SOLUBILITY OF MNS IN FE-NI ALLOYS AS DETERMINED BY IN-SITU OBSERVATION OF PRECIPITATION OF MNS WITH A CONFOCAL SCANNING LASER MICROSCOPE

Solubility of MnS in Fe-Ni alloys has been investigated by ''in-situ'' observation with a confocal scanning laser microscope of specimens wi th various Mn, S and Ni contents which were heated and cooled in an in frared image furnace. Precipitation behavior of MnS at the surface of the specimens on cooling was monitored on a CRT and was recorded on vi deotape. Most MnS precipitates are found to form on alumina inclusion particles and grow in triangular (pyramidal) or rod-like shape. From p recipitation temperatures obtained by the ''in-situ'' observation, the equilibrium constant of the reaction MnS reversible arrow Mn+S is det ermined as logK=log[%Mn][%S]f(S)(Mn)=-9 420/T+3.67, at T=1 329-1 493 K for Fe-42mass%Ni alloy. The K value for gamma-Fe at 1 438 K is in goo d agreement with that by Turkdogan et al., and Ni is found to increase the solubility of MnS.