Selection of High-Quality Raw Materials for Marine Forgings

Selection of High-Quality Raw Materials for Marine Forgings

When selecting high-quality raw materials for marine forgings, factors such as material properties, environmental adaptability, manufacturing processes, and industry standards need to be taken into account comprehensively. The following are the key steps and points:

1. Clarify the material type and application scenarios

For marine forgings, the material selection should be based on the specific purpose:

Carbon steel (such as A-class and D-class marine steel): Used for ship structural components (such as ribs, deck supports), it must meet high strength and weldability requirements.

Alloy steel (such as Cr-Mo steel, Ni-Cr steel): Used for critical components of engines like crankshafts and gears, it must be resistant to fatigue and impact.

Stainless steel (such as 316L, duplex steel): Used for seawater valves, pump bodies, etc. in corrosive environments, requiring high corrosion resistance.

Titanium alloy: Used in high-end ships or special components (such as parts for submarines), it is corrosion-resistant, lightweight, but has a high cost.

2. Chemical composition control

Compliant with standards: Adhere to classification societies (such as ABS, DNV, LR, CCS) or international standards (ASTM, EN).

Low impurity elements: The content of sulfur (S) and phosphorus (P) should be ≤ 0.025%, to avoid hot brittleness and cold brittleness.

Alloy element optimization: Adding nickel (Ni) enhances low-temperature toughness, chromium (Cr) improves corrosion resistance, and molybdenum (Mo) refines grain structure.

3. Mechanical performance requirements

Strength and toughness: Yield strength (≥ 355 MPa), tensile strength (≥ 490 MPa), and impact energy at low temperatures (-40°C: ≥ 27 J).

Corrosion resistance: Choose steel that is resistant to seawater corrosion (such as steel containing copper (Cu) or nickel (Ni)), or perform surface treatment (such as galvanization).

Anti-fatigue performance: Through the forging process and heat treatment, the grain structure is optimized and internal defects are reduced.

4. Production Process Requirements

Smelting Process: Utilize electric furnaces combined with furnace-outside refining (LF/VD) to reduce the content of gases (H, O, N) and improve purity.

Forging process: Ensure a sufficient forging ratio (≥ 3:1), refine the grain structure; Control the final forging temperature to avoid overheating or underheating.

Heat treatment process: Normalizing, quenching and tempering (quenching + tempering) to ensure uniform structure and eliminate residual stress.

5. Supplier Qualifications and Quality Assurance

Certification qualifications: The supplier must obtain certification from a classification society (such as ABS factory recognition) and possess an ISO 9001 quality management system.

Quality records: Provide documents for material traceability (such as melting furnace number, heat treatment batch) and third-party test reports (such as SGS).

Technical support: The supplier is required to assist in resolving process issues (such as optimizing welding parameters).

6. Inspection and Verification

Incoming Inspection:

Chemical composition analysis (detected by spectrometer).

Mechanical property tests (tensile, impact, hardness).

Non-destructive testing (ultrasonic testing UT, magnetic particle testing MT).

Third-party verification: Key materials must undergo on-site inspection by a classification society (such as CCS), or be re-tested at an authoritative laboratory.