Nonmetallic inclusion removal of Si-Mn deoxidized steel by nitrogen absorption and release method

The micro nonmetallic inclusion and oxygen content in steel significantly affect its performance, and removing the inclusion involves a difficult process. A nitrogen absorption and release method has been developed with which nonmetallic inclusions and T[O] were efficiently removed from bearing steel. However, the inclusions in bearing steel are highly different from those in Si-Mn deoxidized steel, and the effect of the nitrogen absorption and release method on the Si-Mn deoxidized steel remains unclear. Based on this, a thermal experiment was carried out in this study to investigate the removal of nonmetallic inclusions from Si-Mn deoxidized steel by nitrogen absorption and release method, where SWRH82B hot rolled wire coil was used as the experimental steel, and five groups of increasing nitrogen pressure (0.02, 0.035, 0.05, 0.065 and 0.08 MPa) were set up. The results show that for all groups, the T[O] and T[N] in the steel reduce to below 1×10^-5 and 5×10^-6, respectively, after the molten steel is subjected to 20 min of increasing nitrogen and 30 min of vacuum treatment. The lowest T[O] and T[N] in the steel is 4×10^-6 and 2×10^-6, respectively, and the inclusion removal rates for all the groups are more than 40%. The T[O] removal rates for all the groups are more than 78%.This result proves that nitrogen absorption and release method is efficient in removing inclusions and T[O] in Si-Mn deoxidized steel. Furthermore, the removal rate of inclusion and T[O] in the steel increases with the nitrogen pressure. When the nitrogen pressure is 0.08 MPa, the removal rates of T[O] and the inclusions are 89.2% and 87.4%, respectively. Theoretical analysis shows that the nucleation rate, number, and density of bubble in molten steel increase with pressure, the efficiency of the inclusions removal can be promoted.