Effects of Microalloying Elements on Mechanical Properties of Reinforcing Bars

Abstract

Reinforcing steel bars are an important material for construction. The strength level of rebar has been increased to as high as, for example, 345, 390 and 490 grade. In order to produce high-strength rebar, V microalloying technology has been successfully applied, while Nb application to reinforcing bars has been tried energetically recently. However, exact discussions about the effect of hot-rolling and cooling condition in Nb microalloyed steel on mechanical properties have not been reported exactly.
This paper reports on the experimental results of the effects of reheating temperature and cooling rate after hot-rolling on the microstructure and mechanical properties of 0.25C–0.5Si–1.2Mn steel and 0.25C–0.5Si–1.2Mn–0.05Nb(+0.05V) steel (mass%).
0.05% Nb and 0.05% Nb+0.05% V additions to 0.25C–0.5Si–1.2Mn steel (mass%) led to an effective increase in strength, especially at high reheating temperature. This strengthening is caused by precipitation hardening and grain refinement hardening. Accelerated cooling after hot-rolling to 700°C was effective in increasing strength and yield point elongation.