(1) Normal Ball Retraction: Heat the steel workpiece to slightly above Ac1 (usually Ac1 + 20-30°C), hold at temperature, and then cool at a rate of 20-50°C/h to below 500°C, and then air cool after removal from the furnace.
(2) Isothermal Spheroid Annealing: After the same heating temperature as the ordinary spheroid annealing, the furnace is cooled to slightly below the Ar1 temperature for isothermal treatment, followed by air cooling after the isothermal process is completed.
(3) Cyclic ball tempering: It involves alternating heating and cooling above and below Ac1, which is equivalent to multiple isothermal ball temperings.
