Spatiotemporal Variations of Creep Damage in Dissimilar Welded Joints

The influence of high-temperature creep on local microstructural, physical and mechanical performance for different regions of dissimilar welded joints of two kinds of martensitic heatresistant steels F92 and Co3W2 is studied, under 873 K and 150 to 200 MPa. The rupture location is located in F92 for all testing specimens under various creep conditions and the fracture morphology exhibits a transgranular plastic fracture. Analysis on creep rupture data yields a 100,000 h creep rupture stress of 93.5 MPa, and a creep damage tolerance of 4.93. Creep damage micromechanisms like external cross section loss, microcavities' nucleation and growth and microstructural deterioration are observed, and creep damages are more complicated in the crept dissimilar welds compared to single material because they are not only location dependent but also time dependent. Nanoindentation technique was implemented to acquire local nanohardness, reduced modulus, plasticity index, strain rate sensitivity and activation volume of different welding microzones with various degrees of creep damage. Co3W2 side displays better local physical and mechanical properties after creep compared to uncrept state due to the positive impact of creep, while the properties of F92 side improve for short creep and are decreased after longer creep, which are consistent with their microstructural evolution during creep.