Characterization of fracture toughness of high strength low alloy steel weldments using stretch zone width measurements

Abstract

Most of the industrial applications involving use of high-strength low-alloy steels require good weldability. Thus it is important to characterize the properties of the welded steels, especially the heat affected zone. Attempts have been made to characterize the fracture toughness of the HAZ by the use of theJ-integral and the crack opening displacement. In the present study, the effect of addition of titanium, vanadium and niobium, as well as combinations of these, on the fracture toughness of the heat affected zone of welded steel plates is examined. Six compositions were used in this study. Three-point bending specimens as well as tensile specimens were prepared. The fracture surfaces were examined in a scanning electron microscope to determine the fracture mode as well as the extent of the stretch zone as the crack blunts. Calculation of the fracture toughness parameter,Jlc, is carried out through a quantitative stereofractographic analysis of the stretch zone at the crack tip. The results show that there is a marked increase inJlc due to the addition of the various alloying elements. Generally, the addition of niobium and titanium alone produce the highestJlc due to the extent of grain refinement that these elements produce.