During austenite to ferrite transformation, the lattice structure transforms from fcc to bcc, resulting in a clearly distinguishable austenite and ferrite interface. The short range diffusion of the Fe and C atoms across the interface causes its movement, referred to as interface migration. On the other hand, the C rejected by the ferrite during the austenite to ferrite transformation in Fe-C alloys accumulates ahead of the moving interface. This pile-up of C atom is dependent on the long range diffusion of C in austenite and also influences the ferrite growth kinetics. Experimental observations indicate that dislocations are always migrating with ledges during ledgewise growth. The local stress field of dislocations is considered to alter the solute concentration at the riser of ledges and causes a complex diffusion field interaction among ledges as they migrate. Some established works by other researchers have already taken the effect into consideration when studying phase transformation kinetics. However, these works were limited in diffusion control cases and could hardly explain some experimental results. In this work, a ledgewise growth model considering migration of austenite/ferrite interface, C diffusion in austenite and especially elastic interactions between dislocations moving with ferrite ledges was established, and all the simulated results were qualitatively similar to the reported experimental results. Calculated results showed that the C concentration at the riser of ledges was changed by the elastic stress of these dislocations, which would further change the growth behavior of ledges. In the growth behavior simulations of two ledges, the horizontal distance of the two ledges was found to be a key role to determine the growth kinetics. When the horizontal distance of two ledges was larger than the critical distance, an attractive phenomenon of the two ledges was found to decelerate the leading step; while a repulsive phenomenon of the two ledges which would accelerate the leading ledge if the horizontal distance was smaller than this value. Compared with the simulation results without considering elastic interactions between dislocations, however, in the growth behavior simulations of multi-ledge with elastic dislocation interactions, the coalescence behavior of ledges and growth rate of the leading step were both changed.
武慧东,张弛,柳文波,杨志刚. 考虑位错相互作用的混合控制模型下先共析铁素体生长动力学模拟[J]. 金属学报, 2015, 51(9): 1136-1144.
Huidong WU,Chi ZHANG,Wenbo LIU,Zhigang YANG. SIMULATION OF GROWTH KINETICS OF PRO-EUTECTOID FERRITE USING MIXED CONTROL MODEL WITH CONSIDERATION OF DISLOCATION INTERACTION. Acta Metall, 2015, 51(9): 1136-1144.