Cold rolling and subsequent annealing processing of low carbon steels is one of the advanced thermomechanical processing which used for the production of nano grained microstructure. In this work, after quenching, the low carbon (0.13 wt. %C) steel was cold rolled up to 90 % reductions of thickness. The cold rolled specimens were annealed at different temperatures for investigating the evolution of microstructure. The microstructural changes occurring during the annealing were characterized by optical, scanning electron, and transmission electron microscope. In addition, color metallography method was used for determining the amount of martensite phase. Kikuchi-line analysis was employed for determining the miss-orientation of grain boundaries. The mechanical properties, and fracture surface of the steel were studied. Also, the restoration kinetics of the low carbon steel during annealing of martensite process was investigated using JMAK model. Results showed that fragmentation of martensite lathes during cold rolling of the quenched steels plays a key role in increasing the nucleation sites for recrystallization. The mean grain size of about 188±4, 200±3, and 230±4 nm were achieved after annealing of the 90, 80, and 70% cold rolled steel at 450, 500, and 550 ?C, respectively. The final microstructure was composed of nano-grained ferrite, carbide precipitations, and blocks of tempered martensite. The major amount of grain boundaries are high angle boundaries type in the final specimens. The mechanical properties of the nano-grained steels increased up to 4 amplitudes with the proper increase of toughness. Scanning electron microscopy investigations showed the ductile fracture mode with the shear dimples in fracture surfaces of the nano-grained low carbon steels. The JMAK model was expressed in terms of hardness data, from which the parameters of the different restoration kinetics were determined. The values of JMAK exponent, n , and the activation energy, Q , for recovery, recrystallization and grain growth were obtained for the steel under investigation. Key Words Low carbon steel, Cold rolling, Annealing, Nanostructured, Recrystallization, Restoration kinet
