ASTM A350 material is a type of forged carbon steel and low-alloy steel specifically designed for low-temperature service in industrial pressure piping systems. Unlike ASTM A105, which is intended for ambient and high-temperature applications, ASTM A350 covers several “LF” grades engineered for toughness at sub-zero temperatures.
Typical products manufactured from ASTM A350 include:
- High-strength pipe flanges
- Forged fittings
- Valve bodies, bonnets, and pressure parts
- Critical components in low-temperature hydrocarbon and LNG systems
Because of its enhanced low-temperature impact resistance, ASTM A350—especially Grade LF2—is widely used in oil & gas, refining, petrochemical, LNG, cryogenic, and pipeline systems operating down to –46°C (–50°F).
What Is ASTM A350 Material?
ASTM A350 is a forged carbon steel specification established by ASTM (American Society for Testing and Materials). It covers several low-temperature forging grades:
- LF1
- LF2 (most widely used)
- LF3 (nickel-enhanced for lower temperature)
- LF5 / LF6 for specific applications
The specification applies to forgings used in valves, pressure vessels, flanges, fittings, and other pressure-containing parts requiring Charpy V-notch impact toughness at low temperature.
ASTM A350 components are commonly supplied to ASME B16.5, ASME B16.11, and ASME B16.34 dimensional standards.
Chemical Composition
| Element | Composition,wt.% | ||||||
| Grade LF1 | Grade LF2 | Grade LF3 | Grade LF5 | Grade LF6 | Grade LF9 | Grade LF787 | |
| Carbon,max | 0.3 | 0.3 | 0.2 | 0.3 | 0.22 | 0.2 | 0.07 |
| Manganese | 0.60-1.35 | 0.60-1.35 | 0.90 max | 0.60-1.35 | 1.15-1.50 | 0.40-1.06 | 0.40-0.70 |
| Phosphorus, max | 0.035 | 0.035 | 0.035 | 0.035 | 0.025 | 0.035 | 0.025 |
| Sulfur,max | 0.04 | 0.04 | 0.04 | 0.04 | 0.025 | 0.04 | 0.025 |
| Silicon【A】 | 0.15-0.30 | 0.15-0.30 | 0.20-0.35 | 0.20-0.35 | 0.15-0.30 | … | 0.40 max |
| Nickel | 0.40 max【B】 | 0.40 max【B】 | 3.3-3.7 | 1.0-2.0 | 0.40 max【B】 | 1.60-2.24 | 0.70-1.00 |
| Chromium | 0.30 max【B】,【C】 | 0.30 max,【B】,【C】 | 0.30 max【C】 | 0.30 max【C】 | 0.30 max【B】,【C】 | 0.30 max【C】 | 0.60-0.90 |
| Molybdenum | 0.12 max【B】,【C】 | 0.12 max【B】,【C】 | 0.12 max【C】 | 0.12 max【C】 | 0.12 max【B】,【C】 | 0.12 max【C】 | 0.15-0.25 |
| Copper | 0.40 max【B】 | 0.40 max【B】 | 0.40 max | 0.40 max | 0.40 max【B】 | 0.75-1.25 | 1.00-1.30 |
| Niobium【E】 | 0.02 max【D】 | 002 max【D】 | 0.02 max | 0.02 max | 0.02 max | 0.02 max | 0.02 min |
| Vanadium | 0.08 max | 0.08 max | 0.03 max | 0.03 max | 0.04-0.11 | 0.03 max | 0.03 max |
| Nitrogen | ··· | ··· | ··· | ··· | 0.01-0.030 | ··· | ··· |
【A】When vacuum carbon-deoxidation is required by Supplementary Requirement S3,the siicon content shall be 0.12%maximum.
【B】The sum of copper,nickel,chromium,vanadium and molybdenum shall not exceed 1.00%on heat analysis.
【C】The sum of chromium and molybdenum shall not exceed 0.32%on heat analysis.
【D】By agreement,the limit for niobium (columbium)may be increased up to 0.05%on heat analysis and 0.06%on product analysis.
【E】Niobium and columbium are interchangeable names for the same element and both names are acceptable for use in A01.22 specifications.
Mechanical Properties
| TABLE 2 Tensile Properties at Room Temperature【A】 | ||||||||
| Grades | ||||||||
| LF1 and LF5 Class 1 | LF2 Classes 1 and 2 | LF3 Classes 1 and 2 LF5 Class 2 | LF6 | LF9 | LF787 | |||
| Class 1 | Classes 2 and 3 | Class 2 | Class 3 | |||||
| Tensile strength,ksi [MPa] | 60-85 [415-585] | 70-95 [485-655] | 70-95 [485-655] | 66-91 [455-630] | 75-100 [515-690] | 63-88 [435-605] | 65-85 [450-585] | 75-95 [515-655] |
| Yield strength,min,ksi [MPa]【B】 | 30 [205] | 36 [250] | 37.5 [260] | 52 [360] | 60 [415] | 46 [315] | 55 [380] | 65 [450] |
| Elongation: | 25 | 22 | 22 | 22 | 20 | 25 | 20 | 20 |
| Standard round specimen,or small proportional specimen, min% in 4D gauge length | ||||||||
| Strip specimen for wallthickness 5/16 in.[7.94 mm]and over and for all small sizes tested in full section;min % in 2 in. [50 mm] | 28 | 30 | 30 | 30 | 28 | 28 | 28 | 28 |
| Equation for calculating min elongation for strip specimens thinner than 5/16 in.[7.94 mm] min%in 2 in.[50 mm] t=actual thickness in inches | 48t+13 | 48t+15 | 48t+15 | 48t+15 | 48t+13 | 48t+13 | 48t+13 | 48t+13 |
| Reduction of area,min,%【C】 | 38 | 30 | 35 | 40 | 40 | 38 | 45 | 45 |
【A】See 7.3 for hardness tests.
【B】Determined by either the 0.2%offset method or the 0.5%extension under load method.
【C】For round specimens only.
ASTM A350 Charpy Impact Test
| TABLE 3 Charpy V-Notch Energy Requirements for Standard Size [10 by 10 mm]Specimens | ||
| Grade | Minimum Impact Energy Required for Average of Each Set of Three Specimens,ft.Ibf [J] | Minimum Impact Energy Permitted for One Specimen only of a Set,ft · Ibf [J] |
| LF1 and LF9 | 13 [18] | 10 [14] |
| LF2,Class 1 | 15 [20] | 12 [16] |
| LF3,Class 1 | 15 [20] | 12 [16] |
| LF5 Class 1 and 2 | 15 [20] | 12 [16] |
| LF787 Classes 2 and 3 | 15 [20] | 12 [16] |
| LF6,Class 1 | 15[20] | 12 [16] |
| LF2,Class 2 | 20 [27] | 15 [20] |
| LF3,Class 2 | 20 [27] | 15 [20] |
| LF6,Classes 2 and 3 | 20 [27] | 15 [20] |
| TABLE 4 Standard Impact Test Temperature for Standard Size [10 by 10 mm]Specimens | |
| Grade | Test Temperature,F[C] |
| LF1 | -20 [-29] |
| LF2 Class 1 | -50 [-46] |
| LF2 Class 2 | -0 [-18] |
| LF3,Classes 1 and 2 | -150 [-101] |
| LF5,Classes 1 and 2 | -75[-59] |
| LF6,Classes 1 and 2 | -60 [-51] |
| LF6,Class 3 | 0[-18] |
| LF9 | -100 [-73] |
| LF787,Class 2 | -75[-59] |
| LF787 Class 3 | -100 [-73] |
Benefits and Limitations
ASTM A350, especially the LF grades, provides excellent toughness and strength at low temperatures and achieves high reliability through mandatory heat treatments such as normalizing or quench-and-temper, which refine the microstructure. The material also offers good weldability and is well-suited for critical low-temperature applications such as LNG systems, cold hydrocarbons, refining, pipelines, valve bodies, and pressure equipment where impact toughness is essential.
Its limitations include unsuitability for high-temperature service (generally −50°C to +260°C), and the need for mandatory impact testing and heat treatment, which makes it more expensive than ASTM A105. As a carbon steel, its corrosion resistance is limited and may require coatings, linings, or alternative alloys for corrosive environments. Additionally, applications that demand verified low-temperature toughness cannot substitute LF2 with general carbon steels unless equivalent impact-tested certification is provided.
ASTM A350 Equivalent Materials
| Standard | Equivalent Grade | Notes |
| ASME / ASTM | A350 LF2 | Original |
| EN / DIN | P245GH, P250GH, C22.8 (with impact test) | Requires impact-qualified version |
| ISO | C22E +N (impact-tested) | Metallurgically similar |
| JIS | SF490A (impact-tested conditions) | Similar application |
| GB (China) | 16Mn / Q345R (impact-tested) | Requires low-temperature qualification |
| BS | 1503-161-430A/B | Forged carbon steel, impact-tested |
Strict equivalence requires proof of low-temperature impact toughness (Charpy).
Non-impact-tested grades cannot replace LF2.
ASTM A350 LF2 vs ASTM A105
| Item | ASTM A350 LF2 | ASTM A105 |
| Material Type | Low-temperature forged carbon steel | General-purpose forged carbon steel |
| Temperature Range | −46°C → +260°C | −29°C → +425°C |
| Impact Test | Mandatory | Not required |
| Heat Treatment | Normalized or Q&T required | As-forged / Normalized optional |
| Toughness | Excellent at low temperature | Drops sharply below −29°C |
| Typical Use | LNG, cryogenic lines, cold hydrocarbons | Standard piping, refineries, high-temp steam |
| Cost | Higher | Lower |
| NACE Service | Easy to meet hardness requirements | Often exceeds hardness limits unless normalized |
Conclusion
ASTM A350 is a specialized forged carbon steel material designed for low-temperature pressure service, offering excellent impact toughness, stable mechanical properties, and high reliability in sub-zero operating environments.
Among its grades, LF2 is the most widely used due to its balance of strength, ductility, and weldability.
Although ASTM A350 has a higher cost and limited high-temperature capability compared with A105, its performance in cold environments, LNG systems, and critical hydrocarbon applications makes it indispensable in global engineering projects.
When selecting equivalent materials across international standards, EN 10222-2 C22.8 (impact-tested) is the closest match, ensuring compatibility with ASTM A350 requirements.
