THE MAKING AND WORKING OF STEEL 413 



474. Test of Steel Strength. Nitric acid will produce a 

 black spot on steel; the darker the spot the harder the steel. 

 Iron, on the contrary, remains bright if touched with nitric 

 acid. Good steel in its soft state has a clean fracture and a 

 uniform gray luster; in its hard state, a dull, silvery, uniform 

 white luster. Cracks, threads, or sparkling particles denote 

 bad quality. 



Good steel will not bear a white heat without falling to 

 pieces. It will crumble under the hammer at a bright red 

 heat, while at a moderate heat it may be drawn out under 

 the hammer to a fine point. 



Iron is more active than copper. If a piece of iron wire 

 is placed in a copper salt solution, the iron wire becomes 

 coated with metallic copper and part of the iron is dissolved 

 in the solution. Thus, when a piece of iron wire is placed 

 in a solution of copper sulphate the copper immediately 

 coats the iron and part of the iron takes the place of the 

 copper which is deposited according to this equation 



Fe + CuSO 4 = Cu + FeS0 4 

 These facts are taken advantage of in marking iron tools. 



Questions 



1. What is steel? Give some of its general physical properties- 



2. How is steel graded? What are the properties of each grade? 



3. Explain the meaning of hardening; annealing; tempering. 



4. What is the meaning of the phrase "drawing to a faint 

 yellow color" in tempering? 



5. What is Bessemer steel? How is it made? 



6. What is the open-hearth method of making steel? 



7. What is crucible steel? Describe its special properties. 



8. How is high-speed steel made? 



