Effect of microstructural features on the hot ductility of 2.25Cr-1Mo steel

Some factors contributing to the hot ductility losses of a 2.25Cr-1Mo steel were identified over the temperature range 750-950 degrees C, after the specimens were austenitized at 1000 degrees C, furnace cooled to different temperatures, and held there for sufficient periods of time, followed by tensile testing. There were two types of ferrite present in the microstructure, namely, pro-eutectoid ferrite and deformation-induced ferrite. The pro-eutectoid ferrite was only formed below Ar-3 (similar to 825 degrees C), which was nucleated on the inclusions and distributed uniformly. Nevertheless, the deformation-induced ferrite was formed in a much wider temperature range. It was distributed mainly along austenite grain boundaries above Ar-3, and around the pro-eutectoid ferrite below Ar-3. The deformation-induced ferrite had a primary effect on the hot ductility, which was mainly responsible for a hot ductility trough. There was a peak in the quantity of deformation-induced ferrite between 800 and 900 degrees C, which was just corresponding to the hot ductility trough. The morphology of ferrite was also essential. The net-like structure of ferrite formed along austenite grain boundaries was the most deleterious to the hot ductility. (C) 2010 Elsevier B.V. All rights reserved.