An Improved Process for Carburizing Steel for Armour Plates and other purposes.
Year: 1899

page_text: [Communicated from abroad by JOHN SIMON UNGER, of Homestead, in the County
of Allegheny, State of Pennsylvania, one of the United States of America,
Chemist.]
An Improved Process for Carburizing Steel for Armour Plates and
other purposes.
I, WILLIAM BURGELAND JOHNSON, of 4, Clayton Square, Liverpool, in the
County of Lancaster, Engineer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement, reference being had to the
accompanying drawings forming part of this specification in which :-
-
Fig. 1 is a longitudinal sectional elevation of the gas furnace or heating cham-
ber, showing the movable hearth in place. Fig. 2 is a horizontal section on the
line 11-11 of Fig. 1.
My invention relates to the super-carburizing of plates or pieces of steel and
is especially designed to be applied in the manufacture of armour plate or of
masses of steel to be shaped into armour plate.
My invention is based on the discovery that carburization can be conducted
most rapidly and most efficiently by using as the carburizing agent soot, the
amorphous form in which carbon is deposited as the result of the decomposition
of hydro-carbon gases.
I shall now describe the preferable mode of practicing my invention referring
to Fig. 1, in which 2 represents a heating furnace having at the opposite sides
gas ports 3 through which the heating gas is introduced at one side of the fur-
nace and discharged after combustion at the other side. 4 is a movable hearth
common in furnaces of this type carried on a truck 5 mounted on wheels 6 and
adapted to be moved into and out of the heating chamber by a suitable motor 7.
The plates of armour steel are placed on the hearth with the faces to be carburized
towards each other and separated by interposed billets or supports 9.
A gas
pipe 10 adapted to deliver hydro-carbon gas, is inserted into the space 11 between
the armour plates, an outlet for the gas is also provided at 12 by drilling at any
convenient spot a hole through one of its billets, and said space is otherwise
sealed to exclude the air by luting with clay the joints between the billets. Inter-
mediate sag-blocks, like the blocks 16 shown in Fig. 2, may also be employed
where the plates are of large area. This is the arrangement which has commonly
been adopted for super-carburizing armour plate by the gas-treatment process.
In such process, it has been the practice first to heat the plates by the passage of
flame through the heating chamber 2 until they are brought to a high tempera-
ture of about from 8750-1000° Centigrade, and after the plates have been thus
heated, to introduce through the pipe 10 into the space between the plates, a
current of hydro-carbon gas, which is caused to flow through the space and out
of the outlet 12 for a period of six days or more, thus gradually carburizing the
inner faces of the plates. When the gas thus introduced comes into the highly
heated space between the plates, it is decomposed and deposits solid carbon upon
the surfaces, and it is this deposited carbon which is absorbed by the metal and
performs the work of carburization. But the carbon thus deposited at the high
temperature of the furnace is graphitic, and I have discovered that by modifying
the conditions so that an initial layer of amorphous carbon or soot is deposited
upon the faces of the steel plates, the carburizing operation can be conducted

page_text: more rapidly and with better results than is otherwise possible. This I effect
by introducing the hydro-carbon gas at an earlier stage than heretofore, while
the armour plate is at a lower heat, such that the carbon will be deposited from
the gas as amorphous carbon and not as graphite. Thus when the plate has been
heated sufficiently to show a faint color, say a temperature of about 550° C. I
introduce the hydro-carbon gas from the pipe 10. The consequence is that the
faces of the plates will be covered with a layer of amorphous carbon or soot
deposited from the gas, and when the plates afterwards become more highly
heated and the carbon deposit becomes graphitic in its nature, the graphitic
carbon is deposited upon and as a covering for the inner layer of amorphous
carbon. The layer of carbon next to the steel surface being amorphous, is in the
most active and efficient condition in which it can be presented. The heating is
continued and the temperature maintained at about 8750-1000° C. for six days
or more, according to the thickness of the plates until the desired degree of car-
burization has been effected. Specifically, I would state for the information of
those practicing my invention, that a plate six inches thick, in a furnace con-
structed as shown in the drawings, should be maintained at a temperature of 900° C.
for about 9 days or at 1000° C. for about 7 days in order to produce with my
invention the degree of carburization ordinarily desired in armour plate, the
length of the operation necessary for different degrees of carburization being
varied as will be understood by those skilled in the art, accordingly as the tem-
perature is kept at a higher or lower degree, and as the plate treated is thicker
or thinner. By my invention applied in this way, the steel absorbs the carbon
readily and quickly enabling me to perform the work at lower temperature
(say 900° C.) than has been common heretofore, without unduly prolonging the
operation, and by using such lower temperature to avoid the danger of semi-
fusing the surface of the plate; or when I use higher temperatures, say 9000-
1000° C. my invention enables me to perform the work in much less time than
heretofore.
I believe I am the first to bring the gas into contact with the armour plate to
be carburized before the plates are brought to full working temperature of 875°—
1000° C.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. The process herein described for super-carburizing steel for armour plates
and other purposes, which consists in heating the steel to a relatively low tem-
perature sufficient to cause the decomposition of hydro-carbon gas and the
deposit therefrom of amorphous carbon or soot, bringing such gas into contact
with the steel so heated, and excluding air, thereby depositing a layer of amor-
phous carbon upon the steel, then continuing at a higher temperature and for a
period of days the heating of the plate and the admission of gas thereto, and
depositing graphite carbon upon the plate at such higher temperature; sub-
stantially as described.
2. The process herein described for super-carburizing steel for armour plates
and other purposes, which consists in introducing into contact with the steel
hydro-carbon gas while the steel is at a temperature less than the working tem-
perature of 875°-1000° C. thereby causing a deposit of carbon at a relatively
low-heat, and then raising the temperature to the working point, continuing
the heating and admission of gas for a period of days, and depositing graphitic
carbon upon the plate at such higher temperature, substantially as described.
Dated the Twenty-first day of September 1899.