544: G. H. Mathewson — Metallo graphic Description 



beta to separate again and a subsequent slow cooling will again 

 develop tbe brittle delta. Alloys containing up to 12 or 13 

 per cent tin may be made very malleable by such treatment. 

 Shepherd and Upton's high values of elongation (1. c, p. 510) 

 are readily explainable upon this basis. 



Malleability in the cast condition is highly dependent upon 

 the quantity and distribution of the alpha-4-delta eutectoid. 

 The principal constituent of this eutectoid, delta, is specifically 

 brittle. A cast bronze with 10 per cent tin will ordinarily 

 contain several per cent of this constituent, but it will not be 

 sufficiently abundant to form a destructive network around the 

 alpha grains and the material may still be worked effectively. 

 With 13 per cent of tin, the metal may usually be worked 

 if handled with care and annealed frequently at low red heat. 

 Such annealing causes gradual absorption of the brittle constit- 

 uent with continual improvement in malleability. The small 

 object, ~No. 2, Table I, illustrated in fig. 10, contains a little 

 over 13 per cent tin and was hammered into the shape of a 

 spatula or spoon at one end. In order to test the cold mal- 

 leability of the metal in its present condition, the end was 

 cut off and a new spatula-tip formed by hammering. This was 

 accomplished without fracture. The grain characteristics of 

 the metal show that light annealing treatment was used to 

 facilitate working. Neither this nor any other specimen 

 examined was quenched after annealing, since no beta struc- 

 ture was observed, while the eutectoid structure was recognized 

 in a number of cases. The unaltered cast structure of this 

 specimen is shown in fig. 41. Aside from the black dendritic 

 cores, a lighter sharply-defined and angular structure-element 

 may be seen within the white matrix of tin-rich alpha. This 

 is the eutectoid constituent which is represented under higher 

 power in fig. 43 on the same page. In quantity, it falls a 

 little short of that required to form a continuous membrane 

 around the casting grains. The structure in this vicinity does 

 not indicate very favorable working properties. 



As previously stated, the highly worked bronzes of the col- 

 lection contain moderate percentages of tin, i. e., less than 10, 

 and, in most cases, only 4 to 6. While such alloys contain a 

 little of the eutectoid constituent in the original cast condition, 

 this is rapidly absorbed on annealing, e. g., in a few minutes 

 at red heat, and the metal is easy to work without any anneal- 

 ing treatment. Finished objects were, as a rule, almost entirely 

 homogeneous and hammer-hardened. It seems fairly obvious 



