CHAPTER X 

 THE TIN BRONZES 



Tin bronzes are alloys of tin and copper. The com- 

 mercial wrought bronzes do not usually contain in excess 

 of 10 per cent of tin. In the casting of these alloj^s it is 

 common practice to add from 0.03 to 0.40 per cent of 

 phosphorus as a deoxidizer in order that sound, dense 

 castings maj^ be secured. Because of the use of this 

 deoxidant, the tin bronzes are known commercially as 

 "phosphor bronzes." 



The tin bronzes when in the completely homogenized 

 condition are single-phase alloys having a structure 

 similar to alpha brass. As the tin increases above 5 per 

 cent, it becomes increasingly difficult to cast tin bronzes 

 that are free of inverse segregation. Inverse segregation 

 in tin bronzes has been identified as a tin-rich, lower 

 melting-point phase and is known as "delta." Unless 

 extreme care is taken during melting and casting to keep 

 reducing gases from the molten metal, inverse segregation 

 will occur. In fact, the amount of delta produced in the 

 tin bronzes during solidification is directly proportional 

 to the amount of gas retained. 



The two most common types of tin bronzes are those 

 containing 5 and 8 per cent of tin. These alloys have 



excellent cold-working properties. Tin bronzes are not 

 considered hot-working alloys since they are only 

 slightly hot plastic within a very narrow temperature 

 range 1150° to 1225°F. 



The phosphor bronzes have corrosion-resisting proper- 

 ties comparable to those of copper. In addition, they 

 possess higher tensile properties than copper in combina- 

 tion with good resistance to fatigue. 



Phosphor bronzes of the Grades A (5 per cent tin), 

 C (8 per cent tin), and D (10 per cent tin) are used 

 extensively- in the form of welding wire for carbon-arc 

 and gas welding of many of the non-ferrous alloys and 

 the brazing of cast iron. 



Grades A and C phosphor bronzes are used iu the 

 manufacture of springs, diaphragms, contact points, and 

 other application requiring good resistance to corrosion 

 and fatigue in combination with high-tensile properties. 

 The physical and general mechanical properties of 

 Grades A and C and other phosphor bronzes may be 

 found in Tables 1 to 10 on pages 266 to 283. Charts 1 to 

 77 on pages 267 to 290 give more detailed data. 



TABLE 1 

 GRADE A— 5 PER CENT PHOSPHOR BRONZE 



General Data — Stkip" 

 Copper, 95.72%; tin, 4.09%; phosphorus, 0.035%, 



Property 



Tensile strength, p.s.i. (000 omitted) 



Elongation, % in. 2 in 



Apparent elastic limit, p.s.i. (000 omitted) 



Yield strength, 0.5% extension, p.s.i. (000 omitted) 



Yield strength, 0.2%, offset, p.s.i. (000 omitted) 



Yield strength, 0.1%, offset, p.s.i. (000 omitted) 



Rockwell hardness F, Jfe-m- ball, 60-kg. load 



Rockwell hardness B, He-m- hall, 100-kg. load 



Rockwell hardness G, /le-in- ball, 150-kg. load 



Rockwell hardness 15-T, } iQ-m. ball, 15-kg. load 



Rockwell hardness 30-T, 3i6-in. ball, 30-kg. load 



Endurance limit (at 10* reversals):' 



Soft, p.s.i. (000 omitted) 



4 B. & S. Nos., hard, p.s.i. (000 omitted) 



8 B. & S. Nos., hard, p.s.i. (000 omitted) 



Young's modulus of elasticity, p.s.i 



Melting point, °F 



Density, lb. per cu. in 



Coefficient of expansion, per °C. from 25-300°C 



Electrical conductivity, <«« % I.A.C.S. at 68°F 



Thermal conductivity, <*'> B.t.u. per sq. ft. per ft. per hr. per °F., 68°F 



<» All tests conducted on 0.040~in. stock. 



* 6 B. & S. Nos., hard, 0.070-0.015 mm. grain,size at ready-to-finish, respectively. 



* Refer to llOO^F. anneal (1 hr. at temperature). 



Hard" 



Soft' 



