Development of Co-free exhaust valve seat insert for automotive engines

Sintered materials have been widely used for valve seat insert(VSI)for automotive engines. They have possessed high flexibility in their alloying design to increase their performance in heat and wear resistance in comparison with that of conventional wrought steel and cast alloys. Especially several high cobalt containing sintered materials are used as exhaust valve seat insert materials because of their high wear and heat resistant properties. Recently, the circumstance of exhaust valve seat inserts has become severe due to the fact that A/F ratio(Air/fuel ratio) of recent engines is set to be leaner than that of conventional engines. This trend has the aim to reduce exhaust gases and fuel consumption. On the other hands, the reduction use of high environmental burden materials such as cobalt has also continually become important. And cobalt is expensive, reduce cobalt content is good for economy of these materials. This paper reports the development and the application detail of cobalt-free, lead-free and environmentally friendly exhaust valve seat insert.