4. Selection of isothermal temperature
The temperature of the isothermal temperature directly affects the hardness of the wheel forgings after isothermal fire. If the isothermal temperature is high, the hardness is low, and if the isothermal temperature is low, the hardness is high. The isothermal temperature is generally 50 ℃ ~ 100 ℃ above the temperature of the wheel forging material. The specific temperature should be determined through experiments according to the material, shape and size of the wheel forging, and adjusted appropriately according to the hardness of the wheel forging after isothermal normalization.
5. Determination of isothermal holding time
In the isothermal normalizing process, pearlite transformation occurs during the isothermal process, so there must be sufficient holding time to ensure that the pearlite transformation is completed. If the isothermal time is too short, the supercooled austenite will not be completely converted into pearlite. It is transformed into bainite during cooling, resulting in high hardness and unqualified microstructure of the wheel forging after isothermal treatment. The isothermal time can be determined initially according to the isothermal transition curve of the material, and adjusted according to the test situation.