Effect of weight per meter of reinforced bar on mechanical properties and microstructure

Reinforced bars (rebars) are Thermo-mechanically treated (TMT) bars hot rolled from steel billets produced from scrap melted in an Electric Arc Furnace (EAF) at a temperature of about 1600 ° (usually 1580°). Weight per meter of a low carbon steel rebar is one aspect which has been neglected by some steel producers during the tensile testing in the rod mill. Determination of weight per metre is explicitly required for a TMT rebar. Any reduction in mass will mean a lowering in capacity of the steel reinforcing bar. A series of "heat" numbers or batches of molten steel from an EAF for the production of steel sample A, (Y10 and Y 12 rebars), were observed at a Steel plant to investigate the effect of weight per meter of reinforced bar on the mechanical properties and microstructure. The rolling speed range was 3m/s to 14 m/s for different "heats". Two other steel samples B and C were sourced from the local market to compare with Sample A. Samples collected from different sources on the local market, however, showed lower values of weight per meter different from the prescribed standards. This did not only affect the ultimate tensile strengths which were higher than normal but also the microstructure which deviated from the standard for this material. Sample A, did not only show a good combination of tensile strength and yield stress of 450MPa and a maximum tensile strength of 650MPa but also a standard pearlite-ferrite microstructure, while sample B and C exhibited excessive high strengths and brittle behaviour and can be prone to failure.