Fracture behavior of a one-step quenching and partitioning steel characterized using uniaxial tension and double edge-notched tension

The fracture behavior was characterized using uniaxial tension and double edge notched tension (DENT) in a one-step quenching and partitioning steel. This steel consisted of lamellar matrix (tempered martensite and bainitic ferrite lath) together with dispersed blocky and film RA/M (retained austenite and/or fresh martensite). Lamellar structure promoted trans-lath fracture; whereas, blocky RA/M island contributed to ductile fracture in uniaxial tension but induced brittle fracture in DENT test because a higher stress triaxiality in the latter enhanced the rate of martensite transformation and in turn boosted early crack nucleation and propagation.