ermanent magnets. In this, its action
is not well understood. In fact, the reason why steel becomes a
permanent magnet is not at all understood. Theories have been evolved,
but all are open to serious questioning. The principal effect of
tungsten, as conceded by leading authorities, is that it distinctly
retards separation of the iron-carbon solution, removing the lowest
recalescent point down to atmospheric temperature.

A peculiar property of tungsten steels is that if a heating temperature
of 1,750 deg.F. is not exceeded, the cooling curves indicate but one
critical point at about 1,350 deg.F. But when the heating temperature
is raised above 1,850 deg.F., this critical point is nearly if not
quite suppressed, while a lower critical point appears and grows
enormously in intensity at a temperature between 660 and 750 deg.F.

The change in the critical ranges, which is produced by heating
tungsten steels to over 1,850 deg.F., is the real cause of the red-hard
properties of these alloys. Its real nature is not understood,
and there is no direct evidence to show what actually happens at
these high temperatures.

It may readily be understood that an alloy containing four essential
elements, namely: iron, carbon, tungsten and chromium, is one whose
study presents problems of extreme complexity. It is possible that
complex carbides may be formed, as in chromium steels, and that
compounds between iron and tungsten exist. Behavior of these
combinations on heating and cooling must be better known before
we are able to explain many peculiarities of tungsten steels.

MOLYBDENUM

Molybdenum steels have been made commercially for twenty-five years,
but they have not been widely exploited until since the war. Very
large resources of molybdenum have been developed in America, and
the mining companies who are equipped to produce the metal are
very active in advertising the advantages of molybdenum steels.

It was early found that 1 part molybdenum was the equivalent of from
2 to 2-1/2 parts of tungsten in tool steels, and magnet steels. It
fell into disrepute as an alloy for high-speed tool steel, however,
because it was found that the molybdenum was driven out of the
surface of the tool during forging and heat treating.

Within the last few years it has been found that the presence of
less than 1 per cent of molybdenum greatly enhances certain properties
of heat-treated carbon and alloy steels used for automobiles and
high-g