Abstract
Laboratory heats of an API X100 steel (Mn–Mo–Nb) with two levels of vanadium (0.004% and 0.063%) were melted and control rolled simulating a coiled plate production process. Extensive microstructural analyses were performed, including optical, EBSD and TEM. Texture analyses of the two alloys were also compared. Mechanical properties were determined for various rolling and pipe axis orientations. Only minor differences in microstructure and texture properties were observed between the two alloys. Yet the 0.063% V alloy had from 8 to 14% higher yield and tensile strengths in all directions, while the toughness and ductility measurements were similar for both alloys. Higher strength of the V added pipeline steel was partially due to its smaller grain size and larger fraction of subgrain boundaries. Some, but perhaps not all, of the strength differences could be related to the observed smaller precipitate size of the higher vanadium steel. The vanadium addition was necessary in this alloy to ensure meeting the required strength properties of X100 steel.
