JPH06256840A - Vacuum degassing refining method - Google Patents

Abstract

PURPOSE:To shorten the treating time of vacuum degassing refining, to reduce the refining cost and to rise the hitting ratio of components in a product by beforehand planning an operational pattern with model formulas precisely hit and executing the treatment. CONSTITUTION:In the vacuum degassing refining for molten steel, the variation of carbon before refining or during refining is estimated by the following formulas to execute the refining. dC/dt=-Kc1''*(C-C*')-Kc2''*(C-C*)...(1), C*'=(P+P ')/(K*O)...(2), C*=P/(K*O)...(3), (wherein, in the case of C<C*', Kc1''=0) C: C in a ladle, P: pressure in a vacuum vessel, K: equilibrium constants of C and O, Kc1', Kc2': decarburizing velocity constant obtd. with fitting, P': bubble generating pressure, t: time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum degassing refining method for molten metal.

[0002]

2. Description of the Related Art A conventional vacuum degassing refining method is disclosed in Japanese Patent Application Laid-Open No.
For the purpose of decarburization, as introduced in 1-81722, the vacuum degassing refining is started by setting an appropriate vacuum pattern predetermined before refining and a target decarburization transition pattern obtained based on the refining time, At any point along the way, the amount of [C] in the molten steel is measured or measured from the component analysis value in the exhaust gas,
From the difference between the measured value and the target decarburization transition value at that time, the oxygen supply amount, the degree of vacuum, and the recirculation flow rate are manipulated to control the decarburization rate so as to match the existing target transition value.

[0003]

The control of decarburization as described above utilizes a model formula for predicting the transition of decarburization.
The higher the accuracy of this model formula, the shorter the processing time,
The refining cost can be reduced and the accuracy of the ingredients of the product can be increased.

A conventional method for predicting the transition of decarburization is C, O as described in JP-A-61-19726.
There is a model formula (equation (4)) configured by the reaction rate formula of. However, in the recent production of ultra-low carbon steel, especially in the ultra-low carbon region where C is 20 ppm or less, the decarburization rate sharply decreased, and the decarburization transition value did not match the actual performance.

1n ((C _t −C ^* ) / (C ₀ −C ^* )) = − Kt (4) C _t ; C value at time _t C ^* ; equilibrium arrival C C ₀ ; C at t = 0 K; Decarburization rate constant For the phenomenon of decarburization rate decrease in this extremely low coal area, there is a mathematical model based on the estimated mechanism (for example, Watanabe et al. CAMP-ISLJ Vol. 1).
(1988) -234). However, (5), (6)
The equations are differential equations, and since it is necessary to solve these equations simultaneously, it is necessary to solve the equations with a mathematically special solution method such as Runge-Kutta. To use this for estimation of decarburization in actual operation requires a considerable amount of memory and requires much more calculation time than general calculation,
It was not adopted because it put a heavy load on the process computer on site.

[0006] Wd (C) _IN / dt = Q ([C] _IN - [C] _OUT) ... (5) Wd [C] _OUT / dt = -Q ([C] _IN - [C] _OUT) + _ρAK ' ([C] _OUT −C ^* ) −ρAK _a ∫ ₀ ^Hm ([C] _OUT −C ^* (h)) dh (6) Hm = 1.48 * (K * C * _OP ′)… ( 7) W; amount of molten steel in pot, W; amount of molten steel in vacuum chamber, Q; recirculation flow rate [C] _IN ; C in pot, [C] _OUT ; C in vacuum chamber

[0007]

A feature of the present invention is that in vacuum degassing refining of molten steel, a carbon transition before refining or during refining is estimated by the following equation, and refining is performed. It is a degassing refining method.

DC / dt = −K _C1 ″ * (C−C ^{* ′} ) − K _C2 ″ * (C−C ^* ) (1) C ^{* ′} = (P + P ′) / (K * O) ... ( 2) C ^* = P / (K * O) (3) (K _C1 "= 0 when C <C ^{* '} ) C; C in pan, P; vacuum chamber pressure, K; C, O Equilibrium constant, k _c1 ", K _C2 "; decarburization rate constant obtained by fitting, P '; bubble generation pressure, t; time

[0009]

[Function] There are many theories about the decarburization reaction, the reaction mechanism and the reaction site of the vacuum degassing refining of molten steel (for example, Watanabe et al. CAMP-ISLJ Vol, 1 (1988)-
234). We have observed decarburization, which is a phenomenon that can be observed as CO gas generated from the inside of molten steel by decarburization of C and O that progresses without interfering with the gas-liquid interface, and the gas-liquid interface (the free surface in the vacuum chamber and the gas in the molten steel). Formula (1) was constructed considering decarburization that occurs on the surface.

Here, the first term on the right side of the equation (1) expresses the decarburization rate of C and O which advances without interfering with the gas-liquid interface,
The second term on the right side represents the decarburization rate that occurs at the gas-liquid interface. Here, K _C1 ”and K _C2 “ are constants obtained by fitting, and are constants that are composed of elements such as reaction rate, mass transfer rate, reflux rate, and interfacial area. It has.

The method of using the formula will be described below in accordance with the vacuum degassing refining method disclosed in Japanese Patent Laid-Open No. 61-19726.

In the present invention, it can be used for 1) operation before processing and 2) operation during processing. A detailed description will be given.

1) Operation before treatment The treatment time, alloy addition timing, and vacuum degree pattern before treatment are set in advance to minimize variations in treatment time due to changes in the treatment method for each treatment and variations in components. In order to mass-produce reproducible products within a predetermined time. In addition, it is necessary to calculate in advance the processing method predicted for estimating the final component value. The amount of alloy added other than [C] is calculated in advance in order to calculate the variation of [C] from the [C] content of the alloy, or by calculating the deoxidation amount due to the reaction with oxygen in steel. This is for connecting to the decarburization reaction calculation. This is to determine the amount of carburization and the amount of decarburization by comparing with a predetermined target value.

When performing these operations, the transition of decarburization can be accurately estimated by the model formula represented by the formula (1). Equation (1) is a differential equation, which can be used easily by mathematically differentiating the program (see FIG. 1 described in the flowchart). Where C ^{* '}
Reported by Watanabe et al. (CAMP-ISLJ Vol. 1).
((1988) -234) P '= 20 at bubble generation pressure
It suffices to calculate using equation (2) using torr. Oxygen cannot be found in the calculation because oxygen flows from the slag into the molten steel. Therefore, based on the actual results, the oxygen change pattern during processing may be used by entering it in the program.

2) Operation during processing is a means for correcting during processing in 1) to 1) described above. If the end [C] estimated value at that time is higher than the predetermined target value, the natural decarburization time is extended until the end [C] estimated value matches the predetermined target value. If the end [C] estimated value is lower than a predetermined target value, the amount of carburization of the existing pattern is corrected.

When performing these operations, the transition of decarburization can be accurately estimated by the model formula represented by the formula (1). Equation (1) is a differential equation, which can be used easily by mathematically differentiating the program (see FIG. 2 described in the flowchart). Where C ^{* '}
Reported by Watanabe et al. (CAMP-ISLK Vol.
(1988) -234) P ^' = 20to at bubble generation pressure.
It may be calculated by the formula (2) using rr. Also, oxygen is
Oxygen inflow from the slag to the molten steel occurs, so it cannot be calculated. Therefore, based on the actual results, the oxygen change pattern during processing may be used by entering it in the program.

For example, the flow chart of the program is as shown in FIG.

[0018]

【Example】

Example 1 When performing secondary refining under the refining conditions described in Table 1, a vacuum pattern (FIG. 3) was determined and treatment was performed. Here, K _C1 "and K _C2 " were determined to be 0.60 and 0.062, respectively, by the actual fitting, and adopted.

For comparison, the same vacuum pattern (FIG. 3)
Then, the processing was carried out by the conventional method (method utilizing an estimated model of C and O described in JP-A-61-19726). The results are shown in Table 1. The vacuum pattern obtained by the present invention was able to obtain a value closer to the target.

[0020]

[Table 1]

Example 2 In carrying out the secondary refining under the refining conditions shown in Table 2, the refining treatment was performed by estimating it by the method described in Example 1. However, since the value of [C] sampled during the process is different from the originally predicted transition of [C], the calculated value of the program configured by the equation (1) as in the second embodiment during the process is
Correct the analysis [C] at the sampling time,
I calculated again from that time and extended the refining time to meet the target value. Here, K _c1 ″ and K _C2 ″ were determined to be 0.60 and 0.062, respectively, by the actual fitting as in Example 1, and adopted. The result is shown in Figure 4.
Shown in. For comparison, the same vacuum pattern (Fig. 3)
The decarburization transition estimated by the conventional method (method utilizing the C and O estimation model described in JP-A-61-19726) is also shown. It was found that the transition of decarburization obtained by the estimation formula of the present invention better represents the transition of C in actual operation.

[0022]

[Table 2]

[0023]

Industrial Applicability According to the present invention, since the operation pattern is planned and the treatment is carried out in advance with a model formula that accurately hits, the processing time of vacuum degassing refining can be shortened, the refining cost can be reduced, and the composition of the product can be reduced. You can increase the hit rate.

Further, in actual operation, there is a case where a change in the components that cannot be predicted during the processing occurs due to the dropping of the metal in the vacuum chamber. Even in such a case, by correcting this model with the values of C and O obtained by sampling during processing, the processing time can be shortened and the refining cost can be reduced as compared with the case of using the conventional model formula. The accuracy of the ingredients of the product can be increased.

[Brief description of drawings]

FIG. 1 is a flowchart of an operation during processing according to the present invention.

FIG. 2 is a flowchart of an operation during processing according to the present invention.

FIG. 3 is a vacuum pattern diagram in the example.

FIG. 4 is a graph showing the relationship between time and C amount as a result of an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Moriguchi 1 Nishinosu, Oita-shi Oita-shi Nippon Steel Corporation Oita Works

Claims (1)

[Claims] 1. A vacuum tax gas refining method characterized in that, in the vacuum degassing refining of molten steel, the carbon transition before refining or during refining is estimated by the following equation to perform refining: dC / dt = -K _C1 " * (C-C ^{* '} )-K _C2 "* (C-C ^* ) ... (1) C ^{* '} = (P + P ') / (K * O) ... (2) C ^* = P / (K * O ) ... (3) (where C <C ^{* 'K} _C1 when the "= 0) C; pot in C, P; vacuum chamber pressure, K; C, O equilibrium constant, K _C1' ', K _C2 ''; Decarburization rate constant obtained by fitting, P '; Bubble generation pressure, t; Time