Multi-pass scratch test behavior of AISI 316L borided steel

Iron borides formed on AISI 316L steel were evaluated by multi-pass scratch tests. The boriding process was carried out by continuous and interrupted boron diffusion at 900 °C during 2 and 4 h for obtained FeB/Fe₂B and Fe₂B systems, with non-thick thicknesses. Residual stresses by X-ray diffraction were determined on the borided surface. A conventional scratch test was carried out to determine damage mechanisms. After, the multi-pass scratch test was employed to evaluate sliding wear behavior at subcritical loads (20, 30 and 40% of chipping critical load). During the interrupted boriding, the total coating thickness and FeB phase were thinner compared with the continuous process. The chipping critical load determine by conventional test was around 53 N. The coefficient of friction (COF) behavior and damage mechanism in the multi-pass scratches were analyzed. The interfacial fracture energy was calculated for chipping mechanism of FeB. According with the results, the wear rate was reduced on AISI 316L borided steel. Hence, the effect of the substrate played an important role when the boride layer was thin avoiding severe damage; the presence of thin thickness of FeB phase was even favorable. The continuous boriding at 2 h showed better performance with total layer thickness around 10 μm.