Factors Influencing the Notch-Rupture Strength of Heat-Resistant Alloys at Elevated Temperatures

Abstract Stress-rupture tests were conducted on notched and unnotched or plain bars of S-816, Inconel “X” Type 550, and Waspaloy alloys at test temperatures ranging from 1200 to 1600 F. The notched specimens had 50 per cent, 60-deg, V-notches with the root radii ranging from 0.005 to 0.100 in. In some tests, as many as three notches of different root radii were used. The test results indicated that S-816 alloy was notch-strengthened by all of the notches used in the temperature range from 1350 F to 1600 F. Inconel “X” Type 550 was always notch-strengthened by all of the notches only at the test temperature of 1600 F. Waspaloy was always notch-strengthened by all notches only at the temperature of 1500 F. Both Inconel “X” Type 550 and Waspaloy could be notch-strengthened for some test conditions (notch sharpness and time) at temperatures below 1600 and 1500 F, respectively. Factors considered to have an influence on stress-rupture behavior have been studied and the results are included. The factors investigated are notch geometry, notched and unnotched ductility, the modes of deformation and fracture, metallurgical changes, and surface condition. The influence of some of these factors can vary considerably from alloy to alloy. It does not appear possible, therefore, to evaluate completely the notch and unnotched stress-rupture behavior of a given alloy by any simple method. Rather, an evaluation should be based upon the combined consideration of those factors that are influential in each individual case.