JPS60230932A - Method for operating electric furnace for manufacturing steel - Google Patents

Abstract

PURPOSE:To reduce the cost of manufacture of a steel ingot by using converter slag formed during the manufacture of steel in place of part of CaO as a slag forming agent to be charged into an electric furnace so as to reduce the amount of CaO used. CONSTITUTION:Converter slag with high basicity formed during the manufacture of steel is used in place of part of CaO as a slag forming agent to be charged into an electric furnace for manufacturing steel. The preferred basicity of the converter slag is >=about 4. By this method, the amount of CaO used is reduced to reduce the cost of manufacture of a steel ingot, converter slag can be effectively utilized, and the yield of manufacture of steel can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating an electric furnace for steelmaking.

When making steel using an electric furnace for steelmaking, we use slag to increase the basicity of the slag to promote desulfurization and dephosphorization reactions, as well as to protect the refractories in the furnace and prevent heat radiation from the molten steel in the furnace. CaO is used as an agent.

Conventionally, this CaO has relatively few impurities, so limestone or quicklime has been mainly used.
I needed an amount of 2 to 30 to 50.

The present inventor has conducted repeated research in an attempt to reduce the manufacturing cost of steel ingots by reducing the amount of limestone and quicklime used. First of all, the inventor of the present invention believes that it is not necessary to use only limestone or quicklime as a CaO source in view of the purpose of use of the slag-forming agent mentioned above. I focused on the good things.

Therefore, from the above-mentioned viewpoint, we investigated other inexpensive raw materials that could be used as slag-forming agents, and found that the slag generated during steelmaking by the basic converter steelmaking method has a high basicity and a comparatively low level of impurities. It was discovered that it could be used as a partial substitute for conventional limestone and quicklime, as it has a small amount of carbon dioxide.

In other words, the basicity of the basic converter steelmaking method is to produce high basicity slag for desulfurization and dephosphorization and for the protection of the converter floor refractories, so the basicity of the slag is It is 3.0 or more. With recent advances in hot metal pretreatment technology, the P and S contents of slag have been significantly reduced.

This invention was made based on the above findings, and
When manufacturing steel using an electric furnace for steelmaking, a feature is that converter steelmaking slag with a high basicity is used as part of the CaO as a slag-forming agent charged into the electric furnace. .

Next, the reduction rate of the amount of CaO used when the method of the present invention is implemented will be explained.

Table 1 The relative ratio α of basicity between the conventional method and the method of the present invention shown in Table 1 is as follows: A/B −α(A′+C)/(B+D)
...(11) The relationship of equation (1) is established, and the basic unit of CaO can be reduced by (AA').

In actual operation of an electric furnace for steelmaking, low basicity operation is possible with the above α up to about 1.25 depending on filtering.

Therefore, the amount of CaO used (A) in the conventional method was reduced to 30
kr/T, usage amount (B) of 5iOz] 2 plums/T
The converter slag (CaO content:
40wt, %, basicity: 4) usage amount at 25 kp/T
Then, the reduction rate of the amount of CaO used by the method of the present invention is as shown in Table 2.

As is clear from Table 2, according to the method of the present invention, when operating at the same basicity as the conventional method, the amount of CaO used was reduced by 12.7 at 26.2 kf/T, compared to the conventional method. For example, when operating at a low basicity of 1.25, Ca
The amount of O used is 19. Oky/T can be reduced by 36.7%.

Next, the method of the present invention will be explained using examples.

Table 3 shows a comparison of operational examples between the method of the present invention and the conventional method. The component composition of the converter slag used in the method of the present invention is: CaQ: 40.0%, 5iOz: 1
0.0%, FeO: 2 5%; , S Co゛O,
1%, MgO: 10.3%, MnO: 5.2
%, At20s: 1.0%, P2O5: 2.
The basicity is 0% (all the above examples are weight %) and the basicity is 4.0.

As shown in Table 3, according to the method of the present invention, the manufacturing cost of steel ingots can be reduced by 93 to 310 yen/T, and the influence of the content of P and S in molten steel is within a negligible range. There were no problems with the operation of the electric furnace.

The converter slag used in the method of the present invention does not necessarily have a basicity of 4.0 or more, but if the basicity is low, it is necessary to increase the amount of converter slag added.
It is better to use converter slag with a basicity of at least 3.5 or more, preferably 4.0 or more.

Furthermore, as mentioned above, converter slag mainly contains F.
It contains a considerable amount of Fe consisting of eO. Therefore,
In the slag generation process during electric furnace refining, the amount of FeO absorbed by CaO is reduced by the amount of CaO substituted for converter slag, and is recovered as metal, so the yield of molten steel can be improved.

As described above, according to the method of the present invention, the amount of CaO used in electric furnace smelting can be reduced, the cost of producing steel ingots can be reduced, and a large amount of CaO can be used in the steelmaking process at a steelworks. Many excellent industrial effects are brought about, such as the ability to effectively utilize converter slag, which has been generated and is difficult to dispose of.

Applicant Toshin Steel Co., Ltd. Agent: Natsuo Shioya (and 2 others)

Claims (1)

[Claims] A steelmaking process characterized in that converter steelmaking slag with a high basicity is used as a part of CaO as a slag-forming agent charged into the electric furnace for producing steel in the electric furnace for steelmaking. How to operate a commercial electric furnace.