Annealing Time Effects on Mechanically Long Fatigue Crack Growth of TRIP-maraging Steels

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