554 C. H. Mathewson — Metallographic Description 



what different form, in that the percentage of coarse fragments 

 will very likely exceed the percentage of fine fragments. This 

 condition is represented by the curves, T 6 T 8 , T 7 T 9 , and T 8 T 9 . 

 Moreover, none of the fragments are likely to be very small 

 and, hence, recrystallization will not start until moderately 

 high temperatures have been attained. Recrystallization accord- 

 ing to the curve T 6 T 8 starts at T 6 , but is confined to small 

 portions of the mass until the temperature rises well towards T 8 . 

 At the latter temperature, the entire alloy is recrystallized. 

 According to the curve T 8 T 9 the extremely light deformation 

 indicated has left 50 per cent of the original T 9 grain unaltered, 

 while the remainder has been broken down sufficiently to cause 

 recrystallization at T 8 , a temperature not greatly below the 

 original annealing temperature. At T 9 , the metal has assumed 

 its original grain characteristics and growth will continue 

 normally as the temperature is further elevated. The curve 

 T 7 T 9 represents an intermediate condition which may easily 

 be interpreted. 



In cases of very light deformation, recrystallization cannot be 

 detected under the microscope, since the recrystallized grains 

 are not greatly inferior in size to the original grains. In this 

 connection, it should be noted that a section through the con- 

 glomerate shows large and small grain sections whatever the 

 true size of grain, since a grain may be cut at any point 

 according to its position with regard to the cutting plane. 

 This renders it difficult to detect recrystallization except where 

 the new grains are considerably smaller than the original grains 

 and are sufficiently numerous to form groups of characteristic 

 appearance. 



The curves of fragmental resolution are purely hypothetical 

 and only represent in a general way what seem to be predomi- 

 nant characteristics of the ordinary deformational processes. 

 The precise form of any curve will be determined by the 

 nature and intensity of the deformation sustained by the metal. 



It is clear from the discussion thus far that the form of the 

 curve of fragmental resolution determines the form of curves 

 representing the cumulative percentage of metal recrystallized 

 as a function of the temperature. Without seeking to estab- 

 lish the exact relationship between these curves, it may be 

 assumed that they are substantially identical in form, the 

 former representing an obscure condition and the latter a 

 visible effect. By careful counting under suitably chosen 

 magnification, the approximate form of some of these curves 



