The main objective of the present investigation was to compare the room temperature erosion behaviour of precipitation hardened (PH) stainless steel in the solution-treated, aged, and overaged conditions and also to evaluate the effect of erodent size and hardness on the erosion behaviour of the steel. The erosion rates of PH stainless steel in all the three heat-treated conditions were determined over a range of impact angles and velocities and with SiC and SiO2 (of two sizes) as erodent. The heat treatment of PH stainless steel had only a marginal effect on the erosion rate irrespective of impact angle and velocity even though such a heat treatment altered the mechanical properties considerably. The erosion rate always exhibited a maximum value at an impact angle of 30° irrespective of the erosion test conditions indicating a ductile erosion response. It was also observed that the erosion rate was independent of size and hardness of the erodent. The marginal effect of material strength and ductility on the erosion rates of PH stainless steel in different heat-treated conditions were rationalized qualitatively on the basis of the localization model. © 1992.