ASTM A320 Bolts

Standard Specification for Impact tested Alloy Steel and Stainless Steel Bolting for Low-Temperature Service. This specification covers alloy and stainless steel bolting for pressure vessels, valves, flanges, and fittings for low-temperature service. Different grade  both ferritic and austenitic steels designated L7, B8, etc are covered under this specification . Selection will depend on design, service conditions, mechanical properties, and low-temperature characteristics.

Most Common ASTM A320 Material Grades

ASTM A320 Grade L7 Bolts – Alloy Steel AISI 4140/4135/4142 Quenched and tempered Impact Test @ -101 Degrees C 20Joules Min

ASTM A320 Grade L7M Bolts – Alloy Steel AISI 4140/4135/4142 Quenched and tempered Impact test @ -73 Degrees C 20Joules Min

ASTM A320 Grade L43 Bolts – Alloy Steel AISI 4340 Quenched and tempered Impact test @ -101 Degrees C 20Joules Min

ASTM A320 Grade B8 Bolts – Class1 Stainless Steel 304 Carbide solution Treated

ASTM A320 Grade B8 Bolts – Class 2 Stainless Steel 304 Carbide solution Treated and Strain Hardened

ASTM A320 Grade B8M Bolts -Class1 Stainless Steel 316 Carbide solution Treated

ASTM A320 Grade B8M Bolts -Class2 Stainless Steel 316 Carbide solution Treated and Strain Hardened

ASTM A320 Bolts, Screws, Studs, Stud Bolts, Threaded Rod Manufacturers and Suppliers

A320 Alloy Steel Bolts, studs, and stud bolts of Grades L7, L7A, L7B, L7C, L43, L1, L70, L71, L72, and L73 shall be equipped with ferritic alloy nuts and shall show a minimum impact energy absorption of 20 ft lbf [27 J] and of Grade L1 a minimum impact energy absorption of 40 ft  lbf [54 J] at the test temperature when tested by the procedure specified in the applicable portions of Sections 19 to 28 of Test Methods and Definitions A370.

  • Compatible nuts conforming to Grade 4 or Grade 7 of Specification A194/A194M or a grade of steel similar to the studs shall be used.Grade 7M nuts at a hardness not exceeding 235 HBW (or equivalent) shall be used with Grade L7M bolts, studs, and stud bolts. All nut materials, including those which may be supplied under Specification A194/A194M, shall be subject to the impact requirements of this specification in the following manner: impact tests shall be made on test specimens taken from the bar or plate from the heat of steel used for manufacturing the nuts, and heat treated with the nut blanks.
  • Washers for use with ferritic steel bolting shall conform to Specification F436 confirming to dimensions as per ASME B18.22.1.
  • Below listed are Alloy Steel Low Temperature Bolting Grades along with their Impact Resistance Temperatures.

ASTM A320 Grade L70 Bolts Impact Tested @ -73 degrees Celcius / -100 Degrees Fahrenheit

ASTM A320 Grade L7A Bolts Impact Tested @ -101 degrees Celcius / -150 Degrees Fahrenheit

ASTM A320 Grade L71 Bolts Impact Tested @ -73 degrees Celcius / -100 Degrees Fahrenheit

ASTM A320 Grade L7B Bolts Impact Tested @ -101 degrees Celcius / -150 Degrees Fahrenheit

ASTM A320 Grade L72 Bolts Impact Tested @ -73 degrees Celcius / -100 Degrees Fahrenheit

ASTM A320 Grade L7C Bolts  Impact Tested @ -101 degrees Celcius / -150 Degrees Fahrenheit

ASTM A320 Grade L73 Bolts Impact Tested @ -73 degrees Celcius / -100 Degrees Fahrenheit

ASTM A320 Grade L1 Bolts Impact Tested @ -73 degrees Celcius / -100 Degrees Fahrenheit

A320 Stainless  Steel Bolts, studs, and stud bolts of Grades B8, B8C, B8T, B8P, B8F, B8M, B8LN, and B8MLN shall be equipped with austenitic Stainless Steel nuts . Bolts with Class 1, 1A, and 2 austenitic steels for temperatures above -325 °F [-200 °C]; Class 1 and 1A austenitic Grades B8, B8A, B8P, B8PA, B8C, B8CA, B8LN, and B8LNA above -425 °F [-255 °C]; and ferritic or austenitic bolting 1⁄2 in. (12.5 mm) and smaller, are exempt from impact testing.

  • A320 Stainless Bolts shall  be equipped with austenitic alloy nuts conforming to Grades 8, 8C, 8T, 8F, 8M, 8LN, and 8MLN for Specification A194/A194M. Impact tests are not required for Grades 8F, 8M, 8T, and 8MLN for temperatures above -325 °F [-200 °C] and for Grades 8, 8P, 8C, and 8LN above -425 °F [-255 °C]. Incase if for particular applications nuts are required with a Charpy impact energy absorption of not less than 20 ft lbf [27 J] at temperatures below -150 °F [-100 °C],  the nuts must conform to Grades 8, 8C, 8M, 8P, 8T, 8F, 8LN, or 8MLN of Specification A194/A194M.
  • Washers for use with austenitic steel bolting shall be be made of austenitic stainless steels viz. 304, 316, 317, 321, 347, 254smo, xm-19 confirming to dimensions as per ASME B18.22.1.
  • Below Mentioned Austenitic Stainless Steel Grades.

Test Requirements

Chemical Composition

ASTM A320 Chemical Composition

ElementL7 (AISI 4140)L43 (AISI 4340)B8 (AISI 304)B8M (AISI 316)
Carbon0.37 – 0.490.38 – 0.430.08 max0.08 max
Manganese0.65 – 1.100.75 – 1.002.00 max2.00 max
Phosphorus, max0.035 40.0350.0450.045
Sulfur, max0.04’ 0.040.030.03
Silicon0.15 – 0.350.15 – 0.351.00 max1.00 max
Chromium0.75 – 1.200.70 – 0.9018.0 – 20.016.0 – 18.0
Nickel —1.65 – 2.008.0 – 11.010.0 – 14.0
Molybdenum0.15 – 0.250.20 – 0.30 —2.00 – 3.00

Mechanical Properties

ASTM A320 Mechanical Properties

GradeMarkingSizeTensile, ksi, minYield, ksi, minCharpy Impact 20-ft-ibf @ tempElong, %, minRA, %, minHardness max
L7L7Up to 2″125105-150° F1650C35
L43L43Up to 4″125105-150° F1650C35
B8 Cl 1B8All7530N/A3050B96
B8M Cl 1B8MAll7530N/A3050B90
Up to 3/4″125100N/A1235C35
B8 Cl 2B87/8″ to 1″11580N/A1535C35
1 1/8″ to 1 1/4″10565N/A2035C35
1 3/8″ to 1 1/2″10050N/A2845C35
Up to 3/4″11095N/A1545C35
B8M Cl 2B8M7/8″ to 1″10080N/A2045C35
1 1/8″ to 1 1/4″9565N/A2545C35
1 3/8″ to 1 1/2″9050N/A3045C35

Download PDF: ASTM A320 at ASTM.org

 Heat Treatment

  • Bolting shall be allowed to cool to room temperature after rolling or forging. Grades L7, L7A, L7B, L7C, L7M, L43, L1, L70, L71, L72, and L73 shall be reheated to above the upper critical temperature and liquid quenched and tempered. Grades B8, B8C, B8M, B8T, B8F, B8P, B8LN, and B8MLN shall receive a carbide solution treatment. Products made from such material are described as Class 1. This shall consist of holding the material for a sufficient time at a temperature at which the chromium carbide will go into solution and then cooling in air or in a liquid medium at a rate sufficient to prevent reprecipitation of the carbide. Material thus treated is described as Class 1. If specified in the purchase order, material shall be solution treated in the finished condition; material so treated is described as Class 1A.
  • When increased mechanical properties are desired, austenitic bolting shall be solution annealed and strain hardened if specified in the purchase order; material so treated is identified as Class 2.
  • If scale-free bright finish is required, this shall be specified in the purchase order.
  • For L7M bolting, the final heat treatment, which may be the tempering or stress-relieving operation conducted at 1150 °F [620 °C] minimum, shall be done after machining or rolling of the threads and any type of cutting.

Related ASTM Specification

ASTM A193 / A193M – 16 : Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service and Other Special Purpose Application

ASTM A194 / A194M – 16 : Standard Specification for Carbon Steel, Alloy Steel, and Stainless Steel Nuts for Bolts for High Pressure or High Temperature Service

ASTM F593 – 13a : Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs

ASTM F594 – 15 : Standard Specification for Stainless Steel Nuts

ASTM F2281 : Standard Specification for Stainless Steel and Nickel Alloy Bolts, Hex Cap Screws, and Studs, for Heat Resistance and High Temperature Applications Designation

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