Three-Dimensional Thermomechanical Simulation and Experimental Validation on Failure of Dissimilar Material Welds

Dissimilar material weld joints, consisting of low-alloy steel and 304LN austenitic stainless steel
(SS), have critical application in boiling water reactors in the nuclear industry. It was predicted
that phase transformation adjacent to the fusion boundary and stress distribution across the
transition joint play a key role in the structural degeneration of these welds. Quantitatively, to
evaluate their contribution, two different joints were considered. One was fabricated with
buttering material 309L SS (M/S Mishra Dhatu Nigam Limited, Hyderabad, India), and the
other was produced with buttering material IN182 (M/S Mishra Dhatu Nigam Limited,
Hyderabad, India). Base materials remained the same for both. Thermomechanical simulation
on dissimilar material welds was performed using finite-element modeling to predict the thermal
effect and stress prone area. Temperature-dependent thermal and structural properties were
considered for simulation. Simulation results were compared with microstructural characteristics,
and data were obtained from the in-situ tensile test. Simulation results exhibited that stress
was at maximum in the buttering material and made the zone weaker with respect to adjacent
areas. During the validation of results, it was observed that failure occurred through buttering
material and endorsed the inference. The variation in mechanical properties of the two welds
was explained considering the effect of thermal state and stress distribution.