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Ferritic stainless steel 409L and ferritic-martensitic stainless steel 409LNi, made via powder metallurgy (P/M) process, are being increasingly used for the manufacture of automotive exhaust flanges and oxygen sensor bosses. High temperature, hydrogen sintering is most commonly utilized for the manufacture of these components, with an aim to achieve a minimum sintered density of 7.25 g/cm3. Alloy 409L is a fully ferritic material, exhibiting a hardness in the range of 55 to 62 HRB. Alloy 409LNi, on the other hand, possesses a 50/50 ferritic-martensitic microstructure, and exhibits a hardness in the range of 85 to 92 HRB. Some amount of machining, such as thread cutting, drilling and turning, is often required in the processing of these components. This study evaluates the effects of adding a machinability enhancing agent, namely manganese sulfide, on the machinability, as well as on the corrosion resistance and mechanical properties of these alloys.

Powder metal (P/M) stainless steel exhaust flanges have been qualified for a number of passenger cars and trucks in recent years. These flanges are currently being produced in high volumes to supply those vehicles. The requirements for these applications will continue to change over time as federal and state governmental mandates for improved emissions become effective. Lower leak rate limits, higher engine operating temperatures, and extended service life for components, are among the consequences of the search for improved emissions. The P/M process offers a high degree of flexibility with product design and related materials development, thus being able to meet these challenges. P/M stainless steel exhaust flanges' performance can be enhanced by 1. optimal design using finite element analysis and 2. modifying alloy compositions to improve strength.