ABSTRACT
The selection of the gear material and its heat treatment is the most basic decision in the design process. The strongest and most durable gear meshes are made up of two surface-hardened gears using the carburizing process. Utilization of surface-hardened gears will result in minimum gearbox size, creating savings in materials, machining, and handling costs. Another common material combination is a surface-hardened pinion meshing with a through-hardened gear. The American Iron and Steel Institute or Society of Automotive Engineers numbers designate steel composition and alloy type. An alloy steel is chosen on the basis of mechanical properties required in the part and the heat treatment available to develop these properties. The maximum hardness that any steel can attain after quenching is a function of its carbon content. In the carburizing process carbon is diffused into surface of the teeth by controlled exposure at temperatures of 1650°F or above for the length of time necessary to achieve the desired case depth.
