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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.

Powder metal (P/M) 400 series stainless steel exhaust components (flanges and oxygen sensor bosses) are being increasingly used in US made automobiles. These components are shown to have superior leak-tightness and resistance to corrosion and oxidation, when compared to wrought stainless steel exhaust components. This paper compares the yield, tensile, impact, and fatigue strengths of two popular exhaust component materials, namely 409LE and 409LNi (a nickel-modified version of 409L), in the as-sintered condition. Data presented are based on samples sintered in 100% hydrogen using a commercial sintering practice, exhibiting sintered densities in the range of 7.2 to 7.3 g/cm3. Fatigue strengths were determined using the rotating beam test method, per MPIF Standard 56.

The use of P/M stainless steel components in automotive exhaust systems continues to grow rapidly. These P/M components have met the stringent requirements demanded for these applications which were formerly only provided by wrought materials. These high density components are being required to pass specific qualification tests designed by OEM's and Tier 1's - Galling, Hot Vibration Leak and High Temperature Oxidation/Corrosion Tests. This paper discusses the performance of P/M stainless steel exhaust flanges and HEGO bosses in a number of OEM and Tier 1 specified performance tests.

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.

Powder Metallurgy (P/M) offers a cost-effective and design-friendly option for the manufacture of stainless steel hot exhaust gas oxygen sensor (HEGO) bosses for automotive exhaust systems. The critical requirements for this application include high temperature mechanical strength, good corrosion resistance, weldability, machine-ability for thread tapping, and resistance to thread galling when exposed to temperatures as high as 1000°C (1832°F). Optimally processed P/M 400-series stainless steel oxygen sensor (HEGO) bosses meet these critical requirements, and are comparable to those made from wrought stainless steel, either cold headed or machined.