Elevated Temperature Microstructural Stability of Austempered Ductile Irons

摘要

The isothermal aging of austempered ductile iron (ADI) at moderately high temperatures (200-400C) has been studied. It was shown that the mechanical and microstructural stability decreases because of the re-initiated decomposition reactions in the ausferrite. The activation energy and other kinetic param- eters for the aging reaction were determined from the.fraction transformed, as measured by non-isothermal dilatometry For the first time, it was shown that the aging reaction is complex, and at least three successive reactions occur:1) tempering of martensite and unreacted austenite,2) decomposi- tion of reacted stable austenite, and 3) coarsening of carbides during aging.