A. W. Stockdale, J. N. DuPont, Lehigh University, Bethlehem, PA
Mo microsegregates during welding of 6 wt% Mo superaustenitic stainless steels, resulting in a decrease in the corrosion performance of the alloy. Current techniques utilize filler metals with a higher Mo content to compensate for this deficiency, and an important aspect in this process is the weld metal dilution level. The dilution level, which is influenced by the welding parameters, will control the nominal and dendrite-core composition of the weld and therefore the resultant corrosion resistance. A study was conducted to better understand the relationship between the welding parameters, microstructural evolution, and the resultant corrosion resistance of cast stainless steel alloys with 6 wt% Mo. Samples were prepared with the Gas Tungsten Arc Welding (GTAW) process, using two different commercial filler metals, IN686 and IN72. The dilution levels were measured and the weld microstructures were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques. Samples were corrosion tested using the ASTM G48a specification and the mass loss was used to characterize the corrosion performance. Post weld heat treatments were investigated to determine the necessary heat treatment for complete homogenization of the weld and to evaluate the concomitant increase in corrosion performance. The results showed that decreasing the dilution level increased the nominal Mo composition and decreased the segregation of Mo, which produced the optimal corrosion performance. These results are significant because they can be used to develop welding guidelines designed to preserve the weld metal corrosion resistance.
Summary: Advanced austenitic stainless steels with additions of molybdenum are used in a variety of military applications. Research was conducted to investigate the influence of filler metal composition, welding parameters, and post-weld heat treatments on the microstructural evolution and resultant corrosion resistance of these alloys.
