Tribological properties of sulfur-containing high-speed steels at elevated temperature

Tribological properties of ferrous-based alloys can be effectively improved by introducing an appropriate amount of elemental sulfur into the alloys. A few samples of sulfur-containing high-speed steels were prepared by powder metallurgy techniques. High temperature friction properties of the samples mating with different counter materials, i.e., self-dual and GT35 steel bonded carbide were studied on a pin-on-disk tribo-meter. Worn surfaces were analyzed using SEM, EDS and XPS, and the friction mechanism was discussed. It is found that for both cases of self-dual and GT35 counter mates, the friction factors gradually decrease and the wear rates increase with rising the temperature. The friction coefficient curves become more stable at 400 °C and 700 °C than at room temperature, and the better friction performance is observed for the GT35. Below 400 °C, friction coefficients drop with rising the temperature, due to sulfide softening. Above 400 °C, friction coefficients drop mainly due to the formation of oxides on the worn surfaces.