Study on the Stability of Microstructure and Mechanical Properties of Gradient Refined Microstructure on Low-Carbon Steel Surface

The stability of gradient grain microstructure on the surface of low carbon steel was studied by different annealing temperature and high temperature friction and wear experiments. The results showed that the surface grain of the low-carbon steel was refined, and the microhardness reached 250 HV. An increase in the annealing temperature, the gradient refined grain microstructure of the surface layer gradually disappeared. When the annealing temperature was lower than 300 °C, the average grain size increased continuously from the surface to the center without obvious interface. The surface layer hardness could reach about 220 HV. However, when the annealing temperature reached 500 °C, the refined microstructure of the surface layer completely disappeared. At the same time, the grain boundaries could be seen clearly indicating the refined grain in the surface layer had recrystallized. Compared with the as-prepared, the grain size of the surface layer grew up and the microhardness reduced to about 150 HV. Moreover, the wear behavior of the gradient refined grain microstructure at high temperature also proved that the disappearance of the surface refined grain leads to an increase in the wear volume at higher temperature.