Steel and Iron 441 



in structure. It is not malleable, but hard and brittle, easily 

 broken by a sharp blow. It contains on the average about 93 

 per cent iron, 4 per cent carbon, and 3 per cent of other sub- 

 stances, chiefly silicon, manganese, phosphorus, and sulfur. It 

 melts at about 1200 F., and expands as it cools. Because of 

 these properties, pig iron (Fig. 144) is generally utilized in three 

 ways : (1) for iron castings ; (2) for making steel ; and (3) for 

 making wrought iron. These three uses of pig iron will be 

 considered in order. 



Iron castings. About one sixth of the pig iron produced is 

 used in foundries. In the foundry the pig iron is remelted and 

 converted into such castings as are desired for machinery, 

 agricultural implements, for car, locomotive, and railroad cast- 

 ings, for stove, range, and furnace castings, for soil and water 

 pipe, pipe fittings, and valves, for structural purposes, for 

 ornamental and many other purposes which cannot be 

 enumerated here. But all such castings are hard, brittle, and 

 comparatively easily broken, chiefly because of the impurities in 

 the iron. The phosphorus is especially objectionable as it 

 renders cold iron in any form very brittle. 



To remove some of these impurities pig iron may be remelted 

 and some of the impurities burned out. It is thus converted 

 into malleable cast iron, a semi-purified product, containing less 

 silicon, manganese, phosphorus and sulfur than pig iron. It is 

 used in similar ways and for purposes similar to those of pig 

 iron, but the castings are hard, stronger, and less brittle. 

 They have three to four times the tensile strength, about 

 35,000 to 50,000 pounds to the square inch, and about the same 

 transverse strength, as the ordinary cast iron castings. 



IV. STEEL 



The use of cast iron and malleable cast iron is rapidly de- 

 creasing in manufacturing and construction. These products 

 of iron contain impurities that make them useless for very many 

 purposes to which they formerly seemed well adapted. They 



