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ASTM A350 LF1, LF2 AND LF3 CARBON/ALLOY STEELS FLANGE
The ASTM A350 LF2 is a forged carbon/ low-alloy steel grade for forged flanges, forged fittings and valves intended primarily for low-temperature service and requiring notch toughness testing. There are two Classes for the LF2 steels: Class 1 and Class 2.
These grades of steel are used as pipeline steels and also in the production of forged flanges. They are suitable for use down to –20ºF (LF1,) –50ºF (LF2) and –150ºF (LF3.)
Chemical Composition Requirements
LF1:
| C% | Mn% | Si% | S% | P% | Cr% | Ni% |
| 0.30 max | 0.6/1.35 | .15/.30 | .040 max | .035 max | 0.30 max | 0.40 max |
LF2:
| C% | Mn% | Si% | S% | P% | Cr% | Ni% |
| 0.30 max | 0.6/1.35 | .15/.30 | .040 max | .035 max | 0.30 max | 0.40 max |
LF3:
| C% | Mn% | Si% | S% | P% | Cr% | Ni% |
| 0.20 max | 0.90 | .20/.35 | .040 max | .035 max | 0.30 max | 3.3/3.7 |
*The sum of Cu, Ni, Cr, V, and Mo shall not exceed 1.00% on heat analysis. The sum of Cr and Mo shall not exceed 0.32% on heat analysis. By agreement, the limit for Nb may be increased up to 0.05 % on heat analysis and 0.06 % on product analysis. The carbon equivalent CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. For both Class 1 and Class 2 of ASTM A350 LF2, if the maximum thickness of the work piece is less than or equal to 2″, the CE shall not exceed 0.47; if the the maximum thickness of the work piece is greater than 2″, the CE shall not exceed 0.48.
Mechanical Properties
| Item | Value |
|---|---|
| Tensile Strength, ksi [MPa] | 70-95 [485–655] |
| Yield strength, ksi [MPa], min. | 36 [250] |
| ELr, min. % | 22 |
| ELs, min. % | 30 |
| ELc, min. % | 48t + 15 |
| Reduction of Area, min. % | 30 |
| Hardness, max. HBW | 197 |
*ELr: elongation for standard round specimen, or small proportional specimen, in 4D gauge lenth.
*ELs: elongation for strip specimen for wall thickness ≥ 5/16″ and for all small sizes tested in full section; in 2″ [50 mm].
*ELc: equation for calculating elongation for strip specimens thinner than 5/16″; in 2″ [50 mm]; t = actual thickness in inches.
*Hardness test shall be carried out after heat treatment.
Charpy V-Notch Impact Test
Since the ASTM A350 LF2 forgings are primarily used for low-temperature services, Charpy V-notch impact test is required to determine the notch toughness of the work piece. The Charpy V-notch impact test shall be conducted in accordance with ASTM A370 or ASTM A1058. Standard test specimens shall be prepared first, the cross section of which shall be 10 mm x 10 mm. Three pieces of test specimens of each heat lot shall be prepared. Generally, the minimum applicable temperature for Class 1 of ASTM A350 LF2 is -46°C [-50°F], while it is 0°C [-18°F] for Class 2 of ASTM A350 LF2. The minimum applicable temperatures are also the standard impact test temperatures for standard-size specimens.
| Grade & Class | Eav min. ft*lbf [J] | Eeamin. ft*lbf [J] |
|---|---|---|
| LF2 Class 1 | 15 [20] | 12 [16] |
| LF2 Class 2 | 20 [27] | 15 [20] |
FLANGE FORGING
LF1 and LF2 grades would ideally be forged at around 2250-2300ºF(1230-1260ºC) and not forged below 1650-1700ºF(900-925ºC.)
LF3 grade would be forged at around 2150-2200ºF (1175-1205ºC) and not forged below 1700ºF (925ºC.)
MACHINABILITY
In the case of forged fittings and flanges, these grades may be machined as required, and ongoing experience will determine if machining is best done on an as-forged structure, a normalized structure or an annealed structure. In either case, in view of the critical nature of the end use, advice should be taken from a recognized heat treatment company.
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