MOST metals, when subjected to cold work, undergo plastic deformation. The grains of metals which have been so strained show a tendency to grow. This tendency toward grain growth is nearly always augmented by an elevation in temperature. Such grain growth is usually attended by an equiaxing of grain structure and by certain other well-known physical changes. Some metals, for example, low carbon steel and aluminum, when subjected to a relatively small strain, undergo such internal changes that upon heating within a certain temperature range a rapid and large grain growth results. Metals so strained are described as critically strained, and the change of grain size is described as exaggerated grain growth.
The amount of cold work necessary to produce this particular degree of strain is often applied in manufacturing processes, such as in cold rolling and in stamping and drawing operations. The presence of critical strain frequently proves troublesome in that annealing subsequent to this cold work often may be carried on only at temperatures at which exaggerated grain growth does not occur, if an undesirable structure is to be avoided. Thus automobile-body sheet steel, after cold rolling, is frequently annealed in boxes to relieve the hardness produced by cold rolling without at the same time destroying the surface. The temperatures used are in the range at which many strained steels show exaggerated grain growth. It was with the object of learning whether this unfavorable condition might be avoided that this investigation was undertaken.
The phenomena of grain growth have been extensively described by many investigators. To attempt even a brief summary here would require too great space. We shall therefore concern ourselves principally with exaggerated grain growth in this paper. In 1912, Sauveur 1 noted that a low annealing temperature (65 ยฐo C.) caused the development of a coarse crystalline * Address delivered Friday, September 19, 1924, on the occasion of the cdebration of the centenary of the founding of The Franklin Institute.
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