IMPROVEMENT OF CORROSION AND WEAR RESISTANCE OF 45 STEEL WITH ANODE PLASMA ELECTROLYTE NITRIDING

Abstract

For citation:Smirnov A.A., Silkin S.A., Belkin P.N., Dyakov I.G., Sevostyanova V.S., Kusmanov S.A. Improvement of corrosion and wear resistance of 45 steel with anode plasma electrolyte nitriding. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 81-86.The wear and corrosion resistance was studied after anode plasma electrolytic nitriding (PEN) the carbon steel in electrolyte containing ammonium chloride and ammonia or ammonium nitrate. Tribological properties of nitrided samples were evaluated using a pin-on-disk and ball-on-disk tribometers under lubricated testing conditions and dry sliding. The effect of processing temperature on corrosion resistance of the PEN samples was examined by means of potentiodynamic polarization in a solution of sodium sulfate (0.1 N). The anode PEN at 750 °C during 5 min in electrolyte containing ammonium chloride (15%) and ammonium nitrate (5%) results in a decrease in a corrosion current density by a factor of 16. The anode PEN at 750 °C during 10 min in electrolyte containing ammonium chloride (10%) and ammonia (5%) results in the decrease in a corrosion current density by a factor of 6. Improving the corrosion resistance of steel takes place due to the formation of the surface oxide layer and the nitride-martensite zone. Results of wear tests under lubricated testing conditions with the speed of 0.49 m/s and load of 208.6 N against hardened steel (50 HRC) diskshow that friction coefficient of nitrided samples decreases at all PEN temperatures. The anode PEN at 750 °C during 10 min in electrolyte containing ammonium chloride and ammonia results in the decrease in wear rate more than 9 times and friction coefficient from 0.17 to 0.12. Nitriding in electrolyte with ammonium chloride and nitrate also results in minimum of the wear rate after the PEN at 750 °C during 10 min but it gives lesser result due to the lower hardness of the nitride-martensite sublayer. Wear tests during dry sliding with the speed of 0.2 m/s and load of 5 N against bearing steel ballshow that friction coefficient of nitrided samples decreases from 0.41 to 0.28. The increasing the load reduces the friction coefficient that means saving mode of elastic contact and a good running-in ability of oxide layer in the studied range. Linear wear decreases from 35 to 21 mm at load of 10 N and sliding speed of 0.4 m/s.