Strain-Induced Precipitation Kinetics of Vanadium Carbonitride Precipitates with the Cubic Structure in High-Strength Weathering Steels

Abstract

The strain-induced precipitation kinetic model of vanadium carbonitride [V(C, N)] precipitates with the cubic structure in vanadium-nitrogen (V–N) microalloyed high-strength weathering steels was constructed and validated. The V(C, N) precipitates possess an fcc structure with the lattice sites and octahedral interstitial sites (O-sites) being occupied with V atoms, and C and N atoms, respectively. The model is based on the cubic structure for V(C, N) precipitates instead of the spherical one, since recent experimental results clearly demonstrate that the strain-induced precipitation of V(C, N) in austenite is of the cubic structure. The nitrogen content effect on precipitation–temperature–time (PTT) curve pattwerns was also studied. With the nitrogen content, the PTT curve nose temperature increased, and the curves shifted left. When the nitrogen content in steels was dropped, PTT curves of V(C, N) precipitates in austenite acquired an S-shape, since free energy conversion is nonlinear. Additionally, thermodynamic software was employed to calculate the phase equilibrium of V(C, N) precipitates in the new high-strength weathering steels. The N site fraction of N during the V(C, N) precipitation was much larger for steels with high N contents, compared to those with low ones.