The uses for medium-carbon steel are defined by the requirement for a high tensile strength and ductility that, despite its brittleness when compared to other forms of steel, make it the preferred choice. Between 0.3 and 0.7 percent carbon is added during the manufacturing process to create a medium or mid-range steel product. This specific range of carbon is combined with a process of quenching (i.e., cooling the steel from the outer surface to the inner) and tempering to create a structure that has a consistent tensile strength (referred to as Martensite) throughout the body.
Shafts and Gearing
Axle shafts, crankshafts and gearing plates are all made from medium-carbon steel. The ductility of the steel allows it to be formed into thin shafts or toothed plates without losing any of its tensile strength.
The ductility of the medium-carbon steel allows it to be shaped into plates for boilers and other tanks that have highly pressurized contents. Medium-carbon steel cannot be used for pressurized tank systems that contain cold liquids or gasses because the Martensite structure of the steel makes it brittle and susceptible to cold cracking. Stainless steel or other high carbon steels are used for those types of applications.
Railway wheels, rails and other steel parts associated with the suspension of rail cars are made of medium-carbon steel. The high tensile strength is necessary to withstand the changing force of the rail cars on the rails.
Structural steel beams, joiner plates and other shapes associated with building require a high tensile strength to resist the torque and pressure of buildings and bridges. Special care must be taken to properly insulate the steel to prevent it from being affected by extremes of heat and cold, which can change the Martensite structure and lessen its structural integrity.