FATIGUE AND FRACTURE OF HIGH-ALLOYED STEEL SPECIMENS SUBJECTED TO PURELY THERMAL CYCLING

High-alloyed steel specimens subjected to hundreds of thermal cycles (heating up in a furnace to about 900 °C, quenching in water, resting in air) are considered. Contrary to standard "low-cycle fatigue" tests with a cyclically varying applied mechanical load, the driving "force" is a cyclic temperature field with self-equilibrating residual stress states. Despite the cyclic character of this temperature field and no applied load, a significant monotonie change of the shape and metallurgical structure of the specimens can be observed depending strongly on the material and the initial geometry. Precipitations along the grain boundaries and remarkable residual stress states are responsible for internal cracks and damage. An experimental program is reported, and metallurgical and mechanical interpretations are presented. © 1990 The Metallurgical of Society of AIME.