Judging The Heat Of Steel

: The Working Of Steel

While the use of a pyrometer is of course the only way to have

accurate knowledge as to the heat being used in either forging or

hardening steels, a color chart will be of considerable assistance

if carefully studied. These have been prepared by several of the

steel companies as a guide, but it must be remembered that the colors

and temperatures given are only approximate, and can be nothing


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The Magnet Test.--The critical point can also be determined by

an ordinary horse-shoe magnet. Touch the steel with a magnet during

the heating and when it reaches the temperature at which steel fails

to attract the magnet, or in other words, loses its magnetism,

the critical point has been reached.

The work is heated up slowly in the furnace and the magnet applied

from time to time. The steel being heated will attract the magnet

until the heat reaches the critical point. The magnet is applied

frequently and when the magnet is no longer attracted, the piece

is at the lowest temperature at which it can be hardened properly.

Quenching slightly above this point will give a tool of satisfactory

hardness. The method applies only to carbon steels and will not

work for modern high-speed steels.