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Phosphorus
PHOSPHORUS is an element (symbol P) which enters the metal fr...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

Chromium
Chromium when alloyed with steel, has the characteristic func...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

Care In Annealing
Not only will benefits in machining be found by careful anne...

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Furnace Data
In order to give definite information concerning furnaces, fu...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Double Annealing
Water annealing consists in heating the piece, allowing it to...

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

Sulphur
SULPHUR is another element (symbol S) which is always found i...

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

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

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



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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