Factors dictating the extent of low elongation in high sulfur-containing bainitic steels

The elongation of two low temperature bainitic steels with different sulfur contents was compared under the same heat treatment. Elongations of 1.0 +/- 0.5 % and 11.4 +/- 1.5 % were achieved for the high- and low-S steels, respectively. A high carbon concentration and fine grain size leading to over stability of the retained austenite in the high-S steel is the main reason for the poor elongation. The differences in carbon concentration and grain size between the two steels can be attributed to pinning by MnS, where the existence of a large number of long slivers of MnS in the high-S steel was responsible for the pinning. The stability of retained austenite was also analyzed by the local tensile elongation and hardness, and the volume fraction of retained austenite that transformed to martensite during the tensile process.