Abstract
La Effects on bainite transformation behavior including transformation kinetics and the nucleation and growth of bainitic plates of Mn–Cr–Mo bainitic rail steel were investigated using dilatometry, laser scanning confocal microscopy (LSCM) and transmission electron microscope (TEM). Dilatometry analyses show that La postpones the bainite transformation and increases the transformation activation energy by 31 kJ/mol. LSCM results indicate that La stimulates sympathetic nucleation at the beginning of bainite transformation but delays the growth of bainitic plates at the late stage which becomes the dominant factor of transformation, decreasing the transformation rate and prolonging the transformation time simultaneously. Eventually, combined with the refining effects of La and M3C pinning the interfaces between sub-plates, a kind of complicated multi-layer microstructure consisted of less and finer subunits can be achieved at cooling rate of 0.8 °C/s just by air cooling on site.
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