Impact of Quenching and Partitioning Time on Microstructures, Mechanical and Fatigue Properties of High-Strength Steel

Abstract

The impact of partitioning time on microstructure, tensile properties, and low-cycle fatigue (LCF) behaviour of prepared steel developed through a single-step quenched and partitioning (Q&P) process has been investigated. The strain rate-controlled (± 0.5%) fatigue (LCF) test was conducted until failure. The microstructure is changed from ferrite-pearlite to lath-type martensite, bainite, temper martensite, and retained austenite after Q&P treatment with various partitioning times. EBSD and TEM analysis identified film-type retained austenite in the martensitic microstructure, which was confirmed by XRD analysis. All quenching and partitioning treated samples show similar cyclic softening behaviour. The hardness, strength, and lowcycle fatigue life are improved significantly after quenching and partitioning treatment. The hardness, strength, and fatigue life increase up to 30 min, then decrease further, partitioning for 60 min. The retained austenite (RA) is transformed to strain-induced martensite under cyclic loading, delaying the fatigue crack propagation rate, and improving fatigue properties.