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

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

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

The Modern Hardening Room
A hardening room of today means a very different place from ...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

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

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...



Effect Of Different Carburizing Material






Category: CASE-HARDENING OR SURFACE-CARBURIZING

[Illustrations: FIGS. 33 to 37.]

Each of these different packing materials has a different effect
upon the work in which it is heated. Charcoal by itself will give
a rather light case. Mixed with raw bone it will carburize more
rapidly, and still more so if mixed with burnt bone. Raw bone and
burnt bone, as may be inferred, are both quicker carbonizers than
charcoal, but raw bone must never be used where the breakage of
hardened edges is to be avoided, as it contains phosphorus and
tends to make the piece brittle. Charred leather mixed with charcoal
is a still faster material, and horns and hoofs exceed even this
in speed; but these two compounds are restricted by their cost
to use with high-grade articles, usually of tool or high-carbon
steel, that are to be hardened locally--that is, pack-hardened.
Cyanide of potassium or prussiate of potash are also included in
the list of carbonizing materials; but outside of carburizing by
dipping into melted baths of this material, their use is largely
confined to local hardening of small surfaces, such as holes in
dies and the like.

Dr. Federico Giolitti has proven that when carbonizing with charcoal,
or charcoal plus barium carbonate, the active agent which introduces
carbon into the steel is a gas, carbon monoxide (CO), derived by
combustion of the charcoal in the air trapped in the box, or by
decomposition of the carbonate. This gas diffuses in and out of
the hot steel, transporting carbon from the charcoal to the outer
portions of the metal:

If energizers like tar, peat, and vegetable fiber are used, they
produce hydrocarbon gases on being heated--gases principally composed
of hydrogen and carbon. These gases are unstable in the presence of
hot iron: it seems to decompose them and sooty carbon is deposited
on the surface of the metal. This diffuses into the metal a little,
but it acts principally by being a ready source of carbon, highly
active and waiting to be carried into the metal by the carbon
monoxide--which as before, is the principal transfer agent.

Animal refuse when used to speed up the action of clean charcoal
acts somewhat in the same manner, but in addition the gases given
off by the hot substance contain nitrogen compounds. Nitrogen and
cyanides (compounds of carbon and nitrogen) have long been known
to give a very hard thin case very rapidly. It has been discovered
only recently that this is due to the steel absorbing nitrogen
as well as carbon, and that nitrogen hardens steel and makes it
brittle just like carbon does. In fact it is very difficult to
distinguish between these two hardening agents when examining a
carburized steel under the microscope.

One of the advantages of hardening by carburizing is the fact that
you can arrange to leave part of the work soft and thus retain
the toughness and strength of the original material. Figures 33
to 37 show ways of doing this. The inside of the cup in Fig. 34
is locally hardened, as illustrated in Fig. 34, spent or used
bone being packed around the surfaces that are to be left soft,
while cyanide of potassium is put around those which are desired
hard. The threads of the nut in Fig. 35 are kept soft by carburizing
the nut while upon a stud. The profile gage, Fig. 36, is made of
high-carbon steel and is hardened on the inside by packing with
charred leather, but kept soft on the outside by surrounding it
with fireclay. The rivet stud shown in Fig. 37 is carburized while
of its full diameter and then turned down to the size of the rivet
end, thus cutting away the carburized surface.

After packing the work carefully in the boxes the lids are sealed
or luted with fireclay to keep out any gases from the fire. The
size of box should be proportioned to the work. The box should
not be too large especially for light work that is run on a short
heat. If it can be just large enough to allow the proper amount
of material around it, the work is apt to be more satisfactory
in every way.

Pieces of this kind are of course not quenched and hardened in
the carburizing heat, but are left in the box to cool, just as in
box annealing, being reheated and quenched as a second operation.
In fact, this is a good scheme to use for the majority of carburizing
work of small and moderate size. Material is on the market with which
one side of the steel can be treated; or copper-plating one side
of it will answer the same purpose and prevent that side becoming
carburized.





Next: Quenching The Work

Previous: Quenching



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