Increasing the yield strength of Niobium micro-alloyed reinforcing bar
Reinforcing bar, which it is commonly abbreviated as rebar, is used in the construction industry to impart tensile strength to concrete structures, which by nature is very brittle. At ArcelorMittal South Africa Newcastle Works, 460 MPa (minimum yield strength) rebar is traditionally produced by using Vanadium as a micro-alloying addition in order for the mild steel to attain the required strength as specified. However, the fluctuating price of Vanadium over the past years necessitated the use of alternative micro-alloying elements. Niobium is currently used successfully instead of Vanadium on the Rod mill, but not on the Bar mill, due to the difference in cooling facilities between these rolling mills. Alternative manufacturing routes and strengthening mechanisms for the cost effective production of rebar containing Niobium on the Bar mill was investigated. It was decided to produce a trial cast containing Niobium as a micro-alloying element with a Chromium addition and subsequently roll it into 10 mm and 12 mm rebar at the Bar mill. The minimum yield strength of 460 MPa was not achieved. The average yield strength was approximately 430 MPa on both these sizes.