US2762701A

US2762701A - Carburizing molten ferrous metal

Info

Publication number: US2762701A
Application number: US413833A
Authority: US
Inventors: Francis T Crego; Philip M Hulme
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1954-03-03
Filing date: 1954-03-03
Publication date: 1956-09-11
Anticipated expiration: 1973-09-11

Description

Sept. 11, 1956 F. T. CREGO ET AL 0 CARBURIZING MOLTEN FERROUS METAL Filed March 3, 1954 INVENTORS FRANCIS T. CREGO PHILIP M. HULME United States Patent-O pany, Incorporated, New York, N. Y., a corporation of New York Application March 3, 1954, Serial No. 413,833

12 Claims. (Cl. 75-48) This invention relates to the treatment of cast iron, and is directed particularly to the provision of an improved method for carburizing molten cast iron. The method of the invention is based on the introduction into molten cast iron of a material composed mainly of elemental carbon by means of a carrier gas employed in a critically limited quantity, and is particularly characterized by the use of a form of carbonaceous material which can be thus introduced without defeating the critical limitation imposed in the quantity of carrier gas employed.

The physical properties which determine the suitability of cast iron for the numerous uses to which it is put depends largely on the amount of carbon present and on the form in which it appears in the microstructure of the metal. Formerly, when pig iron and high carbon cast iron scrap formed the chief raw material of the iron founder, there was little problem in producing molten iron containing suflicient carbon for making castings of good quality. With the enormous growth of the steel industry that has occurred, however, increasing amounts of pig iron have been diverted to steel making, and increasing amounts of low-carbon scrap have had to be absorbed by iron foundries in preparing cupola charges.

'In the normal operation of acid-lined cupolas the amount of carbon picked up by the melted metal is small, and consequently, such cupolas as not suited for preparing cast iron from low-carbon charges. The only practical method heretofore available to meet the problem thus created has been to make increased use of the basic-lined cupola. But since the basic cupola is considerably more costly to operate than its acid counterpart, this solution is economically disadvantageous.

Numerous efforts have been made, over a period of many years, to provide a simple and effective method for incorporating carbon in molten cast iron after it has been melted in an acid-lined cupola or other furnace. Heretofore, however, no procedure for doing so with the necessary close control on the amount of carbon picked up by the molten metal, and with the requisite degree of economy both in operation of the treating method and in the amount of carburizing agent employed, has been developed.

We have found that certain inexpensive carbonaceous materials, in which the carbon is present in elemental form, can be introduced easily and economically into molten cast iron, and a good and accurately predictable recovery of the carbon in the molten metal can be attained, by use of the method and apparatus described in U. S. Patent No. 2,577,764 to Philip M. Hulme. Not any form of commercial carbon-bearing material can be thus introduced, however. The success of the method depends on the use of a very small volume of a carrier gas to carry the solid material in finely divided granular form into the molten metal. If the volume of carrier gas employed exceeds about two cubic feet per pound of solid carbonaceous material, the gas tends to sweep the solid material through the molten metal rather than to bring it into effective contact therewith. We have found that if the carbonaceous material contains any substantial quantity of moisture or volatile matter, the liberation of gases which occurs when such material is heated by introduction into a bath of molten cast iron results in increasing the volume of carrier gas to such an extent as to seriously impair or even destroy the efficacy of the method of introduction.

Based on these findings, the invention provides a method for carburizing cast iron" which comprises introducing a carbonaceous material composed mainly of elemental carbon into a body of molten cast iron at a substantial distance beneath the surface thereof, characterized in that said carbonaceous material is in finely divided granular form (preferably having a screen analysis of 100% minus 10-mesh and at least 50% plus l0O-mesh) and is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about onequarter to about two cubic feet per pound of solid material delivered into the molten metal, and further characterized in that said carbonaceous material is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature'of the molten metal.

Many carbonaceous materials in which the carbon is present predominantly in elemental form are available quite inexpensively. Mostly, however, the economically attractive materials contain prohibitively large amounts of volatile combustible matter. Bituminous coal is quite impractical to use for this reason, and even the hardest grades of carefully dried anthracite coal generally contain too much volatile matter and undesirably large amounts of ash. Petroleum coke as it normally is available likewise contains an excessive amount of volatile material, but a good grade of carbonaceous material for carrying out the method of the invention can be prepared by baking such coke sufiiciently to rid it of its volatiles. Ordinary metallurgical coke also commonly contains excessive volatile matter; and although it can be employed successfully if it has been baked sufficiently and at a high enough temperature during or subsequent to its manufacture to free it quite completely of volatile materials, it quite frequently contains such an amount of ash and sulfur as to make its use undesirable. The most-satisfactory of the relatively inexpensive forms of elemental carbonis electric furnace graphite. This material is readily available in the fine granular form that is most suitable for introduction with a carrier gas, and it is produced by means which insure its freedom from volatile matter.v Moreover, it is free from ash which, if present in substantial amount, may lead to undesirable side reactions between components of the ash and components of the molten cast iron. Natural graphite, on the other hand, is ordinarily too contaminated with undesirable mineral matter to be used satisfactorily.

It is well known that if molten cast iron is treated, just before being cast into molds, with any of a number of leads to an improvement in the properties of the cast product, beyond the change that would be expected simply on account of the increase in carbon content. Accordingly, a feature of the invention resides in treating molten metal having the composition of a gray cast iron with a carbonaceous material by the above-described method of the invention, using the inoculation technique, i. e. casting the molten metal into molds promptly (preferably within five or at the most ten minutes) after the introduction therein of the carbonaceous material.

It is well known that calcium carbide is a most effective reagent for desulfurizing molten cast iron; and in fact the aforementioned Hulme Patent No. 2,577,764 is directed to a method for incorporating calcium carbide into molten ferrous metal for the purpose of desulfurizing it. We have found that it is possible to desulfurize cast iron and to carburize it at the same time by introducing therein a mixture of calcium carbide and carbonaceous material. The invention therefore contemplates treating molten cast iron with an intimate physical mixture of finely divided calcium carbide and a carbonaceous material of the character described above; and further the invention provides such mixture as a new and advantageous product for use in treating molten cast iron.

Various forms of apparatus are available for carrying out the method of the invention. One such form of apparatus, of substantially the same design as is shown in the aforementioned Hulme Patent No. 2,577,764, is shown in Fig. 1.

Referring to Fig. l, a receptacle 5 (such as a ladle, forehearth, induction furnace, or the like) carries a charge 6 of molten cast iron to be treated in a batch operation.

of the carbonaceous material, or a mixture thereof with calcium carbide, in finely divided granular form. The charge 19 descends by gravity flow from the hopper 18 into the tube 11 and is advanced by the screw conveyor 12- tothe end of the tube 11, where it falls by gravity into a feed tube 2% which is protected by a refractory and heat-insulated member 21. When the apparatus is lowered to the position indicated in Fig. 1, the lower end of the tube extends to well beneath the surface of the molten metal, thus permitting the carbonaceous material to be introduced therein.

In order to prevent the molten metal from rising in the member 21, and to enable the carbonaceous material to flow into the molten metal in the receptacle 5, a carrier gas is provided in a container such as a cylinder 22 which is connected through a flowmeter to a pressurereducing regulator valve 23 having a gauge 24 which indicates the pressure. Thence the carrier gas is delivered as required through a pipe 26 which extends to a point adjacent the end of the screw conveyor 12. A by-pass pipe 27 with a valve 27 connects the pipe 26 to the cover 28 of the hopper 18, so that the gas pressure is equalized throughout the injection apparatus.

When the screw conveyor is rotated in a direction to advance the carbonaceous material from the hopper 18 to the tube 20, and when the regulator valve 23 is adjusted to allow only enough flow of carrier gas through the tube 20 to enable the carbonaceous material to flow out the lower end thereof, the carbonaceous material is eifectively delivered into the molten meta The amount so delivered is accurately controlled by the speed of rotation and time of operation of the screw conveyor 12.

As previously stated, there is a critical limit on the maximum amount of carrier gas that can be employed without suffering a serious loss of efficiency in utilization of the carbonaceous material. This limit, for practical purposes, has been found to be approximately two cubic feet of carrier gas, measured at standard temperature and pressure, for each pound of solid material delivered into the molten metal. If the volume of carrier gas relative to the amount of solid material significantly exceeds this limit, then the gas, in bubbling rapidly up through the molten metal, tends to carry much of the solid material to the surface of the metal before it has come into effective contact therewith. When the gas volume is maintained below this limit, however, an eifective contact between the particles of solid material and the molten iron is achieved and a high, and accurately predictable, recovery of the solid reagent in the molten metal is obtained.

Enough carrier gas must of course be used to enable the solid material to flow out the lower end of the tube 29 into the molten metal. In general at least about onequarter cubic foot of carrier gas per pound of solid material introduced should be employed; but in some instances effective and efficient introduction of the carbonaceous material into the molten metal is achieved when the flow of carrier gas is low enough so that the amount used is even less.

It is of some importance in employing the abovedescribed apparatus that the carbonaceous material (and also the calcium carbide when it is employed) be finely divided, and yet be in granular form rather than in the extremely fine, almost colloidal, form that characterizes some carbon blacks. The carbonaceous material must, on the one hand, be time enough so that it will flow with the carrier gas into the molten metal. On the other hand, it must not be so fine that it is readily incorporated in non-settling or difiicultly settling suspension in the carrier gas, for then it is likely to be canied out of the molten metal in the rising gas bubbles without coming into effective contact with the molten metal. Generally speaking, these conditions are met if the carbonaceous material has a screen analysis (Tyler screen series) of minus 10-mesh and at least 50% plus IOO-mesh (i. e. if 100% of the material will pass through a 10-mesh screen while at least 50% by weight will be retained on a lOO-mesh screen).

The character of the carrier gas employed is not in itself critical. It is of course advantageous to use a gas which does not react deleteriously with the molten ferrous metal or with the added treating agents. As pointed out in the aforementioned Hulme patent, an inert gas such as nitrogen is preferable for use in injecting calcium carbide into molten ferrous metal, although reducing gases such as propane or natural gas, or even a mild oxidizing gas such as carbon dioxide, can be employed. For the purpose of injecting a carbonaceous material, all these gases, and even air, may be employed as the carrier gas. If air is used, some of the injected carbon will be oxidized by the oxygen of the air, but the amount lost may be small enough to be less objectionable than the higher cost of the non-oxidizing or reducing gases. When calcium carbide is injected along with the carbonaceous material, then of course an inert or reducing carrier gas should be employed.

Following are examples of the method of the invention:

Example Z.'A hypoeutect-ic gray cast iron composition was prepared having the following analysis:

Percent Total carbon 2.88 Silicon 1.46 Manganese 0.65 Sulfur 0.09 Phosphorus 0.12 Iron Balance Carbon equivalent 3.41

This iron composition was melted and heated to a temperature of 2800 F. Electric furnace graphite, in the form of scrap graphite electrodes crushed to minus mesh particle size, was injected into the molten metal, using nitrogen as the carrier gas, with the aid of apparatus of the character described above. The total amount of graphite thus introduced was 1.25% by weight of the molten iron. Some twenty minutes after the graphite addition, the metal Was cast into molds. A sample of the casting was analyzed and found to contain 3.95% total carbon. Thus the metal had been converted from a hypoeutectic to a hypereutectic composition. Efliciency of the injection, in terms of the proportion of the carbon introduced which was recovered in the cast metal, was 85.5%.

Example II.A melt of the following composition was prepared:

Percent Total carbon 2.75 Silicon 2.03 Manganese 0.63 Sulfur 0.11 Phosphorus 0.12 Iron Balance Carbon equivalent 3.47

The melt was heated to 2800" F. and a mixture of calcium carbide and crushed scrap electrode graphite, minus 10-mesh in particle size, was injected into it, using nitrogen as the carrier gas and using injection apparatus of the character described above. The amount of the mixture, and the proportions therein of calcium carbide to graphite, were such as to introduce a total of 1.5% by weight of calcium carbide and 0.562% by weight of graphite into the molten metal. The metal was cast promptly (two minutes) after introduction of the treating reagent. The cast metal was analyzed and found to contain 0.016% sulfur and 3.28 total carbon. The elfioiency of graphite utilization was 94.0%. Thus excellent desulfurization and highly efiicient recovery of graphite carbon was achieved.

Example III.-A hypoeutectic gray cast iron having the following composition was prepared:

Percent Total carbon 3.15 Silicon 1.80 Manganese 0.65 Sulfur 0.11 Phosphorus 0.12 Iron Balance Carbon equivalent 3.79

The cast iron of this composition was melted and heated to 2600 F., and a mixture of calcium carbide and crushed electric furnace graphite (from scrap electrodes), minus 10-mesh in particle size, was injected in the same manner and in the same amount as in Example II. The metal was cast promptly (four minutes) after introduction of the treated reagents. The cast metal was found to contain 0.006% sulfur and 3.69% total carbon. The efiiciency of recovery of the graphitic carbon was 95.8%. Thus here again, excellent desulfurization and excellent recovery of the graphite carbon in the cast iron were attained.

In each of Examples II and III the carbon content of the added calcium carbide was disregarded in calculating the efficiency of the carbon recovery. Experience has shown that the carbon content of calcium carbide is not recovered in cast iron when the metal is treated with this reagent alone, and no diiferent result appears to be obtained when it is injected in combination with a carbonaceous material such as graphite.

Example I V.A cast iron melt of the following composition was prepared:

Percent Total carbon 3.11 Silicon 2.01

Percent Manganese 0.62 Sulfur I 0.094 Phosphorus 1 0.099 Iron Balance Carbon equivalent 3.81

Electric furnace graphite in the form of crushed scrap electrodes was injected into the melt at a temperature of 2790 F. The injection was made with apparatus of the character described, and using air as the carrier gas. The amount of graphite injected was 0.55% by weight of the cast iron. The metal was cast seven minutes after injection of the graphite. The castings obtained were analyzed and found to contain 3.61% total carbon. Thus the efficiency of carbon recovery in the metal was 91%, despite the use of air as the carrier gas.

Example V.--A molten cast iron of the following composition was prepared:

Percent Total carbon 2.81 Silicon 2.38 Manganese 0.61 Sulfur 0.12 Phosphorus 0.14 Iron Balance Carbon equivalent 3.53

Using apparatus of the form described above, and with nitrogen as the carrier gas, a mixture of calcium carbide and finely divided baked petroleum coke was injected into the molten metal at 2800 F. The amount of calcium carbide in the mixture was 1.0% of the weight of the molten metal, and the amount of baked coke in the mixture was 0.55 of the weight of the molten cast iron. The baked coke contained approximately 97% carbon, and had been substantially completely freed of its volatile matter and moisture by the baking operation. The iron melt was cast three minutes after completion of the injection of the carbide and baked coke mixture. The cast product was analyzed and found to contain 3.29% total carbon, so the recovery of the carbon content of the coke in the cast iron was (as in Examples II and III, the carbon content of the calcium carbide was disregarded for purposes of calculating the efiiciency of carbon recovery in the cast iron). The sulfur content of the cast product was found by analysis to be only'0.018%. Thus highly efiicient desulfurization together with efiicient utilization of the injected coke carbon was achieved.

There is nothing especially critical about the temperature at which the carbonaceous material, alone or in combination with calcium carbide, is injected in the molten iron. The foregoing examples are typical of conventional foundry practice, in that the metal was brought to a temperature of 2600 to 2800 F. preparatory to casting, and the injection was made atthis temperature.

In further tests conducted substantially as described in Examples II and III, but in which substantially longer periods of time elapsed between injection of the calcium carbide and graphite mixture and the time of pouring the metal into molds, the ultimate tensile strength of the cast iron products was notably lower than the tensile strength of the cast products produced in carrying out the tests reported as Examples I and HI above. The evidence of these other tests, while not conclusive, is indicative that injection of carbonaceous material into molten ferrous metal, by the method of this invention, using the inoculation technique of casting the molten metal promptly after introduction of the carbonaceous material, results in a product having improved properties over what can be obtained by introducing carbonaceous material otherwise than by the inoculation technique.

In other tests conducted substantially in accordance with the procedures outlined in the foregoing examples, various commercial forms of carbonaceous material composed mainly of elemental carbon were injected into the molten metal. These tests have indicated that other forms in finely divided granular of carbonaceous material composed mainly of elemental carbon can be injected by the method of the invention into molten ferrous metal, and a good recovery of the carbon can be attained, provided such materials contain but little or no moisture or volatile combustible matter. However, if the ash content of such material is high, it may be undesirable to use because of reactions that may take place between ash components and components of the molten cast iron.

An important advantage of the injection method of this invention is that the increase in the carbon content of the molten metal is readily and accurately controlled by controlling the amount of graphite introduced therein. For example, in a series of three different tests using the cast iron composition of Example II and all conducted substantially as described in that example, and in which the amount of graphite introduced relative to the weight of ferrous metal employed was the same in each case, the total carbon content of the cast metal product was found to be remarkably uniform, varying from a low of 3.28% to a high of 3.31%. Similarly, in a series of four tests using the cast iron composition of Example 111 and all conducted substantially as described in that example and in all of which the proportion of graphite introduced to the amount of ferrous metal used was maintained the same, the total carbon content of the cast product was in the range from 3.69% to 3.75%. Owing to this uniform carbon recovery in the molten metal, and the high efficiency of carbon utilization, the total carbon content of the cast product can be readily and accurately predicted from knowledge of the carbon content of the melt and the amount of carbon injected. This is a particularly important feature of the invention, for it means that by the method of the invention it is possible to produce a cast iron product of accurately predetermined carbon content in a simple and reliable fashion. This is a result not achieved by any carburizing procedure heretofore proposed which has been based on the introduction of a carburizing material into the metal after it has been fully melted. Thus the method of the invention makes available to the foundry industry a wholly new practical tool for controlling the carbon content of cast iron and related products.

We claim:

1. The method of carburizing cast iron which comprises introducing a carbonaceous material composed mainly of elemental carbon into a body of molten cast iron at a substantial distance beneath the surface thereof, characterized in that said carbonaceous material is form and is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about one-quarter to about two cubic feet per pound of solid material delivered into the molten metal, and further characterized in that said carbonaceous material is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the Weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature of the molten metal.

2. The method of carburizing cast iron which comprises introducing finely divided electric furnace graphite into a body of molten cast iron at a substantial distance beneath the surface thereof, characterized in that said graphite is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about onequarter to about two cubic feet per pound of graphite delivered into the molten metal, and further characterized in that said graphite is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said graphite to the temperature of the molten metal.

.3. The method of .carburizing cast iron which comprises introducing finely divided baked coke into a body of molten cast iron at a substantial distance beneath the surface thereof, characterized in that said baked coke is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about onequarter to about two cubic feet per pound of solid material delivered into the molten metal, and further characterized in that said baked coke is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said coke to the temperature of the molten metal.

4. The method of treating cast iron which comprises introducing a carbonaceous material composed mainly of elemental carbon into a body of molten metal having the composition of a gray cast iron at a substantial distance beneath the surface thereof, characterized in that said carbonaceous material is in finely divided granular form and is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about onequarter to about two cubic feet per pound of solid matcrial delivered into the molten metal, and further characterized in that said carbonaceous material is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature of the molten metal, and casting the molten metal into molds promptly after the introduction therein of said carbonaceous material.

5. The method of treating cast iron which comprises introducing electric furnace graphite into a body of molten metal having the composition of a gray cast iron at a substantial distance beneath the surface thereof, characterized in that said graphite is in finely divided granular form and is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about one-quarter to about two cubic feet per pound of graphite delivered into the molten metal, and further characterized in that said graphite is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said graphite to the temperature of the molten metal, and casting the molten metal into molds promptly after the introduction therein of said graphite.

6. The method of treating cast iron which comprises introducing finely divided baked coke into a body of molten metal having the composition of a gray cast iron at a substantial distance beneath the surface thereof, characterized in that said baked coke is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about one-quarter to about two cuic feet per pound of baked coke delivered into the molten metal, and further characterized in that said baked coke is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of carrier gas relative to the weight of solid material delivered into the molten metal results from heating said baked coke to the temperature of the molten metal, and casting the molten metal into molds promptly after the introduction therein of said baked coke.

7. The method of treating cast iron which comprises introducing an intimate mixture of finely divided calium carbide and finely divided carbonaceous material composed mainly of elemental carbon into a body of molten cast iron at a substantial distance beneath the surface thereof, characterized in that said mixture is delivered into said molten metal by means of a carrier gas,

the volume of carrier gas employed being (at standard temperature and pressure) from about one-quarter to about two cubic feet per pound of solid material delivered into the molten metal, and further characterized in that said carbonaceous material is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of gas relative to the weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature of the molten metal.

8. The method of treating cast iron which comprises introducing an intimate mixture of finely divided calcium carbide and finely divided carbonaceous material composed mainly of elemental carbon into a body of molten metal having the composition of a gray cast iron at a substantial distance beneath the surface thereof, characterized in that said mixture is delivered into said molten metal by means of a carrier gas, the volume of carrier gas employed being (at standard temperature and pressure) from about one-quarter to about two cubic feet per pound of solid material delivered into the molten metal, and further characterized in that said carbonaceous material is substantially free of moisture and volatile matter, whereby no substantial increase in the volume of carrier gas relative to the weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature of the molten metal, and casting the molten metal into molds promptly after the introduction therein of said mixture.

9. The method of carburizing cast iron which comprises introducing a carbonaceous material composed mainly of elemental carbon into a body of molten metal having the composition of a gray cast iron at a substantial distance beneath the surface thereof, characterized in that said carbonaceous material (a) is in finely divided granular form having a screen analysis of 100% minus -mesh and at least 50% plus IOO-mesh, (b) is delivered into the molten metal in a current of a carrier gas the volume of which (at standard temperature and pres sure) is from about one-quarter to about two cubic feet per pound of solid material delivered into the molten metal, (c) is substantially free of moisture and volatile matter, whereby no substantial increase in the volume 10 of gas relative to the weight of solid material delivered into the molten metal results from heating said carbonaceous material to the temperature of the molten metal, and (d) is substantially free of ash, whereby the possibility of undesirable side reactions between solid material and molten metal is minimized.

10. A treating agent for molten cast iron consisting essentially of an intimate mixture of calcium carbide and a carbonaceous material composed mainly of elemental carbon, said carbide and said carbonaceous material each being in finely divided granular form, and said carbonaceous material being substantially free of moisture and volatile matter, whereby said mixture can be heated to above the melting point of cast iron with substantially no evolution of gas.

11. A treating agent for molten cast iron consisting essentially of an intimate mixture of calcium carbide and electric furnace graphite, said carbide and said graphite each being in finely divided granular form, and. said graphite being substantially free of moisture and volatile matter, whereby said mixture can be heated to above the melting point of cast iron with substantially no evolution of gas.

12. A treating agent for molten cast iron consisting essentially of an intimate mixture of calcium carbide and a baked coke, said carbide and said baked coke each being in finely divided granular form, and said baked coke being substantially free of moisture and volatile matter, whereby said mixture can be heated to above the melting point of cast iron with substantially no evolution of gas.

References Cited in the file of this patent UNITED STATES PATENTS 468,292 Cole Feb. 2, 1892 684,681 Davis Oct. 15, 1901 1,587,600 Nielsen June 8, 1926 OTHER REFERENCES Paper No. 13, presented at the Forty-first General Meeting of the American Electrochemical Society held at Baltimore, Maryland, in April 1922. Pages and 171.

Claims

1. THE METHOD OF CARBURIZING CAST IRON WHICH COMPRISES INTRODUCING A CARBONACEOUS MATERIAL COMPOSED MAINLY OF ELEMENTAL CARBON INTO A BODY OF MOLTEN CAST IRON AT A SUBSTANTIAL DISTANCE BENEATH THE SURFACE THEREOF, CHARACTERIZED IN THAT SAID CARBONACEOUS MATERIAL IS IN FINELY DIVIDED GRANULAR FORM AND IS DELIVERED INTO SAID MOLTEN METAL BY MEANS OF A CARRIER GAS, THE VOLUME OF CARRIER GAS EMPLOYED BEING (AT STANDARD TEMPERATURE AND PRESSURE) FROM ABOUT ONE-QUARTER TO ABOUT TWO CUBIC FEET PER POUND OF SOLID MATERIAL DELIVERED INTO THE MOLTEN METAL, AND FURTHER CHARACTERIZED IN THAT SAID CARBONACEOUS MATERIAL IS SUBSTANTIALLY FREE OF MOISTURE AND VOLATILE MATTER, WHEREBY NO SUBSTANTIAL INCREASE IN THE VOLUME OF GAS RELATIVE TO THE WEIGHT OF SOLID MATERIAL DELIVERED INTO THE MOLTEN METAL RESULTS FROM HEATING SAID CARBONACEOUS MATERIAL TO THE TEMPERATURE OF THE MOLTEN METAL.