In this study we examined the influence of nitrocarburizing holding time on the surface microstructures and erosion behavior of JIS SKD11 modified cold-work tool steel (DC11 tool steel). The steel was nitrocarburized at 570°C for varying durations of 1, 3, and 5 h. The microstructures and hardness of the nitrocarburized coatings were then analyzed. Particle erosion was examined at different impinging angles (15–90°) and impact speeds (20.2–45.6 m/s).
The results show that a single diffusion zone is formed on the specimens at 1 h nitrocarburizing while a compound layer together with diffusion zone are formed on the specimens for the nitrocarburizing time beyond 3 h. In addition, the compound layer formed on the specimens exhibits a higher erosion resistance. The nitrocarburizing treatment not only increases the surface hardness but also improves the erosion resistance of the experimental steel. This improvement in erosion rates is more obvious at higher impact speeds and lower impinging angles. The maximum erosion rate appears at an impinging angle of 30° for all specimens. In this condition, plough grooves and cutting lips appear in the eroded surface; however, the erosion tracks are more superficial for nitrocarburized specimens than untreated specimen. The exponent in the power law Ė=kVⁿ varied between 1.9–2.3 for impinging angles between 15° and 90°.