A MACHINABLE AUSTEMPERED CAST IRON ARTICLE HAVING IMPROVED MACHINABILITY, FATIGUE PERFORMANCE, AND RESISTANCE TO ENVIRONMENTAL CRACKING AND A METHOD OF MAKING THE SAME

摘要

A machinable austempered cast iron article has improved strength,machinability, fatigue performance, and resistance to environmental cracking.A method of making the machinable austempered cast iron article includesaustenitizing an iron composition having a substantially pearliticmicrostructure in an intercritical temperature range of between 1380~F and1500 ~F. This produces a ferritic plus austenitic microstructure. The ferriticplus austenitic microstructure is quenched into an austempering temperaturerange of between 575 ~F and 750 ~F within 3 minutes to prevent formation ofpearlite. The ferritic plus austenitic microstructure is then austempered inthe austempering temperature range of between 575 ~F and 750 ~F to produce amicrostructure of a continuous matrix of equiaxed ferrite with islands ofaustenite. Finally, the microstructure of the continuous matrix of equiaxedferrite with islands of austenite is cooled to ambient temperature to producethe machinable austempered cast iron article.