Investigation of the Kinetics of the Ferrite/Austenite Phase Transformation in the HAZ of a 2205 Duplex Stainless Steel Weldment

摘要

A semi-quantitative map based on a series of spatially resolved X-ray diffraction (SRXRD) scans shows the progression of the ferrite (δ)/austenite (γ) phase balance throughout the HAZ during GTA welding of a 2205 duplex stainless steel (DSS). This map shows a decrease in the ferrite volume fraction on heating, followed by a recovery to the original value on cooling at locations within the HAZ where no transformation is expected. Even though such behavior is supported by thermody-namic calculations, it has neither been confirmed by experimental methods nor have the transformation kinetics been evaluated over the time scales present during welding. Both Gleeble thermal simulations and time resolved x-ray diffraction (TRXRD) measurements on spot welds in the 2205 DSS have been performed, and both provide additional evidence for this transformation. In addition to the experimental work, calculations using both ortho-equilibrium and para-equilibrium interface conditions have been made to help explain this phase transformation. Only the para-equilibrium calculations have predicted the observed transformation on the same time scale as the SRXRD observations. Work is continuing in this area in order to determine the dominant mechanism of this phase transformation.