Prediction of Bainite Intervened in Ferrite-Pearlite Forging Steel I. Modeling

Abstract

The successive ferrite () + pearlite (P) transformations from austenite () were modeled to predict the presence of bainite in as-forged medium-carbon manganese steels. The kinetics of diffusional transformations were calculated based on classical nucleation and growth theory coupled with CALPHAD multi-component thermodynamics. The description of the growth rate of proeutectoid-includes a time dependence due to the carbon enrichment in the remaining . The / interface was assumed to be in negligible-partitioned local equilibrium (NPLE). The kinetics calculation of P nucleating on the surface was integrated into the model. Given the transformation temperature range in continuous cooling, the growth rate of P was also expressed in the NPLE constraint for /cementite. The concentration of untransformed ( U ) can be monitored and should be dependent on the extent of the preceding transformations. Thus, the energies available for the nucleation and diffusionless growth of bainitic-were evaluated from the thermodynamics of the U single-phase system, which is proposed as a method to predict the inclusion of bainite in the final þ P microstructure.

Kinetic Transition during Ferrite Growth in Fe-C-Mn Medium Carbon Steel

“…Following the previous work of Tanaka et al, [21] the austenite-to-ferrite phase transformation could be modeled as follows. The nucleation rate of a on the c boundary surface was calculated following the classical nucleation theory: [22] …”