Increasing wear and corrosion resistance of low-alloy steel by anode plasma electrolytic nitriding

In this work, we investigate the properties of the low-alloy steel (0.4% C, 1% Cr) which is obtained as a result of anode plasma electrolytic nitriding (PEN) followed by hardening in the same electrolyte. An X-ray diffractometer and a scanning electron microscopy (SEM) were used to characterize the phase composition of the modified layer and its surface morphology. Surface roughness was studied with the use of a roughness tester. The hardness of the treated and untreated samples was measured using a microhardness tester. A pin-on-disk tribometer was occupied to evaluate weight loss of the untreated and treated samples at lubricated conditions. Corrosion properties of the samples treated surfaces were evaluated using potentiodynamic polarisation tests in solution of sodium sulfate. The effect of nitriding regimes on the weight wear and corrosion resistance of treated steel is considered. It is established that competition of the anodic dissolution and iron oxidation determined the oxide layer thickness affects microhardness layer, surface roughness, and wear and corrosion resistance. The electrolyte composition (10 wt% ammonium chloride, 5 wt% ammonia) and processing mode (650 °C, 5 min) of low-alloy steels allowing one to obtain the hardened surface layer with microhardness 780 HV and with decrease in the weight loss after lubricant wear testing of 3 times or 4.6 times for dry friction are proposed. The anode PEN (800 °C, 5 min) can decrease the corrosion current density of steel in 0.05 mol/L solution of sodium sulfate by a factor of 7.7.