The first is the impact of raw materials on the quality of forgings. Good quality of raw materials is a prerequisite for ensuring the quality of forgings. If there are defects in the raw materials, it will affect the forming process of forgings and the final quality of forgings. If the chemical elements of the raw materials exceed the specified range or the content of impurity elements is too high, it will have a greater impact on the forming and quality of the forgings. For example, elements such as S, B, Cu, Sn are prone to form low melting point phases, making the driven inner gear ring forgings prone to hot brittleness.
In order to obtain intrinsic fine-grained steel, the residual aluminum content in the steel needs to be controlled within a certain range. Too little aluminum content will not play a role in controlling the grain size, and it is often easy to make the intrinsic grain size of the forging unqualified; too much aluminum content will easily form wood grain fractures and tear-like fractures under the condition of forming fiber tissue during pressure processing. For example, in austenitic stainless steel, the more n, Si, Al, and Mo content, the more ferrite phases there are, the easier it is to form band cracks during forging, and make the parts magnetic.
If there are defects such as shrinkage tube residue, subcutaneous blistering, severe carbide segregation, and coarse non-metallic inclusions (slag inclusions) in the raw materials, it is easy to cause cracks in the forgings during forging. Defects such as dendrites, severe looseness, non-metallic inclusions, white spots, oxide films, segregation bands, and foreign metal mixing in the raw materials are easy to cause the performance of forgings to deteriorate. Surface cracks, folds, scars, and coarse crystal rings in the raw materials are easy to cause surface cracks in forgings.
Then there is the impact of the forging process on the quality of forgings. The forging process generally consists of the following procedures, namely, blanking, heating, forming, cooling after forging, pickling, and heat treatment after forging. If the process is improper during the forging process, a series of forging defects may occur. The heating process of the forging plant includes charging temperature, heating temperature, heating speed, insulation time, furnace gas composition, etc. If the heating is improper, such as the heating temperature is too high and the heating time is too long, it will cause defects such as decarburization, overheating, and overburning.
For billets with large cross-sectional dimensions, poor thermal conductivity, and low plasticity, if the heating speed is too fast and the holding time is too short, the temperature distribution is often uneven, causing thermal stress and cracking of the billet.
The forging forming process includes deformation mode, deformation degree, deformation temperature, deformation speed, stress state, tool and die conditions, and lubrication conditions. If the forming process is improper, it may cause coarse grains, uneven grains, various cracks, folding, permeation, eddy currents, and residual cast structures. During the cooling process after forging, if the process is improper, it may cause cooling cracks, white spots, and network carbides.