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

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

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

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

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

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

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

Hardness Testing
The word hardness is used to express various properties of me...

Gas Consumption For Carburizing
Although the advantages offered by the gas-fired furnace for ...

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

Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

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

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

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

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

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

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



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.





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Previous: Surface Carburizing



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