Investigation on structural and tribological properties of borided gear steel after phase homogenization

This study focused on the structural and mechanical characterizations of AISI 8620 gear steel after a novel combined treatment (CRTD-Bor: Cathodic Reduction and Thermal Diffusion based boriding and subsequent PH: phase homogenization). Initially the effects of CRTD-Bor process parameters on the modified layer depth and chemistry were investigated at two sets of experiments as follows i) temperature examinations-15 min of CRTD-Bor at 950, 1000, 1050 and 1100 °C ii) duration investigations - at 950 °C for 15, 30, 60 and 120 min of CRTD-bor. After that, PH treatment was integrated into CRTD-Bor to obtain industrially-desired monolithic Fe₂B coatings. The optimized parameter of the dual treatment was found as 15 min of CRTD-Bor and subsequently 45 min of PH at 1000 °C, which resulted in 100 μm thick sole Fe₂B layer having 1600 ± 100 HV hardness along with the perfect adhesion -HF1 quality. The tribological properties were evaluated by sliding wear tests in pin-on-disc configuration under dry and lubricated conditions. Since the wear in gear systems is of concern, wear tests were conducted to unborided pin/unborided disc, borided pin/unborided disc and borided pin/borided disc tribo-couples. For both environments, the unborided tribo-pairs exhibited the highest loss whereas the borided tribo-couples had no measurable wear. Results of tribological tests revealed that the combined treatment successfully improved the wear resistance of the gears working in relative motions.