Effect of fluctuation, modification and surface chill on structure of 20%Cr hypereutectic white cast iron

The microstructural refinement of a cast hypereutectic Fe–20Cr–4C alloy using modification, surface chill and a novel 'fluctuation' approach has been studied. Fluctuation involves the addition during pouring of powder or liquid metal to produce variations in temperature and/or composition in microareas of the liquid near the solidification front. The structures of the alloy were investigated using optical microscopy and image analysis. Increasing the degree of fluctuation (ferroalloy powder) resulted in finer primary and eutectic carbides. The combination of fluctuation with the addition of modifying agents (Fe–Si–Re alloy, aluminium and a laboratory intermediate alloy) and the application of surface chill, was found to increase the refinement of the carbides.