402 



APPLIED SCIENCE 



The following table represents the colors which appear on 

 a polished steel surface when heated in the air. 



Color 

 Very pale yellow 



Approximate 

 Temperature 



430 F. 



Straw yellow 460 



Dark straw color 480 



Brownish yellow 500 



Yellow tinged with purple 520 



Light purple 530 



Dark purple 550 



Dark blue 570 



Pale blue 610 



Blue tinged with green 630 



Used in 

 Tempering 



Hammering tools, lathe 

 and planer tools, scrap- 

 ers. 



Taps and dies 



Reamers, knives, punches, 

 and dies 



Drills, stone-cutting tools 



Angles, draft pins 



Cold chisels for steel, 

 augers 



Springs, screw - drivers, 

 cold chisels for iron, 

 hatches 



Saws for wood 



459. Bessemer Process. The principal grades of steel 

 are made by the Bessemer, Siemens-Martin, and open-hearth 

 processes. Bessemer steel is manufactured from gray pig 

 iron, which is free from phosphorus, sulphur, and manganese. 

 In this process there are two separations the conversion 

 of the molten cast iron into pure iron, and the changing of 

 the pure iron into steel by the addition of a small and definite 

 quantity of alloy of manganese and carbon. 



Steel may be made directly from pig iron by allowing the 

 latter to run from the cupola into a converter lined with 

 fire-brick and by blowing air into the metal through an 

 opening in the bottom for about twenty minutes. This 



