、Ａｌ、Ｓｉ等の添加による脱酸処理を行うことなく、溶存酸素濃度が約０．０４〜０．０８％と比較的高い状態のまま出鋼するのが一般的である。 In the production of ultra-low carbon steel, oxygen is blown into hot metal or molten steel in a converter or electric furnace to reduce the carbon concentration in the molten steel to about 0.03 to 0.07%. However, at this stage, it is common to produce steel with a relatively high dissolved oxygen concentration of about 0.04 to 0.08% without performing deoxidation treatment by adding Al, Si, or the like.
これはその後に、循環脱ガス装置（ＲＨ装置）などの真空脱ガス装置で溶鋼を還流させ、溶鋼中に残存する溶存酸素と溶鋼中の炭素を反応させることにより、ＣＯガスとして溶鋼から炭素を十分に除去し、炭素濃度の著しく低い鋼を得るためである。 After that, the molten steel is refluxed by a vacuum degassing apparatus such as a circulating degassing apparatus (RH apparatus), and the dissolved oxygen remaining in the molten steel reacts with the carbon in the molten steel, whereby carbon from the molten steel is converted into CO gas. This is because the steel is sufficiently removed and the carbon concentration is extremely low.
上記脱炭処理の反応速度を高めるには、溶鋼中の溶存酸素濃度が高いことに加えて、出鋼時に転炉や電気炉から取鍋内へ流入したスラグ（取鍋スラグ）が酸素リッチな状態であることが好ましく、具体的には、取鍋スラグ中のＦｅｘＯ濃度が高いことが好ましい。 In order to increase the reaction rate of the above decarburization treatment, in addition to the high dissolved oxygen concentration in the molten steel, the slag that flows into the ladle from the converter or electric furnace at the time of steel extraction (ladder slag) is rich in oxygen. It is preferable that it is a state, and specifically, it is preferable that the Fe x O concentration in the ladle slag is high.
ところで上記脱炭処理により、溶鋼中の溶存酸素も約０．０１〜０．０２％まで減少するが、諸特性に悪影響を及ぼす溶存酸素を更に低減すべく、脱炭処理後には、金属Ａｌ等を添加して脱酸処理を行うのが一般的である。脱酸処理で生じた脱酸生成物（アルミナ）は、溶鋼を還流させることにより浮上分離して除去する。しかし上述の様に、脱炭処理速度を高めるため取鍋スラグ中のＦｅｘＯ濃度を高めた場合には、添加した金属Ａｌ等が、下記化学式（Ｉ）で示す様にＦｅｘＯと反応してＡｌ２Ｏ３が新たに生成するため、見かけ上Ａｌ２Ｏ３低減速度が低下する。Ａｌ２Ｏ３が十分除去されず鋳片中に残留すると、線状または点状の疵などの欠陥が圧延製品に生じる原因となる。
２Ａｌ＋３ＦｅｘＯ → Ａｌ２Ｏ３＋３ＸＦｅ …（Ｉ）
By the way, the above decarburization treatment also reduces the dissolved oxygen in the molten steel to about 0.01 to 0.02%, but after the decarburization treatment, metal Al, etc. to further reduce the dissolved oxygen that adversely affects various properties. In general, deoxidation treatment is performed by adding. The deoxidation product (alumina) generated by the deoxidation treatment is removed by floating and separating by refluxing the molten steel. However, as described above, when the concentration of Fe x O in the ladle slag is increased in order to increase the decarburization processing rate, the added metal Al or the like reacts with Fe x O as shown in the following chemical formula (I). Since Al 2 O 3 is newly generated, the Al 2 O 3 reduction rate is apparently reduced. If Al 2 O 3 is not sufficiently removed and remains in the slab, defects such as linear or dotted defects will occur in the rolled product.
2Al + 3Fe x O → Al 2 O 3 + 3XFe ... (I)
そこで、脱炭処理を効率良く行いつつ、上記アルミナ等の介在物も低減することのできる極低炭素鋼の溶製方法が提案されている。例えば特許文献１には、転炉出鋼時にスラグ改質剤等を添加し、真空脱炭処理前の取鍋スラグ中の総鉄量を低減すると共に、取鍋耐火物中のＳｉＯ２濃度を低減することで、極低炭素鋼の鋼中介在物を抑制する方法が示されている。
Then, the melting method of the ultra-low carbon steel which can reduce inclusions, such as the said alumina, performing the decarburization process efficiently is proposed. For example, in
特許文献２には、未脱酸溶鋼または弱脱酸溶鋼を取鍋へ出鋼する際に、金属ＡｌまたはＡｌ合金を含有するスラグ改質剤を添加することにより、真空脱炭処理前の取鍋スラグ中のＦｅＯとＭｎＯの合計量を５ｗｔ％以下とし、その後に真空脱炭処理して、それから再度、前記スラグ改質剤を添加して脱酸処理を行う方法が示されている。特許文献３には、出鋼時に流入した取鍋内スラグを除去し、新たな成分組成のスラグを添加して、取鍋スラグ中の総鉄量を６％以下にする技術が開示されている。
In
これらの技術は、脱炭処理後に行うＡｌ脱酸時に、前記化学式（Ｉ）で示した様な反応によりＡｌ２Ｏ３が生成するのを抑制するため、取鍋スラグ中の総鉄量の低減を図ったものである。しかし上記技術では、脱炭処理時における取鍋スラグ中のＦｅｘＯ濃度が低く、結果としてＣを脱炭するための酸素（Ｏ）源が不足するため、脱炭速度が低下して処理に長時間を要し、生産性が低下するという問題が生じる。 These techniques reduce the total amount of iron in the ladle slag in order to suppress the formation of Al 2 O 3 by the reaction shown in the chemical formula (I) during Al deoxidation performed after the decarburization treatment. Is intended. However, in the above technique, the Fe x O concentration in the ladle slag at the time of decarburization treatment is low, and as a result, the oxygen (O) source for decarburizing C is insufficient, so the decarburization rate is lowered and the treatment is performed. The problem is that it takes a long time and productivity decreases.
脱炭速度を低下させずに介在物を低減する方法も提案されている。例えば特許文献４には、スラグ改質剤の添加を転炉出鋼時（真空脱炭処理前）と真空脱炭処理後の２回に分けて行う方法が示されている。また特許文献５や特許文献６には、転炉出鋼時（真空脱炭前）のスラグ改質剤の添加量を調整して、特許文献５では脱炭処理前の取鍋スラグ中のＦｅＯとＭｎＯの合計量を８〜１０％に制御する方法が、また特許文献６では取鍋スラグ中の総鉄量を６〜１２％に制御する方法が提案されている。 A method of reducing inclusions without reducing the decarburization rate has also been proposed. For example, Patent Document 4 discloses a method in which the addition of the slag modifier is divided into two times at the time of steel leaving the converter (before the vacuum decarburization process) and after the vacuum decarburization process. In Patent Document 5 and Patent Document 6, the amount of slag modifier added at the time of converter steelmaking (before vacuum decarburization) is adjusted. In Patent Document 5, FeO in ladle slag before decarburization treatment is adjusted. And a method of controlling the total amount of MnO to 8 to 10%, and Patent Document 6 proposes a method of controlling the total iron amount in the ladle slag to 6 to 12%.
これらの技術は、脱炭処理時に必要な酸素を確保することで、脱炭速度を維持しながら、Ａｌ脱酸で生じるＡｌ２Ｏ３の生成も抑制しようとするものである。しかし、介在物量の極力低減された高清浄度の極低炭素鋼を、脱炭処理時間をより短縮して更に効率よく溶製することのできる技術の確立が切望されている。
本発明は上記事情に鑑みてなされたものであって、その目的は、高清浄度の極低炭素鋼を、短い脱炭処理時間で効率よく溶製するための方法を提供することにある。 The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for efficiently melting a very clean ultra-low carbon steel in a short decarburization time.
本発明に係る極低炭素鋼の溶製方法は、転炉または電気炉から取鍋に出鋼した溶鋼に、真空脱ガス法による脱炭処理（以下「真空脱炭処理」または単に「脱炭処理」という）を施して極低炭素鋼を溶製するにあたり、真空脱炭処理前の取鍋スラグ中の総鉄量［取鍋スラグ中のＦｅｘＯ量をＦｅ濃度（質量％）に換算した値。以下、取鍋スラグ中（Ｔ．Ｆｅ）という］を１２％（質量％の意味、以下同じ）超とし、かつ真空脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下にするところに特徴がある。 The method for melting ultra-low carbon steel according to the present invention involves decarburization treatment (hereinafter referred to as “vacuum decarburization treatment” or simply “decarburization treatment”) to the molten steel discharged from a converter or electric furnace to a ladle. The amount of total iron in ladle slag before vacuum decarburization processing [converted Fe x O in ladle slag into Fe concentration (mass%) Value. Hereinafter, in ladle slag (referred to as T.Fe)] exceeds 12% (meaning mass%, the same applies hereinafter), and in ladle slag after vacuum decarburization treatment (T.Fe) is reduced to 12% or less. There is a feature.
上記の通り、真空脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超にするには、転炉または電気炉の溶鋼およびスラグを弱還元性もしくは非還元性の状態で取鍋へ出鋼することが有効な手段として挙げられる。 As mentioned above, in order to make the ladle slag in the ladle slag before vacuum decarburization treatment (T.Fe) exceed 12%, the ladle in the converter or electric furnace molten steel and slag is weakly reduced or non-reduced. It is an effective means to produce steel.
また、真空脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下にするには、真空脱炭処理後の溶鋼および／または取鍋スラグに、Ａｌ、Ｓｉ、ＣａおよびＭｇよりなる群から選択される１種以上の元素を含む還元剤を添加することが有効な手段として挙げられる。 Moreover, in order to make the ladle slag after vacuum decarburization treatment (T.Fe) 12% or less, the molten steel and / or ladle slag after vacuum decarburization treatment is made of Al, Si, Ca and Mg. An effective means is to add a reducing agent containing at least one element selected from the group.
鋼中介在物（特にアルミナ）の極めて少ない炭素量が０．０２質量％以下の極低炭素鋼を、短い脱炭処理時間で効率良く製造することができ、極低炭素鋼の溶製コストを更に低減することができる。 Extremely low carbon steel with an extremely low carbon content of 0.02% by mass or less of inclusions (especially alumina) in steel can be efficiently produced in a short decarburization process time. Further reduction can be achieved.
本発明者らは、介在物量の著しく低減された高清浄度の極低炭素鋼を、脱炭処理時間を短縮して効率良く溶製するための技術を確立すべく様々な角度から検討した。その結果、転炉または電気炉から取鍋に出鋼した溶鋼に、真空脱ガス法による脱炭処理を施して極低炭素鋼を溶製するにあたり、真空脱炭処理前の取鍋スラグ中の総鉄量を１２％超と比較的高めにした状態で脱炭処理を行い、該脱炭処理終了後には、取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下に抑えることが極めて重要であることを見出した。 The present inventors have studied from various angles to establish a technique for efficiently melting ultra-low carbon steel having a high cleanliness with a significantly reduced amount of inclusions by reducing the decarburization time. As a result, when the ultra-low carbon steel is melted by decarburizing by vacuum degassing to the molten steel that has been discharged from the converter or electric furnace to the ladle, the ladle in the ladle slag before vacuum decarburization It is extremely important to perform decarburization with the total iron content exceeding 12% and keep the content of ladle slag (T.Fe) to 12% or less after the decarburization. I found out.
以下、本発明が完成された経緯に沿って、本発明の作用効果を説明する。まず本発明者らは、介在物の抑制を脱炭処理後に行えるか否かの検討を行った。具体的には、脱炭処理後に取鍋スラグ中（Ｔ．Ｆｅ）を制御することで介在物を抑制できるか否かについて確認するため、取鍋スラグ中（Ｔ．Ｆｅ）を変化させて脱酸処理を行い、Ａｌ添加（脱酸）後の経過時間と取鍋スラグ中（Ｔ．Ｆｅ）とがアルミナ介在物量に及ぼす影響について調べた。 Hereinafter, the operational effects of the present invention will be described along with the background of the completion of the present invention. First, the inventors examined whether inclusions can be suppressed after decarburization treatment. Specifically, in order to confirm whether inclusions can be suppressed by controlling the ladle slag (T.Fe) after the decarburization treatment, the ladle slag (T.Fe) is changed to remove the inclusions. The acid treatment was performed, and the influence of the elapsed time after Al addition (deoxidation) and the ladle slag (T.Fe) on the amount of alumina inclusions was examined.
実験は、取鍋スラグ中（Ｔ．Ｆｅ）の異なる１０種類の溶鋼に、ＲＨ真空脱ガス装置で脱炭処理を施し、該脱炭処理が終了した時点で、Ａｌを溶鋼１トンあたり０．５〜０．７ｋｇ添加して８分間溶鋼を還流した。この脱酸処理において、Ａｌ添加時から２分、４分、６分、８分経過後（ＲＨ脱炭終了時）の溶鋼からサンプルを採取し、後述する方法で２０μｍ以上のアルミナ介在物の個数を調べた。また上記還流後、連続鋳造するためタンディッシュに取鍋内の溶鋼を半分装入した時点で、タンディッシュ内の溶鋼をサンプリングして、上記と同様にアルミナ介在物の個数を調べた。 In the experiment, 10 types of molten steel in the ladle slag (T.Fe) were subjected to decarburization treatment with an RH vacuum degasser, and when the decarburization treatment was completed, Al was reduced to 0.000 per ton of molten steel. 5 to 0.7 kg was added and the molten steel was refluxed for 8 minutes. In this deoxidation treatment, a sample was taken from the molten steel after 2 minutes, 4 minutes, 6 minutes, and 8 minutes had passed since the addition of Al (when RH decarburization was completed), and the number of alumina inclusions of 20 μm or more was measured by the method described later I investigated. Further, after the reflux, when the molten steel in the ladle was half charged into the tundish for continuous casting, the molten steel in the tundish was sampled, and the number of alumina inclusions was examined in the same manner as described above.
この様にして得られた実験データを基に、取鍋スラグ中（Ｔ．Ｆｅ）およびＡｌ添加後の経過時間と溶鋼中アルミナ介在物量との関係を整理して図１に示す。この図１から、Ａｌ脱酸時（還流時）の溶鋼（図１中の◇、□、△、○）は、Ａｌ添加後からの経過時間が長いほど、即ち、還流時間が長いほどアルミナ介在物の個数は減少傾向を示すが、その減少度合いは、取鍋スラグ中（Ｔ．Ｆｅ）に依存していない。 Based on the experimental data thus obtained, the relationship between the elapsed time in the ladle slag (T.Fe) and after the addition of Al and the amount of alumina inclusions in the molten steel is shown in FIG. From FIG. 1, the molten steel at the time of Al deoxidation (at the time of reflux) (脱, □, Δ, ○ in FIG. 1) shows that the longer the time elapsed since the addition of Al, that is, the longer the reflux time, the more the alumina intervenes. Although the number of objects shows a decreasing tendency, the degree of decrease does not depend on the ladle slag (T.Fe).
しかし、タンディッシュに装入された溶鋼（図１中の●）は、アルミナ介在物の個数が取鍋スラグ中（Ｔ．Ｆｅ）に依存しており、取鍋スラグ中（Ｔ．Ｆｅ）が高くなるほどアルミナ介在物量は増加することがわかる。即ち、ＲＨ処理終了からタンディッシュ装入までの取鍋スラグ中（Ｔ．Ｆｅ）が低い状態であれば、アルミナ介在物の個数を効率良く低減できるのである。 However, in the molten steel charged in the tundish (● in FIG. 1), the number of alumina inclusions depends on the ladle slag (T.Fe), and the ladle slag (T.Fe) It can be seen that the higher the amount of alumina inclusion, the higher the value. That is, if the ladle slag from the end of the RH treatment to the tundish charging is low (T. Fe), the number of alumina inclusions can be efficiently reduced.
次に上記データを基に、下記式（１）で示されるアルミナ介在物減少速度定数（Ｋ）を用いて、取鍋スラグ中（Ｔ．Ｆｅ）と各サンプリング時点間のアルミナ介在物減少速度との関係を調べた。その結果を図２に示す。 Next, based on the above data, using the alumina inclusion reduction rate constant (K) represented by the following formula (1), the alumina inclusion reduction rate in the ladle slag (T.Fe) and between each sampling time point I investigated the relationship. The result is shown in FIG.
尚、下記式（２）において、Ｋ＞０の場合はアルミナ介在物個数の減少を意味し、Ｋ＜０の場合はアルミナ介在物個数の増加を意味し、またＫ＝０はアルミナ介在物個数が変化しないことを意味している。 In the following formula (2), when K> 0, it means a decrease in the number of alumina inclusions, when K <0, it means an increase in the number of alumina inclusions, and K = 0 is the number of alumina inclusions. Means no change.
［式(1)中、N１：ある時点でのサンプリンク゛試料中の20μm以上のアルミナ個数(個/kg)
N２：次にサンプリンク゛した試料中の20μm以上のアルミナ個数(個/kg)
t１：サンプリンク゛した時間間隔（分間）］
この図２からも、還流時の溶鋼（図２中の□、△、○）は、Ａｌ２Ｏ３介在物の減少速度が取鍋スラグ中（Ｔ．Ｆｅ）に依存していないが、ＲＨ処理終了後からタンディッシュ装入までの溶鋼（図１中の●）のＡｌ２Ｏ３介在物の減少速度は、取鍋スラグ中（Ｔ．Ｆｅ）に依存しており、特に、取鍋スラグ中（Ｔ．Ｆｅ）が１２％を超えると、Ｋ＜０、即ちアルミナ介在物が増加する場合があることがわかる。
[In formula (1), N 1 : Number of alumina of 20 μm or more in sample at a certain time (pieces / kg)
N 2 : Number of alumina of 20 μm or more in the sample sampled next (pieces / kg)
t 1 : Sampled time interval (minutes)]
Also from FIG. 2, the molten steel at reflux (□, Δ, ○ in FIG. 2) shows that the reduction rate of Al 2 O 3 inclusions does not depend on the ladle slag (T.Fe). The decrease rate of Al 2 O 3 inclusions in the molten steel (● in Fig. 1) from the end of treatment to tundish charging depends on the ladle slag (T.Fe), and in particular, ladle slag It can be seen that when the content of T (Fe) exceeds 12%, K <0, that is, alumina inclusions may increase.
これらの結果から、アルミナ介在物の低減という観点からすると、脱炭処理またはそれ以前にスラグ中（Ｔ．Ｆｅ）を制御する必要はなく、脱炭処理後の脱酸処理工程等で、取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下に抑えれば、図１や図２のタンディッシュ内溶鋼に示される様に、アルミナ介在物を効果的に低減できることが分かる。図２から明らかなように、取鍋スラグ中（Ｔ．Ｆｅ）を好ましくは１０％以下、より好ましくは８％以下に抑えれば、更に効率よくアルミナ介在物を抑制できる。取鍋スラグ中（Ｔ．Ｆｅ）の下限は特に定めないが、脱酸剤の使用コスト等の観点からは約０．５％が下限となる。 From these results, from the viewpoint of reducing alumina inclusions, it is not necessary to control the decarburization process (T. Fe) before or before the decarburization process, and the ladle in the deoxidation process after the decarburization process. It can be seen that if the slag content (T.Fe) is suppressed to 12% or less, the alumina inclusions can be effectively reduced as shown in the molten steel in the tundish of FIGS. As apparent from FIG. 2, alumina inclusions can be more efficiently suppressed if the ladle slag (T.Fe) is preferably 10% or less, more preferably 8% or less. The lower limit of the ladle slag (T.Fe) is not particularly defined, but about 0.5% is the lower limit from the viewpoint of the cost of using the deoxidizer.
本発明は、この様に真空脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下にするための方法まで限定するものでなく、様々な方法を適用でき、例えばＡｌ、Ｓｉ、Ｃａ、Ｍｇ等の還元剤を、金属、合金または酸化物（ＣａＯ、ＭｇＯ）等の形態でスラグに添加して取鍋スラグ中（Ｔ．Ｆｅ）を希釈する等の方法が挙げられる。また、脱炭処理工程では取鍋スラグ中のＦｅｘＯが消費され、取鍋スラグ中（Ｔ．Ｆｅ）はある程度低下するので、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）の値によっては、特に手段を講じなくとも１２％以下になることもある。しかし、真空脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下に確実に抑えるには、脱炭処理後の溶鋼中および／またはスラグに、Ａｌ、Ｓｉ、ＣａおよびＭｇよりなる群から選択される１種以上を含む還元剤を装入して、ＦｅｘＯを還元し（Ｔ．Ｆｅ）を低下させるのがよい。 The present invention is not limited to the method for reducing the ladle slag after vacuum decarburization (T.Fe) to 12% or less, and various methods can be applied. For example, Al, Si, Examples thereof include a method of diluting the ladle slag (T. Fe) by adding a reducing agent such as Ca and Mg to the slag in the form of a metal, an alloy or an oxide (CaO, MgO). In addition, since Fe x O in the ladle slag is consumed in the decarburization treatment process and the amount in the ladle slag (T.Fe) decreases to some extent, the value in the ladle slag before the decarburization treatment (T.Fe) Depending on the case, it may be 12% or less even if no measures are taken. However, in order to surely suppress the ladle slag after vacuum decarburization treatment (T.Fe) to 12% or less, the molten steel after decarburization treatment and / or slag is composed of Al, Si, Ca and Mg. A reducing agent containing at least one selected from the group may be charged to reduce Fe x O and reduce (T.Fe).
上記還元剤としては、具体的にＡｌ金属、Ａｌ−Ｆｅ合金、Ｆｅ−Ｓｉ−Ｍｇ合金、Ｃａ−Ｓｉ合金、Ｆｅ−Ｓｉ合金等が挙げられ、ワイヤー状、粉末状、またはペレット状のものを供給すればよい。 Specific examples of the reducing agent include Al metal, Al-Fe alloy, Fe-Si-Mg alloy, Ca-Si alloy, Fe-Si alloy, and the like. What is necessary is just to supply.
このとき還元剤の添加量は、該還元剤添加前の取鍋スラグ中の（Ｔ．Ｆｅ）濃度に応じて決定すればよく、還元剤添加前の取鍋スラグ中（Ｔ．Ｆｅ）は、例えば前記特許文献６に記載の方法で溶鋼中溶存酸素活量から推定することができる。 At this time, the amount of addition of the reducing agent may be determined according to the (T.Fe) concentration in the ladle slag before the addition of the reducing agent, and (T.Fe) in the ladle slag before the addition of the reducing agent is: For example, it can be estimated from the dissolved oxygen activity in molten steel by the method described in Patent Document 6.
上述の通り、脱炭処理時またはそれ以前の取鍋スラグ中（Ｔ．Ｆｅ）は、アルミナ介在物の低減に寄与しないことから、脱炭処理時には、該処理を促進させるために脱炭処理時の（Ｔ．Ｆｅ）を高めることができる。 As described above, the ladle slag (T.Fe) during or before the decarburization treatment does not contribute to the reduction of the alumina inclusions. Therefore, during the decarburization treatment, the decarburization treatment is performed in order to promote the treatment. (T.Fe) can be increased.
そこで脱炭処理を行うにあたり、取鍋スラグ中（Ｔ．Ｆｅ）をどの程度高めればよいかを把握するため、該（Ｔ．Ｆｅ）と脱炭速度との関係を調べた。具体的には、取鍋スラグ中（Ｔ．Ｆｅ）の異なる溶鋼を１０〜３０分間真空脱ガス法で脱炭処理して処理前後の溶鋼中炭素濃度を測定し、脱炭速度は、下記式（２）で示される見かけの総括脱炭速度定数（Ｋｃ）を用いて評価を行った。 Then, in order to grasp | ascertain how much should raise (T.Fe) in ladle slag in performing a decarburization process, the relationship between this (T.Fe) and a decarburization rate was investigated. Specifically, the molten steel in different ladle slag (T.Fe) is decarburized by vacuum degassing for 10 to 30 minutes, and the carbon concentration in the molten steel before and after the treatment is measured. Evaluation was performed using the apparent overall decarburization rate constant (Kc) shown in (2).
その結果を、取鍋スラグ中（Ｔ．Ｆｅ）濃度と見かけの総括脱炭速度定数（Ｋｃ）との関係として図３に示す。図３から、取鍋スラグ中（Ｔ．Ｆｅ）が高いほど脱炭速度は速くなり、特にＫｃが約０．２付近まで著しく上昇し、約０．２を超えると上昇率が小さくなることがわかる。本発明では、この様な結果に基づき、Ｋｃが約０．２以上となるように、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超に制御することとした。取鍋スラグ中（Ｔ．Ｆｅ）は、好ましくは１４％以上、より好ましくは１５％以上である。取鍋スラグ中（Ｔ．Ｆｅ）の上限は特に定めないが、転炉、ＲＨ、取鍋等に用いる耐火物コストの抑制やスラグの泡立ち現象の防止等を考慮すると３０％を上限とすることが好ましい。 The results are shown in FIG. 3 as the relationship between the concentration in the ladle slag (T.Fe) and the apparent overall decarburization rate constant (Kc). From FIG. 3, the higher the ladle slag (T.Fe), the faster the decarburization speed, and in particular, Kc increases remarkably up to about 0.2, and the increase rate decreases when it exceeds about 0.2. Recognize. In the present invention, based on such results, the ladle slag before decarburization treatment (T.Fe) is controlled to be more than 12% so that Kc is about 0.2 or more. The ladle slag (T.Fe) is preferably 14% or more, more preferably 15% or more. The upper limit of ladle slag (T.Fe) is not particularly limited, but 30% should be the upper limit considering the suppression of refractory costs used in converters, RH, ladle, etc. and prevention of slag foaming phenomenon. Is preferred.
［式（2）中、Ｃｉ：脱炭処理前の溶鋼Ｃ濃度（質量％）
Ｃｆ：脱炭処理後の溶鋼Ｃ濃度（質量％）
ｔ２：脱炭処理時間（分間）］
本発明は、この様に、真空脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超にするための方法まで規定するものではなく、一般的に知られている様々な方法を適用できる。
[In formula (2), C i : Molten steel C concentration (mass%) before decarburization treatment
C f : Molten steel C concentration after decarburization (mass%)
t 2 : Decarburization processing time (minutes)]
As described above, the present invention does not define a method for increasing the content (T.Fe) in the ladle slag before vacuum decarburization treatment to more than 12%. Applicable.
尚、取鍋スラグの泡立ち現象を抑制したり耐火物の損耗を抑制するため、転炉出鋼後の取鍋スラグ上に、Ａｌ等を含む還元剤を少量添加して弱還元性状態とした場合でも、真空脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超にすることができるが、確実に（Ｔ．Ｆｅ）を制御するには、出鋼時の溶鋼およびスラグをともに非還元性状態とすることが推奨される。 In addition, in order to suppress the bubbling phenomenon of ladle slag and to suppress the wear of refractory, a small amount of reducing agent containing Al etc. is added to the ladle slag after the steel from the converter to make it a weakly reducing state. Even in the case, (T.Fe) in the ladle slag before vacuum decarburization treatment can be over 12%, but in order to reliably control (T.Fe), the molten steel and slag at the time of steel output are controlled. It is recommended that both be in a non-reducing state.
尚、本発明では、真空脱ガス法で脱炭処理を行うが、このときの真空脱ガスの形態については特に限定するものではなく、前記したＲＨ法の他、鍋型真空脱ガス法、ＤＨ法等も適用できる。 In the present invention, the decarburization process is performed by the vacuum degassing method, but the form of the vacuum degassing at this time is not particularly limited. In addition to the RH method described above, the pan-type vacuum degassing method, DH Laws can also be applied.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.
２４０トンの転炉で溶銑を吹錬し、溶銑中の炭素量を０．０３〜０．０７％、溶存酸素量を０．０５〜０．０８％まで低減した後、取鍋に出鋼した。そして出鋼後の取鍋スラグ上に、Ａｌ換算で０．１〜０．７ｋｇ／溶鋼トンのＡｌ含有還元剤（１〜２ｃｍ角状の金属Ａｌ粒）を投入するか、または未投入のままとした。その後、還流式真空脱ガス装置（ＲＨ）で脱炭処理を行い、Ｃ濃度を０．００１０〜０．００４０％まで低減した。それから脱炭処理終了直後に、Ａｌ換算で０．３〜０．７ｋｇ／溶鋼トンの金属Ａｌワイヤーを取鍋に投入して脱酸処理を行うか、または未脱酸のままとした（以下、これら脱炭処理および脱酸処理をまとめて「ＲＨ処理」ということがある）。上記各実施条件について表１に示す。 Hot metal was blown in a 240-ton converter, the amount of carbon in the hot metal was reduced to 0.03 to 0.07%, and the amount of dissolved oxygen was reduced to 0.05 to 0.08%. . And, on the ladle slag after steel output, 0.1 to 0.7 kg / mol ton of Al-containing reducing agent (1-2 cm square metal Al particles) in terms of Al is charged or left uncharged. It was. Thereafter, decarburization treatment was performed with a reflux-type vacuum degasser (RH), and the C concentration was reduced to 0.0010 to 0.0040%. Then, immediately after completion of the decarburization treatment, a metal Al wire of 0.3 to 0.7 kg / mol steel ton in terms of Al is introduced into the ladle to perform deoxidation treatment or left undeoxidized (hereinafter, These decarburization treatment and deoxidation treatment may be collectively referred to as “RH treatment”). The implementation conditions are shown in Table 1.
そして上記ＲＨ処理後に連続鋳造設備で鋳造を行い、得られた鋳片に熱間圧延を施して圧延鋼材（厚さ１〜２ｍｍの薄鋼板）を得た。 And after the said RH process, it casted with the continuous casting equipment, and the obtained cast piece was hot-rolled and the rolled steel material (thin steel plate of thickness 1-2mm) was obtained.
前記連続鋳造工程では、鋼材の清浄度を評価するため、タンディッシュ内の溶鋼をサンプリングし、得られた試料のうち約５ｇを酸で溶解し、抽出して得られた長径が２０μｍ以上のアルミナ介在物の個数をＥＰＭＡ（Electron Probe X-ray MicroAnalyzer）で測定し、鋼材１ｋｇ当たりの個数に換算した。 In the continuous casting process, in order to evaluate the cleanliness of the steel material, the molten steel in the tundish is sampled, and about 5 g of the obtained sample is dissolved with acid and extracted to obtain an alumina having a major axis of 20 μm or more. The number of inclusions was measured with EPMA (Electron Probe X-ray MicroAnalyzer) and converted to the number per 1 kg of steel.
また圧延鋼材表面の線状欠陥の発生状況を調べた。具体的には、圧延鋼材の表面（目視観察領域）を目視で観察し、線状欠陥の発生個数を測定した。そして、線状欠陥の発生個数がコイル１ｋｍあたり１個の場合を「線状欠陥発生頻度＝１」と指標を置き、各試料の線状欠陥発生頻度を求めた。これらの結果を表１に併記する。 In addition, the occurrence of linear defects on the surface of rolled steel was investigated. Specifically, the surface (visual observation region) of the rolled steel material was visually observed, and the number of occurrences of linear defects was measured. Then, when the number of occurrences of linear defects was 1 per 1 km of coil, the index “Linear defect occurrence frequency = 1” was set, and the linear defect occurrence frequency of each sample was obtained. These results are also shown in Table 1.
表１より次の様に考察できる（尚、以下のＮｏ．は表１の実験Ｎｏ．を示す）。 It can be considered as follows from Table 1 (note that the following numbers indicate the experiment numbers in Table 1).
Ｎｏ．１〜６は、転炉出鋼から脱炭処理の間（脱炭処理前）に還元剤を添加しないか、またはＡｌ換算で０．１または０．３ｋｇ／溶鋼トンのＡｌ含有還元剤を取鍋スラグ中に添加して、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超にし、脱炭処理後の溶鋼には上記還元剤を投入しなかった比較例である。 No. In Nos. 1 to 6, no reducing agent is added during the decarburization process from the converter steel (before decarburization process), or an Al-containing reducing agent of 0.1 or 0.3 kg / mol steel ton is taken in terms of Al. This is a comparative example in which it is added to the ladle slag so that the ladle slag before decarburization treatment (T.Fe) exceeds 12%, and the reducing agent is not added to the molten steel after decarburization treatment.
これらの例では、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）が高く、脱炭処理は効率良く行えたが、得られた鋼材にはアルミナ介在物が多く、圧延鋼材における線状欠陥発生頻度が高くなっている。 In these examples, the ladle slag before decarburization was high (T.Fe), and the decarburization was performed efficiently, but the obtained steel had many alumina inclusions, and linear defects in the rolled steel The frequency of occurrence is high.
Ｎｏ．７〜９は、転炉出鋼から脱炭処理の間に還元剤を取鍋スラグ上に投入して、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下とし、脱炭処理後の溶鋼には、還元剤を投入しなかった比較例である。これらの例では、得られた圧延鋼材のアルミナ介在物量が少なく線状欠陥の発生頻度は低いが、脱炭処理時間が長くなっている。 No. In Nos. 7 to 9, the reducing agent is introduced into the ladle slag during the decarburization process from the converter steel, so that the content in the ladle slag (T.Fe) before the decarburization process is 12% or less. This is a comparative example in which no reducing agent was added to the molten steel after treatment. In these examples, although the amount of alumina inclusions in the obtained rolled steel is small and the frequency of occurrence of linear defects is low, the decarburization treatment time is long.
これらに対しＮｏ．１０〜１４は、本発明で規定する要件を満たす方法で鋼を溶製した本発明例である。即ち、脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を１２％超にし、脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下とした例であり、具体的には、転炉出鋼から脱炭処理の期間に還元剤を投入しないか、またはＡｌ換算で０．３ｋｇ／溶鋼トンのＡｌ含有還元剤を取鍋スラグ上に添加して脱炭処理前の取鍋スラグ中（Ｔ．Ｆｅ）を比較的高く維持した状態で脱炭処理を行い、該脱炭処理直後の溶鋼中に、表１に示す通り還元剤を投入した。これらの例では、アルミナ介在物の抑制された線状欠陥の少ない極低炭素鋼が、短時間の脱炭処理で得られていることがわかる。 No. 10-14 are the examples of this invention which melted steel by the method of satisfy | filling the requirements prescribed | regulated by this invention. That is, it is an example in which the ladle slag before decarburization treatment (T.Fe) exceeds 12%, and the ladle slag after decarburization treatment (T.Fe) is 12% or less. Specifically, In the decarburization process from the converter steel, do not add a reducing agent, or add Al-containing reducing agent of 0.3 kg / mol steel ton on the ladle slag before conversion to Al. A decarburization process was performed with the slag (T.Fe) maintained relatively high, and a reducing agent was added to the molten steel immediately after the decarburization process as shown in Table 1. In these examples, it can be seen that an ultra-low carbon steel with reduced alumina inclusions and few linear defects is obtained by a short decarburization treatment.
Claims (2)
転炉または電気炉の溶鋼およびスラグを弱還元性状態もしくは非還元性状態で取鍋へ出鋼すると共に、取鍋スラグ上にＡｌ換算で０．３ｋｇ／溶鋼トン以下（０ｋｇ／溶鋼トンを含む）のＡｌ含有還元剤を添加することによって、ＲＨ真空脱炭処理前の取鍋スラグ中の総鉄量［以下、取鍋スラグ中（Ｔ．Ｆｅ）という］を１２％（質量％の意味、以下同じ）超とし、かつ
ＲＨ真空脱炭処理時の脱炭処理時間を、下記式（２）で表される脱炭速度定数Ｋｃが０．１７２以上となる時間とし、かつ
ＲＨ真空脱炭処理後の溶鋼および／または取鍋スラグに、Ａｌ換算で０．３〜０．７ｋｇ／溶鋼トンのＡｌ含有還元剤を添加することによって、ＲＨ真空脱炭処理後の取鍋スラグ中（Ｔ．Ｆｅ）を１２％以下にすることを特徴とする極低炭素鋼の溶製方法。
Ｃ ｆ ：脱炭処理後の溶鋼Ｃ濃度（質量％）
ｔ ２ ：脱炭処理時間（分間）］ When melting ultra-low carbon steel by applying decarburization treatment by the RH vacuum degassing method (hereinafter referred to as “ RH vacuum decarburization treatment”) to the molten steel discharged from the converter or electric furnace to the ladle,
The molten steel and slag of the converter or electric furnace are discharged into the ladle in a weakly reducing state or non-reducing state, and 0.3 kg / molten steel ton or less (including 0 kg / molten steel ton) in terms of Al on the ladle slag ) In the ladle slag before RH vacuum decarburization treatment [hereinafter referred to as (T.Fe) in the ladle slag] 12% (meaning mass%) The same shall apply hereinafter) and
The decarburization treatment time during the RH vacuum decarburization treatment is set to a time when the decarburization rate constant Kc represented by the following formula (2) is 0.172 or more, and
Ladle slag after RH vacuum decarburization treatment by adding an Al-containing reducing agent of 0.3 to 0.7 kg / mol steel ton to molten steel and / or ladle slag after RH vacuum decarburization treatment A method for melting ultra-low carbon steel, characterized in that the content of T (Fe) is 12% or less.
C f : Molten steel C concentration after decarburization (mass%)
t 2 : Decarburization processing time (minutes)]
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2004027862A JP4312068B2 (en) | 2004-02-04 | 2004-02-04 | Method of melting ultra-low carbon steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2004027862A JP4312068B2 (en) | 2004-02-04 | 2004-02-04 | Method of melting ultra-low carbon steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2005220391A JP2005220391A (en) | 2005-08-18 |
| JP4312068B2 true JP4312068B2 (en) | 2009-08-12 |
Family
ID=34996263
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2004027862A Expired - Fee Related JP4312068B2 (en) | 2004-02-04 | 2004-02-04 | Method of melting ultra-low carbon steel |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4312068B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5402259B2 (en) * | 2009-06-03 | 2014-01-29 | 新日鐵住金株式会社 | Method for producing ultra-low carbon steel |
-
2004
- 2004-02-04 JP JP2004027862A patent/JP4312068B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JP2005220391A (en) | 2005-08-18 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5277556B2 (en) | Method for producing Ti-containing ultra-low carbon steel and method for producing Ti-containing ultra-low carbon steel slab | |
| JP2010236030A (en) | Method for refining molten steel | |
| JP2009242912A (en) | Method for melting and manufacturing titanium-added ultra-low carbon steel and method for producing titanium-added ultra-low carbon steel cast slab | |
| JPWO2003002771A1 (en) | Low carbon steel sheet, low carbon steel slab, and method for producing the same | |
| JP3915386B2 (en) | Manufacturing method of clean steel | |
| JP5217478B2 (en) | Method of melting ultra-low carbon steel | |
| JP3893770B2 (en) | Melting method of high clean ultra low carbon steel | |
| JP4312068B2 (en) | Method of melting ultra-low carbon steel | |
| JPH10212514A (en) | Production of high clean extra-low sulfur steel excellent in hydrogen induced cracking resistance | |
| JP6547638B2 (en) | Method of manufacturing high purity steel | |
| JPH10298631A (en) | Method for melting clean steel | |
| JP5509913B2 (en) | Method of melting high Si steel with low S and Ti content | |
| JP4502944B2 (en) | Thin steel plate rich in ductility and method for producing steel ingot to obtain the steel plate | |
| JP5349074B2 (en) | Manufacturing method of high clean aluminum killed steel | |
| JP2010023045A (en) | Continuous casting method for low-carbon steel | |
| JPH07268440A (en) | Deoxidizing method of molten steel | |
| JPH09310113A (en) | Refining method for highly clean stainless steel | |
| JP7318822B2 (en) | Method for processing molten steel and method for manufacturing steel | |
| JP2006233254A (en) | Method for producing high cleanliness steel | |
| JP4354026B2 (en) | Stainless steel manufacturing method | |
| JP7438436B1 (en) | Ni-based alloy with excellent surface quality | |
| JP5387045B2 (en) | Manufacturing method of bearing steel | |
| JP6981589B1 (en) | Manufacturing method of high cleanliness steel | |
| JP4477971B2 (en) | Low carbon steel sheet, low carbon steel slab and method for producing the same | |
| KR101198486B1 (en) | Method of manufacturing Ti added austenitic stainless steel and Ti added austenitic stailess steel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20060925 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20080717 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20080805 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20081006 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20090428 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20090512 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120522 Year of fee payment: 3 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120522 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130522 Year of fee payment: 4 |
|
| LAPS | Cancellation because of no payment of annual fees |