Hydrogen Embrittlement in Galvanized High Carbon Steel Components of Automotive Seat Slider Assembly

This research paper investigates the failure of an isolator clip used in the seat slider assembly, which guides and restricts the sliding motion of the tooth bracket within the seat. The component is made of C80 high-carbon spring steel, known for its high strength. According to the manufacturing process details, zinc plating was applied to the component for corrosion protection, as confirmed by EDS analysis. A fractographic examination of the failed part revealed a brittle, intergranular fracture morphology with visible cracks. Certain areas also exhibited micro-void coalescence, indicating a dimpled fracture surface. The primary failure mode was intergranular (IG) fracture. The delayed fracture was attributed to intergranular fracture mechanisms, micro-void coalescence, and the high strength of the steel, which made the component susceptible to hydrogen embrittlement. Hydrogen embrittlement occurs when hydrogen atoms become trapped along the grain boundaries, where they form hydrogen molecules, leading to crack initiation. Hydrogen embrittlement also impacts on mechanical properties by reducing ductility and increasing brittleness. This suggests that hydrogen absorption likely took place either during the pickling process before galvanization or during the galvanizing process itself. During zinc plating, the electrochemical reaction (H₂ → 2H⁺ + 2e⁻) generates cathodic hydrogen on the surface, ultimately causing hydrogen embrittlement and leading to the sudden and unexpected isolator clip failure under stress. To prevent such failures, a post-fabrication heat treatment (baking) at 200-300°C for a few hours was recommended to remove absorbed hydrogen from the material. Following the implementation of this measure, no further failures of the isolator clip have been reported.