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Steel Making

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

Air-hardening Steels
These steels are recommended for boring, turning and planing...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

The Influence Of Size
The size of the piece influences the physical properties obta...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

Lathe And Planer Tools
TO FORGE.--Gently warm the steel to remove any chill is parti...

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...



Composition And Properties Of Steel






Category: COMPOSITION AND PROPERTIES OF STEEL

It is a remarkable fact that one can look through a dozen text
books on metallurgy and not find a definition of the word steel.
Some of them describe the properties of many other irons and then
allow you to guess that everything else is steel. If it was difficult
a hundred years ago to give a good definition of the term when the
metal was made by only one or two processes, it is doubly difficult
now, since the introduction of so many new operations and furnaces.

We are in better shape to know what steel is than our forefathers.
They went through certain operations and they got a soft malleable,
weldable metal which would not harden; this they called iron. Certain
other operations gave them something which looked very much like
iron, but which would harden after quenching from a red heat. This
was steel. Not knowing the essential difference between the two,
they must distinguish by the process of manufacture. To-day we
can make either variety by several methods, and can convert either
into the other at will, back and forth as often as we wish; so
we are able to distinguish between the two more logically.

We know that iron is a chemical element--the chemists write it
Fe for short, after the Latin word ferrum, meaning iron--it is
one of those substances which cannot be separated into anything
else but itself. It can be made to join with other elements; for
instance, it joins with the oxygen in the air and forms scale or
rust, substances known to the chemist as iron oxide. But the same
metal iron can be recovered from that rust by abstracting the oxygen;
having recovered the iron nothing else can be extracted but iron;
iron is elemental.

We can get relatively pure iron from various minerals and artificial
substances, and when we get it we always have a magnetic metal,
almost infusible, ductile, fairly strong, tough, something which
can be hardened slightly by hammering but which cannot be hardened
by quenching. It has certain chemical properties, which need not be
described, which allow a skilled chemist to distinguish it without
difficulty and unerringly from the other known elements--nearly
100 of them.

Carbon is another chemical element, written C for short, which is
widely distributed through nature. Carbon also readily combines
with oxygen and other chemical elements, so that it is rarely found
pure; its most familiar form is soot, although the rarer graphite and
most rare diamond are also forms of quite pure carbon. It can also
be readily separated from its multitude of compounds (vegetation,
coal, limestone, petroleum) by the chemist.

With the rise of knowledge of scientific chemistry, it was quickly
found that the essential difference between iron and steel was that
the latter was iron plus carbon. Consequently it is an alloy,
and the definition which modern metallurgists accept is this:

Steel is an iron-carbon alloy containing less than about 2 per
cent carbon.

Of course there are other elements contained in commercial steel,
and these elements are especially important in modern alloy steels,
but carbon is the element which changes a soft metal into one which
may be hardened, and strengthened by quenching. In fact, carbon,
of itself, without heat treatment, strengthens iron at the expense
of ductility (as noted by the percentage elongation an 8-in. bar
will stretch before breaking). This is shown by the following table:

--------------------------------------------------------------------------
Elastic UltimatePercentage.
Class by use. Class by Per cent limit strengthelongation
hardness. carbon. lb. per lb. per in 8 inches.
sq. in. sq. in.
---------------------------------------------------------------------
Boiler rivet steelDead soft 0.08 to 0.15 25,000 50,000 30
Struc. rivet steelSoft 0.15 to 0.22 30,000 55,000 30
Boiler plate steelSoft 0.08 to 0.10 30,000 60,000 25
Structural steel Medium 0.18 to 0.30 35,000 65,000 25
Machinery steel Hard 0.35 to 0.60 40,000 75,000 20
Rail steel Hard 0.35 to 0.55 40,000 75,000 15
Spring steel High carbon1.00 to 1.50 60,000 125,000 10
Tool steel High carbon0.90 to 1.50 80,000 150,000 5
--------------------------------------------------------------------------

Just why a soft material like carbon (graphite), when added to
another soft material like iron, should make the iron harder, has
been quite a mystery, and one which has caused a tremendous amount
of study. The mutual interactions of these two elements in various
proportions and at various temperatures will be discussed at greater
length later, especially in Chap. VIII, p. 105. But we may anticipate
by saying that some of the iron unites with all the carbon to form a
new substance, very hard, a carbide which has been called cementite.
The compound always contains iron and carbon in the proportions
of three atoms of iron to one atom of carbon; chemists note this
fact in shorthand by the symbol Fe3C (a definite chemical compound
of three atoms of iron to one of carbon). Many of the properties
of steel, as they vary with carbon content, can be linked up with
the increasing amount of this hard carbide cementite, distributed
in very fine particles through the softer iron.





Next: Sulphur

Previous: Classifications Of Steel



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