Local mechanical properties of radial friction welded supermartensitic stainless steel pipes

• High quality SMSS (defect-free) welds were produced by RF welding using a matching CR.
• RF welded SMSS pipes exihibited a ductile fracture at - 40 °C.
• An increase in hardness levels towards the weld center was found.
• The strength of the weld region was higher than that of the base material (overmatching).
• No significant loss in ductility and fracture toughness of the weld zone was detected.

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their microstructures and local mechanical properties (hardness, fracture toughness and micro-tensile strength) were characterized in the as-welded condition. Defect-free RF welds were produced with a matching consumable ring (CR) under optimized welding conditions. The formation of a fine structure consisting of a mixture of virgin martensite and some stable austenite retained in the CR region was observed. On the other hand, the presence of virgin martensite plus δ-ferrite was found in the microstructures of the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). A ductile fracture was detected in the CR and weld interface regions at −40 °C. Moreover, both the CR and weld interface regions showed higher hardness and strength values than those of the base material (overmatching), without presenting significant losses in ductility and fracture toughness, which was attributed directly to the fine transformed microstructure of the weld region.

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