766 BELL SYSTEM TECHNICAL JOURNAL 



by two tests employing two different pairs of radius blocks to deter- 

 mine the number of bends for this predetermined ratio by interpolation. 

 The ratio finally selected as most representative was 8 to 1. Figure 5 

 gives the bend test results for alloy G brass. 



The bend test reveals the ductility and toughness of the metal 

 under test. It should show a close correlation to the forming and 

 drawing properties of sheet metal. Further studies will be required 

 to work out such relationships. 



Grain Count: 



A series of photomicrographs of annealed brass has been adopted 

 covering the grain sizes 0.010 to 0.200 mm. diameter of average grain.^ 

 Inasmuch as the alpha phase grain structure of nickel silver is sim- 

 ilar to that of brass, one set of standards may be employed for these 

 metals. Those standards were carefully counted by the Jeffries 

 method as described in the note to Section 9 of the A. S. T. M. 

 Standard Rules Governing the Preparation of Micrographs of Metals 

 and Alloys (E 2-27) ^ and were photographed at a magnification 

 of 75 diameters. The grain size of a specimen under examination 

 is estimated by comparing the specimen with the standard photo- 

 micrographs. For alloy A nickel silver, a magnification of 150 is 

 employed because of the smaller grain size of this material compared 

 with brass. The limits of diameter of average grain of the alloys 

 used for drawing purposes are given in Table IV, namely for high 

 brass sheet, alloys C, D, and E brass, and alloy A nickel silver. 

 (See Table VI for chemical composition.) The grain size limits are 

 based on the range of commercial annealing practice. Inasmuch as 

 these annealed materials are employed only for drawing purposes, no 

 tensile strength limits are necessary. Maximum Rockwell hardness 

 limits are given to exclude cold-worked metal. 



Determination of Limits 



High and Clock Brass: 



Three separate rolling series were used for the round-robin hard- 

 ness tests. The first of these consisted of a group of materials so 

 arranged as to give a complete range of the hardnesses desired. The 

 second was high brass with a nominal composition of 65 per cent 

 copper and 35 per cent zinc. The third was nickel silver with a 

 nominal composition of 64 per cent copper, 18 per cent zinc, and 18 



» Report of Committee E-4 on Metallography, presented before the American 

 Society for Testing Materials in June, 1929. 



9 1927 Book of A. S. T. M. Standards, Part I, p. 778. 



