Application of Nitriding Treatments on EN 3 and EN 24 Steels for Rotating Bending Fatigue Resistance

Abstract

Rotating bending fatigue failure increases the lifetime costs of shaftings and may cause catastrophic accidents. Case hardening helps in improving fatigue resistance. The feasibility of plasma nitriding process on mild steel of grade EN 3 for improved fatigue performance was investigated. Ion nitriding was carried out at 490 °C for 8 h. Over 7% by weight nitrogen concentration was found on the surface, but the case obtained was shallow. Later gas nitriding was applied to alloy steel of grade EN 24 at 550 °C for 72 h. Observations were made on the differences of nitriding with pretreatment and without it. Toroidal type of rotating bending fatigue test specimens of EN 24 was manufactured. Two-parametric Weibull distribution was used in order to analyse the results obtained from fatigue testing the nitrided specimens, whereas regression analysis was done on the non-nitrided specimens to obtain the S–N curve. Improvement of 95.88% in the endurance limit was observed on account of gas nitriding.