Recovery in 15%Cr Ferritic Stainless Steel after Large Strain Deformation
15%Cr ferritic stainless steel was machined in rectangular samples and then processed by multiple forging to a total cumulative strain of 7.2 at an ambient temperature. The large strain deformation resulted in almost equiaxed submicrocrystalline structure with a mean grain/subgrain size of 230 nm and about 2.2×1014 m-2 dislocation density in grain/subgrain interiors. The annealing at a relatively low temperature of 500oC did not lead to any discontinuous recrystallizations. The grain/subgrain size and the interior dislocation density slightly changed to 240 nm and 2.1×1014 m-2, respectively, after annealing for 30 min, while the Vickers hardness decreased from 3140 MPa in the as-processed state to 2900 MPa. This annealing softening was attributed to remarkable release (by 50%) of internal stresses, which are associated with a non-equilibrium character of strain-induced grain/subgrain boundaries.
S.-J.L. Kang, M.Y. Huh, N.M. Hwang, H. Homma, K. Ushioda and Y. Ikuhara
A. Belyakov et al., "Recovery in 15%Cr Ferritic Stainless Steel after Large Strain Deformation", Materials Science Forum, Vols. 558-559, pp. 119-124, 2007