Effect of Thermal Exposure on the Charpy Impact Properties of Thermo-Mechanically Treated Reinforcement Steel Bar

The reinforcing bars provide necessary structural support for the buildings made with concrete under normal and demanding conditions. The two most structurally demanding situations in building can arise under seismic activities and fire. This paper deals with the behavior of normal Fe 500D (ASTM 1786) rebars under fire situations. The thermo-mechanically treated (TMT) 12mm rebar samples are heat-treated at different temperatures (150-650 degrees C for 3 h) and are subjected to microstructural, textural characterization, and tensile and Charpy impact testing. Experimental results show that reheating the rebars below 550 degrees C does not cause much deterioration in its properties. However, when the same is heated above 550 degrees C, the temper martensite structure at the rim and mixed ferrite-pearlite-bainite structure at the core region of the rebar is converted into coarse polygonal ferrite grains and carbide particles. These not only reduce the strength, but also significantly increase the impact transition temperature of the TMT rebar. The intensification of detrimental cube and Goss texture with the expense of beneficial gamma-fiber texture and the release of beneficial compressive residual stress upon reheating treatment can also hamper the impact transition behavior of the heat-treated rebar.