he strength of a strictly pearlitic steel over a pure iron is due
to the pearlitic being a layer arrangement of cementite running
parallel to that of a pure iron layer in each individual grain. The
ferrite _i.e._, the iron is increased in strength by the resistance
offered by the cementite which is the simple iron-carbon combination
known to metallurgists as Fe3C. The cementite, although adding
to the tensile strength, is very brittle and the strength of the
pearlite is the combination of the ferrite and cementite. In the
event of the cementite being strengthened, as in the case of strictly
chromium steels, an increased tensile strength is readily obtained
without loss of ductility and if the ferrite is strengthened then
the tensile strength and ductility of the metal is still further
improved.

Nickel-chromium alloy represents one of the best combinations available
at the present time. The nickel intensifies the physical characteristics
of the chromium and the chromium has a similar effect on the nickel.

For case-hardening, nickel-chromium steels seem to give very excellent
results. The carbon is very rapidly taken up in this combination,
and for that reason is rather preferable to the straight nickel steel.

With the mutually intensifying action of chromium and nickel there
is a most suitable ratio for these two alloys, and it has been found
that roughly 2-1/2 parts of nickel to about 1 part of chromium
gives the best results. Therefore, we have the standard types of
3.5 per cent nickel with 1.5 per cent chromium to 1.5 per cent
nickel with 0.6 per cent chromium and the various intermediate
types. This ratio, however, does not give the whole story of
nickel-chromium combinations, and many surprising results have
been obtained with these alloys when other percentage combinations
have been employed.

VANADIUM

Vanadium has a very marked effect upon alloy steels rich in chromium,
carbon, or manganese. Vanadium itself, when combined with steel very
low in carbon, is not so noticeably beneficial as in the same carbon
steel higher in manganese, but if a small quantity of chromium
is added, then the vanadium has a very marked effect in increasing
the impact strength of the alloy. It would seem that vanadium has
the effect of intensifying the action of chromium and manganese, or
that vanadium is intensified by the action of chromium or manganese.

Vanadium has the peculiar property of readily entering into solution
w