Research and practice of calcium treatment processes in sulfur-containing free-cutting steel
Due to its good mechanical properties and cutting performance,sulfur-containing free-cutting steel is widely used in industries such as automotive manufacturing,machinery manufacturing,and shipbuilding industry.With the development in the fields of infrastructure,passenger vehicles,and maritime transportation in recent years,the production volume and quality requirements of sulfur-containing free-cutting steel have also increased.The method of calcium treatment is usually used to regulate the inclusions in the steel.However,the sulfur-containing characteristics of sulfur-containing steel have a significant negative effect on the cleanliness and castability of the steel during the smelting and casting processes.Therefore,establishing a reasonable calcium treatment pro-cess is of great importance for improving the castability of sulfur-containing free-cutting steel.The effects of factors such as the timing of sulfur wire addition,the time interval between feeding calcium wire and sulfur wire,and the amount of calcium wire added on the cleanliness of the steel and the clogging of nozzle were systematically investi-gated,analyzing the main reasons for the nozzle clogging in sulfur-containing free-cutting steel.The research shows that inclusions with CaS on the surface and Al2O3 in the core are generated in the steel after feeding sulfur wire and calcium treatment.The continuous deposition and adhesion of these inclusions on the inner wall of the nozzle are the main cause of nozzle clogging.In steel with w([Al])=0.03%,when w([S])exceeds 0.015%,it is prone to the formation of high melting point inclusions,deteriorating the castability of the steel.For 140 t of 45S sulfur-containing free-cutting steel,feeding the sulfur wire separately after LF and RH,extending the feeding interval between calcium wire and sulfur wire to over 10 minutes,and reducing the total feeding amount of calcium wire to below 100 m can effectively reduce the quantity of CaS·Al2O3 inclusions in the steel.This can increase the number of continuous casting heats for 45S steel to over 15 heats.It provides a theoretical basis for optimizing the calcium treatment process of sulfur-containing free-cuttingsteel,which helps improve production efficiency and product qual-ity.It is of great significance for promoting the application and development of sulfur-containing free-cutting steel in the fields of machinery,transportation,and other industries.Future research will focus on how to control the quan-tity and morphology of inclusions in sulfur-containing steel,the impact of inclusions on the quality of steel plates after rolling,and how to reduce the amount of calcium added.
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