HAZ Toughness in Vanadium-microalloyed Steels

The present paper refers to the situation of single-pass welds in structural steels and,in particular,the mechanical properties and microstructures of the coarse grained heat affected zones (CGHAZs) that exist in the parent material close to the fusion line. Frequently,the toughness in these areas is lower than that of either the base steel or the weld metal and so they may represent the weakest link in the structure with respect to fracture. We concentrate on the characteristics of a vanadium-microalloyed plate but a similar strength niobium steel is included as a relevant comparison. To best utilize the strengthening effect of vanadium in steel it is necessary to enhance the nitrogen level to typically 0.01% and it is the combination of V and N that must be considered when attempting to rationalize the properties of the steels.