Interphase and fibrous precipitation in a thermomechanically processed V-Nb-Mo microalloyed steel

A novel V-Nb-Mo steel was thermomechanically processed to promote ferrite grain refinement and precipitation during the austenite to ferrite transformation. Transmission electron microscopy and three-dimensional atom probe tomography confirmed the formation of two main types of precipitates: nano-scale interphase precipitates and fibrous precipitates (FP). Both the precipitates had a Baker-Nutting orientation relationship with the ferrite matrix, but with different variants. Interphase precipitates exhibited a disc shape with an average distance between precipitate rows of 15 +/- 2 nm and an average Guinier radius of 3.9 +/- 1.7 nm, whereas FP had a rod-shape 2.5 +/- 0.5 nm in radius and 8-25 nm in length. It appeared that the FP are formed along the plane perpendicular to the interphase precipitates plane.