Acceleration of final cooling of forgings in isothermal annealing

1. The temperature differential in a charge in final cooling of forgings is determined by the difference in cross sections of the forgings, the point of their location in the furnace, and the allowable specified rates and method of cooling. In the case of location of forgings with thin sections at the charging door in acceleration of the process of final cooling by gradual opening of the door the temperature differential between forgings of different cross sections (1000 and 330 mm) reaches 190°C and between the sections of a stepped forging 100°C. 2. Acceleration of final cooling by supplying air through the burners and partial opening of the door provides more stable cooling of the forgings than gradual opening of the door. As the result of elimination of inflow of cold air the temperature differential between the sections of a stepped forging does not exceed 30–60°C. 3. In acceleration of cooling by gradual opening of the door the maximum temperature differential is observed in the 540–350°C range, that is, for the majority of constructional steels in the area of the elastic-plastic transition, while in supplying air through the burners it is in the area of the plastic or the elastic condition of the metal. 4. In supplying air through the burners the cooling rate of the surfaces of the forgings of the charge does not exceed the specified values if the furnace is cooled at rates allowed by the specification. 5. To accelerate the final cooling process of production charges of forgings the method of supplying air through the burners with partial opening of the furnace door, which provides stable cooling of forgings with a minimum temperature differential in the charge, may be recommended.