Multi-step isothermal bainitic transformation in medium-carbon steel

The effect of multi-step low-temperature bainitic transformation on the microstructure and mechanical properties of a medium-carbon steel was investigated. Compared with the microstructure obtained by conventional bainitic transformation, the blocky microstructure was almost eliminated due to the formation of higher volumes of nanoscale bainitic–ferrite plates and film-like austenite, which lead to a refinement in the average thickness of the bainite plates. The samples with refined microstructure showed superior mechanical properties.

Super bainitic structure in a medium carbon steel has been obtained at the temperatures below the Ms temperature of the bulk alloy by conducting multi-step low temperature transformation. The blocky microstructure in bainitic steels has been reduced and refined, and the average thickness of bainitic ferrite plates has also been reduced, which thus resulted in superior mechanical properties. SEM micrographs (low and high magnifications) show microstructure of various samples after (a and d) conventional bainite transformation, (b and e) two-step bainite transformation, (c and f) three-step bainite transformation.Figure optionsDownload high-quality image (217 K)Download as PowerPoint slide