Effects of Ti-Mg Complex Inclusions on Acicular Ferrite Nucleation

摘要

The alloys of Ti and Mg are added in molten carbon structural steel in sequence to reveal their influence on features of inclusion and microstructure. Compared with non-treated steel, it is found that they leads to the formation of Ti-Mg-O inclusion and reduction in portion of pure MnS. Experimental results indicate that average inclusion size in treated steel significantly decreases and its number per unit volume increases by 48%. Moreover, the margin mole ratio of Mg/Ti in all Ti-Mg-O inclusions is larger than 2, which hints they are more complex than single assumption of MgTi_2O_4. After etching, intragranular acicular ferrite (IAF) microstructure is observed. EDS line analysis suggests that Mn-depletion zone exists in steel matrix, which is proposed to explain the IAF nucleation effect induced by Ti-Mg-O inclusions. Through comparison with only Mg-treated sample, the refinement of inclusion and increase in portion of pure MnS due to Ti adding are revealed.