Abstract

In this paper, the strengthening effects of Nb in VN-strengthened rebars have been investigated, to clarify the metallurgical mechanisms behind the metallurgical phenomenon why addition of small amount of Nb can increase the tensile-to-yield ratio. Based on the simulation results, it was found that the addition of small amounts of Nb can increase the pearlite fraction while it does not demonstrate a significant grain refinement effect. The TEM+EDS results show that the addition of small amounts of Nb can promote the precipitation of V(C,N) around 5nm, which can contribute to the precipitation hardening. Based on empirical equations, we calculated the contribution to the yield and tensile strength from different microstructural factors, and it turns out that the Nb-bearing rebars benefits more from the pearlite phase and precipitation hardening in tensile strength than in yield strength. As a result, the tensile to yield ratio, namely, the seismic performance improves by adding small amounts of Nb. The research results provide new insight into the effect of Nb in VN-strengthened high-strength rebars, in particular on the precipitation behavior of nanosized VN precipitates.

Keywords:Nb microalloying; Tensile-to-yield ratio; Precipitation hardening