JP2003138308A - Method for blowing molten stainless steel in converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently perform a stable blowing based on a blowing index value by devising the blowing index value which can be applied in wide blowing condition. SOLUTION: In the blowing of molten stainless steel in a converter, a relation between the blowing index value S (=I×k/h) related with an apparent spouting momentum I of a top-blown oxygen spouted from a nozzle provided with a lance, a lance height h as the interval between the lance and the molten steel surface and an operational condition constant k, and a loss weight ΔW as the weight difference between the weight of molten chromium-containing iron and additive charged into the converter and the weight of the molten stainless steel tapped from the converter, is obtained. The loss weight ΔW can be in the suitable range by controlling so that the blowing index value S becomes a target range based on the above relation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for blowing molten stainless steel in a converter.

[0002]

2. Description of the Related Art Conventionally, molten stainless steel is made by melting raw materials in an electric furnace to produce chromium-containing hot metal, performing decarburization in the converter and performing rough refining such as adjusting components, and using a vacuum ladle degassing device. It is melted by finishing smelting. FIG. 6 is a diagram showing a blown state in the conventional converter 1. In the coarse refining in the converter, as shown in FIG. 6, a chromium-containing molten pig iron and an additive such as an alloy for adjusting the components are charged into the converter 1, and then a melt 2 (hereinafter, abbreviated as molten metal 2). Nozzle 4 provided at the end of the lance 3 facing the surface of the molten metal 2 provided at intervals above the surface of the molten metal
It is performed by ejecting oxygen gas from the molten metal toward the molten metal 2. Such a treatment is generally called oxygen blowing, and oxygen gas is called top-blown oxygen.

The distance from the surface of the molten metal 2 to the nozzle 4 provided at the end of the lance 3 is called the lance height h. The oxygen blowing is a treatment for performing a decarburizing treatment by reacting mainly carbon and oxygen in the chromium-containing hot metal,
As a result, molten stainless steel having a predetermined amount of carbon is produced. The molten stainless steel melted by the coarse refining is tapped from the converter 1 into a ladle. Such a series of processes from charging to the converter 1 to tapping is repeatedly performed.
Note that, hereinafter, the operation unit in which the series of processes is performed may be referred to as charge.

[0004]

In oxygen blowing in a converter, the blowing conditions are selected so that the top-blown oxygen and the molten metal can be efficiently contacted to perform the decarburizing treatment efficiently. ing. The blowing conditions of the converter are mainly the specifications of the nozzle 4,
It is determined by the fed oxygen amount F, which is the amount of oxygen supplied to the molten metal 2 for blowing, and the lance height h.

FIG. 7 is a cross-sectional view showing the structure near the tip of an example of the nozzle 4. FIG. 7 shows an example of a nozzle 4 called a Laval nozzle. The nozzle 4 is a hollow columnar body made of copper casting, and has a nozzle hole 6 which is an oxygen gas flow path for supplying top-blown oxygen to the molten metal 2 and a partition wall which is formed so as to surround the nozzle hole 6. A water supply / drainage channel 7 for supplying / draining water for cooling the nozzle 4 is formed.

The diameter (inner diameter) of the nozzle hole 6 is
Is not uniform in the direction of the axis 8 and there is a portion called the throat portion 9 which is formed in the middle of the direction of the axis 8 and has a minimum diameter, and the diameter increases as it goes to the outlet of the nozzle hole 6 thereafter. To be done. The diameter of the throat portion 9 of the nozzle hole 6 is called the nozzle throat diameter Dt, and the diameter of the outlet of the nozzle hole 6 is called the nozzle outlet diameter De. Although FIG. 7 exemplifies a Laval nozzle having one nozzle hole 6, a plurality of nozzle holes are generally formed in the nozzle, and the number of nozzle holes is represented by n. The specifications of the nozzle 4 described above include the nozzle throat diameter Dt, the nozzle outlet diameter De, the number of nozzle holes n, and the like.

The blowing conditions are selected by setting the nozzle specifications (Dt, De, n, etc.), the oxygen supply amount F, and the lance height h to desired values, and the upper blowing oxygen is jetted onto the surface of the molten metal 2. The so-called steel bath dent depth L, which is the depth to be formed, is hard blown in such a state that it is blown to increase, or the soft blow is the state in which it is blown to decrease the steel bath dent depth L. Bring out.
Such a state in which the steel bath is blown at various dent depths represented by hard blow or soft blow may be referred to herein as a blow situation.

In the case of hard blow, decarburization efficiency is high and spatter of molten metal containing slag called splash adheres to the refractory forming the inner wall of the furnace body to suppress wear of the refractory, but splash occurs. Since the amount is large, the yield decreases. On the other hand, in the case of soft blow, the generation of splash is suppressed, so that the yield is good, but the decarburization efficiency decreases, the amount of splash that adheres to the furnace wall refractory is small, and the wear of the refractory increases. Therefore, in actual blowing, it is necessary to operate between the hard blow and the soft blow so as to obtain the target blowing conditions suitable for the type of stainless steel to be blown and the temperature of the steel bath. For that purpose, it is necessary to obtain a quantitative relationship between the blowing condition and the depth L of the steel bath depression.

Conventionally, the depth L of the indentation in the steel bath is quantitatively obtained by, for example, the formula (1). L = 63 (10aF / nDt) ^2/3 · exp [−780h / {63 (10aF / nDt) ^2/3 }] (1) where a: the axis of the nozzle body and the axis of the nozzle hole The correction term F depending on the ejection angle, which is an angle, is the amount of oxygen to be fed n: the number of nozzle holes Dt: the nozzle throat diameter. Formula (1) is, for example, Showa 44, Nikkan Kogyo Shimbun
It is described on page 95 of "Iron Metallurgical Reaction Engineering", issued February 27, 1995.

In this equation (1), the nozzle throat diameter Dt
Is included, but the nozzle outlet diameter De is not included. The reason for this is that the Laval nozzle is designed to satisfy the relationship of the following equation (2) in order to obtain the maximum oxygen gas flow velocity, so the nozzle of oxygen supplied from the top-blown oxygen supply source is used. This is because if the nozzle front pressure P and the nozzle throat diameter Dt, which are the pressures at the inlet, are given, and the nozzle outlet pressure Pe at the oxygen nozzle outlet is set to atmospheric pressure, for example, the nozzle outlet diameter De is uniquely determined. That is, the depth L of the steel bath dent according to equation (1)
Is a nozzle in which the relationship given by equation (2) is established between the nozzle throat diameter Dt and the nozzle outlet diameter De, that is, the geometry in which the relationship of equation (2) is established although the size of each nozzle is different. It is an index that can be used when a nozzle having a similar shape is used for blowing.

[0011]

[Equation 2]

Here, Ae is the nozzle outlet area and At is the nozzle throat area. Formula (2) is described, for example, in "Steel Handbook I Basics", page 179, published by Maruzen Co., Ltd. June 20, 1981.

Although it is desired to shorten the decarburizing time in the blowing of molten stainless steel, the decarburizing time is reduced by using a nozzle having a uniform shape that satisfies the relationship of the formula (2). If the oxygen flow rate F is increased in order to shorten it,
It becomes a hard blow and the yield decreases. Therefore, the present invention is not limited to the nozzle having the shape satisfying the relationship of the formula (2), and the nozzle having the shape in which the nozzle throat diameter Dt and the nozzle outlet diameter De are arbitrarily selected is used, and the nozzle is in a wider range of conditions. It is desirable to select appropriate conditions from the above and to perform blowing efficiently. However, when blowing is performed using a nozzle having a shape deviating from the relationship of the formula (2), a divergence occurs between the steel bath dent depth obtained by the formula (1) and the actually formed steel bath dent depth. However, there is a problem that efficient blowing cannot be performed using the depth of depression in the steel bath as an index.

An object of the present invention is to devise a blowing index value which can be applied to a wide range of blowing conditions, and to perform efficient and stable blowing based on the blowing index value. To provide a method for blowing molten stainless steel in a converter.

[0015]

According to the present invention, a chromium-containing molten pig iron and an additive are inserted into a furnace, and thereafter, an end portion of the lance facing the molten metal surface is provided above the molten metal surface with a gap. In a method for blowing stainless steel in a converter, in which a predetermined amount of upward-blown oxygen is jetted from the nozzle toward the molten metal, and a series of processes for melting and producing the molten stainless steel is repeated, and is jetted from the nozzle. The blowout index value S (= I × k / h) related by the apparent jetting momentum I of the top-blown oxygen, the lance height h which is the distance between the lance and the surface of the molten metal, and the operating condition constant k, and to the converter. The relationship between the weight of the chromium-containing molten pig iron and the additive charged and the loss weight ΔW, which is the weight difference between the molten stainless steel discharged from the converter, is calculated, and the loss weight ΔW falls within the target range based on the relationship. To blow A blowing method of the stainless molten steel in the converter, characterized by controlling the index value S.

However, the apparent ejection momentum I of the top-blown oxygen and the operating condition constant k are respectively given by the following equations: I = 13.92Dt ² Po√ {1- (1.033 / P
o) ^2/7 } k = Po / Pp Here, Dt: nozzle throat diameter Po: nozzle front pressure (absolute pressure) in actual operation Pp: nozzle front pressure (absolute pressure) determined by the nozzle shape, depending on the nozzle shape Predetermined nozzle pressure Pp
Is further given by

[Equation 3]

Where Ae: nozzle exit cross-sectional area At: Nozzle throat cross section γ: Specific heat ratio of oxygen Is.

According to the invention, the delivery of oxygen flow F, the lance height h, a nozzle throat diameter Dt and the nozzle exit diameter De (nozzle exit cross-sectional area Ae is given by Ae = πDe ^2/4) and the nozzle front A blowing index value that includes the pressure P and can be applied to a wide range of blowing conditions using a nozzle in which the nozzle throat diameter Dt and the nozzle outlet diameter De can be independently set to arbitrary values. S is devised, the relationship between the blowing index value S and the loss weight ΔW is determined, and the blowing index value S is controlled so that the loss weight ΔW is within the target range, so that efficient and stable blowing is achieved. It becomes possible to do ren.

In the present invention, the blowing index value S is 12
It is characterized in that control is performed so as to be 0 or more and 180 or less.

According to the present invention, by setting the blowing index value S to 120 or more and 180 or less, the life of the converter furnace body can be extended and a high refining yield can be realized. That is, by setting the blowing index value S to 120 or more, the amount of splash generated by the top-blown oxygen can be set to an appropriate amount. Splash that occurs in an appropriate amount adheres to the refractory that constitutes the inner wall of the converter and suppresses its wear and contributes to maintaining the shape of the furnace inner surface of the converter, which can prolong the life of the converter furnace. it can.

Further, by setting the blowing index value S to be 180 or less, it is possible to suppress an excessive hard blow state, and therefore it is possible to prevent an excessive generation of the splash amount due to the upper blown oxygen. Therefore, the loss weight ΔW, which is almost equal to the amount of splash adhering to the converter furnace wall during blowing, does not become excessive, and a high refining yield is realized. Further, by performing oxygen blowing so that the blowing index value S falls within the range of 120 to 180, it is possible to increase the supply oxygen flow rate while realizing the protection of the converter furnace body. It is possible to improve the contact efficiency between the molten metal and the molten metal, and to shorten the blowing time for decarburizing treatment.

The present invention is also characterized in that the blowing index value S is controlled by changing one or both of the lance height h and the nozzle front pressure Po.

According to the present invention, the blowing index value S and thus the loss weight Δ are changed by changing the set values of one or both of the lance height h and the nozzle front pressure Po.
It becomes possible to easily control W.

[0024]

1 is a sectional view showing a simplified structure of a converter 11 to which the method for blowing molten stainless steel according to the present invention can be suitably applied. The configuration of a converter 11 to which the method for blowing molten stainless steel of the present invention is applied will be described with reference to FIG.

The converter 11 comprises a converter body 13 and a lance 14.
And a duct 15. This converter 11
Is configured so that the chromium-containing hot metal can be decarburized by oxygen blowing to produce molten stainless steel. The converter main body 13 is a heat-resistant container for storing the molten metal 16, a furnace opening 18 having a circular opening is formed in the upper part thereof, and a tuyere 19 for blowing an inert gas such as argon gas is formed in the bottom part thereof. Are formed. Further, a tap hole 20 for discharging the molten metal 16 is formed on the peripheral wall of the converter body 13, and a tilting device (not shown) for tilting the converter body 13 is provided.

The lance 14 is a steel pipe for blowing in top-blown oxygen for performing oxygen blowing, and is provided above the surface of the molten metal so as to be movable up and down at intervals. A nozzle 21 is provided at the tip of the lance 14, and an oxygen gas supply pipe 23 is connected to the base of the lance 14. The oxygen gas supply pipe 23 is provided with a pressure gauge 24, a flow meter 25, and a flow rate adjusting valve 26 in this order from the lance 14 side. The lance 14 and the nozzle 21 are cooled by cooling water. The duct 15 is a pipe line for collecting waste gas containing dust discharged from the converter main body 13, and is provided above the furnace port 18. Further, an alloy charging port 27 is provided at a position of the duct 15 that faces the furnace port 18. Slag 17 is generated on the surface of the molten metal 16.

FIG. 2 is a sectional view showing a simplified configuration of the nozzle 21 shown in FIG. 1, and FIG. 3 is a section line III of FIG.
It is sectional drawing seen from -III. The nozzle 21 is a hollow columnar body made of copper casting, and has an oxygen gas flow passage 2 inside thereof.
9, water supply channel 30, drainage channel 31, and nozzle hole 33
And are formed. The oxygen gas flow path 29 is connected to the nozzle 21.
Is a flow path formed around the axis 34 of the drainage flow path 3
Reference numeral 1 denotes a flow path formed so as to surround the oxygen gas flow path 29 with the first partition wall 35 interposed therebetween, and the water supply flow path 30 surrounds the drainage flow path 31 with the second partition wall 36 provided therebetween. It is a flow path to be formed.

The first partition wall 35 and the second partition wall 36 are coaxial with the axis 34 of the nozzle 21, and the inner and outer peripheral surfaces thereof have a circular cross section perpendicular to the axis. Therefore, the oxygen gas flow path 29 is
The space surrounded by the first partition wall 35, and the drainage channel 3
1 is a space between the first partition wall 35 and the second partition wall 36,
The water supply channel 30 includes a second partition wall 36 and a peripheral wall 37 of the nozzle 21.
It is a space between and. The cooling water is introduced from the water supply passage 30 and is drained through the drain passage 31 while cooling the nozzle 21.

The nozzle hole 33 is a communication hole that connects the oxygen gas flow path 29 and the external space, and one end of the nozzle hole 33 is the nozzle 2.
An opening is formed in the tip surface 39 that faces the molten metal 16 of No. 1. Since the nozzle holes 33 are formed at a plurality of positions, for example, three positions at equal intervals in the circumferential direction of the nozzle 21, the nozzle holes 3
The number n of 3 is 3. The diameter of the nozzle hole 33 (inner diameter, hereinafter the same) is not uniform over the entire length,
In the middle of the direction of the axis 38, there is a portion called throat portion 40 that is formed to have a minimum diameter, and the diameter is formed so as to increase from the throat portion 40 toward the outlet portion 41 of the nozzle hole 6. The nozzle diameter of the throat portion 40 is the nozzle throat diameter Dt, and the nozzle diameter of the outlet portion 41 is the nozzle outlet diameter De.

The axis 38 of the nozzle hole 33 is inclined with respect to the axis 34 of the nozzle 21, and the tip surface 3 of the nozzle 21 is formed.
It is configured so as to be more distant from the axis 34 of the nozzle 21 as it goes to 9. The angle formed by the axis 38 of the nozzle hole 33 and the axis 34 of the nozzle 21 is called the ejection angle θ. In the present embodiment, the nozzle throat diameter Dt, the nozzle outlet diameter De, the number of nozzle holes n, and the ejection angle θ are referred to as nozzle specifications.

Chromium-containing hot metal is poured into the converter main body 13, and argon gas is blown from the tuyere 19 to stir it. Additives consisting of alloys for adjusting composition and steel scraps are
It is charged into the chromium-containing hot metal from the alloy charging port 27. The upper blown oxygen is adjusted to a predetermined flow rate by the flow rate adjusting valve 26 and is supplied to the oxygen gas flow path 29 via the lance 14. The pressure of oxygen gas in the oxygen gas passage 29, which is a space before reaching the nozzle hole 33, is the nozzle front pressure P.
In the calculation of the blowing index value S, which will be described later, the pre-nozzle pressure P
Is used separately for both the nozzle front pressure Po in the actual operation and the proper nozzle front pressure Pp determined by the nozzle shape. The oxygen gas supplied to the oxygen gas flow path 29 further flows through the nozzle hole 33 and is ejected toward the surface of the molten metal 16. The flow rate and pressure of the top-blown oxygen are measured by the flow meter 25 and the pressure gauge 24. The molten stainless steel that has been blown in the converter 11 is tapped from the tapping port 20 into a ladle (not shown).

Oxygen blowing, which is the crude refining of molten stainless steel, is performed by the converter 11 as described above. In the method for blowing molten stainless steel of the present invention, the nozzle throat diameter D
a blowing index value S (hereinafter simply referred to as a blowing index value S) that can be applied between nozzles in which t and the nozzle outlet diameter De are independently determined and have geometrically dissimilar shapes. The relationship with the loss weight ΔW is obtained, and the blowing index value S is controlled based on the relationship so that the loss weight ΔW falls within the target range. The blowing index value S is obtained as the blowing index value S = I × k / h by the apparent ejection momentum I of the top-blown oxygen ejected from the nozzle 21, the lance height h, and the operating condition constant k.

However, the apparent ejection momentum I of the top-blown oxygen and the operating condition constant k are given by the equations (3) and (4), respectively. I = 13.92 Dt ² Po√ {1- (1.033 / Po) ^2/7 } (3) k = Po / Pp (4) where Dt: nozzle throat diameter [cm] Po: actual operation Nozzle front pressure (absolute pressure) [kgf / c
m ² ] Pp: Pre-nozzle pressure (absolute pressure) [kgf / cm ² ] determined by the nozzle shape. Formula (3) is described, for example, in "Steel Handbook I Basics", page 179, published by Maruzen Co., Ltd. June 20, 1981.

The nozzle pre-pressure Pp determined by the nozzle shape is given by the equation (5).

[0035]

[Equation 4]

Here, Ae: nozzle outlet cross-sectional area, At:
Nozzle throat cross-sectional area, γ: specific heat ratio of oxygen. The nozzle throat cross-sectional area (At) and the nozzle outlet cross-sectional area (A
e) is the nozzle throat diameter Dt and the nozzle outlet diameter D
can be expressed by using e, and At = πDt ² /
It is 4 and Ae = πDe ^2/4. The specific heat ratio is the ratio of the constant pressure specific heat to the constant volume specific heat, and is 1.40 for oxygen gas, which is a diatomic molecule.

As described above, the blowing index value S includes the nozzle front pressures Pp and Po, the nozzle throat diameter Dt, the nozzle outlet diameter De, and the lance height h, and the nozzle outlet diameter De.
Is used as an independent condition factor, not a condition factor dependent on the nozzle front pressure Pp and the nozzle throat diameter Dt. Therefore, the steel bath dent obtained under the limited blowing condition setting in which the nozzle having the similar shape in which the nozzle outlet diameter De is uniquely determined corresponding to the nozzle front pressure Pp and the nozzle throat diameter Dt is used. Compared with controlling the blowing situation by using the depth L as an index, it becomes possible to control the blowing situation by selecting an appropriate condition from a wider range of blowing conditions. That is, even when the nozzle front pressure Pp and the nozzle throat diameter Dt are the same, the nozzle outlet diameter De is not limited to the nozzle outlet diameter De determined based on the relationship of the equation (2), and the nozzle outlet diameter De can be arbitrarily increased. The energy of the oxygen gas ejected from the nozzle is positively changed by reducing the value to a small value, and an appropriate condition is selected from a wide range of blowing conditions based on the blowing index value S to control the blowing condition. be able to.

The actual operation of blowing molten stainless steel can be carried out, for example, as follows. The lance height h corresponding to the steel type of the charge to be blown, the temperature of the steel bath, and the like and the oxygen flow rate F to be fed can be estimated in advance, and the blowing index value S can be set within the target range based on the estimated value. Such nozzle specifications, that is, the nozzle throat diameter Dt, the nozzle outlet diameter De, and the like are determined. Prepare a nozzle according to the specified nozzle specifications, and change the set value of either or both of the lance height h and the nozzle front pressure Po to change the blowing index value S during actual blowing operation. Control to reach the target range.

As the nozzle front pressure Po in actual operation, a value measured by a pressure gauge 24 provided in the oxygen gas supply pipe 23 is used. Strictly speaking, a slight pressure loss occurs from the pressure gauge 24 through the oxygen gas supply pipe 23 to the nozzle inlet, but since the pressure loss is slight, the measured value by the pressure gauge 24 is used as the nozzle front pressure Po. I was there.

The blowing index value S qualitatively represents the magnitude of the ejection momentum of the oxygen jet blown onto the molten stainless steel per unit time. Therefore, the blowing index value S
By controlling the blowing condition on the basis of the above, on the phenomenon side, the value of the loss weight ΔW, which is the amount of splash on the converter furnace wall of the splash generated by the oxygen jet, is set to a target range, in other words, an appropriate range. Can be controlled. The loss weight ΔW is an amount that is closely related to the wear and yield of the refractory material forming the inner wall of the converter, and the blowing index value S
By controlling the blowing condition, that is, the loss weight ΔW is within an appropriate range, the wear of the refractory that constitutes the furnace wall of the converter is suppressed, and the furnace volume is kept substantially constant. It becomes possible to efficiently perform blowing with a high refining yield while maintaining the shape.

The blowing index value S is 120 or more and 180
It is desirable to control so that it becomes as follows. By controlling the blowing index value S as described above, the loss weight Δ
The value of W can be set within an appropriate range. That is, by setting the blowing index value S to 120 or less, the loss weight ΔW
The generation of splash due to top-blown oxygen, which is mainly composed of, can be set to an appropriate amount. The splash generated in an appropriate amount adheres to the refractory forming the inner wall of the converter and contributes to the shape retention of the inner surface of the converter, so that the life of the converter furnace can be extended.

Further, by setting the blowing index value S to 180 or less, it is possible to suppress the excessive hard blow state, so that the excessive generation of the splash amount due to the upper blowing oxygen is prevented and a high refining yield is realized. It

Further, by performing oxygen blowing so that the blowing index value S falls within the target range, the value of the loss weight ΔW becomes within an appropriate range, and the oxygen flow rate of the fed oxygen is controlled while realizing the protection of the converter furnace body. Since it can be increased, the contact efficiency between the top-blown oxygen and the molten metal can be improved, and the blowing time for the decarburization treatment can be shortened.

(Examples) Examples of the present invention will be described below. A converter 11 having a capacity of 80 tons was prepared, and top-blown oxygen blowing of stainless molten steel was performed using eight types of nozzles (Nos. 1 to 8) having different specifications. Each nozzle (N
o. 1-8), the operating conditions in the charge are maintained by changing the lance height h or the nozzle front pressure Po so that the blowing index value S is in the range of 110-220. You controlled the fortune situation. The specifications and the like of each nozzle (No. 1 to 8) are also shown in Table 1.

The blowing condition was represented by the loss weight ΔW (kg / T). In addition, T represents ton. As described above, the loss weight ΔW is the amount of the splash generated on the converter furnace wall that is generated by the top-blown oxygen blowing, and the splash amount and the blowing condition such as hard blow or soft blow are Since it corresponds well, it is possible to represent the blowing situation by the loss weight ΔW. In this embodiment, each nozzle (No. 1 to 1) having a geometrically non-similar relationship is used.
In the blowing of the molten stainless steel using 8), the blown index value S is changed and the loss weight Δ for each blown index value S
W was determined, and it was examined whether or not the loss weight ΔW can be set corresponding to the blowing index value S. For comparison, the relationship between the loss weight ΔW and the depth L of the steel bath dent in the above formula (1) is determined, and whether or not the loss weight ΔW can be set using the depth L of the steel bath as an index is also included. investigated.

FIG. 4 is a diagram showing the relationship between the blowing index value S and the loss weight ΔW, and FIG. 5 is a diagram showing the relationship between the steel bath dent depth L and the loss weight ΔW. Line 42 shown in FIG.
Indicates the correlation between the blowing index value S and the loss weight ΔW, and it can be seen from the line 42 that the blowing index value S and the loss weight ΔW have a high correlation with a nearly one-to-one correspondence.
By controlling the blowing index value S as shown in FIG. 4, the loss weight ΔW could be set to a target value with high accuracy.

By controlling the blowing index value S to be in the range of 120 to 180, the loss weight ΔW is 2
It was possible to blow in the range of 5 to 50 kg / T. By blowing at a loss weight ΔW in the range of 25 to 50 kg / T, the life of the converter furnace body can be extended by up to 25% and blowing at a high yield can be realized, and the feed oxygen flow rate F can be up to 30. %, The contact efficiency between the top-blown oxygen and the molten metal was increased, and the blowing time for decarburization treatment could be shortened by up to 30%.

On the other hand, as shown in FIG. 5, there is almost no correlation between the depth L of the steel bath depression and the loss weight ΔW.
It was difficult to set the loss weight ΔW to a target value using the depth L of the steel bath as an index.

[0049]

[Table 1]

[0050]

According to the present invention, a blowing index value S that can be applied to a wide range of blowing conditions is devised, and the relationship between the blowing index value S and the loss weight ΔW is determined, and the relationship is obtained. Since the blowing index value S, that is, the blowing condition is controlled so that the loss weight ΔW falls within the target range based on the above, the furnace body shape is maintained at a high value while maintaining the furnace internal volume to be substantially constant. It becomes possible to efficiently perform blowing with a yield.

Further, according to the present invention, the blowing index value S is 12
By setting it to 0 or more and 180 or less, the life of the converter furnace body can be extended and a high refining yield can be realized. Further, by performing oxygen blowing according to the blowing index value S set in the target range, it is possible to increase the feed oxygen flow rate while realizing the protection of the converter furnace body. The contact efficiency can be increased and the blowing time can be shortened.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a simplified configuration of a converter 11 to which a method for blowing molten stainless steel according to the present invention can be suitably applied.

2 is a sectional view showing a simplified configuration of a nozzle 21 shown in FIG.

FIG. 3 is a sectional view taken along section line III-III in FIG.

FIG. 4 is a diagram showing a relationship between a blowing index value S and a loss weight ΔW.

FIG. 5 is a diagram showing a relationship between a depth L of a steel bath depression and a loss weight ΔW.

FIG. 6 is a view showing a blown state in a conventional converter 1.

FIG. 7 is a cross-sectional view showing a configuration near a tip portion of an example of a nozzle 4.

[Explanation of symbols]

11 converter 13 Converter body 14 Lance 16 molten metal 21 nozzles

Claims (3)

[Claims] 1. A chrome-containing molten pig iron and an additive are inserted into a furnace, and thereafter, a nozzle provided at an end of the lance provided above the surface of the molten metal and facing the surface of the molten metal is directed toward the molten metal. In the blowing method of molten stainless steel in a converter, in which a series of treatments are performed, in which a high flow rate of oxygen is jetted, molten stainless steel is melted, and tapped, the apparent momentum of jetted oxygen blown from a nozzle I, the blowing index value S related by the lance height h, which is the distance between the lance and the surface of the molten metal, and the operating condition constant k
The relation between (= I × k / h) and the loss weight ΔW, which is the weight difference between the weight of the chromium-containing hot metal and the additive charged to the converter and the weight of the stainless molten steel tapped from the converter, A method for blowing molten stainless steel in a converter, wherein the blowing index value S is controlled so that the loss weight ΔW falls within a target range based on the relationship. However, the apparent ejection momentum I of top-blown oxygen and the operation condition constant k are respectively given by the following equations: I = 13.92Dt ² Po√ {1- (1.033 / P
o) ^2/7 } k = Po / Pp, where Dt: nozzle throat diameter Po: nozzle pre-pressure (absolute pressure) in actual operation Pp: nozzle pre-pressure (absolute pressure) determined by nozzle shape, depending on nozzle shape Predetermined nozzle pressure Pp
Is further given by Here, Ae: nozzle outlet cross-sectional area At: nozzle throat cross-sectional area γ: specific heat ratio of oxygen. 2. The method for blowing stainless molten steel in a converter according to claim 1, wherein the blowing index value S is controlled to be 120 or more and 180 or less. 3. The blowing index value S is controlled by changing a set value of one or both of a lance height h and a nozzle front pressure Po. Method for Molten Stainless Steel in Converters in Japan.