Metal forging temperature range refers to the temperature range between the start forging temperature (start forging temperature) and the end forging temperature (final forging temperature). The determination principle of forging temperature range of aluminum alloy forgings in forging plants is that they can have higher plasticity and smaller deformation resistance within the forging temperature range, and can enable shaft forgings to obtain the required structure and properties. On this premise, the forging temperature range shall be as wide as possible to reduce forging fire, reduce consumption, improve production efficiency and facilitate operation.
The basic method to determine the forging temperature range of aluminum alloy forgings is to conduct a comprehensive analysis from the three aspects of plasticity, deformation resistance and shaft forging microstructure and properties, determine a reasonable forging temperature range, and verify and modify it in production practice.
Generally speaking, the forging temperature range of forgings is determined only according to the iron carbon phase diagram. For most alloy structure and alloy tool steels, due to their small content of alloy elements, there is no obvious influence on the form of iron carbon phase diagram. The forging temperature range can also be preliminarily determined according to the iron carbon phase diagram. For aluminum alloy, titanium alloy, copper alloy, stainless steel, superalloy and other shaft forgings, various methods are often used to determine the reasonable forging temperature range.
1. Initial forging temperature
If the initial forging temperature is high, the metal plasticity is high, the resistance is small, and the energy consumption during deformation is small, the process with large deformation can be adopted. However, if the heating temperature is too high, it will not only oxidize and seriously decarburize, but also lead to overheating and overheating. When determining the initial forging temperature, it is necessary to ensure that the metal will not overheat and overheat, and sometimes it is limited by the high-temperature precipitation stage. For carbon steel, in order to prevent overheating and overheating, the initial forging temperature is generally 150-250 ℃ lower than the solidus of the iron carbon phase diagram.
The starting forging temperature also needs to be adjusted according to the specific situation. When high speed hammer forging is used, the heat effect temperature rise caused by high speed deformation may cause the billet to overheat. At this time, the starting forging temperature should be about 100 ℃ lower than the normal starting forging temperature.
2. Final forging temperature
The final forging temperature is too high. After the forging is stopped, the internal particles of the shaft forging will continue to grow, with coarse grain structure or precipitation in the second stage to reduce the mechanical properties of the shaft forging. If the final forging temperature is lower than the recrystallization temperature, the internal part of the forging will work hardening, reduce the plasticity, and the deformation resistance will increase sharply. It is easy to crack in the forging process, or a large residual stress will be generated in the billet, which will cause the shaft forging to crack in the cooling process or the subsequent process. In addition, incomplete thermal deformation will also lead to uneven structure of shaft forgings. In order to ensure that the internal structure of the rear axle forging is recrystallized, the final forging temperature is generally 50-100 ℃ higher than the metal recrystallization temperature. The deformation resistance diagram of metal is usually one of the main bases for determining the final forging temperature.