Tougher valve seats use two hard particles but no cobalt

Japanese researchers have produced a new material for internal combustion engine valve seats inserts (VSI) of cobalt, and which is more environmentally friendly, and cheaper. Nissan Motor Co. and Hitachi Powdered Metals have developed and used a high-speed steel based sintered material for exhaust VSI which is both cobalt and lead free. A new exhaust VSI fulfill the needs such as sufficient wear resistance in conventional engines, cobalt and lead free, good machinability characteristics and reduced production costs. To obtain a sufficient adhesive resistance, it is necessary to select a matrix and hard particles with superior strength and hardness at high temperatures, good lubrication, and the capability to form an oxide film.