Creep-fatigue interaction behaviour of type 308 stainless steel weld metal and type 304 stainless steel base metal

Abstract

The effects of hold condition (tension-only, compression-only and tension-plus-compression holds of 1 min duration) and hold time (up to 10 min in tension) on the low-cycle fatigue behaviour of type 304 stainless steel base metal and type 308 stainless steel all-weld metal were investigated at 923 K. All the tests were performed in total axial strain control in air, employing a strain range of 1.0%. The welds were prepared by a submerged metal arc welding process. The microstructure of the base metal and the weld consisted of gamma phase and duplex gamma-delta ferrite respectively. The results clearly indicated a reduction in continuous cycling as well as creep-fatigue interaction life of type 308 SS weld metal compared with type 304 SS base metal under identical testing conditions. Hold times displayed an effect on life that was dependent not only on material condition but also on the position of the hold in the cycle. Fatigue lives recorded for type 308 SS weld in the 1 min hold-time tests were in the order: compression hold → continuous cycling → tension-plus-compression hold → tension hold. Fatique lives of 304 SS were in the order: continuous cycling → compression hold → tension-plus-compression hold → tension hold. A significant reduction in the life of the weld metal was noted on increasing the duration of tension hold time to 10 min. 308 SS weld metal exhibited cyclic softening whereas 304 SS base metal showed rapid initial hardening followed by a saturation stage. The observed variations in life are explained on the basis of crack initiation and propagation modes and microstructural changes that occured during low-cycle fatigue and creep-fatigue interaction testing.