In this study, our aim is to present a compilation about different applications of the Gleeble® thermal–mechanical system concerning material testing, characterization of advanced thermomechanically controlled processes and modeling the multiaxial forging technique. The first topic aims to provide an accurate input dataset for developing an energy-based fatigue model for 15Ch2MFA reactor steel. The process characterization intends to quantify the effect of deformation-stored energy on the start temperature and kinetic of the austenite–ferrite transformation. The modeling topic purposes to predict the evolution of the flow stress and the hardening behavior during processing a mild steel by multiaxial forging. All of these experiments were carried out on a Gleeble® 3800 simulator using different mobile conversion units. The fatigue tests were conducted under uniaxial tension–compression loading with in-phase thermal cycles. To develop a new energy-based low-cycle fatigue (LCF) model, the energy balance of the plastic deformation was also investigated. Moreover, the evolution of the microstructure was observed by transmission electron microscopy (TEM) studies at the different stages of the nominal failure lifetime. The deformation-induced ferrite transformation (DIFT) effect was characterized by a high-resolution dilatometer under uniaxial hot compression tests. An advanced simulation program and experimental setup have been developed for the calculation of reliable flow curve from the data, sampled during the multiaxial forging simulation. Concerning the thermomechanical fatigue tests, the experimental results correspond to the Coffin–Manson curve. Furthermore, temperature evolution measurements were performed to provide input data to the calculation of the plastic strain energy partition converted to heat. Finally, the effect of the deformation stored energy on the start and finish temperature of austenite transformation was obtained and quantified.