STUDY ON GRANULATION MECHANISMS OF gamma + (Fe,Mn)_3C EUTECTICS IN AUSTENITE STEEL COMPOSITES

摘要

Results presented in this paper contribute to investigation of the granulation mechanisms of gamma + (Fe, Mn)_3 C eutectics in the austenite matrix composites (abbreviated EAMC). The specimens corresponding to the nominal composition of eutectic with controlled RE(Ce)-Mg agent modifier additions have been unidirectional solidified with a constant growth rate of 2.18 mum/s at a fixed temperature gradient of 800 K/cm using vertical Bridgeman method. With the RE-Mg agent modifier, the transition of solid/liquid (S/L) interface from columnar to dendrite (CDT), refinement and developed branching of gamma and (Fe, Mn)_3 C phases in the eutectics, and the transition of growth style from faceted-nonfaceted (F/NF) to nonfaceted-nonfaceted (NF/NF) for gamma and (Fe, Mn)_3 C phases in the eutectic have been observed and investigated theoretically. Those can explain the granulation of gamma + (Fe, Mn)_3 C eutectics in the as cast because the roundness increases with the developed lateral branching of primary austenite dendrites, refinement of eutectics, and NF/NF growth of gamma and (Fe, Mn)_3 C phases in the eutectic.