Microstructures and reaction kinetics of bainite transformation in Si-rich steels

The microstructures and kinetics of upper and lower bainite formed in three high silicon steels with high, medium, and low carbon content have been studied. Carbide precipitation in carbon-enriched austenite is retarded by the addition of silicon (∼2 wt.%). The width of upper bainite sub-unit was found to decrease with decreasing temperature, while the number of sub-units in a single sheaf exhibits a reverse trend. Carbide particles in the ferrite of lower bainite could precipitate along a single or multiple variants. Separate C-curves for upper and lower bainite reactions were found in time–temperature-transformation (TTT) diagrams, indicating a sudden change of reaction kinetics across the LBs temperature.