Applying an electron beam weld (EBW) at the base of the notch has modified Charpy test specimens to provide a reduced scatter, sharper transition, higher upper-shelf energy and higher transition temperature for tough, high-strength steels. The procedure considerably improves determination of the ductile-brittle transition temperature (DBTT) and the reproducibility of the test.
Sectioning of the specimens after testing showed that the weld acts as a brittle crack starter at temperatures up to the transition temperature. In other words, the weld initiates cracking without absorbing significant energy itself. Therefore the test is measuring the energy necessary to drive a sharp crack through the 5.8-mm-wide unwelded ligament.
At temperatures above the transition, the fracture path switches from the weld zone to lower strength, ductile parent metal. The fracture is ductile because cracking initiates and travels through the lower strength parent metal that is ductile at these temperatures. This reflects the practical situation in which brittle weld zones may be present in steel that is inherently tough at the testing temperature.