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INVESTIGATION OF CEMENTATION
WITH GASEOUS CARBURIZERS.

A Report Submitted to the

Faculty of the
Michigan Agricultural College

By

ih

Harold Y. Hartl ey

Candidate for the Degree of
Bachelor of Soience.

June, 1921.
INVESTIGATION OF CEMENTATION WITH GASEOUS CARBURIZERS.
HISTORY AND THEORY OF CEMENTATION.

Case-oarbonising is the poocess of oarburising
the outer sone of a piece of steel low in carbon, with-
out subjecting it to fusion.

The history of this process dates baok to the
early stages of the world's development. It is probably
the least developed of any of the steel-treating methods,
in spite of the fact that it is the oldest. It was not
until the nineteenth century that ideas were propounded
whioh correctly explained the theory of the process.

Our forefathers have made steel for centuries, using
different material and processes, but without mowing

that the carbon added in those methods produced the desired
results. Toward the end of the nineteenth century several
theories were advanced regarding the aotion of the carbon
upon the iron or steel. Oaron maintained that cementation
was the result of the action of oyanides alone in giving
oarbon to the iron. Various ideas were advanced, but in
1841 Leplay brought forth the idea that it was the action
of carbon monoxide upon the steel which produced the
desired results. The action was explained in this manner -
the oxygen in the air united with the charooal to form

carbon dioxide, and then carbon monoxide; the carbon

YS o1b6
monoxide the gave to the iron part of its carbon, thus
being oonverted back to CO»; this COp reacted with more
carbon to form 00, and the process was repeated; thus
the carbon monoxide acts as a carrier of carbon. This
hypothesis of Leplay has been confirmed within very
recent times.

Dr. ¥rederica Gielitt£ has carried out
extensive experimental work upon all phases of ocase-
hardening. He has proven by heating steel in a vacuum
in contact with carbon that it is possible to carburise
iron by contact, and without the intervention of my gases.
However, he has shown that ocarburisation by oontact plays
@ negligible part in practical work; that the gas acting

as a carrier is the important factor in cementation.
REQUIREMENTS FOR CasE CAKBORIZING.

There are five factors which enter into
cementation:

ile Phe composition of the steel,

2. The nature of the ocarhurizer,

3. The temperature of carburizing,

4. The concentration of the ocarburiser and its
contact with the steel,

5. fhe time of carburizing.
These will be discussed throughout the paper,
but the nature of the carburizer will be discussed
quite thoroughly, as this is the main subject under

oons ideration.
THE COMPOSITION OF PHE STEEL.

The absorption of oarbon by the steel depends
upon the various elements in the steel. Elements which
form double carbides suqd as manganese, chromium,
tungsten, and molybdenum, inorease the absorption of
carbon, while on the other hand, such elements as nickel,
silioon, and aluminum decrease the percentage of carbon
in the case. Steel which is low in oarbon, and which
may contain one or wor 6 of the above elements, is used

for general case hardening work.
THE NATURE OF THE CAKBUKIZER.

There are three kinds of carburisers in use
today - solid, liquid, and gaseous. The solid cement is
used far more than either of the others. In the selection
of a 801id cement, we have to take into oonsideration the
charaoter of the case it prodices, the deterioration of
the oarburiser, and the rate of time in which it heats
up. A chart showing the comparison of three common
oarburisers in the time whioh it takes to produce different
renetrations is shown in Fig. l.
As the process of case oarbonising is

brought about by the intervention of gases given off

by the solid carburisers, White end Hood have revealed

the composition of the gases.evolved on heating some
#011d carburisers, as indicated in the Mllowing table:

Composition of carburisers -

No.
No.
No.
HO.
No.

No.

i.
2
rs
5.
7.

De

wood charcoal,

90% Wood charcoal plus 10% barium carbonate,
70% Wood charcoal plus 30% barium carbonate,
Wood charooal previously ignited at 1800° FPF.
20% soot plus 40% gypsum, 40% potassium
ferro-cyaanide.

20% animal refuse (hide, bone, hoof, eto)
50% plant mtter, 11% soda, 5% silica brick,
14% moisture.

Analysis of Gases Evolved -

Sample No. 1 2 5 &§& 7 9

(00 11.3 28.1 25.3 42.0 29.4 54.4

1560° FP. Hp 74.0 652.8 657.7 20.0 28.6 34.8
(oH, 10.0 8.7 8.7 2.0 1.2 1.7

(00 19.6 37.3 66.1 71.7 65.6 36.8

192° ¥. Hp 73.6 60.0 32.0 15.0 19.2 61.4
(ott, 6 9 9 97 9 12

Thus we see that the gas wh ich does

-

most of the
work in oarbonising with a 801id cement is carbon
monoxide. Working on this fact and the hypothesis of
Leplay as a basis, several experimaters have gone quite
thoroughly into the field of carbonising with various
gases, the results of whioh will be brought forth later.
fhe future of gas carbonizing seems to hold
forth many promising results to the process of cémentation.
Liquid cements are not used very extensively on
account of the high concentration of carbon in the oase.
Cyanide solutions are used as liquid cemnts, but only
On pieces which require a very thin case. There is
aleo the danger to the life and health of the workmen,
on account of the poisonous gases given off on heating.
The danger of exfoliation or chipping off of the case
is also enoountered on socount of the abrupt change in
concentration from the core to the case.
fhe solid cement is the most widely used at
present, but further develapmemts along the line of gas
carbonising will exert a preponderant influence upon

the process of cementation.
THE TEMPERATURE OF CAKBUXIZING.

Experiments have been carried out by several
men to determine the temperature at which carburisation
takes place. Giolitti Places this point at 780° © or
1436° F, while Langenberg states that it is somewhere
between 725° and 810° C, although he plots his curves

on the basis of 720° C. Fig. 2 shows the results obtained
by Langenberg in determining the solubility of carbon

in steel at various temperatures. He shows that at

910° 6, the point of change from beta to gamma iron,

the solubility of aarbon increases.

A rise in temperature while using the solid
carburisers usually brings about an inoreased rate of
penetration and a greater concentration.

The effect of change of temperature with the

use of various gases will be showm later in the disaqesion.

THE CONCENGRATION OF HE CAXBUKIZER aNb ITS
CONTACT WITH THE STEXL.

By the concentration of the ocarburiser is
meant the strength of the carburiser if using so iid
cement, or of the pressure and rate cf flow, if gas is
used for carburising. In the use of s0lid cement, new
material mst be added after each zun, to produce the
required results.

In carburizing by contact, the carbon must be
in intimate contact with the steel in order to produce
any results, and even the best results in “direot”

carburisation are of no practical value.
THE TIME OF CAKBUKIZING.

The time of carburising has very ma to do
with the success of the undertaking. Inorease in time
increases the depth of case and the concentration of
the carbon in the case. The steel under treatment
must be left in the furnace long q@iough 80 that the
piece will stand up under the use to which it is put.
However, the time element is one of great importance,
because with the modern methods of inoreased production
the time element mst be reduced to its lowest pos sible
value. COarburizing with gas will solve this phase of

the mtter to a very great extent.
PAULTS OF THE PRESENT CARBURIZING PROCESS.

How that we have seen what the requirements for
carburising are, we will take up the out-standing faults
of the carburizing process as it exists today.

It has bem stated before that although case
carboning is one of the oldest methods of steel treating,
it is still the least developed. In order to effeot
any cure for the troubles and develop the process, the
causes of all the troubles must be made clear. The chief

causes for imperfect carburization are faulty heating of
the steel, poor and imperfect carburizers, and im-
perfeot timing of the operation.

} Very much trouble is experimoed in heating
the steel. In many cases we will find that the piece
under treatment will be carbonized on one side and not
on the other. This is due to the laok of uniformity
of temperature on the inside of the box; it will usually
be found that the temperature will be higher near the
outside and lower near the center of the box. Mr.

Theo. G. Selleck of Deere & Company, MOline, Illinois,
has gotten around this fault to a certain extent. He
uses no boxes in carbonizing, but instead uses the fixed
chamber mthod. The furnace is first heated above the
carbonising temperature, then the steel is put in.

When the steel comes near the ocarbonising point, the
carburiser is added. In a short time a uniform tempera-
ture throughout can be obtained. This precess not only
furnishes better means of control of carburising, but

4t saves labor, fuel, compound, and the great expense
of iron boxes. It also hdlps eliminate the third great
fault, the imperfect timing of the operation.

Too, imperfect carburisers often bring bad
results. A compound may be used which will hinder the
uniform heating of the steel, or it may give off the
gases way below the carbonising temperature, either one

of whioh will result in wery inefficient operation.
Imperfect timing is also one of many faults
of the process. The operator of the oarbonising
furnace mst be guided by his experience in the allow-
ance of time in coming up to heat. He cannot tell by the
furnace temperature whether the contents of the box
are at a lower or higher temperature than that of the
furnace. As a result some of the boxes are undertimed
and some are overtimed, thus producing a lack of unifornm-
ity in the finished prodot.

Gas carbonising or oarbonising with a gaseous
cement, will tend to eliminate many of the faults of
the present day process. <A person familiar with the
present practice knows what an immense amount of time
and labor is consumed in packing the boxes and handling
them throughout the operation. He is only too familiar
with the immense expense involved in the use of iron
and alloy boxes. When he sees the flames coming from
the boxes as they are taken from the furnace, he realises
what a vast amount of valuable gases are wasted. The
element of time is also extremely important in the
carbonising process. Knowing all these facts, we oan
realise the need for development in case carburising.
Why go to all the expense in time, labor, md maney, in-
volved in the present day practice, in the use of solid
carburisers, when we know that gas is the essential
Clement in carburising? This problem will probably be
10

solved in due course of time.

EXPERIMENTAL RESEARCH IN GAS CARBONIZ ING.

In the year 1907, Giolitti began some
experiments for the scientifio study of cementation.
fhe results of his investigations have been published
in a book entitled “The OCementation of Iron and Steel"
which was translated from the Italian by J. W. Richards
and 0. A. Rouiller. fPhese experiments by Giolitti have
been meinly to determine the action of the various gases
in the oarburisation of steel. F. 0. Langenberg of
Harvard University also carried out some experiments
along the same line as those of Giolitti. The results of
all investigations in gas carburising up to the present
time will be outlined here.

THE APPARATUS.

Before we take up the results of the experingmtal
research, it will probably be best to give a description
of the apparatus. The furnace desoribed below is shown
in Fig. 3, and is an improved type used by F. C. Langen-
berg in his work. The furnace is a combined vacuum and
pressure furnace. The heating unit consists of a ooil of

Ho. 16 niohrome wire with a total resistance of 10 ohms,
1

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wound on an alundum tube threaded on the outside. A
mixture of alundum cement and water was prepared and
firmly pressed on over the wire. An asbestos steam
pipe cover was fitted on over this, and over this
covering was wrapped a layer of asbestos felt. Cast
iron end plates were made to fit on over the ends of
the heating unit. Por vacuum or pressure work the unit
Was Placed in a steel jaoket and supported in it by
perforated asbestos wood rings. Joints in the jacket
were made air-tight by using asbestos-graphite gaskets.
Me heads were tapped for spark plugs which served to
supply the ourrent to the heating unit. The cooling is
accomplished by the thermo-syphon system of oil
eiroulation. Rubber gaskets were used satisfactorily
in making tight joints.

fo complete installation for vacuum or pressure
work oonsists of the following: motor, oompressor,
storage tank, pressure gage, valves, Vacuum Pump, Vacuum
gage, and eleotrical oontrol for furnace.

By the use of this type of furnace accurate
resulta may be obtained in determining the effeot of a
certain gas passing at a constant rate and temperature for
a given time. The furnace is exhausted while cold, and
then heated to the desired temperature. The gas is pass-
ed through for the given time, after which the furnace
is exhausted and allowed to coool. Operating the furnace
12

in this way eliminates all effects from heating to and
cooling from the working temperature.

THE ACTION OF CARBON MONOXIDE AS A CARBURIZING GAS.

We have seen from the analysis of a eommon
s0l114 cement that the main carburiser is Carbon Monoxide
gas. CO differs oonsiderably from the numerous hydro-
carbons and cyanogen. fhe higher hydrocarbons present
quite a complex study regarding the nature of the
chemical equations involved. The process of carburising

with 00 may be represented by the reversible equation
2 CO<—+00p + C.

In cemntatior with cyanog@m and hydrocarbons,
a case of high ooncentration of carbon is formed. Ina
case formed by either of the above gases, there are three
distinot sones - the outer or hyph-eutectoid zOne whiah
contains more than .9% 06, the center or eutectoid sone of
9% C, and the inner or hypo-eutectoid gone of less than
-9% C. In oarburizing with oarbon monoxide, we do not
find any concentration greater than .9% 0. This feature
with many others is shown in the results of Giolitti'’s
experiments show in the following table.
TABLE 1.

CARBURIZABION WITH OO aT CONSTANT VELOCITY.

 

Length Pressure Temper- Volume

of « of gas ature of gas

Number cementatien in mm. Deg. 0 used in

in hours. HG liters
1 6 761 810 10
5 7 761 760 10
6 7 657 760 20
7 7 568 770 10
8 7 450 770 10
LO 7 760 780 LO
22 5 760 900 7
235 5 461 900 7
30 5 760 1000 7
31 5 462 . 1000 7
38 3 960 1100 5
39 3 461 1100 5
44 3 760 1100 9
45 10 760 1100 9

13
ABLE 1 (Cont'd)

CAKBURIZATION WITH CO AT CONSTANT VELOCITY.

 

Total Hyper- Maximum
thickness Suteoto Ag Eutectoiad Hypo- ooncen-
of case (mm) | (mm) Butectoid tration
(mm) (mn) of 0.
ol — --- el 26
05 --= oon 05 —
22 ~-- --- 22 ~--
1.0 on ~m— 1.0 05
6 — oon 06 od
2.0 oe --= 2.0 35
14 --= “<= Led 24
8.0 <= “<= 5.0 018
3.0 “m= --- 5-0 el2
4.0 -<= -o= 4.0 03

4.9 “<= “<= 4.0 027
15

By comparing 22 to 30, ani 23 to dl, fe
find that wa the temperature inoreases, all other oon-
ditions remaining the same, the concentration de-
creases and the penetration increases. A comparison
between 223 and 23, 30 and 30, shows that as the preemre
inoreases the rate of penetration and concentration also
inorease. Fig. 4 shows a “concentration-depth” diagram
using 0O as a cement; it shows that the conoentration
is very low and gradually decreases with the depth of
carbon. By referenoé to 5, 6, 7, and 8, we see that no
cementation takes place below 780°. TPhis value varies
some with different experimenters, but it depends upon
the accuracy of the work, whether or not there is a
neu$ral atmosphere.in the furnace, ani the basis of
determining the cementation.

fhe action of 0O upon the conoentration of
carbon makes it the most valuable for practical use.
Hydrocarbons give a oase of high oarbon content, and the
use of a mixture of CO and hydrocarbons produces results
varying between the two according to the percentage of
each gas in the mixture. In Fig. 4 we have a mixture of
CO plus 3.1% of ethylene. Carbon monoxide has algo been
used satisfactorily in conneotion with pure carbon.
fable & gives the results of experiments carried out using
granular wood charooal and O00.
16

PABLE 2.

Temper- Time of Volume Hyper- Euteo- Hypo-
ature cement—- of CO Eatec- toid Euteo-~

 

No. in Deg. ations: in toid case toid
0 in hres. liters case mm. Me case

— ym.

L 900 4 2 ome 74 )
2 1000 4 2 ome 1.0 06
3 1000 4 6 one 1.0 o7

A phenomenon which presents great interest in
carburising under strong presmres with 00 plus oarbon
is the fact that the cemented steel is uxidised.
Charpy noticed that pure CO at 1000°O oxidised ochromiun,
manganese, and various chrome-hiokel steels. He states that
the chromium decomposes the ©O and the two elements C and
O dDehave as if isolated. Thus we have the oarburisation

of the steel going on and at the same time the reaction -
2 Or + 8 00 = Org 0g + 30.

fhe rate of flow of the carmrising gas or its
eoncentration has e mrked effect on cementation. an
inorease in the rate of flow, all other conditions remain-
ing constant, will inorease the penetration and concen-
tration of the carbon, as indicated by a study of No. 38
and 44.

The above results indicate briefly am fairly
well the results that mgy be expected by using oarbon

monoxide as a carburiser.
17

THE USE OF HYDHOCAKBONS WOK CAKBURIZATION.

Under hydrocarbons oome such gases as
methane, ethylene and coal gas or illuminating gas.

At high temperatures these gases decompose and the
ultimate products formed are carbon and hydrogen.
Methane is the most stable of all the hydrocarbons.
There is a very slight decomposition of methane at

1900° ¥, while the others decompose rapidly above 1700°
¥. When methane is used to carbonise steel, it forms

a hard compact soale on the metal, but more carbon from
the methane is dissolved by the steel than from the other
jydrocarbons. The other gases usually form only a soot
which aids in carburising.Methane is more effective than
the other hydrooarbons, but only at temperatures higher
than 1700° F.

One characteristic feature about all of the
hydrocarbons is that they form a case with a high carbon
contact. Unlike carbon monoxide, the concentration in-
creases with a rise in temperature. Usually in a case
formed by the use of hydrocarbons as a oarburiser, and
especially at the higher temperatures, there is a
noticable line of demarkation between the different sones.
This rapid change in concentration between sones umally
cause a splitting off of the case, or expoliation, as it
is called. This makes the use of hydrocarbons alone for
18

oarburising very undesirable commercially.
PURE HYDROCARBONS.

Umier the heading of pure hydrocarbons may
be discussed the action of mthane, ethylene, and
acetylene. The singular action of mthane has been
touched upon briefly in the above paragraph. The other
hydrooarbons behave similarly to each other. Acetylene,
CpHp, oould not be used under pressure, s0 experiments
with it were confined to the effect of temperature, and
rate of flow. The extent of oarburiszation seems to be
a direot function of the rate of flow, and varies with
the different temperatures, as indicated in Pig. 5. In
this set of curves there seems to be a sudden change be-
tween 880° and 910°, which is explained by the increased
solubility of carbon in gamma iron.

Ethylene ani methane were used quite extensive-
ly in Giolitti's investigations,

Below is show a table of the results which
he obfgained.
 
  
    
 
   
      
       
  
 
     

   

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TABLE 3.

ACTION OF ETHYLENE AND METHANE Ii CARBURIZING.

 

ETHYLENE.
Length Pressure Pemper- Volume
of <.- of gas ature of gas
Number cementatten. in mm. Deg. C. used in
in hours HG. Liters.
Al 7 759 780 10
12 7 454 780 7
13 7 454 780 12
19 5 760 900 7
20 5 609 900 7
21. 5 458 900 7
28 5 760 1000 7
£9 5 462 1000 7
36 3 760 1100 5
37 3 458 1100 5
46 3 760 1100 2
47 3 760 1100 15
48 10 760 1100 11
METHANE |
14 7 759 780 8
15 7 453 780 8
24 5 760 900 7
25 5 462 900 7
32 5 760 1000 7
33 5 466 1000 7
40 3 760 1100 5
41 3 463 1100 5

19
FABLE 3 (Cont'd)

ACTION OF ETHELENE AND METHANE IN CARBURIZING.

 

ETHYLENE.

Total Hyper - Maximum

thickness Eutectoid Butectoid Hypo- conoen-

of case (ram) (mm) Kutectoid tration
(ram) | (ram) of 0.
+ od ol el ===
ed od ed el oo
ed ed ed ol one
1.3 ed 05 05 Led
09 of 03 o4 1el
od 005 ed e15 1.1
2.0 6 ocf 1.0 1.3
1.8 05 o4 9 LS
2.9 1.6 04 09 1.3
2.9 9 04 a 1.5
bes ~-- oe wnwe .9
4.4 2.5 04 1.5 1.5
Hyper-eutectoid steel to axis of oylinder : 1.5

METHANE

8 o 015 o 25 o4 1.0
06 el o2 oS 1.0
2.0 e7 od 1.0 13
2.0 o7 oS 1.0 1.3
2.6 L282 04 1.-@ 1.3

2.5 1.3 04 8 13
£1

We notioe that methane will not carburise
steel at as low temperatures as ethylene will. A
comparison of 19, 20, and £1, and 24 and 256 shows thet
an inorease in pressure increases the rate of penetra-
tion. An increase in the rate of flow of gas increases
the penetration and concentration. One fact that is
brought out wery olearly, that the pee of ethylene at
higher temperatures produces quite a noticeable break
in concentration between sones, is show in Fig. 6.

From the above data we have the results of

carburization with the pure hydrocarbons as standing out
clearly from those of carbon monoxide in the fact that

the Kydroocarbons give a case of high concentration while
carbon monoxide gives a case of low concentration but at

@ rapid rate of penetration.
ILLUMINATING GAS.

The next gas which is just as important from
a practical viewpoint as the ones heretofore discussed
is illuminating gas. Before the oarburising aotion of
this gas is examined, let us look into Sts composition.
Below are analyses of two samples of illuminating gas.

GASES fl #2
Oarbon ALOX1de ccccccscccccccce Lolh eevsee 106%

Heavy hydTroacarbonBeccscccccccecs 2B ceovcee Soh
22

GASES #1 #2
OXYHON coccccccccccccccccsescsccce 0 secsee 0f&
CarbOn MONOXLAE cccccccccccscces DoT eoveelDeG
Hydrogen scccccccsccccccccccscceble? coseeblo95
Methane ceocecccccccsccsccsescee Wed sovesdLe BG
BACKOTEN cevcccccvcccccceorsceccs GeB coves ob?

These analyses reveals the fact that
illuminating gas is a mixture of carbon monoxide, hydro-
carbons, am other gases of no special importance to the
subject at hed.

Several experimenters have disagreedas to the
value of illuminating gas ak a carburiser, but some late
investigarions together with the fact that this gas is
today used commercially for carbonising, indicate thet it
is of some practical value. Whe Lengenbert first started
his experiments using this gas, he found that under the
gonditions which existed the gas decarburised the steel
instead of oarburising it. He explained this phenomenon
in the following manner. Taking as an illustration the
reaction 2 CO= -005 + C6, he says that at 500° © about
oneshalf of a given velume of OO would be dissociated into
CO, and C, and at 1000° © only about 03% would be
dissociated. When the 001d gas engers the tube, it
gradually heats up and deposits carbon until an equili-
brium is reached for the temperature in question. The

gas, however, never reaohes equilibrium as it is constantly
changing temperature. If the rate of flow is not too
rapid, the gas will get to the hot sone impoverished in
carbon, and in order to reach equilibrium it mst absorb
carbon, 48 it has passed the sone of oarbon deposit,
the only place from which it may obtain carbon is from
the sample of steel unier treatment. This is the ex-
Planation given by Langenberg for the decerburising of
steel when using illuminating gas at low rates of flow.
In later work he placed som oarbon in the hot sone and
obtained satisfactory results. He obtained some interest-
ing results by using pressure on the cerburizing gas.
fhese are shown graphically in Fig. 7. From this chert,
we see that the degree of carburization is different at
different pressures, but at all temperaturos the point
of highest efficienay seems to be about 40 lbs. pressure
per square inah.

The resulte of som of Giolitti's experiments
along this line are shown in the following table.
TABLE, 4.

ILLUMINATING GAS AS A OARBURIZ ING AGENT

 

Length Pressure femper- Volume
of « -- of car- ature of gas
Number cementation. burising Deg. 0. used in

in hours gas in liters

_ mn. HG

16 7 760 780 15
17 7 613 780 15
18 7 463 780 15
26 5 470 900 8
27 5 463 900 8
34 5 760 1000 10
35 5 460 1000 10
42 5 760 1100 7
43 3 459 1100 7
25

TABLE 4 (Cont'd)

ILLUMINATING GaS AS A CARBURIZING AGENT.

 

Total Hyper- Maximm
thickness Eutectoid  Euteotoid Hypo- ooncen-
of case case mm case mm. KButeotoiad tration
BED. case mn. in %
ease
8 one om m= 8 8
5 oom -—@ 5 06
2 e 5 =o e 2 le S ® 9
12 mae o-m 102 85
Zed mon 3 1-8 9
2 e 1 ae e 3 1 e 8 e 9

¥Yrom these results, the following facts are
made-clear;: the concentration and penetration increase
with the temperature; inorease of pressure increases the
penetration; and the carburizing action inoreases with
the rate of flow of gas. To get the maxima rate of
oarburising there should be a than coat of carbon on
the sample /

Giolitti’s mifim objection to cementation by
hydrocarbons and illuminating gas was that a case t00
high in oarbon was found and therefore there was danger
of the case splitting off. However, White and Hood alaim
26

to have eliminated this effect by letting the sample
s0ak in the retort after the gases were turned off.
Their procedure was to carburise the pieces with coal
gas at a high temperature for a short time, produoing
a thin case of high concentration. The gas was then
shut off and the pieces were allowed to soak in the
hot furnace until the carbon had diffused in toward the
center of the pieces and the case was of ths desired
quality. An idea of the tim allowed may be obtained
from the following breatment:
i Le Pen minutes allowed for coming up to heat.
2. Oarburisation at 1900° F for 30 minutes.
3. sOaking for 30 minutes.

The sample treated in this manner, originally
004% carbon steel, had a oase of .03 inoh and approximate-
ly euteoctoid composition. No hyper -euteotoid case re-
sulted and there was no sudden line of demarkation be-
tween the case and the core. Practically the same re-
sults can be obtained by the use of a mixture of carbon
monoxide and hydrooarbons.
27

THE USE OF OYanOGEN GAS.

fhe action of the gases of most practical
importance in case carburising has been studied in
the foregoing pages. another gas which is of leas
interest bat which is used in practice to some extent
is that of cyanogen. One reason why cyanogen is not
used more extensively is that it is poisonous and
thus very dangerous to the lives of the workmen.
Organio compounds containing nitrogen are also some-
what expensive. «another reason for the limited use
of ayanogen is that if forms a case which is very
irregular and high in carbon with an abrupt change be-
tween the case and the core, and thus comes the danger
Of exfoliation. some people advocate the addition of
oombined nitrogen, such as sal ammoniac, to the
oarburiser with the idea in mind that it sids in the
formation of cyanogen. However, it has been found that
such practice is objectionable because of the fact that
a hard, brittle nitride of iron is formed.

Fig. 8 shows a diagram of @ furnace recently
developed for the oarburizsing of shafts by cyanogen
gas. In this type of furnace, the carburiser is
wyanogen gas formed by the vaporisation of a cyanide
Salt which is heated by a gas burner. ‘the shaft is
suspended inside the muffier whioh is eleotrically
 

 
heated. he gas passes up around the shaft and into
the upper chamber from whioh it is conducted by a
suction fan back to the furnace, thus creating a
pressure. ‘fhe top of the upper chamber is provided
with a safety cap to relieve the pressure should it
beoome excessive and also to allow the gases to
escape during charging. ‘this furnace thus far has
been used only for carburizing shafts, but perhaps
with knife-edged supports it might be utilised for
carburising other parts.

PUTURE INVEST IGsTIONS.

It has already bem@m stated that the process
of case carburising is yet in its early stages of
development, although it is a very old steel treating
method. While quite a bit of research work has been
oarried out in theoretical and soientifio work] there
still remains much to be done in developing methods to
put some of the recent discoveries into actual practice.
there also remain many phases of soientifio study to be
carried out in oase carburizing. Some of these topics
which will probably afford some interesting researoh
will be outlined briefly in the following pages.
Ll. AOFION OF VAKIOUS MIXTUKEd OF 00 AND HYDROCARBONS.

It has been shown what aotion each of the
above gases has upon steel in the process of
carburisation, and also what a mixture of carbon
monoxide andi the hydrooarbons will do. Yet results
of both are interesting and a practical nature can be
obtained from the study of the results of carbonising
with various mixtures of oarbon monoxide and different
hydrocarbons. For instance, use different percentages
of CO with methane, then ethylene, eto., and make a
shart of the results of carburization. Tham the most
efficient point of carburizing can be easily obtained
for a given type of case. if a case high in oarbon is
needed, or if a case of comparatively low concentration
is wanted, reference to the chart will show the exact
percentage of the carburizing gases, and the proper

temperature and time of cementation.

2. A OOVERING TO PREVENT ORRTaIN PaR?S FROM CARBUKIZING
WHEN USING THE GaS REOKT MADE BY THE AMEKICAN Gas
FURNACE COMPaNY.

quite a lot of commercial work is carried on
at the present time in case oarburising with illuminat-
ing gas by use of the special gas furnace made by the
American Gas Furnace Uompany. <A brief desoription of
the furnace will be given to make the idea alear. The
mffle of the furnace is of metal and is about 6 inches
in diameter and about 30 inohes long. Around this is
a cylindrical jacket which houses the heating chamber.
‘fhe furnace is heated uniformly by two sets of gas
burners located on opposite sides of the ohamber.
Connections are made at the rear end of the mffle for
allowing the carburising gas to enter at atmospheric
pressure. The waste gas after oarburising is burned
as it comes from the furnace. Aktached to the mffle
is a worm and worm wheel motor driven, which keeps the
muffle and contents rotating during carburisation.

Vhen copper plating is used for proteoting
the parts which must not be carburised, it chips off
due to the knooking about of the pieces during rotation.
Pherefore some other means must be found to protect
these parts, perhaps by using some other means now in
use Or by inventing a new process whic will produce the
desired results.

Then too, investigations oouléd be carried on
to determine whether it would be a paying proposition to
use some sort of purifier and e means of utilising the
waste heat in the carburising gas as it comes from the
mffle. Gas mest be passed through the miffle at a
certain rate to produce the best results, and therefore
1

some of the gas is wasted. The exhausted gases could
be analyzed and then one could determine whether there
was enough useful gas going to waste to pay to purify it
and use it over. Or perhaps the waste heat in the gas
could be used to preheat the entering gas or for some
other useful purpose which would be practical. Many
points come up in oonnection with gas carbonising which
it will pay to investigate.

S- DIFFUSION OF CARBON BY "SOAKING".

Carburisation of steel by the hydrocarbons and
by cyanogen result in a case high in carbon ané with
abrupt changes between the core and the case. TO over-
come the danger of exfoliation resulting from this type
of case, it has been found that by letting the piece
"soak" in the furnace for a time after oarburising,
the carbon will diffuse into the interior. Some
experimental work might be carried out to determine the
time of soaking for different qualities of cases desired.
fhe rate of diffusion may depend upon the difference in
ooncentration between the case and the oore and if so,
it might be interesting to find out whether the rate of
diffusion oould be expressed always as a function of the
Gifference in concentration. The same may hold in re-
gard to the temperature of the piece. Perhaps this
subjeot does not furnish moh material for investigation
but some valuable results might be obtained.

4. THE EFFECT ON STEFL OF NITROGEN AS USED I
VARIOUS OEMENTS.

Very little has been done in determining the
effect of nitrogenous cements on steel. A little work
of theoretical nature has been done by J. Kirner along
this line. His experiments indicate in all probability
two things:

1. That certain nitrogenous cements under certain
comitions give rise to the diffusion of
nitrogen into the steel, am

£2. That nitrogen exerts quite an influense on
cementation. It is know that small
quantities of nitrogen exert quite an
influence on the mechaniacak properties
of steel, and it follows that interesting
remlts could be obtained from experiments
along this line.

5. HRAT TREATMENT OF IRON AND STEEL IN A
NEUTRAL ATMOSPHERS.

Ae H. White and H. T. Hood have show that it
is possible to heat pieces of iron and steel in an
internally fired muffle without any oxidation or
formation of soale on the pieces. The mixture which
enables this to be carried ont is about one volume of
illuminating gas and two volumes of air, the furnace
being heated by means of illuminating gas. This mixture
is so rioh that it will not burn unlese preheated.
Although no oxidation takes place during heating at high
temperatures, steel is slowly decarburised, but not as
much as in the ordinary furnace atmosphere. The de-
carburizing action may be decreased by increasing the
amount of 41 luminating gas in the mixture. However, at
the normal heat treatment temperature the decarburising

action does not exist.

It does not seem impossible to assume that a
furnace embodying such a feature oould be built for
practical work in heat treatment and oase carburising.
The pieces may be heated in a neutral atmosphere,
carburised in gas, and kept hot in the furnace in a
neutral atmosphere during the time of diffusion. Such a
type of furnace, besides being of great practical
importance, could be used in experimental wrk to obtain
acourate results in case carburizing investigations. The
results of White and Hood oan be well used as a guide
for the design of such a furnace.
 
The above suggestions are only a very few
of the numerous problems to be worked out in the
development of the gas aarbonising process. The work
has only begun. There are very few men who have gone
into these problems to any extent. What has been done
has been accomplished only during the last fifteen
years. There yet remain many problems of both a
theoretical and a practical nature to be solved by the

research engineer.
SUMMAKY.

It has been pointed out that cementation
atarted back with the early development of civilisation,
and has come down to us almost wholly undeveloped. The
theory of the process has been explained to be the
action of the gases as ocarriezs of carbon. Taking this
as the basis of the investigations, the action of all
of the gases found in carburisers has bem studied with
interesting results.

fhe conclusions reached with the study of
earbon monoxide are as follows:

lL. CO produces a case of low concentration; the
higher the temperature the lower the
concentration.

Ze The penetration inoreases with the temperature

and pressure. The rate of penetration is

more rapid with CO than with other gases.
55

3. The rate of flow of gas increases the rate of
penetration and the concentration of the
carbon.

The following are the general results obtained
with the hydrocarbons and cyanogen:

l. Hydrogarbons and cyanogen give a case high in
earbon, and danger of exfoliation is
enoounteread. fPanger of exfoliation, however,
is overcome by the process of "soaking".

2. Concentration and penetration increase with a
rise in temperature with hydrocarbons.

3. Presmre increases the rate of penetration but
does not offset the concentration.

4. Carburisation seems to be a direct funotion
of the rate of flow of gas, and varies with
the different temperatures.

5. Methane is more effective than the other hydro-
carbons, but only at temperatures higher
than 1700° F.

6. Tliluminating gas, being a mixture of carbon
monoxide and hydrocarbons, gives results
between the two.

7. If the rate of flow of gas is not rapid enough,
decarburisation will take place instead of

cenentation.

8. A Ssinghlar faot which is true of all carburising
o
wee
56

gases at all temperatures is that a

pressure of about 40 pounds per sq. in. is

the most efficient presmre. An inorease

in pressure beyond that value results in a

very small increase in penetration.

Rxperimental research along the lines of gas
carbonising has just begun. <A few of the many problems
to be solved are outlined in the foregoing pages. There
are still numerons theoretical and practical problems to
be worked out.

Carbanising with gaseous carburisers in due
course of time will probably take the place of the
present pack-hardening process on account of the saving
of time, labor, material, and money in the operations
carried out in the process. The time has come for the
development of the oase carburizing methods, end probably
in the course of a few years vast ohanges will take place

in the process of cementation.
Le

Be

3

4.

5.

66

Te

8.

37

BIBLIOGRAPHY.

fhe Cementation of Iron and steel - -
Dr. Frederico Giolitti.

Gas as a Oase-Hardening agent - - White & Hood in
1915 keport of Michigan Gas association.

Cementation by Gas under Pressure - - F. 0. Langenberg.

Oase Carbonising - - Merots T. Lathrop. |
A. 5. Me. B. Journal.

The Application of Heat in Case-Hardening - -
Theodore G. Selleck, Ded. 1918, Issue of
gournal of american steal Tfreaters pociety.

Yailure of the Carbonising Process - - &. ¥. Lexe,
april Issue of Proceedings of the steel
freating nesearch Society.

Paultes of the Uarbonizing Process ani their Cure - -
Yheodore G. selleck. March Iseue of Proceed-
ings of the steel treating xesearch boaiety.

Heat ‘treatment of Iron and bteel in a Neutral
Atmosphere - - White & Hood in 1915 keport
of Michigen Gas association.
1. History and Theory of Cemerntation cccscecccsee
2. Requirements for vase Oarburising eocccccvece

Se
4.

Ae
B.
0.
De

Z.

TaHLE OF CONTENTS.

fhe Composition Of the steel ccccccccvcccce
fhe Nature of the Oarburiser cccccccccsece

a wo of ww

the temperature Of Oarburising cccccccecee
fhe Concentration of the Carburiser.

and its contact with the steel wcccssccsee 6
The time Of Oarburizing cecccccccccccccsccsee 7

Yaults of the present oarburising process eo 7

Mxperimental research in Gas Carbanising .... 10

Ae
Be

0.

De
B.

THE APPATATUS coccccccccccccvccccseceosesos LO
fhe action of Oarbon Monoxide as a
Oarburising UaS cccccccccccccccccccccccece LE
fhe use of Hydrocarbons for
Carburisation ceccccccccessccccccccccccsecs A?
(a) Pure hydrocarbons ceccccccccccccccccce 18
(>) Illuminating gas eccccccccccccccsccccce BL
The use Of GYBMOBEN GAB ccccccccccccsecsee 27
Yauture investigations ceccccccccccccccsece £8
(a) aotion of various mixtures of 00

and hydrocarbon eccccecvcccsccvccceses 29
(b) a covering to prevent certain parts

from carburizing when using the gas

retort made by the America Gas

PurBace COMPANY ccccccccccccccccsccscce 29
TABLE OF CONTENTS (Cont'd)
Page
(o) Diffusion of Carbon by "Soaking" ....+. Sl
(4) the effeot on steel of nitrogen as
used in the various coments wscccccsees BE
{e) Heat treatment of iron and steel in a
neutral atmosphere eesecccccccccceccces Se
Be SUMMALY cvocccccccccccccccccecccccccceccccecccs Of
6. BADLLOGraphy cecccccccccccccccccccscccecscccces B7
   

Thin