Effect of Processing Parameters on Crystal Orientation of Microstructure in High Niobium-Bearing Microalloyed Steel

摘要

The present studies are aimed at understanding the effect of cooling rate and prior strain on the evolution of morphology,orientation relationship (OR) and variant selection in pipeline steel with 0.09wt% niobium.In identical prior austenite grain,all products include granular bainite(GB) by coherent transformation,keep orientation relationship (OR) with parent austenite.Fast cooling and large deformation below T nr both can raise drive force of coherent transformation and weaken variants selection,and it can generate higher frequency of high angle boundaries (HABs) (≥15degree).Moreover,large deformation by few passes below T nr can accelerate nucleation of ferrite grains at the austenite boundary by incoherent transformation.These fine grains haven't OR with prior austenite grain in any side of boundary,and exhibit significant misorientations between themselves.