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The performance of stainless steel (SS) powder metallurgy (P/M) materials in automotive exhaust system applications continues to be a subject of interest. Reported within are results of several investigations into the properties of several P/M stainless steel alloys at elevated temperatures. Elevated temperature tensile testing was conducted to determine the strength of P/M alloys at exhaust system operating conditions. Cyclical elevated temperature corrosion/oxidation/quench testing was also conducted to determine corrosion/oxidation performance of various alloys in exhaust system environments. Both 300 and 400 series alloys, as well as some specially modified and specially processed alloys, were subjected to the above tests. Various processing parameters were used to illustrate the dramatic effects of processing on material performance. Recommendations are provided for alloy selection and alloy properties in exhaust system applications.

The performance of stainless steel(SS) powder metallurgy (P/M) materials in elevated temperature applications has become a subject of interest with P/M now being considered for automotive exhaust type applications. This study will outline the results of an investigation into the properties of several P/M stainless steel materials at elevated temperatures and relate these P/M materials to ingot metallurgy counterparts. Recommendations on the manufacturing of stainless steel P/M exhaust system components will also be presented.

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.