Quantitative analysis of precipitation and strengthening mechanisms of V and V-Ti hot-rolled microalloyed steels

In the present work, hot-rolled V and V-Ti microalloyed steels are comparatively investigated by multi-scale characterizations and electrolytically extracted phase analysis, aiming at quantitatively revealing the influence of microalloying elements on microstructure, precipitation behavior and mechanical properties. The results demonstrate that the substitution of trace Ti slightly refines and homogenizes the ferrite grain size (10.8 -> 12.8 mu m), but aggravates the banded structure and decreases the precipitation ratio of V (39 -> 30%). Simultaneously, Ti induces the compound precipitation of V-Ti carbonitrides, which reduces the amount of V in austenite, resulting in substantially reduced precipitation strengthening due to the smaller volume fraction (0.0058 -> 0.0027%), the larger particle size (34.1 -> 65.8 nm) and inter-particle spacing (74 -> 127 nm) of fine nano-precipitates in ferrite. The yield strength predicted by semi-empirical models agrees well with the results of tensile testing, which indicates that microcrystalline Ti substitution for V reduces the yield strength of traditional hot-rolled steel.