» Technical » ASTM A350 LF2


September 27, 2019

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.

ASTM A350 LF2 Class 2 flanges

Weld neck flange, RF, ASME B16.5; Material: ASTM A350 Gr. LF2 Cl. 2; Anti-rust light oil painted.

Chemical Composition Requirements

ElementWeight %
C≤ 0.30
P≤ 0.035
S≤ 0.040
Ni≤ 0.40
Cr≤ 0.30
Mo≤ 0.12
Cu≤ 0.40
Nb≤ 0.02
V≤ 0.08
*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

Tensile Strength,
ksi [MPa]
Yield strength,
ksi [MPa], min.
36 [250]
min. %
min. %
min. %
48t + 15
Reduction of
Area, min. %
max. HBW
*The yield strength is determined by 0.2% offset method.
*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 & ClassEav min.
ft*lbf [J]
ft*lbf [J]
LF2 Class 115 [20]12 [16]
LF2 Class 220 [27]15 [20]
*Eav: minimum average impact energy required for each set of 3 specimens; *Eea: minimum impact energy for each specimen.

When sub-size specimens are used, the impact energy values obtained shall conform to Table-S below at energy values proportional to standard size. Intermediate values can be obtained by straight-line interpolation.

Standard Size
10 x 10 mm
3/4 Size
10 x 7.5 mm
2/3 Size
10 x 6.6 mm
15 [20]12 [16]10 [14]
13 [18]10 [14]9 [12]
12 [16]10 [14]9 [12]
10 [14]8 [11]7 [10]
1/2 Size
10 x 5 mm
1/3 Size
10 x 3.3 mm
1/4 Size
10 x 2.5 mm
8 [11]5 [7]4 [6]
7 [10]5 [7]4 [6]
7 [10]4 [6]3 [5]
5 [7]3 [5]3 [5]
*Table-S: minimum equivalent absorbed energy, in ft*lbf [J] units.

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