Effect of Loading Sequence on Notch Strength of Warm Prestressed Alloy Steel

Abstract

An experimental study of the effects of warm prestressing on the fracture strength of notched and fatigue-cracked bend bars of a Ni-Cr-Mo, low-alloy forging-grade steel was conducted. The steel was tested in four heat treatment conditions simulating four thickness fractions of a 23-1/2-in-thick forging. Three load-temperature paths were investigated: (1) preload-cool-fracture, (2) preload-cool-unload-fracture, (3) preload-unload-cool-fracture. The fracture strengths of the prestressed bars were compared with the fracture strengths of unprestressed bars. The benefits of prestressing for each load-temperature path decreased in the order listed, although prestressing was always beneficial. The benefits also decreased with decreasing fracture-test temperature relative to the 50-percent FATT.