Study on the Microstructure, Properties, and Strengthening Mechanism of V-N Microalloyed High-Strength Anti-Seismic Rebars

The microstructure, precipitates, and mechanical properties of high-strength anti-seismic rebars with varying V-N contents were investigated by using physical and chemical phase analysis, tensile testing, and HRTEM, among others. The results indicate that, as the V-N content increases, both the yield strength and tensile strength of the tested rebars are increased, but the strength–yield (Rm/Rel) ratio decreases significantly. This reduction in the Rm/Rel ratio for 88 V steel, and the Rm/Rel ratio falling below 1.25 for 140 V steel, can be attributed to factors such as the lesser impact of fine grain strengthening on enhancing tensile strength compared to yield strength, and the inability to continuously refine the ferrite grains in high-strength seismic rebars with substantial increases in V-N content. The proportion of large precipitates increases with the V-N content, and the relatively low precipitation rate in V-containing steel implies that the increment in precipitation strengthening is not linearly related to the V-N addition. Moreover, the volume fraction of precipitates in the steel increases with V-N content, leading to a significant reduction in both the total elongation (A) and the elongation at maximum forces (Agt) for V-N microalloyed high-strength anti-seismic rebars.