Surface modification of low-carbon nano-crystallite bainite via laser remelting and following isothermal transformation

The low-carbon carbide-free bainite was surface modified by laser remelting and following isothermal transformation (LRFIT). The microstructure and nanomechanical properties of the bainite were investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM) and nanomechanical tester. The microstructure of the surface modified bainite can be refined and the hardness distribution interval of the surface of bainite can be obviously improved. Meanwhile, the nanohardness of the modified bainite is evidently increased from 5.605 GPa to 5.868 GPa. The martensite start temperature of the steel can be declined by LRFIT at a relative lower temperature due to the decrease of the retained austenite (RA) fraction and the bainite can be obtained at the temperature which is lower than the martensite start temperature of the original specimen.