The Influence of Notches on Mechanical Behavior at Elevated Temperatures: Some Metallographic Observations

A metallographic study of ruptured and unruptured notch bars is reported in this paper. The alloys are Cr-Mo-V steels tested in the range 1000–1050 deg F. Crack initiation and propagation in these alloys are studied as a function of the steel’s ductility with test bar section size and notch geometry as variables. It is shown that these factors interact in a complex way to control crack initiation and propagation. The mode and rate of crack initiation and propagation in ductile alloys depend mainly on shear processes although principal stress components are important under certain conditions. Alternatively, the maximum principal stress dominates the behavior in low ductility steels. In the former case, notched bar life is limited by crack propagation while in the latter case it is controlled by crack initiation. The influence of geometrical variables and metallurgical factors are discussed.