Strengthening Mechanisms of Tempered Martensite in Vanadium-Added Steels

Abstract

To clarify the effects of vanadium additions on the strengthening mechanisms of tempered martensitic steel, the microstructures, precipitates, dislocation densities, and tensile properties of water-quenched and tempered Fe–0.2C–0.5Si–2.5Mn–xV (mass%; x = 0–0.82) steels were analyzed. The vanadium carbide precipitates were plate-shaped and had a Baker–Nutting orientation relationship with the ferrite matrix. The size and shape of the vanadium carbide precipitates on the slip plane were considered when evaluating the contribution of precipitation strengthening. The increase in yield strength upon adding 0.82 mass% vanadium to the tempered steel was mainly caused by precipitation strengthening owing to the vanadium carbide precipitates and dislocation strengthening owing to the high dislocation density. This study demonstrates that the contribution of precipitation strengthening might be overestimated if it is assumed that the precipitates all hinder dislocation motion by the Orowan mechanism.