Seznam abstraktů 2025: SEKCE B - TVÁŘENÍ KOVŮ

With rising energy costs, efficient and accurate heating of the charge to rolling temperature is critical to reducing operating costs and improving the quality of the finished product. The surface temperature of the charge obtained from non-contact measurements after exiting the furnace does not provide information about the internal temperature of the charge, nor does it reveal the temperature profile prior to exiting the furnace. As a result, charge overheating, low internal temperature, or insufficient soaking time at target temperature may go undetected. This paper presents a methodology that includes operational temperature measurements inside steel billets during heating in industrial furnaces and subsequent numerical calculation of the heat transfer coefficient. The operational measurements were carried out using thermocouples placed inside the billet, which allowed precise monitoring of the temperature profile throughout the heating process. The data showed that the furnace design significantly affects the thermal homogeneity of the charge. In a rotary hearth furnace, a significant influence of the furnace bottom on the thermal homogeneity of the charge was observed, especially when the billet was in full contact with the bottom. To better understand these phenomena, a numerical inverse calculation was performed to determine the heat transfer coefficient as a function of position and temperature within the furnace. This coefficient is critical for accurate numerical modelling of the heating process without the need for complex combustion flow and radiative exchange calculations. Knowledge of the heat transfer coefficient allows process optimization, minimization of energy consumption, and improvement of final product quality. The results presented provide valuable insights for industrial practice and demonstrate possible approaches to improve heating efficiency.

Proper design of long-term and complex forming processes, such as multi-stage hot forging of steel products, requires consideration of a number of factors. This applies in particular to forgings of small masses, from a few to several dozen kilograms, which quickly lose ductility due to heat transfer to the environment and tools. During forging on hydraulic presses, the process cannot be significantly accelerated, therefore, if the final shape of the forging requires many individual deformations, the temperature of the forged charge significantly decreases. This causes, among other things, the need for inter-operational reheating, during which the temperature is raised to the upper limit. As a result, the process is carried out in a wide temperature range and cannot be maintained in the most favourable range. The selection of appropriate parameters and process conditions must therefore take into account the different plasticity of the material. For the above reasons, when developing subsequent stages of forging, it is necessary to take into account not only the relationships between the thermo-mechanical parameters of the process and the microstructure created in the assumed deformation conditions, but also to design the forging strategy in such a way as to avoid product defects, such as near-surface clamping, distortions or cracks. Among other factors, it is necessary to take into account such factors as the selection of appropriate anvil shapes, the strategy for conducting inter-operational reheating, appropriate values of relative feed or revolutions, and other factors. This approach allows for the production of correct forgings, free from defects. Numerical modelling can be used to implement this approach. Having developed data on the material intended for forging, such as flow curves, thermal parameters or relationships between thermo-mechanical process parameters and the state of the microstructure after deformation, it is possible to numerically develop a correct technological chain, which should then be, of course, verified.
Selected research results are presented, the aim of which was to develop parameters and other conditions of the multi-stage hot forming process of forgings made of 80MnSi8-6 steel. To achieve this goal, numerical modelling of the finite element method (FEM) was used, conducted using a database of material and process developed based on our own research. FEM analysis was carried out in multi-stage sequences, using the capabilities of the QForm UK program. Modelling results were verified based on forging tests in laboratory conditions, conducted using numerically designed sets of anvils.

Acknowledgement: This study was funded by the National Science Centre, Poland under ”M-ERA.NET 2 Call 2020”, Grant No. 2020/02/Y/ST8/00107.