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Spatially Optimized Diffusion Alloys: A Novel Multi-Layered Steel Material for Exhaust Applications
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
A novel Spatially Optimized Diffusion Alloy (SODA) material has been developed and applied to exhaust systems, a very aggressive environment with high temperatures and loads, as well as excessive corrosion. Traditional stainless steels disperse chromium homogeneously throughout the material, with varying amounts ranging from 11% to 18% dependent upon its grade (e.g. 409, 436, 439, and 441). SODA steels, however, offer layered concentrations of chromium, enabling an increased amount along the outer surface for much needed corrosion resistance and aesthetics. This outer layer, approximately 70µm thick, exceeds 20% of chromium concentration locally, but is only 3% in bulk, offering selective placement of the chromium to minimize its overall usage. And, since this layer is metallurgically bonded, it cannot delaminate or separate from its core, enabling durable protection throughout manufacturing processes and full useful life. The core material may be of various grades, however, so this study employs interstitial free steel (low carbon), which offers not only commercial advantages, but also eases manufacturing operations, as it is more formable than stainless steel grades. The material and its manufacturing process is described, including characterization measurements comparing its forming and corrosion resistance response to baseline exhaust materials. Rolled, stamped, and spun mufflers are manufactured with high-volume manufacturing equipment and processes without incident, demonstrating the ease of material substitution versus aluminized 409 (409AL). Each application is exposed to various test conditions, including fatigue, corrosion, and thermal cycling, and compared against baseline materials. Results overall demonstrate favorable performance, even along exposed and welded edges, which may be further protected locally with cold spray. SODA offers unique value in performance versus baseline materials, enabling a competitive alternative with much less chromium, significantly reducing surcharge dependencies, as well as associated commercial uncertainty and risk.