Abstract
The fatigue crack growth rate (FCGR) of 10Ni5CrMoV steel under variable load ratios was investigated. The microscopic observations of growth direction and microstructural analysis were conducted by means of electron backscatter diffraction and transmission electron microscopy. The results showed that FCGR of 10CrNi5MoV steel increased with the increasing load ratio in the mid-growth rate regime; however, it did not completely conform to the Paris Formula. A nonlinear zone existed in the logarithmic coordinate system of the FCGR curve and was unaffected by load ratio. The main impact factors for the appearance of the nonlinear zone were grain size and the size of the plastic zone surrounded fatigue cracks. In the nonlinear zone of the FCGR curve, an apparent crack deflection phenomenon occurred.
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