Free cutting mild steel and process for manufacturing same

摘要

A soft steel for machine cutting with high machinability performances having a content of C/=0.25%, a content of Mn of 0.8 to 1.5%, a content of P of /=0.1%, a content of S of 0.15 to 0.40%, and a content of Si of 0.05 to 0.40%, expressed in percentages by weight. After finishing of the metal, the inclusions of manganese sulfide are surrounded by a plastic oxide layer of an average composition SiO2: 35 to 45%; Al2O3: 10 to 20%; CaO: 15 to 25%; MnO: 10 to 20%. In producing this grade, after the addition of silicon and manganese, the liquid metal is agitated in the presence of a slag of a composition CaO: 20 to 55%; SiO2: 35 to 65%; Al2O3: 15 to 40%; with a CaO %/SiO2% ratio of about 1.