Abstract
Effect of molybdenum on the behavior of reversion of deformation induced martensite to austenite and the mechanical properties of specimens containing reversed austenite were investigated within (15.5 13)% Cr-11%Ni-(02.5)%Mo steels by means of transmission electron microscopy, magnetic analysis and tensile testing. Reversion treatment of martensite to austenite was performed at a higher heating rate using a salt bath and at lower heating rate using an electric furnace. The results obtained are as follows.
(1) The steels used almost transform to lath martensite ( a') from austenite (γ) by 90% cold rolling at 290 K. Effect of molybdenum on y stability against deformation is almost same as that of chromium.
(2) The temperature range for reversion rises with increasing molybdenum content.
(3) In case of 923 K annealing at a higher heating rate, a process of reversion is changed from a martensitic type to a diffusional one with increasing molybdenum content. A 13%Cr-11%Ni-2.5%Mo steel which reverts to γ by a diffusional process has an ultra fine austenitic structure with a mean grain size of 0.2 μm giving a high 0.2% proof stress of 0.8 GPa, tensile strength of 1.0 GPa, and elongation of 30%.
(4) In case of 923 K annealing at a lower heating rate, a' reverts to γ by a diffusional process at lower heating temperatures. Therefore, molybdnum content of 0.5% is enough to obtain a high strergth steel.
