JPS6143409B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of refining steel in a metal smelting furnace using a solvent containing an alkali metal carbonate as a main component, and more specifically to a method of actively performing dephosphorization and desulfurization. In recent years, experiments have been underway to dephosphorize and desulfurize hot metal using a solvent containing an alkali metal carbonate as a main component, such as soda ash. However, as shown in Figure 1, the heat possessed by the hot metal itself is 1300 ~
There is a phenomenon that if the soda ash basic unit is constant at 1500℃, the dephosphorization rate decreases as the temperature rises. Therefore, in order to increase the dephosphorization rate, a large amount of expensive soda ash must be used, which has been a major problem in actual operation. In view of the above-mentioned problems, the inventors conducted various experiments and discovered a phenomenon completely different from the dephosphorization and desulfurization phenomenon of soda ash in hot metal described above in a method for dephosphorizing and desulfurizing steel using soda ash. The present invention is a method in which a solvent is added after the carbon content in molten steel is reduced to a certain value or less. A method in which a part of the total amount of solvent is added at the beginning of metal smelting furnace blowing, the carbon content in the molten steel is lowered to a certain value, and then the remaining solvent is added. A method in which hot metal is desiliconized before being charged into a metal smelting furnace, and then the above steps are carried out. A method in which a solvent is added when most of the decarburization reaction is completed, and stirring is performed by blowing gas below the bath surface. A method combining the above with initial addition of a solvent. This is a new steel refining method that combines desiliconization treatment of hot metal and the above or the above. In the present invention, the solvent containing an alkali metal carbonate as a main component includes, in addition to the above-mentioned soda ash containing Na ₂ CO ₃ as a main component, those containing K ₂ CO ₃ as a main component. Metal refining furnaces include top-blowing converters, bottom-blowing converters, composite blowing furnaces with nozzles below the bath surface, AOD furnaces, and VOD furnaces.
The present invention is applicable to a wide range of steel refining methods, including furnaces, electric furnaces, etc. The dephosphorization reaction of steel in the present invention proceeds according to equation (1). 4/5P+Na ₂ CO ₃ →Na ₂ O+2/5P ₂ O ₅ +C...(1) On the other hand, in the case of hot metal, the amount of water in the slag is determined by equation (2).
Na ₂ O decreases, the activity a′P ₂ O ₅ of P ₂ O ₅ in the slag increases, and the reaction of equation (1) and equation (3) are controlled.
Since rephosphorization occurs due to the reduction reaction of P ₂ O ₅ , it is thought that dephosphorization does not proceed as a result. Na ₂ O + C → 2Na + CO ... (2) P ₂ O ₅ +5 C → 2 P + 5 CO ... (3) Figure 2 shows the dephosphorization and desulfurization effect of undeoxidized molten steel using soda ash according to the present invention. =1650℃
Dephosphorization using soda ash in low-carbon undeoxidized molten steel of The loss of Na ₂ O due to the reaction is small, the rephosphorization reaction of equation (3) is small, and the evaporation rate of the soda ash itself is slower than previously thought (if there is no reduction by C), T = 1650 This is thought to be because it sufficiently reacted with molten steel even at ℃ and became stable as Na ₂ O-P ₂ O ₅ -based slag. Based on the above explanation, the present invention will be explained in more detail. Figure 3 shows the relationship between the amount of [C] in molten steel and the dephosphorization rate when soda ash is used. It has declined dramatically. The conditions at this time were: soda ash basic unit: 20 kg/T, [Si] = tr, and molten steel temperature: 1600°C. As is clear from the above results, for example, if soda ash is added to the molten steel during blowing in a converter when C=0.50% or less, good results can be obtained that are completely different from the dephosphorization rate during hot metal. is obtained. Furthermore, even if the amount of [C] in the molten steel is 0.50% or less, a portion of the total amount of soda ash used during converter blowing should be added at the beginning of converter blowing. The dephosphorization of steel as shown in Figure 3 can also be achieved by performing blowing while improving the fluidity of the slag, and adding the remaining soda ash when the amount of [C] in the molten steel reaches below the above-mentioned level. rate is obtained. Furthermore, [Si] in the hot metal before charging into the converter is 0.30%.
In the above cases, desiliconization is preferable. The reason is based on FIG. Figure 4 shows P=0.100 for a system with a certain carbon content.
% hot metal P = 0.010, this shows the relationship between the soda ash unit required to make molten steel and the hot metal [Si]%.In actual operation, the amount of [Si] in hot metal is
If the carbon content is 0.30% or more, the hot metal that has been desiliconized by adding iron oxide-containing substances or by blowing O ₂ or both between the time of tapping in the blast furnace and entering the converter is heated to a carbon content of 0.50% in the converter. This shows that it is possible to efficiently dephosphorize steel by adding soda ash to it after blowing it into molten steel. In other words, the lower the Si level is, the more desirable it is, and the lower the C level is, the more desirable it is, and these are all in a proportional relationship with the soda ash basic unit. Another method of implementing the present invention is, for example, by adding soda ash to molten steel that has been blown in a converter to near the final [C] target value, and then injecting O ₂ from a top blowing lance. After that, for example, a gas mainly composed of inert gas, neutral gas, carbon dioxide, and/or carbon monoxide is supplied at a rate of 1Nm ³ /t to Stir the molten steel by blowing at a flow rate of about 5Nm ³ /t,
Thereby, there is a method of obtaining an initial dephosphorization rate without increasing the basic unit of soda ash as described above. Figure 5 shows the relationship between the molten steel temperature and the phosphor removal rate in an experiment in which soda ash removal P was performed after the final [C] of the molten steel was reduced to 0.10% and Si=Tr or less. This experiment involved blowing hot metal with P=0.100~0.150% in a converter, C=0.10% or less, and temperature 1650~1700℃.
After converting it into molten steel, the basic unit is 15Kg/T, 10
The dephosphorization rate when treated with Kg/T of soda ash was determined, and both showed a very high rate of dephosphorization of about 85% to 95%, and at the same time, the basic unit of soda ash was also very high. shows low results. Methods for adding the solvent containing an alkali metal carbonate as a main component of the present invention include adding using a hopper installed at the top of the metal smelting furnace, and adding gas etc. as a medium through a nozzle installed below the bath surface. The method of addition is not particularly limited, and there are methods such as blowing, and even simple charging before tilting the furnace. Next, examples of the present invention will be shown. Example 1 250 tons of hot metal with the following composition and temperature was charged into a converter.

【table】 Decarburized by blowing to the following composition

[Table] 15 kg/ton of soda ash was continuously added for about 5 minutes, the blowing was completed, the composition and temperature of the final molten steel, and the composition of the slag were as follows:

[Table] As above, C=0.10%, Mn=0.25%, P=
As a result of using soda ash with a basic unit of 15 kg/t for molten steel with a concentration of 0.130% and S = 0.032%, P and S in the final molten steel can be extremely low at 0.009% and 0.010%, respectively, and the basic unit of use of soda ash is 1/3 to 1/3 compared to conventional
We were able to significantly reduce the number to 2. Furthermore, it is possible to recover phosphorus, vanadium, etc. from the slag generated by the present invention. Example 2 Hot metal with the following composition and temperature was charged into a converter.

[Table] At the end of _O2 blowing, the composition and temperature of molten steel are

[Table] Soda ash 15Kg/ton added without O ₂ blowing (top blowing), stirring for 5 minutes with CO ₂ gas only blowing (bottom blowing), composition and temperature of molten steel

【table】 Example 3 When a part of the total amount is put in at the beginning of blowing Charge hot metal with the following composition and temperature into the converter.

[Table] Initial addition of 4 kg/ton of soda ash, composition and temperature of molten steel at the end of O ₂ blowing

[Table] Addition of soda ash 14Kg/ton Bubbling with CO ₂ gas for 5 minutes, composition and temperature of molten steel

【table】 [Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between hot metal temperature and dephosphorization rate when the soda ash consumption rate is constant. Figure 2 is a diagram showing the time course of dephosphorization and desulfurization effects on undeoxidized molten steel by soda ash. , Figure 3 is a diagram showing the relationship between the amount of [C] in molten steel and the dephosphorization rate when soda ash is used,
Figure 4 is a diagram showing the relationship between the soda ash basic unit and the amount of [Si] in the hot metal, using the amount of [C] in the hot metal as a parameter. Figure 5 is a diagram showing the relationship between the molten steel temperature and the dephosphorization rate. It is a diagram showing units as parameters.

Claims (1)

[Scope of Claims] 1. In a method of refining steel in a metal refining furnace using a solvent containing an alkali metal carbonate as a main component, the solvent containing an alkali metal carbonate as a main component is used during oxygen blowing. A method of refining steel that is added to molten steel. 2. The method according to claim 1, wherein steel is refined by adding a solvent whose main component is an alkali metal carbonate as a part of the total input amount at the initial stage of blowing in a metal refining furnace. 3 Claims 1 or 2, in which steel is refined after desiliconizing hot metal before charging it into a metal smelting furnace.
The method described in section. 4. In a method of refining steel in a metal smelting furnace using a solvent mainly composed of alkali metal carbonates, the solvent mainly composed of alkali metal carbonates is added to molten steel when the decarburization reaction is mostly completed. A method of refining steel in which the steel is poured into a bath and stirred by blowing gas below the surface of the bath. 5. The method according to claim 4, wherein steel is refined by adding a solvent whose main component is alkali metal carbonate to a part of the total input amount at the initial stage of blowing in the metal refining furnace. 6 Claims 4 or 5, in which steel is refined after desiliconizing hot metal before charging it into a metal refining furnace.
The method described in section.