Relationships Between Microstructure and Creep Fracture of a Low Carbon Austenitic Steel

摘要

Austenitic steel deformed by creep fracture at temperatures of 700 exp 0 C has intergranular fractures. The initiation and propagation mechanism of these cracks are still not well understood. The goal of the study is to follow the development of the microstructure during creep fracture tests, and particularly during the phase called ''tertiary creep'' which preceeds the fracture. The tests were done using a Z CND 17/13 steel with a low carbon content and deformed by creep fracture at 700 exp 0 C under an initial stress of 90 NPa. The development of the microstructure and the density of the dislocations were followed using electron microscopy during the different stages of the deformation. After a multiplication period corresponding to a primary creep stage, the dislocations arranged themselves in layers during the secondary stage. These layers delimit cells of different sizes, which quite often are smaller near the grain joints. At the end of the deformation, the number of cells decreases and the layers of dislocations are refined. A larger number of cells in the areas near the grain joints is interpreted as the result of a larger deformation in these zones. This incidence of greater deformation in intergranular fracturing will be discussed. (ERA citation 03:001109)