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
includes austenitizing an iron composition having a substantially
pearlitic microstructure in an intercritical temperature range of between
1380.degree. F. and 1500.degree. F. This produces a ferritic plus
austenitic microstructure. The ferritic plus austenitic microstructure is
quenched into an austempering temperature range of between 575.degree. F.
and 750.degree. F. within 3 minutes to prevent formation of pearlite. The
ferritic plus austenitic microstructure is then austempered in the
austempering temperature range of between 575.degree. F. and 750.degree.
F. to produce a microstructure of a continuous matrix of equiaxed ferrite
with islands of austenite. Finally, the microstructure of the continuous
matrix of equiaxed ferrite with islands of austenite is cooled to ambient
temperature to produce the machinable austempered cast iron article.