Which company has good technology for alloy steel and carbon steel forgings?

I. Forging Process and Equipment: Determining the Basic Form and Properties of Forgings
The selection of forging process directly affects the metal flow line, structural uniformity and dimensional accuracy of forgings:
1. Process Type Adaptation
Open Die Forging: Suitable for large, single-piece or small-batch forgings with simple shapes (such as power station rotors and large shafts). It relies on the experience of blacksmiths to control deformation, ensuring metal flow lines are distributed along the stress direction to avoid defects such as folding and cracking.
Impression Die Forging: Suitable for mass production of complex-shaped forgings (such as automotive connecting rods and construction machinery gears). Metal flow is constrained by dies, improving dimensional accuracy and reducing machining allowances. Reasonable die design must consider parting surfaces, draft angles and flash grooves to prevent insufficient filling or stress concentration.
Precision Forging: Using precision dies or isothermal forging technology to achieve near-net-shape forming and reduce subsequent machining costs. It is especially suitable for thin-walled alloy Steel Parts or high-precision components (such as aero-engine blades). Forging temperature, pressure and deformation rate must be controlled to ensure dimensional tolerance within ±0.1 mm.
2. Equipment Advancement
The tonnage and precision of large hydraulic presses (e.g., above 10,000 tons) are core guarantees for producing heavy forgings; their pressure stability directly affects the internal structural density of forgings.
Automatic forging production lines (e.g., robot-assisted loading/unloading, continuous induction heating) improve production consistency and reduce human error.
Isothermal forging equipment completes deformation at a constant temperature, avoiding structural defects in alloy steel caused by temperature fluctuations.
II. Material Control: Ensuring Forging Properties from the Source
The composition purity and uniformity of alloy steel and carbon steel are the technical core:
1. Precise Composition Control
Carbon Steel: Carbon content must be strictly controlled (low carbon steel C ≤ 0.25%, medium carbon steel 0.25%–0.6%, high carbon steel ≥ 0.6%). Harmful elements such as sulfur and phosphorus must be reduced (S ≤ 0.035%, P ≤ 0.035%) to prevent hot brittleness or cold brittleness.
Alloy Steel: Alloy element ratios are adjusted according to application scenarios:
Chromium (Cr) improves wear resistance;
Nickel (Ni) enhances toughness;
Molybdenum (Mo) increases high-temperature strength;
Titanium (Ti) refines grains.
For example, 42CrMo alloy steel is commonly used for high-strength shafts, requiring Cr content of 1.0%–1.5%, Mo content of 0.15%–0.25%, with composition uniformity deviation within ±0.05%.
2. Material Purity
Inclusions (oxides, sulfides) in molten steel are removed through secondary refining (e.g., LF furnace, VD furnace), with inclusion size controlled to ≤5 μm to avoid becoming initiation points of fatigue cracks.
For example, turbine rotor forgings for power stations require non-metallic inclusions to meet Grade 1 in GB/T 10561.
III. Heat Treatment Technology: Optimizing Forging Structure and Properties
Heat treatment is the key step to improve the mechanical properties of forgings:
1. Quenching and Tempering
Quenching + high-temperature tempering is a common process for alloy steel forgings, obtaining uniform tempered sorbite structure with balanced strength and toughness.
For example, after quenching and tempering, construction machinery gear forgings can reach hardness HRC28–32 and impact toughness ≥50 J/cm².
2. Normalizing / Annealing
Carbon steel forgings are often normalized to refine grains and relieve forging stress; annealing reduces hardness for easier subsequent machining.
For example, low-carbon steel forgings have hardness ≤HB187 after annealing, ensuring good machinability.
3. Surface Heat Treatment
For wear-resistant forgings (such as gears and crankshafts), carburizing, nitriding or induction hardening is used to increase surface hardness (HRC58–62) while maintaining core toughness.
Case depth (e.g., carburized layer 0.8–1.2 mm) and uniformity must be controlled to prevent surface cracking.