Effect of Mg, La and Ca addition order on inclusions and microstructure of Ti-bearing C-Mn steel

The influence of addition sequence of Mg, La and Ca on the characteristics of inclusions and the formation of acicular ferrite (AF) were investigated. Results show that inclusions mainly consisted of La-Ca-Mg-Al-Ti-O+MnS in the steel. There was no change to types of inclusions while the layered structure of inclusions was different under different alloy elements addition sequence. The number density of inclusions was the largest in case of Mg was added first, while the average size of inclusions was the smallest. The main type of effective inclusions (nucleus of AF formation) was oxide with MnS shell. The statistical results indicated that the proportion of effective inclusions in case of Mg addition first was the largest among the three samples, which induced more AF formation.