Solubility of MnS in Fe-Ni Alloys as Determined by In-situ Observation of Precipitation of MnS with a Confocal Scanning Laser Microscope

Abstract

Solubility of MnS in Fe-Ni alloys has been investigated by "in-situ" observation with a confocal scanning laser microscope of specimens with various Mn, S and Ni contents which were heated and cooled in an infrared image furnace. Precipitation behavior of MnS at the surface of the specimens on cooling was monitored on a CRT and was recorded on videotape. Most MnS precipitates are found to form on alumina inclusion particles and grow in triangular (pyramidal) or rod-like shape. From precipitation temperatures obtained by the "in-situ" observation, the equilibrium constant of the reaction MnS ⇌Mn + S is determined as log K=log[%Mn] [%S]fMnS = -9420/T+3.67, at T=1 329-1 493 K for Fe-42mass%Ni alloy. The K value for γ-Fe at 1 438 K is in good agreement with that by Turkdogan et al., and Ni is found to increase the solubility of MnS.