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Article by NITREX
In the world of automotive engineering, optimizing brake rotor performance is crucial for vehicle safety and efficiency. Advanced technologies such as ferritic nitrocarburizing and post-oxidation treatments play a key role in enhancing brake rotors, improving their corrosion resistance, wear resistance, and overall durability.
This article is the first in a two-part series that delves into the critical aspects of brake rotor technology. Part 1 focuses on design and manufacturing, addressing how these surface hardening processes impact rotor performance. Part 2 will explore the metallurgical aspects of brake rotors, including the effects of various heat treatments and surface layers, as well as the practical applications and real-world performance of brake rotors.
The questions discussed in this article are drawn from a webinar on Ferritic Nitrocarburizing technology for greener brake rotors, which you can view here. Through this discussion, we aim to provide valuable insights into the practical benefits and considerations of nitrocarburizing and oxidation treatments, helping manufacturers and engineers optimize brake rotor technology to meet both performance and regulatory standards.
1. Is Post-Oxidation Requested/Required by OEMs? Is Ferritic Nitrocarburizing (FNC) Enough for Fulfilling Euro 7 Regulations?
Post-oxidation is a process requested by some OEMs but not universally required. It enhances braking performance by improving corrosion resistance. While ferritic nitrocarburizing alone offers a slight improvement in corrosion resistance compared to untreated gray cast iron rotors, combining ferritic nitrocarburizing with controlled post-oxidation proves to be far more effective. This dual treatment forms a highly corrosion-resistant magnetite phase layer, offering superior protection against rust. Together, these processes provide a robust solution for corrosion resistance and hardness, with the potential to meet Euro 7 regulations. However, their effectiveness can vary depending on vehicle use conditions, driving habits, surrounding environment, types of pads used, and so on. The combination of ferritic nitrocarburizing and post-oxidation offers a balanced approach, effectively addressing both performance and regulatory requirements.
2. Why is Post-Oxidation Beneficial?
Post-oxidation primarily enhances corrosion resistance. The process involves creating an oxide layer, typically composed of magnetite—a compact and stable form of iron oxide. Although this oxide layer is usually thin (1-3 microns), it effectively protects the rotor against corrosion, especially in non-braking areas. After several driving cycles, the thin oxide layer wears off due to contact and friction. However, it remains intact and continuous to offer corrosion protection in non-braking area of the rotor.
3. How Durable Are Brake Rotors After Ferritic Nitrocarburizing?
The durability of brake rotors treated with ferritic nitrocarburizing depends significantly on the type of brake pads used. Consequently, a well-selected brake pad formulation can make a big difference. Non-asbestos organic, low-metallic, and semi-metallic brake pads generally offer better heat dissipation and can extend the service life of ferritic nitrocarburized treated rotors. Braking conditions that generate excessive heat can also impact the longevity of both the ferritic nitrocarburizing process and the rotors themselves. While ferritic nitrocarburizing enhances the fatigue, wear, and corrosion resistance of rotors, its effectiveness can be influenced by external factors.
4. Does Smart ONC® and Ferritic Nitrocarburizing Work for All Brake Applications?
Smart ONC® with Ferritic Nitrocarburizing is not universally applicable across all brake applications. It is particularly effective with brake systems using NAO and low-metallic pads, which benefit from its heat-dissipating properties and enhanced service life. This technology is also well-suited for ceramic brake pads, as it provides protection for non-friction surfaces such as the hat, edges and ventilated areas from corrosion. Furthermore, many electric vehicles successfully use nitrocarburized rotors on their rear wheels, demonstrating the adaptability of this technology across diverse applications.
5. How Does the Application of Smart ONC® Technology Differ Between Passenger Vehicles and Heavy-Duty Trucks?
The application of Smart ONC® technology does not differ between passenger vehicles and heavy-duty trucks. Both types of vehicles benefit from the combination of Smart ONC® and Ferritic Nitrocarburizing processes. This uniform approach ensures that the technology’s benefits—such as improved surface hardness and corrosion resistance—are applied consistently, regardless of the vehicle type.
6. Is It Recommended to Deburr the Brake Rotor After Ferritic Nitrocarburizing Due to the Higher Surface Roughness?
In general, deburring is applied to remove burrs from metal parts, reducing the risk of corrosion and enhancing durability. In the case of ferritic nitrocarburizing or ferritic-nitrocarburizing-post oxidation treatments, deburring is unnecessary. Typically, applying ferritic nitrocarburizing to the surface of a metal increases both hardness and roughness. This roughness, however, can be managed through careful control of the nitriding process parameters and the rotor’s initial surface finish.
Bloc wear test results show that the increased roughness observed on the ferritic nitrocarburized or ferritic-nitrocarburized-post oxidized grey cast iron brake rotor diminishes after few braking cycles. The high roughness facilitates in depositing a transfer film from friction material onto the friction surfaces. This transfer film helps improve braking performance and contributes to the longevity of the rotors.
This discussion highlights the complexities involved in designing and manufacturing brake rotors, revealing the impact of heat treatments on their performance and durability. By examining the effects of ferritic nitrocarburizing and post-oxidation processes, we gain valuable insights into how these treatments enhance corrosion resistance, wear resistance, and overall rotor longevity. As technology continues to advance, staying informed about these treatments will be essential for achieving superior braking performance and ensuring compliance with evolving industry standards and environmental requirements.
About NITREX
NITREX is a Novacap portfolio company and the leading global provider of fully integrated heat-treating solutions and technologies. Our portfolio is built on proven science and technology to enhance material strength and optimize performance.
Learn more at www.nitrex.com.
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