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Requirements for automotive exhaust system components include room temperature and elevated temperature mechanical integrity, oxidation resistance, corrosion resistance, and weldability. Powder metallurgy offers sufficient flexibility with material and process selection to meet these challenges. This presentation will cover the effects of alloy composition, density, and process parameters on the performance of P/M S.S. components in O.E.M. specified thermal, mechanical, and corrosion tests.

The successful use of P/M methods for the production of sensor rings used in antilock brake systems is predicated upon the attainment of a combination of mechanical, magnetic, and corrosion resistance properties. This paper summarizes these properties for high temperature vacuum and hydrogen sintering in commercial furnaces. Properties are also compared with parts sintered at lower temperatures and the effects of repressing and annealing are included. The results are analyzed with respect to microstructure and chemical analysis.

The change from gasoline to alternate fuels such as those based on methanol, is expected to create material compatibility problems because of the enhanced reactivity of the powder metal (P/M) materials currently in use. These problems are most serious for the steels containing copper or those that have been copper infiltrated. P/M austenitic stainless steels offer the possibility of overcoming the inherent corrosion problems of the current P/M alloys. Test samples of 304L and 316L were processed on production equipment and sintered in pure hydrogen or a simulated dissociated ammonia mixture. Corrosion testing was performed in SAE-approved mixtures of “aggressive methanol” and gasoline (termed CM15A and CM85A). To accelerate the corrosion test and simulate an auto-oxidized fuel mixture, a small amount of t-Butyl Hydroperoxide was added. These preliminary tests confirm that Fe-0.8 %C and Fe-2% Cu-0.8%C steels will rust in these test fuels, within 24 hours.

Evaluation of commercial high temperature H2-sintered 410L ABS sensor rings, after use for over 10 years and/or over 100,000 miles in various automobiles and in various locations across the USA and Canada, showed only small amounts of rusting; less than which results in a 100-hour Salt Spray Test (ASTM B117); and no loss of their mechanical strength and ductility. Although sensor rings made of 434L and 434L-Modified (18 Cr, 2 Mo) show even lesser amounts of rusting and pitting, 410L sensor rings made by the above process are deemed adequate for this application. The 1000-hour Salt Spray Test is found to be much too severe for this application. A 100-hour test is considered to be more suitable in this regard.

Progress in the understanding of corrosion and corrosion resistance properties of sintered stainless steels has lead to new applications that benefit from net shape processing and more efficient material utilization. Powder Metallurgy Stainless Steels includes extensive graphics, and tabular summaries provide a comprehensive reference to obtain good corrosion resistance properties of sintered stainless steels with careful processing, starting with powder selection, avoidance of contamination, efficient delubrication, and controlled sintering and cooling. Contents cover: Metallurgy and Alloy Compositions, Manufacture and Characteristics of Stainless Steel Powders, Compacting and Shaping, Sintering and Corrosion Resistance Alloying Elements, Optimal Sintering, and Surface Modification in PM Stainless Steels Mechanical Properties, Magnetic and Physical Properties, Corrosion Testing and Performance, Secondary Operations, and Applications.