Characterization of the effect of alloying elements on the fracture toughness of high strength, low alloy steels

The effect of small alloy additions on the ductile fracture toughness of ferritic high strength, low alloy steels was characterized by determining the fracture toughness parameter JIc and by microstructural analysis on six compositions of these steels. Small additions of niobium (0.10 wt.%) or titanium (0.08 wt.%) resulted in material with significantly improved JIc values. Additions of vanadium (0.085 wt.%), however, resulted in little improvement in JIc values compared with the base steel and the other two alloying elements. The improvements in fracture toughness due to the additions of niobium and titanium are explained in terms of the dependence of ductile fracture toughness on the effects of grain size, inclusion diameter and inclusion volume fraction.