Abstract: Bainitictransformation processesin austempered ductile iron( ADI) have been discussed at presentstudy. Typicalupper bainitictransformation isconsidered as austenitetransformstobainiticferritediffussionless. When austemperingtimeisextended afterbainitictransforma tion hasceased, carbide will appear in bainitic ferritelaths. During typicallower bainitictransformation ,thefreshlyformed bainiticferriteonlypartitionssomeofitsexcesscarbonin toresidualaustenite, mostofthe restcarbon inthefreshly formed bainiticferriteisprecipi tatedin form ofcarbideatsametime. When austemperingtimeisextended,morecarbideis precipitatedin bainitic ferrite platelets. Carbide also appears atthe austenite/ferriteinter facesbecauseof retained austenite decomposition.

Key words: bainitictransformation, austempered ductileiron, carbide