3. Fatigue failure of the mold
The root cause of mold fatigue failure is stress concentration and cyclic loading. Although the load on the mold is sometimes significantly lower than its yield strength, due to local stress concentration, microcracks are still formed at the stress concentration under low load. While the mold is usually serviced under high strength and low plasticity, when microcracks are formed, the microcracks easily expand under the cyclic load of the mold and eventually cause fatigue fracture.
4. Cold and hot fatigue failure of the mold
For the hot work die, the surface temperature of the mold often rises to the range of 600-900 ° C due to interaction with the hot billet during operation. In order not to lower the strength of the mold, it is necessary to spray a coolant on the mold after the mold release to cool it. This cycle is repeated, the process of the mold surface repeatedly undergoes rapid cooling and rapid heat accumulation, and a considerable cyclic thermal stress is accumulated on the surface of the mold, and the stress is finally released in the form of thermal fatigue, forming a thermal fatigue crack. As for the high temperature oxidation, the corrosion of the coolant and the friction between the mold and the high temperature billet, the process of accelerating the thermal fatigue is accelerated.
5. Failure under the influence of comprehensive factors
Because the actual working conditions of the mold are extremely complicated, a variety of damage forms can often occur on a pair of molds at the same time. Once these damages occur, they may promote each other and eventually accelerate the failure of the mold.