MICROSTRUCTURAL INVESTIGATION OF A RAPIDLY SOLIDIFIED 12CR-MO-V STEEL

Rapidly solidified martensitic stainless steel (11.59Cr-0.98Mo-0.28V ( in wt pct)) ribbons have been produced by the melt-spinning process. T he microstructure of the ribbons showed three distinct zones: a column ar, a cellular, and a cellular-dendritic zone. The height of the colum nar grain zone is independent of the process parameters such as the wh eel material or the wheel velocity. Due to a high level of undercoolin g and a high growth velocity of the solid/liquid interface, the rapid solidification process is found to suppress the formation of delta-fer rite and enhance the formation of austenite. The austenite is transfor med into martensite upon cooling. In comparison with conventional soli dification, a reduction in the initial austenite grain size has been f ound to result in a very fine lath martensite (M) structure. Investiga tions of the texture within the ribbons along the growth direction sho w a weak fiber texture. Transmission electron microscopy (TEM) has rev ealed a [111](M1) parallel to [011](M2) and (011)(M1) parallel to (110 )(M2) orientation relationship between two neighboring martensite lath s. The observed orientation relationship is a result of a superpositio n of both the Kurdjumov-Sachs (KS) and Nishiyama-Wasserman (N-W) orien tation relations.