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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.

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.

Increasing efficiency of the high performance automobile engines results in higher temperatures in the valves, valve seat inserts and valve guides. This fact demands a higher heat transfer rate in order to lower these temperatures. This paper deals with new sintered materials, based on dispersion strengthened copper, used to produce valve seat inserts and valve guides with a superior thermal conductivity. In rig tests these high thermal conductivity valve seat inserts reduced the valve temperature and wear rate. These results were later confirmed in engine tests. The wear results of the copper based materials were comparable to those of the standard series of iron based materials. Initial results of rig tests on the valve guides are reported. The wear rates of the dispersion copper based materials were lower than those of the P/M iron based materials and brass.

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.