US Patent 7628870 Heat treated valve guide and method of making

A valve guide of alloyed gray cast iron comprising from about 3 to about 3.5 wt. % carbon, about 0.2 wt. % phosphorous maximum, from about 0.35 to about 0.75 wt. % molybdenum, from about 1.8 to about 3 wt. % silicon, from about 0.6 to about 1 wt. % manganese, from about 0.8 to about 1.5 wt. % chromium, balance essentially iron, is heat treated by austenitizing, quenching, and tempering, to obtain a Rockwell C hardness from about 35 to about 45. The microstructure comprises at least about 3% intercellular carbide in a matrix of tempered martensite. Such valve guide exhibits improved wear resistance during use in an internal combustion engine.