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

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

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

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

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

The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

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

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

Hardening
Steel is hardened by quenching from above the upper critical....

High Speed Steel
For centuries the secret art of making tool steel was handed ...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Preparing Parts For Local Case-hardening
At the works of the Dayton Engineering Laboratories Company, ...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Annealing
There is no mystery or secret about the proper annealing of d...

Gears
The material used for all gears on the Liberty engine was sel...

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

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...



Rate Of Absorption






Category: CASE-HARDENING OR SURFACE-CARBURIZING

According to Guillet, the absorption of carbon is favored by those
special elements which exist as double carbides in steel. For example,
manganese exists as manganese carbide in combination with the iron
carbide. The elements that favor the absorption of carbon are:
manganese, tungsten, chromium and molybdenum those opposing it,
nickel, silicon, and aluminum. Guillet has worked out the effect
of the different elements on the rate of penetration in comparison
with steel that absorbed carbon at a given temperature, at an average
rate of 0.035 in. per hour.

His tables show that the following elements require an increased
time of exposure to the carburizing material in order to obtain
the same depth of penetration as with simple steel:

When steel contains Increased time of exposure
2.0 per cent nickel 28 per cent
7.0 per cent nickel 30 per cent
1.0 per cent titanium 12 per cent
2.0 per cent titanium 28 per cent
0.5 per cent silicon 50 per cent
1.0 per cent silicon 80 per cent
2.0 per cent silicon 122 per cent
5.0 per cent silicon No penetration
1.0 per cent aluminum 122 per cent
2.0 per cent aluminum 350 per cent

The following elements seem to assist the rate of penetration of
carbon, and the carburizing time may therefore be reduced as follows:

When steel contains Decreased time of exposure
0.5 per cent manganese 18 per cent
1.0 per cent manganese 25 per cent
1.0 per cent chromium 10 per cent
2.0 per cent chromium 18 per cent
0.5 per cent tungsten 0
1.0 per cent tungsten 0
2.0 per cent tungsten 25 per cent
1.0 per cent molybdenum 0
2.0 per cent molybdenum 18 per cent

The temperature at which carburization is accomplished is a very
important factor. Hence the necessity for a reliable pyrometer,
located so as to give the temperature just below the tops of the
pots. It must be remembered, however, that the pyrometer gives
the temperature of only one spot, and is therefore only an aid to
the operator, who must use his eyes for successful results.

The carbon content of the case generally is governed by the temperature
of the carburization. It generally proves advisable to have the
case contain between 0.90 per cent and 1.10 carbon; more carbon
than this gives rise to excess free cementite or carbide of iron,
which is detrimental, causing the case to be brittle and apt to chip.

T. G. Selleck gives a very useful table of temperatures and the
relative carbon contents of the case of steels carburized between
4 and 6 hrs. using a good charcoal carburizer. This data is as
follows:

TABLE 15.--CARBON CONTENT OBTAINED AT VARIOUS TEMPERATURES

At 1,500 deg.F., the surface carbon content will be 0.90 per cent
At 1,600 deg.F., the surface carbon content will be 1.00 per cent
At 1,650 deg.F., the surface carbon content will be 1.10 per cent
At 1,700 deg.F., the surface carbon content will be 1.25 per cent
At 1,750 deg.F., the surface carbon content will be 1.40 per cent
At 1,800 deg.F., the surface carbon content will be 1.75 per cent

To this very valuable table, it seems best to add the following
data, which we have used for a number of years. We do not know
the name of its author, but it has proved very valuable, and seems
to complete the above information. The table is self-explanatory,
giving depth of penetration of the carbon of the case at different
temperatures for different lengths of time:

---------------------------------------------------------
Temperature
Penetration -----------------------------
1,550 1,650 1,800
------------------------------------------------------
Penetration after 1/2 hr. 0.008 0.012 0.030
Penetration after 1 hr. 0.018 0.026 0.045
Penetration after 2 hr. 0.035 0.048 0.060
Penetration after 3 hr. 0.045 0.055 0.075
Penetration after 4 hr. 0.052 0.061 0.092
Penetration after 6 hr. 0.056 0.075 0.110
Penetration after 8 hr. 0.062 0.083 0.130
---------------------------------------------------------

From the tables given, we may calculate with a fair degree of certainty
the amount of carbon in the case, and its penetration. These figures
vary widely with different carburizers, and as pointed out immediately
above, with different alloy steels.





Next: Carburizing Material

Previous: Surface Carburizing



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