Generally, steel contains less than 2% carbon while cast iron has in the range 2.4 - 4%. It makes cast iron more brittle and difficult to forge by hammering. Steel can be hammered without breaking.
Steel is more difficult to cast than iron. It has a higher melting point and greater shrinkage rate which requires a consideration during mould design. Risers should be given more capacity to draw molten metal from the mould as the metal cools and shrinks. Attention should be paid to the thickness of mould cavities as thinner areas will cool quicker than thicker areas which can create internal stress points. Finally, it leads to fracture.
Molten steel is also less fluid than molten iron. It makes it more difficult to pour and fill intricate gaps in a mould cavity. Molten steel is also more likely to react with internal mould surfaces. It makes more unpredictable results.
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