ASTM A320 L7M Stud Bolt

ASTM A320 Grade L7M is a standard material specification for alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 Grade L7M is heat treated chromium molybdenum alloy steel (AISI 4140/AISI 4140H) with notch toughness properties. Please find chemical composition, mechanical properties, impact test requirement, and reference standards for product dimensions, threads, coatings and recommended nuts and washers.

ASTM A320

Standard Specification for Alloy-Steel and Stainless Steel Bolting for Low-Temperature Service

ASTM A320 Chemical Composition

Element	Composition, % A
	Chromium Molybdenum B
Carbon, max	0.38 – 0.48
Manganese	0.75 – 1.00
Phosphorus, max	0.035
Sulfur, max	0.040
Silicon	0.15 – 0.35
Chromium	0.80 – 1.10
Molybdenum	0.15 – 0.25

ASTM A320 Mechanical Properties

Diameter, in. [mm]	Tensile Strength, min, ksi [MPa]	Yield Strength min, ksi [MPa] (0.2% offset)	Elongation in 2 inch or 50mm, min, %	Reduction of Area, min, %	Hardness, max
					HBW	HRC
2 1/2 [65] and under A	100 [690]	80 [550]	18	50	235	99

ASTM A320 L7M STUD BOLT Heat Treatment :

.

the tempering operation if conducted at 1150° (620°C) minimum, shall be done after machining and forming operations, including thread rolling and any type of cutting.

 

 

ASTM A320 Impact Test Requirements (Notch Toughness)

Size of Specimen, mm	Test Temperature		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]
	°F	°C
10 X 10	-100	-73	20 [27]	15 [20]
10 X 7.5			16 [22]	12 [16]

ASTM A320 L7M STUD BOLT Threads

all threads shall be formed after heat treatment

ASME B1.1-2024: Unified Inch Screw Threads 

ASTM A320 L7M STUD BOLT Hardness Requirement

The maximum hardness of Grade L7M shall be 235 HBW or 99 HRB (conversion in accordance with Table
Number 2B of Test Methods and Definitions A370). Minimum hardness shall not be less than 200 HBW or 93 HRB.Conformance to this hardness shall be ensured by testing each bolt or stud by Brinell or Rockwell B methods in accordance
with 6.3.1

Hex nuts for ASTM A320 L7M STUD BOLT 

 Grade 7 of Specification A194/A194M or a grade of steel similar to the studs. Grade 7M nuts at a hardness not exceeding 235 HBW (or equivalent) shall be used with Grade L7M bolts, studs, and stud bolts

Washer for ASTM A320 L7M STUD BOLT 

Washers for use with ferritic steel bolting shall conform to Specification F436.

 Washer dimensions shall be in accordance with requirements of ASME B18.22.1, unless otherwise specified in
the purchase order

ASTM A320 L7M STUD BOLT MARKING

In addition to the requirements of Specification A962/ A962M, the grade symbol marked shall be as shown in Table 3. . Grade L7M shall be 100 % evaluated in conformance with this specification and shall have a line under the grade symbol. 13.2 Nuts from materials that have been impact tested shall be marked with the letter “L.”

ASTM A320 L7m stud bolt Surface Treatments

We can provide the ASTM A320 L7m stud bolt with following different surface treatments

1. 1. Plating
      • Zinc (White / Yellow / Black)
      • Cadmium (White / Yellow / Black)
      • Zinc Nickel
      • ZINC PLATED/BICHROMATE TREATED

1. 1. Galvanising
      • Hot-Dipped Galvanise
      • Mechanical Galvanise

1. 1. Fluorocarbon Coating
      Xylan® / Dupont Coating Systems:

       

      • Xylar 2
      • Xylan 1070
      • Xylan 1424

1. Customised Coating Systems
   • Zinc + Fluorocarbon / PTFE coated stud bolt
   • Cadmium + Fluorocarbon /PTFE coated stud bolt
   • Zinc Nickel + Fluorocarbon /PTFE coated stud bolt
   • Zinc Plating + Xylan 1424 Blue PTFE coated stud bolt
   • Xylar 2 + Xylan 1070 coated stud bolt
   • stud bolt ZINC PLATED/BICHROMATE TREATED
   • Zinc Yellow Bichromated