Isothermal growth kinetics of bainite in 0.5% C steels

A model of the growth of bainite in steels is proposed taking into account the diffusion of carbon in austenite, the presence of cementite precipitates left behind the growing front and the influence of substitutional alloying elements. Experimental data have been measured by metallography in different 0.5% C steels alloyed with Ni and Si or collected in the literature for Ni-steels exhibiting different carbon contents. The growth rate is calculated following the Trivedi equation for plate precipitates and assuming that paraequilibrium controls the interfacial concentrations during growth. A good agreement is found for both the effects of temperature and carbon content. An accelerating effect due to the cementite precipitation accompanying the transformation is emphasized. Finally, the existence of a nickel atom-interface interaction which hinders the propagation of the front through a solute-drag effect is suggested by comparing of the model predictions with literature experimental data in a series of alloys with increasing Ni contents.