Effects of hold times, pre-notching, and environment on the elevated temperature fatigue life of bainitic 2.25 Cr - 1 Mo steel

Creep-fatigue-environment interaction in bainitic 2.25 Cr - 1 Mo steel is investigated. Tests were conducted in both air and vacuum at 566 C (1050 F) using a variety of strain-controlled waveforms in an effort to determine the influence of environment and cyclic waveforms on the material's fatigue resistance. A fully reversed strain range of 0.5% was utilized exclusively as this is a realistic estimate of actual service conditions and can be compared to several other studies which tested over larger strain ranges. This material is cyclic softening, which has important implications for allowable service stress and strain levels. Pre-flawed specimens were examined in an attempt to separate the effects of crack initiation and propagation. Tiny electro-discharge machined (EDM) notches reduced life by about 25% for tests in air, verifying that crack propagation is the dominant fatigue mechanism under these loading conditions