Creepové chování a mikrostruktura heterogenních svarů P92/S 304H

Abstract

Thesis deals with results of long-term stress rupture tests on heterogeneous Super 304H-P92 welds. Stress rupture tests were carried out at temperatures of 625 °C and 650 °C with times to rupture up to 20 000 hours. The goal of the thesis was to characterize creep properties of these heterogeneous welds, evaluate preferential locations of failure of “cross-weld” samples and study microstructure evolution in individual regions of welds. Based on experimental results values of creep rupture strength for 104 hours at temperatures of 625 °C and 650 °C were calculated. Preferential location of failure was the intercritical part of the heat affected zone of P92 steel, which has got lower creep resistance than Super 304H steel. Local changes of hardness were evaluated by hardness profiles across the “cross weld” samples. Metallographic investigations were performed in individual parts of heterogeneous welds. A special attention was paid to precipitation processes in base materials and in heat affected zones. A residual content of vanadium in Super 304H steel affected precipitation processes. Vanadium partially substituted niobium in the modified Z phase ((V,Nb)CrN).