Preliminary investigation on creep-fatigue regime in extrusion dies

Aim of this work was to investigate the effect of process parameters on the creepfatigue behaviour of a hot-work tool steel for aluminium extrusion die. To this aim, a technological test in which the specimen geometry resembled the mandrel of a hollow extrusion die was developed. Tests were performed on a Gleeble thermomechanical simulator by heating up the specimen using joule’s effect and by applying cyclic loading up to 6.30 h or till specimen failure. During the tests performed at 380°C, 490°C, 540°C and 580°C and under the average stresses of 400, 600 and 800 MPa the displacements of the mandrel were determined. A dwell time of 3 min was introduced in the fatigue cycle to simulate the time required to extrude a single billet and to understand the creep behaviour. The results proved the capability of the test to physically simulate the loading conditions acting on hollow dies during extrusion and revealed the main mechanisms of creep-fatigue interaction.