Technical Requirements for Forging Raw Materials

To ensure the reliability and longevity of forged parts, selecting high-quality raw materials is essential. Effective quality control of raw materials spans their production, processing, technical specification, and final application. In high-demand industries such as aerospace, the technical requirements for forging materials are particularly stringent, covering aspects like chemical composition, mechanical properties, microstructure, and process capabilities to meet challenging operational environments and functional needs.

Principles of Material Selection

The choice of materials for forgings is generally dictated by product design and specified in the part drawings. Selection follows key principles.

1. Mechanical Performance Needs

These include basic indicators like yield strength, tensile strength, ductility, and fracture toughness, which directly affect the strength and stability of the forging.

2. Specific Strength and Stiffness

Particularly important in aerospace, specific strength (strength-to-weight ratio) and specific stiffness (stiffness-to-weight ratio) contribute to material lightness, enhancing structural efficiency.

3. Physical and Process Properties

Beyond basic performance, physical properties like thermal and electrical conductivity and process properties such as forgeability, hardenability, machinability, weldability, and cost must be considered, as they impact manufacturing processes and costs.

Key Quality Control Aspects for Forging Raw Materials

The quality of a forging depends heavily on the selection and handling of raw materials, with main control points including:

1. Chemical Composition

The content of alloying elements, harmful impurities, gases, and residual elements must meet industry standards. Harmful elements, gases, and residual elements should be minimized during production, ensuring uniform distribution of alloying elements to prevent adverse effects on forging performance.

2. Melting Process

Different materials require specific melting techniques. Ultra-high-strength steels, titanium alloys, and superalloys often use vacuum arc remelting to ensure purity and reduce inclusions. Titanium and superalloys typically undergo secondary vacuum remelting, while alloy and stainless steels are often refined using electric arc and electroslag remelting. Aluminum alloys, however, are melted in flame, resistance, or induction furnaces to tightly control impurities and enhance performance through heat treatment.

3. Variety Specifications, Surface Quality, and Dimensional Tolerances

The shape and specifications of raw materials (ingots, bars, billets, flat stock, etc.) must align with production needs, and material should be chosen according to the flow direction. Surface quality must be free from cracks and folds to avoid negatively impacting the surface quality of the forging. Strict dimensional tolerance control is also crucial for the precision of the final forging.

4. Forging Ratio

The forging ratio is a measure of material deformation, typically enhancing internal structure and density. Large aerospace forgings usually require a forging ratio greater than 6–8 to eliminate casting defects, produce uniform fine microstructure, and improve overall forging performance.

Mechanical Properties and Microstructure Requirements

The mechanical properties and microstructure of forging materials are directly tied to the strength, durability, and reliability of the final product. In aerospace and high-precision equipment, forgings must maintain stability under extreme conditions, making strict technical requirements for material properties essential.

1. Mechanical Properties

Material must meet performance requirements under various conditions, covering strength, ductility, impact toughness, hardness, fracture toughness, sustained strength, creep resistance, fatigue performance, and stress corrosion resistance. Larger raw materials may exhibit lower mechanical properties, which should be considered during material selection.

2. High-Magnification Microstructure Requirements

The microstructure in the final heat-treated state significantly impacts forging performance, necessitating specific standards for grain size and purity to avoid abnormal structures (such as excess ferrite in austenitic and martensitic stainless steels or coarse beta grain boundaries in titanium alloys) that degrade material properties and increase rejection rates.

3. Low-Magnification Microstructure Inspection

Low-magnification inspection aims to identify metallurgical defects like shrinkage, porosity, and cracks that could compromise mechanical performance and process compatibility. These defects must be controlled and inspected according to standards.

Supply Condition and Process Performance

The supply condition and process performance of forging raw materials are critical to the quality and processability of the final forging. Appropriate supply conditions and excellent process performance can enhance production efficiency, reduce defects, and increase yield.

1. Supply Condition

Before production, raw materials should be in a specified state, including any required pre-heat treatment, surface peeling, or specific roughness. An optimal supply condition significantly improves subsequent forging processability and quality.

2. Process Performance

Process performance indicators such as forgeability, hardenability, machinability, and weldability directly affect forging difficulty and quality. Forgeability, assessed by plasticity and deformation resistance, is typically measured by hot upset tests. Hardenability, machinability, and weldability influence further processing and should be outlined in technical standards.

Conclusion

The technical requirements for forging raw materials play a decisive role in the quality and lifespan of the final product. Rigorous control over chemical composition, microstructure, mechanical properties, surface quality, and process performance ensures compliance with standards and design specifications. In aerospace, the quality of raw materials directly impacts the reliability and safety of forgings. Through standardized technical requirements and advanced manufacturing processes, forged products can achieve the high quality and performance needed to support the development of demanding industries.