Damage Evolution in Thermomechanical Loading of Stainless Steel

Abstract

Superaustenitic stainless steel Sanicro 25 has been subjected to in-phase and out-of-phase thermomechanical fatigue (TMF). Different amplitudes of mechanical strain and the changes of the temperature in the interval 250 to 700°C were applied to standard cylindrical specimens. Early fatigue damage has been studied using scanning electron microscopy combined with FIB cutting and EBSD imaging. TMF loading resulted first in developing thin oxide layer. In in-phase loading grain boundaries were preferentially oxidized and fatigue cracks developed by alternating oxidation and cracking. Fatigue cracks developed rapidly in oxidized grain boundaries and propagated intergranularly. During out-of-phase TMF loading the cracked oxide layer resulted in local oxidation and crack initiation. The crack grew transgranularly.Superaustenitic stainless steel Sanicro 25 has been subjected to in-phase and out-of-phase thermomechanical fatigue (TMF). Different amplitudes of mechanical strain and the changes of the temperature in the interval 250 to 700°C were applied to standard cylindrical specimens. Early fatigue damage has been studied using scanning electron microscopy combined with FIB cutting and EBSD imaging. TMF loading resulted first in developing thin oxide layer. In in-phase loading grain boundaries were preferentially oxidized and fatigue cracks developed by alternating oxidation and cracking. Fatigue cracks developed rapidly in oxidized grain boundaries and propagated intergranularly. During out-of-phase TMF loading the cracked oxide layer resulted in local oxidation and crack initiation. The crack grew transgranularly.