Transitional behavior in sliding wear of martensitic layer obtained with SHPTN process on AISI 409 steel

Abstract

Samples of AISI 409 were thermochemically treated by the Solution Heat Treatment after Plasma Nitriding (SHTPN) process. SHTPN process consisted of a nitriding step followed by solution annealing at 1100 °C and rapid cooling down to room temperature. The second cycle of quenching (950 or 1050 °C), followed by tempering (250, 450, or 650 °C), was performed sequentially to SHTPN. Lubricated reciprocating tests were employed to analyze friction and wear behaviors. A bearing steel ball was used as a counterpart. The analysis of worn surfaces was assessed using optical interferometry and depth-sensing indentation. The last technique allows determining the work hardening caused by the wear process. Friction behavior was related to the deformation component: the higher the hardening, the lower the friction coefficient. Abrasion is the primary mechanism observed in all specimens, but there is a transitional behavior that depends on the original hardness of the surface. Samples with a similar hardness of bearing ball presented delaminated regions caused by highly deformed thin layer fatigue. Amongst SHTPN conditions NS-Q950-T2 and NS-Q1050-T2 presented the best balance of wear and corrosion performances.