Stanovení lomové houževnatosti potrubí z oceli ČSN 15 128 po provozní expozici pomocí instrumentované indentace

Abstract

The purpose of this work is to investigate in more detail the fracture properties of 15 128 heat resistant steel pipe after long term service exposure and to verify the use of fracture properties to identify creep damage. The theoretical part of the thesis presents the basic concepts of fracture mechanics used to characterize the fracture behaviour of materials, a description of standardized measurements, a method to identify the fracture behaviour of materials using instrumented indentation, and information on creep damage of 15 128 steel. The experimental part of this thesis includes fracture toughness and impact toughness tests, which were further complemented by the study of microstructure using light microscopy and fracture surfaces using SEM. It was found that the components exhibited a lower to moderate degree of creep damage with isolated cavities after service exposure. Analysis of the inclusion’s distribution indicated coarsening of the precipitates after operational exposure, which had the effect of reducing the impact and fracture toughness. Fractographic analysis revealed an increased occurrence of coarse inclusions on the fracture surfaces. The instrumented indentation results differed significantly from the standard test results.