ASTM A320 L7 vs ASTM A193 B7 Comparison
Same 4140 / 4142 chemistry, different test regime
ASTM A320 Grade L7 and ASTM A193 Grade B7 share an identical chemistry (AISI 4140 or 4142 chromium-molybdenum alloy steel) and identical heat treatment (quench-and-tempered to a minimum tensile strength of 125 ksi). The decisive difference is Charpy V-notch impact testing. A320 L7 must be Charpy-tested at -150°F (-101°C) with a minimum average energy of 40 ft-lbf for full-size 10 x 10 mm specimens; A193 B7 has no Charpy requirement and is intended for service temperatures above the A320 window.
What is the same
- Chemistry: AISI 4140 / 4142, chromium-molybdenum alloy steel
- UNS designation: G41400
- Heat treatment: quench-and-tempered
- Minimum tensile strength: 125 ksi (860 MPa)
- Minimum yield strength: 105 ksi (725 MPa) for diameters up to 2-1/2 in
- Maximum hardness: 321 HBW
What is different
- A320 L7: Charpy V-notch impact testing mandatory at -150°F (-101°C), 40 ft-lbf min average for full-size specimens
- A193 B7: no Charpy requirement
- A320 L7: priced higher due to the test regime and qualification overhead
- A320 L7: required when project minimum metal temperature falls below the A193 threshold
Cost and selection
A320 L7 stud bolts cost more than A193 B7 stud bolts of the same diameter and length because each lot must include Charpy V-notch impact testing, which adds qualification cost. For project specifications that allow either, A193 B7 is the economical choice. When the minimum design metal temperature (MDMT) drops below the A193 window, A320 L7 is the mandatory selection.