JP3577351B2 - Method of manufacturing molten steel for high workability thin steel sheet - Google Patents
Method of manufacturing molten steel for high workability thin steel sheet Download PDFInfo
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- JP3577351B2 JP3577351B2 JP01331695A JP1331695A JP3577351B2 JP 3577351 B2 JP3577351 B2 JP 3577351B2 JP 01331695 A JP01331695 A JP 01331695A JP 1331695 A JP1331695 A JP 1331695A JP 3577351 B2 JP3577351 B2 JP 3577351B2
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- molten steel
- steel
- concentration
- decarburization
- high workability
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Description
【0001】
【産業上の利用分野】
本発明は、溶鋼に含有されている炭素[C]と窒素[N]を減圧・真空下で効率良く除去すると同時に、溶鋼中に分散する個体脱酸生成物を低減し、高加工性薄鋼板用溶鋼を効率良く溶製する方法に関するものである。
【0002】
【従来の技術】
高加工性薄鋼板は炭素や窒素を極微量まで除去し、かつ、鋼板表面清浄が美麗であることが要求される。一般に、溶鋼の脱炭処理は、例えば、第3版鉄鋼便覧II製銑製鋼編671〜685ページに示されているような、各種の真空精錬設備を用い、(3)式で示される反応を活用して実施している。
【0003】
[C]+[O]=CO …(3)
しかし、[C]がおよそ0.0030mass%以下になると脱炭速度が極端に低下する。脱炭処理の効率化を図るため、従来、溶鋼中の溶解酸素濃度[O]を高濃度に保持しつつ脱ガス処理を実施している。しかし、脱炭処理終了と同時に脱炭剤を添加して、[O]を0.0010mass%を以下まで脱酸するため、多量な個体脱酸生成物が溶鋼に懸濁して結果として鋼片に残留し、薄鋼板の表面清浄を損い健全な鋼板の歩留りを低下させている。
【0004】
【発明が解決しようとする課題】
本発明は溶鋼の減圧・真空処理を実施して経済的に極低炭・低窒素で、しかも清浄な高加工性薄鋼板用溶鋼を効率良く溶製するための精錬方法を提供することを目的とするものである。
【0005】
【課題を解決するための手段】
本発明は、真空脱ガス精錬設備を用いて高加工性薄鋼板用溶鋼を溶製するにあたり、脱炭処理初期の真空槽内の圧力が10mmHg以下で、且つ、炭素濃度[C]が(1)式で示される値以上の領域では、溶鋼中酸素濃度[O]をできるだけ高濃度に保持しつつ脱ガス処理を実施する第1工程と、溶鋼温度がT(K)で、[C]の値が(1)式で示される値以下の領域においては、[O]の値を、溶鋼温度T(℃)と溶鋼の硫黄濃度[S]に応じて、(2)式で示される濃度範囲に制御脱酸して脱炭・脱窒する第2工程と、真空処理終了時に脱酸剤を溶鋼に添加して成分調整を実施する第3工程からなることを特徴とする高加工性薄鋼板用溶鋼の製造方法。
【0006】
【数2】
【0007】
【作用】
本発明の技術的思想の根源は、反応形態の相違に応じて最適な処理条件を付与する事で脱炭・脱窒反応を速やかに進行させると同時に、脱酸生成物を除去し、高加工性薄鋼板用溶鋼を溶製するものである。
【0008】
本発明者らは、特公平6−19102で開示したごとく、[C]が0.005mass%の以下の領域で、[S]に応じて[O]を制御する事で速やかに脱炭反応を進行させる極低炭素溶鋼の溶製方法を提示した。
【0009】
一般に、脱炭反応の進行は、▲1▼溶鋼内部でのCO気泡の発生と、▲2▼気相/溶鋼界面でのCO生成の総和として進行する。本発明者らは、前期▲1▼のCO気泡発生反応進行の有無は溶鋼のPCO * (=K・[O]・[C]:mmHg)と真空槽内圧力Pt (mmHg)との大小関係で決定され、(4),(5)式で示される関係により脱炭反応の進行形態が異なる事を見出した。
【0010】
ここで、Kは平衡定数であり、760×10(1160.0/(T+273)+2.003)であることが良く知られている。
【0011】
PCO * >Pt +25(mmHg) …(4)
:溶鋼内部からのCO気泡発生による脱炭進行
P CO * <P t +25(mmHg) …(5)
:気相/溶鋼界面での脱炭支配領域
CO気泡発生反応による脱炭反応は、[O]が高濃度であるほど速やかに進行し、その速度は大きい。つまり、第1工程はCO気泡が溶鋼内部から発生する領域であり、脱炭速度を大きくするためには、[O]は高濃度ほど有利であるから、実用的には0.040〜0.080mass%の範囲に保持する。
【0012】
一方、気相/溶鋼界面でのCO生成反応の進行は界面吸着元素である[O]と[S]の存在により阻害される。つまり、本発明者らの基礎的な研究により、気相/溶鋼界面でのCO生成反応速度定数kovは次式で示される事を見出した(鉄と鋼、vol,74(1981),p.449)。
【0013】
【数3】
【0014】
したがって、kovを最大にするための最適[O]の値[O]max は(6)式を微分することで(7)式のように決定できる。
【0015】
【数4】
【0016】
ただし、kr,κS ,κO は定数である。
【0017】
従って、[S]の値に応じて[O]を制御する事で脱炭速度を大きくできる。つまり、反応形態に応じて、最適な[O]制御を付与する事で脱炭反応を速やかに進行させる事が出来る。
【0018】
一般的な脱炭処理においては、[C]が0.0050mass%以下の領域のPt はおよそ10mmHg以下であり、実用上は1mmHg程度であるから、CO気泡発生反応が停止する時の[C]の値は(1)式で示される。ただし、[O]は、Pt が10mmHg以下であるときの酸素濃度である。
【0019】
【数5】
【0020】
したがって、[C]が(1)式で示される値以下では、脱炭反応は気相/溶鋼界面で進行するため、脱炭速度を最大にするために、[S]に応じて[O]を(2)式の範囲で制御する。上記工程が第2工程である。
【0021】
【数6】
【0022】
ただし、[O]を狭い範囲で精度よく制御する事は非常に難しい。したがって、実用上、最適[O]値の+0.0100mass%の範囲を許容する。この範囲では、脱炭反応阻害作用の影響が小さい。この時、界面吸着元素である[O]が低濃度になるため、脱炭と同時に脱窒反応が進行する。さらに、第2工程の初期の[O]制御によって生成した非金属介在物は、第2工程での脱ガス処理中の溶鋼循環で殆ど除去され、極低炭・低窒素で高清浄な溶鋼が溶製できる。
【0023】
第3工程は、第2工程で制御された[O]を完全に除去する工程であり、目的に応じてAlもしくはTiの1種もしくは2種を溶鋼に添加して脱酸し、成分調整を実施する。
【0024】
この時の脱酸量は従来の製造方法に比較して1/3程度であり、極めて清浄性の高い高加工性薄鋼板用溶鋼が溶製できる。
【0025】
本発明の方法において、[O]を(2)式で示される範囲に制御するための方法は、すでに一般的に用いられている脱酸剤(Al,Ti等)を溶鋼に添加する方法が有効である。この際、目的の[O]に制御するための脱酸剤の添加時間は、脱炭反応を阻害しないように、好ましくは、1〜2min程度の時間をかけて実施するのが好ましい。すなわち、短時間での添加では、真空槽内溶鋼の一時的な強脱酸がおこり、脱炭反応の進行が阻害されるからである。
【0026】
(1)式で示される[C]への到達時間は、これまでに開示されている[C]推定方法(例えば、特願平05−266557)に基づく予測時間で決定してもよく、直接分析によって確認してもよく、その精錬炉の経験に基づく特性値の積み上げによって決定してもよい。
【0027】
【実施例】
実施例1
RH脱ガス設備を用いて、250トンの溶鋼の脱炭処理を実施した。[S]は0.012mass%である。第1工程では[O]を0.045〜0.050mass%とした。溶鋼温度は1600±10℃である。図1に[C],[O]および[N]の経時変化を示す。脱炭開始10min後には、雰囲気圧力Pt は10mmHg以下であった。PCO * =25mmHgの時に、Alを真空槽に落としこみ、[O]を制御した。Alの添加時間は1.0min間である。従来の方法に比較して、本発明の方法により極低炭素・低窒素溶鋼の溶製が効率的に実施でき、図2に示すように、成品薄鋼板の表面欠陥も従来法に比較して1/3に減少した。ここで、表面欠陥とは、鋼中の非金属介在物に起因する欠陥であり、仕上圧延後に鋼板表面に観察される疵を指す。表面欠陥指数とは、比較例の表面欠陥個数n(個/m2 )を1としたときの相対比較を表わす。
【0028】
【発明の効果】
極低炭素・低窒素濃度でかつ清浄性の高い高加工性薄鋼板用溶鋼の溶製が効率良く実施できるようになった。
【図面の簡単な説明】
【図1】RH脱ガス炉での[C],[O]および[N]の経時変化を示す図面。
【図2】薄鋼板の表面欠陥の低減度合いを示す図面。[0001]
[Industrial applications]
The present invention efficiently removes carbon [C] and nitrogen [N] contained in molten steel under reduced pressure and vacuum, and at the same time, reduces solid deoxidation products dispersed in the molten steel, thereby obtaining a highly workable thin steel sheet. The present invention relates to a method for efficiently producing molten steel for use.
[0002]
[Prior art]
A highly workable thin steel sheet is required to remove carbon and nitrogen to an extremely small amount and to have a beautiful clean surface of the steel sheet. In general, the decarburization treatment of molten steel is performed, for example, by using various vacuum refining equipment as shown in the third edition of the Iron and Steel Handbook II, Iron and Steel Making, pages 671 to 685, and carrying out the reaction represented by the formula (3). Utilized and implemented.
[0003]
[C] + [O] = CO (3)
However, when [C] is about 0.0030 mass% or less, the decarburization rate is extremely reduced. Conventionally, in order to improve the efficiency of the decarburization treatment, the degassing treatment is conventionally performed while maintaining the dissolved oxygen concentration [O] in the molten steel at a high concentration. However, a decarburizing agent is added at the same time as the decarburization treatment, and [O] is deoxidized to 0.0010 mass% or less. It remains and impairs the surface cleanliness of thin steel sheets, lowering the yield of sound steel sheets.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a refining method for efficiently producing a molten steel for a thin steel sheet with extremely low carbon and low nitrogen, which is economically economical by performing decompression and vacuum treatment of the molten steel. It is assumed that.
[0005]
[Means for Solving the Problems]
According to the present invention, the pressure in the vacuum chamber at the initial stage of the decarburization treatment is 10 mmHg or less and the carbon concentration [C] is (1) when the molten steel for high workability thin steel sheet is melted using the vacuum degassing and refining equipment. In the region not less than the value indicated by the expression (1), the first step of performing the degassing treatment while maintaining the oxygen concentration [O] in the molten steel as high as possible, and the case where the molten steel temperature is T (K) and [C] In the region where the value is equal to or less than the value represented by the equation (1), the value of [O] is changed according to the molten steel temperature T (° C.) and the sulfur concentration [S] of the molten steel in the concentration range represented by the equation (2). A highly workable thin steel sheet, comprising: a second step of decarburizing and denitrifying by controlled deoxidation, and a third step of adding a deoxidizing agent to molten steel at the end of vacuum processing to adjust the composition. Method of manufacturing molten steel for steel.
[0006]
(Equation 2)
[0007]
[Action]
The roots of the technical idea of the present invention are that, by giving optimal treatment conditions according to the difference in the reaction form, the decarburization / denitrification reaction proceeds rapidly, and at the same time, the deoxidation products are removed, and high processing is performed. It is for producing molten steel for conductive thin steel sheets.
[0008]
As disclosed in Japanese Patent Publication No. 6-19102, the present inventors control decarburization reaction quickly by controlling [O] according to [S] in the region where [C] is 0.005 mass% or less. A method for producing extremely low carbon molten steel to be advanced is presented.
[0009]
In general, the progress of the decarburization reaction proceeds as the sum of (1) generation of CO bubbles inside the molten steel and (2) generation of CO at the gas phase / molten steel interface. The present inventors have found that year ▲ 1 P CO * of the presence or absence of CO bubble generation reaction proceeds molten steel ▼ (= K · [O] · [C]: mmHg) and the vacuum chamber pressure P t (mmHg) It has been found that the progress of the decarburization reaction is different depending on the relationship determined by the magnitude relation and represented by the equations (4) and (5).
[0010]
Here, K is an equilibrium constant, which is well known to be 760 × 10 (1160.0 / (T + 273) +2.003) .
[0011]
P CO *> P t +25 ( mmHg) ... (4)
: Progress of decarburization due to generation of CO bubbles from inside molten steel
P CO * <P t +25 (mmHg) ... (5)
: Decarburization dominant region at gas phase / molten steel interface The decarburization reaction by the CO bubble generation reaction proceeds more rapidly as the [O] concentration is higher, and the rate is higher. In other words, the first step is a region where CO bubbles are generated from inside the molten steel, and [O] is more effective at a higher concentration in order to increase the decarburization rate. It is kept in the range of 080 mass%.
[0012]
On the other hand, the progress of the CO generation reaction at the gas phase / molten steel interface is hindered by the presence of interfacial adsorption elements [O] and [S]. In other words, the basic research of the present inventors has found that the CO formation reaction rate constant k ov at the gas phase / molten steel interface is represented by the following equation (iron and steel, vol, 74 (1981), p. .449).
[0013]
(Equation 3)
[0014]
Therefore, the optimal value [O] max of [O] for maximizing k ov can be determined as in the expression (7) by differentiating the expression (6).
[0015]
(Equation 4)
[0016]
Here, kr, κ S and κ O are constants.
[0017]
Therefore, by controlling [O] according to the value of [S], the decarburization speed can be increased. That is, by giving the optimal [O] control according to the reaction mode, the decarburization reaction can be promptly advanced.
[0018]
In a typical decarburizing process, P t of [C] is 0.0050 mass% or less of the region is less than about 10 mmHg, since practically is about 1 mmHg, at which CO bubble generation reaction is stopped [C ] Is shown by equation (1). However, [O] is the oxygen concentration at P t is 10mmHg or less.
[0019]
(Equation 5)
[0020]
Therefore, when [C] is equal to or less than the value shown in the equation (1), the decarburization reaction proceeds at the gas phase / molten steel interface, and therefore, in order to maximize the decarburization rate, [O] is changed according to [S]. Is controlled within the range of Expression (2). The above step is the second step.
[0021]
(Equation 6)
[0022]
However, it is very difficult to accurately control [O] in a narrow range. Therefore, a range of +0.0100 mass% of the optimal [O] value is practically allowed. In this range, the effect of the decarburization reaction inhibitory effect is small. At this time, since the concentration of the interfacial adsorption element [O] becomes low, the denitrification reaction proceeds simultaneously with the decarburization. Further, nonmetallic inclusions generated by the initial [O] control of the second step are almost removed by the molten steel circulation during the degassing treatment in the second step, and highly clean molten steel with extremely low carbon and low nitrogen is obtained. Can be melted.
[0023]
The third step is a step of completely removing [O] controlled in the second step. One or two kinds of Al or Ti are added to the molten steel according to the purpose to deoxidize and adjust the components. carry out.
[0024]
The amount of deoxidation at this time is about 1/3 as compared with the conventional production method, and it is possible to smelt molten steel for highly workable thin steel sheets with extremely high cleanliness.
[0025]
In the method of the present invention, a method for controlling [O] to be in the range represented by the formula (2) is a method of adding a deoxidizing agent (Al, Ti, or the like) which is already generally used to molten steel. It is valid. At this time, the addition time of the deoxidizing agent for controlling the target [O] is preferably set to about 1 to 2 minutes so as not to inhibit the decarburization reaction. That is, if the addition is performed in a short time, the molten steel in the vacuum chamber will be temporarily strongly deoxidized, thereby inhibiting the progress of the decarburization reaction.
[0026]
The arrival time to [C] represented by the equation (1) may be determined by a prediction time based on the [C] estimation method disclosed so far (for example, Japanese Patent Application No. 05-266557). It may be confirmed by analysis, or may be determined by accumulation of characteristic values based on the experience of the refining furnace.
[0027]
【Example】
Example 1
Using a RH degassing facility, 250 tons of molten steel were decarburized. [S] is 0.012 mass%. In the first step, [O] was set to 0.045 to 0.050 mass%. The molten steel temperature is 1600 ± 10 ° C. FIG. 1 shows changes over time of [C], [O] and [N]. After decarburization start 10min, atmospheric pressure P t were 10mmHg or less. When P CO * = 25 mmHg, Al was dropped into a vacuum chamber to control [O]. The addition time of Al is between 1.0 min. Compared with the conventional method, the method of the present invention can efficiently carry out the production of extremely low carbon and low nitrogen molten steel, and as shown in FIG. Reduced to 1/3. Here, the surface defect is a defect caused by nonmetallic inclusions in the steel, and refers to a flaw observed on the surface of the steel sheet after finish rolling. The surface defect index indicates a relative comparison when the number of surface defects n (pieces / m 2 ) in the comparative example is set to 1.
[0028]
【The invention's effect】
It has become possible to efficiently produce molten steel for highly workable thin steel sheets with extremely low carbon and nitrogen concentrations and high cleanliness.
[Brief description of the drawings]
FIG. 1 is a drawing showing changes over time of [C], [O] and [N] in an RH degassing furnace.
FIG. 2 is a view showing a degree of reduction in surface defects of a thin steel plate.
Claims (1)
Priority Applications (1)
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JP01331695A JP3577351B2 (en) | 1995-01-31 | 1995-01-31 | Method of manufacturing molten steel for high workability thin steel sheet |
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JP01331695A JP3577351B2 (en) | 1995-01-31 | 1995-01-31 | Method of manufacturing molten steel for high workability thin steel sheet |
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JPH08209229A JPH08209229A (en) | 1996-08-13 |
JP3577351B2 true JP3577351B2 (en) | 2004-10-13 |
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