Fracture Toughness in Niobium Treated Steels

While niobium can significantly improve the yield strength of microalloyed steels, such additions frequently result in low toughness and heat-affected-zone embrittlement. A direct correlation between fracture surface appearance, fracture profile, microstructure and precipitation behavior may be used to explain differences in toughness as a function of niobium content in steels containing 0.03, 0.06 and 0.21 wt.% niobium.