03 



Si 







556 C. H. Mathewson — Metallographic Description 



these incipient effects are completely masked by the primary 

 casting structure, e. g., fig. 47, magnified 12 X- At ordinary 

 magnifications, both effects may usually be seen, e. g., fig. 91, 

 magnified 72 X> while, at the higher magnifications, the finer 

 detail of recrystallization is very apparent, e. g., fig. 48, and 

 fig. 92, both magnified 220 X- 



A number of the structural changes resulting from thermal 

 and mechanical treatment of a chill-cast bronze containing 94 

 per cent copper are illustrated by the six photo-micrographs 



Fig. 7. 



40 

 30 





92%Cu 





























































94-%Cu 































96%Cu 





















































































































i 

































Time in hours I 



Growth of grain on annealing after 25$ reduction by cold-rolling. 

 Annealing temperature 625°. 



assembled on p. 603. Fig. 30 shows the cast structure of this 

 bronze magnified 10 X after a contrasty etching with ferric 

 chloride. A hole was drilled in the lower part of the specimen as 

 shown. The photo-micrograph represents the upper portion of a 

 transverse section through the small bar and, accordingly, the 

 extension of the grains at right angles to the upper cooling 

 surface can be plainly seen along with the grouping of small 

 grains in the vicinity of this surface. The internal structure 

 of the grains can also be seen. We may call particular atten- 

 tion to the small grain section with striations inclined at an 

 angle of about 45° to the horizontal which is enclosed within a 

 larger grain with vertical striations near the upper right-hand 

 corner of the photo-micrograph. The next figure, numbered 



