Weldability of higher niobium X80 pipeline steel

Low carbon higher niobium-bearing microalloying design has been applied to develop X80 pipeline steel which can meet the requirement of the second west-east pipeline project (2nd WEPP). Since the beginning of application of X80 hot strip and plate steel, weldability of this steel has been paid serious attention. Results from recent simulation researches show that the optimum heat input energy for Nb-bearing X80 steel should be lower than 30 kJ/cm. Characterization of the CGHAZ in the actual welding sample of the higher Nb-bearing steel shows that the size of Nb(CN) precipitates does not coarsen obviously compared to the normal precipitates (≤ 30 nm) in the X80 pipeline steel with conventional Nb content. Furthermore, the prior austenite grain size in the HAZ of 0.09%Nb steel is smaller than in 0.06%Nb steel. The industrial DSAW results show that the higher Nb (0.09%) X80 steel can be successfully, more efficiently welded to get good performance. Many industrial testing results show that with appropriate welding processing control, the mechanical properties of the HAZ in higher Nb X80 steel, especially the toughness, could reach high levels. That promises a great insurance for the success of the construction of the 2nd WEPP. (AU) Copyright © 2013 Companhia Brasileira de Metalurgia e Mineração (CBMM) All Rights Reserved