Patent ID: 7070666
Filing Date: 2006-07-04
Classification: C21D,C22C

Abstract:
1. A method of making a machinable austempered cast iron article from an iron composition having a substantially pearlitic microstructure that includes carbon, silicon, nickel, copper, and molybdenum, said method comprising the steps of: austenitizing the 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 formation of pearlite; austempering the 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 the microstructure of the continuous matrix of equiaxed ferrite with islands of austenite to ambient temperature to produce the machinable austempered cast iron article having improved strength, ductility, machinability, fatigue performance, and resistance to environmental cracking.