ASTM A320 Grade L7 Specification
ASTM A320 Grade L7 is a material specification for bolts, studs, nuts and other fasteners, intended for use in high temperature bolting applications. ASTM A320 Grade L7 is classified into 4 property class namely A, B, C & D, each designated with different tensile and stress rupture properties. Grade 660 fasteners are used in bolting boilers, pressure vessels, pipeline flanges and valves, intended for high temperature service. . ASTM A320 Grade L7 material is chemically equivalent to ASTM B638 grade 660 stainless steel alloy, also known by alloy A286 and UNS S66286, heat treated to achieve properties defined in ASTM A453 specification.
Find more information on chemical composition, mechanical properties, tensile class, heat treatment definition, available products, bar stock sizes, applicable dimension standards, etc.
ASTM A320 Grade L7 Chemical Composition
| Elements |
Content, % |
Allowable Variation, Over or Under, % |
| Carbon |
0.08 max |
0.01 over |
| Manganese |
2.00 max |
0.04 |
| Phosphorus |
0.04 max |
0.005 over |
| Sulfur |
0.03 max |
0.005 over |
| Silicon |
1.00 max |
0.05 |
| Nickel |
24.00 - 27.00 |
0.20 |
| Chromium |
13.50 - 16.00 |
0.20 |
| Molybdenum |
1.00 - 1.50 |
0.05 |
| Titanium |
1.90 - 2.35 |
0.05 |
| Aluminum |
0.35 max |
0.05 over |
| Vanadium |
0.10 - 0.50 |
0.03 |
| Boron |
0.001 - 0.010 |
0.0004 under to 0.001 over |
ASTM A320 Grade L7 Mechanical Properties
| Tensile Class |
Tensile Strength, min |
Yield strength, 0.2% offset, min |
Elongation in 4D min, % |
Reduction of Area, min, % |
| ksi |
MPa |
ksi |
MPa |
| A, B and C |
130 |
895 |
85 |
585 |
15 |
18 |
| D |
130 |
895 |
105 |
725 |
15 |
18 |
ASTM A320 Grade L7 Hardness
| Tensile Class |
Brinell Hardness Number |
Approximate Rockwell Hardness B & C |
| min |
max |
| A, B and C |
248 - 341 |
24 HRC |
27 HRC |
| D |
248 - 321 |
24 HRC |
35 HRC |
ASTM A320 Grade L7 Stress Rupture Requirements
| Tensile Class |
Test Temperature °F [°C] |
Stress, min |
Time to Rupture, min, h [Note] |
Elongation, min, % |
| ksi |
Mpa |
| A, B and C |
1200 [650] |
56 |
385 |
100 |
5 |
| D |
1200 [650] |
40 |
275 |
100 |
5 |
Note : The combination bar specimen shall be tested continuously at the temperature and at the minimum stress specified or at a greater stress and shall rupture in a time not less than that specified.
