| The effects of high pressure hydrogen environment on the mechanical properties, expecially on the low-cycle-fatigue behavior at room temperature in quenched and tempered SCM4 (AISI 4140) steel, have been investigated. The softening phenomenon and the strength-differential effects were almost the same in air and hydrogen environment. However, the fatigue life in hydrogen environment was reduced significantly. Also the parameters describing the fatigue properties, such as ε＾t_f, Nt, etc. were shown to be very sensitive to the environment. As the hydrogen pressure increases the critical fatigue life, Nc was reduced to a certain limit value. It has been shown that absorption theory among mechanisms of H.E. (hydrogen embrittlement) can not be directly applied. The modes of crack-propagation and faillure revealed that the fatigue crack propagated according to the “Laird’s Model”in air, whilst to the micro-void coalescence, tongue formation and secondary cleavage in hydrogen environment The results of this study may be extremely useful for the prediction of the fatigue life in high pressure hydrogen environment and may verify that the phenomenon of hydrogen embrittlement could be explained by a combination of two effects, the decohesion theory and the planar pressure theory. |
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