Combination of Experiments and Continuum Damage Mechanics Approach for Prediction of Creep Fracture in an Advanced 9%Cr Steel

Abstract

As candidate materials for high-temperature components, most attention has been paid to improving tempered martensitic creep-resistant 9-12%Cr steels. In this work, creep damage and fracture behaviour of an advanced W-modified P92 steel (ASTM Grade P92) was investigated at 600 and 650°C. Tensile creep tests were followed by fractographic analysis of crept and broken specimens. Besides experimental investigations, the creep damage tolerance parameter λ has been used to assess the creep fracture mode. In accordance with experiments the values of λ indicate variety in the fracture mode and provide some evidence on accelerated degradation of the creep strength. The SEM investigations of creep fracture surface revealed substantial changes in microfractographic features of creep fracture. At high applied stress level, the fracture was frequently transgranular due to local loss of a stability of plastic deformation. The fracture ductility drops with decreasing applied stress, demonstrating ductile dimple (transgranular) to brittle (intergranular cavitation) transition of the fracture mode. It was suggested that both the creep deformation and fracture processes are controlled by the same processes and the rate controlling mechanism is most probably climb of intergranular mobile dislocations.