Microstructural, mechanical, and fracture mechanical characterization of SA 508-Alloy 182 dissimilar metal weld in view of mismatch state

• The strength mismatch state and the microhardness profile predict similar crack growth behavior in the ferrite-austenite interface.
• The highest mismatch between two adjacent zones was found at the weld fusion boundary area between the weld interface and the buttering layer.
• The Alloy 182 buttering layer showed high fracture resistance and the fusion boundary and the SA 508 HAZ exhibited lower fracture resistance.
• The crack propagation occurred towards the SA 508 base metal in SA 508 HAZ specimens and towards the Alloy 182 buttering in fusion boundary specimens.
• The crack propagation occurred towards the weld zone with under-matched strength and hardness.

In dissimilar metal welds (DMWs), the mismatch in material properties between the two joined materials and their abrupt local variation in different narrow zones of the weld are of importance because the local strength mismatch state plays an important role in the fracture behavior. For the experimental determination of the narrow local property variations in DMWs, a weld mock-up consisting of SA 508 pressure vessel steel with AISI 309L/308L cladding and AISI 304 piping steel base metals, an Alloy 182 buttering layer, and Alloy 82 and 182 weld metals was manufactured. In the characterization special attention was paid to the narrow interface zones (NIZ) between SA 508 steel and Alloy 182 buttering. The Alloy 182 buttering and weld metal were found under-matched in strength compared to the SA 508 base metal and the highest strength mismatch existed between the SA 508 heat-affected zone (HAZ) and the Alloy 182 buttering layer. The highest fracture resistance was observed in the Alloy 182 buttering and the fracture resistance of the SA 508 HAZ was similar to that of the fusion boundary. The fracture surfaces consisted of ductile fracture in all investigated samples. The differences in fracture resistance between the different DMW zones were found to relate to the hardness/strength of the particular weld zone as well as to the size and distribution of the MnS-inclusions in the microstructure.