Hot forging is often used in the production of automotive components. This technology also brings many pitfalls, because due to the high production speed and other physical factors, thermomechanical stresses are produced in the tool steels. The article deals with the issue of the gradual degradation of the fatigue life of the dies as a result of the reduction of the service life of the tool steels from which they are made. In practice, there are several reasons for discarding a damaged die used in hot forging. We could include thermomechanical fatigue and wear among the most important criteria. With this contribution, the authors point to the fact that the effect of gradual cyclic damage due to the presence of thermal fatigue will have little effect on the lifetime of the hot forging die itself. A much more significant phenomenon seems to be the wear of the damaged cavity of the die, which occurs during its operation and which must be repaired several times by milling. On the other hand, mechanical fatigue significantly shortens the service life of hot forging dies, which is confirmed by real operational tests. The article thus deals with the influence of those factors which the authors noticed most influenced the fatigue resistance of the die stressed under heat. The contribution points to the influence of the gradual deterioration of the mechanical properties of the surface layers of the material of the cavity of the hot-forged die.

This research work was supported by the KEGA 002ŽU-4/2023.