A novel Spatially Optimized Diffusion Alloy (SODA) material has been developed
and applied to exhaust systems, which are an aggressive environment subject to
high temperatures and loads, as well as excessive corrosion. Traditional
stainless steels disperse chromium homogeneously throughout the material, with
varying amounts ranging from 10% to 20% dependent upon its grade (e.g. 409, 436,
439, 441, and 304). 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, typically about 70μm
thick, exceeds 20% of chromium concentration locally, but is less than 3% in
bulk, offering selective placement of the chromium to minimize its overall
usage. 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 comprised of various
grades, however, this study employs interstitial free steel (low carbon), which
eases manufacturing operations, as it is more formable than stainless steel
grades. The material and its manufacturing process are described, including
characterization measurements comparing its forming and corrosion resistance
response to baseline exhaust materials. Rolled mufflers are manufactured with
high-volume manufacturing equipment and processes without incident,
demonstrating the ease of material substitution versus aluminized 409 stainless
steel (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.
