552 C. H. M athew son— Metallo graphic Description 



In order that the annealing effect may be felt at a given 

 temperature, it is clear that the mechanical destruction of the 

 original grain must have been sufficiently pronounced to pro- 

 duce fragments inferior in size to the recrystallized grain 

 characteristic of this temperature. Thus, if the T 9 grain 

 previously cited is to recrystallize at T 5 it must have been 

 artificially reduced by deformation to a point where the grain 

 size characteristic of T 5 can develop. In general, the grain 

 fragments produced by deformational processes will vary 

 widely in size, so that certain of them will be able to coalesce 

 below T 5 , while others will remain unaffected at this tempera- 

 ture. The particular factors which apply in any given 

 deformational process will combine to determine a curve of 

 Fragmental Resolution of Grain* for this particular process in 

 which the cumulative percentage of fragments below a given 

 size appears as a function of the size of the fragments. 



The curve T 4 T 7 is a hypothetical curve of this sort and 

 signifies, in the present case, that, by deformation of the original 

 T 9 grain, approximately 65 per cent of the material has been 

 sufficiently reduced (by internal slip) to recrystallize by the 

 time the temperature T 5 is reached. At T 5 then, 65 per cent 

 of the material will have reached the mean grain size charac- 

 teristic of this temperature, while 35 per cent will remain 

 unannealed. 



Little can be said relative to the distribution of the unan- 

 nealed fragments and the recrystallized grains. In general, 

 the former occur in patches of irregular outline and, when 

 present in comparatively small amount, as in the present case, 

 cannot usually be distinguished from the latter. When present 

 in large amount, however, the patches are large, compared with 

 the size of the recrystallized grains, and often bear evidence 

 of strain. Such a condition is shown in fig. 48. Large patches 

 of metal bearing distinct lines of deformation can be seen 

 along with small recrystallized grains. 



The first formation of recrystallized grains usually occurs 

 at the boundaries of the parent grains, since, at such localities, 

 maximum inhomogeneity of the lines of force may be expected 

 and, consequently, maximum fragmental resolution of grain. 

 Initial recrystallization around the primary grains is well 



* I have introduced this phraseology to aid in defining the disintegrating 

 effect of cold-working without regard to the specific nature of the frag- 

 ments, or particles, formed. Most theories freely admit that sub-granular 

 units possessing some degree of individuality are produced during 

 permanent deformation of the metal. 



