JP7043915B2 - Method of raising the temperature of molten steel - Google Patents

Description

The present application discloses a method for raising the temperature of molten steel by blowing oxygen onto the surface of molten steel under reduced pressure in the vacuum chamber of the RH vacuum degassing device.

In the secondary smelting process after converter steelmaking, the composition of molten steel is adjusted, degassing treatment, etc. are performed, but since the molten steel temperature drops significantly during the processing, the molten steel temperature is adjusted to an appropriate temperature for casting, which is the next process. The temperature rise process is performed for the purpose. As a general method for raising the temperature of molten steel, in a recirculation type vacuum degassing device equipped with a vacuum chamber typified by RH, oxygen is blown onto the surface of the molten steel from a top-blown lance in the vacuum chamber and reacted with Al in the molten steel. A method of utilizing the heat of oxidation can be mentioned.

When trying to improve the acidation rate in the temperature raising process, it is generally effective to control the top-blown oxygen jet to hard blow. For example, in Patent Document 1, when the oxygen supply pressure is constant and the ratio of the pressure to the degree of vacuum is larger than the Mach number calculated from the ratio of the nozzle throat area to the nozzle discharge port area, the decarburization rate is improved, and conversely. If it is made smaller, the heat of the molten metal can be efficiently increased. In the former case, the oxygen jet can be properly expanded at the nozzle outlet and hard blowed to improve the acidation rate, and in the latter case, the jet is used as a soft blow to cause a secondary combustion reaction with CO. The idea is that the temperature of the molten metal can be raised efficiently by making the molten metal warm.

However, if the oxygen jet is hard blown during the decarburization period, the furnace wall is significantly worn due to severe molten steel scattering (molten steel splash), and the molten steel is in a peroxidized state and FeO is excessively generated. Further, on the premise of molten steel containing a large amount of Al, the secondary combustion reaction cannot be utilized because CO gas is hardly generated, and it is difficult to heat the molten steel according to the idea described in Patent Document 1.

In response to the problem of molten steel splash during acid feeding, in Patent Document 2, the throat diameter of the Laval nozzle is set to 30 to 80 mm and the outlet diameter is set to 80 to 140 mm, so that the dynamic pressure of the jet is not too high and not too low. It is said that it can be controlled to a large extent and the molten steel splash during acid feeding can be greatly reduced.

However, the jet jet behavior due to the rubber lance is greatly affected by factors such as the oxygen flow rate and the degree of vacuum in addition to the nozzle diameter. Therefore, even if the nozzle shape is controlled within the range of Patent Document 2, the molten steel splash is not necessarily suppressed. I can't do it.

On the other hand, depending on the oxygen supply conditions to the molten steel, Si, Mn and Fe may be burned in addition to Al to form lower oxides such as SiO ₂ , MnO and FeO. In addition to significantly promoting the melting damage of refractories, such lower oxides increase the degree of oxidation of the slag by being absorbed by the ladle slag, which also has adverse effects such as reoxidation and desulfurization of the molten steel. Cause. For example, in Patent Document 3, the ratio of the flow rate of the oxygen gas to be blown and the ring flow rate of the molten steel is adjusted to an appropriate range, and the atmospheric pressure in the vacuum chamber before the heat treatment is changed stepwise in the vacuum chamber. A method for heating molten steel, which is characterized by controlling the stirring of the gas, is disclosed. This technology suppresses the formation of lower oxides by suppressing local Al deficiency by promoting the supply of Al to the reaction region. The pressure is reduced toward the end of the treatment, which makes it difficult to suppress Al deficiency due to the decrease in the Al concentration of the molten steel, and the stirring is strengthened, aiming at the reduction of lower oxides.

However, the index of ring flow rate is an index for describing the circulation of molten steel in the entire RH vacuum degassing device, and the ratio of oxygen gas flow rate to ring flow rate describes in detail the local mixing in the vacuum chamber. Can't. Further, the degree of vacuum varies greatly on the low pressure side, and it takes time from the start of exhaust to reach a predetermined pressure, so that it is extremely difficult to precisely control the degree of vacuum according to the refining time.

Japanese Unexamined Patent Publication No. 4-59913 Japanese Unexamined Patent Publication No. 2017-75399 Japanese Patent No. 4277819

With the conventional method as described above, there is a problem that it is difficult to obtain a high temperature rise efficiency while suppressing adverse effects such as the formation of molten steel splash and lower oxides generated at the time of acid feeding.

The present application is a method of spraying oxygen on the surface of molten steel under reduced pressure to raise the temperature of the molten steel in a vacuum chamber of an RH vacuum degassing device as one of means for solving the above-mentioned problems. The tip shape of the spraying lance consists of a throat portion with a diameter D _t (m) and a conical enlarged portion with an outlet diameter _De (m), and the appropriate nozzle front pressure P ₀ ^* obtained from the following formula (1). Disclosed is a method for raising the temperature of molten steel so that the ratio P ₀ / P ₀ ^* of (Pa) and the operating nozzle pre-pressure P ₀ (Pa) obtained from the following formula (2) is 0.408 or more and 0.718 or less. ..

(D _t / De _e ) ⁴ = 14.92 × (P _e / P ₀ ^* ) ^1.43 × {1- (P _e / P ₀ ^* ) ^0.286 }… (1)
P ₀ = P _e + 12.89 × Q _T / D _t ² … (2)
(Here, _Pe : Vacuum chamber pressure (Pa), _QT : Top-blown oxygen flow rate (Nm ³ / min).)

In the method for raising the temperature of molten steel of the present disclosure, the stirring power ε _T (W) of the molten steel in the vacuum chamber by the oxygen jet top-blown from the lance obtained by the following equations (3) and (4) and the following equation (5). The ratio ε _T / ε _B to the stirring power ε _B (W) of the molten steel in the vacuum chamber by the gas blown for the purpose of the molten steel recirculation of the RH vacuum degassing device obtained from Is preferable.

ε _T = 5.24 × 10 ³ × Q _T D _t M ² / _HT … (3)
M = [5 × {(P ₀ / P _e ) ^0.285 -1}] ^0.5 ... (4)
ε _B = 6.18 × Q _B T {2.3 log (1 + ρH _B / P _e ) + (1-T _g / T)}… (5)
(Here, M: Mach number of top-blown oxygen jet, HT: Lance-hot water surface distance (m), Q _B : Circulating gas flow rate (Nm ³ / min), _T : Molten steel temperature (K), ρ: Molten steel density (kg / m ³ ), H _B : Circulation gas blowing tuyere-distance between molten steel molten metal surface in vacuum tank (m), T _g : Recirculation gas temperature (K).

According to the method for raising the temperature of molten steel of the present disclosure, the ratio of the appropriate nozzle pre-pressure to the operating nozzle pre-pressure is controlled within a predetermined range, and the expansion state of the oxygen jet in the vicinity of the nozzle is controlled to send acid. It is possible to obtain high heating efficiency while suppressing adverse effects such as the generation of molten steel splash and lower oxides that sometimes occur.

It is a figure which shows the relationship between Al combustion rate and P ₀ / P ₀ ^* . It is a figure which shows the relationship between the refractory wear rate and P ₀ / P ₀ ^* . In the figure, ◯, Δ, and × correspond to ◯, Δ, and × in FIG. 1, respectively. It is a figure which shows the relationship between the temperature rise rate and ε _T / ε _B. In the figure, ◯, Δ, and × correspond to ◯, Δ, and × in FIGS. 1 and 2, respectively.

1. 1. Definition of terms In the present application, "circulation" refers to introducing recirculation gas from a dipping tube in an RH vacuum degassing device to recirculate molten steel, and "OB (Oxygen Blooming) treatment" means in a vacuum chamber. It refers to the process of spraying oxygen from the lance onto the surface of the molten steel, reacting it with Al in the molten steel, and raising the temperature of the molten steel by the heat of the reaction. The "reaction region" refers to a region in which oxygen blown over the surface of the molten steel and the molten steel component directly react with each other, and the "lower oxide" refers to Si, Mn, and Mn, which have a weaker affinity for O than Al. Refers to an oxide produced by the reaction of Fe with O.

2. 2. Details of the method for raising the temperature of molten steel In the Laval nozzle, considering the continuous equation from the throat to the outlet and the equation of the isentropic flow, the ratio D _t / De _e of the throat diameter to the outlet diameter and the atmospheric pressure (vacuum tank). The ratio P _e / P ₀ ^* between the internal pressure) and the proper nozzle pre-pressure holds the relationship shown in the following equation (1) (for example, E. Lavalschnan et al .: "Theory of compressive flow (Maruzen Publishing)). (Issued on June 15, H20). Looking at the following equation (1), it can be seen that if D _t , De and _Pe are determined, the appropriate _nozzle front pressure P ₀ ^* is uniquely determined.
(D _t / De _e ) ⁴ = 14.92 × (P _e / P ₀ ^* ) ^1.43 × {1- (P _e / P ₀ ^* ) ^0.286 }… (1)

In addition, the nozzle pre-pressure P ₀ in actual operation can be obtained from the empirical formula shown in the following formula (2) as a function of the top-blown oxygen flow rates Q _T and D _t (Otani et al .: Iron and Steel, 62 (1976)). , 1795.).
P ₀ = P _e + 12.89 × Q _T / D _t ² … (2)

It is generally known that the jet expands properly under the condition that P ₀ ^* and P ₀ are equal, and the dynamic pressure of the jet becomes the highest, that is, hard blow. However, according to the findings of the present inventors, the hard blow of the jet significantly increases the molten steel splash and promotes Al deficiency near the reaction region where oxygen is blown, resulting in lower oxides. It will significantly increase the production. For this reason, the present inventors intentionally remove the nozzle prepressure from the appropriate expansion conditions and control P ₀ / P ₀ ^* to an appropriate range to increase the heat rise rate without increasing the molten steel splash. I found that it could be improved.

On the other hand, in order to further suppress the formation of lower oxides, it is important to discharge the oxygen absorbed in the molten steel to the outside of the vacuum chamber by the flow of the molten steel and uniformly disperse it throughout the apparatus. The present inventors control the dispersed state of absorbed oxygen by controlling the stirring power density of the molten steel in the vacuum chamber by the top-blown oxygen jet and the recirculation gas, and the balance ε _T / ε _B of ε _T and ε _B. I found out what I could do. This is because the oxygen concentration in the vicinity of the reaction region is determined by the balance between the rate at which oxygen is absorbed and the rate at which the absorbed oxygen moves from the reaction region, and these are generally correlated with the stirring power density. Because there is.

As described above, as a result of repeated diligent studies, the present inventors have completed the method for raising the temperature of molten steel described below.

That is, the method for raising the temperature of the molten steel of the present disclosure is a method of spraying oxygen on the surface of the molten steel under reduced pressure in the vacuum chamber of the RH vacuum degassing device to raise the temperature of the molten steel, and the tip of the lance for blowing the oxygen. The shape consists of a throat portion with a diameter D _t (m) and a conical enlarged portion with an outlet diameter _De (m), and the appropriate nozzle front pressure P ₀ ^* (Pa) obtained from the following equation (1). It is characterized in that the ratio P ₀ / P ₀ ^* with the operating nozzle front pressure P ₀ (Pa) obtained from the following equation (2) is 0.4 or more and 0.75 or less.

(D _t / De _e ) ⁴ = 14.92 × (P _e / P ₀ ^* ) ^1.43 × {1- (P _e / P ₀ ^* ) ^0.286 }… (1)
P ₀ = P _e + 12.89 × Q _T / D _t ² … (2)
(Here, _Pe : Vacuum chamber pressure (Pa), _QT : Top-blown oxygen flow rate (Nm ³ / min).)

The closer the ratio P ₀ / P ₀ ^* of the proper nozzle pre-pressure P ₀ ^* (Pa) to the operating nozzle pre-pressure P ₀ (Pa) is to 1, the more proper the oxygen jet expands and the hard blow becomes. However, as described above, when P ₀ / P ₀ ^* is excessively increased, the splash of molten steel is remarkably increased, and Al deficiency in the vicinity of the reaction region where oxygen is blown is promoted, so that the lower oxide It will significantly increase the production. On the other hand, if P ₀ / P ₀ ^* is excessively lowered, the oxygen jet becomes a soft blow and the absorption rate of oxygen into the molten steel is significantly lowered. The present inventors OB-treated 250 ton of molten steel with an RH vacuum degassing device according to the method for confirming the effect described later, and investigated the relationship between Al combustion rate and refractory wear rate and P ₀ / P ₀ ^* . did. The results are shown in FIGS. 1 and 2. It can be seen that in the range of P ₀ / P ₀ ^* of 0.4 or more and 0.75 or less, the Al combustion rate is high and the refractory wear rate is low. Therefore, in order to solve the above problems, it is necessary to control P ₀ / P ₀ ^* in the range of 0.4 or more and 0.75 or less. The lower limit of P ₀ / P ₀ ^* is preferably 0.45 or more, more preferably 0.50 or more, and the upper limit is preferably 0.70 or less, more preferably 0.60 or less.

In the method for raising the temperature of the molten steel of the present disclosure, the stirring power ε _T (W) of the molten steel in the vacuum chamber by the oxygen jet top-blown from the lance obtained by the following equations (3) and (4) and the following equation (5). ), The ratio ε _T / ε _B to the stirring power ε _B (W) of the molten steel in the vacuum chamber by the gas blown for the purpose of recirculating the molten steel of the RH vacuum degassing device is 0.3 or more and 0.6 or less. It is preferable to do so.

ε _T = 5.24 × 10 ³ × Q _T D _t M ² / _HT … (3)
M = [5 × {(P ₀ / P _e ) ^0.285 -1}] ^0.5 ... (4)
ε _B = 6.18 × Q _B T {2.3 log (1 + ρH _B / P _e ) + (1-T _g / T)}… (5)
(Here, M: Mach number of top-blown oxygen jet, HT: Lance-hot water surface distance (m), Q _B : Circulating gas flow rate (Nm ³ / min), _T : Molten steel temperature (K), ρ: Molten steel density (kg / m ³ ), H _B : Circulation gas blowing tuyere-distance between molten steel molten metal surface in vacuum tank (m), T _g : Recirculation gas temperature (K).

The oxygen concentration in the vicinity of the reaction region where oxygen is blown is determined by the balance between the rate at which oxygen is absorbed and the rate at which the absorbed oxygen moves from the reaction region. Therefore, it was considered that there is a constant phase between ε _T / ε _B and the rate of temperature rise, which is the ratio of the stirring power given to the molten steel in the vacuum chamber by the top-blown oxygen jet and the recirculation gas. Therefore, the present inventors performed OB treatment under the condition that ε _T / ε _B was changed within the range where P ₀ / P ₀ ^* was 0.4 or more and 0.75 or less, and measured the temperature rise rate. .. The results are shown in FIG. It was found that the rate of temperature rise shows a high value in the range of ε _T / ε _B of 0.3 or more and 0.6 or less. This is because when ε _T / ε _B is less than 0.3, the dynamic pressure of the jet becomes low and the acidation rate drops significantly, and when it exceeds 0.6, the energy of the jet becomes excessive and it is due to the reflux gas. It is probable that the flow of molten steel was hindered and the absorbed oxygen was not efficiently dispersed. Therefore, ε _T / ε _B is preferably in the range of 0.3 or more and 0.6 or less. The lower limit is more preferably 0.4 or more, still more preferably 0.45 or more.

3. 3. Supplement: OB processing conditions If the degree of vacuum Pe in the vacuum chamber is too high, the jet jet that has been injected _entrains the atmosphere and is greatly attenuated, resulting in a significant decrease in temperature rise efficiency. From this point of view, Pe is usually less than 13.3 _kPa (100 Torr) at the time of oxygen top blowing, and it is desirable to control it to such a value even in the method for raising the temperature of molten steel of the present disclosure. As is clear from the above equations (1) and (2), in the method for raising the temperature of the molten steel of the present disclosure, the tip shape of the _lance (D _t , D) is set to a specific value in this way. By adjusting the top-blown oxygen flow rate _QT according to _e ), P ₀ / P ₀ ^* can be controlled in the range of 0.4 or more and 0.75 or less.

Generally, if the lance height _HT at the time of oxygen blow is too low, it becomes an ultra-hard blow and the metal is likely to adhere to the molten steel splash and the lance, and conversely, if it is too high, it becomes a soft blow and the oxygen absorption rate decreases. The jet collides with the inner wall surface of the vacuum chamber, and it is easy to accelerate the wear of refractory materials. Therefore, it is desirable that the _HT is in the range of 2.0 m or more and 5.0 m or less in normal operation.

Further, the higher the absolute value of the nozzle front pressure P ₀ , the harder the jet becomes, and the higher the oxygen absorption rate becomes. Therefore, in addition to setting P ₀ / P ₀ ^* to 0.4 or more and 0.75 or less, it is desirable to set the absolute value of P ₀ to 0.1 MPa or more.

Further, the stirring power density of the molten steel in the vacuum chamber greatly affects the distance HB between the _tuyere for blowing the reflux gas and the molten steel surface in the vacuum chamber. This value can be controlled by adjusting the immersion depth of the vacuum tank immersion pipe in the ladle molten steel, the degree of vacuum in the tank, that is, the suction height of the molten steel. Although it depends on the operating conditions, the value of _HB is usually about 1.5 m or more and 3.0 m or less, and it is desirable to control it to this extent even in the method for raising the temperature of molten steel of the present disclosure.

As the RH vacuum degassing device itself used in the method for raising the temperature of molten steel of the present disclosure, any known device can be adopted. As for the top-blown lance, any general lance can be adopted as long as the tip shape has the above-mentioned throat portion and enlarged portion. Since these configurations are self-explanatory, detailed description thereof will be omitted here.

Further, as for the molten steel applied to the method for raising the temperature of the molten steel of the present disclosure, any general carbon steel excluding high alloys such as stainless steel can be adopted via the RH vacuum degassing process after the converter is ejected. be. Since the molten steel after the transfer from the converter contains Al and the like, the molten steel can be appropriately heated by reacting Al with oxygen by the method of the present disclosure.

Hereinafter, the method for raising the temperature of the molten steel of the present disclosure will be described in more detail with reference to Examples and Comparative Examples.

1. 1. Evaluation Criteria The method for raising the temperature of molten steel according to the examples and comparative examples shown below is evaluated using three indexes: Al combustion rate (ratio of top-blown oxygen reacting with Al), refractory wear rate, and temperature rise rate. did.

1.1. Al combustion rate The Al combustion rate was calculated using the following formulas (6) and (7) from the Al concentration [Al] (mass%) obtained by collecting molten steel samples immediately before and after the OB treatment and performing chemical analysis. ..

Al combustion rate = ([Al] _{before OB-} [Al] _{after OB} ) / OB amount ... (6)
OB amount = 32 x 100 x _QT x OB time / 22.4 / molten steel mass ... (7)

Here, the OB amount is a value obtained by converting the total oxygen amount blown up into the concentration in the molten steel, and the Al combustion rate indicates the ratio of the total oxygen amount blown up to be used for burning Al. A low value means that a large amount of oxygen was used for exhaust loss or the formation of lower oxides, leading to a decrease in the rate of temperature rise and wear of refractories due to the lower oxides. Therefore, it is desirable that the Al combustion rate is 70% or more.

1.2. Refractory wear rate For the refractory wear rate, 100 channels of OB treatment were performed under the same conditions, and the amount of decrease in the wall thickness of the refractory on the inner wall of the vacuum tank between the lower end of the lance and the surface of the molten metal was divided by the number of channels. It was set as a value. The main factors for wear of refractory refractories are the adhesion of bare metal due to the splash during acid transfer and the erosion due to the chemical reaction between the lower oxide and the refractory. I thought it was suitable for the evaluation of. Further, although it depends on the size of the vacuum tank used, the thickness of the refractory on the furnace wall is often several hundred mm, and when considering the continuous use of the tank for several hundred channels, the rate of wear of the refractory is 3. It is desirable that it is 0 mm / ch or less.

1.3. Temperature rise rate The temperature rise rate was set to a value obtained by the following formula (8) from the temperature at which the temperature of the molten steel was measured with an oxygen probe immediately before and after the OB treatment. If the temperature rise rate is slow, the treatment time is significantly extended and the oxygen intensity is increased. Therefore, the temperature rise rate is preferably 3.0 ° C./min or more.

Temperature rise rate = ( _after TOB- _before TOB) / OB time ... (8)

As described above, in the examples and comparative examples shown below, the Al combustion rate was 70% or more, the refractory wear rate was 3.0 mm / ch or less, and the temperature rise rate was 3.0 ° C./min or more. It was judged that the desired effect was obtained, and in addition to these, those having a temperature rising rate of 4.0 ° C./min or more were judged to have obtained the desired effect particularly remarkably.

2. 2. Method for raising the temperature of molten steel according to Examples and Comparative Examples After the molten steel that has been blown in a converter is put out in a pan, a vacuum tank equipped with a top-blown lance is inserted into the molten steel in the pan, and the molten steel is sucked. The recirculation treatment was started, and the OB treatment was started at an arbitrary timing. In both Examples and Comparative Examples, the amount of molten steel was 250 ton scale, and the molten steel temperature was 1600 to 1640 ° C. During OB processing, vacuum chamber pressure P _e , nozzle throat diameter D _t , outlet diameter D _e , top blown oxygen flow rate Q _T , recirculation gas flow rate Q _B , lance-to-water surface distance _HT , recirculation gas blowing tuyere. _-The distance between the molten steel surfaces in the vacuum chamber HB was changed as an operating factor as shown in Tables 1 and 2 below. For simplification of calculation, the molten steel density ρ when calculating ε _B is constant at 7000 kg / m ³ , the molten steel temperature T is 1873 K, and the reflux gas temperature T g is 300 K, and other refining conditions are as follows. did.

Molten steel composition before OB treatment:
[C]: 0.05 to 0.20% by mass
[Si]: 0.05 to 0.50% by mass
[Mn]: 0.30 to 1.00 mass%
[Al]: 0.10 to 0.20% by mass
OB processing time: 10 min

A molten steel sample was taken before and after the OB treatment, and a part of the sample was subjected to chemical analysis to obtain the Al concentration before and after the OB treatment, and the Al combustion rate was calculated from the above formulas (6) and (7). Further, the amount of decrease in the wall thickness of the refractory in the vacuum chamber was measured at the timing when the OB treatment was carried out for 100 channels under the same conditions, and the wear rate of the refractory was calculated. Further, in addition to the molten steel sample, the temperature was measured with an oxygen probe before and after the OB treatment, and the temperature rise rate was calculated from the above formula (8). The Al combustion rate and the refractory wear rate in Examples and Comparative Examples are shown in Table 1 below, and the values of the temperature rise rate are shown in Table 2 below.

As is clear from the results shown in Tables 1 and 2, when P ₀ / P ₀ ^* is 0.4 or more and 0.75 or less, the Al combustion rate, the refractory wear rate, and the temperature rise rate are all good. The result was (Examples 1 to 7). In particular, when P ₀ / P ₀ ^* was set to 0.4 or more and 0.75 or less, and at the same time, ε _T / ε _B was set to 0.3 or more and 0.6 or less, the heating rate was significantly increased (implemented). Examples 1-5). In Example 6, it is probable that ε _T / ε _B was small, the dynamic pressure of the top-blown oxygen jet was low, and the absorption rate of oxygen into the molten steel was slightly low. On the other hand, in Example 7, the Al combustion rate was slightly low because the ε _T / ε _B was large and the top-blown oxygen jet obstructed the flow of the molten steel in the vacuum chamber and the absorbed oxygen was not efficiently dispersed. It is probable that it was. When trying to maximize the desired effect in this way, it is desirable to control not only P ₀ / P ₀ ^* but also ε _T / ε _B.

On the other hand, as is clear from the results shown in Tables 1 and 2, when P ₀ / P ₀ ^* is set to less than 0.4 or more than 0.75, the desired effect cannot be obtained (Comparative Example). 1-4). In Comparative Example 1, it is considered that the pressure in the vacuum chamber was high, the oxygen jet ejected from the nozzle was significantly attenuated, and the oxygen was not efficiently absorbed due to the decrease in dynamic pressure. On the contrary, in Comparative Example 2, P ₀ / P ₀ ^* was very high and the oxygen jet was a hard blow, and in addition to the remarkable combustion of molten steel components other than Al, a large amount of molten steel splash was generated. As a result, the rate of wear of refractories has increased significantly. In Comparative Example 3, since P ₀ / P ₀ ^* was extremely low, the jet attenuation was remarkable, and it is considered that oxygen was not efficiently absorbed due to the decrease in dynamic pressure as in Comparative Example 1. Further, in Comparative Example 4, in addition to the low P ₀ / P ₀ ^* , the ε _T / ε _B was too high, so that both absorption of oxygen into the molten steel and dispersion of the absorbed oxygen were insufficient. The desired effect was not obtained.

As described above, in the method of spraying oxygen on the molten steel surface under reduced pressure to raise the temperature of the molten steel in the vacuum chamber of the RH vacuum degassing device, adverse effects such as the formation of molten steel splash and lower oxides generated during acid feeding are suppressed. In order to obtain high temperature rise efficiency, it is important to set P ₀ / P ₀ ^* to 0.4 or more and 0.75 or less. In addition to setting P ₀ / P ₀ ^* to 0.4 or more and 0.75 or less, setting ε _T / ε _B to 0.3 or more and 0.6 or less ensures higher temperature rise efficiency. can.

The method for raising the temperature of molten steel of the present disclosure can be used in the secondary refining step after converter steelmaking to adjust the molten steel temperature to be appropriate for casting, which is the next step.

Claims (2)

In the vacuum chamber of the RH vacuum degassing device, oxygen is blown onto the surface of the molten steel under reduced pressure to raise the temperature of the molten steel.
The tip shape of the lance that blows oxygen consists of a throat portion with a diameter of D _t (m) and a conical enlarged portion with an outlet diameter of _De (m).
The ratio P ₀ / P ₀ ^* of the proper nozzle front pressure P ₀ ^* (Pa) obtained from the following formula (1) and the operating nozzle front pressure P ₀ (Pa) obtained from the following formula (2) is 0.408 or more. 0.718 or less,
How to raise the temperature of molten steel.
(D _t / De _e ) ⁴ = 14.92 × (P _e / P ₀ ^* ) ^1.43 × {1- (P _e / P ₀ ^* ) ^0.286 }… (1)
P ₀ = P _e + 12.89 × Q _T / D _t ² … (2)
(Here, _Pe : Vacuum chamber pressure (Pa), _QT : Top-blown oxygen flow rate (Nm ³ / min).) The stirring power ε _T (W) of the molten steel in the vacuum chamber by the oxygen jet blown from the lance obtained by the following formulas (3) and (4) and the molten steel of the RH vacuum degassing device obtained from the following formula (5). The ratio ε _T / ε _B to the stirring power ε _B (W) of the molten steel in the vacuum chamber by the gas blown for the purpose of recirculation shall be 0.3 or more and 0.6 or less.
The method for raising the temperature of molten steel according to claim 1.
ε _T = 5.24 × 10 ³ × Q _T D _t M ² / _HT … (3)
M = [5 × {(P ₀ / P _e ) ^0.285 -1}] ^0.5 ... (4)
ε _B = 6.18 × Q _B T {2.3 log (1 + ρH _B / P _e ) + (1-T _g / T)}… (5)
(Here, M: Mach number of top-blown oxygen jet, HT: Lance-hot water surface distance (m), Q _B : Circulating gas flow rate (Nm ³ / min), _T : Molten steel temperature (K), ρ: Molten steel density (kg / m ³ ), H _B : Circulation gas blowing tuyere-distance between molten steel molten metal surface in vacuum tank (m), T _g : Recirculation gas temperature (K).

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