Effect of NbO Additions on the Grain Size of 1010 Steel Castings

This paper describes a set of experiments that used NbO powder additions to decrease the final as-cast microstructure of 1010 steel castings. NbO has excellent crystallographic matching between its (002) plane and the (001) plane in ferrite, making it a possible heterogeneous nucleation site for delta ferrite. A set of 1010 steel plates were cast in green sand molds and then sectioned into tensile bars. NbO powder was added via the downsprue during pouring. The yield strength and ultimate tensile strength increased with the amount of NbO added. Percent elongation was unaffected in the samples with 6 ppm of NbO powder. Specimens with higher NbO powder additions had a significantly lower elongation than the baseline material. The microstructure of the NbO containing samples was finer than the baseline castings. The increase in strength and drop in ductility was theorized to be more consistent with a grain pinning strengthening mechanism than heterogeneous nucleation.