CHAPTER VIII 

 THE SILICON BRONZES 



The silicon bronzes are essentially alloys of copper 

 and silicon containing usually from 0.25 to 1.25 per cent 

 of one of the four elements: tin, manganese, zinc, iron. 



These alloys were introduced in the United States 

 about 1925, and since that time their use has increased 

 continuously. There are many silicon bronzes in com- 

 mercial use, differing one from the other primarily in 

 the silicon content and nature of the third constituent. 



Within the past several years there has been a com- 

 mercial division of the silicon bronzes into two general 

 types, which are known as Grades A and B. 



The Grade A silicon bronzes are those containing the 

 maximum of silicon and of the third constituent and 

 are used in those applications which require the highest 

 tensile properties in combination with a i-esistance to 



Grade A silicon bronze work-hardens much more 

 rapidly than Grade B silicon bronze. As a consequence 

 it is possible to attain tensile properties greatly in excess 

 of those attainable with Grade B. This latter grade 

 has cold-working and work-hardening properties similar 

 to 70-30 brass, which is one of the most ductile and 

 malleable of the brasses. 



Annealing in both grades is carried out within the 

 temperature range of 700 to 1400°F., depending upon 

 the degree of anneal required. When annealing is 

 carried out under oxidizing atmospheres, the scale 

 formed on the silicon bronzes is very refractory and 

 difficult to remove by ordinary cleaning methods. A 

 cleaning solution of 10% H2SO4 + 20% HNO3 -|- 5% 

 HF, balance water, has been found effective. 



TABLE 1 

 COMMERCIAL SILICON BRONZES' 



corrosion equal to or better than that of copper. These 

 Grade A alloys possess welding characteristics similar 

 to those of the mild steels. 



Grade B silicon bronzes are those which contain 

 smaller amounts of silicon and of the third constituent 

 and are characterized by unusually good cold-working 

 properties in combination with tensile properties com- 

 parable to 70-30 brass, corrosion resistance similar 

 to that of copper, and welding properties only slightly 

 inferior to the Grade A alloys. 



Both grades of silicon bronzes have excellent hot- 

 working properties and can be readily rolled, forged, 

 and extruded. As in the case of copper and copper-rich 

 brasses, lead must be controlled to trace amounts in 

 order to avoid cracking in hot forging or hot rolling. 



Grade A silicon bronzes are most commonly used in 

 the form of sheet, strip, plate, and rod for the construc- 

 tion of welded tanks, range boilers, chemical equipment, 

 and the like. Since ease of welding in combination with 

 the strength of mild steel and the corrosion resistance of 

 copper is the important specific property of these alloys, 

 detailed recommended practice is given on page 250. 



Grade B silicon bronzes are used almost exclusive^ 

 for the manufacture of products requiring excellent 

 cold-working properties in their manufacture. Cold- 

 headed bolts, nuts, screws, lag bolts, and similar items 

 annually account for the consumption of large quantities 

 of these materials. 



The physical and mechanical properties of competitive 

 grades of silicon bronzes are essentially the same. 



