Effects of Vanadium Microalloying and Intercritical Annealing on Yield Strength–Ductility Trade-Offs of Medium-Manganese Steels

Abstract

In this paper, we investigate the effects of vanadium on the strength and ductility of medium-manganese steels by analyzing the microstructural evolution and strain hardening rates and performing quantitative calculations. Two significantly different contents of vanadium, 0.05 and 0.5 wt.%, were independently added to model steel (0.12C-10Mn) and annealed at different intercritical temperatures. The results show that higher vanadium addition increases the yield strength but decreases the ductility. The maximum yield strength can increase from 849 MPa to 1063 MPa at low temperatures. The model calculations reveal that this is due to a precipitation strengthening increment of up to 148 MPa and a dislocation strengthening increment of 50 MPa caused by a higher quantity of V4C3 precipitates. However, the high density of vanadium carbides leads them to easily segregate at grain boundaries or phase interfaces, which prevents strain from uniformly distributing throughout the phases. This results in stress concentrations which cause a high strain hardening rate in the early stages of loading and a delayed transformation-induced plasticity (TRIP) effect. Additionally, the precipitates decrease the austenite proportion and its carbon concentrations, rendering the TRIP effect unsustainable. Accordingly, the ductility of high vanadium steels is relatively low.

Microstructural Evolution and Mechanical Properties of V-Containing Medium-Mn Steel Adopting Simple Intercritical Annealing

“…However, Park et al [20] added different contents of Nb, Ti, and V into medium-Mn steel to investigate the effect of micro-alloying and found that the formation of MC carbides increased the strength of the steel, but the TEL decreased due to precipitation hardening. Bi et al [21] also indicated that a higher V addition increased the YS but decreased the ductility, which is caused by a higher quantity of V 4 C 3 precipitates. In fact, the precipitation of carbonitrides also has a considerable impact on the stability of RA.…”