On arriving at a good forging heat it is swung around
to the 100 ton hammer, under which it is worked down to the required
shape. A seventy-five ton ingot requires about eight reheatings before
being reduced to shape. Having been reduced to shape, the plate is
carefully annealed, then raised to a high tempering heat, and the face
tempered in oil. It is reannealed to take out the internal strains,
care being taken not to reduce the face hardness more than necessary.
The Schneider process of tempering is based upon the utilization of
the absorption of heat caused by the fusing or melting of a solid
substance, and of the fact that so long as a solid is melting or
dissolving in a liquid substance, the liquid cannot get appreciably
hotter, except locally around the heating surface. The body to be
hardened is plunged at the requisite temperature into a bath
containing the solid melting body, or is kept under pressure in the
solid material of low melting point until the required extraction of
heat has taken place, more solid material being added if necessary as
that originally present melts and dissolves.
Nickel steel armor is made in a similar manner to the steel plates,
the material used in casting the ingot being an alloy of nickel and
steel containing between three and four per cent. of nickel.
The Harvey process of making armor consists in taking an all-steel
plate and carbonizing the face.
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