Investigation of thermo-mechanical fatigue on a hot forging die steel using a new simulative test

Service life of hot forging dies is affected by different damage mechanisms such as wear, plastic deformation and thermo-mechanical fatigue (TMF): the last one consists on crack initiation at the die surface and its propagation. Neglecting experience and general guidelines, engineers involved in the design of hot forging processes are not so confident with prediction of tool service life. At the present, estimation of die life can not be achieved neither by experimental tools, nor by simulation software. To this aim a new laboratory test has been developed being able to reproduce on specimen thermo-mechanical conditions derived from industrial cases. Description of the test equipment and the relevant procedure is detailed in the first part of the work. Then the paper focuses on the experimental investigation on a hot-working steel; effects on specimen life of i) maximum temperature cycle, ii) minimum temperature cycle and iii) stress state are evaluated.