Secondary Hardening Behavior in Super Duplex Stainless Steels during LCF in Dynamic Strain Ageing Regime

Abstract

Cyclic deformation behaviors in five modified duplex stainless steel S32705 grades have been studied at 20 °C, 200 °C, 250° and 350 °C. The influence of temperature and nitrogen concentration on the occurrence of the second hardening phenomenon, in the stress response curve was focused. An increase in nitrogen concentration can have a positive effect on dynamic strain ageing by increasing the first hardening and also the second hardening behavior during cyclic deformation. Furthermore, an increase in nitrogen concentration in the super duplex stainless steel increases the fatigue life in the strain ageing temperature range. The occurrence of strain ageing in duplex stainless steel has greatly changed dislocation structures. The formation of irreversible dislocation structures and stacking faults can contribute to the formation of second hardening in the stress response curve