Effect of large-strain deformation by equal channel angular pressing on the microstructure of a martensitic age hardenable steel, namely 18 Ni (3 0 0) maraging steel, was studied by means of transmission electron microscopy. Equal channel angular pressing was carried out on the solution-annealed steel up to four passes at room temperature through the route Bc using a die with an inner angle of 90°. It was found that the initial martensitic structure of the solution-annealed steel evolves to a heterogeneously deformed structure consisting of ultrafine grains and lamellar dislocation cell blocks. Selected-area electron diffraction patterns revealed large orientation spread within the deformed structure. High density of dislocations and elastic lattice distortions were found in the deformed and aged microstructures.
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