Short fatigue crack growth behavior in 18Ni marageing steel

In recent decades, it has been found that the fatigue crack growth rate could be slowed down by the zigzag crack growth path in some materials, but the mechanism was not well clarified. In this study, the effect of crack growth path on the fatigue crack growth rate of 18Ni maraging steel under three different heat treatment states was studied, and two factors influencing the fatigue crack growth rate were outlined. It was found that, firstly, the main factor affecting the fatigue crack growth rate was the strength of the material; secondly, the zigzag crack growth path did not slow down the crack growth rate but increased the crack growth rate. Therefore, a two-phase model was established to understand the influence of crack growth path on the growth rate. In different phases, their resistances to the crack growth are different, and the difference in the strength between the two phases determines whether the zigzag cracking path can depress the fatigue crack growth or not. Specifically, when the difference in the strength between the second phase and the matrix is greater than a certain value, the zigzag cracking path leads to the acceleration of fatigue crack growth. The consequences show that not all the zigzag crack propagation paths are beneficial for the higher fatigue cracking resistance, and the specific analysis should be combined with the material microstructure in detail.