Deformation of MnS-MnTe Inclusions in a Sulfur-Containing Free-Cutting Steel With Tellurium Treatment

In the current study, laboratory experiments were carried out to reveal the modification and deformation of MnS-MnTe inclusions in a Te-treated free-cutting steel. With the increase of the Te/S mass ratio in steel, the average equivalent diameter of inclusions increased, while the average aspect ratio decreased. Pure MnTe inclusions generated in steel with a high Te/S mass ratio in steel. There was an optimal Te/S mass ratio of 0.33 to modify inclusions to spherical and short rod-like ones. After rolling, almost all MnS-MnTe inclusions deformed along the rolling direction. The deformation ability of dendritic MnS-MnTe was better than that of spherical MnS. The deformation ratio of inclusions was 1.1-1.5 during the hot rolling process with the rolling reduction of 50 pct. There was a lowest value of the deformation ratio of inclusions in steel with the 0.33 Te/S mass ratio. The precipitation temperature of MnTe was lower than that of MnS. The addition of tellurium in steel reduced the initial precipitation temperature of sulfides below the solidus temperature and retarded the precipitation of MnS. Combined with evolutions of surface roughness, matrix hardness, and chip lengths, the cutting performance of the sulfur-containing free-cutting steel increased first then decreased as the mass of Te/S in steel increased gradually, reaching an optimum Te/S mass ratio of 0.33.