JPH08104911A - Method for melting phosphorus-containing steel - Google Patents

Abstract

PURPOSE: To improve the yield of phosphorus concn. at the time of stopping the blowing of a converter and to reduce the consumption of FeP ferro alloy by using desulfurized molten iron in a specific condition and blowing a reducing agent into slag produced in a furnace, at the time of adjusting the component of molten steel containing a specific condition of the phosphorus in a top (bottom) blowing converter. CONSTITUTION: Desulfurizing treatment is applied by blowing lime powder and soda ash powder at a ratio of 2-2.5:1 from an outher pipe while adding gaseous oxygen at 0.056-0.090Nm<3> /min.tom from an inner pipe throuth a lance nozzle immersed in the molten iron in a molten iron ladle. Thereafter, at the time of melting the phosphorus-containing steel having 0.03-0.10% phosphorus concn. in the molten steel in the top-blowing or the top-bottom combined blowing converter by using the molten iron after removing the desulfurized slag, the reducing material is blown into the slag produced in the furnace. The above range advantageous to the desulfurizing efficiency is adopted for the ratio of the lime powder and the soda ash powder in the desulfurizing treatment and in this case, at the time of executing the lower limit of the gaseous oxygen blowing rate, the producing rate of graphite becomes zero, but at the time of exceeding the upper limit thereof, de-Si quantity is increased and the heat source in the converter at the following process is lowered.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a desulfurization treatment of hot metal tapped from a blast furnace, in which a desulfurization treatment is carried out within a range where the desulfurization efficiency is not deteriorated, and then a desulfurization treatment is carried out by adding oxygen gas in a hot metal ladle. By performing the above, when melting phosphorus-containing steel with desulfurized hot metal that enables cost reduction of converter secondary materials, the reducing agent is blown into the slag generated in the converter to oxidize the molten steel into slag. The present invention relates to a method for producing phosphorus-containing steel in which the removed phosphorus is forcibly reduced into molten steel and the alloy iron cost is reduced.

[0002]

2. Description of the Related Art Conventionally, in a phosphorus-containing steel manufacturing method, molten iron is charged into a converter, the [P] concentration in molten steel at the end of blowing is estimated, and the target [P] The deficiency with respect to the concentration is adjusted with phosphorus-containing alloy iron (hereinafter referred to as FeP alloy iron). This conventional manufacturing method causes an increase in manufacturing cost in that expensive FeP alloy iron is used.

[0003]

When adjusting the composition of phosphorus-containing steel molten steel with [P] in the molten steel of 0.03% to 0.1% in a top-blown or top-bottom blow converter, the molten pig iron is converted into a converter. It is charged into the tank and the molten steel [P] concentration at the end of blowing is estimated. Based on the estimation result, the target [P] concentration including the deficiency is included.
An object of the present invention is to improve the [P] concentration (hereinafter referred to as blow stop [P]) yield at the end of blowing in a smelting method of phosphorus-containing steel adjusted by ferroalloy and reduce the manufacturing cost.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The means is to immerse a lance nozzle in the hot metal contained in the hot metal ladle, 0.056 ~ from the inner tube through the nozzle
While adding 0.090 Nm ³ / min · ton oxygen gas, quicklime powder and soda ash powder are added from the outer tube to 2 to 2.5: 1.
Of the phosphorus content of 0.03 to 0.10% in the molten steel in the top-blown or top-bottom converter using the hot metal from which desulfurization slag was discharged. When melting steel, a method for melting phosphorus-containing steel, characterized in that a reducing material is blown into the slag produced in the furnace, and

, Si content of 0.20% to 0.30%
The lance nozzle is immersed in the hot metal of No. ⁵ , and 0.056 to 0.090 Nm ³ / mi is introduced from the inner pipe through the lance nozzle.
While adding n · ton oxygen gas, quick lime powder and soda ash powder were blown from the outer tube at a ratio of 2 to 2.5: 1 to perform desulfurization treatment, and then the hot metal from which the desulfurization slag was discharged was used. When a phosphorus-containing steel having a [P] concentration of 0.03 to 0.10% in molten steel is melted in a top-blown or bottom-blown converter, a reducing material is blown into the slag generated in the furnace. Method for melting phosphorus-containing steel, and

The method for producing phosphorus-containing steel characterized in that the reducing agent blown into the slag produced in the furnace is coke, silicon alloy iron or aluminum whose maximum particle diameter is not more than 5 mm, and The method for injecting phosphorus-containing steel, characterized in that the start timing of the reducing agent blown into the in-furnace slag produced in the above or is within 5 minutes from the scheduled blowing end time, and the in-reactor production described above. According to another aspect of the present invention, there is provided a smelting method for phosphorus-containing steel, characterized in that the timing of ending the blowing of the reducing material blown into the slag is after the end of blowing.

[0007]

The present invention is processed by a hot metal treatment method capable of preventing graphite from scattering during desulfurization, cleaning the torpedo car by desulfurization in a hot metal ladle, and reducing the cost of converter submaterials by light desiliconization. It is intended to reduce the amount of expensive FeP alloy iron used in the production of phosphorus-containing steel by using the hot metal and to reduce the production cost. When desulfurizing the hot metal tapped from the blast furnace, As shown in 1, Si in hot metal does not deteriorate the desulfurization effect.
Light desiliconization treatment was performed with a torpedo car to a content range of 0.20% to 0.30%, and then the light desiliconized treatment hot metal was dispensed into the hot metal ladle, inside the hot metal contained in the hot metal ladle. The lance nozzle is immersed in the lance nozzle, and 0.056 to 0.090 Nm ³ / min from the inner tube through the lance nozzle.
-By adding ton's oxygen gas and blowing quicklime powder and soda ash powder from the outer tube at a ratio of 2 to 2.5: 1, slag can be added by oxygen gas during light desiliconization treatment and desulfurization treatment. The precipitated graphite inside is burned and removed, and desulfurization treatment is performed while preventing the graphite from scattering during the desulfurization treatment.

As for the ratio of quicklime powder and soda ash powder in the desulfurization treatment in this case, when the desulfurization efficiency is evaluated as shown in FIG. So this value is adopted. Furthermore, regarding the oxygen gas amount in this case, as shown in FIG.
When it exceeds 56 Nm ³ / min · ton, the graphite generation rate becomes 0%, but the oxygen gas amount is 0.090 Nm ³ / mi.
If it exceeds n · ton, on the other hand, the amount of Si removed during the desulfurization process increases and the heat source in the converter in the next step decreases, so the amount of oxygen gas in the desulfurization process is 0.056 to 0.090 Nm.
³ / min · ton.

Further, by performing light desiliconization treatment in a torpedo car and desulfurization treatment in a hot metal ladle, a cleaning operation can be performed on the torpedo car, which also has an effect of improving productivity. Further, by performing desulfurization and desiliconization treatment, quick lime for adjusting the basicity in the converter can be reduced, and the converter auxiliary material cost can be reduced. In the present invention, the phosphorus-containing steel is melted using the hot metal that has been subjected to such a pretreatment.

Here, the [P] yield at the time of molten steel blowing in the converter can be expressed by the following equation (1). That is,

[0011]

[Equation 1]

[0012]

[Equation 2]

Here, SV: amount of slag produced by converter (kg / t) (P) / [P]: P distribution ratio between slag and molten steel (% CaO): CaO concentration in slag (%) (% T) .Fe): Iron content concentration (%) in slag EPT: Blown-out temperature (° C) A, B, C: Positive constant,

Therefore, the inventors of the present invention use the above formulas (1) and (2) to reduce the amount of generated slag, decrease (% CaO), and decrease (% T.Fe) in order to improve the blow stop [P] yield. Focusing on the fact that the blow-off temperature rise is effective, we examined the optimization of each condition in actual operation, and conducted an experiment,
Under the above conditions, it is effective to reduce the degree of slag oxidation and the amount of generated slag, and the CaO concentration in the slag and the blow-off temperature have a small degree of freedom in the converter process, which improves blow-off [P] yield. It turned out that there is almost no effect of.

That is, it was confirmed that by decreasing the CaO concentration in the slag, an abnormal operation such as a rapid increase in sloping occurrence frequency and an increase in the meltdown rate of the refractory material of the converter occurred, which is not feasible as an industrial production method. Was done. In addition, the blow-off temperature is often determined by other factors than the converter such as secondary refining process, casting process, molten steel solidification temperature determined by the component system, and the set value is increased only by the converter process. This causes an increase in the cost of the coolant and a significant increase in the melting loss of the refractory in the converter, which causes an increase in the manufacturing cost.

The reducing agent blowing timing has proper timing in terms of improving the reduction efficiency in the slag (P) by reducing the slag oxidation degree. The degree of oxidation of the slag in the converter increases as the efficiency of decarboxylation in the converter decreases. For example, in bottom-blown converters,
When the concentration of [C] in the molten steel is about 0.2 to 0.4% or less, the decarboxylation efficiency decreases, and the excess oxygen that does not contribute to decarburization increases the degree of oxidation of slag. Therefore,
Even if the reducing agent is blown at the peak of decarburization, the [P] yield improvement effect cannot be obtained due to the slag reoxidation accompanying the decrease in decarboxylation efficiency in the final stage.

In the present invention, in consideration of the mechanism of increasing the degree of slag oxidation, the reducing agent is blown into the slag during or after the increase in the degree of slag oxidation due to the decrease in decarboxylation efficiency at the end of blowing, and the degree of slag oxidation is increased. It is intended to reduce. Therefore, as the blowing start timing, the point at which the decarboxylation efficiency begins to drop sharply from around 100% (hereinafter CB
The following is appropriate. As described above, the CB point is such that the [C] concentration in the molten steel is about 0.2 to 0.4 in the upper-bottom blow converter.
%, It is necessary to set a time when the [C] concentration in the molten steel is about 0.2 to 0.4% or less as the start time of blowing.

Based on such knowledge, the inventors of the present invention investigated the accuracy of [C] concentration estimation and the time required for powder injection in the actual operation, and as a result, the reducing agent was added within 5 minutes before the scheduled blowing end time. Found that it was necessary to start blowing. The closer the blowing start time is to the blowing end time, the greater the phosphorus yield improving effect, so
Upon application, it is desirable to select an appropriate time point according to the blowing time and blowing speed capability. When the blowing start time is after the end of blowing, the phosphorus yield improving effect can be received most greatly.

Further, it is desirable that the end of blowing the reducing agent is after the end of blowing. When blowing is completed during blowing, excess oxygen is continuously supplied to the slag even after the completion of blowing, and as a result, the degree of slag oxidation once reduced by the reducing agent is reduced by reoxidation due to excess oxygen. Since it rises again and causes a decrease in phosphorus yield, the effect of blowing the reducing agent cannot be fully received. Further, by reducing the [Si] content in the hot metal to 0.2 to 0.3%, the amount of slag generated in the converter furnace is reduced,
It is possible to improve the P yield.

The reducing agent to be supplied may be coke, silicon alloy iron (ferrosilicon), or Al. The reduction reaction rate depends on the particle size of the reducing agent.
That is, FIG. 4 shows the relationship between the maximum particle size of powder coke and blow stop [P]. As is clear from the figure, the reaction rate decreases as the particle size increases. In actual operation, in order to complete the reaction without extending the converter processing time, the maximum particle size of the reducing agent needs to be 5 mm or less. 5m
If the particle size exceeds m, the reaction interfacial area is insufficient and the effect of extending the processing time or improving the [P] yield cannot be sufficiently obtained.

FIG. 5 shows the relationship between the blown coke amount and the blow stop P. The precondition for this is that the reducing agent blowing start timing is 0 to 3 minutes before the scheduled blowing end time,
The hot metal [Si] was in the range of 0.35 to 0.50%, and the blow stop [C] was in the range of 0.045 to 0.060%. As is clear from the figure, the blow stop [P] rises as the coke blowing amount increases. It is desirable to select an appropriate blowing amount in the actual operation depending on the time margin with the next process and the blowing facility capacity (tank capacity, blowing speed). It is desirable to inject the reducing agent from a position where the reducing agent can reach the slag, such as a tap hole and the abdomen of the furnace body.

[0022]

EXAMPLES Hereinafter, specific examples in which the phosphorus-containing steel is produced by the present invention will be described. According to the present invention, phosphorus-containing steel was melted by the melting method shown in Table 1. By carrying out the melting method of the present invention, the [P] yield of blow stop is increased by about 20% to 38%, and the blow stop [P] value is 0.030% compared with the conventional 0.016%.
It rose dramatically by ~ 0.059%. As a result, Fe which has been conventionally fed at 2.96 kg / t for [P] adjustment
The amount of P alloy iron can be reduced from 0 to 2.07 kg / t, and the cost reduction effect is extremely large.

[0023]

[Table 1]

[0024]

EFFECTS OF THE INVENTION According to the phosphorus-containing steel smelting method of the present invention, the [P] yield at the time of blowing out of the converter is improved, and it is used in the secondary refining step during or after the conventional tapping. In addition, the FeP alloy iron input amount can be reduced, and the manufacturing cost can be effectively reduced.

When FeP alloy iron is added immediately after tapping, the oxygen content in the melt and slag is large and the deviation is large, so that the [P] addition yield due to the introduced FeP alloy iron is unstable. In order to bring the components into the specified range, it is usual to carry out molten steel component analysis after the introduction of FeP alloy iron to confirm and readjust the components. The P-containing steel smelting method of the present invention improves the [P] yield at the time of blowing off the converter, reduces the component deviation by reducing the FeP alloy iron input amount, and blows a reducing agent into the slag. Therefore, the oxygen content in the slag is stabilized at a low level, and F
The yield of molten steel when eP alloy iron is added is stabilized. Since it becomes possible to reduce these [P] yield deviations,
[P] Industrial effect such as improved controllability, no need to confirm components after alloy addition, cost reduction of probe for analysis sample collection, decrease of molten steel temperature due to waiting for analysis, reduction of blowout temperature, etc. Is big.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between hot metal Si before S removal treatment and S removal efficiency.

FIG. 2 is a diagram showing a relationship between a basic unit of a S-removing agent and a S-removing efficiency, showing a S-removing rate for each ratio of quicklime powder and soda ash powder.

FIG. 3 is a diagram showing the relationship between the oxygen gas amount during the de-S treatment, the graphite generation rate, and the de-Si amount during the de-S treatment.

FIG. 4 is a diagram showing the relationship between the maximum particle size of powder coke and blow stop [P].

FIG. 5 is a diagram showing the relationship between the amount of powder coke blown and the blow stop [P].

Claims (5)

[Claims] 1. A lance nozzle is immersed in the hot metal contained in a hot metal ladle, and 0.056 to 0.090 Nm ³ / min · ton of oxygen gas is added from the inner tube through the lance nozzle. , 2 quicklime powder and soda ash powder from the outer tube
˜2.5: 1 blown in to perform desulfurization treatment, and then using hot metal from which desulfurization slag is discharged, the [P] concentration in the molten steel is 0.03 to 0 in a top-blown or top-bottom converter. .10
% Of phosphorus-containing steel is melted, a reducing material is blown into the slag produced in the furnace. 2. A lance nozzle is immersed in hot metal having a Si content of 0.20% to 0.30%, and 0.056 to 0.090 Nm ³ / min from the inner pipe through the lance nozzle.
・ While adding ton's oxygen gas, quick lime powder and soda ash powder were blown from the outer tube at a ratio of 2 to 2.5: 1 for desulfurization treatment, and then the hot metal from which the desulfurization slag was discharged was used. [P] concentration in molten steel in a blowing or top-bottom converter is 0.
A method for smelting phosphorus-containing steel, which comprises blowing a reducing agent into the slag produced in the furnace when smelting 03-0.10% phosphorus-containing steel. 3. The reducing agent blown into the slag produced in the furnace,
The method for smelting phosphorus-containing steel according to claim 1 or 2, which is coke, silicon, silicon alloy iron or aluminum having a maximum particle diameter of not more than 5 mm. 4. The melting of the phosphorus-containing steel according to claim 1 or 2, wherein the start timing of blowing the reducing material blown into the slag produced in the furnace is within 5 minutes from the scheduled blowing end time. Manufacturing method. 5. The method for smelting phosphorus-containing steel according to claim 1 or 2, wherein the end timing of blowing the reducing material blown into the slag generated in the furnace is after the end of blowing.