Cold deformation and subsequent annealing of the martensite microstructure in low carbon steels, known as the martensite process, is one of the most practical advanced thermomechanical processes to produce ultrafine/nano grained microstructures. The aim of the present work was to compare the cold roll-annealing and the plane strain compression-annealing processes in a low carbon steel containing 13 wt.% C. A fully martensitic microstructure was first achieved by quenching and then was subjected to both cold rolling and plain strain compression up to 65, 75 and 85% reduction in thickness. The microstructures were subsequently annealed at temperature range of 400 to 550?C for 0 to 180 min. The microstructures were characterized by optical and scanning electron microscopes. Color metallography was used to determine the martensite phase. The texture formed in the cold deformed specimens was studied. The logarithmic curves of hardness were used to evaluate tempering mechanism during annealing of the deformed specimens. The results showed that fragmentation of lath martensite during plastic deformation in two methods resulted in a remarkable increase of suitable nucleation sites during annealing. Comparison of texture-induced plastic deformation indicated that the texture including (110) plane was present in the most deformed specimens by plane strain compression and in the all deformed specimens by cold rolling. The deformed specimens by the plane strain compression showed further drop in hardness after annealing at all temperatures compared with the deformed specimens by cold rolling. The most suitable temperature for achieving fully recrystallized microstructure in two methods was 500 °C. The final microstructure after annealing included equiaxed ferrite grains, nano-sized precipitates of carbide and tempered martensite. Microstructural and kinetic investigations indicated that increasing strain in the two methods resulted in a decrease on the recrystallization time and mean grain size. The smallest grain size was 155 nm for cold roll-annealing and 125 nm for plane strain compression-annealing, both obtained at 85% reduction in thickness. The closest mean grain size for two deformation methods was obtained at 65% reduction with about 11 nm deviation. Increasing the reduction up to 85% resulted in an increase in the difference of the mean grain size of the two methods due to the difference in the strain path.
