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ASTM A320
Scope
Originally approved in 1948, the ASTM A320 specification covers alloy steel and stainless steel bolting materials for low temperature service. This standard covers rolled, forged, or strain hardened bars, bolts, screws, studs, and stud bolts used for pressure vessels, valves, flanges, and fittings. Like the ASTM A193 specification, unless otherwise specified, the 8UN thread series is specified on fastener larger than 1” in diameter.
Below is a basic summary of a few of the common grades within the ASTM A320 specification. A number of other less common grades of ASTM A320 exist, but not covered in the description below.
Grades
L7 Alloy steel
AISI 4140/4142 Quenched and tempered
L43 Alloy steel
AISI 4340 Quenched and tempered
B8 Class 1 Stainless steel
AISI 304, carbide solution treated
B8M Class 1 Stainless steel
AISI 316, carbide solution treated
B8 Class 2 Stainless steel
AISI 304, carbide solution treated, strain hardened
B8M Class 2 Stainless steel
AISI 316, carbide solution treated, strain hardened
Mechanical Properties
Grade
Size
Tensile,
ksi, min
Yield,
ksi, min
Charpy Impact
20-ft-lbf
@ temp
Elong,
%, min
RA, %, min
L7
Up to 21/2
125
105
-150° F
16
50
L43
Up to 4
125
105
-150° F
16
50
B8
Class 1
All
75
30
N/A
30
50
B8M
Class 1
All
75
30
N/A
30
50
B8
Class 2
Up to 3/4
125
100
N/A
12
35
7/8 - 1
115
80
N/A
15
35
11/8 - 11/4
105
65
N/A
20
35
13/8 - 11/2
100
50
N/A
28
45
B8M
Class 2
Up to 3/4
110
95
N/A
15
45
7/8 - 1
100
80
N/A
20
45
11/8 - 11/4
95
65
N/A
25
45
13/8 - 11/2
90
50
N/A
30
45
Recommended Nuts and Washers
Grade
Nuts
Washers
L7
L43
B8 Class 1
SS304
B8M Class 1
SS316
B8 Class 2
A194 Grade 8, strain hardened
SS304
B8M Class 2
A194 Grade 8M, strain hardened
SS316
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