CONTROL OF INITIAL SOLIDIFICATION STRUCTURE OF RAPIDLY SOLIDIFIED 18CR-8NI STAINLESS-STEEL

Initial solidification structure of stainless steel droplets has been investigated in relation to mold temperature and pouring temperature. Results of present experiments are compared with the previous ones which are related to surface roughness and surface materials of subtrates and pouring temperature. On the onset of the solidification, undercooling is observed under various casting conditions. The undercooling at the initial solidification depends only on cooling rate, and has a linear dependence on cooling rate. Initial solidification length which corresponds to the region of cellular structure increases, but primary arm spacing and surface grain size decreases with increasing cooling rate. There exists the critical cooling rate at which a primary phase changed from delta-phase to gamma-phase, and the value of the critical cooling rate is estimated to be about 0. 5 X 10(4) Ks-1. The morphology of solidification structure is cellular for primary gamma-phase and dendritic for primary delta-phase. The results indicate that the initial solidification structure is controllable by changing the cooling rate.