Observation of a compound layer with very low friction coefficient in ion-nitrided martensitic 410 stainless steel

Samples of AISI 410 martensitic stainless steels were ion-nitrided between 400 and 566 °C for 6–120 h and studied by SEM, electron probe microanalysis. X-ray diffraction, Knoop microhardness, and unlubricated sliding wear measurements. Treatments at 400 °C for 96 and 120 h were extremely effective in improving friction and wear properties compared both to the baseline, quenched-and-tempered condition as well as to samples nitrided at higher temperatures. The favorable treatments resulted in the formation of an incipient compound layer of an as-yet undetermined complex martensitic structure, detectable by metallography and X-ray diffraction, but extending only to a depth of a few micrometers. The effectiveness of this low-temperature nitriding treatment in improving the friction and wear behavior is thought to be due to the gradual nature of both the decrease of nitrogen content with depth and, accordingly, the hardness increase due to this martensite formation.