JPS621442B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing molten stainless steel at low cost, safely, and in a short time that enables continuous casting by rationally combining pretreated hot metal with molten metal in an electric furnace. Generally, when melting stainless steel, scrap containing Cr and Ni is charged into an electric furnace and melted, and then refined in the electric furnace as is, or the molten metal is transferred to an AOD furnace, a VOD ladle, etc. , a bottom blowing converter (CLU), or recently, a melting method has been adopted in which Cr is charged into a top and bottom blowing converter and heated to decarburize without oxidizing the Cr. If the time for such electric furnace melting and decarburization furnace steps is too long, the next continuous casting step will be a one-heat single-shot casting. Continuous casting is performed continuously to multiple times, which results in lower steel manufacturing costs, so it is desired to shorten the process from melting in an electric furnace to decarburization. The present inventors have made various attempts to shorten this process. First, when we increased the power of the electric furnace to shorten the time required for melting, hot spots appeared.
It was found that the electric furnace wall was damaged by melting, and that unmelted parts were likely to remain due to cold spots.
It has been found that shortening the operating time of electric furnaces is extremely difficult. Therefore, by reducing the charging amount of the electric furnace and relatively increasing the electric power load, the melting time can be shortened, and the insufficient raw material can be removed by removing P and S by light charging of the electric furnace.
We investigated the possibility of combining hot metal with pre-treated hot metal. In this case, unless the hot metal is sufficiently pretreated and dephosphorized, no dephosphorization can be expected during the decarburization process in stainless steel refining.
It goes without saying that regulations need to be regulated at the raw material blending stage. Regarding the method of combining electric furnace molten metal and pretreated hot metal, the first method is to separately charge each molten metal into a converter charging ladle and mix them within the converter. This method is
Since the converter is charged twice, the charging time is extended, and since a small amount of molten metal is handled, the temperature of the molten metal decreases significantly due to heat transfer to the ladle refractory and heat dissipation, and subsequent desorption inside the converter is required. Severe oxidation of Cr during charcoal blowing
Cr yield decreased. The second method of pouring is to pour pre-treated hot metal into a converter charging ladle that holds molten metal in an electric furnace. In this method, when the C value of the electric furnace molten metal is low, the oxygen content is high, and when the molten metal is injected, the C-
The reaction may cause the molten metal to protrude, and if the electric furnace slag contains a large amount of iron oxide, the molten metal may protrude due to the reaction between iron oxide and hot metal C when charging the hot metal, which is dangerous. Ta. The third method of combining hot metal is to charge molten metal into a converter charging ladle, pre-treating the hot metal, and then charging the molten metal from an electric furnace into the converter charging ladle. This method is safe because the temperature drop of the molten metal is small and there is no risk of protrusion. Since only one ladle is used, heat transfer to the ladle refractory and heat dissipation are reduced, and as a result of suppressing temperature drop, the Cr yield in the subsequent converter refining process is improved. Furthermore, we investigated the relationship between the Cr yield and the temperature of the molten metal after joining, and found that the Cr yield improved at temperatures above 1350°C. The present invention has been completed based on the above knowledge, and when producing molten stainless steel, hot metal is received in a converter charging ladle, the hot metal is pretreated, and then the stainless steel is prepared in an electric furnace. The molten iron whose composition has been adjusted is melted, and the molten iron is charged into the converter charging pot and combined with the pretreated hot metal, and the temperature of the molten iron after the combining is preferably 1350°C or higher. It is characterized by ensuring a temperature of 1400°C or higher and charging the combined metal into a bottom blowing or top and bottom blowing converter. In the present invention, pre-treated hot metal and molten iron for stainless steel made in an electric furnace are charged into one converter charging pot in a certain order and combined, and then bottom-blown or top-bottomed Basically, it is refined in a blowing converter. By the method of the present invention, molten stainless steel can be produced safely, inexpensively, and in a short time while maintaining an appropriate temperature, making it possible to continuously cast stainless steel, which has technical and economical effects. Extremely large. The cost of manufacturing stainless steel is determined by the cost of the main raw materials, the amount of Cr oxidized in the oxidation process, the unit consumption of gas such as oxygen or argon, operating time, continuous casting cost, etc. These entire processes are streamlined. Converter steelmaking enables the use of blast furnace hot metal and inexpensive high-carbon Fe-Cr, contributing to high productivity and reduction of thermal energy due to high decarburization rate, and is a refining method that can prevent oxidation of Cr. It is. As described above, the method of the present invention has not only established a stable melting process to obtain inexpensive stainless steel, but also made it possible to perform multiple continuous castings, which not only reduces steel manufacturing costs but also improves quality. It had a very noticeable effect on stability. Example 50 tons of desiliconized hot metal was discharged into a converter charging pot using a torpedo car. The components of the hot metal at this time are
It was as shown in Table A. Treatment was carried out by injecting 45 kg/t of CaO-based flux into the hot metal in the converter charging ladle using an immersion lance. As a result of this treatment, the hot metal components and temperature in the converter charging ladle became as shown in Table 1B. Next, the converter charging pot was loaded with 85t of processed hot metal.
The steel was set at the tapping port of the electric furnace, and the molten iron from the electric furnace was charged into the converter charging pot and mixed. The amount of molten iron charged into the electric furnace was 53.5 tons. The components and temperature of the electric furnace molten iron were as shown in Table 1C, and the components and temperature after mixing were as shown in Table 1D. The melting process is extremely stable, and the molten metal temperature is
We were able to easily maintain a temperature of 1400℃ or higher.

[Table] After combining, 103 tons of stainless steel mother metal was charged into a top-bottom blowing converter, and after efficient normal decarburization blowing, reduction with Si was performed and steel was tapped.

Claims (1)

[Claims] 1. In producing molten stainless steel, hot metal that has been received into a converter charging ladle and subjected to hot metal pretreatment, and molten iron made in an electric furnace that has been adjusted and melted for stainless steel are placed in the converter equipment. A stainless steel mother molten metal characterized by combining the metal in a pot, ensuring the temperature of the molten metal after the combining is 1350°C or higher, and then charging the combined metal into a bottom-blown or top-bottom-blown converter. Production method.