Effect of Selenium on Sulfide Formation and Machinability of 303Cu Free‐Cutting Stainless Steel

This study systematically investigates the influence of selenium on the morphology and distribution of sulfides in as‐cast and hot‐rolled 303Cu stainless steel under varying oxygen content conditions. The role of selenium in improving machinability is examined, and the underlying modification mechanisms are thoroughly elucidated. Selenium primarily dissolves in MnS to form the Mn(S,Se) phase. In both relatively high‐oxygen and low‐oxygen as‐cast steels, selenium effectively suppresses the aggregation tendency of sulfides and promotes the formation of isolated sulfides; this effect intensifies with increasing selenium content. Concurrently, the microhardness of the sulfides gradually increases with higher selenium content, enhancing their resistance to rolling deformation and leading to a significant reduction in the aspect ratio of sulfides after hot rolling. Turning test results further show that selenium addition reduces cutting forces and increases the proportion of short chips in the chip stream, thereby improving machinability. Based on these experimental findings, it is recommended that in industrial production, the dosage of deoxidizers be moderately reduced, the oxygen content be reasonably controlled, and the addition of selenium be employed to further optimize the morphology and distribution of sulfides, thereby enhancing the overall performance of the steel.