Very high carbon steel (0.96 to 2.11%) is hard and not very ductile (difficult to mold or shape). It is also difficult to weld, but has the lowest melting point.
As the carbon content is reduced, the steel becomes softer, more ductile and melts at a higher temperature.
Stainless steel is an alloy of Iron, Carbon, Chromium. The fourth element would depend upon the grade of steel, but Nickel is probably the most common.