HAZ Properties of Nb containing high strength pipeline steels
Proceedings Publication Date
The combination of high strength and excellent low-temperature toughness of modern linepipe steels is a direct result of the thermo-mechanically controlled process (TMCP), which leads to a reduced grain size after rolling. Addition of niobium is an effective measure to inhibit recrystallization during finish rolling, which is the key to obtaining a fine-grained microstructure. An experimental investigation was carried out at Salzgitter Mannesmann Forschung GmbH (SZMF) in which the niobium content of laboratory heats was varied between 0.02% and 0.10%. These heats were thermomechanically rolled to a wall thickness of 25 mm and subsequently used for double-layer submerged arc welding trials. It was found that high levels of toughness in the heat-affected zone could be reached even at high niobium contents.