What is the difference between ASTM A350 LF2 and LF3?
Here’s a concise technical comparison between ASTM A350 LF2 and LF3, two common carbon steel grades for low-temperature forged fittings, flanges, and valves:
1. Chemical Composition (%)
| Element | LF2 (A350) | LF3 (A350) | Key Difference |
|---|---|---|---|
| Carbon (C) | ≤0.30 | ≤0.20 | LF3 has lower C for better weldability |
| Manganese (Mn) | 0.60–1.35 | 0.90–1.35 | LF3 requires higher Mn |
| Nickel (Ni) | Not required | 0.40–1.06 | LF3 adds Ni for low-temp toughness |
| Phosphorus (P) | ≤0.035 | ≤0.035 | Same |
| Sulfur (S) | ≤0.040 | ≤0.040 | Same |
Note: LF3’s Ni content is critical for sub-zero performance.
2. Mechanical Properties
| Property | LF2 | LF3 |
|---|---|---|
| Tensile Strength | 485–655 MPa (70–95 ksi) | 485–655 MPa (70–95 ksi) |
| Yield Strength | ≥250 MPa (≥36 ksi) | ≥250 MPa (≥36 ksi) |
| Impact Toughness | -46°C (-50°F) ≥20 J | -101°C (-150°F) ≥20 J |
| Elongation | ≥22% | ≥22% |
Key Difference:
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LF3 is qualified for colder temperatures (-101°C vs. LF2’s -46°C) due to Ni addition.
3. Applications
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LF2:
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Low-temperature (but not extreme) environments (e.g., -46°C).
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Common in oil/gas pipelines, valves, and flanges for moderate climates.
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LF3:
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Arctic/Cryogenic service (e.g., LNG terminals, polar pipelines).
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Critical for -73°C to -101°C applications where brittle fracture is a risk.
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