JPH0160525B2 - - 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. Undeoxidized molten steel melted in a furnace and having an oxygen concentration of 400 ppm or more is allowed to flow down from the refining furnace into a container, and a predetermined amount of quicklime is poured into the container while the molten steel is flowing down. and adding a predetermined amount of oxidizing molten slag used for refining molten iron in the refining furnace to the molten steel in the container, and forcibly stirring the molten steel in the container. This method is characterized in that the molten steel is dephosphorized by this method. 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. At this time, a predetermined amount of quicklime (CaO) is poured from the chute 4 into the container 2 where the molten steel 3 is flowing down from the converter 1, aiming at the falling point of the molten steel 3.
Insert. Then, a predetermined amount of oxidizing molten slag (hereinafter referred to as smelting furnace slag) having the composition shown in Table 1 below, which has a dephosphorizing ability until used for refining molten iron in the converter 1, is transferred from the converter 1. It is added to the molten steel in the container 2.

[Table] As mentioned above, quicklime (CaO) needs to be added to the molten steel in the container 2 when the molten steel 3 is flowing down from the converter 1 into the container 2. That is, the charged quicklime is sufficiently turned into slag by the stirring force generated by the falling flow of the molten steel 3 in the container 2, and as a result, the molten steel is efficiently dephosphorized. In addition, in the method of receiving steel in a container in which quicklime is charged in advance, the quicklime is not sufficiently turned into slag, and the dephosphorization rate of molten steel is low. In this way, dephosphorization of the molten steel 3 progresses due to the quicklime and smelting furnace slag added to the molten steel 3 in the container 2, and dephosphorization slag is produced by the quicklime and smelting furnace slag. Next, as shown in FIG. 1B, an inert gas such as argon gas is injected from a lance 5 into the molten steel 3 to which quicklime and smelting furnace slag have been added, and the molten steel 3 is forced by the gas. Stir thoroughly. By such forced stirring of the molten steel 3,
The slag formation of the dephosphorization slag is promoted, 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. Refined in a 250T converter, P content 0.010~
Molten steel of 0.020 wt%, oxygen concentration of 500 to 700 ppm, and a temperature of 1670°C was supplied from the converter into the vessel.
Then, 15Kg/T and 20Kg/T were added to the molten steel in the container.
T of converter slag was added, and 2 to 6 kg/T of quicklime (CaO) was charged into the container in which the molten steel was flowing down. Next, 2000/mm of argon gas was blown into the molten steel in the container to forcibly stir the molten steel to perform a dephosphorization treatment, and then the slag was removed using a vacuum slag removal device. The temperature of the molten steel after dephosphorization was 1580°C. Figure 2 shows the dephosphorization rate when 15 kg/T of converter slag is added, and Figure 3 shows the dephosphorization rate when 20 kg/T of converter slag is added. In FIGS. 2 and 3, white circles indicate the dephosphorization rate when quicklime is charged into a container in which molten steel is flowing according to the method of the present invention, and black circles indicate the dephosphorization rate when quicklime is charged into the container in advance. As can be seen from FIGS. 2 and 3, the dephosphorization rate of molten steel when dephosphorized by the method of this invention was 60 to 65%, and an excellent dephosphorization effect was obtained. As described above, according to the method of the present invention, it is possible to use inexpensive quicklime as a dephosphorizing agent, maximize the dephosphorizing ability of the quicklime, and perform efficient dephosphorization treatment. As a result, an excellent industrial effect is produced 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 FIGS. 2 and 3 are graphs showing the dephosphorization rate when treated by the method of this invention. In the drawings, 1... converter, 2... container, 3... molten steel, 4...
Chute, 5... Lance, 6... Vacuum slag removal device.

Claims (1)

[Claims] 1. Undeoxidized molten steel melted in a refining furnace and having an oxygen concentration of 400 ppm or more is supplied into the container by flowing down from the refining furnace into the container, and a predetermined amount of the molten steel is poured into the container while it is flowing down. of quicklime, and adding a predetermined amount of oxidizing molten slag used for refining molten iron in the refining furnace to the molten steel in the container,
A method for dephosphorizing molten steel, characterized in that the molten steel in the container is dephosphorized by forcibly stirring the molten steel.