When specifying forged carbon steel flanges and piping components under ASME B16.5 and ASME B31.3, two primary material grades dominate industrial requisitions: ASTM A105 and ASTM A350 LF2. While both are forged carbon steels with comparable tensile strengths at room temperature, their behavior in sub-zero ambient environments and low-temperature process conditions is fundamentally different.
Standard carbon steel undergoes a ductile-to-brittle transition when chilled. At temperatures below its transition threshold, steel can shatter catastrophically without prior plastic deformation under sudden pressure surges or mechanical impact.
To achieve superior sub-zero impact toughness, A350 LF2 features tighter chemical limits, particularly for carbon content, carbon equivalent (CE), and deoxidation practice:
| Element | ASTM A105 (Standard) | ASTM A350 Grade LF2 Class 1 |
|---|---|---|
| Carbon (C) | 0.35 max | 0.30 max (Lower carbon improves toughness) |
| Manganese (Mn) | 0.60 – 1.05 | 0.60 – 1.35 |
| Phosphorus (P) / Sulfur (S) | 0.035 / 0.040 max | 0.035 / 0.040 max (0.015 max in NACE LF2) |
| Silicon (Si) | 0.10 – 0.35 | 0.15 – 0.30 (Fully killed steel) |
| Nickel (Ni) / Chromium (Cr) | 0.40 max each | 0.40 max Ni / 0.30 max Cr / 0.12 max Mo |
Heat treatment is the key mechanism enabling fine grain size and cryogenic impact performance:
At Remax Forge, our engineering team advises clients to specify ASTM A350 LF2 Class 1 in the following applications:
Projects in Northern US, Canada, Central Asia, and high-altitude facilities where winter temperatures routinely drop below -20°C.
Natural gas expansion lines and pressure letdown stations where rapid gas decompression produces severe local freezing.
Yes. A350 LF2 has mechanical properties equal to or superior to A105 at ambient temperatures. Many oil & gas operators dual-certify or standardize on A350 LF2 Class 1 across their plant piping specs to avoid stocking duplicate warehouse inventory.
Class 1 is standard low-temperature grade with Charpy impact testing at -46°C (-50°F) and minimum yield strength of 250 MPa (36 ksi). Class 2 has higher minimum yield strength (290 MPa / 42 ksi) but is impact tested at a higher temperature (-18°C / 0°F). Class 1 is used in >95% of piping orders.
Remax Forge maintains extensive billet inventory of certified ASTM A105 and ASTM A350 LF2 Cl. 1 steels with complete EN 10204 3.1 MTC documentation and Charpy impact reports.