High Carbon steel refers to a steel with a high carbon content generally accepted as being above 0.55%. This allows the steel to be heat treated in a way that dramatically hardens the metal and improves edge retention and overall resilience. Anything 0.96% or over is considered to be very high in its carbon content and although useable for making knives, is simply too brittle for using as a good sword metal. 1060 is a good example of a mid range carbon steel. 1045 falls too far short and is classed as a medium carbon steel. Spring steels fall into this category too.