Patent ID: 7497915

Claim:
A machinable austempered cast iron article, said article made by the steps of: austenitizing an iron composition having a substantially pearlitic microstructure in an intercritical temperature range of from 1380° F. to 1500° F. for a period of at least 10 minutes to produce a ferritic plus austenitic microstructure; quenching the ferritic plus austenitic microstructure at a rate sufficient to prevent the formation of pearlite; austempering said ferritic plus austenitic microstructure in an austempering temperature range of from 575° F. to 750° F. for a period of at least 8 minutes to produce a microstructure of a continuous matrix of equiaxed ferrite with islands of austenite; and cooling said microstructure of said continuous matrix of equiaxed ferrite with islands of austenite to ambient temperature to produce said machinable austempered cast iron article having improved strength, machinability, ductility, fatigue performance, and resistance to environmental cracking.