Surface hardening is a process whereby the metallic structure in the outer layer of a component is changed by heating and quenching, to improve properties in only a selected area of the component. For instance, the bearing track only in a bearing element, the gear tooth only on a gear, the slideway surface only on a guideway, or the cam track area only of a cam. It is neither a coating process nor a finishing process, i.e. it does not add any further elements to the material or lay on different materials. The process is highly energy efficient, since heat is applied only to those areas requiring improved properties and not to the whole bulk of the component. Many engineering components can fulfil their desired functions satisfactorily, without a particularly high core strength in the material - providing that the surface under load is adequate. Examples of such components include steel wheels on railway rolling stock, or on pleasure park and fairground rides. The process is also highly regarded in the mining and quarrying industries, where abrasive materials in the working environment cause excessive wear.
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