ASTM A320 Technical Data

 

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ASTM A320 Grades and Markings

The ASTM A320 specification encompasses the standard that covers high-strength low-alloy steel shapes for bolting material used for pressure valves, flanges, vessels, and fittings for high-temperature applications.  For this specification, it covers wire, bars, bolts, studs, stud bolts, and screws. They are mainly used in chemical construction and petroleum applications. Although, this material is often utilized in national coarse thread pitches, but threads are specified 8 threads per inch (tpi) for diameters above 1 inch when being used in traditional applications.

Grades and Markings

Marking of Ferritic Steels
Grade Grade Symbol
L7L7
L7ML7M
L70L70
L7AL7A
L71L71
L7BL7B
L72L72
L7CL7C
L73L73
L43L43
L1L1
Marking of Austenitic Steels
Class GradeGrade Symbol
Class 1B8
B8C
B8M
B8F
B8P
B8T
B8LN
B8MLN
B8
B8C
B8M
B8F
B8P
B8T
B8F or B8LN
B8G or B8MLN
Class 1AB8A
B8CA
B8MA
B8FA
B8PA
B8TA
B8LNA
B8MLNA
B8A
B8B or B8CA
B8D or B8MA
B8FA
B8H or B8PA
B8J or B8TA
B8L or B8LNA
B8K or B8MLNA
Class 2B8
B8C
B8M
B8F
B8P
B8T
B8SH
B8CSH
B8MSH
B8FSH
B8PSH
B8TSH

 

ASTM A320 Mechanical Properties

ASTM A320 Specifications for Mechanical Properties governs the material specification defining mechanical properties, chemical composition, and preferential heat treatment. In addition, it governs product marking, hardness requirements, certifications, and more. ASTM A320 defines both SI (Metric) and inch-pound units.

MECHANICAL PROPERTIES

Class and Grade, Diameter, in. [mm]Heat TreatmentMinimum Tempering Temperature, F°[C°]Tensile Strength,
min,
ksi [Mpa]
Yield Strength,
min,
0.2 % offset,
ksi
Elongation in 2 in. or 50mm,
min,
%
Reduction of Area,
min,
%
Hardness,
max
L7, L7A, L7B, L7C, L70, L71, L72, L73
2 1/2 [65] and underA
Quenched and Tempered1100 [593]125 [860]105 [725]1650321 HBW or 35 HRC
L43
4 [100] and underA
Quenched and Tempered1100 [593]125 [860]105 [725]1650321 HBW or 35 HRC
L7M
2 1/2 [65] and underA
Quenched and Tempered1150 [620]100 [690]80 [550]1850235 HBW or 99 HRB
L1
1[25] and underA
Quenched and Tempered  125 [860] 105 [725] 16 50  
Class and Grade, Diameter, in. [mm]Heat TreatmentBTensile Strength,
min,
ksi
Yield Strength,
min,
0.2 % offset, ksi
Elongation in 2in or 50mm,
min,
%
Reduction of Area,
min,
%
Hardness, max
Class 1: B8, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN, all diametersCarbide solution treated75 [515]30 [205]3050223 HBWB or 96 HRBC
Class 1A: B8A, B8CA, B8MA, B8PA, B8FA,
B8TA, B8LNA, B8MLNA, all diameters
Carbide Solution Treated in the Finished Condition75 [515]30 [205]3050192 HBW or 90 HRB
Class 2: B8, B8C, B8P, B8F, B8T: 3/4 [20] and under

over 3/4 to 1 [20 to 25], incl
over 1 to 1 1/4 [25 to 32], incl
over 1 1/4 to 1 1/2 [32 to 140], incl
Carbide Solution Treated and Strain Hardened125 [860]

115 [795]
105 [725]
100 [690]
100 [690]

80 [550]
65 [450]
50 [345]
12

15
20
28
35

35
35
45
321 HBW or 35 HRC

321 HBW or 35 HRC
321 HBW or 35 HRC
321 HBW or 35 HRC
Class 2: B8M: 3/4 [20] and under

over 3/4 to 1 [20 to 25], incl
over 1 to 1 1/4 [25 to 32], incl
over 1 1/4 to 1 1/2 [32 to 140], incl
Carbide Solution Treated and Strain Hardened110 [760]

100 [690]
95 [655]
90 [620]
95 [655]

80 [550]
65 [450]
50 [345]
15

20
25
30
45

45
45
45
321 HBW or 35 HRC

321 HBW or 35 HRC
321 HBW or 35 HRC
321 HBW or 35 HRC

AThese upper diameter limits were established on the basis that these were the largest sizes commonly available that consistently met specification property limits.
They are not intended as absolute limits beyond which bolting materials could no longer be certified to the specification.
B To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
C Class 1 products are made from solution-treated material. Class 1A products are solution treated in the finished condition for corrosion resistance;
heat treatment is critical for enhancing this physical property and meeting the mechanical property requirements.
Class 2 products are solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3⁄4 in. in diameter.
DFor sizes 3/4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.

ASTM A320 Materials & Chemical Properties

Material and Chemical Property Requirements for the ASTM A320 governs minimum and maximum carbon, phosphorus, manganese, sulfur, silicon, chromium, nickel, and molybdenum percent content of steel fasteners within the ASTM A320 specification. The properties also include the minimum tempering temperature requirements. 

MATERIALS & CHEMICAL PROPERTIES

Ferritic Steels
Grade Description and UNS DesignationCarbonManganesePhosphorous, maxSulfur, maxSiliconNickelChromiumMolybdenumBoron
L7, L7M, L70Chromium-MolybdenumB0.38-0.48C0.75-1.000.0350.0400.15-0.35...0.80-1.100.15-0.25...
Product Variation, %
Over or Under
0.020.040.005 over0.005 over0.02...0.050.02...
L7A, L71Carbon-Molybdenum (AISI 4037)0.35-0.400.70-0.900.0350.040.15-0.35......0.20-0.30...
Product Variation, %
Over or Under
0.020.030.005 over0.005 over0.02......0.02...
L7B, L72Chromium- Molybdenum (AISI 4137)C 0.35-0.400.70-0.90
0.0350.0400.15-0.35
0.80-1.100.15-0.25...
Product Variation, %
Over or Under
0.020.030.005 over0.005 over0.02...0.050.02
L7C, L73Nickel-Chromium-Molybdenum (AISI 8740)0.38-0.430.75-1.000.0350.0400.15-0.350.40-0.700.40-0.600.20-0.30...
Product Variation, %
Over or Under

 

0.020.040.005 over0.005 over0.020.030.030.02...
L43Nickel-Chromium-Molybdenum (AISI 4340)0.38-0.430.60-0.850.0350.0400.15-0.351.65-2.000.70-0.900.20-0.30...
Product Variation, %
Over or Under

 

0.020.030.005 over0.005 over0.020.050.030.02...
L1Low-Carbon Boron0.17-0.240.70-1.400.0350.0500.15-0.30.........0.001-0.003
Product Variation, %
Over or Under

 

0.010.040.005 over0.005 over0.02............

 

Austenitic Steels
GradeDescription and UNS DesignationClassCarbonManganesePhosphorousSulfurSiliconNickelChromiumNiobiumE + TantalumMolybdenumSeleniumTitaniumNitrogen
B8, B8A 304, S304001, 1A, 2D0.082.000.0450.0301.008.00-11.00 18.0-20.0 ...............
Product Variation, %
Over or Under
0.010.040.0100.0050.050.150.20...............
B8C, B8CA 347, S316001, 1A, 2D0.082.000.0450.0301.009.00-12.00 17.0-19.0 10 x carbon content, min. -1.10 max............
Product Variation, %
Over or Under
0.010.040.0100.0050.050.20.05 under............ ...
B8T, B8TA321, S321001, 1A, 2D0.082.000.0450.030 max1.009.0-12.0 17.0-19.0 ... ......5 x (C+N) min - 0.7 max0.10 max
Product Variation, %
Over or Under
0.010.040.0100.0050.050.150.20.........0.05 under0.01
B8P, B8PA S305001, 1A, 2D0.122.000.0450.030, max1.0011.0-13.0 17.0-19.0 ...............
Product Variation, %
Over or Under
0.010.040.0100.0050.050.150.20...............
B8F, B8FA 303, S303001A, 1B, 2D0.152.000.200.15, min.1.008.0-10.0 17.0-19.0 ... ...0.15-0.35 (303Se only)......
Product Variation, %
Over or Under
0.010.040.0100.0200.050.100.20......0.03 under (303Se only)......
B8M, B8MA316, S316001A, 1B, 2D0.082.000.0450.030, max1.0010.0-14.0 16.0-18.0 ... 2.00-3.00.........
Product Variation, %
Over or Under
0.010.040.0100.0050.050.150.20...0.10.........
B8LN, B8LNAS304531, 1A0.032.000.0450.0301.008.0-11.0 18.0-20.0 ... ... ... ... 0.10-0.16
Product Variation, %
Over or Under
0.0050.040.0100.0050.050.150.20............0.01
B8MLN, B8MLNA 316531, 1A0.032.000.0450.0301.0010.0-13.0 16.0-18.0 ...2.0-3.0......0.10-0.16
Product Variation, %
Over or Under
0.0050.040.0100.0050.050.150.20... 0.10...... 0.01

AThese upper diameter limits were established on the basis that these were the largest sizes commonly available that consistently met specification property limits.
They are not intended as absolute limits beyond which bolting materials could no longer be certified to the specification.
B To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
C Class 1 products are made from solution-treated material. Class 1A products are solution treated in the finished condition for corrosion resistance;
heat treatment is critical for enhancing this physical property and meeting the mechanical property requirements.
Class 2 products are solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3⁄4 in. in diameter.
DFor sizes 3/4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.