Phase transformation and welding characteristics of stroloy 2A

Abstract

A low-alloy quenched and tempered steel, such as Stroloy 2A, requires control of welding heat input to maintain adequate impact toughness in the weld heat-affected zone. Gleeble specimens are subjected to peak temperatures and controlled cooling rates which simulate weld heat-affected zone areas. Charpy V-notch impact tests on Gleeble treated specimens defines the critical minimum cooling rate essential to maintain empirically chosen minimum notch toughness values. For Stroloy 2A, a 30°F per second critical cooling rate was required for 6 foot-pounds V-notch impact strength at -50°F. Metallographic and hardness studies suggest that grain coarsening and mixed microstructures at high peak temperatures and slow cooling rates are responsible for degradation of heat-affected zone impact toughness. In actual welding, control of maximum heat input can be employed to give calculated cooling rates faster than the critical minimum cooling rate. Using controlled heat inputs to weld Stroloy 2A, actual weld heat-affected zone V-notch impact properties were observed to be much greater than those found in Gleeble simulated studies. This is due to the integrated toughness values of different microstructural constituents that are present in a multipass weld heat-affected zone. Thus, this study suggests that multipass welds will have equal or greater Charpy V-notch impact toughness in the heat-affected zone when welded with heat input controls, as compared to the impact values found from Gleeble studies.