JPH04263004A - Method for pretreating molten iron - Google Patents

Abstract

PURPOSE:To reduce loss of a molten iron and to enable efficient treatment by blowing a dephosphorizing agent into the molten iron from an immersion lance and, on the other hand, adding a basicity adjusting agent and a softening agent on the molten iron at the time of pre-treating the molten iron. CONSTITUTION:The dephosphorizing agent composed of oxidizing agent of mill scale, etc., and slag making agent such as lime together with carrier gas such as N2 are blown from an immersion lanced immersed into the molten iron. In the initial period (desiliconizing period) of dephosphorizing treatment, particularily, in the period of low basicity, the basicity adjusting agent as lime and the softening agent such as fluorite are added on the bath to control the slag-making. By this method, foaming of the slag is restrained and over-flow from the vessel is prevented, and also treating time can be shortened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pre-treating hot metal, and in particular aims to reduce iron loss during the pre-treatment and to improve the efficiency of the treatment time.

0002

[Prior Art] In recent years, the combined blowing method of bottom blowing and top and bottom blowing has been implemented, and the treatments of desiliconization, dephosphorization, and desulfurization in the pretreatment stage of hot metal are essential, and various processes are It has been developed and implemented. As one of the hot metal pretreatment methods, JP-A-58-16006 discloses
A flux consisting of an oxidizing agent such as mill scale, a slag forming agent such as quicklime, and a softening agent such as fluorite is blown below the surface of the hot metal bath together with a carrier gas such as N2 or compressed air, and the oxidizing agent and P in the hot metal are mixed. A method has been proposed in which P2O5 is generated through a reaction, floated onto the surface of the hot metal bath, and then fixed with a slag-forming agent for efficient dephosphorization.

0003

[Problems to be Solved by the Invention] However, in this method, during the preliminary treatment of hot metal, if there is a problem where the slag overflows from the container due to bubbling, it is necessary to reduce the flux blowing speed or It was necessary to take measures to lengthen the processing time, such as by adjusting the mixing ratio of the basicity regulator and oxidizing agent. In particular, when the treatment time is extended, the slag hardens due to temperature drop and the reaction interface area decreases, so even if P2O5 floats to the surface, it dissociates without being fixed to the slag, and there is a problem that effective dephosphorization cannot be performed. Ta. Although some attempts have been made to address this issue by incorporating a softener into the flux, it is necessary to increase the blending ratio of the softener in the flux in response to the drop in temperature of the slag over the course of processing time. At present, it cannot be said that efficient dephosphorization treatment is possible.

It is an object of the present invention to propose a hot metal pretreatment method that solves the above-mentioned conventional problems and enables efficient treatment.

[0005]

[Means for Solving the Problems] In the dephosphorization treatment of hot metal, the present invention involves blowing a dephosphorizing agent consisting of an oxidizing agent and a slag-forming agent together with a carrier gas through an immersion lance whose one end is immersed in a bath of hot metal; This hot metal pretreatment method is characterized in that slag formation is controlled by adding a basicity regulator and a softener onto the hot metal bath surface.

[0006]

[Operation] During dephosphorization, a flux consisting of an oxidizing agent such as mill scale, a slag forming agent such as quicklime, and a softening agent such as fluorite is blown into the surface of the hot metal bath together with a carrier gas such as N2 or compressed air. As mentioned above, the processing time may have to be extended due to the processing conditions and flux blending ratio. Here, slag overflow during dephosphorization is often seen in the initial stage of dephosphorization (desilication stage), especially when the concentration of SiO2 in the slag is high and the basicity (CaO/SiO2) is 1.5 or less. Occurs when the temperature is low. For this reason, in this invention, a basicity regulator such as quicklime is added to the hot metal surface at this time to increase the basicity of the slag, thereby suppressing foaming of the slag and preventing overflow from the container. Furthermore, the temperature of the slag decreases with the passage of processing time, and as mentioned above, the processing efficiency decreases due to hardening of the slag, so it was decided to add a slag softener such as fluorite to the surface of the hot metal bath. In this invention, the basicity regulator and slag softener are added onto the surface of the hot metal bath because it is not necessary to change the addition ratio of the oxidizing agent blown into the hot metal bath and is advantageous in shortening the processing time. be. In particular, when suppressing slag overflow, there is no need to reduce the blowing speed of the basicity regulator, and the processing time can be shortened.

FIG. 1 shows an example of an apparatus suitable for carrying out the present invention. In the figure, 1 is a torpedo car containing hot metal, 2 is a torpedo car containing hot metal, 3 is a slag, and 4 is a torpedo car containing one end. An immersion lance 4 is immersed in a hot metal bath, and this lance 4 blows a slag forming agent for dephosphorization into the hot metal bath together with a carrier gas such as N2. Reference numerals 5 and 6 designate containers containing basicity regulators and softeners, 7 a device for discharging the contents in the containers 5 and 6, and 8 an oxygen blowing lance used for temperature compensation.

[0008]

[Example] In a torpedo car as shown in Figure 1 above, 2
It accommodates 80 tons of blast furnace hot metal and produces 15k per ton of hot metal.
g of mill scale was added to perform Si removal treatment until the Si content became 0.10%, and then the slag produced in the Si removal treatment was removed until it became about 1.0 kg/t-p. Using an immersion lance, add 1 ton of mill scale, a dephosphorizing agent and a slag-forming agent consisting of quicklime and fluorite to hot metal.
30kg, 10kg, and 2kg of each are blown into the hot metal bath together with N2 gas to perform dephosphorization treatment, reduce hot metal loss,
We investigated the time required for dephosphorization treatment. In addition, from above the surface of the hot metal bath, 5 liters of quicklime was added at the beginning of the dephosphorization process.
kg/t-p, and 2 kg of fluorite in the middle stage of dephosphorization treatment.
/t-p added. The results are shown in Table 1 in comparison with the results when dephosphorization was performed according to the conventional method.

[0009]

[Table 1]

[0010] Compared to the conventional method in which a dephosphorizing slag agent, basicity regulator, and softener are all blown into the hot metal bath, the adapted example according to the present invention can shorten the processing time and reduce the amount of slag. It was confirmed that the loss of hot metal due to overflow was extremely small.

[0011]

Thus, according to the present invention, (1) overflow due to foaming of slag during dephosphorization treatment can be suppressed, so iron loss is small and operational troubles are extremely small. (2) Productivity can be significantly improved by shortening processing time. (3) Since highly efficient dephosphorization treatment can be performed, the dephosphorization load in downstream processes can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of equipment suitable for use in implementing the present invention.

[Explanation of symbols]

1 Torpedo car 2 Welding 3. Slag 4 Immersion lance 5 Container 6 Container 7 Dispensing device 8 Oxygen blowing lance

Claims (1)

[Claims] Claim 1: During the dephosphorization treatment of hot metal, a dephosphorizing agent consisting of an oxidizing agent and a slag-forming agent is blown in together with a carrier gas through an immersion lance whose one end is immersed in the hot metal bath, while a basicity A hot metal pretreatment method characterized by controlling slag formation by adding a conditioner and a softener.