Correlations Betwen Microstructure and Physical-Mechanical Properties in Local Microzones of Dissimilar Welded Joints During High-Temperature Service in Usc Unit

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 heat resistant steels F92 and Co3W2 was studied. The rupture location is located in F92 for all testing specimens under different conditions and the fracture morphology indicates a transgranular plastic fracture. Creep damages like microcavities’ nucleation and growth and microstructural deterioration are observed, and Co3W2 exhibits slower coarsening rate of precipitates comparing to F92. Nanoindentation technique was implemented to acquire local nanohardness, reduced modulus, plasticity index, strain rate sensitivity and activation volume of different welding microzones under various creep conditions. Co3W2 side displays better local physical and mechanical properties after long term creep than short creep while F92 side behaves in the opposite way, which are consistent with their microstructural evolution during creep.