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T wo series oJ Fc-O.OI, 0 .03, and O.l o~Al alloys that contain O.OJ 5% N and eitlzer 0 .0 1 or 0 . 02~~ C were used to stud), tlze states oj AIN p recipitates and tlzeir effects on tlze yield poin t oj a -iron. R esults obtained were as fo llows.(1) AIN p recip itates tlze most in tlze temperature range between 80 0° and 900°C during isotlzermal aJter solution treatment.(2 ) Carbon content affects tlze total amount, slzap e, size, and dispersion of AIN precipitates.(3 ) Variation oj yield point is weU exjJlained by tlze individual con tributions of p recip itated AIN and dissolved nitrogen . Fe-A I-O.OJ % N aUoys with aluminullZ contents vGlying from 0 .005 to jO ~ led to the Jollowing conclusions. I nvestigation on ductili!)' and work hardening oj extra low carbon(4) T he behavior of dissolved nitrogen as revealed by internal friction s!lggests that the reversion oj A IN /Jreci/Jitation occurs.(5) I n the same hea t treat ment that w ill cause tlze intergranular brittle Jracture . ductility call be im/Jroved by fixing more nitrogen . I n tlze ductile state, on the other hand, the contribution of A IN jJrecipitates to duc tility is the greater, the smaUer tlzeir effect on hardening.(6) OJ the Jactors that influence work Izardening the grain size is tlze main; nitrogen in solution orfine AIN particles increase tlze work Izardening rate, w hereas grown jJrecipitates and quenched-in dislocations decrease it.

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