Cost Reduction Processes for Transfer Case Sprockets: Part 1: Metallurgical Aspects

Transfer case sprockets usually require quenching to improve hardness and mechanical properties. This additional process step can be avoided with sinter hardening. Indeed, sinter hardening allows the production of P/M parts with high strength and apparent hardness directly from sintering because the martensitic transformation takes place during the cooling portion of the sintering operation. Therefore, this process eliminates the need for a post-sintering heat treatment with all the inherent related problems such as part distortion, oil contamination and added processing costs. Many low alloy steel powders have been developed for sinter hardening applications. These materials, combined with the availability of sintering furnaces equipped with enhanced cooling capacity, make sinter hardening particularly attractive for parts that are difficult to quench because of their size and shape. Moreover, the powder mix formulation and processing conditions can be tailored to achieve a specific microstructure.

The objective of this paper is to review the metallurgical aspects involved in sinter hardening and to relate these to the characteristics of the base powder, admixed additions and processing conditions in order to develop appropriate mix formulations for the production of transfer case sprockets.