Structural Changes of Die Forgings

Structural changes of die forgings
During the gradual forming process of die forging, the softening process is mainly based on dynamic recovery, and its structure will also change to a certain extent. During the initial stage of forging deformation, a high density of dislocation substructures is formed. These dislocations can be uniformly distributed or can become subgrain boundaries of brittle substructures. It can also be observed in cold deformation, when the softening process is not obvious, this stage of hot deformation can be called the hot work hardening stage.
Then in the second stage of structural change of die forging, polygonal sub-grain boundaries are formed due to the strengthening of the softening process, and the sub-grain boundary region has a higher density of free dislocations. During deformation, the polygonal substructure gradually replaces the hot-worked structure. The polygonal substructure itself is also changing, leading to the formation of near-equiaxed subgrains.
At the end of the die forging structure change, the equiaxed polygonal substructure remains unchanged, corresponding to the rising part of the deformation diagram, and the stress and metal substructure change continuously. During the next stage of thermal deformation, the stress and the resulting polygonal structure do not change.
There are many reaming methods for die forgings, including punch reaming, mandrel reaming and slot reaming. Punch reaming is the use of a small punch to first punch a hole in the blank and then a larger punch through it, which can slightly enlarge the hole and gradually enlarge the hole to the desired size. It is mainly used for reaming holes with a diameter of less than 300 mm.
The mandrel reaming is mainly used in the forging process of annular die forgings. It is necessary to insert the core rod into the hole and support it on the horse frame. During the forging process, the billet is fed while hammering so that the billet is repeatedly forged around the circumference and extends between the mandrel and the upper anvil until the inner diameter reaches the desired size.
The splitting and reaming of die forgings is to first punch out two small holes in the blank, then cut metal between the two holes, and then use a punch to expand the cut and ream to achieve the required size of the forging. This method is suitable for the forging of large-diameter thin-walled forgings or thin-walled forgings with irregular-shaped holes.