抄録
The grain refinement of ferritic stainless steel was achieved by the addition of Fe-Nb-C alloy inoculants containing primary NbC crystals. The grain size of SUS430 was reduced to about 60μm when the inoculation condition was optimized. In order to investigate the grain refinement mechanism of ferritic stainless steel using Fe-Nb-C alloy inoculants, the interface between NbC derived from the inoculants and SUS430 was observed by TEM. From the results of the TEM observation on NbC/SUS430 interface, a crystallographic orientation relationship at the α-Fe/NbC interface was found and was identified as (002)Nbc//(110) α-Fe. The calculated interface misfit suggests that the NbC/SUS430 interface has a semi-coherent interface. These results indicate that NbC derived from the inoculants can act as nuclei on the solidification of ferritic stainless steel. The dissolution behavior of Fe-Nb-C alloy inoculants in the stainless steel melt suggests that first the matrix in the inoculants would rapidly dissolve due to its low melting point and then primary NbC crystals would gradually dissolve. The dissolving NbC crystal will be dispersed into the whole stainless steel melt, resulting in the formation of a fine equiaxed grain structure.
