(1. School of Metallurgical and Ecological Engineering， University of Science and Technology Beijing，
Beijing 100083, China；2. Steelmaking Plant， Fujian Sansteel Minguang Co.， Ltd.， Sanming 365000， Fujian， China)
The type，number，size and morphology of nonmetallic inclusions have an important influence on cracking of SWRCH22A cold heading steels. In order to investigate the transformation of nonmetallic inclusions in SWRCH22A cold heading steels during cooling and solidification，the type，number，size and morphology of nonmetallic inclusions during the continuous casting process were analyzed using Aspex inclusions analyzer. In industrial production，inclusions in molten steel were mainly Al2O3CaO，but inclusions in billet were mainly MgOCaOAl2O3CaS，which indicated that inclusions shifted from Al2O3CaO to MgOCaOAl2O3CaS during the continuous casting process. Number density and area fraction of inclusions in billet were smaller than those of inclusions in tundish. Moreover，the transformation and composition of inclusions during cooling and solidification were calculated using FactSage，which can provide a theoretical explanation for the experimental results.
