Fatigue crack growth behavior of a type of novel advanced high-strength steel in a FeCrNiBSi alloy system: A comparison between heat-treated cast and hot-rolled specimens

The fatigue crack growth (FCG) behavior of a type of novel advanced high-strength steel in a FeCrNiBSi alloy system was investigated at room temperature. Two heat-treated cast and hot-rolled specimens were used to compare their FCG rate results obtained at a load ratio of 0.2 and at a frequency of 5 Hz. FCG paths and fracture surfaces of the specimens in the Paris regime, as well as unstable fracture surfaces, were observed by field emission gun scanning electron microscopy. The results showed that besides the dimension of matrix grains (austenite), the volume fraction, dimension, and morphology of second hard phases (boride phases) were also main factors in retarding crack propagation in the Paris regime. Fatigue striations and tearing ridges were observed in the fracture surfaces of both heat-treated cast and hot-rolled specimens, while quasi-cleavage facets and secondary cracks were only observed in the heat-treated cast and hot-rolled specimens, respectively. Roughness-induced, crack branching, and plasticity-induced crack closure mechanisms were more effective in retarding crack propagation in the heat-treated hot-rolled specimen than in the heat-treat cast specimen.