What are the methods for heat treatment of wheel forgings?

What are the methods for heat treatment of wheel forgings?

Wheel forgings often adopt the following heat treatment methods depending on the steel type and process requirements: annealing, normalizing, quenching and tempering, quenching and low-temperature tempering, quenching and aging, etc. Next, let's take a look at exactly how it is.

Annealing: There are various forms of annealing processes for forgings, such as full annealing, spheroidizing annealing, low-temperature annealing, and isothermal annealing. The selection should be based on the material and deformation of the forging.

After the wheel forgings undergo annealing treatment, the recrystallization refines the grains, eliminates or reduces the residual stress, thereby lowering the hardness of the wheel forgings, enhancing their plasticity and toughness, and improving their machinability.

Normalizing: Normalizing usually involves heating the forging to 50-70℃ above the GSE line, and for some high alloy steel forgings, it is heated to 100-150℃ above the GSE line. After appropriate holding, it is cooled in the air. If the hardness of the forging is relatively high after normalizing, in order to reduce the hardness of the forging, high-temperature tempering should also be carried out. Generally, the tempering temperature is 560-660℃.

Quenching and tempering: Quenching is carried out to obtain an unbalanced structure, thereby enhancing strength and hardness. Heat the steel forgings to 30-50℃ above the Ac1 line. Cool rapidly after being kept warm.

Tempering is carried out to eliminate quenching stress and obtain a relatively stable structure. The forging is heated to a certain temperature below the Ac1 line, held for a period of time, and then air-cooled or rapidly cooled.

Quenching and aging: Superalloys and alloys that can be strengthened through heat treatment often undergo quenching and aging treatment after forging. Quenching involves heating the alloy to an appropriate temperature, holding it at that temperature for a long time, allowing certain structural products in the alloy to dissolve into the matrix to form a uniform solid solution, and then rapidly cooling it to become a supersaturated solid solution. Therefore, it is also called solution treatment. The aim is to improve the plasticity and toughness of the alloy and prepare the microstructure for further aging treatment. Aging treatment involves placing the supersaturated solid solution or the alloy that has undergone cold working deformation at room temperature or heating it to a certain temperature and holding it for a period of time, so that the substances previously dissolved in the matrix precipitate uniformly and diffusely. The purpose of aging treatment is to enhance the strength and hardness of the alloy.

The heat treatment of forgings is carried out in accordance with certain heat treatment specifications, which are formulated based on the steel type, cross-sectional dimensions and technical requirements of the forgings, and with reference to relevant manuals and materials. Its contents include: heating temperature, holding time and cooling method, etc. It is generally represented by the temperature-time variation curve.