Reversion Mechanism from Deformation Induced Martensite to Austenite in Metastable Austenitic Stainless Steels.

Abstract

Reversion mechanismfrom deformation induced martensite (o() to austenite (y) has been investigated in two metastable austenitic stainless steels, 15.6/*Cr-9.8"/Ni ( the 16Cr-10Ni) and 17,6/Cr-8.8/Ni (the 18Cr-9Ni) steels, by means of magnetic analysis and transmission electron microscopy. Metastable y almost completely transforms to lath a:' by 90"/ cold rolling, and the c( again reverts to */ during annealing at temperatures above 700 K, Deformation induced c( in the 1 6Cr-1 ONi steei undergoes a martensitic shear reversion during heating to 923K annealing, while that in the 18Cr-9Ni steel does a diffusional nucleation-growth reversion on 923 K annealing. Grain refining processes are greatly influenced depending on the reversion mechanism, Martensitically reversed y has a high density of dislocations immediately after the reversion and the y grains are refined through recovery and recrystallization process just like that taking place in a deformed y. On the other hand, diffusionally reversed y is characterized by the nucieation of equiaxed y grains within the c(' matrix and the y grains gradually grow during annealing.