Manufacturing a qualified large or medium-sized forging is by no means simple "hammering"; it is a complex system engineering project involving materials science, thermodynamics, and precision control.

1. Core Process: "Rebirth" Through High Forging Ratio

Large and medium-sized forgings (especially shafts and cylinders) typically adopt the open die forging process.

Smelting and Ingot Preparation: To obtain a pure matrix, steel for large forgings is usually produced using large-capacity smelting furnaces, combined with technologies such as electroslag remelting and vacuum degassing, to reduce harmful impurities and gases to extremely low levels.

High Forging Ratio Deformation: The classic process of "upsetting - drawing out - finishing" is adopted, with strict control over the forging ratio (typically ≥ 3.5). Through tens of thousands of powerful hammer blows, the coarse cast structure is broken up, internal porosity and gas holes are closed, and the metal fiber flow lines are continuously distributed along the direction of stress, thereby significantly enhancing torsional and bending resistance.

Precision Ring Rolling: For ring-shaped forgings (such as flanges and bearing races), large CNC radial-axial ring rolling machines are used. Through multiple passes of gradual expansion, the roundness error of the ring is minimized, achieving dimensional accuracy of IT8 grade or higher.

2. Heat Treatment and Stress Relief

Due to the enormous size of large forgings, there is a significant difference in cooling rates between the interior and exterior, making them highly susceptible to residual stress and non-uniform microstructure.

Slow Cooling After Forging: After forming, forgings cannot be air-cooled directly. They must undergo furnace cooling or pit cooling to prevent micro-cracks and deformation caused by temperature differences between the interior and exterior.

Quenching and Tempering: Through quenching and high-temperature tempering, forging stresses are eliminated, grains are refined, and a uniform tempered sorbite structure is obtained, imparting excellent comprehensive mechanical properties to the forging.

3. Non-Destructive Testing

Finally, large-scale ultrasonic testing, magnetic particle inspection, and other methods must be employed to ensure there are no tiny inclusions, cracks, or white spots inside the forging, achieving "absolute reliability."