13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- (a) RH 25% (b) RH 85% Figure 13. Crack morphology observed in Steel B (Blank and solid arrows indicate origin of crack initiation and crack tips, respectively. Axial stresses applied in the horizontal direction) 4. Conclusions The effects of humidity and the aging structure on the initiation and propagation of a fatigue crack of maraging steels were investigated in various relative humidity (RH). Fatigue strength was largely decreased by high humidity, though the decrease in fatigue strength was very small below the humidity of RH50%. The main reason for the decrease in fatigue strength was the acceleration of both crack initiation and small crack growth. The propagation of larger cracks was not influenced by humidity. The promotion of crack initiation was due to anodic dissolution and the acceleration of crack propagation was caused by hydrogen embrittlement in accompany with cathode reaction. The hydrogen embrittlement assisted crack propagation was suppressed by the formation of reverted austenite. Acknowledgements Chen is grateful to the financial supports by JSPS KAKENHI through grant number 22560097 and by JKA through grant number JS23-99. References [1] R.F. Decker, C.J. Novak, T.W. Londig, Developments and projected trends in maraging steels, Journal of Metals, (1967)60-66. [2] K. Komai, S. Kita, K. Endo, Corrosion-fatigue crack growth of a high-tension steel in 1% NaCl, Transactions of the Japan Society of Mechanical Engineers, Series A, 49 (1983)1029-1035. [3] Y. Kawabe, M. Fukamachi, S. Muneki, J. Takahashi, Increased susceptibility of 13Ni-15Co-10Mo maraging steel to hydrogen embrittlement by aging at lower temperatures, Tetsu to Hagane, 70 (1984) 896-903.
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