The Tin Brasses 



133 



so that the delta or eutectoid phase, which may be pro- 

 duced during solidification of the casting, may be 

 absorbed. The presence of this phase produces "hot 

 shortness" and causes cracking. 



In Table 4 on page 144 are given the important 

 physical properties and general mechanical properties 

 of admiralty-metal tube, sheet, and strip. 



Fig. 1. — Hot-rolled Roman-bronze shafting rod (longitudinal section). 

 Etchant NHiOH -|- H2O2. 75 X 



Naval brass is a generic term for those alloys contain- 

 ing 60 per cent of copper, 1 per cent of tin, and 39 per 

 cent of zinc. When prepared from materials of especially 

 high purity and fabricated by hot rolling rather than 

 extrusion, an increase in resistance to corrosion fatigue 

 is effected, and the alloy is ordinarily offered under 

 various trade names, the best known of which are Tobin 

 bronze, Roman bronze, and Chamet bronze. 



In apphcations involving resistance to corrosion 

 fatigue, such as marine shafting, it has been established 

 that hot-rolled non-ferrous metals have a much higher 

 endurance limit in fatigue than the same alloys produced 

 by the extrusion process. Hot rolling produces a fine- 

 grained uniform structure, while the extruded structure 

 tends to be coarse and non-uniform. Figures 1 and 2 

 show typical structures of hot-rolled Roman Bronze rod 

 and extruded naval brass. 



These hot-rolled bronzes are widely used for marine 

 shafting and similar applications where good resistance to 

 fatigue is required and naval brass for those applica- 

 tions where comparable corrosion resistance and struc-: 

 tural strength are necessary but where resistance to 

 fatigue is not a vital factor. Naval brass is extensively 

 used in the manufacture of heat exchangers for tube 

 sheets and plates. 



It is common commercial practice to add lead to the 

 naval brasses to improve their machinability. The 

 amount of lead added is dependent upon the nature of 

 the intended application and the amount of machining 

 involved. There are two general types of leaded naval 



brass: a low-leaded and a high-leaded. The low-leaded 

 has improved machinability over plain naval brass and 

 is ductile enough to withstand light cold heading and 

 upsetting operations. The high-leaded alloy is designed 

 primarily for high-speed machining and is not suitable 

 for bending or upsetting operations Its machinability 

 compares favorably with fiee-cuttmg brass 



m 





VW^ 



Fig. 2. — Extruded naval-brass rod (longitudinal section). Etchant 

 NH4OH + H2O2. 75 X 



When naval brass is intended for cold heading or 

 upsetting operations as in the manufacture of bolts and 

 nuts, it is customary to increase its copper content 

 moderately. 



7^1 the tin brasses in the naval-brass range with the 

 exception of the leaded alloys have excellent hot-working 

 as well as reasonably good cold-working properties. 

 They can be fabricated by hot rolling, hot forging, and 

 extrusion. Those naval brasses containing lead are not 

 commercially hot-rollable although they can be hot- 

 extruded without any difficulty. Hot working is best 

 accomplished within the temperature range of 1250 to 

 1400°F. 



Tables 6 to 10 on pages 152 to 165 give detailed data 

 on the effect of cold working and annealing of the naval 

 brasses. 



"Manganese bronze" is an alloy of the Muntz-metal 

 type modified with tin, iron, and manganese in which 

 manganese is of minor importance. This alloy possesses 

 the highest mechanical properties of all the brasses and 

 at the same time has almost as good resistance to salt- 

 water corrosion as have the naval brasses. It is largely 

 used in the form of rod and finds extensive application 

 in the marine field as shafting, hardware, bolts, and tie 

 rods. Its hot-working properties are similar to those of 

 the naval brasses. Because of its lower copper content 

 it is not ordinarily processed or fabricated by cold work- 

 ing. Table 11 lists the more important physical and 

 mechanical properties. For greater detail see Charts 

 106 to 127 on pages 168 to 174. 



