The carbon steels are subdivided into low, medium, and high grades based on the percentage of carbon they contain. High carbon steels contain greater amounts of carbon, and are, therefore, the hardest. However, low carbon steels have the advantage of being more ductile. Medium carbon steels, which are usually 0.2 to 0.49 percent carbon, can be heat treated to have a good blend of the favorable qualities of both and are popular for their combination of strength and ductility.