DEPENDENCE OF MICROSTRUCTURE SCALES OF EUTECTICS ON Ca-Si MODIFIER AMOUNT IN AUSTENITE STEEL COMPOSITES

Results presented in this paper contribute to investigation of the effect of the added Ca-Si modifier amount (αk) on the microstructure scales of granular γ-(Fe, Mn)3C eutectics such as the volume fraction (39 and diameter (d) in the austenite steel matrix composites (EAMC).Directional solidification of EAMC has been carried out using vertical Bridgman method at 50.6μms^-1 with a constant temperature gradient about 800Kcm^-1. The higher constitutional supercooling ahead of solid-liquid interface attributing to the larger αk results in the enlargement of γ-(Fe, Mn)3C coupled-zone and the increment of the nucleation rate of eutectics. Therefore, f increases with increasing αk. The branches of the primary austenite dendrites develop more greatly as αk increases, which limits the growth of eutectics. As a result, d decreases with increasing αk.