Low carbon steel has low hardness, good ductility, easy to produce built-up edge, and the workpiece surface is easy to be rough. Increasing carbon content can improve machinability, increase hardness, and reduce ductility. -Low carbon steel: Carbon content is between 0.05%-0.2% Commonly used to manufacture fasteners, gears, cams, etc. Can be surface hardened Usually hardness is 90-130HB Easy to have problems of continuous chips and sticky chips -Medium carbon steel Carbon content is between 0.25%-0.45% Commonly used for gears, shafts, etc. Not prone to problems -High carbon steel Carbon content is above 0.5% Commonly used for springs, fixtures, spindles, train wheels, etc. Tools are easy to wear