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Key technology of smelting stainless steel in combined blowing converter

[09/10/2018]

Hot metal dephosphorization technology. When the hot-smelting converter uses molten iron to smelt stainless steel, the dephosphorization of the molten iron is first carried out, or the dephosphorization is carried out by a mixed iron car, or the dephosphorization is carried out in a double-blown converter.

Converter thermal compensation technology. Since stainless steel is a high-alloy steel, it is necessary to add a large amount of cold alloy during smelting. For example, only the sensible heat and oxidation heat of molten iron are used to make steel in the converter, and the heat energy is obviously insufficient. According to the calculation, the heat shortage of the stainless steel SCTS304, SC1S316, SC1S410, SC1S420 and SUS430 in the whole molten iron condition is about 11.5%, 14.6%, 6.1%, 8.0% and 5.4%, respectively, for which the development cost is low. Technology is an indispensable technology for smelting stainless steel in a combined blown converter. Nowadays, the thermal compensation technology of the secondary combustion (called PC gun) of the top of the furnace and the broken coke block (granule) and the double-flow oxygen lance are generally used.

Thermal compensation technology for crushing coke blocks (grain) on the top of the furnace: The thermal compensation technology using broken coke particles as a heat source has the following advantages over the method using FeSi as a heat source:

a. The remaining coke blocks (granules) remaining in the steel plant can be used, and the source is wide and the price is cheap;
b. Even if used in large quantities, the amount of slag increases a lot;
c. The generated CO gas can be effectively utilized as a heat source.
Thermal compensation through secondary combustion: The secondary combustion thermal compensation technology of the dual-flow oxygen lance can tap the potential of chemical heat in the furnace, thereby reducing the amount of coke thermal compensation, thereby shortening the blowing time and oxygen consumption.

The use of a dual-flow oxygen lance increases the secondary combustion rate of CO.

The secondary combustion rate is increased by controlling the ratio of the oxygen amount of the main and auxiliary oxygen holes. The secondary combustion rate is the highest when the ratio of the secondary pore oxygen to the main pore oxygen is 20%. In addition, increasing the height of the lance is also beneficial to increase the secondary combustion rate.

Since the main alloy of stainless steel, the inscription element, is easily oxidized at high temperatures, it is necessary to have sufficient decarburization capability in the converter to smelt stainless steel, and also to suppress the oxidation loss of chromium.

According to the principle of metallurgy, the higher the temperature of molten steel, the better the decarburization reaction; the lower the partial pressure of CO in the converter is beneficial to the reduction of chromium, and the oxidation loss of chromium can be suppressed while blowing oxygen decarburization. In order to meet the requirements of thermodynamic theory, the converter is usually diluted or refined to dilute the concentration of CO generated in the converter due to the decarburization reaction with a large flow of bottom-blown inert gas to reduce the partial pressure of CO. At the same time, it can also promote the stirring of molten steel and accelerate the decarburization reaction. In addition, in the control of molten steel temperature, we must first overcome the problem of insufficient heat source, and then effectively achieve high temperature (≥1700 °C) operation.

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