Thermo-mechanical treatments play an important role in the processing of many materials and it is now of the greatest importance in obtaining reliable mechanical properties in steels for pipelines, bridges, buildings and many other products.

Depending on the deformation condition (e.g. temperature, strain and strain rate) displacive and reconstructive transformations are influenced by deformation. For example, the plastic deformation of austenite before its transformation retards the growth of martensite, a phenomenon known as mechanical stabilization.

In some solid state welding operations, such as pressure gas welding, forge welding, flash butt welding, friction welding and upset welding, steel parts are subject to high pressures leading to macroscopic deformation of the samples and a subsequent phase transformation under stress and plastic deformation. Thus for these welding processes it is important to construct relevant welding continuous cooling diagrams (WCCT) in which the influence of plastic deformation of austenite is considered.

Grain size is an important factor in determining the strength and toughness of a material. In steels austenite grain size is a microstructural parameter that must be carefully controlled during hot working operations (and heat treatment, including those in the heat affected zone (HAZ) of welds. The austenite grain size resulting from these thermal or thermo-mechanical processes provides the initial condition for the subsequent phase transformation during cooling and thus affects the final microstructure and resulting mechanical properties. For example, increasing the austenite grain size shifts the CCT diagram to longer times, thereby increasing the hardenability of steel. The addition of small amounts of grain refining elements such as Nb, Ti, V or Al can be used to form fine precipitates to control austenite grain growth during welding or heat treatment. During processing of steels, coarsening or dissolution of theses precipitates play an important role in the austenite grain size.

Austenite grain growth kinetics in a microalloyed steel grade has been studied using laser ultrasonic technique as the grain size measurement tool. Based on the experimentally measured limiting grain sizes at various reheat temperatures an approach has been proposed to evaluate the initial precipitate distribution in the as received material. To simulate the austenite grain growth behaviour a grain growth model is coupled with the thermo-kinetic software MatCalc , which enables integration of the precipitate kinetics with the grain growth model in a generalized way.