2002 Volume 43 Issue 2 Pages 129-134
The influence of purity and cooling-rate on the microstructure of hot-forged pure irons was investigated by using two kinds of pure irons. One was K-Iron of 99.981 mass% purity and the other was M-Iron of 99.993 mass% purity. After forging at 1263 K, above the α-γ transformation temperature, the specimens were immediately cooled to room temperature at various cooling-rates: by water-quenching, oil-quenching, air-cooling, ash-cooling, and furnace-cooling. The microstructure of forged iron was strongly affected by the purity and the cooling-rate. It should be emphasized that in M-Iron columnar grains grew in parallel to the forging direction independent of the cooling-rate. On the other hand, equiaxed grains were formed in all specimens of K-Iron forged at 1263 K. On both M-Iron and K-Iron, α-grains became larger with decreasing cooling-rate. The crystal orientation of α-grains on the forged plane of each specimen was measured by electron back-scattering diffraction-pattern method. On the forged plane of M-Iron, {101} of α-grains was predominant in the case of water-quenching and {111} or {221} was predominant in the other cases; on the other hand, the crystal orientation in K-Iron was random at all cooling-rates. Metallurgical factors controlling these characteristic microstructures in M-Iron were discussed in terms of growth of recrystallized of α- and γ-grains, mobility of γ⁄α interface, nucleation site and cooling-rate.
