Abstract
Structural changes occurring during the annealing of nitrided Fe-Ti alloys have been investigated by transmission. electron microscopy, by electron diffraction, and by X-ray diffractometry. Extremely high values of hardness (1300 HV) are obtained in nitrided Fe–3%Ti alloys; this is associated with tetragonal distortion of the ferrite lattice by nitrogen and coherency between the matrix and thin plates on {100}α planes. On annealing at 850° C, softening occurs and TiN plates were identified lying on {100}α at planes with a Bain orientation relationship with the matrix. Although detailed electron-diffraction analysis has been carried out, it is not possible to be certain that the plates formed on nitriding are very thin TiN precipitates or GP zones, since both structures could account for the diffuse streaks in 〈100〉α directions on diffraction patterns. Discussion of the possible strengthening mechanisms shows that the hardness data from the alloys studied are consistent with predictions made by a chemical strengthening mechanism.
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