Brake discs are subject to various types of punishments, ranging from wear to enduring harsh environmental conditions, releasing non-exhaust emissions that contribute to traffic pollution and make it difficult to comply with stricter environmental standards. Therefore, with the upcoming Euro 7 regulations, the automotive industry will need to find cost-effective solutions to reduce emissions from the braking systems of both, internal combustion engine vehicles (ICEVs) and electric vehicles (EVs). EVs and ICEVs differ significantly in their braking systems. Conventional vehicles primarily use friction braking, in which kinetic energy is converted into heat by brake discs and pads. In contrast, EVs use regenerative braking to convert kinetic energy into electrical energy, which is then used to charge the batteries. Until the batteries are fully charged, EVs rely almost exclusively on recuperation up to speeds of about 20 km/h and use friction braking only to bring the vehicle to a complete stop. This reduces the frequency of friction brake use. Since cast iron (GCI) rotors are susceptible to corrosion, they will rust if not used. In GCI rotors that have not been treated to resist corrosion, the corrosion goes inside the rotor, damaging the surface and penetrating deeper. When braking, the rust is removed and with it some of the surrounding material. This results in a higher mass loss compared to a non-corroded GCI rotor and effects such as pedal pulsation. Thus, the reduction in particulate mass (PM) comes mainly from reduced brake use, and the brakes can survive these conditions with less corrosion without being de-rusted by brake use. This problem can be effectively addressed by using a ferritic nitrocarburizing (FNC) in conjunction with specific oxidation, resulting in rotors that experience less corrosion overall and only on the surface. To further improve the corrosion resistance of FNC rotors, Nitrex R&D has developed an advanced nitrocarburizing technology using a dual heat treatment process that combines nitrocarburizing with in-process intelligent post-oxidation. The result of this new approach has led to a remarkable increase in corrosion resistance. The treated rotors can be exposed to salt spray for up to 120 hours without corrosion. This is a significant improvement over the FNC-treated rotors, which can only be exposed to salt spray for less than 20 hours.
Dr. Saadia Nousir, R&D Process Technology Manager, Nitrex Metal Inc.; Mr. Karl-Michael Winter, Vice President R&D and Engineering Management, Nitrex Metal Inc.