Microstructure of ultra-fine-grained high carbon steel prepared by equal channel angular pressing

Equal channel angular pressing of a fully pearlitic Fe–0.8C steel was carried out at 923 K. The microstructure, before and after processing, was analyzed by scanning and transmission electron, and atomic force microscopy. After one pass of the equal channel angular pressing, the cementite lamellae is bent, kinked, and fractured, with its spacing significantly decreased. The shape of the local cementite is a short or elliptical bar. After four passes, an ultrafine microduplex structure (ferrite + cementite), with a grain size at the sub-micrometer level, was observed and the planar lamellae was converted to equiaxed three-dimensional grains. The cementite lamellae was fully spheroidized, with the average diameter of the cementite particle being equal to about 150 nm. Equiaxed ferrite grains, with an average size of 400 nm, are developed due to the dynamic, continuous recrystallization during the equal channel angular pressing deformation.