Ultrafine-Grained Low Carbon Steel via Cold Rolling and Annealing ofMartensite

The formation of ultrafine grained microstructures during annealing of cold rolled martensite at a moderate temperature in a low carbon steel with ~ 0.12 wt% C was taken into account. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness measurements,and tensile testing were used to characterize the evolution of microstructure and mechanical properties. It was revealed that by annealing of the cold rolled martensite at 550 °C, a unique trend in hardness can be observed, in which a peak in hardness was achieved after 45 min annealing that isrelated to the formation of ultrafine grains with the mean grain sizes of ~ 0.9 μm. A much coarser microstructure with ferrite grain size of ~ 3.5 μm was obtained after 135 min annealing at the same temperature due to growth of fine grains formed after 45 min. It was shown that a wide range ofmechanical properties can be obtained by this simple thermomechanical process.

Keywords:

Ultrafine grained materials , Thermomechanical treatment , Mechanical Properties , Microstructure