How is forging quality determined

　　The determining factors of forging quality involve multiple links and key technical parameters. The following is a systematic summary:

　　1. Quality of raw materials

　　Chemical composition: The material must comply with standards (such as ASTM, GB, etc.), and the content of impurity elements (such as S, P) must be strictly controlled.

　　Metallurgical defects: To avoid defects such as porosity, inclusions, and segregation, purity can be improved through external refining or vacuum melting.

　　Blank state: Uniform grain structure and appropriate initial size (such as diameter/thickness ratio) are crucial for subsequent forging.

　　2. Forging process parameters

　　Temperature control:

　　Initial forging temperature: Too high can easily lead to overburning, while too low can increase deformation resistance (such as carbon steel, which is usually controlled at 1100-1200 ℃).

　　Final forging temperature: Below the recrystallization temperature will cause work hardening (such as low carbon steel requiring ≥ 800 ℃).

　　Deformation amount:

　　Critical deformation degree: Generally, it needs to exceed 20% to refine the grain, but excessive deformation (>70%) may cause cracks.

　　Forging ratio: Free forgings usually require ≥ 3, while important parts can reach 6-8.

　　Deformation rate: High speed forging (such as hammer forging) is prone to adiabatic heating, and local overheating should be avoided.

　　3. Equipment and molds

　　Equipment type: Hydraulic press is suitable for large slow deformation, forging hammer is suitable for high-energy impact; The equipment tonnage needs to match the workpiece size (such as a 10000 ton press used for aviation forgings).

　　Mold design:

　　Streamlined mold cavity reduces metal flow resistance (such as the division of labor between pre forging die and final forging die).

　　The preheating temperature of the mold (such as preheating the aluminum alloy mold to 200-300 ℃) and lubrication (graphite based lubricant) affect the surface quality.

　　4. Heat treatment and subsequent processing

　　Cooling after forging:

　　High carbon steel requires slow cooling (sand cooling or furnace cooling) to prevent white spots, while austenitic stainless steel can be air-cooled.

　　Heat treatment process:

　　Refine the grain size through normalization, quenching and tempering (e.g. the grain size of 42CrMo after quenching and tempering needs to reach 5-8 levels).

　　Stress relief annealing (such as 600 ℃ × 2h) eliminates residual stress.

　　5. Process control and detection

　　Online monitoring: Infrared thermometer monitors temperature in real-time, and force sensor provides feedback on deformation resistance.

　　Non destructive testing:

　　Ultrasonic testing (detecting internal defects>Φ 2mm).

　　Penetration testing (surface crack detection sensitivity 0.01mm).

　　Destructive testing: Sampling for tensile and impact testing (such as aviation forgings that must meet the requirement of σ b ≥ 900MPa).

　　6. Common defects and countermeasures

　　Folding: Optimize the mold fillet radius (generally R ≥ 5mm) and billet positioning.

　　Crack: Control the final forging temperature (such as titanium alloy final forging ≥ 700 ℃) and deformation uniformity.

　　Coarse grain: uniformly deformed through multiple upsetting pulling processes.

　　Example: Quality control of aviation turbine disk forgings

　　Material: Inconel 718 nickel based alloy.

　　Process: Isothermal forging (mold heated to 950 ℃), deformation of 60%, double aging after forging (720 ℃× 8h → 620 ℃× 8h).

　　Testing: 100% ultrasonic testing+metallographic examination (grain size above ASTM level 6).

　　Summary

　　Forging quality is the comprehensive result of four dimensions: materials, processes, equipment, and testing. It needs to be achieved through standardized operations (such as ISO 9001 system) and digital control (such as finite element simulation) to achieve stable output. The key indicators include the mechanical performance compliance rate, defect detection rate, and size qualification rate.