JPH11279625A - Manufacture of super-low carbon steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a super-low carbon steel having a carbon concentration close to the target value. SOLUTION: An arithmetic unit 15 in which an analysis value of an exhaust gas analyzer 9 and a measured value of an exhaust gas flow meter 10 are inputted operates the estimated value of the carbon concentration in a molten steel from these values, considering the delay time of each measured value. The sampling of the molten steel is performed by a molten steel sampling device 11, and the carbon content in the molten steel is analyzed by a carbon concentration in molten steel analyzer 13. The arithmetic unit 15 corrects the estimated value of the carbon concentration in the molten steel considering the time when the molten steel sampling device 11 performs the sampling. The arithmetic unit 15 corrects the estimated value of the carbon concentration of the molten steel, and then, determines the coefficients of the regression formula from these corrected values by substituting the carbon concentration in the molten steel in the regression formula expressed by the time function. The estimated carbon concentration in the molten steel considering the delay time due to the analysis is calculated from the obtained regression formula, and the decarburizing is completed when the carbon concentration reaches the final target.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ultra-low carbon steel using an RH vacuum degassing apparatus. The present invention relates to a method for producing an ultra-low carbon steel having a carbon amount close to a target value by accurately determining.

[0002]

2. Description of the Related Art In the case of producing ultra-low carbon steel, molten steel blown in a converter is transferred to an RH vacuum degassing apparatus, and the carbon content in the molten steel is reduced by vacuum degassing so that the target carbon content is reduced. The amount is going to be done.

Conventionally, as a method of estimating the amount of carbon in molten steel in RH vacuum degassing and determining the end of decarburization, decarburization is performed in advance using the same equipment under the same operating conditions. The carbon concentration in the molten steel and the decarburization rate are estimated by a model formula, and the constants necessary for this model formula are obtained from the aging of the carbon concentration in the molten steel. The carbon concentration in the molten steel is predicted by using the model formula determined by determining the constant, and the end point of the decarburization is determined. In general, the procedure was as follows.

An example of such a method is disclosed in Japanese Patent Laid-Open No. 7-1.
There is a method disclosed in Japanese Patent No. 18730. This means that the molten steel is sampled at an arbitrary time after the start of evacuation, and the carbon analysis value of the sampled molten steel, the temperature of the molten steel measured at the same time, and the oxygen concentration value obtained by an oxygen concentration sensor using a solid electrolyte are measured. Based on the model formula using the difference method,
This model formula estimates the time at which the target carbon concentration is achieved.

As an example of the prior art including the above-mentioned steps, there is a method disclosed in Japanese Patent Application Laid-Open No. Hei 5-239540. In this method, the actual operation values during refining (reflux gas flow rate, vacuum degree, alloy input results, exhaust gas component results, etc.) are input in real time, and the carbon concentration of molten steel, oxygen concentration, etc. during operation are estimated every moment using a model formula. And estimating the time at which the target carbon concentration is achieved by collecting the molten steel sample at least once during smelting and correcting the model formula based on the analysis value to estimate the carbon concentration in the molten steel. It is.

[0006]

However, as disclosed in Japanese Patent Application Laid-Open No. Hei 7-118730, in the method having the above-mentioned steps, in order to preliminarily set a constant required for a model equation, There is a problem that it is impossible to follow a change in the actual operation state, and an error occurs in the estimated value of the carbon concentration in the steel. Also, in measuring exhaust gas flow rate and exhaust gas analysis values, the actual measurement value is delayed due to the fact that the measuring instrument is located at a position away from the vacuum chamber and the analyzer has a large response delay. However, since these delays are not taken into account in the model equation, there is a problem that an error occurs in the estimated value of the carbon concentration in steel.

The method disclosed in Japanese Patent Application Laid-Open No. Hei 5-239540 has no problem that it cannot follow the actual operation state because it does not have the steps described above. Since this is not taken into account, the problem of an error in the estimated value of the carbon concentration in steel is inevitable.

[0008] The present invention has been made in view of such circumstances, and by accurately predicting the carbon concentration in steel and accurately predicting the end time of refining, extremely low carbon having a carbon concentration close to the target carbon concentration. It is an object to provide a method for producing carbon steel.

[0009]

The object of the present invention is to provide a method for producing ultra-low carbon steel using an RH vacuum degassing apparatus, which comprises the following steps: (a) Exhaust gas in consideration of molten steel weight, initial carbon concentration of molten steel, and detection delay flow rate, CO considering the analysis time delay, from the CO ₂ concentration, in a process of the process for estimating the carbon concentration in the molten steel by a carbon mass balance (b) the (a), the molten steel sample was taken one or more times,
Based on the analysis values of the sampled molten steel, considering the analysis delay time, the step of correcting the estimated carbon concentration in the molten steel estimated in the step (a) (c) the (a), (b) From the estimated carbon concentration in the molten steel estimated by the step of, the step of obtaining the estimated carbon concentration in the molten steel as a regression equation that is a function of time (d) using the regression equation obtained in the step (c), Obtaining an estimated carbon concentration in molten steel that compensates for the delay time of the exhaust gas flow rate and the exhaust gas analysis value, and terminating the process when the estimated value reaches the target end-point carbon concentration. The problem is solved by a method for producing low carbon steel.

In this means, in the steps (a) and (b), the estimation and correction of the carbon concentration in the molten steel are performed in consideration of the detection delay time and the analysis delay time. The concentration can be measured accurately. From the estimated carbon concentration in the molten steel thus obtained, the estimated carbon concentration in the molten steel was obtained as a regression equation that is a function of time, and the regression equation compensated for the exhaust gas flow rate and the delay time of the exhaust gas analysis value. An estimated carbon concentration in the molten steel is obtained, and the time when the estimated value reaches the target end-point carbon concentration is defined as the end of the decarburization process. The regression equation is obtained every time the step (a) or the step (b) is performed. That is, the steps (c) and (d) are:
Each time the step (a) or (b) is performed, it is performed successively.
However, before the step (b) is performed, it is not always necessary to perform the steps (c) and (d) after the step (a).
Since the decarburization does not end before the step (b) is performed, the steps (c) and (d) may be sufficiently started even after the step (b) has been performed at least once. It is. Thus, according to this means, the carbon content in molten steel at the end of refining can be made closer to the target value.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of equipment for implementing an embodiment of the present invention. In FIG. 1, 1 is a ladle containing molten steel, 2 is molten steel, 3 is a vacuum tank body of an RH degassing device, 4 is an ascending side immersion pipe, 5 is a descending side immersion pipe, and 6 is a supply of argon gas for reflux. Pipe, 7 is an exhaust pipe,
8 is an exhaust gas analysis pretreatment facility, 9 is an exhaust gas analyzer, 10 is an exhaust gas flow meter, 11 is a molten steel sampling device, 12 is a molten steel sampling control device, 13 is a molten steel carbon concentration analyzer,
14 is an operation control device, and 15 is a calculation device.

An ascending-side immersion pipe 4 and a descending-side immersion pipe 5 are attached to a lower portion of the vacuum tank main body 3 of the vacuum degassing apparatus, and their tips are immersed in molten steel 2 in a ladle 1. I have. The vacuum chamber main body 3 is connected to a vacuum exhaust device (not shown) via an exhaust pipe 7, and the inside of the layer is in a vacuum state. The exhaust pipe 7 is provided with an exhaust gas flowmeter 10 for measuring the exhaust gas flow rate and an exhaust gas analysis pretreatment device 8.
The exhaust gas analysis pretreatment device 8 is connected to an exhaust gas analyzer 9.

In the vacuum refining, the molten steel 2 in the vacuum vessel main body 3 is circulated as indicated by an arrow by blowing argon gas from a reflux argon gas supply pipe 6 provided in the rising side immersion pipe 4. At this time, the inside of the vacuum chamber main body 3 is in a vacuum state, and a vacuum decarburization process is performed.

The flow rate of the exhaust gas flowing through the exhaust pipe 7 is measured by an exhaust gas flow meter 10.
Between the actual value of the amount of gas generated in the vacuum chamber body 3
There is a transport delay due to the time during which the exhaust gas flows from the exhaust gas flow meter 10 to the position of the exhaust gas flow meter 10.

The components of the exhaust gas (CO, CO ₂ )
The gas is analyzed by the exhaust gas analyzer 9, and between this measured value and the component value of the exhaust gas in the gas generated in the vacuum chamber main body 3, the transport time of the exhaust gas in the exhaust pipe 7, the exhaust gas analysis pretreatment A delay corresponding to the processing time of the device 8 and the response time of the exhaust gas analyzer 9 occurs.

The analysis values of the exhaust gas analyzer 9 and the exhaust gas flow meter 1
The measured value of 0 is input to the arithmetic unit 15 and the arithmetic unit 15
Calculates the estimated value of the molten steel carbon concentration from these values in consideration of the delay time of each measured value.

At a predetermined timing during smelting, the molten steel is sampled by the molten steel sampling device 11 at least once, and the carbon content in the molten steel is analyzed by the molten steel carbon concentration analyzer 13. The analysis value is sent to the arithmetic unit 15. Arithmetic unit 1
5 corrects the estimated value of the molten steel carbon concentration in consideration of the time at which the molten steel sampling device 11 performs sampling.

After correcting the estimated values of the molten steel carbon concentration, the arithmetic unit 15 applies these corrected values to a regression equation expressing the molten steel carbon concentration as a function of time to determine the coefficients of the regression equation. Then, a time at which the molten steel carbon concentration reaches the target end-point concentration is calculated from the obtained regression equation, and the time is set as the end point of the decarburization process.

Hereinafter, examples of numerical calculations used for these controls will be described in detail. First, the initial value of the C weight in molten steel is calculated by the following equation. Wc (0) = (Ws · [C] (0)) · k ₃ (1) where Wc (0): Initial value of C weight in molten steel [Kg] Ws: Initial value of molten steel weight [Ton] [C] (0): Initial value of C analysis value in molten steel [ppm] k ₃ : Coefficient (0.001)

Next, the estimated carbon concentration in molten steel [C] (i) at each time is calculated as follows. ΔWc (i) = (k ₁ · CO (i−τ ₁ ) + k ₂ · CO ₂ (i−τ ₂ )) · F (i−τ ₃ ) · τ ₀ (2) where ΔWc (i ): Estimated amount of decarburization at time i [Kg] CO (i): Analysis value of CO in exhaust gas at time i (based on molten steel surface) [%] CO ₂ (i): Analysis value of CO ₂ in exhaust gas at time i ( F (i): Exhaust gas flow rate at time i (based on molten steel surface) [Kg /
h] k ₁ : CO concentration conversion coefficient (1.063 × 10 ⁻⁶ ) k ₂ : CO ₂ concentration conversion coefficient (1.063 × 10 ⁻⁶ ) τ ₀ : Calculation cycle [sec] τ ₁ : CO analysis delay time (τ ₀ Τ ₂ : CO ₂ analysis delay time (normalized by τ ₀ ) τ ₃ : exhaust gas flow detection delay time (normalized by τ ₀ ). The time i is also normalized by τ ₀ , and is a value indicating the number of calculations.

Wc (i) = Wc (i−1) −ΔWc (i) (3) [C] (i) = (Wc (i) / Ws) · k_Four …(Four)  Here, Wc (i): estimated value of C weight in molten steel at time i
 [Kg] [C] (i): Estimated value of C concentration in molten steel at time i [ppm] k_Four: Conversion coefficient (1000.0) Thus, the calculation cycle τ₀Of C concentration in molten steel for each case
Find the value [C] (i).

FIG. 2 is a diagram in which the time from the start of refining is plotted on the horizontal axis and the carbon concentration in molten steel [C] is plotted on the vertical axis. In FIG. 2, points a to i indicate the C concentration [C] (i) in the molten steel estimated in this manner.

During the smelting, the molten steel is sampled at a predetermined timing (at the time indicated as molten steel sampling in FIG. 2), and the carbon concentration in the molten steel is analyzed and input (FIG. 2).
At the time point described as rapid analysis value input). The sampling time of the molten steel normalized at the calculation cycle τ ₀ is defined as nA (that is, sampling is performed at the time of the nAth calculation), and the analysis value is expressed as [C] ′ (nA) (ppm). Then, the estimated value of C weight in molten steel at timing nA is calculated and corrected by the following equation. Wc (nA) = (Ws · [C] ′ (nA)) · k ₅ (5) where k ₅ : [C] analysis value weight conversion coefficient (0.001).

In FIG. 2, since the point g corresponds to the nA sampling time (the molten steel sampling time), as a result of inputting the rapid analysis value (the analysis value of the C concentration in the molten steel), the g point is assumed to be the g point. The C concentration has been replaced by g ', a rapid analysis.

After the rapid analysis values have been entered, the C
The concentration estimate is calculated as follows. ΔWc (j) = (k ₁・ CO (j−τ ₁ ) + k ₂・ CO ₂ (j−τ ₂ ) ・ F (j−τ ₃ ) ・ τ ₀ … (6) Wc (j) = Wc ( j−1) −ΔWc (j) (7) [C] (j) = (Wc (j) / Ws) · k ₄ (8) where j = nA + 1, nA + 2,. .

In FIG. 2, based on equations (6) to (8),
The estimated values of the C concentration in the molten steel from g ′ to l ′ have been calculated. The current time is the time indicated as “current” in FIG. 2, but the latest estimated value of the C concentration in molten steel obtained is up to l ′ due to the delay of the analyzer and the like.

The estimated C concentration in molten steel is calculated using the new estimated C concentration g ′ to l ′ in molten steel thus obtained.
[C] "(i) [ppm] as a function of time, ie
Assuming that [C] "(i) = α · exp (−β · i) + γ (9) as a function form, the obtained data g ′ to l ′ are applied to equation (9), and the minimum 2 The coefficients α, β, and γ are obtained by a multiplication method, where i is the number of calculations normalized by τ ₀ in Expression (9), and has the same meaning as i in Expression (2) and the like. Is calculated at every calculation cycle τ _{0 and at the} time of rapid analysis value input. However, before the rapid analysis value is input for the first time, it is not always necessary to perform the calculation of the regression equation and the end point determination described below. This is because the end of decarburization before rapid analysis values are input cannot be a normal operation.

When the coefficient is determined in equation (9) and the function form is determined, it is possible to calculate the estimated values A to F of the C concentration in the molten steel after the latest obtained C concentration l 'in the molten steel. In FIG. 2, since F is equal to the end point C concentration target value,
[C] "The point at which (i) becomes F is the end point of the decarburization treatment. Each time the carbon concentration in the molten steel is newly calculated, the coefficient in equation (9) is calculated, and the coefficient is calculated using equation (9). Is calculated, and when the current carbon concentration in the molten steel reaches the target end-point concentration, the decarburization process is terminated.

In the above description, an example in which molten steel sampling is performed once has been described. However, when performing multiple samplings, the analysis of the C concentration in molten steel in the latest sampling is always used. Equation (9) may be calculated, and the end point of decarburization may be determined based on these calculations.

[0030]

As described in the foregoing, in the present invention, molten steel weight, the molten steel initial carbon concentration, exhaust gas flow rate in consideration of the detection delay, CO considering the analysis time delay, from the CO ₂ concentration, the molten steel by a carbon mass balance The medium carbon concentration is estimated, during which time the molten steel sample is collected at least once, and the estimated molten steel carbon concentration estimation value is corrected based on the analysis value of the collected molten steel sample in consideration of the analysis delay time. At the same time, the estimated carbon concentration in the molten steel is estimated from the estimated carbon concentration in the molten steel as a regression equation that is a function of time, and the carbon concentration in the molten steel compensated for the exhaust gas flow rate and the delay time of the exhaust gas analysis value from the regression equation. An estimated value is obtained, and the time when the estimated value reaches the target end-point carbon concentration is set as the end of the decarburization process. It is possible to improve the predictive value of the target value of the oxygen concentration. Thereby, it is possible to prevent the treatment time from being prolonged due to the excessive decarburization treatment and to improve the quality of the molten steel.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of equipment for carrying out an embodiment of the present invention.

Fig. 2 Elapsed time from the start of refining and carbon concentration in molten steel
FIG. 6 is a diagram showing a relationship with [C].

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ladle 2 ... Molten steel 3 ... Vacuum tank main body of RH degassing device 4 ... Upside dipping tube 5 ... Downside dipping tube 6 ... Argon gas supply pipe for reflux 7 ... Exhaust pipe 8 ... Pretreatment equipment for exhaust gas analysis 9 ... Exhaust gas analyzer 10 ... Exhaust gas flow meter 11 ... Metal steel sampling device 12 ... Metal steel sampling control device 13 ... Metal steel carbon concentration analyzer 14 ... Operation control device 15 ... Computing device

Continuation of the front page (72) Inventor Tsuyoshi Murai 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. A method for producing an ultra-low carbon steel using an RH vacuum degassing apparatus, comprising the following steps. (a) the molten steel by weight, the molten steel initial carbon concentration, exhaust gas flow rate in consideration of the detection delay, analysis CO considering a time delay from the CO ₂ concentration, step to estimate the carbon concentration in the molten steel by a carbon mass balance (b) the ( In the process of a), take the molten steel sample at least once,
Based on the analysis values of the sampled molten steel, considering the analysis delay time, the step of correcting the estimated carbon concentration in the molten steel estimated in the step (a) (c) the (a), (b) From the estimated carbon concentration in the molten steel estimated by the step of, the step of obtaining the estimated carbon concentration in the molten steel as a regression equation that is a function of time (d) using the regression equation obtained in the step (c), A process of obtaining an estimated carbon concentration in molten steel that compensates for the delay time of the exhaust gas flow rate and the exhaust gas analysis value, and terminating the process when the estimated value reaches the target end-point carbon concentration.