Chapter 6 - Microstructure Evolution and Mechanical Properties of the Final Product

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One of the objectives of the hot rolling process is to create steel with small, uniform ferrite grains. The properties required of the product are high strength, good ductility, good weldability, and formability. The process of controlled rolling, in which the process parameters are chosen to suit a particular steel and a particular mill in order to attain those attributes, is the preferred technique followed to attain those attributes. The parameters available are the temperature, the strain and the strain rate per pass, the interstand and the pre-coiler cooling rates. The advantages of using the finite-element method in the microstructure evolution modeling are twofold. The first is a possibility of investigation of local situations in the deformation zone, using conventional closed-form microstructure evolution equations. Solving these equations using temperatures, strain rates and strains, calculated by the finite-element method, allows the prediction of the distribution of the grain size, recrystallization kinetics and other microstructural phenomena in the volume of the deformed body. Variations of the temperature in time can be accounted for using the additivity rule. The second advantage is a possibility of using more advanced phenomenological models to examine the evolution of the microstructure, which are usually based on the internal variable method.