ANISOTROPIC AND HETEROGENEOUS NUCLEATION DURING GAMMA TO ALPHA TRANSFORMATION IN IRON

An (001)[uvw] texture was observed in iron sheet after annealing in a hydrogen atmosphere in the gamma region and slowly cooling through the phase change. This oriented structure resulted from the gamma to alpha transformation and not normal grain growth in the alpha region because the alpha grains contained a substructure. Subsequently, the selective driving force was found to reside at the annealing atmosphere-metal interface and to be dependent on the sulfur concentration in the annealing atmosphere. The selective driving force was hypothesized to be an anisotropy of surface energy effected by selective absorption of an element like sulfur on the (001). The anisotropy of surface energy was found to produce (001)[uvw] by effecting preferred nucleation at the atmosphere-metal interface. A spherical cap model and several assumptions were used to estimate the anisotropy of surface energy required to effect (001)[uvw]. © 1968.