Modified austempering effect on fracture toughness J(IC) of Fe-0.6C-1.5Si-0.8Mn steel

The effect of the modified austemper coupled with interrupted quenching (IQ Aus) on the fracture toughness,. J(IC), of Fe-0.6C-1.5Si-0.8Mn steel has b een studied to determine the validity of using IQ Aus steel in possible env ironmentally conscious material applications. The J(IC) of the steel can be significantly improved by IS Aus; conventional austenitization at 1173 K f ollowed by interrupted quenching at 533 K and then austempering at 673 K fo r a required time followed by subsequent water quenching and 473 K temperin g. The IQ Aus steel had a triple structure with a carbide-free upper bainit e, 26 vol.% retained austenite and 10 vol.% tempered martensite. Compared t o the conventional austemper and quench and temper, the IQ Aus had an incre ased J(IC) at increased strength and ductility levels. These results are de scribed and the modified austempering effect on fracture toughness, J(IC), is discussed.