Papers by Keyword: Bainite Nucleation

Abstract: Bainite is an essential constituent in the microstructure of many advanced high strength steels, e.g. ferrite-bainite dual-phase, transformation induced-plasticity (TRIP) and complex phase (CP) steels. A complex thermo-mechanical processing is employed in industry such that following ferrite formation a desired fraction of bainite can be obtained during austenite decomposition. In order to evaluate robust processing routes it would be very useful to have a bainite transformation model with predictive capabilities. In this work a transformation start criterion for bainite is proposed by defining a critical driving pressure concept. Subsequent bainite formation kinetics from a mixture of ferrite-austenite is described using phenomenological modelling methodologies. In particular, the predictive capabilities of two approaches will be critically discussed, i.e. (i) the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model in conjunction with Rios treatment of the additivity rule and (ii) a nucleation-growth based model that describes simultaneous formation of bainitic ferrite and carbides. Using experimental transformation data for TRIP and CP steels, status and limitations of these models will be delineated.

Abstract: The maximum number of carbon atoms adsorbed at edge dislocation was calculated using a model based on Boltzmann distribution. The number of carbon atoms adsorbed by edge dislocation increases with bulk concentration increasing and temperature decreasing. When the interfacial energy was chosen as 0.2J/mol, the maximum radius of carbon depleted zone is smaller than the critical radius required for displacive nucleation at 700K, however, larger than the critical radius at 600K. Moreover, the radius of carbon depleted zone around the dislocation at 600K is larger than that at 700K. It seems that bainite may nucleate by a displacive mechanism at lower temperature.