13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- The crack growth curve and the dependence of crack growth on stress intensity factor range in Steel B are shown in Figs. 11 and 12 respectively. As seen in Figs. 11 and 12, the effects of both humidity and reverted austenite on the propagation of small cracks are not distinguished in Steel B, though the crack initiation of Steel B is truly promoted by high humidity. Further observation on crack morphology of Steel B fatigued in both low and high humidity reveals that the effect of humidity on macroscopic crack growth in Steel B is really limited, as shown in Fig. 13, implying that the reverted austenite in the matrix of Steel B does play an important role in the process of crack propagation [4], i.e. the widely distributed reverted austenite phases become trap sites of hydrogen [5, 6] and suppress the acceleration of crack propagation in high humidity due to hydrogen embrittlement. Figure 11. Crack growth curves of Steel B Figure 12. Crack growth rate vs. stress intensity factor range 10 100 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 Crack growth rate, da/dN m/cycle Stress intensity factor range, ΔK MPa･m1/2 RH 25% 85% Steel A Steel B 0 1x10 5 2x10 5 3x10 5 0.01 0.1 1 10 Crack length, a mm Number of cycles, N cycle RH 25% 85% SteelB ( σ a =650MPa)
RkJQdWJsaXNoZXIy MjM0NDE=