ASTM A320 is a standard material specification covering alloy and stainless steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 specification includes chemical composition, mechanical properties, dimensional reference standards, recommended nuts and washers for grades like L7, L43, B8, B8M, B8C, B8T and many others with notch toughness requirements.

Supplementary requirements includes Impact properties and hardness testing of class 2 bolting materials for ASME applications.

ASTM A320 Grades

Grade	Raw Material
L7	13% Chromium Ferritic Steel
L7M	Chromium Molybdenum Alloy Steel, Quenched & Tempered
L43	Chromium Molybdenum Alloy Steel, Quenched & Tempered
B8	AISI 304 Stainless Steel, Carbide Solution Treated
B8 Class 2	AISI 304 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8M	AISI 316 Stainless Steel, Carbide Solution Treated
B8M Class 2	AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8T	AISI 321 Stainless Steel, Carbide Solution Treated
B8T Class 2	AISI 321 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8C	AISI 347 Stainless Steel, Carbide Solution Treated

ASTM A320 Chemical Composition

Element	Grade L7, L7M	Grade L43	Grade B8	Grade B8M	Grade B8T	Grade B8C
Carbon	0.38 - 0.48	0.38 - 0.43	0.08 max	0.08 max	0.08 max	0.08 max
Manganese, max	0.75 - 1.00	0.75 - 1.00	2.00 max	2.00	2.00	1.00
Phosphorus, max	0.035	0.035	0.045	0.045	0.045	0.040
Sulfur, max	0.040	0.040	0.030	0.030	0.030	0.030
Silicon	0.15 - 0.35	0.15 - 0.35	1.00 max	1.00	1.00	1.00 max
Nickel	-	0.40 - 0.70	8.0 - 11.0	10.0 - 14.0	9.0 - 12.0	8.00 - 11.00
Chromium	0.80 - 1.10	0.40 - 0.60	18.0 - 20.0	16.0 - 18.0	17.0 - 19.0	18.0 - 20.0
Molybdenum	0.15 - 0.25	0.20 - 0.30	-	2.0 - 3.0	-	-
Titanium	-	-	-	-	5 x C, min	-

ASTM A320 Mechanical Properties

Grade	Diameter, in.	Tensile Strength, ksi	Yield Strength ksi	Elongation, %	Reduction, %	Hardness
B7	2.5 and under	125	105	16	50	321 HBW or 35 HRC
B7M	4 and under	125	105	16	50	321 HBW or 35 HRC
B16	2.5 and under	100	80	18	50	321 HBW or 35 HRC
B8, B8M, B8C, B8T Class 1	1" and under	75	30	30	50	223 HBW or 96 HRB
B8, B8C, B8T, Class 2	3/4 and under	125	100	12	35	321 HBW or 35 HRC
	Over 3/4 to 1, inclusive	115	80	15	30	321 HBW or 35 HRC
	Over 1 to 1 1/4", inclusive	105	65	20	35	321 HBW or 35 HRC
	Over 1 1/4" to 1 1/2", inclusive	100	50	28	45	321 HBW or 35 HRC
B8M, Class 2	3/4 and under	110	95	15	45	321 HBW or 35 HRC
	over 3/4 to 1, inclusive	100	80	20	45	321 HBW or 35 HRC
	over 1 to 1 1/4, inclusive	95	65	25	45	321 HBW or 35 HRC
	over 1-1/4" to 1-1/2", inclusive	90	50	30	45	321 HBW or 35 HRC

ASTM A320 Impact Test Requirements

Grade	Test Temperature
	°F	°C
L7M, L70, L71, L72, L73	-100	-73
L7, L7A, L7B, L7C	-150	-101
L43	-150	-101
L1	-100	-73

ASTM A320 Temperature Requirement For Impact Testing

Size of specimen, mm	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)
All Grade Except L1A
10 by 10	20 [27]	15 [20]
10 by 7.5	16 [22]	12 [16]
Grade L1
10 by 10	40 [54]	30 [41]
10 by 7.5	32 [44]	24 [32]

ASTM A320 Recommended Nuts & Washers

Bolt Grade	Nut Grade	Washer Grade
L7	ASTM A194 Grade 7	ASTM F436 Type 1
L7M	ASTM A194 Grade 7M	ASTM F436 Type 1
L43	ASTM A194 Grade 4 OR Grade 7	ASTM F436 Type 1
B8	ASTM A194 Grade 8	AISI 304
B8M	ASTM A194 Grade 8M	AISI 316
B8T	ASTM A194 Grade 8T	AISI 321
B8C	ASTM A194 Grade 8C	AISI 347

Reference Standards