A consortium led by Fraunhofer IWU has unveiled a nitrided stainless steel brake disc that the project team says cuts wear by more than 85 percent compared to gray cast iron and offers a projected service life of up to 300,000 kilometers (186,000 miles). The disc, developed with TU Chemnitz, ElringKlinger AG, and ANDRITZ AWEBA GmbH, is designed to meet upcoming Euro 7 limits on brake particulate emissions. Full details are available in the Fraunhofer IWU project announcement.
Highlights
- Nitrided stainless steel disc paired with inorganic friction material reduces wear by more than 85% versus gray cast iron with organic linings
- Projected service life of up to 300,000 km, with a set of four discs up to 5 kg lighter than cast iron equivalents
- System passed SAE J2522 (AK Master) testing on the inertia dynamometer at TU Chemnitz
- Project funded under the “Ufo-Brems” program by the German Federal Ministry for Economic Affairs and Energy
Why Nitrided Stainless Steel
The project team selected nitrided stainless steel for its tribological and thermal properties, citing prior experience with stainless steel discs on motorcycles. According to the consortium, structural steel discs lose dimensional stability above 650°C, where phase transformations can also degrade material properties. Carbon-ceramic discs remain limited to high-end vehicles by cost, and laser cladding of gray cast iron is not yet ready for series production.
The disc is produced through forming rather than casting. The project team built the discs with a slightly larger diameter than conventional gray cast iron units to provide adequate surface area for braking force, which in turn allows the disc thickness to be reduced. The starting material is supplied in square format, generating cutting scrap that the team notes can be remelted.
Weight, Range, and Vehicle Dynamics
A set of four stainless steel discs can be up to 5 kg lighter than comparable gray cast iron discs, depending on the vehicle. The reduction lowers both overall vehicle mass and unsprung mass, which the consortium says improves suspension response and vertical dynamics.
For battery-electric vehicles in particular, lower unsprung mass translates to reduced energy consumption. The system also addresses a known issue in EVs: corrosion of underused gray cast iron discs caused by regenerative braking, which Hagman Media has covered in prior reporting on Euro 7 surface treatments.
Euro 7 Compliance and Cost Balance
The Euro 7 standard takes effect at the end of 2026 for newly type-approved vehicles and at the end of 2027 for all newly registered passenger cars and light commercial vehicles. It sets brake particulate (PM10) limits of 3 mg/km for battery-electric vehicles and 7 mg/km for other powertrains in the M1 and N1 categories.
The consortium states that conventional brake systems generally fail to meet these limits even when paired with high-quality pads. The cost case for the new disc, the team argues, extends beyond regulatory compliance: gray cast iron discs typically require replacement well before 300,000 km, often after fewer than 40,000 km in conditions involving road salt, short trips, or aggressive driving, with labor costs accounting for the largest share of replacement expense.
Test Results
The disc has been tested on the inertia dynamometer at TU Chemnitz and passed the SAE J2522 (AK Master) standard. The system, consisting of the stainless steel disc paired with an inorganic friction material, showed approximately 85 percent less wear than solutions currently on the market, according to the project team.
ElringKlinger AG contributed coating technology and metal-processing expertise. ANDRITZ AWEBA GmbH handled tooling for the forming, cutting, and die-casting processes. The Chair of Vehicle System Design at TU Chemnitz provided testing infrastructure and was responsible for disc design. Fraunhofer IWU led the finite element simulation and the experimental implementation of the forming stages. The “Ufo-Brems” project was coordinated by Projektträger Jülich.
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