Lcf loop shape in near pearlitic steels – influence of temperature

Specimens of near pearlitic railway wheel steels have been exposed to isothermal, uniaxial low cycle fatigue tests at constant total strain amplitudes from 0.4 – 1.0%. Temperatures have been varied from -60\ub0C to 500\ub0C. The data recorded has been analysed by fitting polynomial expressions to different parts of the loop. A technique used for extracting the unloading stiffness was presented at the previous conference, LCF6 in Berlin 2008. This procedure has now been extended to characterize the entire loop. The degree of micro plasticity and its effect on unloading stiffness, the strain energy and the cyclic stress development have been characterized. An increased cyclic hardening during the main part of the fatigue life was identified on cycling at 300\ub0C at total strain amplitude of 0.6%. At 500\ub0C the viscous behaviour dominates over the cyclic strain hardening yielding decreasing stress amplitude