What materials are commonly used for shafts and why?

Medium carbon steels (C40, C45, EN8) are most common due to good strength, machinability, and cost-effectiveness. Alloy steels (EN19, EN24, AISI 4140) are used for higher strength and fatigue resistance in critical applications like crankshafts. Stainless steel is used in corrosive environments. The choice depends on required strength, surface hardness, fatigue life, and operating conditions like temperature and corrosion.