LOW CYCLE FATIGUE BEHAVIOUR OF 316L(N) AUSTENITIC STAINLESS STEEL BASE METAL, WELD METAL AND WELD JOINT

摘要

The low cycle fatigue (LCF) behaviour of 316L(N) base metal, 316 weld metal and 316L(N) weld metal in the temperature range, 300 to 873 K is presented. These results are compared with the LCF behaviour of weld joints. Tests were carried out at various strain amplitudes and strain rates. In these test conditions, cyclic hardening observed was attributed mainly in dynamic strain ageing, whereas cyclic softening seen in the weld metal was ascribed to annihilation of dislocations. 316L(N) base metal exhibited better fatigue life than 316 weld metal at 773 K, whereas 316 weld metal showed superior fatigue resistance at specific strain rates at 823 and 873 K. The better fatigue life of 316 weld metal was due to the beneficial effects of crack deflection by numerous transformed #delta# - ferrite boundaries in the austenite matrix. The transformation of #delta#-ferrite to brittle phases was less pronounced in 316L(N) weld metal, which in turn, showed a lesser tendency for crack deflection leading to reduced fatigue life. At high temperatures, oxidation served to reduce the fatigue life. Weld joints showed the least fatigue life which was associated with the accelerated intergranular crack initiation and propagation in the coarse grained heat affected zone.