Environmentally Influenced Fatigue in High Strength Steels

摘要

A study was conducted to identify the environmental influence on fatigue crack growth behavior of three high strength steels: AerMet 100, 300M, and 4340. These steels were subjected to fatigue tests under constant amplitude loading of frequency 10 Hz and stress ratios R = 0.1 and 0.9, in vacuum, air, and 3.5 % NaCl solution. The fatigue crack growth was characterized with two driving force parameters, stress intensity range, ΔK, and maximum stress intensity, K_(max). Especially, the variation of fatigue crack growth per time, da/dt, with K_(max) in 3.5 % NaCl solution was evaluated with respect to R, environment, and threshold stress intensity for environmentally assisted cracking (EAC), K_(IEAC). In addition, the environmental influence on fatigue crack growth was examined with the fractographic features and trajectory path, drawn with the limiting values of ΔK and K_(max), ΔK~* and K_(max)~*.