Stress-rupture tests were carried out on a number of low-alloy steels, ferritic stainless steels and austenitic alloys. Both unnotched and sharply notched bars were tested at various temperatures. The ductilities were determined for both the unnotched and notched specimens.

It was found that all alloys tested were subject to notch weakening. The time and temperature range of this weakening effect and its magnitude varied greatly with the alloy composition. Tests carried out at 900, 1000, 1100, and 1200 F on a low alloy chromium-molybdenum-vanadium steel indicated the notch sensitivity to be time-temperature dependent. The general trends of the data conform to the conception that a precipitation reaction is responsible for the notch sensitivity.

No definite conclusions regarding notch-rupture sensitivity can be made by an examination of the data for the unnotched bars except possibly when this quantity is extremely low. The notch apparently can reduce the ductility of an otherwise ductile metal to the point where there is insufficient plastic flow to eliminate the initial stress concentration.