Mechanisms operating during high-temperature fatigue with hold periods in two chromium ferritic steels

High temperature total strain control fatigue tests with a 2 minute hold period at either maximum compressive strain or maximum tensile strain were performed on two chromium ferritic steels. The two steels, annealed 2.25%Cr 1%Mo and a modified form of 9%Cr 1%Mo steel, are used in high temperature applications in the power generation industry. The nature of the hold period (tensile or compressive) affects fatigue life and the surface crack patterns. Fatigue experiments on 2.25%Cr steel were all done at the total axial strain range of 1.0%, at 500;Fatigue tests were performed on the 9%Cr steel at a series of total axial strain ranges between 0.65% to 2.3%. Tests on the 9%Cr steel were conducted in air, 10...