Low-carbon Mn-Ni-Nb steel: Part 2 Weldability

Abstract

The weldability of a 0·5Ni-0·15Nb steel has been investigated using welding-simulation procedures, laboratory testing, pipe production welding of spiral and V-O pipes, and manual and automatic field welding. It has been shown that the weld heat-affected zones exhibit a tough bainitic microstructure over a wide range of cooling rates encountered in pipe welding. The optimum weld-metal microstructure and properties are obtained with a Mo-B-Ti wire are enhanced by the diffusion of Nb from the baseplate. The excellent strength and toughness of the weldments can therefore be matched with the baseplate properties of X65 to X75 pipe obtained with this Ni-Nb steel. Freedom from cold cracking and relatively low maximum hardness values are additional features of the weldments.