THE HIGH CYCLE FATIGUE and FINAL FRACTURE BEHAVIOR OF AN ALLOY STEEL USED IN HYDROGEN PRESSURE VESSELS: INFLUENCE OF NOTCH

摘要

In this paper, the results of a recent study aimed at understanding the extrinsic influence of exposure to diatomic hydrogen gas on high cycle fatigue properties and fracture behavior of alloy steel 4140, a viable candidate for use in hydrogen-containing pressure vessels, is presented and discussed. The specific heat treatment given to this steel was quenched and tempered condition. Test specimens of the alloy were precision machined and conformed to the standards specified in ASTM E8. Test specimens were prepared both without and with a notch. Test specimens of the alloy in both the smooth condition and those containing a notch were exposed to gaseous hydrogen in a specially designed and constructed environmental chamber. The unexposed and exposed samples were then cyclically deformed over a range of maximum stress, at a load ratio of 0.1 and frequency of 5 Hz, and the number of cycles to failure recorded. The specific significance of exposure to hydrogen environment on cyclic fatigue life of both the smooth and notch specimens of this alloy steel 4140 is highlighted. The fatigue fracture surfaces were examined in a scanning electron microscope to examine the macroscopic fracture mode and to characterize the intrinsic features on the fatigue fracture surfaces. The conjoint influence of microstructure, maximum stress, local stress concentration effects arising from the presence of a notch, and environment exposure, on cyclic fatigue life is presented and discussed.