232 



STRENGTH OF MATKKIALS 



COMPOSITION AND TENSILE STRENGTH OF CAST 

 WATERTOWN AK-I \\i. REPORT, 1895 



Carbon occurs a> fmnf.ined carbon or as graphit'f /</////*/<. (\\u\- 

 bined carbon makes the metal bard, brittle, white, weak in tension, and 

 strong in compression, whereas graphitic carbon makes tin- iron soft, 

 gray, and weak in both tension and compression. (Jraphitie carbon 

 occurs in the metal as a foreign substance, which probably accounts 

 for its weakening effect. Silicon in cast iron up to 0.5 per cent in- 

 creases its compressive strength. The tensile strength is increased up 

 to 2 per cent. Manganese as it usually occurs is not injurious Mow 

 1 per cent. When more is present the shrinkage, hardness, and brittle- 

 ness are rapidly increased. Phosphorus makes the iron weaker and 

 less stiff, becoming a serious impurity when it occurs in juair 

 above 1.5 per cent. Sulphur causes whiteness, brittleness, hard- 

 and greater shrinkage, and is, in general, a very objectionable impurity. 



Cast iron has an average tensile strength of 22,500 lb./in. 2 , the 

 range being from 13,000 lb./in. 2 to 35,000 lb./in. 2 . Its compressive 



