Exhaust Valve Materials for Internal-Combustion Engines

Exhaust valve performance and exhaust valve materials in gasoline engines have been recognized as a serious limitation to engine development since about 1910. There is good reason to believe that exhaust valve behavior was limiting engine performance even prior to 1910. With the best of current exhaust valve materials and designs, exhaust valve behavior is today only a minor limitation to engine performance and development. However, in some cases cost precludes the use of such materials or designs. Exhaust valves operate at elevated temperatures, usually in the range of about 1200 to 1400 F., but parts of the valve may in some cases reach 1600 F. and more. It is obvious that an exhaust valve material should possess, at operating temperature, a maximum of strength, of resistance to stretching, and of chemical inertness to oxygen and other constituents of the combustible charge prior to and after burning. Hardness of the material at operating temperature has recently been recognized as an additional desirable property, in order to avoid pounding, pitting, etc., of the portion of the valve which makes contact with the seat in the cylinder. A number of additional properties are now recognized as desirable or necessary attributes of an outstanding exhaust valve material, as will be pointed out later.