Ductile—brittle transition of steel electron beam weld metal in small punch test

Abstract

Toughness evaluation of narrow high energy beam welds via the conventional Charpy V notch (CVN) impact test is not always successful because cracks often deviate from the fusion zone into the heat affected or unaffected base metal zones. The small punch (SP) test was applied to electron beam welds of a 490 MPa strength steel to evaluate the toughness by measuring the ductile-brittle transition temperature (DBTT). The steel was electron beam welded using various heat inputs and the welds were examined via CVN and SP tests at 40-298 K. The SP DBTTs obtained from the SP energy showed a linear correlation with the CVN DBTTs. The load-deflection curves during the SP tests and the fractography of SP tested specimens indicated the existence of ductile-brittle transitions. The results suggest that the SP test can be used to predict the DBTTs of electron beam welds, which cannot be accomplished via the conventional CVN impact test.