RECRYSTALLIZATION IN OXIDE-DISPERSION STRENGTHENED MECHANICALLY ALLOYED SHEET STEEL

Systematic annealing at temperatures between 1300 degrees C and 1380 d egrees C was applied to sheets of INCOLOY MA-956, an oxide-dispersion strengthened (ODS), mechanically alloyed, iron-base steel containing ( in mass percent) 20.8Cr, 5.0Al, 0.5Y(2)O(3), and 0.5Ti. The billets, c omprised of hot isostatically pressed (''hipped''), mechanically alloy ed powder, were hot- and cold-rolled to produce a 0.5-mm-thick sheet w ith a strong (100)[110] deformation texture. Light and transmission el ectron microscopy established that recrystallization initiated by nucl eation at the sheet centerline. Initial rapid growth of the centerline -nucleated grains, designated stage I, resulted in plate-shaped grains oriented parallel to the rolling plane at the sheet centerline. Subse quent growth, designated stage II, was developed by planar growth fron ts through the sheet thickness at a slower rate. The final product was a very coarse grain structure, sometimes with only a single grain thr ough the sheet thickness. The recrystallization kinetics were typified by an incubation time, a temperature dependance; characterized by an activation energy of 506 kJ/mole, and a decreasing rate of boundary mi gration with increasing time at temperature. The microstructural evolu tion is discussed in terms of the influences of deformation texture, r esidual stress, dislocation substructure, and oxide dispersion on the recrystallization process.