Effect of Nb microalloying on the heat affected zone microstructure of girth welded joints

The effect of Nb content in the range 0.07-0.10% on the HAZ microstructure of large diameter pipes is reported in this paper. Results show that Nb is able to influence the size of the bainitic packet and cells in the heat affected zone, i.e. the microstructural parameters affecting impact toughness and hardness behavior. Such an effect leads to an improvement of both toughness and hardness for the steel with higher Nb content.