Quenched zones and material structures at gears teeth

Gears are used in most types of machinery, including the automotive industry as a wide known application. Different types of gears are specified through many (inter)national standards, mainly their geometry, design specifications or requirements while the (micro) structures of gear's teeth are less known. In diagnostics of damage or rupture, when it is happened, the microstructure undergoes to investigation but this is usually too late. From that reason the (micro)structure and hardness of gear tooth should be known in advance and here is defined. In manufacturing of a gear many methods are available rather by cutting (milling, hobbing, shaving or grinding) than forging. Those cutting methods have no great influence on the structure. If the grinding was not performed correctly than the hardened surface may be softened, even with cracks. The main influences on the structure to be obtained lie in a kind of production techniques such as: casting, forging, rolling and finely by a kind of chemical heat-treating of gear teeth surface. Here are presented typical zones and microstructures realized through the chemical heat-treating of teeth, and those should be known, especially for providing an incoming control of a gear in industrial conditions. Those data are of a crucial importance for a gear life.