Surface microstructure and microhardness of(ferrite+cementite)microduplex structure of the ultrafinegrained high carbon steel after laser shock processing(LSP)with different impact times were investigated by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and microhardness measurements.Equiaxed ferrite grains were refined from 400 to 150nm,and the cementite lamellae were fully spheroidized,with a decrease of the particle diameter from 150 to 100nm as the impact times increased.The cementite dissolution was enhanced significantly.Correspondingly,the lattice parameter ofα-Fe and microhardness increased with the impact times. Surface microstructure and microhardness of (ferrite + cementite) microduplex structure of the ultrafine grained high carbon steel after laser shock processing (LSP) with different impact times were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) ray diffraction (XRD) and microhardness measurements. Equiaxed ferrite grains were refined from 400 to 150 nm, and the cementite lamellae were fully spheroidized with a decrease of the particle diameter from 150 to 100 nm as the impact times increased. .Correspondingly, the lattice parameter of α-Fe and microhardness increased with the impact times.