A manganese steel of 11 to 14 per cent. is too hard to be machined. It
has to be cast or ground into shape and is used for burglar-proof safes
and armor plate. Chrome steel is also hard and tough and finds use in
files, ball bearings and projectiles. Titanium, which the iron-maker
used to regard as his implacable enemy, has been drafted into service as
a deoxidizer, increasing the strength and elasticity of the steel. It is
reported from France that the addition of three-tenths of 1 per cent. of
zirconium to nickel steel has made it more resistant to the German
perforating bullets than any steel hitherto known. The new "stainless"
cutlery contains 12 to 14 per cent. of chromium.
With the introduction of harder steels came the need of tougher tools to
work them. Now the virtue of a good tool steel is the same as of a good
man. It must be able to get hot without losing its temper. Steel of the
old-fashioned sort, as everybody knows, gets its temper by being heated
to redness and suddenly cooled by quenching or plunging it into water or
oil.
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