Effect of Mg on the Evolution of Inclusions and Formation of Acicular Ferrite in La–Ti‐Treated Steels

Abstract

The size distribution and compositions of inclusions and microstructures in steels with different Mg contents are systematically investigated. The results show that Mg treatment modified and refined the inclusions. With Mg addition, the dominant inclusions in the samples evolve from LaAlO3 with MnS to a Mg‐enriched core enwrapped by a La‐enriched shell with MnS. While the Mg content increases from 11 to 66 ppm, the core changes from MgO·Al2O3 to MgO, and the shell develops from LaAlO3 to La2O2S. With the increase in Mg content from 0 to 44 ppm, the number density of effective inclusions is improved, and the proportion of acicular ferrite (AF) increases from 15% to 39%. However, the AF fraction decreases to 16% due to the relatively low amount of effective inclusions in the sample Mg3 with 66 ppm Mg.