THE INFLUENCE OF SUB-CRITICAL THERMOCHEMICAL PROCESSING ON FATIGUE RESISTANCE OF 42CrMo4 STEEL

The machine parts, fasteners and many other components require high fatigue resistance as well as other properties. The paper aims to determine the influence of nitriding and nitrocarburizing realized at temperatures below the eutectoid transformation temperature in the Fe-N system on the fatigue resistance of 42CrMo4 steel. The effects of performing these thermochemical treatments both on annealed as well as quenched - tempered matrixes on change of fatigue resistance under rotary bending stresses are taken into analysis. It was concluded that, independently of the matrix structural condition, the subsequent sub-critical thermochemical treatments applied after heat treatments, will lead to the fatigue resistance enhance; the nitriding is constantly providing better results than nitrocarburizing performed in ammonia/endogas mixtures. Economic reasons, recommend however the nitrocarburising in atmospheres with high ammonia contents to be applied in order to provide appropriate increase of the fatigue resistance of 42CrMo4 alloy steel components.