Quenching





It is considered good practice to quench alloy steels from the pot,

especially if the case is of any appreciable depth. The texture

of carbon steel will be weakened by the prolonged high heat of

carburizing, so that if we need a tough core, we must reheat it

above its critical range, which is about 1,600 deg.F. for soft steel,

but lower for manganese and nickel steels. Quenching is done in

either water, oil, or air, depending upon the results desired.

The steel is then very carefully reheated to refine the case, the

temperature varying from 1,350 to 1,450 deg.F., depending on whether

the material is an alloy or a simple steel, and quenched in either

water or oil.






There are many possibilities yet to be developed with the carburizing

of alloy steels, which can produce a very tough, tenacious austenitic

case which becomes hard on cooling in air, and still retains a

soft, pearlitic core. An austenitic case is not necessarily file

hard, but has a very great resistance to abrasive wear.



The more carbon a steel has to begin with the more slowly will it

absorb carbon and the lower the temperature required. Low-carbon

steel of from 15 to 20 points is generally used and the carbon

brought up to 80 or 85 points. Tool steels may be carbonized as

high as 250 points.



In addition to the carburizing materials given, a mixture of 40

per cent of barium carbonate and 60 per cent charcoal gives much

faster penetration than charcoal, bone or leather. The penetration

of this mixture on ordinary low-carbon steel is shown in Fig. 32,

over a range of from 2 to 12 hr.





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