Steering Gear Component - Quench Cracks

A critical steel component in a passenger car steering system broke in the field. The component was manufactured from cold drawn, medium carbon steel and induction hardened for wear resistance. The cracking was present on the induction hardened surfaces. Fractographic (visual and scanning electron microscopy) and metallurgical examination indicated the component was cracked prior to assembly and the crack was due to excessively high cooling rate during the quenching operation (quench cracks).

Investigation of the quench medium indicated that the polymer concentration was below the recommended concentration. This insufficient polymer concentration had an adverse effect on the cooling rate of the quench medium. The polymer concentration was inadequate because the measuring system to determine the polymer concentration, which is used throughout the industry, was not well understood by the supplier. Training was given to the inspectors and a secondary measurement system was implemented.

Skill set needed to analyze problem : Failure analysis of heat treated steels and knowledge of induction hardening and quenching system.

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