ASTM · ASTM A350 M / ASME SA350 M
Technical Standard ASTM A350 / ASME SA350: Low-Alloy Steel Forgings for Low-Temperature Systems
Scope of the ASTM/ASME A/SA 350 specification
The ASTM/ASME A/SA 350 specification establishes technical requirements for forged flanges, valves, and fittings manufactured from carbon and low-alloy steel grades. A key feature of these products is their operation in low-temperature conditions, which requires mandatory impact toughness testing (Charpy V-notch). Products supplied by EV Group China comply with dimensional standards ASME B16.5, ASME B16.9, as well as API 600, 602, and 605.
It is important to note that the standard regulates requirements for finished products but does not apply to the metallurgical raw materials (billets) used for their production. There are no technological size limitations, which allows EV Group China to manufacture parts according to customer-specific drawings. Steel grade LF787 (Class 3) is subject to mandatory quenching or specific heat treatment.
All additional product testing requirements must be clearly specified in the order. The specification supports two systems of measurement (inch-pound and SI). In the absence of the "M" index in the designation, the inch-pound values are fundamental. Each system is independent and mixing values is not permitted to avoid deviations from the specification.
Chemical composition of steels according to ASTM A350 / A350M
| Grade | LF1 | LF2 | LF3 | LF5 | LF6 | LF9 | LF787 |
|---|---|---|---|---|---|---|---|
| C max. | 0.30 | 0.30 | 0.20 | 0.30 | 0.22 | 0.20 | 0.07 |
| Mn | 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 |
| P max. | 0.035 | 0.035 | 0.035 | 0.035 | 0.025 | 0.035 | 0.025 |
| S max. | 0.40 | 0.040 | 0.040 | 0.040 | 0.025 | 0.040 | 0.025 |
| Si | 0.15-0.30 | 0.15-0.30 | 0.20-0.35 | 0.20-0.35 | 0.15-0.30 | - | 0.40 max. |
| Ni | 0.40 max. | 0.40 max. | 3.3-3.7 | 1.0-2.0 | 0.40 max. | 1.60-2.24 | 0.70-1.00 |
| Cr max. | 0.30 | 0.30 | 0.30 | 0.30 | 0.30 | 0.30 | 0.60-0.90 |
| Mo max. | 0.12 | 0.12 | 0.12 | 0.12 | 0.12 | 0.12 | 0.15-0.25 |
| Cu max. | 0.40 | 0.40 | 0.40 | 0.40 | 0.40 | 0.75-1.25 | 1.00-1.30 |
| Cb | 0.02 max. | 0.02 max. | 0.02 max. | 0.02 max. | 0.02 max. | 0.02 max. | 0.02 min. |
| V max. | 0.08 | 0.08 | 0.03 | 0.03 | 0.04-0.11 | 0.03 | 0.03 |
| N | - | - | - | - | 0.01-0.030 | - | - |
When meeting S4 requirement (carbon deoxidation), silicon is limited to 0.12%. The total mass fraction of Cu, Ni, Cr, V, and Mo must not exceed 1.00%, and the sum of Cr and Mo must not exceed 0.32%.
Mechanical properties of ASTM A 350 products
| Steel Grade | LF1, LF5 CL 1 | LF2 CL 1, CL 2 | LF3 CL 1, CL 2, LF5 CL 2 | LF6 CL 1 | LF6 CL 2, CL 3 | LF9 | LF787 CL 2 | LF787 CL 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] | 60-85 [450-585] | 75-95 [515-655] |
| Yield Strength (ksi [MPa]) | 30 [205] | 36 [250] | 37.5 [260] | 52 [360] | 60 [415] | 46 [315] | 55 [380] | 65 [450] |
| Elongation on 4D, % | 25 | 22 | 22 | 22 | 20 | 25 | 20 | 20 |
| Elongation on 2" (50mm), % | 28 | 30 | 30 | 28 | 28 | 28 | 28 | 28 |
| Reduction of Area, % | 38 | 30 | 35 | 40 | 40 | 38 | 45 | 45 |
| Hardness HB max. | 197 | 197 | 197 | 197 | 197 | 197 | 197 | 197 |
Impact toughness temperature tests
| Steel Grade | LF1 | LF2 CL 1 | LF2 CL 2 | LF3 CL 1/2 | LF5 CL 1/2 | LF6 CL 1/2 | LF6 CL 3 | LF9 | LF787 CL 2 | LF787 CL 3 |
|---|---|---|---|---|---|---|---|---|---|---|
| Temperature (°F) | -20 | -50 | 0 | -150 | -75 | -60 | 0 | -100 | -75 | -100 |
| Temperature (°C) | -29 | -46 | -18 | -101 | -59 | -51 | -18 | -73 | -59 | -73 |
Technological processing features
LF1 and LF2 steel grades are optimally hot-worked at temperatures of 1230-1260 °C; processing below 900 °C is not recommended. For the LF3 grade, the forging range is 1175-1205 °C. Heat treatment is a mandatory quality control step, especially for welded joints, where preheating and subsequent stress-relieving annealing are critical.
All steels in this group have excellent weldability using standard industrial methods. The choice between normalizing, forging, or annealing is determined by the operating conditions of the final assembly. EV Group China specialists recommend strictly adhering to the manufacturer's process charts to ensure the longevity of pipeline systems.