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

Complete Calibration Of Pyrometers
For the complete calibration of a thermo-couple of unknown e...

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

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

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

Machineability
Reheating for machine ability was done at 100 deg. less than ...

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

Molybdenum
Molybdenum steels have been made commercially for twenty-five...

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

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

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

Drop Forging Dies
The kind of steel used in the die of course influences the he...

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

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...

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



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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