JPH0160526B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for dephosphorizing molten steel. As a method for removing phosphorus, an impurity element in steel,
The following methods are known. Preliminary treatment method for hot metal Dephosphorization method during converter blowing Converter double slag method Dephosphorization method for molten steel in a vessel However, the above methods have high processing costs, and the above methods have limited dephosphorization ability. The above method had a negative effect on the converter body, and the above method had the problem of increasing processing costs because the dephosphorization flux added was expensive. Recently, there has been a strong demand for ultra-low phosphorus steel, but
Ultra-low phosphorus steel of 0.005wt% or less cannot be produced by the above method, and the above method has a large negative effect on the converter body. Therefore, such ultra-low phosphorus steel is usually manufactured by the above-mentioned method, but these methods have the problem of high cost as described above. From the above-mentioned viewpoints, the present invention provides a method for dephosphorizing molten steel that can perform dephosphorization treatment at low cost and efficiently produce ultra-low phosphorus steel of excellent quality. A predetermined amount of oxidizing molten slag used for refining molten iron in a smelting furnace and quicklime were added to undeoxidized molten steel with an oxygen concentration of 400 ppm or more, which was housed in a smelting furnace. heated by
Further, the present invention is characterized in that the molten steel is dephosphorized by forcibly stirring the molten steel. Next, the present invention will be explained with reference to the drawings. FIG. 1 is a process diagram showing one embodiment of the method of this invention. In Figure 1, 1 is a converter as an example of an oxidation refining furnace, 2 is a container, and as shown in Figure A, the oxygen concentration in the steel refined by the converter 1 is
Undeoxidized molten steel 3 having a concentration of 400 ppm or more is tapped from a converter 1 and stored in a container 2. Next, in the molten steel 3 in the container 2, a predetermined amount of quicklime and a predetermined amount of oxidizing molten metal having the composition shown in Table 1 below, which has been used for refining the molten iron in the converter 1 and still has dephosphorizing ability, are added. Slag (hereinafter referred to as smelting furnace slag) is added. Next, the quicklime and smelting furnace slag are

[Table] As shown in FIG. 1B, the added molten steel is heated by arc heat from an electrode 4 and stirred by an inert gas such as argon gas injected from a lance 5. As a result, the dephosphorization slag in the molten steel 3 housed in the container 2 is promoted to become slag, and the molten steel 3 is efficiently dephosphorized. Next, the slag after dephosphorization of the molten steel on the surface of the molten steel after the dephosphorization process is absorbed and removed by the vacuum slag removal device 6 as shown in FIG. Prevents rephosphorization. In this invention, the molten steel to be dephosphorized needs to be undeoxidized molten steel with an oxygen concentration of 400 ppm or more. In other words, the oxygen concentration in the steel is
At less than 400 ppm, active dephosphorization reaction cannot occur. The amount of refining furnace slag added to molten steel is
15 to 30 kg per tonne is preferred. That is, if the amount of smelting furnace slag added is less than 15 kg/T, the dephosphorization effect is insufficient, while if it exceeds 30 kg/T, a problem arises in which molten slag overflows from the ladle when stirring the molten steel. Further, the amount of quicklime (CaO) added to the molten steel is preferably 2 to 10 kg per ton of molten steel. That is,
If the amount of added quicklime is less than 2 kg/T, the dephosphorization effect will be insufficient, while if it exceeds 10 kg/T, there is a risk that the molten steel will cool and solidify. Next, the present invention will be explained with reference to examples. The phosphorus content contained in the container is 5×10 ^-3 to 8×
Refining furnace slag in an amount of 16 to 20 Kg/T and quicklime in an amount of 4 to 6 Kg/T were added to 10 ^-3 wt% of molten steel. Next, the molten steel to which the smelting furnace slag and quicklime have been added is heated for about 10 minutes by arc heat using an electric power of 2000 to 3000 KWH, and
Forced stirring was carried out for about 10 minutes by blowing in argon gas in an amount of mm. FIG. 2 shows the phosphorus content after the above treatment. In Figure 2, white circles indicate the case of dephosphorization using the above-mentioned method of the present invention, white triangles indicate the case of adding only quicklime and smelting furnace slag as a comparative example, and black triangles indicate the case of smelting as a comparative example. The cases in which only furnace slag is added are shown in each case. As can be seen from Figure 2, the dephosphorization rate when only adding smelter slag is about 35%, and when only quicklime and smelting furnace slag are added, the dephosphorization rate is about 45%. The dephosphorization rate for the invented method is approximately 65
%. Table 2 shows the dephosphorization rates when the amounts of smelter slag and quicklime added, the heating time using arc heat, and the stirring gas injection conditions were changed. As can be seen from FIG. 2 and Table 2, the dephosphorization rate of molten steel when dephosphorized by the method of this invention was 55 to 70%, and an excellent dephosphorization effect was obtained. As described above, according to the method of this invention, inexpensive quicklime is used as a dephosphorizing agent, and the quicklime is

【table】

[Table] Efficient dephosphorization can be carried out by maximizing the dephosphorizing ability, and therefore, an excellent industrial effect is brought about in which ultra-low phosphorus steel of excellent quality can be manufactured at low cost. .

[Brief explanation of drawings]

FIG. 1 is a process diagram showing one embodiment of the method of this invention, and FIG. 2 is a graph showing the dephosphorization rate when treated by the method of this invention. In the drawings: 1... Converter, 2... Container, 3... Molten steel, 4... Electrode, 5
...Lance, 6...Vacuum slag removal device.

Claims (1)

[Claims] 1. To undeoxidized molten steel with an oxygen concentration of 400 ppm or more housed in a container, predetermined amounts of oxidizing molten slag used for refining molten iron in a smelting furnace and quicklime are added, and then the molten steel is A method for dephosphorizing molten steel, characterized in that the molten steel is dephosphorized by heating with arc heat and forcibly stirring the molten steel.