Microstructural and mechanical characterization of radial friction welded supermartensitic stainless steel joints

This paper reports on an investigation of the microstructural aspects and mechanical properties of radial friction (RF) welded supermartensitic stainless steel (SMSS) joints in the as-welded condition. RF SMSS welds were produced with a matching consumable ring (CR). A detailed microstructural analysis of the weld region was carried out by optical microscopy (OM) and X-ray diffraction (XRD) allied to microhardness measurements. Conventional tensile and micro-tensile tests were also conducted to evaluate the global and local mechanical properties of the welded joints. The results of these analyses allowed that the local microstructure-property relationship was established. 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 themo-mechanically affected zone (TMAZ). The microhardness profiles measured along the as-welded HAZ, TMAZ and CR regions of the RF welded SMSS joints indicated that they fell within the maximum hardness limit of 350 HV for application requirements. The results of the tensile and micro-tensile tests revealed higher weld region strength than that of the base material (overmatching), without presenting a significant loss in weld zone ductility, which is directly linked with the fine transformed microstructure observed in the weld region.