Precipitation Behavior and Microstructural Evolution of Vanadium-Added TRIP-Assisted Annealed Martensitic Steel

The precipitation behavior and microstructural evolution of vanadium-added TRIP-assisted annealed martensitic (TAM) steel are investigated using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe. The results indicate that final microstructure after heat treatment is refined with the addition of vanadium. The yield strength and ultimate tensile strength of the TAM steel increase obviously, while the total elongation slightly decreases with increase of V-content. The product of strength and elongation (PSE) increases from 28.0 to 30.1 GPa% with the increase of V-content. According to the analysis of three-dimensional atom probe, remarkable concentration peak of V occurs within retained austenite and at the interface between retained austenite and BCC phases; additionally, it is concluded that the granular areas are VC precipitates, and V and C atoms distribute along dislocation within retained austenite. The addition of V leads to the increase of the volume fraction of retained austenite and the decrease of the carbon content in retained austenite.