THE MAKING AND WORKING OF STEEL 401 



example, one kind of steel makes excellent razor blades, 

 where keenness is demanded, while another is able to resist 

 blows as well to hold a lasting edge. While it is possible to 

 use the same grade of steel for different tools, it is very 

 necessary to vary the treatment of the steel for the different 

 purposes to which the tool will be put. 



In making tools, the steel is forged into the desired shape. 

 Care must be taken not to overheat it while it is being 

 worked. After forging, the steel is brought to a good red 

 heat and then plunged into water, to render it hard and 

 brittle. The cutting edge is then rubbed bright with a piece 

 of emery cloth tacked on a piece of wood. After being 

 thoroughly rubbed, the tool is held over a fire and heated 

 slowly. Here it begins to show color at first a faint yellow, 

 then a tinge of blue. It finally assumes the color possessed 

 by the bar previous to forging. 



The operation of reheating, polishing, and allowing the 

 color "to run" is called "drawing." The faint yellow 

 color indicates that the steel has become toughened 

 that it has lost its hardness or brittleness and become 

 springy. 



458. Tempering. When steel and iron are heated to a 

 high temperature they first become red, then orange, and 

 then white. The temperatures may be approximately told 

 by the color as follows: 



First sign of red 957 F. Dull orange 2010 F. 



Dull red 1290 Bright orange 2190 



Cherry red 1655 White heat 2370 



Bright red 1870 Bright white 2550 



Dark cherry 1470 Dazzling white 2730 to 2910 

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