Effect of Ti addition on the potency of MnS for ferrite nucleation in C-Mn-V steels

Abstract

The variation of precipitation behavior of MnS has been thermodynamically calculated in V-bearing C-Mn steels by substituting Ti for V. The use of two different set of solubility data for Ti4C2S2 and TiS reported in literatures leads to a completely reversed precipitation behavior of MnS. The result of experimental observations is in qualitative agreement with the calculated result using the solubility data of Liu and Jonas. The calculated result showed, contrary to the case of V-containing steel, that the precipitated amount of MnS in steels bearing Ti-only rather decreases with decreasing temperature and that this is due to the formation of Ti4C2S2. Controlled cooling experiments with interrupted quenching technique showed that MnS directly acts as the nucleation site for ferrite and that its nucleation potency depends on the precipitation behavior of MnS. Namely, MnS rarely acts as a nucleation site for ferrite in steels where its precipitated amount decreases with decreasing temperature.