Effects of microstructure on fracture toughness of a high-strength low-alloy steel

Fracture toughness and ductile-brittle transition behavior were measured for a copper-bearing HSLA steel. The value ofK _lc for cleavage failure was independent of heat treatment, whileJ _lc for ductile failure decreased monotonically with increasing strength level. With both failure modes, fracture appears to be controlled by cracking of sulfide inclusions. The decrease in ductile-failureJ _lc is caused by decreased work-hardening rates that suppress cleavage and facilitate void coalescence. Both higher austenitizing temperature and quenching rate after austenitization influence the ductile/brittle transition temperature, either through grain-size and precipitate refinement or through an increase in the resistance of the steel to shear failure. Formerly Graduate Student, The Ohio State University