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Abstract
Mn was introduced, with graphite, as fine ferromanganese particles to form compacts of Fe–3%Mn–0·5%C. Each was sintered in dry 25%H2 + 75%N2 for 3 min at 770, 1040, 1080, 1170 and 1220°C respectively, held for 3 min and quenched. The surface of a successively heated specimen was similarly examined. Specimens were sectioned and, especially the reacting ferromanganese particles and adjoining regions, investigated using light and scanning electron microscopy and EDX. Development of microstructure and microcompositions during sintering was related, from 740°C, to diffusion and condensation of Mn vapour on iron particle surfaces and subsequent chemical reactions. Above 1080°C microstructures included features resulting from a transient liquid phase, in accord with a ∼45 wt%Mn ternary eutectic calculated by ThermoCalc. The thicknesses of the highly Mn enriched regions were substantially higher than those resulting from bulk Mn diffusion in the Fe lattice; our interpretation invokes predominant operation of another type of mechanism: diffusion induced grain boundary migration.