Gear forging billet is processed by hot forging die process

The hot forging die is a mold for plastic forming of a high temperature forging in a mold cavity. The hot forging die has a service temperature of about 1000 ° C, which has a long contact time with the forging blank and is subjected to a large pressing force and impact force. Due to the harsh working conditions of the hot forging die, the performance of all aspects is in a limit state. Therefore, it is easy to cause various failure modes. In view of the above reasons, it is necessary to strengthen the heat treatment process improvement of the hot forging die and improve the service life of the hot forging die.

1. Hot forging die failure mode

(1) The combined force of the hot forging die of the hot forging die, such as the compressive stress and the impact force, is broken when the strength limit of the die material is exceeded. The fracture forms include transgranular fracture and intergranular fracture. The transgranular fracture is mainly the cleavage fracture caused by tensile stress. When the toughness of the mold material is poor, there are macroscopic or microscopic surface defects, which cause stress concentration under the action of tangential stress and expand fracture along the crack source. The intergranular fracture is a brittle fracture in which the crack propagates along the crystal interface. Since the inclusions and the second phase are segregated at the grain boundary, the intergranular bonding force is lowered, and the grain boundary is weakened, and the intergranular fracture is likely to occur under the action of an external force. The hot forging die works under the harsh environment of high temperature, high pressure and repeated heating and cooling, and the surface of the mold cavity alternately forms tensile stress and compressive stress. Under the repeated action of thermal stress, beyond the limit of the strength of the mold material, cracks appear on the surface of the mold.

(2) Wear of hot forging die When the structural properties of the die material are not uniform, both the hard phase of the inclusion and the second phase of the material cause wear. Under the action of high temperature and high pressure, the surface of the mold softens, forming deformation, pitting and grooves and causing spalling. The scratched grooves appearing on the surface of the mold are sources of cracks that induce mold fracture.

(3) Deformation of hot forging die The hot forging die is in contact with the high-temperature forging blank for a long time. Under the action of high temperature and high pressure, the yield strength of the die is drastically reduced, and the external force is easy to cause the hot forging die to collapse, upset and invade. The plastic deformation causes the hot forging die to lose its effect.

2. Hot forging die strengthening mechanism

(1) Selection of hot forging die Hot forging die should use high-quality steel such as vacuum smelting steel and electroslag remelting steel. This steel has a high degree of purity, low inclusion content, fine grain, fine carbide particles, and uniform structure and chemical composition.

Hot forging dies must meet the main performance indicators, high hardness and wear resistance, high thermal strength and thermal stability, sufficient plastic deformation resistance and impact fracture resistance, and strong fatigue resistance. Long service life, etc.

In view of the combination of the harsh conditions of the hot forging die service conditions, the size and shape of the forging blank, the accuracy grade and the material, a suitable hot forging die material is selected. Through the best forging method and heat treatment optimization process, the hot forging die has high thermal strength and wear resistance, and high fracture resistance and other excellent comprehensive mechanical properties. According to the process performance test and production practice, the high toughness 3Cr3Mo3W2V and 4Cr5MoSiV1 electroslag remelting steel are used to manufacture hot forging die for gear forging blank, which has high performance and economic benefits.

3Cr3Mo3W2V high-strength toughness electroslag remelting steel is an air-cooled hard-type hot forging die steel with a slightly lower carbon content, less quenching deformation, better hardenability and uniform hardness of the hardened layer. The steel is suitable for hot forging of small and medium gear forgings.

4Cr5MoSiV1 high-strength toughness electroslag remelting steel, which contains high carbon content and alloying elements, and both are strong carbide forming elements, have high phase transition points, and maintain high hardness at high temperatures and Toughness, high temper resistance and thermal crack resistance, suitable for hot forging of larger gear forgings.

For more details, please see the attached content or "Metal Processing (Hot Processing)" No. 19, 2013

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