Computational Modelling and Experimental Analysis of Hardness and Microstructure of Reinforcing Bars Produced by Tempcore Process

The reinforcing bar (rebar) produced by Tempcore process had tempered martensite structure on its surface, owing to quenching and tempering, and ferrite–pearlite structure at the core owing to slow cooling rate. Bainite, a low-temperature transformation phase, was observed in the transition area. Mechanical properties of the rebar are significantly influenced by area ratio and hardness of the tempered martensite. In this study, microstructure and area ratio of the tempered martensite of the rebar produced by the Tempcore process were predicted using finite volume method and a continuous cooling transformation diagram. The area ratio of the tempered martensite was predicted with error range of ± 6%. Furthermore, association between the microstructure and hardness was determined by a non-isothermal tempering experiment. The hardness of the tempered martensite was successfully predicted using the tempering temperature with R-squared 98%. The proposed methodology can be effectively used to control the mechanical properties of the rebars.