ASTM B446
ASTM B446 Basic Info
ASTM B446 governs the mechanical properties of nickel-chromium-molybdenum-columbium alloys in the form of rod and bar. These alloys, including UNS N06625 and UNS N06690, exhibit high tensile strength, excellent toughness, and superior corrosion resistance. Engineered to withstand harsh environments, they find application in aerospace components, chemical processing equipment, and high-pressure systems where reliability and performance are paramount.
Characteristics of materials specified under ASTM B446:
- High Temperature Resistance: ASTM B446 materials exhibit excellent resistance to high temperatures, making them suitable for use in applications where elevated temperatures are present, such as aerospace components and gas turbine engines.
- Corrosion Resistance: These materials offer outstanding resistance to corrosion and oxidation, making them suitable for use in harsh environments, including chemical processing and marine applications.
- High Strength: ASTM B446 materials are known for their high strength and excellent mechanical properties, allowing them to withstand heavy loads and stress conditions without compromising performance.
- Versatility: ASTM B446 covers a range of nickel-chromium-molybdenum-columbium alloys, providing versatility in applications. This allows for the selection of the most appropriate alloy based on specific requirements, such as temperature resistance, corrosion resistance, and mechanical properties.
ASTM B446 Data Sheet
Steel Grade
Dimensions and Tol.
Standards
Chemical Composition
Mechanical Properties
Manufacturing and Welding
Steel Grade
Alloy 625
Alloy 718
Alloy 725
Alloy 925
Dimensions and Tol.
Round Bars:
Size Range: Diameter from 0.250″ to 14″
Tolerances: Diameter tolerance of +/- 0.010″ to +/- 0.030″
Square Bars:
Size Range: 0.250″ to 8″
Tolerances: Size tolerance of +/- 0.010″ to +/- 0.030″
Hexagonal Bars:
Size Range: Across flats from 0.250″ to 4″
Tolerances: Across flats tolerance of +/- 0.010″ to +/- 0.030″
Flat Bars:
Size Range: Thickness from 0.125″ to 4″
Tolerances: Thickness tolerance of +/- 0.010″ to +/- 0.030″
Wire:
Size Range: Diameter from 0.010″ to 1″
Tolerances: Diameter tolerance of +/- 0.001″ to +/- 0.005″
Standards
United States (USA):
- Equivalent Grades: Alloy 625, Alloy 718, Alloy 725, Alloy 925
- Standard: ASTM B446
European Union (EU):
- Equivalent Grades: 2.4856, 2.4668, 2.4669, 2.4858
- Standard: EN 10095
China:
- Equivalent Grades: GH276, GH4169, GH5188, GH3625
- Standard: GB/T 1234, GB/T 14976
Chemical Composition
Alloy 625:
- Nickel (Ni): 58.0% minimum
- Chromium (Cr): 20.0% – 23.0%
- Molybdenum (Mo): 8.0% – 10.0%
- Columbium (Cb): Not specified
- Iron (Fe): 5.0% maximum
- Carbon (C): 0.10% maximum
- Silicon (Si): 0.50% maximum
- Manganese (Mn): 0.50% maximum
- Sulfur (S): 0.015% maximum
- Phosphorus (P): 0.015% maximum
- Aluminum (Al): Not specified
- Titanium (Ti): Not specified
- Cobalt (Co): Not specified
- Copper (Cu): Not specified
- Tantalum (Ta): Not specified
Alloy 718:
- Nickel (Ni): 50.0% – 55.0%
- Chromium (Cr): 17.0% – 21.0%
- Molybdenum (Mo): 2.8% – 3.3%
- Columbium (Cb): 4.75% – 5.50%
- Iron (Fe): Balance
- Carbon (C): 0.08% maximum
- Silicon (Si): 0.35% maximum
- Manganese (Mn): 0.35% maximum
- Sulfur (S): 0.015% maximum
- Phosphorus (P): 0.015% maximum
- Aluminum (Al): 0.35% maximum
- Titanium (Ti): 0.65% – 1.15%
- Cobalt (Co): Not specified
- Copper (Cu): Not specified
- Tantalum (Ta): Not specified
Alloy 725:
- Nickel (Ni): 54.0% minimum
- Chromium (Cr): 19.0% – 22.5%
- Molybdenum (Mo): 7.0% – 9.5%
- Columbium (Cb): 1.5% – 2.5%
- Iron (Fe): Balance
- Carbon (C): 0.03% maximum
- Silicon (Si): 0.35% maximum
- Manganese (Mn): 1.00% maximum
- Sulfur (S): 0.015% maximum
- Phosphorus (P): 0.015% maximum
- Aluminum (Al): Not specified
- Titanium (Ti): Not specified
- Cobalt (Co): 1.0% maximum
- Copper (Cu): Not specified
- Tantalum (Ta): Not specified
Alloy 925:
- Nickel (Ni): 42.0% – 46.0%
- Chromium (Cr): 19.5% – 22.5%
- Molybdenum (Mo): 2.5% – 3.5%
- Columbium (Cb): Not specified
- Iron (Fe): Balance
- Carbon (C): 0.03% maximum
- Silicon (Si): 0.50% maximum
- Manganese (Mn): 0.50% maximum
- Sulfur (S): 0.03% maximum
- Phosphorus (P): 0.03% maximum
- Aluminum (Al): Not specified
- Titanium (Ti): Not specified
- Cobalt (Co): Not specified
- Copper (Cu): 2.0% – 3.0%
- Tantalum (Ta): 1.5% – 2.5%
Mechanical Properties
Tensile Strength (ksi):
- Alloy 625: 120 min
- Alloy 718: 180 min
- Alloy 725: 150 min
- Alloy 925: 150 min
Tensile Strength (MPa):
- Alloy 625: 827 min
- Alloy 718: 1241 min
- Alloy 725: 1034 min
- Alloy 925: 1034 min
Yield Strength (ksi):
- Alloy 625: 60 min
- Alloy 718: 150 min
- Alloy 725: 105 min
- Alloy 925: 70 min
Yield Strength (MPa):
- Alloy 625: 414 min
- Alloy 718: 1034 min
- Alloy 725: 724 min
- Alloy 925: 483 min
Elongation (%):
- Alloy 625: 30 min
- Alloy 718: 12 min
- Alloy 725: 25 min
- Alloy 925: 30 min
Manufacturing and Welding
Formability:
Nickel-chromium-molybdenum-columbium (Ni-Cr-Mo-Cb) alloys specified under ASTM B446 exhibit good formability, allowing for a variety of fabrication processes such as bending, punching, and cutting.
Machinability:
These alloys generally have good machinability, although tooling and machining parameters may need to be adjusted for optimal results.
Weldability:
Nickel-chromium-molybdenum-columbium (Ni-Cr-Mo-Cb) alloys specified under ASTM B446 are generally weldable using common welding methods such as TIG, MIG, and SMAW.
Preheating and Interpass Temperature:
Preheating and interpass temperature control may be required for thicker sections or specific alloys to minimize the risk of cracking during welding.
Post-Weld Heat Treatment (PWHT):
Some alloys may require post-weld heat treatment to restore mechanical properties and reduce residual stresses, especially for critical applications.
Welding Consumables:
Matching filler metals and electrodes should be used to ensure compatibility and optimize weld quality.
Welding Procedure Qualification (WPQ):
Welding procedures should be qualified through testing to ensure compliance with applicable standards and requirements, especially for critical applications.
Weld Inspection and Quality Assurance:
Welds should be inspected using appropriate non-destructive testing (NDT) methods such as visual inspection, radiography, ultrasonic testing, or dye penetrant testing.
Surface Preparation:
Proper surface preparation, including cleaning and removal of surface contaminants, is essential to ensure sound welds and minimize the risk of defects.
ASTM B446 Welding Procedures
ASTM B446 nickel based alloy welding technology recommendations ensure that the material can achieve optimal mechanical properties after welding.
Pre-Weld Preparation:
Clean the welding area thoroughly to remove any contaminants, such as oil, grease, or dirt, which can adversely affect weld quality.
Ensure proper fit-up and alignment of the welding components to minimize gaps and ensure uniform weld bead formation.
Welding Process Selection:
Tungsten Inert Gas (TIG) welding is commonly used for welding ASTM B446 nickel-based alloys due to its precise control over heat input and excellent weld quality.
Metal Inert Gas (MIG) welding can be used for higher deposition rates and increased productivity, especially for thicker sections, with proper shielding gas selection.
Shielded Metal Arc Welding (SMAW) may be suitable for field welding applications where accessibility is limited, although it may require more extensive preheating measures.
Welding Parameters Adjustment:
Control heat input and welding parameters, including voltage, current, travel speed, and shielding gas flow rate, to minimize the risk of overheating and distortion.
Maintain a consistent arc length and travel speed to ensure uniform penetration and fusion throughout the weld joint.
Post-Weld Heat Treatment (PWHT):
Some ASTM B446 nickel-based alloys may require post-weld heat treatment (PWHT) to relieve residual stresses and enhance mechanical properties, especially for critical applications.
Follow specific PWHT procedures recommended by the material manufacturer to avoid detrimental effects on the microstructure and mechanical properties of the welded joint.
Weld Inspection and Quality Assurance:
Inspect welded joints using non-destructive testing (NDT) methods such as radiography, ultrasonic testing, or dye penetrant testing to detect defects and ensure weld quality.
Perform visual inspection to assess weld appearance, including bead profile, penetration, and surface cleanliness, in accordance with applicable standards and specifications.
