EFFECTS OF DEFORMATION ON MICROSTRUCTURE AND σ-PHASE FORMATION IN Cr_(25)Ni_(20) STAINLESS STEEL

The microstructure of Cr_(25)Ni_(20)stainless steel under plastic deformation up to 50% has re-vealed an even distributed twins,micro-twins and deformation bands.The σ-phase formationin 800℃ aged specimens is accelerated by its nucleation at either deformation twins orrecrystallized grain boundaries under less or more deformation respectively.In therecrystallized zone,the recrystallization is prior to the precipitation of σ-phase.Althoughrecrystallization may accelerate the formation of σ-phase,it is not essential.The twins andmicro-twins produced by deformation may also provide the additional nucleation sites.