EFFECT OF WELDING PROCESS ON FATIGUE-CRACK GROWTH-BEHAVIOR OF AUSTENITIC STAINLESS-STEEL WELDS IN A LOW-ALLOY (Q-AND-T) STEEL

Fatigue crack growth behaviour from a lack of penetration (LOP) defect in austenitic stainless steel weld metals of cruciform joints made of a low alloy high strength (Q&T) steel has been studied to understand the effect of two welding processes, namely, shielded metal are weldin g (SMAW) and flux cored are welding (FCAW). Fatigue crack growth studi es were carried out at a stress ratio of R=0 and a frequency of 90 to 110 Hz in a resonant testing equipment (Rumul, Model:8601). Crack grow th rates were relatively lower in the weld metal obtained by flux core d are welding process. Microstructural features observed revealed mark ed difference in the morphology of delta ferrite for the welded joints obtained from the above two welding processes. Long streaks of delta ferrite in austenite matrix were found in case of SMAW-weld metal whic h seem to have lowered the resistance to the fatigue crack propagation . A discontinuous network of delta ferrite found in austenite matrix i n the case of FCAW-weld metal seems to have contributed to slower prop agation of fatigue crack. Fractographic features also substantiate the observed trends in the fatigue crack growth behaviour.