Investigation of Surface Properties of EN8, EN24, and EN41B Low Alloy Steel Treated by Active Screen Plasma Nitriding

Abstract

In this work, active screen plasma nitriding (AS_PN) of EN8, EN24, and EN41B low alloy steel was carried out to improve its surface properties. The process parameters of 500 °C temperature for 4 h with the gas flow in the ratio of H2:N2 = 1:1 were used for the treatment. The improvement in the surface was assessed by the microhardness as well as characterized by SEM and XRD. The microhardness measurements reveal an increase in surface hardness by more than 4, 3.4, and 2.7 times from the base material for EN41B, EN8, and EN24. The compound zone/layer ranges from 4.9 microns (μm) for EN8 to as high as 9.1 microns (μm) for EN41B after nitriding. On analyzing the nitride layer thickness through SEM, the results found from microhardness measurement were confirmed. The XRD results also approve the predominant development of γ'-Fe4N and ɛ-Fe2–3 N phases on the treated sample surface, although its compound layer surges with different nitride forming elements. Further, SEM analysis also reveals a white layer formation without transformed austenite (γ). Further, EDS analysis was also performed on the treated samples. Finally, a comparative corrosion study for AS_PN treated and bare (untreated) material samples were done to find the influence of the treatment.