High-temperature behaviour of thermo-mechanically treated and cold-drawn twisted steel bars

This paper presents the results of experimental testing at elevated temperatures of two types of steel rebars locally available in Pakistan. These include cold-drawn twisted (CDT) bars and hot-rolled thermo-mechanically treated (TMT) bars. Two rebar diameters (12 and 16 mm) of both types of bars were included in the testing programme. The bars were heat treated in an electrical furnace at 100−900°C in increments of 100°C. The yield strength of the 12 mm dia. hot-rolled TMT bar was less than the recommended strength of 500 MPa at ambient temperature. The yield phenomenon and strain hardening were not observed in the CDT bars either at ambient or high temperatures. The yield plateau of the hot-rolled TMT bars also disappeared after 300°C of heating. The ultimate strength of the hot-rolled TMT bars up to 300°C was higher than the strength at ambient temperature due to the precipitation of iron nitride in these bars (termed as blue brittleness effects). The reduction coefficients for yield strength and elastic modulus for the investigated bars were similar at all exposure temperatures. The behaviour of bars tested in this study are compared with those reported in the literature and differences in the bar behaviour are discussed.