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Cast Iron will have more free standing carbon and gas bubbles, which makes it a very good conductor of heat. Also, cast iron does not cut as easily with an oxy-acetylene torch, while steel cuts very well. Although the higher carbon content of some grades of steel do cut differently than low carbon grades. Steel is more refined, in that it is also contains carbon, but in more controlled amount. Steel is also pressed and rolled, and believe it or not, develops a grain similar to wood, although it is much harder to detect. Cast Iron also has a tendency to be much more stiffer than steel as it goes through a quenching (loses heat faster) going through the casting process. Larger billets of steel that are thick, often have more carbon added to their mix, as they cool slower, and otherwise have a tendency to be softer than steel that is rolled or shaped thinner, and have a tendency to cool fast. Usually, with most metals, the faster it cools coming from a molten state, the stronger and tougher they tend to be. However, if they are cooled too fast and not tempered (re-heated to remove brittleness), they have a tendency to crack more easily. I use to be a welder for many years, and there are a ton of tricks to dealing with different metals...very fascinating field for someone who likes that sort of thing.