TOUGHNESS CHARACTERIZATION OF NIOBIUM-BEARING HSLA STEELS

Estimates of toughness in terms of Charpy impact energy and the critic al stress intensity factor, K(ICV) using deeply chevron-notched specim ens were made for two casts of niobium-bearing high-strength low-alloy (HSLA) steels. K(ICV) determinations are carried out for the first ti me using both three- and four-point bend loading configurations for th is material. Quantitative analyses of the material microstructures are made with, respect to the amount of the phases, ferrite grain size, a nd the volume fraction, length, aspect ratio, and mean inter-spacings of the inclusions. A comparative study of impact and fracture toughnes s with regard to the microstructural parameters, indicates that the la tter toughness characterization approach is far superior to the former . The compatibility of the estimated values of K(ICV) using the two di fferent loading configurations is discussed.