Heat treatment of large forgings

Conclusions

• 1. The use of the similarity theory to analyze the quenching process makes it possible to obtain a generalized quenching graph for oil and water that characterizes the temperature field during cooling of forgings (machine parts) of different diameters.

• 2. A method was developed for determining the hardenability by means of superposing the quenching graph on the thermokinetic diagram of the steel. This method makes it possible to determine the hardened zone in forgings of different diameters with given requirements (absence of pearlitic transformation, absence of transformation in the upper bainite range, etc.).

• 3. To obtain high mechanical properties (high strength and low ductile-brittle transition temperature) it is necessary that the cooling time during quenching of large forgings be sufficient to lower the temperature in the center of the forging to 200–300°C.

• 4. To obtain high mechanical properties due to decomposition of austenite in the martensite transformation range and in the lower bainite range it is expedient to quench large forgings with unvarying section in water or through water in oil.

• 5. For parts varying in section (barrels and necks) the best method is water-air or sprayer cooling, permitting separate cooling of the barrel and the neck and thus permitting prolonged cooling of the barrel to the required temperature.