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Effect of temperature on fatigue properties of Din 35 NiCrMoV 12 5 steel

Önem, Orkun Umur
DIN 35NiCrMoV125 (equivalent to AISI 4340), which is a high strength low alloy steel (HSLA), is mainly used at military applications in the production of gun barrels. The main aim of this study was to determine the low cycle fatigue (LCF) behaviour and the influence of temperature on low cycle fatigue failure properties of that steel. Three different temperatures (room temperature, 2500C and 4000C) were used in the experiments in order to analyze the effect of temperature. For each temperature, five strain amplitudes (in the range of 0.2% offset yield point to 2% strain) were applied and the duplicates of each experiment were performed to obtain more accurate results. Strain amplitudes and the corresponding stresses were calculated from tension tests performed at each temperature. Strain amplitude versus fatigue life (e- N) curves for three different temperatures predicted that fatigue life at a given strain increases with increasing temperature. The transition lives of those three curves were observed at 1 % strain amplitude and no significant effect of temperature on transition lives was observed. For stress based analysis, stress versus fatigue life (S-N) curves were drawn. These curves pointed that fatigue strength at a given number of cycle decreases with increasing temperature. Fractographic analyses of the fracture surfaces were performed to examine the effects of load and temperature on the specimens. It was observed that the number of crack initiation sites increases with increasing strain.