抄録
The reversion process of martensite (α') to austenite (γ) was investigated using 15.62%Cr-9.83%Ni(16-10) and 17.62%Cr-8.78%Ni(18-9) steels with metastable austenitic structure by means of transmission electron microscopy and magnetic analysis. The steels used almost transform to lath α' from γ by 90% cold rolling, and reverse to γ again by the following annealing at temperature above about 900 K. But, the reversion processes are greatly different in the two steels. The difference is clear for 923 K isothermal annealing after 90% cold rolling. The results are as follows :
(1) For 16-10 steel, α' reverses to γ during heating up to 923 K by a martensitic shear transformation.The γ structure contains high density of dislocations and traces of α' block which was induced by cold rolling. During annealing at 923 K, the reversed γ is refined to 0.5 μm in grain size by a recovery process, that is, the formation of dislocation cells and subgrains.
(2) For 18-9 steel, α' reverses to γ during annealing at 923K by a diffusional nucleation-growth process.
(3) The reversion process of α' to γ is greatly dependent on the composition of steels and annealing temperature. The increase in Cr content and the decrease in Ni content lead to the increase in martensitic shear transformation temperature, resulting in an occurrence of a diffusional nucleation-growth process.
