Evaluation of P/M ferritic stainless steel alloys for automotive exhaust applications

The acceptance and incorporation of stainless steel exhaust systems by North American automotive companies presents a significant opportunity to the powder metallurgy (P/M) industry. Several exhaust components, including coupling flanges and hot exhaust gas oxygen sensor (HEGOS) bosses, are excellent candidate applications for P/M partsmakers to manufacture. However, in order to capitalize on this business opportunity, the establishment of valid mechanical property and wear data on the selected P/M alloys is necessary. Automotive design engineers need to have access to such information in order to make responsible material, design, and sourcing decisions. This study represents a concerted effort by a part fabricator, a powder supplier, and an academic institution to pool resources, knowledge, and assets in order to develop a set of meaningful data that, together with other recently published, related information, provides sufficient property and performance results on ferritic P/M stainless steels to the design engineer. The data generated in this study focuses on two commercially available grades - 434L and 409Cb - processed to high densities via conventional and elevated sintering temperatures in hydrogen. The resultant properties of these grades are reported, compared to a stamped, wrought `equivalent' 409 material, and analyzed in consideration of known performance requirements and other expectations. Among the test results discussed are specimen density, as-sintered composition, microstructure, weldability, ambient and elevated temperature tensile properties, as well as an evaluation of corrosion resistance.