Case-hardened gear

High speeds require relatively lightweight gear elements. All case-hardening procedures produce distortion—to keep this distortion to a minimum, nitriding is the preferred hardening method. This method is employed after all machinery operations are complete and no further corrections are to be made to the tooth geometry. 

Figure 3. Residual stresses in automotive steel crown gears (a) net-shaped and submitted to nitrocarburation surface treatment machined by standard technology and submitted to (b) multi-frequency induction tempering, (c) quenching and nitriding, (d) case-hardening.

Figure 83. Finish machining a case-hardened automotive gear with DBC50.

Case-hardened steel gears are used m automobile transmissions, similar to the one shown in the photograph directly below the gear. 

D4 The wear resistance of a steel gear is to be improved by hardening its surface, as described in Design Example 5.1. However, in this case, the initial carbon content of the steel is 0.15 wt%, and a carbon content of 0.75 wt% is to be established at a position 0.65 mm below the surface. Furthermore, the surface concentration is to be maintained constant, but may be varied between 1.2 and 1.4 wt% C. Specify an appropriate heat treatment in terms of surface carbon concentration and time, and for a temperature between lOOO C and 1200 C. 

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