Wear Mechanism Analysis of Engine Exhaust Valve Seats with a Laboratory Simulator

Abstract

Engine valve seat wear affects engine performance. A common goal for both valve and engine manufacturers is to improve both valve quality and life. By performing tests on a simulator which is verified to be capable of simulating an engine operating environment, the wear resistance of various valve materials is ranked, and the wear mechanisms are investigated. Four commonly used exhaust valve materials, 23–8N, 21–4N Mod, Pyromet 31 and Stellite 6 (hardfacing), were tested with insert material made of Sil XB at an operating temperature of 538° C. Tests run for three million cycles showed that Pyromet 31 had the lowest wear rate and 21-4N Mod had the highest. Then, three valve materials, 23-8N, 21-4N Mod and Pyromet 31, were tested with insert material made of Eatonite 6 at an operating temperature of 649° C. These tests gave the same ranking as those tested with the Sil XB inserts. However, all three valve materials in the second group showed much less wear than those in the first group. The valve seat wear mechanisms were found to be a complex combination of abrasive wear, adhesive wear/material transfer, plastic deformation and oxidation. Based on analysis of the test specimens by scanning electron microscopy and energy dispersive X-ray, the degree to which these mechanisms appeared varied with different materials. Some ways to make valve materials more wear resistant to these mechanisms would be to select more compatible valve and insert materials and to improve the operating environment. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995