Effects of residual stresses and distortion on the nickel 200 and stainless steel 304 weldments

Autogenous bead-on-plate welds made on nickel 200 and stainless steel 304 (SST) using the gas tungsen arc welding process. The transient thermal repsonses and displacement were monitored during welding using spot-welded thermocouples and linear voltage displacement transducers (LVDT).Variations in the parameters included plate thickness, current, heat input, travel speed, and restraint conditions. Electrode geometry and shielding gas were kept constant. Residual stresses were measured after welding using the blind-hole drilling technique. Comparison were then made between the fusion zone geometry as determined metallographically, and the resultant residual stress and distortion distributions. Results of the thermal responses indicated that the two materials differ significantly in peak temperatures and cooling rates, which could be attributed to the differences in their thermal properties. Due to its lower thermal conductivity, the SST maintained heat in a smaller localized region, resulting in steeper thermal gradients and greater tendency to buckle than did nickel. On cooling, these gradients produced higher thermal stresses, which were responsible for the formation of residual compressive stresses in the heat-affected zone (HAZ). The photomacrographs showed that penetration increased with a simultaneous increase in both current and travel speed. In addition, the fusion zone geometry changed from a radial symmetry to themore » bell-shaped weld and then to a flat and shallow weld, if one parameter was increased while the other was held constant.« less