Browse Publications Technical Papers 2024-01-3031
2024-09-08

Niobium Alloyed Ferritic Nitrocarburized Brake Rotors 2024-01-3031

Brake rotor wear durability and resistance to dust generation are under increasing demands to meet proposed environmental requirements. Improved rotor output, or the ability to turn kinetic energy into heat are driving more aggressive friction materials that increase wear of the brake rotor. Regenerative braking systems have unique challenges in corrosion cleanability that require aggressive friction materials in combination with good corrosion performance. Grey cast iron remains the material of choice for brake rotors due to the advantages of near net shape capability, good thermal conductivity, and low cost. Niobium (Nb) alloyed Grey cast iron in combination with Ferritic Nitrocarburize (FNC) case hardening heat treatment is proposed to improve wear resistance and reduce brake dust generation of brake rotors. Niobium additions in cast iron were shown in prior investigations to reduce the eutectic cell size and refine the pearlite matrix. Reduced eutectic cell size and refinement of the pearlite matrix improves the strength of Grey cast iron. FNC is a commonly specified process for Grey cast iron brake rotors to improve the corrosion resistance and reduce pedal pulsation. Combining the Niobium carbides into the FNC case hardened zone can improve wear resistance. Standard Eutectic and Hypereutectic Grey irons alloyed with Niobium were evaluated in comparison to baseline unalloyed compositions. Brake speed snub sensitivity tribological testing was performed on a matrix including Niobium alloyed, Unalloyed, FNC, Non FNC, Non-Asbestos Organic (NAO) friction and Low metallic (Low Met) friction materials. Full size brake rotors were evaluated by Block Wear and Corrosion Cleanability. Improved wear, corrosion resistance and reduced brake dust debris were demonstrated by the Niobium alloyed FNC brake rotor combinations. Corrosion is an important consideration when evaluating brake performance. Combining cyclic corrosion and brake rotor testing provides the best comparison with field exposure.

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