APPLICATION OF MATHEMATICAL-MODELING TO HOT-ROLLING AND CONTROLLED COOLING OF WIRE RODS AND BARS

A set of integrated mathematical models for simulating hot rolling and controlled cooling of wire rods and bars has been developed through extensive laboratory research work and validation against carefully monitored results from industrial mills. Experimental tests have been carried out on C-Mn and eutectoid steels selected as representative of the various applications of wire rods and bars. Static and dynamic recrystallization of austenite, fraction of transformed austenite, final microstructures and mechanical properties are all calculated by modelling physical phenomena and using quantitative relationships between the microstructural and kinetic parameters and the process variables, i.e. strain, strain rate, temperature and time. The models have been applied to predict the microstructure evolution during hot rolling and to investigate the effect of working conditions and recrystallization mechanisms on the formation of heterogeneous austenitic microstructures. The effects of the cooling pattern on the temperature profile and the austenite phase transformation have also been studied to prevent: coarse pearlite and martensite formation at the centre of wire rods which have cores enriched in C and Mn; surface hardening of bars when water tube cooling systems are used to control the temperature at the cooling beds. The models provide an important insight into the process that is beneficial to enhance the quality of long products.