Influence of rare earth metals on non-metallic inclusion in 25cr-7Ni-3Mo-0.25N duplex stainless steel

Abstract

The influence of rear earth (RE) addition (from 0.22 to 0.78 kg/t) on non-metallic inclusions in Fe-25Cr-7Ni-3Mo-0.25N duplex stainless steel (DSS) was investigated experimentally using 1 kg vacuum induction furnace in order to understand the formation (including composition and geometry), modification and deformation during the rolling of RE inclusions in this steel. A maximum amount of 0.67 kg/t RE addition is necessary to avoid an increased inclusion population because the RE inclusions have very low floatability with higher RE additions. With increasing RE addition the formed inclusions refine to smaller than 3 pm. Total replacement of manganese in the inclus-ions is occurred by the increase of RE content in inclus-ion to over 57% and the RE inclusions are heterogeneous sulphides and oxysulphides. The RE inclusions have not been deformed after rolling besides two-partial (RE), (Mn)S inclusion. The methods of inclusion shape control are reviewed.