Creepové vlastnosti a struktura heterogenních svarových spojů pro energetiku

Abstract

Dissimilar welds are commonly used in the power plant industry for applications in boiler tubing to compensate differences of temperature, pressure and corrosion conditions between various locations. Great attention is being paid today to heterogeneous welds between modified 9-12% Cr steels and low alloy steels. An important degradation mechanism of dissimilar welds is related to the migration of interstitial elements, especially carbon, from low alloy side to high alloy side of the weld. This redistribution of interstitial elements significantly affects microstructural evolution in the vicinity of the fusion zone between low and high alloy materials during long-term creep exposure. Degradation of the microstructure and properties of dissimilar welds in general significantly depends on the combination of welded base materials, including the selection of the weld metal and parameters of exposure. Therefore, it is necessary to have detailed knowledge of the heat resistant properties of these types of heterogeneous welded joints in terms of their prospective applications in power generation. The Ph.D. thesis is focused on the study of dissimilar weld joints made between a low alloy P23 steel and a P91 steel during creep exposure at temperatures from 500 to 600oC. Two types of filler metals 9Cr1Mo (Thyssen Chromo 9V) and 2,25CrWV (Thyssen Chromo 3V) with chemical compositions matching one or another base materials were applied. Experimental results of microstructural evaluation have been compared with thermodynamic and kinetics calculations using TermoCalc and Dictra software packages.