The effect of the cementite phase on the surface hardening of carbon steels by shot peening

This study investigates the effect of the cementite phase on the surface hardening of carbon steels when they are shot-peened. Three carbon steels were used in this study: 0.1% C, 0.45% C, and 0.8% C steels. The results show that the surface hardness after shot peening is proportional to its carbon content. Grains at the surface were transformed into grains with lamellar structures. The cementite was spheroidized by energy generated from the severe plastic deformation at the surface, the ferrite grain size was refined noticeably, and the carbon dissolved in the ferrite. The higher the carbon content in the ferrite, the higher the degree of grain refinement was observed. The primary reason for the noteworthy enhancement of surface hardening likely originates from both the grain refinement and supersaturation of the carbon in the ferrite following cementite dissolution.