Refinement of Boride by Rapid Solidification in Boronated Stainless Steel

Boronated stainless steel containing up to 2 mass%B, which is used for storage and transportation of spent nuclear fuel, has been well known as a poor workable material with large volume fraction of coarsely dispersed plate-like borides. Rapid solidification processes were applied to boronated stainless steels for refining borides and improving ductility and toughness. Borides were a little refined by the casting process using a water-cooled Cu mold. It was found that boron almost existed as solute atoms in a nonequilibrium state for as-solidified powders produced by N2-gas and water atomizations. Fine spherical borides precipitated during HIP treatment. HIP compacts and hot rolled plates processed from gas atomized powder exhibited a microstructure with finely dispersed sperical borides below 3μm in diameter and had superior ductility and toughness. Furthermore, it was found that refined borides also improved the corrosion resistance. A phenomenon similar to crevice corrosion was considered to occur at the interface between coarse plate-like borides and matrix.