Camshaft

A ductile cast iron camshaft made according to the process of:

• casting into an elongated shaft a cast iron composition comprising by weight percent:
• 3.40-3.90 carbon
• 1.90-2.70 silicon
• 0-1.40 manganese
• 0-1.5 molybdenum
• 0-0.8 phosphorous
• 0-2.0 copper
• balance iron
• said elongated shaft having a plurality of eccentric lobes spaced therealong;
• selectively heating at least some of the lobes in non-austempered condition to a temperature in the range of 1450.degree. F. to 2100.degree. F. to austenitize only surface portions of said lobes while maintaining the remainder of said shaft in non-austempered condition.
• quenching the heated lobes rapidly to a bainite transformation temperature to essentially prevent the formation of pearlite in the heated lobe portions;
• holding the quenched lobe portions at the bainite transformation temperature for a time sufficient to transform at least a substantial portion of the austenite into bainite while avoiding the formation of pearlite;
• cooling the quenched lobe portions to room temperature to further transform some of the remaining austenite to bainite or martensite;
• wherein the camshafts have selectively hardened lobes which have a microstructure comprising by volume 25% to 75% bainite, 5% to 50% martensite, 5% to 50% unreacted low-carbon austenite, approximately 10% graphite nodules, and less than 1% cementite.