The usage of CHT (Continuous Heating Transformations) diagrams for a given steel or equivalent grade, requires knowledge of heating temperature, average heating rate, and the heating time. Definition of these technological parameters are primarily based on the complex relationship system between the geometric, thermal parameters and the heating device. In our research, we mainly focused on those physical key parameters that can mostly influence the heating and transformation rate. These parameters provide realistic, usable data for analysing the process of thermal diffusion and FEA (Finite Element Analysis) tests. During analysis, an easy-to-use function relationship was determined for approaching the heating rate more precisely. This method allows handling the CHT charts easily, within a selected range, regarding weldable mild steels.