JP7180645B2 - Method for estimating hydrogen concentration in molten steel and vacuum degassing refining method for molten steel - Google Patents

Description

The present invention provides a method for estimating the hydrogen concentration in molten steel before vacuum degassing refining for removing hydrogen in molten steel under reduced pressure, and a vacuum degassing equipment such as an RH vacuum degassing device. The present invention relates to a vacuum degassing refining method for molten steel in which hydrogen is removed from the molten steel by refining the molten steel under reduced pressure.

In steel materials, hydrogen is a harmful element that causes hair cracks, white spots, hydrogen embrittlement, delayed fracture, and the like. Therefore, in the steelmaking process, it is desired to reduce the hydrogen content of molten steel. In the facility, vacuum degassing refining (also referred to as “dehydrogenation treatment”) of molten steel is performed to refine the molten steel under reduced pressure to remove hydrogen in the molten steel.

In the vacuum degassing refining of molten steel, the conventional method of controlling the hydrogen concentration in the molten steel after refining to be below the target hydrogen concentration is as follows: (1) Direct measurement of the hydrogen concentration in the molten steel online, (2) a method of setting a longer refining time based on past performance so that the hydrogen concentration in molten steel is below the target hydrogen concentration; There are roughly three methods of estimating the concentration and securing a refining time in which the estimated hydrogen concentration of the molten steel is below the target hydrogen concentration.

However, the method of directly measuring the hydrogen concentration of molten steel online requires a dedicated measuring device for measuring the hydrogen concentration. There is a problem that a consumable measurement probe is required and the vacuum degassing refining cost increases. In addition, in the method of setting the refining time of vacuum degassing refining longer, the longer refining time increases the refractory cost, the gas cost for stirring, and the power cost, and the vacuum degassing refining cost increases. There is

Therefore, in order to solve these problems, a method of estimating the hydrogen concentration of molten steel using a model formula has attracted attention, and various proposals have been made so far.

For example, in Patent Document 1, in vacuum degassing refining, the degree of vacuum (pressure) in the vacuum tank is predicted based on the amount of exhaust gas predicted by the operation pattern of the exhaust gas device, and based on this predicted degree of vacuum, The hydrogen concentration is estimated in advance, and after the start of refining, the actual degree of vacuum is compared with the predicted degree of vacuum, and the deviation is corrected to predict the transition of the degree of vacuum. Methods for estimating concentration have been proposed.

However, Patent Document 1 does not show a method for estimating the hydrogen concentration in molten steel before vacuum degassing refining, that is, the hydrogen concentration in molten steel at the start of vacuum degassing refining. There is a problem that the estimation accuracy is insufficient in actual operation where the hydrogen concentration in molten steel before vacuum degassing refining changes greatly depending on the type and content of the steelmaking refining process used.

In Patent Document 2, the hydrogen concentration in molten steel before vacuum degassing refining is directly measured by an on-line rapid hydrogen analyzer, and the vacuum degassing refining period is divided into three periods, and the dehydrogenation rate constant in each period is calculated. A method of estimating the refining time of vacuum degassing refining has been proposed by determining according to the amount of molten steel by prior measurement.

However, in Patent Document 2, in order to determine the hydrogen concentration in molten steel before vacuum degassing refining, it is necessary to measure the hydrogen concentration of molten steel before each vacuum degassing refining. is expensive, and there is a problem that the vacuum degassing refining cost will rather increase.

In addition, in Patent Document 3, after an alloy for component adjustment and aluminum are put into molten steel to make the free oxygen concentration in the molten steel 10 ppm by mass or less, the hydrogen concentration in the molten steel is measured, and the measurement result and the previously obtained A method of calculating the refining time for dehydrogenation is proposed using a dehydrogenation prediction model formula based on the dehydrogenation rate constant set in advance.

However, even in Patent Document 3, in order to obtain the hydrogen concentration in molten steel, the hydrogen concentration is measured using a probe after the free oxygen concentration in molten steel is reduced to 10 ppm by mass or less each time vacuum degassing refining is performed. There is a problem that the vacuum degassing refining cost increases.

JP-A-9-209027 JP-A-5-70821 JP 2018-109212 A

The present invention has been made in view of the above circumstances, and its object is to remove hydrogen from molten steel when performing vacuum degassing refining of molten steel by refining molten steel under reduced pressure to remove hydrogen in molten steel. To provide a method for estimating the concentration of hydrogen in molten steel, capable of accurately estimating the concentration of hydrogen in the molten steel before vacuum degassing refining without incurring an increase in cost due to analysis of the concentration. Another object is to apply the dehydrogenation model formula to the estimated hydrogen concentration in the molten steel before vacuum degassing refining, thereby achieving vacuum degassing without extending the refining time of vacuum degassing refining. An object of the present invention is to provide a method for vacuum degassing refining of molten steel, capable of estimating the hydrogen concentration in molten steel during refining with high accuracy.

The present inventors diligently conducted experiments and studies in order to solve the above problems. As a result, it was found that the hydrogen concentration in molten steel before vacuum degassing refining depends on the operating conditions of the steelmaking refining process prior to vacuum degassing refining.

The present invention was made based on the above findings, and the gist thereof is as follows.

[1] A method for estimating the hydrogen concentration in molten steel before vacuum degassing refining for removing hydrogen in molten steel under reduced pressure is performed,
Hydrogen concentration estimation in molten steel, characterized in that the hydrogen concentration in molten steel before vacuum degassing refining is estimated using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable. Method.

[2] The function with the amount of auxiliary raw materials used in the steelmaking refining process as a variable is the total amount of auxiliary raw materials added per unit mass of molten steel in refining in a converter or an electric furnace, the output steel from a converter or an electric furnace Total amount of auxiliary materials added per unit mass of molten steel in the steelmaking process from steel to before the start of vacuum degassing refining, and amount of auxiliary materials containing calcined lime added per unit mass of molten steel in refining in a converter or electric furnace total amount of auxiliary raw materials containing calcined lime per unit mass of molten steel in the steelmaking process from the output of converter or electric furnace to the start of vacuum degassing refining; The total amount of auxiliary materials that do not contain calcined lime per unit mass of molten steel, and does not contain calcined lime per unit mass of molten steel in the steelmaking refining process from the output steel from converter or electric furnace to the start of vacuum degassing refining The method for estimating the concentration of hydrogen in molten steel according to [1] above, wherein the function includes at least one of the total amount of auxiliary materials added as a variable.

[3] The method for estimating hydrogen concentration in molten steel according to [1] above, wherein the following formula (1) is used as a function with the amount of auxiliary raw materials used in the steelmaking refining process as a variable.
[H] ₀ = b ₁ ×W ₁ +b ₂ ×W ₂ +β (1)
Here, in equation (1), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, _W The total amount of raw materials added (kg/ton), _W2 is the added amount of auxiliary materials per unit mass of molten steel in the steelmaking refining process from converter or electric furnace output steel to the start of vacuum degassing refining. Total (kg/ton), b ₁ and b ₂ are influence coefficients determined by the type and management state of individual sub-raw materials, and β is a correction constant.

[4] The method for estimating the concentration of hydrogen in molten steel according to [1] above, wherein the following formula (2) is used as a function with the amount of auxiliary material used in the steelmaking refining process as a variable.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual sub-raw materials, and α is a correction constant.

[5] The method for estimating hydrogen concentration in molten steel according to [4] above, wherein the auxiliary raw material containing calcined lime is an auxiliary raw material containing free lime.

[6] Any one of the above [3] to [5], characterized in that at least one of the influence coefficient and the correction constant is determined by regression analysis of past operational data. Method for estimating hydrogen concentration in molten steel.

[7] A method for vacuum degassing refining of molten steel for refining molten steel under reduced pressure to remove hydrogen in the molten steel, comprising:
Estimate the hydrogen concentration in the molten steel before vacuum degassing refining using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable,
Furthermore, the hydrogen concentration in the molten steel during vacuum degassing refining is estimated sequentially using the dehydrogenation model formula, and when the hydrogen concentration estimated by the dehydrogenation model formula becomes less than the target hydrogen concentration, vacuum degassing refining is started. A method for vacuum degassing refining of molten steel, characterized by finishing.

[8] The function with the amount of auxiliary raw materials used in the steelmaking refining process as a variable is the total amount of auxiliary raw materials added per unit mass of molten steel in refining in a converter or an electric furnace, the output steel from a converter or an electric furnace Total amount of auxiliary materials added per unit mass of molten steel in the steelmaking process from steel to before the start of vacuum degassing refining, and amount of auxiliary materials containing calcined lime added per unit mass of molten steel in refining in a converter or electric furnace total amount of auxiliary raw materials containing calcined lime per unit mass of molten steel in the steelmaking process from the output of converter or electric furnace to the start of vacuum degassing refining; The total amount of auxiliary materials that do not contain calcined lime per unit mass of molten steel, and does not contain calcined lime per unit mass of molten steel in the steelmaking refining process from the output steel from converter or electric furnace to the start of vacuum degassing refining The method for vacuum degassing refining of molten steel according to [7] above, wherein the function includes at least one of the sum of the additive amounts of the auxiliary materials as a variable.

[9] The method for vacuum degassing refining of molten steel according to the above [7], wherein the following formula (1) is used as a function with the amount of auxiliary raw materials used in the steelmaking refining process as a variable.
[H] ₀ = b ₁ ×W ₁ +b ₂ ×W ₂ +β (1)
Here, in equation (1), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, _W The total amount of raw materials added (kg/ton), _W2 is the added amount of auxiliary materials per unit mass of molten steel in the steelmaking refining process from converter or electric furnace output steel to the start of vacuum degassing refining. Total (kg/ton), b ₁ and b ₂ are influence coefficients determined by the type and management state of individual sub-raw materials, and β is a correction constant.

[10] The method for vacuum degassing refining of molten steel according to [7] above, characterized in that the following formula (2) is used as a function with the amount of the auxiliary raw material used in the steelmaking refining process as a variable.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual sub-raw materials, and α is a correction constant.

[11] The method for vacuum degassing refining of molten steel according to [10] above, wherein the auxiliary material containing calcined lime is an auxiliary material containing free lime.

[12] Any one of the above [9] to [11], characterized in that at least one of the influence coefficient and the correction constant is determined by regression analysis of past operational data. Vacuum degassing refining method for molten steel.

[13] Vacuum degassing of molten steel according to any one of [7] to [12] above, wherein the following equations (3) and (4) are used as the dehydrogenation model equations. smelting method.
[H]={[H] ₀ −[H] _e }×exp(−K _H ×t)+[H] _e (3)
[H] _e = 10 ^{- (1905/T) - 1.591} x P ^1/2 (4)
Here, in the formula (3), [H] is the hydrogen concentration (mass ppm) in the molten steel during vacuum degassing refining, [H] ₀ is the use of auxiliary raw materials in the steelmaking refining process prior to vacuum degassing refining. Hydrogen concentration (mass ppm) in molten steel before vacuum degassing refining estimated using a function with quantity as a variable, [H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum tank, K _H is the dehydrogenation rate constant (1/min) in vacuum degassing refining, t is the elapsed time (min) from the start of vacuum degassing refining, and in equation (4), [H] _e is The equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, T is the molten steel temperature (K) during vacuum degassing refining, and P is the pressure (atm) in the vacuum chamber.

[14] The vacuum degassing refining is vacuum degassing refining in an RH vacuum degassing apparatus, and the dehydrogenation rate constant (K _H ) is expressed by the following equations (5), (6) and (7) The method for vacuum degassing refining of molten steel according to the above [13], characterized in that the determination is made using the formula.
_KH =(Q/V)×{ak/(Q+ak)} (5)
Q=11.4×G1 ^/3 ×D4 ^/3 ×{ln( _P1 /P)} ^1/3 / _ρL (6)
ak=2500× _DH1 ^/2 ×(G× ^10-3 ) ^1/2 × _dL /2 (7)
Here, in equations (5), (6) and (7), _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, Q is the molten steel circulation flow rate to the vacuum tank (m ³ /min), V is the volume of molten steel to be vacuum degassed (m ³ ), ak is the dehydrogenation reaction capacity coefficient (m ³ /min), and G is the flow rate of reflux gas (NL/min). , D is the inner diameter of the ascending immersion tube (m), P ₁ is the atmospheric pressure (atm), P is the pressure in the vacuum chamber (atm), ρ _L is the density of molten steel (ton/m ³ ), D _H is the diffusion coefficient of hydrogen in molten steel (m ² /min), and _dL is the inner diameter (m) of the vacuum chamber.

[15] Measure the hydrogen concentration of molten steel during vacuum degassing refining prior to the vacuum degassing refining, determine the change in hydrogen concentration over time from the measured hydrogen concentration, and dehydrate based on the determined change in hydrogen concentration over time. An elementary rate constant (K _H ) is determined in advance, and the hydrogen concentration in molten steel during vacuum degassing refining is sequentially estimated using the predetermined dehydrogenation rate constant (K _H ). The vacuum degassing refining method for molten steel according to [13].

[16] A method for vacuum degassing refining of molten steel for refining molten steel under reduced pressure to remove hydrogen in the molten steel,
Estimate the hydrogen concentration in the molten steel before vacuum degassing refining using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable,
The vacuum degassing refining is performed by satisfying the following formula (8) obtained from the estimated hydrogen concentration in the molten steel before vacuum degassing refining and the target value of the hydrogen concentration in the molten steel after vacuum degassing refining. A method for vacuum degassing refining of molten steel, characterized in that it ends at a point in time.
t≧(1/K _H )×ln{([H] ₀ −[H] _e )/([H] _f −[H] _e )} (8)
Here, in formula (8), t is the elapsed time (min) from the start of vacuum degassing refining, and [H] ₀ is the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining. The hydrogen concentration in the molten steel before vacuum degassing refining (mass ppm), [H _] , estimated using the function to H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, ln is the natural logarithm.

[17] The method for vacuum degassing refining of molten steel according to [16] above, characterized in that the following formula (1) is used as a function with the amount of the auxiliary raw material used in the steelmaking refining process as a variable.
[H] ₀ = b ₁ ×W ₁ +b ₂ ×W ₂ +β (1)
Here, in equation (1), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, _W The total amount of raw materials added (kg/ton), _W2 is the added amount of auxiliary materials per unit mass of molten steel in the steelmaking refining process from converter or electric furnace output steel to the start of vacuum degassing refining. Total (kg/ton), b ₁ and b ₂ are influence coefficients determined by the type and management state of individual sub-raw materials, and β is a correction constant.

[18] The method for vacuum degassing refining of molten steel according to [16] above, characterized in that the following formula (2) is used as a function with the amount of auxiliary materials used in the steelmaking refining process as a variable.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual sub-raw materials, and α is a correction constant.

[19] The vacuum degassing refining is vacuum degassing refining in an RH vacuum degassing apparatus, and the dehydrogenation rate constant (K _H ) is expressed by the following equations (5), (6) and (7) The method for vacuum degassing refining of molten steel according to any one of [16] to [18] above, characterized in that the determination is made using a formula.
_KH =(Q/V)×{ak/(Q+ak)} (5)
Q=11.4×G1 ^/3 ×D4 ^/3 ×{ln( _P1 /P)} ^1/3 / _ρL (6)
ak=2500× _DH1 ^/2 ×(G× ^10-3 ) ^1/2 × _dL /2 (7)
Here, in equations (5), (6) and (7), _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, Q is the molten steel circulation flow rate to the vacuum tank (m ³ /min), V is the volume of molten steel to be vacuum degassed (m ³ ), ak is the dehydrogenation reaction capacity coefficient (m ³ /min), and G is the flow rate of reflux gas (NL/min). , D is the inner diameter of the ascending immersion tube (m), P ₁ is the atmospheric pressure (atm), P is the pressure in the vacuum chamber (atm), ρ _L is the density of molten steel (ton/m ³ ), D _H is the diffusion coefficient of hydrogen in molten steel (m ² /min), and _dL is the inner diameter (m) of the vacuum chamber.

ADVANTAGE OF THE INVENTION According to this invention, the hydrogen concentration in the molten steel before vacuum degassing refining can be accurately estimated, without causing the cost increase of vacuum degassing refining. In addition, when the dehydrogenation model formula is applied to the estimated hydrogen concentration in the molten steel before vacuum degassing refining, the molten steel during vacuum degassing refining can be obtained without extending the refining time of vacuum degassing refining. It is possible to estimate the hydrogen concentration in the medium with high accuracy.

1 is a schematic longitudinal sectional view of an example of an RH vacuum degasser; FIG.

Hereinafter, the method for estimating hydrogen concentration in molten steel and the vacuum degassing refining method for molten steel according to the present invention will be specifically described.

Vacuum degassing equipment that can perform the vacuum degassing refining method for molten steel according to the present invention includes RH vacuum degassing equipment, DH vacuum degassing equipment, REDA vacuum degassing equipment, VAD vacuum refining equipment, etc. The most representative of them is the RH vacuum degasser. Therefore, first, the vacuum degassing refining method in the RH vacuum degassing apparatus will be described.

FIG. 1 shows a schematic longitudinal sectional view of an example of an RH vacuum degassing apparatus. In FIG. 1, 1 is a RH vacuum degassing device, 2 is a ladle, 3 is molten steel, 4 is slag, 5 is a vacuum tank, 6 is an upper tank, 7 is a lower tank, 8 is an ascending dip tube, and 9 is 10 is a circulating gas blowing pipe, 11 is a duct, 12 is a raw material inlet, 13 is a top blowing lance, D is the inside diameter of the rising side dipping pipe, and _dL is the inside diameter of the vacuum chamber. The vacuum chamber 5 is composed of an upper chamber 6 and a lower chamber 7. A top blowing lance 13 is a device for blowing and adding oxygen gas or a solvent to the molten steel in the vacuum chamber. , and can move up and down inside the vacuum chamber 5 .

In the RH vacuum degassing apparatus 1, a ladle 2 containing molten steel 3 is raised by a lifting device (not shown), and an ascending immersion tube 8 and a descending immersion tube 9 are immersed in the molten steel 3 in the ladle. . Then, the inside of the vacuum chamber 5 is evacuated by an exhaust device (not shown) connected to the duct 11 to decompress the inside of the vacuum chamber 5, and the inside of the rising side immersion pipe 8 from the reflux gas blowing pipe 10 is discharged. Reflux gas is blown into the When the pressure inside the vacuum chamber 5 is reduced, the molten steel 3 in the ladle rises in proportion to the difference between the atmospheric pressure and the pressure (degree of vacuum) in the vacuum chamber, flows into the vacuum chamber, and flows back into the vacuum chamber. Due to the gas lift effect of the circulating gas blown from the gas blowing pipe 10, the rising side immersion pipe 8 rises together with the circulating gas and flows into the vacuum chamber 5. RH vacuum degassing refining is performed by forming a flow returning to the pot 2, the so-called reflux. The molten steel 3 is exposed to an atmosphere under reduced pressure in the vacuum tank, hydrogen in the molten steel moves to the atmosphere in the vacuum tank, and the dehydrogenation reaction of the molten steel 3 proceeds.

In the vacuum degassing refining (dehydrogenation treatment) of molten steel in which the hydrogen in the molten steel is removed by refining the molten steel under reduced pressure using a vacuum degassing facility such as an RH vacuum degassing apparatus, the present inventors By estimating the hydrogen concentration in molten steel before vacuum degassing refining with high accuracy, and applying the dehydrogenation model formula to the estimated hydrogen concentration in molten steel before vacuum degassing refining, the hydrogen concentration during vacuum degassing refining Research and consideration have been made on estimating the concentration of hydrogen in molten steel. As a result, the hydrogen concentration in molten steel before vacuum degassing refining is greatly affected by the amount of auxiliary materials added per unit mass of molten steel in the steelmaking process prior to vacuum degassing refining, and the amount of auxiliary materials used is a variable. We found that it is possible to estimate with high accuracy using a function.

As a result of investigation by the present inventors, the hydrogen concentration ([H] ₀ ; mass ppm) in the molten steel before vacuum degassing refining is variable with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining. It turns out that it can be estimated using a function.

As a function of the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable, the total amount of auxiliary raw materials added per unit mass of molten steel in refining in a converter or an electric furnace, Total amount of auxiliary materials added per unit mass of molten steel in the steelmaking process from electric furnace tapping to vacuum degassing refining, auxiliary materials containing calcined lime per unit mass of molten steel in refining in converter or electric furnace the total amount of added calcined lime-containing auxiliary materials per unit mass of molten steel in the steelmaking refining process from the output of converter or electric furnace to the start of vacuum degassing refining, converter or electric furnace calcination per unit mass of molten steel in the refining process, calcination per unit mass of molten steel in the steel refining process from converter or electric furnace output to vacuum degassing refining A function containing as variables at least one of the total added amount of non-lime-containing adjuncts can be used.

For example, the total amount of auxiliary materials added per unit mass of molten steel in refining in a converter or electric furnace is W ₁ (kg/ton), and from the steel output from the converter or electric furnace to the start of vacuum degassing refining If the total amount of auxiliary materials added per unit mass of molten steel in the steelmaking refining process is W ₂ (kg/ton), the hydrogen concentration ([H] ₀ ; mass ppm) in the molten steel before vacuum degassing refining is , is expressed by the following formula (1).

[H] ₀ = b ₁ ×W ₁ +b ₂ ×W ₂ +β (1)
Here, in the formula (1), b ₁ and b ₂ are influence coefficients determined by the type and management state of each sub-material, and β is a correction constant.

(1) Formula, the influence coefficient and the correction constant are the actual value of the additive amount of the auxiliary material per unit mass of molten steel in the steelmaking process prior to the vacuum degassing refining in each vacuum degassing refining, and the vacuum degassing refining It is obtained by regression analysis with the previous measurement result of hydrogen concentration in molten steel. In particular, it is preferable to determine the influence coefficient and the correction constant by regression analysis of past operational data. According to the results of various experiments conducted by the present inventors, the values of b ₁ and b ₂ are 0.02≦b ₁ ≦0.05, 0.07≦b ₂ ≦1.3, −3≦ β≦3.

In addition, with regard to _W2 , "from the steel output from the converter or electric furnace until before the start of vacuum degassing refining" means from the time when steel output from the converter or electric furnace is started to the vacuum degassing refining in the vacuum degassing equipment. Specifically, it refers to the addition of auxiliary materials into the ladle during tapping, and the ladle that takes place during the period from tapping to the start of vacuum degassing refining. Refers to the addition of auxiliary materials in refining in a smelting furnace.

In addition, in the influence coefficient obtained from the results of experiments conducted by the present inventors, the total amount of auxiliary materials added per unit mass of molten steel (W ₁ ) in refining in a converter or an electric furnace The reason why the total amount of auxiliary materials added per unit mass of molten steel (W ₂ ) in the steelmaking refining process from the start of vacuum degassing refining to the start of vacuum degassing refining has a large effect is that dehydrogenation treatment is performed after tapping. Since molten steel is basically deoxidized, the rightward reaction in equation (10) described later, that is, the hydrogen absorption reaction in molten steel tends to proceed.

Furthermore, by classifying the auxiliary raw materials into auxiliary raw materials containing calcined lime and auxiliary raw materials not containing calcined lime, and using a function with the usage amount of each as a variable, the hydrogen concentration in the molten steel before vacuum degassing refining can be determined more accurately. I found out that it can be estimated.

Here, the mechanism of the auxiliary raw material containing calcined lime will be described. Part of the CaO in the calcined lime-containing auxiliary raw material absorbs water vapor (H ₂ O (g)) in the atmosphere and converts it into slaked lime (Ca(OH) ₂ ) by the hydration reaction of the following formula (9). Therefore, when the auxiliary raw material containing calcined lime is added to the molten steel, the decomposition reaction of the following formula (10) occurs, the moisture in the slaked lime moves into the molten steel, and the hydrogen concentration of the molten steel increases It depends.

CaO+H ₂ O (g)→Ca(OH) ₂ (9)
Ca(OH) ₂ →CaO+2H+O (10)
With regard to the calcined lime-free auxiliary raw material, this is because the moisture adhering to the surface of the calcined lime-free auxiliary raw material moves into the molten steel by the reaction of the following formula (11), increasing the hydrogen concentration of the molten steel.

H ₂ O (l)→2H+O (11)
As a result of investigation by the present inventors, the hydrogen concentration ([H] ₀ ; mass ppm) in molten steel before vacuum degassing refining is It was found that more accurate estimation can be achieved by using a function with the used amount of the contained auxiliary material as a variable. That is, the total amount of auxiliary raw materials containing calcined lime per unit mass of molten steel in refining in a converter or an electric furnace is w ₁ (kg/ton), and vacuum degassing refining is performed from the output steel from the converter or electric furnace. Let w ₂ (kg/ton) be the total amount of auxiliary raw materials containing calcined lime added per unit mass of molten steel in the steelmaking refining process before the start, and w 2 (kg/ton) per unit mass of molten steel in refining in a converter or electric furnace Let w ₃ (kg/ton) be the total additive amount of auxiliary raw materials that do not contain calcined lime, and the sintering per unit mass of molten steel in the steelmaking refining process from the steel output from the converter or electric furnace to the start of vacuum degassing refining Assuming that the total amount of lime-free auxiliary materials added is w ₄ (kg/ton), the hydrogen concentration ([H] ₀ ; mass ppm) in molten steel before vacuum degassing refining is given by the following equation (2): found to be represented.

[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in the formula (2), a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual auxiliary materials, and α is a correction constant.

(2) The formula, the influence coefficient and the correction constant are the addition of auxiliary raw materials containing calcined lime and auxiliary raw materials not containing calcined lime per unit mass of molten steel in the steelmaking process prior to vacuum degassing refining in each vacuum degassing refining It is obtained by regression analysis between the actual value of the amount and the measurement result of hydrogen concentration in molten steel before vacuum degassing refining. In particular, it is preferable to determine the influence coefficient and the correction constant by regression analysis of past operational data. According to the results of various experiments conducted by the present inventors, the values of a ₁ , a ₂ , a ₃ and a ₄ are 0.01≦a ₁ ≦0.1 and 0.1≦a ₂ ≦0. .5, 0≦a ₃ ≦0.05, 0≦a ₄ ≦0.25, −3≦α≦3.

In addition, regarding _w2 and _w4 , "from the steel output from the converter or the electric furnace until the start of vacuum degassing refining" means that from the time when the steel output from the converter or electric furnace starts to the vacuum degassing equipment. It represents the period until the start of degassing refining. Refers to the addition of auxiliary raw materials containing calcined lime and auxiliary raw materials not containing calcined lime in the refining in the ladle smelting furnace before the start of refining.

In the influence coefficient obtained from the results of _the experiments conducted by the present inventors, the output The reason why the total addition amount (w ₂ ) of auxiliary raw materials containing calcined lime per unit mass of molten steel in the steelmaking refining process from steel to before the start of vacuum degassing refining has a large effect is that after tapping, dehydrogenation treatment Since molten steel is basically deoxidized in the type of steel to which is applied, the rightward reaction in the equation (10), that is, the hydrogen absorption reaction in the molten steel tends to proceed.

In addition, in the influence coefficient obtained from the results of the experiments conducted by the present inventors, the total addition amount (w ₃ ) of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or an electric furnace It is also for the same reason that the total addition amount (w ₄ ) of non-calcined lime-containing auxiliary materials per unit mass of molten steel in the steel refining process from tapping to before the start of vacuum degassing refining has a large effect.

Furthermore, the fact that the influence coefficient _a3 and the influence coefficient _a4 are values including 0 indicates that in many cases, the amount of water adhering to the surface of the auxiliary material not containing calcined lime is so small that it can be ignored.

Here, the additive amount of the calcined lime-containing auxiliary material is the sum of the additive amounts added before vacuum degassing refining of the auxiliary material containing 10% by mass or more of CaO as a component. Specifically, the target calcined lime-containing auxiliary material is selected and determined in advance from a group of auxiliary materials such as calcined lime (quicklime), calcined dolomite, lightly burned dolomite, and recycled slag. When selecting and determining the auxiliary raw material containing calcined lime to be targeted, it is preferable to determine whether or not it contains free lime. That is, it is preferable to select an auxiliary material containing free lime as the auxiliary material containing calcined lime. In addition to the auxiliary raw materials exemplified above, any auxiliary raw material containing free lime is selected as the auxiliary raw material containing calcined lime.

The presence or absence of free lime may be determined, for example, by performing differential thermal analysis of a sample taken from the auxiliary raw material to be used and detecting an endothermic reaction caused by the reaction shown in the following formula (12). . That is, when an endothermic reaction is detected, it can be determined that free lime is contained.

Ca(OH) ₂ →CaO+H ₂ O (g) (12)
Moreover, the added amount of the calcined lime non-containing auxiliary material is the total amount of the added amount of the auxiliary material not corresponding to the calcined lime containing auxiliary material added before the vacuum degassing refining. An auxiliary raw material that does not contain free lime even if it contains 10% by mass or more of CaO as a component and is not selected as an auxiliary raw material containing calcined lime may be treated as an auxiliary raw material that does not contain calcined lime.

Secondary raw materials not containing calcined lime specifically include raw dolomite, limestone, manganese ore, carbon material, heat insulating material, iron ore, iron scrap, silicon carbide, brick scrap, silica stone and various pure metals and ferroalloys. is.

Even if the auxiliary raw material exemplified as the auxiliary raw material not containing calcined lime, if it contains free lime, not only the reaction of the formula (11) but also the reaction of the formula (9) occurs, and the hydrogen concentration of the molten steel treated as an auxiliary raw material containing calcined lime because it contributes significantly to the increase in

In addition, after tapping, the molten steel is basically deoxidized in the type of steel subjected to dehydrogenation treatment, so the rightward reaction in equation (10), that is, the reaction of hydrogen absorption into molten steel, tends to proceed. Therefore, it is desirable to set the influence coefficient separately before and after tapping. However, for steel grades that are not deoxidized, the molten steel is not deoxidized before vacuum degassing refining starts. be a value. Therefore, it is desirable to create a unique estimation formula for each form of tapping for steel types with different deoxidizing methods during tapping.

In the above, the case of estimating the hydrogen concentration in the molten steel before vacuum degassing refining using the functions represented by the formulas (1) and (2) has been shown, but the form of the function is not limited to these. For example, the equations (1) and (2) are both represented by linear equations of variables, but they do not have to be linear equations.

In the present invention, the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining, which is obtained by a function such as formula (1) and formula (2) with the amount of auxiliary materials used as a variable, is As the hydrogen concentration of the molten steel at the start, the hydrogen concentration of the molten steel during vacuum degassing refining is successively estimated using the dehydrogenation model formula, and the time when the hydrogen concentration estimated by the dehydrogenation model formula becomes less than the target hydrogen concentration to end the vacuum degassing refining. The dehydrogenation model formula used in the present invention will be described below.

Since the dehydrogenation reaction of molten steel is generally represented by a first-order reaction formula, the dehydrogenation model formula is the following formula (3). The formula (3) is obtained by integrating the following formula (3′), which is a general form of the first-order reaction formula, with the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining as the initial condition. is a formula for

[H]={[H] ₀ −[H] _e }×exp(−K _H ×t)+[H] _e (3)
d[H]/dt=−K _H ×([H]−[H] _e ) (3′)
Here, in formulas (3) and (3′), [H] is the hydrogen concentration (mass ppm) in the molten steel during vacuum degassing refining, and [H] ₀ is the molten steel before vacuum degassing refining. of hydrogen concentration (mass ppm), [H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, K _H is the dehydrogenation rate constant (1/min) in vacuum degassing refining, t is the elapsed time (min) from the start of vacuum degassing refining.

In the equation (3), the equilibrium hydrogen concentration [H] _e at the interface of the molten steel in the vacuum chamber was obtained from the following equation (4). However, the hydrogen partial pressure in the vacuum chamber was approximated to be equal to the pressure (degree of vacuum) in the vacuum chamber, and the pressure in the vacuum chamber was used as the value of the hydrogen partial pressure.

[H] _e = 10 ^{- (1905/T) - 1.591} x P ^1/2 (4)
Here, in equation (4), T is the molten steel temperature (K) during vacuum degassing refining, and P is the pressure (atm) in the vacuum chamber. The molten steel temperature is the temperature measured by immersing a thermocouple in molten steel in a ladle.

Further, when the vacuum degassing equipment is the RH vacuum degassing device 1, the dehydrogenation reaction of the molten steel 3 is obtained by using the following equation (5) as the dehydrogenation rate constant (K _H ) of the equation (3). can be accurately grasped.

_KH =(Q/V)×{ak/(Q+ak)} (5)
Here, in equation (5), _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, Q is the molten steel recirculation flow rate to the vacuum tank ( ^m3 /min), and V is the vacuum degassing rate. The volume (m ³ ) of molten steel to be gas-refined, ak is the dehydrogenation reaction capacity coefficient (m ³ /min).

As the molten steel recirculation rate (Q) in the formula (5), the following formula (6), which is generally used as an empirical formula for calculating the recirculation rate of the molten steel 3 in the RH vacuum degassing apparatus 1, can be used.

Q=11.4×G1 ^/3 ×D4 ^/3 ×{ln( _P1 /P)} ^1/3 / _ρL (6)
Here, in the formula (6), G is the flow rate of the reflux gas (NL / min), D is the inner diameter of the rising side immersion tube (m), P ₁ is the atmospheric pressure (atm), P is the vacuum chamber The internal pressure (atm), ρ _L is the density of molten steel (ton/m ³ ).

Further, as the dehydrogenation reaction capacity coefficient (ak) in the formula (5), the following formula (7), which is an empirical formula for the surface degassing reaction in the water model experiment, can be used. However, the constant of proportionality 2500 in the equation (7) is a correction value adapted to the actual RH vacuum degassing device.

ak=2500× _DH1 ^/2 ×(G× ^10-3 ) ^1/2 × _dL /2 (7)
Here, in equation (7), _DH is the diffusion coefficient of hydrogen in molten steel (m ² /min), G is the flow rate of recirculation gas (NL/min), _dL is the inner diameter of the vacuum chamber (m ).

Also, when using a vacuum degassing equipment other than the RH vacuum degassing equipment, the hydrogen concentration of the molten steel is measured during vacuum degassing refining before the vacuum degassing refining in the vacuum degassing equipment, and the measurement is performed. Based on the obtained hydrogen concentration, the dehydrogenation rate constant ( K _H ) is determined in advance as a fitting parameter, it is possible to estimate the hydrogen concentration in molten steel using the equation (3).

As an example of the vacuum degassing refining method for molten steel according to the present invention, a case of using the RH vacuum degassing apparatus 1 shown in FIG. 1 will be described.

First, before starting vacuum degassing refining in the RH vacuum degassing apparatus 1, the total amount of auxiliary materials added in refining in the converter or electric furnace (W ₁ ), from tapping to before the start of vacuum degassing refining Using the total amount of auxiliary materials added in the steelmaking refining process (W ₂ ) and the influence coefficients b ₁ and b ₂ , the hydrogen concentration in the molten steel before vacuum degassing refining ([ H] ₀ ). Here, the influence coefficients were b ₁ =0.035, b ₂ =0.100, and β=0 based on the results of previous measurements.

Further, when the auxiliary raw materials are classified into auxiliary raw materials containing calcined lime and auxiliary raw materials not containing calcined lime, refining in a converter or an electric furnace is performed before vacuum degassing refining is started in the RH vacuum degassing device 1. The total amount of auxiliary raw materials containing calcined lime added (w ₁ ), the total amount of auxiliary raw materials containing calcined lime added in the steelmaking refining process from tapping to before the start of vacuum degassing refining (w ₂ ), Sum of additive amounts (w ₃ ) of non-calcined lime-containing auxiliary materials added during refining in a furnace or electric furnace, addition of non-calcined lime-containing auxiliary materials added during the steelmaking refining process from tapping to before the start of vacuum degassing refining Using the sum of the amounts (w ₄ ) and the influence coefficients a ₁ , a ₂ , a ₃ , and a ₄ , the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining is calculated from the equation (2). calculate. Here, the influence coefficients were a ₁ =0.031, a ₂ =0.294, a ₃ =0.044, a ₄ =0.074, and α=0 based on the previous measurement results.

In the vacuum degassing refining in the RH vacuum degassing apparatus 1, the pressure (degree of vacuum) inside the vacuum chamber 5 is reduced to 2 torr (0.266 kPa) or less, and the molten steel 3 is moved between the ladle 2 and the vacuum chamber 5. circulate. Here, the hydrogen concentration ([H] ₀ ) obtained by the formula (1) or (2), the molten steel temperature, the flow rate of the reflux gas, and the pressure in the vacuum chamber are added to the above-described formulas (3) to (7). and other actual values are input at any time to estimate the hydrogen concentration in molten steel in the elapsed time from the start of vacuum degassing refining. After the estimated hydrogen concentration falls below the target hydrogen concentration determined in advance based on the hydrogen standard for each steel type, the vacuum degassing refining is terminated. Argon gas is usually used as the reflux gas, but other inert gases such as nitrogen gas can also be used depending on the purpose.

Further, in the above equation (3), the hydrogen concentration ([H]) in the molten steel during refining is substituted with the target value ([H] _f ) of the hydrogen concentration in the molten steel after vacuum degassing refining, By transforming the equation (3), the following equation (8') is derived.

t=(1/K _H )×ln{([H] ₀ −[H] _e )/([H] _f −[H] _e )} (8′)
Here, in equation (8′), t is the elapsed time (min) from the start of vacuum degassing refining, and [H] ₀ is the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining. The hydrogen concentration (mass ppm) in _the molten steel before vacuum degassing refining, estimated using the function of [H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, ln is the natural logarithm.

Formula (8′) is a formula representing the elapsed time (processing time) until the hydrogen concentration in the molten steel after vacuum degassing refining reaches the target value, and the elapsed time (t ), the hydrogen concentration in the molten steel is reduced to the target value or less by subjecting the molten steel to vacuum degassing refining for a treatment time equal to or longer than the target value. That is, by ending the vacuum degassing refining when the condition of the following formula (8) is satisfied, the hydrogen concentration in the molten steel after the vacuum degassing refining becomes equal to or less than the target value.

t≧(1/K _H )×ln{([H] ₀ −[H] _e )/([H] _f −[H] _e )} (8)
That is, in the vacuum degassing refining in the RH vacuum degassing apparatus 1, the equilibrium hydrogen concentration ([H] _e ) obtained from the above equation (4), the dehydration obtained from the above equations (5) to (7) Elementary rate constant (K _H ), hydrogen concentration ([H] ₀ ) in molten steel before vacuum degassing refining determined from equation (1) or (2), molten steel after vacuum degassing refining determined by steel grade standards The target value ([H] _f ) of the hydrogen concentration in the molten steel is input to the formula (8) at any time, and the elapsed time from the start of the vacuum degassing refining required for the hydrogen concentration in the molten steel to decrease to the target hydrogen concentration ( t) may be estimated, and the degassing refining treatment may be performed for a treatment time equal to or longer than the estimated elapsed time (t). However, it is preferable that the processing time does not exceed 1.1 times the estimated elapsed time (t) so as not to reduce production efficiency and increase costs.

Here, the vacuum degassing refining method using the RH vacuum degasser was described as an example, but other vacuum degassing equipment such as the DH vacuum degasser, the REDA vacuum degasser, and the VAD vacuum refining equipment can be used. can also carry out the vacuum degassing refining method for molten steel according to the present invention.

As described above, according to the present invention, the hydrogen concentration in molten steel before vacuum degassing refining can be accurately estimated without directly measuring the hydrogen concentration in molten steel. In addition, when the dehydrogenation model formula is applied to the estimated hydrogen concentration in the molten steel before vacuum degassing refining, the molten steel during vacuum degassing refining can be obtained without extending the refining time of vacuum degassing refining. It is possible to estimate the hydrogen concentration in the medium with high accuracy.

A test in which 300 tons of molten steel produced by decarburizing and refining molten iron in a converter is tapped from the converter into a ladle, and the molten steel in the ladle is vacuum degassed and refined with an RH vacuum degasser (RH). did In the test, the amounts of calcined lime-containing auxiliary materials and calcined lime-free auxiliary materials used in decarburization refining in a converter, and the amount of calcined lime-containing auxiliary materials and calcined lime-free auxiliary materials used in the molten steel in the ladle at the time of tapping. The amounts of raw materials added and the amounts of auxiliary raw materials containing calcined lime and auxiliary raw materials not containing calcined lime in desulfurization refining in a ladle refining furnace (LF) after tapping were variously changed. Then, from the amount of the auxiliary raw material containing calcined lime and the auxiliary raw material not containing calcined lime in the converter and ladle refining furnace, which are steelmaking refining processes prior to vacuum degassing refining, it is calculated by formula (1) or (2) The hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining and the measured hydrogen concentration were compared and investigated (test numbers 1 to 18). In the test, in formula (1), b ₁ =0.035, b ₂ =0.100, β=0, and in formula (2), a ₁ =0.031, a ₂ =0.294, a ₃ = 0.044, a ₄ = 0.074, and α = 0.

In this example, the auxiliary raw materials used as auxiliary raw materials containing calcined lime that affect the hydrogen concentration in the molten steel before vacuum degassing refining were two kinds of calcined lime and light burned dolomite in the converter decarburization refining. In addition to molten steel in a ladle during steelmaking and in desulfurization refining in a ladle refining furnace, there are two types: calcined lime and light calcined dolomite. In addition, the auxiliary raw materials used as auxiliary raw materials that do not contain calcined lime are raw dolomite, iron scrap, iron ore, silicon carbide, silica, and brick waste in the converter decarburization refining, and in the refining after tapping, , metal aluminum, brick waste, anthracite, silicon manganese, and ferrosilicon.

Further, in the vacuum degassing refining in the RH vacuum degassing apparatus, the hydrogen concentration ([H] ₀ ) calculated by the formula (1) or (2) is set as the initial hydrogen concentration in the molten steel in the vacuum degassing refining, Applying the dehydrogenation model equations (3) to (7) to the set hydrogen concentration ([H] ₀ ), when the hydrogen concentration estimated by the dehydrogenation model equation becomes less than the target hydrogen concentration Tests (Inventive Examples 1 to 16) were conducted to terminate the vacuum degassing refining.

For comparison, the hydrogen concentration of molten steel was actually measured every 3 minutes during vacuum degassing refining in the RH vacuum degassing apparatus, and when the measured hydrogen concentration became less than the target hydrogen concentration, vacuum degassing refining (Comparative Examples 1 and 2), the hydrogen concentration in the molten steel before vacuum degassing refining was actually measured, and the dehydrogenation model equations (3) to (7) were applied to the actually measured hydrogen concentration. , a test in which vacuum degassing refining is terminated when the hydrogen concentration estimated by the dehydrogenation model formula becomes less than the target hydrogen concentration (Comparative Examples 3 to 6), and the refining time is set in advance according to the hydrogen concentration standard for the steel type. Tests (Comparative Examples 7 to 10) were conducted in which the vacuum degassing refining was terminated when the set refining time (20 minutes) had elapsed.

Here, the same vacuum chamber was used in all tests. In addition, in order to evaluate the estimated value of the hydrogen concentration in molten steel by the dehydrogenation model formula, that is, to confirm whether the estimated value of the hydrogen concentration in molten steel by the dehydrogenation model formula matches the actual situation, all In the test, the hydrogen concentration in the molten steel was measured before and after the vacuum degassing refining.

The chemical composition of the molten steel used in the test before vacuum degassing refining is C: 0.04 to 0.06 mass%, Si: 0.15 to 0.25 mass%, Mn: 1.2 to 1.4 mass %, P: 0.02% by mass or less, S: 0.003% by mass or less, and the molten steel temperature before vacuum degassing refining was 1640 to 1670°C. The ultimate vacuum in the vacuum chamber was set to 0.5 to 1.0 torr, and the flow rate of argon gas for reflux was set to 2000 to 2200 NL/min.

Table 1 shows the hydrogen concentration ([H] ₀ ) and the measured value of hydrogen concentration are shown in comparison.

As shown in Table 1, the estimated value of the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining calculated by the formula (1) and the measured hydrogen concentration in the molten steel before vacuum degassing refining The value is consistent with high accuracy even if the amount of auxiliary raw material used varies greatly, and the hydrogen concentration ([H] ₀ ) in molten steel before vacuum degassing refining can be estimated with high accuracy by equation (1). was confirmed. Furthermore, when using the formula (2), the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining can be estimated more accurately than when using the formula (1). It could be confirmed.

In addition, Table 2 shows the hydrogen concentration in molten steel before degassing refining (actual value) and the hydrogen concentration in molten steel during degassing refining (actual value) in Examples 1 to 16 of the present invention and Comparative Examples 1 to 10, and degassing. Gas refining time (estimated time and actual time), showing reduced refining time. In addition, in Examples 1 to 8 of the present invention, the amount of the calcined lime-containing auxiliary raw material and the calcined lime-free auxiliary raw material used in the converter and ladle refining furnace, and the amount of the calcined lime-containing auxiliary raw material and the calcined lime-free auxiliary raw material The hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining calculated from the amount used by the formula (1) is shown. In addition, in Examples 9 to 16 of the present invention, the amount of the calcined lime-containing auxiliary raw material and the calcined lime-free auxiliary raw material used in the converter and ladle refining furnace, and the amount of the calcined lime-containing auxiliary raw material and the calcined lime-free auxiliary raw material The hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining calculated from the amount used by the formula (2) is shown. Here, the "estimated time" of the degassing refining time in Table 2 is the elapsed time (t) calculated by the formula (8'). In addition, the “reduced refining time” in Table 2 indicates a time shortened from the refining time of 20 minutes in Comparative Examples 7 to 10, which is the refining time preset according to the hydrogen concentration standard for the steel type. . Further, the refining cost shown in Table 2 is the result of evaluating the refining cost in the conventional refining method according to the following criteria.

<Degassing refining cost evaluation criteria>
◎；Large cost reduction (no use of hydrogen measurement probe and shortened refining time of 3 minutes or more)
○: Cost reduction in progress (hydrogen measurement probe not used and refining time shortened from 1 minute to less than 3 minutes)
△: Small cost reduction (use of hydrogen measurement probe and shortened refining time of 3 minutes or more)
×; No cost reduction (use of hydrogen measurement probe and reduced refining time of less than 3 minutes, or no use of hydrogen measurement probe and reduced refining time of less than 1 minute)

In Examples 1 to 16 of the present invention, the hydrogen concentration in molten steel could be accurately estimated without measuring the hydrogen concentration in the molten steel, and the vacuum degassing refining could be completed near the target hydrogen concentration. As a result, the refining cost was not increased, and the refining time was shortened while significantly reducing the refining cost. In particular, better results were obtained in Examples 9 to 16 in which the formula (2) was used to estimate the hydrogen concentration ([H] ₀ ) in the molten steel before vacuum degassing refining. Further, in Examples 1 to 16 of the present invention, the actual degassing refining time was 1.1 times or less the estimated degassing refining time calculated by the formula (8′).

On the other hand, the hydrogen concentration of molten steel was actually measured, and vacuum degassing refining was performed based on the measured hydrogen concentration. In Comparative Examples 3 to 6, the refining time was shortened, but the refining cost increased due to the use of a probe for hydrogen concentration analysis. In addition, in Comparative Examples 7 to 10, the refining time was set long so as not to exceed the target hydrogen concentration, so the dehydrogenation process was performed excessively.

1 RH vacuum degassing device 2 ladle 3 molten steel 4 slag 5 vacuum tank 6 upper tank 7 lower tank 8 rising side dipping pipe 9 descending dipping pipe 10 reflux gas blowing pipe 11 duct 12 raw material inlet 13 top blowing lance D rise Inner diameter of side immersion tube d Inner diameter of _L vacuum chamber

Claims (9)

A method for estimating the hydrogen concentration in molten steel before the molten steel is subjected to vacuum degassing refining for removing hydrogen in the molten steel under reduced pressure, comprising:
Estimate the hydrogen concentration in the molten steel before vacuum degassing refining without actual measurement using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable ,
A method for estimating the concentration of hydrogen in molten steel, characterized by using the following formula (2) as a function with the amount of auxiliary raw materials used in the steel refining process as a variable.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual auxiliary raw materials, α is a correction constant, the calcined lime-containing auxiliary raw material contains free lime, and the calcined lime-free auxiliary raw material contains free lime. The raw material does not contain free lime. 2. The method for estimating hydrogen concentration in molten steel according to claim 1 , wherein at least one of said influence coefficient and said correction constant is determined by regression analysis of past operational data. A vacuum degassing refining method for molten steel for refining molten steel under reduced pressure to remove hydrogen in the molten steel, comprising:
Estimate the hydrogen concentration in the molten steel before vacuum degassing refining without actual measurement using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable,
Furthermore, the hydrogen concentration in the molten steel during vacuum degassing refining is estimated sequentially using the dehydrogenation model formula, and the hydrogen concentration estimated by the dehydrogenation model formula is used without exceeding the refining time according to the hydrogen concentration standard for the steel type. Vacuum degassing refining will be terminated when the concentration of hydrogen becomes less than the target hydrogen concentration,
A vacuum degassing refining method for molten steel, wherein the following formula (2) is used as a function with the amount of auxiliary raw materials used in the steel refining process as a variable.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual auxiliary raw materials, α is a correction constant, the calcined lime-containing auxiliary raw material contains free lime, and the calcined lime-free auxiliary raw material contains free lime. The raw material does not contain free lime. 4. The vacuum degassing refining method of molten steel according to claim 3 , wherein at least one of said influence coefficient and said correction constant is determined by regression analysis of past operational data. The method for vacuum degassing refining of molten steel according to claim 3 or 4 , wherein the following equations (3) and (4) are used as the dehydrogenation model equations.
[H]={[H] ₀ −[H] _e }×exp(−K _H ×t)+[H] _e (3)
[H] _e = 10 ^{- (1905/T) - 1.591} x P ^1/2 (4)
Here, in the formula (3), [H] is the hydrogen concentration (mass ppm) in the molten steel during vacuum degassing refining, [H] ₀ is the use of auxiliary raw materials in the steelmaking refining process prior to vacuum degassing refining. Hydrogen concentration (mass ppm) in molten steel before vacuum degassing refining estimated using a function with quantity as a variable, [H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum tank, K _H is the dehydrogenation rate constant (1/min) in vacuum degassing refining, t is the elapsed time (min) from the start of vacuum degassing refining, and in equation (4), [H] _e is The equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, T is the molten steel temperature (K) during vacuum degassing refining, and P is the pressure (atm) in the vacuum chamber. The vacuum degassing refining is vacuum degassing refining in an RH vacuum degassing apparatus, and the dehydrogenation rate constant (K _H ) is calculated using the following equations (5), (6) and (7). The method for vacuum degassing refining of molten steel according to claim 5 , characterized in that the determination is made as follows.
_KH =(Q/V)×{ak/(Q+ak)} (5)
Q=11.4×G1 ^/3 ×D4 ^/3 ×{ln( _P1 /P)} ^1/3 / _ρL (6)
ak=2500× _DH1 ^/2 ×(G× ^10-3 ) ^1/2 × _dL /2 (7)
Here, in equations (5), (6) and (7), _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, Q is the molten steel circulation flow rate to the vacuum tank (m ³ /min), V is the volume of molten steel to be vacuum degassed (m ³ ), ak is the dehydrogenation reaction capacity coefficient (m ³ /min), and G is the flow rate of reflux gas (NL/min). , D is the inner diameter of the ascending immersion tube (m), P ₁ is the atmospheric pressure (atm), P is the pressure in the vacuum chamber (atm), ρ _L is the density of molten steel (ton/m ³ ), D _H is the diffusion coefficient of hydrogen in molten steel (m ² /min), and _dL is the inner diameter (m) of the vacuum chamber. The hydrogen concentration of the molten steel is measured during the vacuum degassing refining prior to the vacuum degassing refining, the change in hydrogen concentration over time is obtained from the measured hydrogen concentration, and the dehydrogenation rate constant is determined based on the change in hydrogen concentration over time. (K _H ) is determined in advance, and the hydrogen concentration in the molten steel during vacuum degassing refining is sequentially estimated using the predetermined dehydrogenation rate constant (K _H ). A method for vacuum degassing refining of molten steel as described. A vacuum degassing refining method for molten steel for refining molten steel under reduced pressure to remove hydrogen in the molten steel, comprising:
Estimate the hydrogen concentration in the molten steel before vacuum degassing refining using a function with the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining as a variable,
The vacuum degassing refining is performed without exceeding the refining time according to the hydrogen concentration standard for the steel type, and the estimated hydrogen concentration in the molten steel before vacuum degassing refining and the hydrogen concentration in the molten steel after vacuum degassing refining It is decided to end when the condition of the following formula (8) obtained from the target value is satisfied,
A vacuum degassing refining method for molten steel, wherein the following formula (2) is used as a function with the amount of auxiliary raw materials used in the steel refining process as a variable.
t≧(1/K _H )×ln{([H] ₀ −[H] _e )/([H] _f −[H] _e )} (8)
Here, in formula (8), t is the elapsed time (min) from the start of vacuum degassing refining, and [H] ₀ is the amount of auxiliary raw materials used in the steelmaking refining process prior to vacuum degassing refining. The hydrogen concentration in the molten steel before vacuum degassing refining (mass ppm), [H _] , estimated using the function to H] _e is the equilibrium hydrogen concentration (mass ppm) at the molten steel interface in the vacuum chamber, _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, ln is the natural logarithm.
[H] ₀ = a ₁ ×w ₁ +a ₂ ×w ₂ +a ₃ ×w ₃ +a ₄ ×w ₄ +α (2)
Here, in equation (2), [H] ₀ is the hydrogen concentration (mass ppm) in the molten steel before vacuum degassing refining, and w ₁ is the calcination per unit mass of molten steel in refining in a converter or electric furnace. The total amount of lime-containing auxiliary materials added (kg/ton), w ₂ is the content of calcined lime per unit mass of molten steel in the steelmaking refining process from converter or electric furnace tapped steel to before the start of vacuum degassing refining Total additive amount of auxiliary raw materials (kg/ton), w ₃ is the total additive amount of auxiliary raw materials not containing calcined lime per unit mass of molten steel in refining in a converter or electric furnace (kg/ton), w ₄ is the total addition amount of non-calcined lime-containing auxiliary materials per unit mass of molten steel (kg/ton) in the steelmaking refining process from converter or electric furnace output steel to before the start of vacuum degassing refining, a ₁ , a ₂ , a ₃ , and a ₄ are influence coefficients determined by the types and management conditions of individual auxiliary raw materials, α is a correction constant, the calcined lime-containing auxiliary raw material contains free lime, and the calcined lime-free auxiliary raw material contains free lime. The raw material does not contain free lime. The vacuum degassing refining is vacuum degassing refining in an RH vacuum degassing apparatus, and the dehydrogenation rate constant (K _H ) is calculated using the following equations (5), (6) and (7). The vacuum degassing refining method of molten steel according to claim 8 , characterized in that it is determined by
_KH =(Q/V)×{ak/(Q+ak)} (5)
Q=11.4×G1 ^/3 ×D4 ^/3 ×{ln( _P1 /P)} ^1/3 / _ρL (6)
ak=2500× _DH1 ^/2 ×(G× ^10-3 ) ^1/2 × _dL /2 (7)
Here, in equations (5), (6) and (7), _KH is the dehydrogenation rate constant (1/min) in vacuum degassing refining, Q is the molten steel circulation flow rate to the vacuum tank (m ³ /min), V is the volume of molten steel to be vacuum degassed (m ³ ), ak is the dehydrogenation reaction capacity coefficient (m ³ /min), and G is the flow rate of reflux gas (NL/min). , D is the inner diameter of the ascending immersion tube (m), P ₁ is the atmospheric pressure (atm), P is the pressure in the vacuum chamber (atm), ρ _L is the density of molten steel (ton/m ³ ), D _H is the diffusion coefficient of hydrogen in molten steel (m ² /min), and _dL is the inner diameter (m) of the vacuum chamber.

Images