Enhancement of Wear and Corrosion Resistance in Medium Carbon Steel by Plasma Electrolytic Nitriding and Polishing

Abstract

The effect of plasma electrolytic polishing on the characteristics of medium carbon steel after anodic nitriding in a nitrate–chloride electrolyte was investigated. The structure, morphology, and phase composition of the layers were studied using an x-ray diffractometer and a metallographic microscope. Nitrided and polished specimens were tested under dry friction conditions with a counter-body made of bearing steel. Corrosion studies were performed using potentiodynamic polarization curves in 3% sodium chloride solution. Nitriding in a nitrate–chloride electrolyte was determined to increase the surface hardness up to 1040 HV due to the formation of a nitride–martensite layer with an outer oxide layer. After polishing of the nitrided surface, the loose outer part of the oxide layer containing microcracks and pores was removed. The reduction in the corrosion current density of 2.27 times of nitrided steel by plasma polishing without changing the structure of the diffusion layers was shown. The wear rate of the samples decreased from 560 μg/(N m) for untreated steel to 60 μg/(N m) as a result of nitriding and dropped to 8 μg/(N m) after plasma electrolytic polishing.