Network optimisation information.
Thermal fatigue properties reflect the working life of a material before thermal fatigue cracks erupt. Materials with high thermal fatigue resistance have more thermal cycles of thermal fatigue crack sprouting; the rate of mechanical fatigue crack expansion reflects the growth of each stress cycle as the crack expands internally under forging after thermal fatigue crack sprouting, and fracture toughness reflects the resistance of the material during the destabilising expansion of existing cracks. For materials with high fracture toughness, the crack must have a sufficiently high stress intensity factor at the crack tip, i.e. a large crack length. When the stress is constant, fatigue cracking already occurs in dac mould steels. If the fracture toughness of the mould material is high, the crack must extend further before unstable extension occurs.
That is, thermal fatigue resistance determines the life before fatigue crack emergence; while crack expansion rate and fracture toughness determine the sub-critical extension life of automotive die steel after crack emergence. 4cr13 die steel needs to have high thermal fatigue resistance, low crack expansion rate and high fracture toughness in order to obtain long life.
