Thermodynamic Analysis of Precipitation of La-O-S-As Inclusions in Steel

The formation of RE-O-S-As inclusions and corresponding arsenic content of equilibrium solid solubility were two core issues concerned when adding rare earth to restrain the harm of residual arsenic in steel. In this paper, some databases of rare earth inclusion were supplied. The influence of different La content on the formation of inclusions during solidification of As-bearing steel was calculated. The results showed that with the increase of rare earth content, the original inclusions MnS, Al6Si2O13 and Mn2Al4Si5O18 in steel were replaced by La2Al2O6, La2O2S, La2S3, La3S4 and LaS. The formation mechanism of As-bearing rare earth inclusions was analysed under the condition of excess rare earth, and the results showed that the As-bearing rare earth inclusions were formed during the solidification process due to enrichment of solidification frontier elements.