Characterisation of Hardened Thermo-Mechanical Treated Reinforcement Bars

Abstract

Thermo-mechanically treated (TMT) reinforcement bars (rebars) are key materials in the construction industry by virtue of their high strength, high ductility and a host of other properties such as bendability and weldability. Characterisation of the TMT rebar is one fundamental requirement used to evaluate typical features, which include and not limited to the hardness and the uniformity of the martensite rim. Extensive and excellent work by other co-workers have so far been conducted on the characterisation of rebars. This study, however, aims at taking the efforts made by other co-workers further. Therefore, macrostructural analysis was conducted on the low carbon steel rebars in transverse and longitudinal sections respectively. The results indicate that, the uniformity of the hardened case of martensite for these rebars was within the 20–30% threshold with the average area of martensite $(A_{M} )$ being 29%. Interestingly, Pearlite colonies, comprising ferrite lamellae and cementite were revealed in the microstructure. It was observed that, the two phases were aligned alternately and parallel to each other. This alignment is due to their common growth direction during the transformation of pearlite. In addition, quantitative analysis by scanning electron microscope (SEM) revealed annealing and mechanical twins, the latter of which is symbolic of the material deforming at extremely high strain rates especially during hot rolling. The properties obtained in mechanical twining are remarkable and worthy reporting about.