ASTM A320 Grade L7 Specification

ASTM A320 Grade L7 is a standard material specification for alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade L7 is heat treated chromium molybdenum alloy steel (AISI 4140/AISI 4140H) with notch toughness properties. Please find chemical composition, mechanical properties, impact test requirement, and reference standards for product dimensions, threads, coatings and recommended nuts and washers.

ASTM A320 Chemical Composition

Element Composition, % A
Chromium Molybdenum B
Carbon, max 0.38 - 0.48
Manganese 0.75 - 1.00
Phosphorus, max 0.035
Sulfur, max 0.040
Silicon 0.15 - 0.35
Chromium 0.80 - 1.10
Molybdenum 0.15 - 0.25

Notes :
A The intentional addition of Bi, Se, Te, and Pb is not permitted except for Grade B8F, in which selenium is specified and required.
B Typical steel compositions used for this grade include 4140, 4142, 4145, 4140H, 4142H, and 4145H.
C For the L7M grade, a minimum carbon content of 0.28 % is permitted provided that the required tensile properties are met in the section sizes involved; the use of AISI 4130 or 4130H is allowed.

ASTM A320 Mechanical Properties

Diameter, in.
[mm]		 Tensile Strength, min, ksi [MPa] Yield Strength min, ksi [MPa] (0.2% offset) Elongation in 2 inch or 50mm, min, % Reduction of Area, min, % Hardness, max
HBW HRC
2 1/2 [65] and under A 125 [860] 105 [725] 16 50 321 35

Heat Treatment : Quenched and Tempered at 1100°F [593°C] minimum.

ASTM A320 Impact Test Requirements (Notch Toughness)

Size of Specimen, mm Test Temperature Minimum impact value required for average of each set of three specimens, ft-lbf [J] Minimum impact value permitted for one specimen only of a set, ft-lbf [J]
°F °C
10 X 10 -150 -101 20 [27] 15 [20]
10 X 7.5 16 [22] 12 [16]

ASTM A320 Recommended Nuts & Washers

Bolt Grade Nut Grade Washer Grade
ASTM A320 Grade L7 ASTM A194 Grade 7 ASTM F436 Type 1
ASTM A320M Grade L7 ASTM A194M Grade 7 ASTM F436M Type 1

Reference Standards