Metal processing conditions include deformation temperature, deformation speed and deformation mode.
Increasing the temperature of metal deformation is an effective measure to improve the forgeability of metal. During the heating process of metal, as the heating temperature rises, the mobility of metal atoms increases, and the attraction between atoms is weakened, which is easy to produce slippage. The plasticity is improved, the deformation resistance is reduced, and the forgeability is significantly improved, so forging is generally carried out at high temperatures.
The heating of metals is an important link in the entire production process, which directly affects productivity, product quality, and the effective use of metals.
The requirements for metal heating are:
Under the condition of uniform heat penetration of the billet, the temperature required for processing can be obtained in a short time, while maintaining the integrity of the metal, and minimizing the consumption of metal and fuel. One of the important contents is to determine the forging temperature range of the metal. That is, reasonable initial forging temperature and final forging temperature. The initial forging temperature is the initial forging temperature. In principle, it should be high, but there must be a limit. If this limit is exceeded, the steel will have heating defects such as oxidation, decarburization, overheating and overburning. The so-called overburning refers to the metal heating temperature. If it is too high, oxygen will penetrate into the metal to oxidize the grain boundaries and form brittle grain boundaries, which are easily broken during forging, so that the initial forging temperature of scrap carbon steel forgings should be about 200°C lower than the solidus.
The final forging temperature is the stop forging temperature. In principle, it should be low, but not too low, otherwise the metal will undergo work hardening, which will significantly reduce its plasticity and increase its strength. The forging is laborious. It is difficult for high-carbon steel and high-carbon alloy tool steel. In terms of even cracking.
Deformation speed level The degree of deformation per unit time. The effect of deformation speed on the forgeability of metal is contradictory. On the one hand, as the deformation speed increases, recovery and recrystallization are too late, and work hardening cannot be overcome in time. Phenomenon, the plasticity of the metal decreases, the deformation resistance increases, and the forgeability deteriorates. On the other hand, during the metal deformation process, part of the energy consumed in plastic deformation is converted into heat energy, which is equivalent to heating the metal to increase the plasticity of the metal. , Deformation resistance decreases and forgeability becomes better The greater the deformation speed, the more obvious the thermal effect.
The deformation methods are different, and the internal stress state of the deformed metal is different. For example, the state of three-way compression during extrusion deformation; the state of two-way compression and one-way tension during drawing; the stress state of the central part of the blank when the pier is thick Compressive stress, the upper and lower peripheral part and radial direction are compressive stress, and the tangential direction is tensile stress.
Practice has proved that among the stresses in the three directions, the more the number of compressive stresses, the better the plasticity of the metal; the more the number of tensile stresses, the worse the plasticity of the metal. The deformation resistance caused by the same stress state is greater than that of the different stress state. Deformation resistance and tensile stress in the state increase the distance between metal atoms, especially when there are defects such as pores and micro-cracks in the metal, under the action of tensile stress, stress concentration is easy to occur at the defect, which causes the crack to expand, and even destroys the scrap. The degree of compressive stress reduces the interatomic distance of the metal, and it is not easy to expand the defect. Therefore, the plasticity of the metal increases, but the compressive stress increases the internal friction resistance of the metal, and the deformation resistance also increases. In summary, the forgeability of metal depends not only on the nature of the metal, but also on the deformation conditions during the press working process. Strive to create the most advantageous deformation strip to give full play to the plasticity of the metal, reduce deformation resistance, minimize energy consumption, and perform deformation to achieve the best processing effect.
Post time: Mar-16-2021