Relationship between MnS precipitation and respective effects of Ti-Mg bearing inclusions on the induction of intergranular acicular ferrite

摘要

The role of MnS in the nucleation of intragranular acicular ferrites (IAF) has been explored in Ti-Mg treated steel sample through scanning electron microscope (SEM) and energy dspersive spectrometer (EDS). When compared with a non-treated sample, Ti-Mg treatment evolves from Al-Mn-Si-O inclusion to Ti-Mg bearing inclusion and causes a reduction in pure MnS. In addition to this reduction in pure MnS, a precipitation of MnS around the Ti-Mg bearing inclusion can be observed. Moreover, after etching, it can be found that Ti-Mg bearing inclusions can induce IAF nucleation. Based on EDS line analysis and a comparison with Al-Mn-Si-O inclusion in non-treated sample, this effect can be explained by the presence of an Mn-depletion zone (MDZ) caused by the vacancy property and crystal structure of the inclusion. It should be added, however, that in the same sample, a similarly induced nucleation effect as well as an MDZ, have not been observed around pure MnS. This comparison implies that the formation of an MDZ may be independent of MnS precipitation.