1.The hardness of the forging is too high or too low
The reasons for the excessive hardness of the forging are: the cooling rate is too fast after normalizing; the heating time of normalizing or tempering is too short; the chemical composition of raw materials is not qualified.
The reasons for the low hardness of the forgings are: low quenching temperature or short quenching time; high tempering temperature; the surface decarbonization of forgings is caused by repeated reheating; the chemical components of the raw materials are not qualified.
2. uneven hardness distribution
The reasons for the uneven hardness distribution on the same forgings are as follows: the heat treatment process is reasonable, such as the excessive amount of furnace loading and the insufficient heat preservation time; the position of the forgings in the furnace is not appropriate, for example, some parts of the same forging are close to the heat source, some parts are far away from the heat source, and the local decarbonization on the forgings.
The primary link to ensure the quality of the heat treatment of the forgings is to ensure the uniformity of the temperature of the heat treatment furnace. For most of the low alloy hardened steel, the temperature deviation of austenitizing should be 15 degrees C, but for the nickel base alloy, the heat treatment temperature, especially the aging temperature should be controlled within the range of + 5, and the aging temperature deviation of the titanium alloy should be + 8.5 C.