A Study on the precipitations of rare earth metals inclusion phase in Fe-Cr-Ni-RE System

Abstract

A study has been carried out to develope a general relationship bdween steel compositions and inclusion types, inclusion structure and morphologies. The condition to form and exist RE-inclusion types has also been dete-rmined. Analysis and the methods of measurement for chem-ical composition, microstructure. SEM, X-ray and quantit-ative QTM has bet:n developed. The formed inclusions are of the type - (RE) AI1,Olx' (RE)AIO" (RE)P2S, (RE)AI02S, REP3 and (RE)Si02S. Inclusions with only RE are globular and undeformed. Simple sulphides 01'4.75flm with high deformation are harmful for rolling.The inclusion number having grain size> 4 ~lmhas been more than 1.07 grain/mm2. The lowest projection of sulphide inclusions in steel is found to be 90 to 99 flm/mm2 when RCcontents are from (L02 to 0.05% and attained the smallest deformation. A semi-thcoretical method for inclusion typc predictions based on cxperimental data and fundamental theories of thermo dynamics micro segregation and nucleation has been deve-loped. The conditions for precipitation of CcPJ and Ce202S by prediction are given by Qcep3 and Qce202S around 2.6 to 3.2. The inclusion size decreases with the increase of fraction inclusion phase. The oxysulphides have higher grain size than RE sulphides and RE oxides.