Prediction of hardness of the tempered martensitic rim of TMT rebars

Thermo-mechanically treated or TMT rebars, have a ferrite–pearlite microstructure at the core and a tempered martensitic rim. A property prediction model for rebars is deemed necessary for controlling the rolling parameters in the mill so as to maintain consistent mechanical properties. The strength of the TMT rebars depends on the thickness of the rim as well as on the distribution of various phases inside the wire rod. Prediction of the strength or hardness of the tempered martensitic rim is not very simple, primarily because it undergoes non-isothermal tempering. In this work, a technique for calculating the hardness of the tempered martensitic rim as a function of chemical composition and non isothermal tempering parameters was developed. The agreement between the hardness values calculated in this manner with the actual hardness measured was found to be reasonably good.