The effect of forging process on improving material strength

　　The forging process changes the internal structure of metals through plastic deformation, significantly improving the strength, toughness, and fatigue life of materials. The following are the specific impact mechanisms, quantitative data, and typical application cases of forging technology on material strength.

　　1、 The core mechanism of forging to enhance strength

　　1. Grain refinement (Hall Petch effect)

　　Principle: During the forging process, metal grains are crushed and rearranged, increasing the number of grain boundaries and hindering dislocation movement.

　　2. Fiber streamline reinforcement

　　Forging characteristics: Metal forms a continuous fibrous structure (streamline) along the deformation direction.

　　Advantages:

　　The tensile strength along the streamline direction increases by 20-30% (such as forged steel connecting rods being 25% higher than cast steel).

　　Anisotropy reduction (50% reduction in lateral performance loss).

　　3. Defect elimination (porosity, shrinkage)

　　Casting vs Forging:

　　Defect types, common problems in castings, improvement effects on forgings

　　Pore volume accounts for 1-3% and is completely eliminated (resulting in increased density)

　　Shrinkage and local strength decrease by 30-50%, with uniform tissue (no weak areas)

　　2、 Comparison of strength improvement of typical materials

　　Material casting state strength (MPa), strength after forging (MPa) improvement range, application scenarios

　　AISI 4140 steel 650 (as cast) 850-1000 (as forged)+30-50% aviation landing gear

　　Ti-6Al-4V 830 (as cast) 950-1100 (as forged)+15-30% engine blades

　　Aluminum alloy 6061 150 (as cast) 240-290 (as forged)+60-90% aircraft structural components

　　Inconel 718 1100 (as cast) 1400-1600 (as forged)+25-45% turbine disk

　　Note: The data refers to ASTM and AMS standards, and the actual values are affected by process parameters.

　　3、 The differential influence of forging process on strength

　　1. Hot forging vs cold forging

　　Hot forging and cold forging parameters

　　Temperature>Recrystallization temperature Room temperature

　　Grain size 10-50 μ m (coarser) 1-5 μ m (ultrafine)

　　Strength increase by 20-40%, increase by 50-100%

　　Typical case: Large crankshaft, flange quasi tight gear, bolt

　　2. Isothermal forging (aerospace specific)

　　Characteristics: Low temperature and low-speed deformation (titanium alloy: 900 ℃, 0.001-0.01s ⁻¹).

　　Strength effect:

　　Titanium alloy tensile strength increased by 15% (compared to conventional hot forging).

　　Anisotropy is almost eliminated (transverse/longitudinal strength difference<5%).

　　4、 Practical application cases

　　1. Aircraft engine turbine disc (Inconel 718)

　　Process: Radial forging+isothermal precision forging

　　Result:

　　Room temperature tensile strength: 1600MPa (as cast only 1100MPa)

　　High temperature strength at 650 ℃: ↑ 40% (creep life extended by 3 times)

　　2. Automotive connecting rod (42CrMo steel)

　　Process: Hot forging+temperature controlled cooling

　　Effect:

　　Fatigue increased significantly from 300MPa to 500MPa (↑ 67%)

　　Weight reduction of 20% (through topology optimized forging design)

　　3. Aluminum alloy wheels (A356)

　　Process: Liquid forging (squeeze casting)

　　Advantages:

　　Tensile strength 290MPa (traditional casting only 180MPa)

　　Pore porosity<0.1% (usually 2-5% for castings)

　　5、 The strength of forging process is very challenging

　　1. The theory is very strong

　　Fine grain strengthening is very effective: when the grain size is ≥ 0.1 μ m, the Hall Petch effect fails.

　　Material limitations: Ultra high strength steel (such as 300M) can reach 2000MPa after forging, but requires heat treatment.

　　2. Current technological bottlenecks

　　Uniformity of large-sized parts: Grain coarsening (strength reduction of 10-15%) in forgings with a diameter greater than 1m.

　　High alloy hard to deform materials, such as TiAl intermetallic compounds, require superplasticity forging (which is costly).

　　6、 Future Development Direction of High Strength Forging

　　Nano structure forging:

　　Obtaining nanocrystals (<100nm) through severe plastic deformation (such as ECAP process) results in a 200% increase in strength.

　　Composite forging:

　　3D printing prefabricated porous billet+forging densification (titanium alloy strength increased by 30%, weight reduced by 15%).

　　Intelligent shape control:

　　Forging parameter optimization based on big data (real-time adjustment of temperature/strain rate).

　　Summary: The logic of strength improvement in forging technology

　　Grain refinement → Dislocation resistance ↑ → Yield strength ↑

　　Streamline optimization → Load transfer efficiency ↑ → Tensile strength ↑

　　Defect elimination → stress concentration ↓ → fatigue strength ↑

　　By selecting appropriate forging processes (hot forging/cold forging/isothermal forging), material strength can be increased by 30-100%, becoming a "performance multiplier" for equipment manufacturing!