form optimum conditions of deeper case depths and therefore performance of the part in industry. This method is applied particularly to steels with low case hardenability, such as the seat of the valve. The process applied is initially carburizing to the required case depth (up to 2.5 mm) at around 900-955°C, and then carbonitriding to achieve required carbonitrided case depth. The parts are then oil quenched, and the resulting part has a harder case than possibly achieved for carburization, and the addition of the carbonitrided layer increases the residual compressive stresses in the case such that the contact fatigue resistance and strength gradient are both increased. Studies are showing that carbonitriding improves corrosion resistance. Applications Typical applications for case hardening are gear teeth, cams, shafts, bearings, fasteners, pins, hydraulic piston rods, automotive clutch plates, tools, dies and tillage tools. See also Differential hardening Nitridization Quench polish quench Surface engineering References Metal heat treatments ru:Нитроцементация сталей