Strain-controlled low cycle fatigue behaviour of type 304 stainless steel base material, type 308 stainless stell weld metal and 304-308 stainless steel weldments

Abstract

Total-axial-strain-controlled low cycle fatigue (LCF) tests have been conducted in air at 823 and 923 K on type 304 stainless steel (SS) base material, type 308 SS weld metal and 304-308 weldments prepared by the manual metal arc welding process. A symmetrical triangular waveform and a constant frequency of 0.1 Hz were employed for all the tests performed over strain amplitudes in the range from ±0.25% to ±0.80%. Crack initiation and propagation modes were studied. Microstructural features prior to and during LCF deformation were evaluated. Deformation and damage mechanisms which influence the stress response and endurance have been identified. The results indicated that the LCF resistance of base material was superior to that of the weldment at both the temperatures investigated. A reduction in fatigue life was noticed for all the conditions when the temperature was raised from 823 to 923 K. The δ-ferrite in welds and weldments transformed to M₂₃C₆ and σ phase duringk LCF testing. The transformed portion of δ-ferrite increased with increasing number of cycles to failure and increasing temperature. Solution annealing (at 1173 K for 3 h) the weldment prior to LCF testing caused an improvement in the fatigue life.