Yes, Charpy impact testing can be performed at specific test temperatures. Grades L7 and L43 require testing at -150 degrees Fahrenheit unless otherwise specified. Since passing this test can be a challenge, engineers will often allow for Charpy testing at a temperature that more closely resembles service temperatures for those fasteners. When Charpy testing at temperatures other than -150 degrees Fahrenheit is performed, the test temperature must be permanently stamped on the bolt heads or ends of studs.

Unless otherwise specified, A320 bolts larger than 1” diameter will use 8UN thread series.

Although A320L7 and A320L43 bolts are considered high strength, they can be galvanized. Bolts that exceed 150 KSI in tensile strength are at risk for hydrogen embrittlement.

The raw material used to make L7 bolts is 4140 steel, whereas L43 is made from 4340 steel. They both will have similar mechanical properties. L43 bolts are more common larger than 2 ½” diameter due to raw material availability and 4340 has greater success passing the Charpy testing requirements at -150 degrees fahrenheit.

L7M bolts will have lower mechanical properties than L7. In addition, a hardness test is required for each bolt. There are certain applications in which L7M bolts are used instead of L7. The final heat-treatment for L7M bolts must be performed after machining or rolling of the threads and any type of cutting.