| Abstract Scope |
This study proposes microstructural and crystallographic texture analysis as a viable method for assessing suitability of candidate filler metals for GTAW. Dissimilar welds between super-duplex stainless steel and pipeline steel have been fabricated using two different filler metals for GTAW: austenitic stainless steel Type 309L and super-duplex stainless steel Type 2594. The fabricated welds have been characterized and assessed for tensile strength, impact energy, crystallographic texture, and microstructure. Thermodynamic calculations have been performed for equilibrium phases and Scheil solidification for segregations.
The microstructure of the weld made with Type 309L filler has ferrite dendrites with eutectic/peritectic austenite occupying the interdendritic spaces, while the Type 2594 filler weld has solid-state precipitations of austenite in the ferritic microstructure. Type 309L filler weld has lower proportion of high angle grain boundaries (HAGBs) and lower degree of misorientations (KAM), possibly indicating a higher aqueous corrosion resistance and a lower residual stress. The grain size variation in Type 2594 filler weld is higher, and the grains are more randomly oriented, thereby possibly offering a higher resistance to crack propagation. Type 2594 weld undergoes a greater degree of recrystallization because it has a lower proportion of sub-structured grains than that of Type 309L weld, although the proportion of deformed grains remains low for both welds. Most of the austenite grains in both welds are in the <100> direction, with minor randomness in Type 2594, showing orientations towards <111> as well. The texture intensity of Type 309L weld is higher than that of Type 2594 filler weld. Ferrite in both welds has 90º Rotated Goss texture as the major component. Presence of γ fibers in welds may have contributed to a higher impact energy of super duplex stainless steel filler weld. |