ASTM A668
Basic Info
ASTM A668 specifies the properties of stainless steel and heat-treated carbon steel forgings used in general industrial applications. This standard ensures the quality, reliability, and performance of forgings used in critical components such as pressure vessels, valves, and machinery parts, where material integrity is crucial for safety and functionality.
Characteristics
Forging Properties: A668 specifies the properties of steel forgings, ensuring they meet stringent requirements for forging processes.
Chemical Composition: The standard outlines limits for carbon, manganese, sulfur, phosphorus, and other elements to achieve desired properties.
Heat Treatment: A668 specifies heat treatment requirements for steel forgings to achieve the desired strength and toughness.
Dimensional Tolerances: A668 provides guidelines for dimensional tolerances to ensure the forgings meet required specifications.
ASTM A668 Data Sheet
Dimensions and Tolerances
Equivalent Steel Grades
Chemical Composition
Mechanical Properties
Fabrication and Welding
Dimensions and Tolerances
Shape
- Description: Round, square, octagonal, rectangular, hexagonal, or other
- Tolerance: N/A
Width
- Description: Maximum: 120 inches (3048 mm)
- Tolerance: N/A
Thickness
- Description: Maximum: 72 inches (1829 mm)
- Tolerance: N/A
Length
- Description: Maximum: 360 inches (9144 mm)
- Tolerance: N/A
Weight
- Description: Maximum: 150,000 lbs (68,039 kg)
- Tolerance: N/A
Straightness Tolerance
- Description: 1/8 inch in 5 feet (3.2 mm in 1524 mm)
- Tolerance: +/- 1/8 inch
Flatness Tolerance
- Description: 1/8 inch in 3 feet (3.2 mm in 914 mm)
- Tolerance: +/- 1/8 inch
Width Tolerance
- Description: N/A
- Tolerance: +/- 1/2 inch (12.7 mm)
Thickness Tolerance
- Description: N/A
- Tolerance: +/- 1/2 inch (12.7 mm)
Property: Length Tolerance
- Description: N/A
- Tolerance: +/- 3/8 inch (9.5 mm)
Equivalent Steel Grades
United States
- Equivalent Steel Grade: ASTM A668
Country: Germany
- Equivalent Steel Grade: DIN 17100 St52-3
United Kingdom
- Equivalent Steel Grade: BS 1501-224 Gr 490
France
- Equivalent Steel Grade: NF A 35-501 E36-2
Chemical Composition
Element | Composition Range (%)
- Carbon (C): 0.20 – 0.35
- Manganese (Mn): 0.70 – 1.50
- Phosphorus (P): 0.035 (Max)
- Sulfur (S): 0.040 (Max)
- Silicon (Si): 0.15 – 0.35
- Nickel (Ni): 0.25 (Max)
- Chromium (Cr): 0.25 (Max)
- Molybdenum (Mo): 0.15 (Max)
- Vanadium (V): 0.08 (Max)
- Copper (Cu): 0.25 (Max)
- Aluminum (Al): 0.05 (Max)
- Nitrogen (N): 0.012 (Max)
- Boron (B): 0.0005 – 0.003 (Range)
- Cobalt (Co): 0.05 (Max)
- Tungsten (W): 0.05 (Max)
- Titanium (Ti): 0.01 (Max)
Mechanical Properties
Tensile Strength: The material has a tensile strength range of 60 to 85 ksi (414 to 586 MPa).
Yield Strength: The minimum yield strength is 36 ksi (248 MPa).
Elongation: The minimum elongation over a 2-inch (50 mm) length is 22%.
Reduction of Area: The material’s reduction of area is at least 35%.
Hardness: The material typically has a maximum hardness of 187 HBW.
Charpy V-notch Impact: At a temperature of -20°F (-29°C), the minimum Charpy V-notch impact energy is 15 ft-lbs (20 J).
Fabrication and Welding
Preheat Temperature: Preheat to 400°F – 600°F (200°C – 315°C) for most grades; higher temperatures may be required for certain alloys and heavier sections.
Interpass Temperature: Maintain within 400°F – 600°F (200°C – 315°C) range during welding.
Post-Weld Heat Treatment (PWHT): Required for heavy sections and certain alloys, typically at 1100°F – 1200°F (590°C – 650°C).
Heat Input: Keep low to prevent excessive grain growth and distortion.
Welding Method: SMAW (Shielded Metal Arc Welding), GTAW (Gas Tungsten Arc Welding), GMAW (Gas Metal Arc Welding).
Filler Metal: Use matching or slightly higher carbon and manganese filler metal for welds.
Joint Preparation: Clean, smooth, and free of contaminants for optimal weld quality.
Welding Positions: All positions, depending on welding process and technique.
Cooling Rate: Slow cooling after welding to prevent cracking.
Post-Weld Inspection: Visual inspection for defects, UT (Ultrasonic Testing) for critical applications.
Machining: Precautions to prevent work hardening and distortion, use appropriate tooling.
Surface Treatment: Shot blasting or grinding to remove surface imperfections, followed by protective coatings if required.
Weld Repair: Follow ASTM A488 guidelines for repair welding, ensure proper preheat and PWHT if required.
Strength, Versatility, Reliability: The Superiority of ASTM A668 Mechanical Properties
Strength, versatility, and reliability are the hallmarks of ASTM A668 materials, making them a top choice for diverse industrial applications. With a minimum yield strength of 36 ksi (248 MPa) and a broad tensile strength range from 60 to 85 ksi (414 to 586 MPa), these materials ensure robust structural integrity, crucial for components under heavy loads and harsh conditions.
The impressive elongation requirement of 22% minimum signifies exceptional formability, allowing for easy shaping and fabrication without compromising strength. Coupled with a minimum reduction of area of 35%, ASTM A668 materials offer the resilience needed for demanding applications, ensuring they can withstand deformation without failure.
Another significant advantage is the Charpy V-notch impact test requirement of 15 ft-lbs (20 J) minimum at -20°F (-29°C). This demonstrates the material’s ability to absorb energy and resist fracture, essential for industries such as construction, oil and gas, and transportation where sudden impacts are common.
