Secondary refining technology plays a crucial role in modern steel - making, offering a wide range of functions. It can effectively uniformize the temperature and composition of molten steel, adjust its chemical makeup, and carry out various purification processes such as degassing (including decarburization, denitrification, and dehydrogenation), deoxidation, desulfurization, and dephosphorization. Additionally, it enables precise temperature control of the molten steel and the management of inclusion shapes. To meet different functional requirements, such as molten steel stirring, powder injection, alloy addition, furnace atmosphere control, decompression, and heating, a variety of secondary refining processes are currently under development.
During the period of rapid economic growth, Japanese iron and steel conglomerates made significant strides in steel - making technology. They established a "converter - secondary refining" steelmaking process with the aim of enhancing the quality of converter steel. This approach not only expanded the range of steel grades that could be produced by the converter but also increased its productivity. By integrating secondary refining into the converter - based production, they successfully developed a mass - production method for multi - variety, high - quality steel. This was a strategic move to meet the growing market demand for diverse and high - performance steel products.
In the realm of electric furnace steelmaking, the LF (Ladle Furnace) method emerged as a game - changer. It transferred the smelting operations during the reduction period of electric furnace steelmaking to the secondary refining stage. This transfer significantly improved the productivity of electric furnaces. At present, various secondary refining equipment has been put into use in electric furnace steelmaking. These equipment are designed to meet the requirements of electric furnaces with multiple functions, such as oxygen blowing, and the demand for high - quality steel production. They enable more efficient and precise control over the steel - making process, resulting in better product quality.
In the 1980s, the proportion of refining treatment for high - purity steel, exemplified by ultra - low carbon steel, increased. This led to higher demands for mass treatment of molten steel and the simplification of the treatment process. As various processing technologies improved, additional processing functions were incorporated into existing secondary refining processes. This transformation accelerated the development of reaction vessels, shifting them from simple processing units to intensive and multifunctional ones. However, one challenge in the secondary refining process was the rapid drop in the temperature of molten steel. To address this, equipment with the function of raising the temperature was actively developed and introduced. This not only helped maintain the appropriate temperature for subsequent processes but also reduced the load on the refractory materials of the converter after tapping, as the initial tapping temperature could be better controlled.
To cut the production cost of low - phosphorus steel, hot metal pretreatment technology was introduced. On one hand, this technology optimized the smelting functions of the converter and secondary refining, making the overall process more efficient. On the other hand, it spurred the development of various refining processes aimed at achieving high - purity and ultra - high - purity clean molten steel. The rapid development of these production technologies has enabled the steel industry to produce steel with extremely low levels of impurities, meeting the stringent requirements of high - end applications in industries such as automotive, aerospace, and electronics.
In conclusion, the development of secondary refining technology has been a continuous process driven by the need for higher - quality steel, increased productivity, and cost - effectiveness. Through technological innovations and process optimizations, the steel industry has been able to meet the evolving market demands and stay competitive in the global market.
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