Effect of temperature on tensile and low fatigue behavior of medium carbon steels

The effect of temperature on tensile and cyclic deformation is studied on SAE 1045 and SAE 4140 commercial steels. Tensile and low cycle fatigue (LCF) tests were performed at room temperature and 250 degrees C. For a temperature of 250 degrees C, an induction heating system was used during the tests. The temperature of the specimen was homogenized 600 s before testing. The tension-compression LCF tests were carried out at total strain amplitudes of f 0.6%, f 0.8%, and f 1.0%. The Coffin-Manson-Basquim model was used to predict the LCF properties of steels. Scanning electron microscopy was used to evaluate the microstructure and the fracture surface. The fracture surfaces of samples tensile tested at room temperature and 250 degrees C were similar. For fatigue testing, the surfaces obtained were also similar with regions of fatigue crack initiation and propagation, and rupture. A crack initiation near the surface was observed for the LCF specimens. Dynamic strain aging and recovery influenced the tensile and fatigue results, for example, the number of reversals to failure decreased for the fatigue test performed at 250 degrees C. For fatigue tests performed at strain of 0.6% in the SAE 1045, the stress increased by 65% at 250 degrees C when compared to testing at room temperature. Consequently, the number of reversals was reduced by 58%.