rade machinery.

In general, molybdenum when added to an alloy steel, increases the
figure for reduction of area, which is considered a good measure
of "toughness." Molybdenum steels are also relatively insensible
to variations in heat treatment; that is to say, a
chromium-nickel-molybdenum steel after quenching in oil from 1,450 deg.F.
may be drawn at any temperature between 900 and 1,100 deg.F. with
substantially the same result (static tensile properties and hardness).

SILICON

Silicon prevents, to a large extent, defects such as gas bubbles
or blow holes forming while steel is solidifying. In fact, steel
after it has been melted and before it has been refined, is "wild"
and "gassy." That is to say, if it would be cast into molds it
would froth up, and boil all over the floor. A judicious amount
of silicon added to the metal just before pouring, prevents this
action--in the words of the steel maker, silicon "kills" the steel.
If about 1.75 per cent metallic silicon remains in a 0.65 carbon
steel, it makes excellent springs.

PHOSPHORUS

Phosphorus is one of the impurities in steel, and it has been the
object of steel makers for years to eliminate it. On cheap grades
of steel, not subject to any abnormal strain or stress, 0.1 per
cent phosphorus is not objectionable. High phosphorus makes steel
"cold short," i.e., brittle when cold or moderately warm.

SULPHUR

Sulphur is another impurity and high sulphur is even a greater
detriment to steel than phosphorus. High sulphur up to 0.09 per
cent helps machining properties, but has a tendency to make the
steel "hot short," i.e., subject to opening up cracks and seams
at forging or rolling heats. Sulphur should never exceed 0.06 per
cent nor phosphorus 0.08 per cent.

Steel used for tool purposes should have as low phosphorus and sulphur
contents as possible, not over 0.02 per cent.

We can sum up the various factors something as follows for ready
reference.

The ingredient Its effect

Iron The basis of steel
Carbon The determinative
Sulphur A strength sapper
Phosphorus The weak link
Oxygen A strength destroyer
Manganese For strength
Nickel For strength and toughness
Tungsten Hardener and heat resister
Chromium For resisting shocks
Vanadium Purifier and fatigue resister
Silicon Impurity and hardener
Titanium Removes nitrogen and ox