Annealing time effects on mechanically long fatigue crack growth of TRIP-maraging steels

Compact tension tests for fatigue crack growth were carried out on transformation-induced plasticity (TRIP) maraging steel with two different annealing times (1 h and 8 h). Interestingly, resistance to the long crack growth increased with increasing annealing time at a ΔK ranging from 33 to 50 MPa∙m^1/2, while short crack growth resistance, e.g., crack growth in a smooth specimen, was reported to show an inverse trend. It is also noteworthy that increasing annealing time in TRIP-maraging steel decreases both yield and tensile strengths. Namely, the resistance to the long crack growth showed totally inverse trend to the tensile properties, in terms of annealing time. The major microstructural change by increasing annealing time was retained austenite fraction. Specifically, increasing annealing time increases austenite fraction, which may have assisted TRIP-related phenomena and associated resistance to the long crack growth, e.g. transformation-induced crack closure.