High temperature low cycle fatigue properties of 316(N) weld metal and 316L(N)/316(N) weld joints

Abstract

In the present paper, cyclic stress evolution and fracture behavior of 316(N) weld metal and 316L(N)/316(N) weld joints are reported under strain controlled low cycle fatigue tests. Axial total-strain controlled tests have been conducted at temperatures 773, 823 and 873 K with strain amplitudes of ±0.4, ±0.6 and ±1.0%. Though weld metals have shown higher plastic strain accumulation, observed fatigue life is better than the weld joints. Microstructural heterogeneity across the weld joint has resulted in poor fatigue life with most of the failures being initiated in heat affected zone, particularly at low to medium strain amplitudes. Few failures have been observed in weld metal zone of weld joint at high strain amplitudes. Differences in elastic modulus of weld metal and base metal creates strain incompatibility between the respective zones in the weld joint. As a first approximation to this strain incompatibility, plastic strain contribution from the weld metal and base metal zones of the weld joint are calculated by the rule of mixtures under equi-stress conditions and it is observed that base metal zone contributes to most of the plastic strain in weld joint.