JPS58181815A - Preliminary desiliconizing method of molten pig iron in converter - Google Patents

Abstract

PURPOSE:To efficiently and economically desiliconize molten pig iron preliminarily in a converter, by using as a desiliconizing agent slag which has been formed during refining molten pig iron in the converter. CONSTITUTION:The slag produced in a molten steel-making process which has been formed during blowing pig iron containing at least carbon and phosphorus as a main raw material in a converter is wholly or partially left in the furnace to use it as a desiliconizing agent, and fresh molten pig iron is poured in the converter and desiliconized preliminarily. This desiliconizing agent is generally used by about 20-50kg per ton of molten pig iron, and other desiliconizing agents may be conjunctly used up to a ratio of about a third of said desiliconizing agent.

Description

[Detailed Description of the Invention] This invention provides a method for refining hot metal in a converter.
The present invention relates to a method for preliminary desorption of hot metal using a converter, which efficiently and economically removes silicon, which is an impurity in hot metal.

In recent years, from the viewpoints of the need to produce ultra-low phosphorus and ultra-low IA'i14, to improve the total iron yield during hot metal refining, and to reduce the amount of slag generated and use it effectively, hot metal has been used before converter steelmaking. Preliminary refining is carried out in stages to remove impurities in the hot metal. Among such preliminary refining of hot metal, preliminary desulfurization of hot metal for producing low sulfur steel is almost completely established in refining operations, and recently it has been used for the production of ultra-low phosphorus copper.
Preliminary desiliconization of hot metal prior to preliminary dephosphorization is attracting attention.

Conventionally, such a preliminary deborening means for hot metal is carried out before refining the hot metal in a converter, for example, in a tap trough through which the hot metal tapped from the blast furnace flows, during the hot metal receiving into the hot metal ladle, or in a separately provided hot metal This was done by adding a desiliconizing agent into a container containing hot metal in a pre-treatment yard, or by adding a desiliconizing agent to hot metal in a converter and performing oxidative refining.

In the above-mentioned method, the desiliconizing agent added to the hot metal is conventionally a single substance or a mixture of scale, sintered ore, iron ore, or CaO, CaF, , and other fluxes are used, and this has a certain degree of desulfurization effect.

However, in the above method, the desulfurization agent used is expensive;
Moreover, the desulfurization process takes a long time due to the delay in desulfurization agent slag formation, resulting in increased heat loss and refractory erosion.In addition, undesirable decarbonization and deMn reactions progress during the desulfurization stage, causing the desulfurization reaction to slow down. There was a problem with it being incomplete.

From the above-mentioned viewpoint, the present invention provides a preliminary desulfurization method for hot metal that efficiently and economically removes silicon from hot metal using a converter. This method is characterized in that the molten steelmaking slag produced during production is used to oxidize and refine the hot metal to be pre-desulfurized in a converter using the molten steelmaking slag as a desulfurization agent.

In this invention, all or all of the molten steel slag produced when blowing is performed in a converter using pig iron containing at least carbon and phosphorus, such as ordinary pig iron, desulfurized pig iron, and desulfurized pig iron, as a main raw material. A portion of the molten steel slab remains in the furnace and is used as a desulfurizing agent, and the molten iron to be desulfurized is received in the converter where the molten steel slab remains for desulfurization treatment.

Table 1 shows an example of the composition of ordinary pig iron, and Table 2 shows an example of the composition of steelmaking slag produced when producing carbon steel by refining ordinary pig iron in a converter. In addition,
Desulfurized pig iron means pig iron in which only the amount of Si is less than 0.15%, and desulfurized pig iron means pig iron in which only the amount of S is less than 0.020%.

Table 1 (wt%) Table 2 (section 1) ('f', Fe: iron present as iron oxide) The amount of the molten steel slab as described above left in the converter as a desulfurization agent is usually It may be 20 to 50 kg per IT, and up to about two-thirds of it may be a conventional desulfurization agent, and both may be used in combination.

Next, the present invention will be explained with reference to examples.

After blowing 290T of hot metal into low carbon steel in a 300T capacity pure oxygen top-blowing converter, the molten steel is tapped and only the generated slag is placed in the furnace for about 12T.

(About one-third of the total slab amount) was left behind. Table 3 shows the composition and temperature force of the hot metal and molten steel;
The table shows the composition of the slag produced.

Table 3 Next, Table 4 shows the desulfurization process to be performed in the converter in which molten steel slag with the composition shown in Table 4 below remains.
(wt%) 290T of hot metal was charged and heated to 1500T for 3 to 4 minutes.
Oxidative refining was carried out by spraying 02 gas in an amount of ~250 ON- onto the hot water surface.

Table 5 shows the composition and temperature of the hot metal before desulfurization smelting and after desanding scouring, and Table 6 shows the composition of slag produced by desulfurization smelting.

Table 5 Table 6 (Weight %) According to the method of this invention, as shown in Table 5 above,
The desanding process was completed in an extremely short time of 3 to 4 minutes, and the 81 content in the hot metal could be reduced from 0.45% to 0.3%, while the amount of carbon removed was 0.43%. Seed amount is 0
．． We were able to keep it to an extremely low value of 0.8%. In addition, the iron oxide content in the slag after desorption refining is 3.5% in T, Fe as shown in Table 6, compared to 25.7% before desorption refining as shown in Table 4. It has decreased significantly. Therefore, it can be seen that this slag reacts effectively as a desiliconizing agent, and that the Fe yield is improved by 0.5% or more due to the reduction of iron oxide. In addition, the molten pig iron that has been desanded and refined has been dephosphorized by <0.023% as shown in Table 53, and the heat of the molten slag that remains in the converter when the desiliconizing agent is injected into the converter causes the reaction to take place. The temperature of the hot metal after desorption refining was raised by 172°C compared to before desorption refining, demonstrating extremely good thermal efficiency.

Furthermore, the slag after desorption refining has a CaO/SiO□ of 2.
Although it is slightly expensive at 29, it does not contain any unsludged lime, so it can be used effectively as it is for roadbed materials, etc.

Next, the effects of this invention will be described.

(1) The steelmaking molten slag used in the method of this invention is
Since it is already in a slag and molten state, it immediately contributes to the desanding reaction, and its retained heat is effectively used for the reaction, and desanding is carried out in an extremely short time, reducing heat loss.
Erosion loss of refractories is reduced, and de-C1 de-Mn reactions are suppressed.

(2) Since steelmaking slag itself is waste, it is inexpensive.

(3) The Fe content (reduced part of granular iron and iron oxide) in steelmaking slag is effectively recovered, and the total iron yield is improved.

+4+ Since steel slabs usually contain unsludged lime and have the property of expanding and collapsing, they could not be used as roadbed materials, etc. However, the slag produced after using this method as a desiliconizing agent , because it does not contain unsludged lime,
This can be effectively used as is for roadbed materials, etc.

The above-mentioned embodiment describes the case where desanding and refining is carried out using a pure oxygen top-blown converter, but it is not limited to a pure oxygen top-blowing converter.
Similar effects can be achieved by performing sand removal and refining using a bottom blowing converter or a top and bottom blowing combined blowing converter.

Applicant: Nippon Kokan Co., Ltd. Agent: Keitabe and 1 other person

Claims (1)

[Claims] In a method of preliminarily desiliconizing the hot metal by adding a desiliconizing agent to hot metal in a converter and performing oxidation refining, as the desiliconizing agent,
It is characterized by using a molten steel slab produced when refining hot metal in a converter to produce steel, and oxidizing and refining the hot metal to be preliminarily desiliconized in the converter using the molten steelmaking slag as a desiliconizing agent. A method for preliminary desorption of hot metal using a converter.