Erosion–corrosion behavior of plastic mold steel in solid/aqueous slurry

Abstract

Erosion–corrosion behavior of a precipitation hardenable plastic mold steel (NAK80) has been investigated by using a rotated slurry erosion rig containing a slurry comprising 20 wt% Al₂O₃ particle and 3.5% NaCl solution. The erosion–corrosion rate and the synergism between erosion and corrosion have been determined under various conditions. The major environmental parameters considered are impact angle, impact velocity, and particle size. Post-test examination was conducted to identify the material degradation mechanism involved. The erosion–corrosion mechanisms of NAK80 mold steel at high-impact angles are dominated by the formation of impact pits, dissolution of metallic matrix, and plastic deformation fatigue spalling, whereas at low-impact angles, the mechanisms are dominated by the formation of impact pits, dissolution of metallic matrix, fatigue cracks, and cutting. The observed synergism between these mechanisms is much more accentuated at an oblique impact angle than that at a normal impact angle. At a given impact angle, the erosion–corrosion rate is found to increase with the impact velocity and the size of solid particles. The maximum peak of the erosion rates lies at oblique angles between 30° and 45°, whereas the maximum peak of the erosion–corrosion rates appears at 45°, and the erosion–corrosion rate is higher than the erosion rate alone at all angles examined. There is a positive synergism between erosion and corrosion for NAK80 mold steel in solid/aqueous slurry. The synergistic effect is 40–60% of the total weight loss. The contribution of synergism to the total weight loss depends upon the impact velocity; however, it is almost independent of the impact angle and particle size.