1. Shape effect is mainly caused by design factors, such as small fillet R, inappropriate location of acupoints, poor cross-sectional transition.
2. Overheating (overheating) is mainly caused by improper temperature control or running temperature, excessive process setting temperature, uneven furnace temperature and other factors. Preventive measures include overhaul, calibration of temperature control system, correction of process temperature, the addition of pad iron between the workpiece and furnace floor, etc.
3. Decarbonization is mainly caused by overheating (or overburning), unprotected heating of air furnace, small machine surplus, residual decarbonization layer of forging or preparatory heat treatment, etc. The preventive measures are controlled atmosphere heating, salt bath heating, vacuum furnace and box furnace using box-packing protection or oxidation-proof coating; the machining surplus increases by 2-3 mm.
4. Improper cooling, mainly due to improper choice of coolant or supercooling, should master the cooling characteristics of Quenchant or tempering treatment.
5. Poor structure of raw materials, such as serious carbide segregation, poor forging quality, improper preparatory heat treatment, etc. The preventive measures are to adopt correct forging process and reasonable preparatory heat treatment system.