CHAPTER XXXIII 

 THE MAKING AND WORKING OF STEEL 



455. Properties of Steel. Steel is a chemical compound 

 of iron and carbon, but contains no carbon in the free state 

 as cast iron does. Its tensile strength is greater than that 

 of wrought iron and its compressive strength greater than 

 that of cast iron. It is by far the strongest metal used in 

 the mechanical arts and its strength varies greatly with its 

 purity and the amount of carbon it contains. Steel is divided 

 into high, medium, and low grade. The high-grade steel 

 contains the most carbon, and, unlike wrought iron, is 

 fusible. Unlike cast iron, steel can be forged, and, with 

 the exception of the higher grades, can be welded by heating 

 and hammering, although care must be exercised in perform- 

 ing this operation. 



456. Hardening and Tempering. The special character- 

 istics of steel, except the very lowest grades, are that when 

 raised to a cherry red heat and suddenly cooled, it becomes 

 brittle and exceedingly hard; and that by subsequent heat- 

 ing and slow cooling the hardness may be reduced to any 

 desired degree down to the point of least hardness that 

 steel possessing that amount of carbon can have. The first 

 process is called hardening' 'and the second tempering. 



457. Tools and Tool Steel. Practically all tools are made 

 from a selected grade of steel called crucible steel. For 



400 



