Influence of Treatment Time and Temperature on Surface Property of Active Screen Plasma-Nitrided EN24 Low Alloy Steel

Abstract

Active screen plasma nitriding is a newly developed technique utilized to enhance low alloy steel's surface property by placing them inside a steel case and supplying biased voltage to the cage. In this work, low alloy steel EN24 samples are plasma nitrided using active screen at different process parameters to improve its surface properties. The EN24 samples are treated at 500˚C and 550˚C treatment temperature for 2 h, 4 h and 6 h with gas flow ratio of ${H}_{2}/{N}_{2}=4:1$.The active screen plasma-nitrided samples are analyzed with various analytical techniques such as SEM, XRD, EDS, microhardness test, weight loss technique and potentiodynamic polarization test. From the SEM analysis, it is found that the compound layers vary from 12.680 to 22.025 µm. Further, the SEM analysis also reveals the formation of transformed austenite phases with increasing temperature and treatment time. Phase identification is performed on treated samples by XRD, which reveals the formation of $\varepsilon ({Fe}_{2-3}N)$ and $\upgamma ({Fe}_{4}N)$ on the surface of the samples. Using the microhardness test, it is found that the hardness value of treated samples has increased by 3.5 times (approx.) from the base material. From the weight loss technique, the minimum weight loss is seen for the treated sample at 500˚C for 6 h. Finally, it is observed from the potentiodynamic polarization test of the sample treated at 550˚C for 6 h has the minimum corrosion rate of 446.20 mm/year × 10⁻³.