The application of new forming processes as the high temperature hot forging in closed dies in an industrial environment still requires further investigation due to the lack of flow stress data at these temperatures. To determine the flow behavior of the 42CrMo4 steel at high temperatures hot compression tests have been carried out in a Gleeble® 3800 thermomechanical tester for a temperature range that covers the material behavior from the hot forging until the Nil Ductility Temperature (1250 °C-1375 °C) and for three different orders of magnitudes for the strain rates (0.1 s⁻¹, 1 s⁻¹ and 10 s⁻¹). Then, the Hansel-Spittel model, widely used in automotive commercial software as FORGE®, has been employed to obtain the adequate constants of the constitutive equation for high temperatures.

Low alloyed martensitic resistant steels could become a solution for material saving and components lightweighting in the industrial activity due to the combination of high strength and good weldability and toughness characteristics. However, it is known that martensitic resistant steels are susceptible to temper embrittlement (TE), which can cause undesirable brittle fracture during service of components. In this investigation the influence of the cooling rate after a high temperature tempering (650 ºC) on TE of a low alloyed martensitic Mn-Cr-Ni steel was studied. Charpy impact tests and metallurgical analysis using emission Scanning Electron and Transmission Electron Microscopy were carried out on specimens cooled in different cooling media after the tempering to stablish a relation between the microstructures and the TE. Obtained results shown a considerable influence of the tempering-carbides location at grain boundaries at low post-tempering cooling rates on the TE of the selected steel.