Three-dimensional characterization of low-cycle fatigue crack morphology in TRIP-maraging steel: Crack closure, geometrical uncertainty and wear

Low-cycle fatigue resistance of laminated transformation-induced plasticity (TRIP)-maraging steels is excellent due to roughness-induced crack closure (RICC). An increase in annealing time at 873 K simultaneously enhances retained austenite fraction and reduces hardness, but no difference in fracture surface roughness between the steels annealed for 1 h (1 h-steel) and 8 h (8 h-steel). Using three-dimensional characterization to investigate fatigue sub-cracks and roughness, RICC on specimen surface was observed in 8 h-steel, instead of 1 h-steel. However, due to hardness-dependent wear resistance, interior crack morphology in 1 h-steel presented remarkable asymmetric surfaces, sub-μm-scale roughness and RICC, compared to 8 h-steel.