Experimental investigation of hot-work tool steels performances under the creep-fatigue regime

In the present research, an innovative testing method, specifically developed to characterize the tool steels under creep-fatigue conditions, was carried out on a TQ1 (X36CrMoV5-2) hot-work tool steel in cooperation with Constellium R&D center. The experimental campaign consisted of different testing conditions, and most of the specimens were nitrided to account for the specific surface state of the tools. Tests were performed on a 100 kN MTS fatigue machine equipped with a heating furnace. A creep-fatigue loading type was applied to the specimens, i.e., a cyclic load with a dwell time, in order to properly reproduce the conditions acting on extrusion tools and dies. Under a constant temperature of 520 °C, the effects of four different load levels and two different values of dwell times were evaluated. In addition, selected test conditions were replicated with specimens not nitrided with the aim to evaluate and quantify the influence of the superficial treatment. Final results were presented in terms of fatigue diagram of the TQ1 steel and compared to the performances of the H11 tool steel tested in a previous research by the same authors.