SEDL / STP / STP520-EB / STP38842S

High-Temperature Fatigue Testing of Automotive Valve Steels

Vitcha, ET
Manager, Materials Engineering Laboratory, TRW Valve Division, TRW Inc., Cleveland, Ohio

Pages: 11    Published: Jan 1973

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Abstract

The elevated temperature bending fatigue strength of seven automotive exhaust valve alloys has been determined. Inconel 751 shows the highest fatigue strength of 45 ksi at 10⁸ cycles 760 C (1400 F). Coatings in air atmosphere at elevated temperature generally reduced the fatigue strength. In corrosive atmospheres consisting of a simulated lead oxide environment or a carbon monoxide/carbon dioxide atmosphere, no protection was afforded by coatings of aluminum or aluminum chromium. Within the varying surface roughness tested only the as-forged surface representing a high surface roughness and decarburization showed a drop of 24 percent in fatigue strength. Compressively stressed Stellite 6 faced valves showed ten times improvement in thermal fatigue life.