Steel and Iron 449 



V. WROUGHT IRON 



The third way in which a small fraction, less than three per 

 cent, of the total output of pig iron is utilized, is by its conver- 

 sion in the puddling mill into wrought iron. Wrought iron is 

 useful in blacksmith work. A small amount of it is used in the 

 manufacture of crucible or cast steel (page 446). Because of 

 its electrical conductivity and magnetic capacity, it is valuable 

 as wire for such electrical communication as the telegraph, and 

 as material for the cores of electromagnets and for the armatures 

 of dynamos. 



Wrought iron differs from low-carbon or soft steel in that it 

 contains at least one per cent of slag. It has been described as 

 a bundle of fibers with each fiber enveloped in slag. The slag 

 and the purity of the iron are supposed to give wrought iron 

 its chief value. It is nearly pure iron, never containing more 

 than one tenth per cent each of carbon and phosphorus. But 

 steel of the best quality contains less phosphorus. 



Wrought iron melts at about 1700 F., but when heated red 

 hot, becomes so plastic that it may be converted into any desired 

 form. When it is cooled suddenly, it does not, like steel, be- 

 come hard and brittle. It is generally tough, strong, and 

 elastic. When red hot it is easily welded. 



Wrought iron is produced from pig iron in a puddling furnace. 

 The pig iron is melted, then while maintained at a somewhat 

 lower temperature, is constantly agitated. Nearly all the 

 impurities are thus oxidized and removed. As the iron becomes 

 pure, it grows stiff and pasty. This is because the melting 

 point of pure iron is higher than that of iron with its usual 

 impurities. The pasty mass of iron is called " iron that has 

 come to nature." The mass is divided into several parts, each 

 of which is then rolled into a somewhat spherical form. Each 

 mass is squeezed by a special machine into a smaller and 

 somewhat cylindrical shape, weighing perhaps one hundred 

 seventy-five pounds. By the squeezing, some of the slag or 

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