US2181093A - Heat treatment of metals - Google Patents

Description

NOV. 21, 1939. H, 1 NESS l 2,181,093

HEAT TREATMENT 0F METALS Filed Jan. 26, 1938 AT oRNEY Patented Nov.v 21, 1939 t t UNITED STATES PArENToFFiCa HEAT TREATMENT FV METALS imola J. Ness, Bloomfield, N. J., signor to Nesaloy Products, Inc., New York, N. Y., a corporation of New Jersey Application January 26, 1938, Serial No. 186,941 27 Cl'llml. (Cl. 14R- 16) This invention relates to the metallurgy of both surface of the part and may be discovered only ferrous and non-ferrous metals and more particuon failure of the part in use. Similar decarburilarly to the provision of an atmosphere for the zation and scaling problems arise in the reheating heating and heat treatment of such metals. for of billets and the heating of bars, wire bars and mechanical working, normalizing, hardening', etc. slabs for rolling, piercing, as in tube making, in 5 This application is a continuation in part of the soaking of steel ingots, and in the heat treatmy applications Serial No. 67,547, filed March 6, ment of finished or partially nished parts for 1936, and entitled Metallurgical process and aphardening, normalizing, etc. Troublesome oxide paratus", Serial No. 79,968, filed May 15,V 1936, formations also occur in the heating and heat and entitled Metallurgical process, and Serial treatment of such-metals as brass, copper and l0 No. 84,413, led June 6, 1936, and entitled Prealuminum, for forging, rolling, drawing, spinvention of scale formation on ferrous metals. ning, etc. y

In the forging of steel for the fabrication of It is, therefore, one of the objects of the pressuch parts as connecting rods, crank shafts, autoent invention to eliminate decarburization and/or mobile axles, aircraft engine cylinders, gears, scaling of iron and steel parts during heating in 15 cutlery, etc., it is lnecessary to heat the steel to preparation forthe mechanical working thereof, the forging temperature, usually between 2000 F. or lfor normalizing or hardening thereof. and 2600 F. During such heating decarburiza- Another object ls to provide uniformity in tion of the surface of the metal occurs and a weight and size of parts being heated or treated.

heavy layer of scale accumulates on the surface Still another object is to provide a method of 20 thereof, which scale must be removed before preventing carburization, and/or scale formation forging. This is usually accomplished by impact during heating of iron and steel, which method and scraping and by directing a stream of live will be simple, inexpensive and dependable. steam at considerable pressure against the bars Another object is to prevent oxide formation or blanks. These procedures, however, do not on non-ferrous metals, such as copper, brass 25 completely remove the scale, and as a conseand aluminum, during heating thereof. quence there is a large proportionof rejections Another object is to enable forgings and other of forged parts due to the scale falling into the mechanically worked metal parts of superior qualforging die and being hammered or forced into ity to be obtained. Y

the surface of the forging during the forging op- Another object is to prevent detrimental alter- 30 eration. Moreover, due to the abrasive action of ation of the composition or structure of metal, this scale, the life of the forging dies is materially ordinarily resulting from contact with the furshortened. In the forging of large or complicatnace gases, during the heating thereof. ed parts many operations are required and often Another object is to protect the metal both it is necessary to reheat the parts several times, physically and chemically, against oxidation, de- 35 before the forging operation is completed. Each carburization or detrimental alteration of its heating of the metal, of course, causes additional composition Vor structure, during the heating scale formation, decarburization, etc., and the thereof and during the subsequent working resultant reduction in size of the part caused and/or cooling thereof.

40 by the removal of the scale or the deepened-de- A still further object is to degasify metal, im- 40 carburization thereof must be allowed for. Howprove itsk grain refinement and enhance its physiever, the depth of scale formation or decarburical properties. zat-ion is variable depending. on the length and Another object is to condition steel to facilitemperature of the heating and the compositate nitrltlng thereof.

tion of the furnace gases and of the metal, and A still further object is to enable the foregoing 46 hence they cannot be accurately compensatedfor. objects to be accomplished in a furnace of the Therefore, considerable machining of the parts electric, oil or gas fired type. to remove the decarburized surface portion there- Other objects and advantages willl hereinafter of and to bring the parts to accurate size is usuappear.

ally required. Moreover, any scale driven into In accordance with the present invention!! 50 the forging in one of the early operations is heat the metal for treatment or in preparation forl worked deeper into the metal as subsequent opmechanical working, in an atmosphere containerations are performed thereon and may weaken ing lithium, which in contact with the metal and render the part defective. Such defects are serves to deoxidize orpartially deoxidize the same not always detectable by an examination of the and prevent decarburization of the metal or oxide as flame. reducing side, that is, with a slight deficiency 0f formations on the surface thereof. In the production and maintenance of the required lithium containing atmosphere in the treating furnace, I prefer to employ a lining for the furnace which does not absorb too great a quantity of the lithium or react detrimentally therewith during the heating process. It is desirable to condition the lining before use by heating the lining, either before or after assembly in the furnace, in the presence of a vapor of lithium or compound of lithium, preferably at a temperature of about 2000 F. The treatment can also be effected by applying to the lining a compound of lithium, such as lithium chloride. The compound may be applied as a water solution or suspended or dissolved in other volatile vehicles, as fully set forth in my copending application Serial No. 112,988, filed November 27, 1936, and entitled Furnaces.

While a furnace lining so treated will give off lithium vapor for a considerable period, it is desirable, in order to maintain such atmosphere, that additional amounts of lithium be supplied as the process continues. This may be accomplished by generating a vapor from a supply of lithium contained in the furnace but I prefer to introl duce it into the furnace from the outside. A very effective way I have found of supplying lithium to the furnace is mixed with the air or fuel either continuously or periodically. When introduced periodicaly, the lining serves as a storage and liberating medium whereby the desired atmosphere is maintained within the furnace between the periods of introduction of the lithium.

In place of introducing metallic lithium into the furnace, a compound thereof, such as the chloride, fluoride, hydroxide, or carbonate of lithium, or lithium containing ores such as spodumene or amblygonite, or mixtures thereof, may be used. The lithiated atmosphere may be provided in a gas fired furnace, for instance, by introducing a small quantity of a compound of lithium in powdered form, into the air or gas stream leading into the furnace or it may be injected or blown directly into the furnace through an aperture provided in the walls thereof. An apparatus for introducing the powdered lithium compounds directly into the furnace or into the air or gas conduit extending lthereinto is fully disclosed in my copending application Serial No. 143,410, led May 19, 1937, and entitled Injecting apparatus. In an oil fired furnace the lithium compounds may be added directly to the oil, either as an oil soluble compound or in colloidal suspension. A process of treating fuel oil with lithium compounds is disclosed in my copending application Serial No. 154,203, filed July 1'7, 1937, and entitled Promotion of combustion. In the case of electric furnaces the lithium compounds may be mixed with powdered carbon, such as graphite, and the mixture blown in a fine spray into the furnace in the manner set forth in my copending application Serial No. 143,411, led May 19, 1937, and entitled "Metallurgical process.

The amount of lithium compound-required to produce the requisite condition of the furnace atmosphere is very small but is not critical and may be readily determined by experiment for any particular furnace. It should be sumcient to produce a rich scarlet colored iiame when the furnace gases leaving the furnace are viewed with the' naked eye. Too great a quantity cannot be used, however, since it tends to extinguish the 'I'he furnace should be operated on the oxygen from that required for complete combustion so that the furnace gases will contain a small percentage of carbon monoxide, the purpose of which will hereinafter appear. The lithium compounds introduced into the furnace results in the formation of lithium metal, lithium oxide and lithium carbonate in the furnace atmosphere. The lithium metal serves to eliminate free oxygen from the furnace atmosphere with the formation of lithium oxide. The lithium oxide unites with carbon monoxide in the furnace atmosphere to form lithium carbonate and metallic lithium. 'I'he lithium carbonate thermally dissociates into carbon dioxide and lithium oxide. When the metal to be heated is placed in the furnace, compounds of lithium, mainly the oxide or carbonate so present in the atmosphere condense thereon and form a protective coating over the surface, protecting the same from any oxidation, decarburization or other detrimental alteration of the composition or structure of the metal that might otherwise occur. 'I'his protective coating remains on the metal throughout the heating process and the subsequent working and/or cooling of the metal, and will remain on the parts during a subsequent limited heating thereof in a non-lithiated atmosphere.

In carrying out the heat treating process of the present invention, the furnace is brought up to the proper treating temperature and the lithium compound is continuously or substantially continuously introduced into the furnace or into the air or fuel stream leading to the furnace in such quantity as to produce a rich lithium color in the flame. 'I'he lithium not only neutralizes the oxidizing effect of the furnace gases but the metal, as stated, immediately becomes coated with a protective layer composed4 primarily of lithium compounds. At the time the metal is placed in the furnace and for a brief interval thereafter, a copious supply of the lithium compound may be introduced into the furnace, if desired, in order to promote a rapid formation of the protective coating on the parts to be heated, and thereafter the supply of the compound may be reduced to the minimum amount required to maintain the coating thereon. The coating tends to vaporize from the parts as the heating continues and by maintaining a small continuous supply of the compound to the furnace, this evaporation is either prevented or additional amounts of the compound are deposited on the parts as the evaporation occurs, so that the coating is retained intact.

The invention will be more fully understood by reference to the accompanying drawing in which:

Figure 1 is a vertical sectional view of a forging furnace showing the preferred location of the blanks and a means of producing and maintaining a lithium containing atmosphere or condition in the furnace;

Figure 2 is a vertical sectional view of a hearth type furnace with a modified apparatus for introducing lithium compounds thereinto.

Figure 3 is a photomicrograph of a section of chrome nickel steel heat treated in a normal unv tended purpose.

alumina 25%, titanium oxide 1.2%, and the remainder impurities and volatile constituents. It is not necessary, however, that the lining be of this particular composition, since linings have been found satisfactory having a silica content of about 31% with approximately 62% alumina and the remainder mainlyiron oxide and titanium oxide. Linings of magnesium oxide,v aluminum oxide and chromium oxide may also be employed or the furnace lining may be composed of hard burned brick of low permeability and low porosity containing approximately 50% silica and 44% alumina, having a bulk density of about 1.2 oz'. per cu. inch and a fusion point of about 32D0 F. For furnaces operating attemperatures below about 1800 F. a less dense and less refractory brick may be employed. A suitable cement for bonding the bricks, such as. sillimanite, cyanite, andulusite, and mullite may analyse as follows: silica 38.07%, alumina. 56.63%, titanium 1.14%, iron oxide .73%. ignition loss 2.78% and the remainder moisture and other impurities. This cement may also be used as a coating for the bricks after their assembly in the furnace. In

lgeneral, cellular insulating brick or moulded or tamped-in linings have not been as satisfactory as linings built upfrom hard burned refractories, apparently due to the high permeability thereof or the reaction of the lithium or one of its compounds with the binder employed in such moulded linings. Linings, hearths and other refractory parts of the furnace consisting of or containing silicon carbide have been found to react detrimentally with the lithium of the atmosphere, due possibly to the nature of the binder commonly employed, causing breakdown of the refractory and to some extent. reduction in the efficiency of the lithium containing atmosphere for its in- When the lithium or its compounds are introduced into the furnace through the burner -or at a point adjacent thereto, the

. flame should not impinge directly on the refractory, particularly in furnaces operated at high temperatures. In the embodiment shown, the ame is directed, as indicated, to the rear of the furnace, the products of combustion being reflected by the rear wall towards the front outlets I3. As stated the lining ||l may be preconditioned, if desired, by introducing lithium or a compound thereof into the furnace while the furnace is at an elevated temperature or the lining may be painted with a water solution of a lithium compound, such as lithium chloride, and the furnace brought up to heat. Thereafter the furnace may be used for successive heats by introducing lithium metal or compounds into the furnace either continuously or at such periods as isneces- ,sary to maintain the requisite amount of lithium y I have shown means for introducing measured.

amounts of lithium metal orcompounds thereof into the furnace, comprising a sleeve I4 threaded into an eblow I5 in the air intakelG. A piston slidable in the sleeve I4 is` provided with an annuzar recess I8 adapted in the retracted position of the piston to be positioned beneath a hopper I9, containing comminuted lithium or powdered compounds thereof, so as to receive aV chargeth'ereof and to convey the same into the air and gas line when the piston is moved inwardly. The charge thus introduced into the air and gas mixture is carried by the same into the furnace whereupon, as stated, it passes through the hottest part of the flame. The piston may be operated manually from time to time throughout the process as determined by experience or an inspection of the gases escaping from the furnace, or if desired the plunger may be reciprocated by a continuously `operating crank or other means, as shown in my aforesaid application Ser. No. 79,968, so as to supply the lithium in definitely timed increments.

The. steel bars being heated are positioned c-n the fioor of the furnace remote from the burners and at a place where the furnace temperature is substantially uniform. The vapor produced by the lithium metal or compound thereof pervades the entire furnace and prevents decarburization of the metal and the formation of oxide scale on the surface of the parts being heated. l

In Fig. 2 I have shown a modified apparatus for the continuous introduction of lithium compounds into a furnace. Referring to this figure, I have shown a conventional furnace I0 provided with burners I2' designed to burn gas, al-

though the apparatus may be equally well em-A ployed with an oil burning furnace. The furnace is provided with a supply of a' compoundof lithium, such as lithium carbonate, through a conduit 2| extending through the wallof the furnace above one of theburners. While the inlet 2| has been shown relatively close to the burners, it may be more remotely disposed' and in the case of a hearth type furnace, as shown, in which the burners are below the hearth, it may be disposed either above or below the hearth. A supply of lithium compound may be provided by an injecting apparatus of the form shown in the aforesaid application Serial No. 143,410. In Fig. 1 I have shown a modified form of such apparatus comprising a container 23 consisting of a cylindrical tube 24, preferably of glass, having flanged upper and lower closure members and 26 respectively, clamped against the ends of the tube 24 in any suitable manner, with interposed gaskets 21, Extending axially through the container 23 is a shaft 28, journaled in the closure members 25 and 26. The l shaft 28 is driven through suitable reducing gears 29 by a motor 3|.

Mounted vupon the shaft 28 are several sets of blades 32, adapted to agitate the powdered lithium compound which is'contained in the chamber 23. A combustiblemixture of air and gas Lunder pressure is supplied by a blower 3 3 also driven by the motor 3|, theair and gas mixture being conducted by a tube 3 4, into the lower Wall of the container 23 and passing out of the container laden with the .powdered compound, through the conduit 2|, extending into the'furnace.

A valve controls the ow of the air and gas into the chamber 23 and consequently the amount of lithium compound blowninto the furnace.

In order to prevent fusing of the lithium compound as it passes through the tip of theconduit 2|,` I bypass a part of the air and gas mixture from the blower 33 through a conduit 31, provided with a suitable regulating valve 38. The air and gas mixture iiowing in conduit 3T is conducted through a Venturi tube 39, disposed adjacent the outlet 40 of the container 23, so as to assist in the withdrawal of the compound laden air and gas from said container. The additional air and gas provided through the conduit 31 not only serves to maintain the terminal of the conduit 2| cool, but is supplied at sufficient pressure to blow the powdered compound through the conduit at such speed that fusing thereof to the wall ofthe tube adjacent its tip is prevented. By supplying a gas and air mixture to the blower, the ratio of gas and air in the furnace is not disturbed by the iluid medium employed to conveyl the powders into the furnace. A flame arresting valve 36 is included in the line 2| extending into the furnace to prevent back flash through the line and if desired, a screen or mesh 4| may be disposed about the end of the conduit 2| to break up the flame and also to prevent ash back. In place of the mixture of air and gas, either air alone or gas alone may be employed to convey the powdered compound into the furnace, although the use of air alone tends to create localized hot zones in the furnace and somewhat detracts from the eiliciency of the action of the lithium compound in such zones. Excessive moisture in the air, Ysuch as results from high compression of the same, or in the gas employed, also detrimentally effects the action of the lithium compound and the maintenance o f the proper lithiated atmos-v phere within the furnace, and should be avoided. The inlet 2| should preferably be located relative to the parts to be heated so that the lithium compound laden gas stream does not impinge directly on such parts but that the compound will be first reduced to metallic form and diffused into the furnace atmosphere, particularly when air is used as 'the inspirating or carrying medium.

In carrying out the present process the furnace is brought up to heat and the motor 3| started. The valve 35 is then opened to permit,

the inspirating medium to pass through the chamber 23. In so doing it picks up some of the Y powdered lithium compound carrying it into the furnace |0. Under the conditions prevailing in the furnace the compound, or at least a portion thereof, breaks down liberating free metallic lithium. The reaction is apparently ilrst -the formation of lithium oxide which reacts with car- -bon monoxide as follows:

2Li2O+CO=Li2COa|2Li 'The lithium is thus freed to combine with the oxygen of the furnace or of the 'metal being.

heated and the lithium carbonate of the above reaction is again thermally broken down to lith- .ium oxide liberating carbon dioxide. The reaction is then repeated with the lithium oxide so formed. As will be noted from the reactions set forth above, each particle of lithium present in the furnace goes through the above cycle repeatedly, until A it ultimately escapes with the furnace gases, and it is necessary, therefore, to supply additional lithium or lithium compounds only to replace that so escaping and that deposited on the material being heated or on parts of the furnace.

The valve 35 should be adjusted so as to cause a sufficient fiow of the lithium compound into the furnace, to produce a rich lithium color in the furnace gases. The amount of the compound required varies with the compoundl used, the type and construction of the furnace, the location therein of the metal to be heated and the temperature attained in the furnace. For instance, lithium hydroxide is approximately twice as rich in lithium per unit of weight as the carbonate quired.

and consequently a lesser amount thereof is rea considerably lower temperature. It is less convenient to use, however, due to ,its extreme caustic nature but where production of the protective atmosphere is required with a furnace temperature as low as about '100 F. the hydroxide or a mixture of the hydroxide and the carbonate may be employed. However, the carbonate is preferred for general use due to its ease of handling, and its relatively cheap cost. The amount of any particular lithium compound to be used. in order to provide the desired protective coating. and lithiated atmosphere can be readily determined by making one or more test heats or the metal being heated can be observed as the heating continues to determine if a proper coating is forming thereon. In certain furnaces red with artificial gas excellent results have been obtained with the use of as little as about 0.003 ounce of lithium carbonate per cubic foot of gas but the amount required is not critical and may vary either side of the figure mentioned. Equivalent amounts are required in oil burning furnaces for equal heat generation. In electric furnaces I add carbon monoxide to the furnace or a supply of carbon from which carbon monoxide may be generated, in order to obtain a reduction of the lithium oxide in accordance with the foregoing equation. When the proper lithiumvcondition is obtained in the furnace, the metal to be heated is introduced therein. If desired, the metal to be heated may be placed on a traveling conveyor and passed through the furnace at such rate as to complete the heating or heat treatment during its passage therethrough. The furnace may be opened freely during the process, for the introduction or removal of parts, or it may be left open continuously, if desired, without danger of oxidation of the parts.

The presence of the lithium metal in the furnace gases permits the heating to be carried out without the use of protective muiiles, and directly in the furnace gases without scaling, carburization, decarburization or other detrimental effect on the metal parts being heated. In factl none of the embrittling effects or. other modification of the grain structure obtained in heating in hydrogen or other reducing gases, are experienced. Furthermore, as stated, there is a deposition or condensation of the lithium and/or lithium compounds which forms very quickly on the parts and which physically protects the surfaces thereof from any contaminating or oxidizing influence ofthe furnace atmosphere. As a result of the protective atmosphere and this protective coating high carbon steels and alloy steels, including aluminum containing steels vmay be heated together without oxidation, decarburization or other deleterious alteration of the composition thereof. The coating deposits apparently either as an oxide or a carbonate of lithium or both and adheres to the lparts throughout the heat treatment and after removal from the furnace, so that when the heating is complete the parts may be immediately removed from the furnace and worked or cooled in the air. Upon cooling the coating appears to be mostly the carbonate of lithium.

The valve 35 is kept open or partially open throughout the process so as to supply the lithium compound continuously to the furnace during the heating but, of course, if desired, the amount of tcompound may be varied as the heating coninues.

It also breaks down tolithium oxide at I The nature, appearance and color of the protective coating varies with the type of furnace employed, the location and composition of thel parts therein, the amount of lithium compound used, and the temperature and period of heating. In some instances the coating formed is not visible, the parts, however,remaining unoxidized. In heat treating where the period of heating is short and the coating thin, it may be removed during quenching of the parts and in any case the coating may be readily removed by dipping the parts, either when hot or after cooling, in a weak acid solution, such as acetic or hydrochloric acid. An inhibitor is preferably added to the acid to prevent etching of the metal.

The parts, after the coating has been dissolvedtherefrom are bright, the entire process being enected without the removal of any detectable amount of metal from the parts.

In 3 I have shown a microphotograph of 100X magnification, of a specimen of S. A. E. No.

3312 chrome nickel steel, showing the microstructure at the carburized surface thereof after heating at 1500 F. for fteen minutes in an unlithiated normal furnace atmosphere, and water quenched. It should be noted that the specimen is noticeably decarburized for approximately 0.005 inch in depthat the surface 42 and further that there was a heavy scale on this surface, as indicated by the rough and irregular contour thereof. Where such a condition exists, it is necessary to turn, mill, grind or otherwise remove the surface down to the full depth of the decarburization. It will be readily appreciated that such operation is expensive, inconvenient and results in a considerable loss of metal.

Fig. 4 shows a similar microphotograph of the same magnification of an identical specimen showing the micro-structure at the surface thereof after heating to the same temperature for thirty minutes in a lithium containing atmosphere maintained by introducing lithium carbonate into the furnace by the apparatus shown in Fig. 2. It will be noted that the surface 43 is entirely free from decarburization or scale. Such a specimen may be worked to exact size.

While the invention has been described with particular reference to the heating of steel for forging operations, it applies equally Well to the heating of iron and steel for normalizing, annealing or hardening, as for instance for rolling and annealing operations as used in steel mill practice and in the annealing of metal stampings. 'Ihe protective .atmosphere may also be used in the heat treatment of non-ferrous metals, as for instance brasses, bronzes, copper and aluminum,

the protective coating forming equally well on any metal and-the lithium containing atmosphere and thecoating serving to prevent oxidation or contamination thereof.' The atmosphere is particularly suitable for such operations as bright annealing of brass. The term. ferrous metals as used in the claims includes iron, steel and alloys thereof.

The heating of iron and steel in the lithium containing atmosphere in addition to preventing scale formation, also effects a reduction or partial reduction of any scale thereon at the time of its introduction into the furnace. For instance, hot rolled iron or steel as ordinarily supplied by the manufacturer is usually coated with a layer of mill scale. This scale is hard and brittle and in forging, drawing and shearing op- Y erations is injurious to the dies. The heating of preparatory to hot working, reduces this scale to a greater or less extent depending on the length of heating, thus eliminating it or converting it into a soft powdery form.

The heating of metals in the lithium containlng atmosphere also serves to refinethe grain,

presumably by the elimination of impurities or by preventing the absorption of impurities into the metal during heating. Whatever the cause, microscopic examination of the metal after being heated in acc'ordance with the teachings of this invention shows the metal to have a deflnitely improved grain structure than that resulting from similar heating in the absence of lithium. As a result the metal has better physical properties, greater tensile strength and elongation and increased izod, creep and fatigue values.

It will be understood, of course, that changes may be made in the process without departing from the invention, and I contemplate all such changes as are within the scope of the appended claims.

What I claim is:

1. The method of preventing substantial oxidation of metals during the heating thereof comprising conducting the heating at the required .temperature in an atmosphere containing a lithium compound and carbon monoxide.

2. The method of producing a lithium'atmosphere in a metallurgical furnace containing carbonaceous gases comprising introducing lithium containing metal or a compound thereof into the furnace substantially at the point of maximum temperature thereof.

3. The method of producing a lithium containing atmosphere in a furnace heated by carbon containing gas or oil ame comprising introducing lithium metal or a compound thereof into substantially the hottest portion of the flame. a

4. The method of treating ferrous metals comprising heating same in a furnace to a temperature above '100 F. and generating lithium in the furnace by reduction of a lithium compound with carbon monoxide.

5. The method of treating metals which comprises heating the same in a furnace containing a reducing gas, to the desired temperature and introducing a lithium compound into the furnace during said heating.

6. The method of treating metals which comprises heating the same ina furnace containing carbonaceous gases, and introducing into the 8. The method of treating metals which comprises heating the same in a furnace in the presence of carbonaceous gases to above about 700 VI4". and supplying a sumcient quantity of lithium or a compound thereof in the furnace to provide. said parts with a protective coating of a lithium salt throughout the heating and subsequent cooling of said parts.

9. The method of preventing oxidation or the metal inthe lithium containing atmosphere, decarburization of ferrous metals which comdeposition of a lithium compound on said l0. The method of treating metals comprising heating the same in a carbon containing gas fired furnace to the required treating temperature and introducing lithium carbonate into the 'fur.

nace in an amount of the order of magnitude of 0.003 ounce per cubic foot of gas consumed.

11. The method of promoting grain refinement in metals comprising heating the same in a furnace to the normal grain rening temperature '15 thereof and supplying a sumcient quantity of lithium or a compound thereof and a carbonaceous gas to said furnace to provide said metal during such heating with a protective coating of a lithium compound.

12. The method of preventing ovidation, or decarburization, or effecting deoxidation or grain refinement of ferrous and non-ferrous metals during heating thereof comprising conducting said heating in an atmosphere the chemical composition of which substantially throughout the process is oxidizing towards the metal,

-and containing lithium or a compound `therelzo ature, andthe lithium or its compound being lithium compound to form on said metals.

13. The method of rendering innocuous to heatedmetals a furnace atmosphere, the chemical -composition of which throughout. the process'is oxidizing towards such metals, which includes comprising in said atmosphere carbon lmonoxide and a small percentage of lithium.

' -14. In the heating of metals, an atmosphere, the chemical composition of which is oxidizing towards the metals. containing carbon monoxide and lithium.

15. The method of producing a lithium containing atmosphere in a furnace containing a carbonaceous gas which comprises introducing lithium chloride into the furnace while the furnace is at such elevated temperature as to cause the lithium chloride to become decomposed.

16. The method of treating metals which comprises heating 'said metals in a furnace containing4 a carbonaceous gas and introducing a lithium compound into the furnace at intervals, during the heating, of such frequency as to maintain a continuous lithium containing at,- mospherein the furnace.

55 taining atmosphere in a furnace containing a carbonaceous gas, which comprises introducing lithium carbonate into -the furnace atmosphere while the furnace is operating. Y

18. The method of treating metals which comprises heating said metals in a furnace containing a carbonaceous gas and introducing a lithium compoundinto the furnace during the heating, in such quantities as to maintain a lithium containing atmosphere in the furnace.

19. The method of producing a protective atmosphere in a furnace containing carbonaceous present 1n such quantity as to cause a nlm of a e 17. The method of producing a lithium conf prises introducing a decomposable lithium compound into the furnace atmosphere at spaced intervals while the furnace islatan elevated temperature. e

- 21. The method of producing a lithium containing atmosphere in a furnace containing carbonaceous combustion gases which comprises introducing into the furnace atmosphere while the furnace is at an elevated temperature, measured amounts of a lithium compound, at a frequency to maintain a lithium line ln the spectrum of the atmosphere of the furnace',l substantially. continuously. l

22. The method of producing 5a lithium containing atmosphere in a furnace containing carbonaceous combustion gases which comprises producing heat within the furnace above the decomposition temperature of a lithium halide unof, the heating being conducted at such temperder the conditions prevailing inv the furnace and introducing such lithium halide into thefurnace.

23. The method of producing a lithium containing atmosphere in a furnace containing carbonaceous combustion gases which comprises providing such furnace with a lining composed largely of silicon oxide and introducing a lithium compound into the furnace atmosphere while the furnace is in operation.

24. The method .of producing'. a lithium containing atmosphere in a furnace containing carf bonaceous combustion gases which comprises providing such furnace withl lining composed of a refractory material which does not react detrimentally with lithium vapor under the normal conditions existing during the operation of the furnace and introducing a lithium compound into the furnace while it is in operation.

25. The method of producing a lithium containing atmosphere in a furnace containing carbonaceo'us 'combustion gases which. comprises providing such furnace with"a lining composed largely of chromium oxide and introducing a lithium compound into the furnace atmosphere while'the furnace is in operation. l

26. The method of producing a' lithium containing atmosphere in a furnace containing carbonaceous combustion gases which comprisesproviding such furnace with a lining composed largely of magnesium oxide and introducing a lithium compound into the furnace atmosphere lwhile the furnace is in operation.

27. The method of creating an atmosphere containing lithium metal in a furnace or the like comprising introducing a compound of lithium into the furnace in the presence of carbon monoxide and producing suillcient heat therein to effect a reduction of said compound to metallic form by said,carbon monoxide.

, HAROLD J. NESS.

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