Abstract: The industrial test of inclusions modification by calcium treatment in sulfurcontaining non quenched and tempered steel was carried out. The effect of calcium treatment on inclusions evolution was obtained by the qualitative study in which inclusions changing with the development of process was analyzed by using SEM and EDS. In order to control sulfides morphology, the type，quantity and size of sulfides before and after calcium treatment were quantitatively analyzed by INCA Feature with automatically scanning inclusions function. It is found that calcium treatment can increase the quantity of compound sulfides, especially the calciumcontaining compound sulfides, and then in favor of reducing the proportion of long strip sulfides by forming more globular or spindle sulfides, finally improve the anisotropy of steel. The mechanism of sulfides modification by calcium treatment was further analyzed, it is concluded that under the premise that does not affect mechanical properties of steel, calcium treatment is advantageous to the control of sulfides morphology in sulfurcontaining non quenched and tempered steel through properly lowering molten steel cleanliness. It is feasible to use calcium treatment for sulfides morphology control in industrial production.

Key words: calcium treatment, sulfur-containing non quenched and tempered steel, inclusions evolution, sulfides, morphology control