Effects of Mg and La on the evolution of inclusions and microstructure in Ca-Ti treated steel

The evolution of inclusions and the formation of acicular ferrite(AF)in Ca-Ti treated steel was systematically investigated after Mg and La addition.The inclusions in the molten steel were Ca-Al-O,Ca-Al-Mg-O,and La-Mg-Ca-Al-O after Ca,Mg,and La addition,respectively.The type of oxide inclusion in the final quenched samples was the same as that in the molten steel.However,unlike those in molten steel,the inclusions were Ca-Al-Ti-O+MnS,Ca-Mg-Al-Ti-O+MnS,and La-Ca-Mg-Al-Ti-O+MnS in Mg-free,Mg-containing,and La-containing samples,respectively.The inclusions distributed dispersedly in the La-containing sample.In addition,the average size of the inclusions in the La-containing sample was the smallest,while the number density of inclusions was the highest.The size of effective inclusions(nucleus of AF formation)was mainly in the range of 1-3μm.In addition,the content of ferrite side plates(FSP)decreased,while the percentage of AF increased by 16.2%due to the increase in the number of effective inclusions in the La-containing sample in this study.