Effect of sub-zero treatments on hardness and corrosion properties of low-alloy nickel steel

Low alloy nickel steel was chosen for this experiment because it is suitable for grinding balls application due to its high hardness and corrosion resistance. This study aimed to see the effect of different sub-zero treatments on the hardness, fractography and corrosion properties of low alloy nickel steel. The prepared specimens were heated to the austenitizing temperature of 980 ℃ in a furnace for one hour and water-quenched until they reached room temperature. Furthermore, the quenched specimens were chilled in liquid nitrogen for a variated time of 10, 60 or 360 min, followed by tempering treatment at 200 ℃ for one hour. According to the hardness test, the sub-zero treatment is effective in hardening materials, where the hardness value increases as the sub-zero treatment time increases, ranging from 204.93 to 417.98 HV. The fractography test indicated ductile fracture characterized by dimples at the fractured surface. Moreover, the corrosion test showed an enhancement of corrosion resistance with increased sub-zero treatment time.