Over 2% carbon is cast iron while steel typically is in the .1 to .5 range, but can get up to that 2% line. Wrought iron is roughly .08 and under. I’m not sure of how wide the buffer zone is where one starts to become the other

Think of steel as a mud pie. The iron is the dirt and the carbon is the water. Too much dirt and it won’t clump together, too much water and it will fall apart but if you can get the mixture just right it will be able hold its shape much much better than either of the other two scenarios

Edit: it will be easier to fall apart on either side without the precise ratio