Cast iron and steel are largely similar materials, cast iron just has the carbon precipitated out of solution instead of trapped in a crystalline structure
But we're talking specifically about cast iron. We're not talking about carbon steel at all, hence my confusion on why it was brought up in this comment chain
cast iron is basically steel, but has it's own name because it's brittle. roughly between half a percent to 3 percent carbon (among other things) is the base of many steels. "cast iron" is about 4 percent carbon and pretty much no ductility