US1869497A - Process of treating molten ferrous metals and alloys with compositions containing "lithium-alkali" alloys and products resulting from such treatments - Google Patents

Description

Patented Aug. 2,1932

UNITED STATES HANS OSBORG, OF FRANKFORT-ON-THE-MAIN, GERMANY PROCESS OF TREATING MOLTEN FERROUS METALS AND ALLOYS WITH COMPOSITIONS CONTAINING LITHIUM-ALKALI ALLOYS AND PRODUCTS RESULTING FROM SUCH TREATMENTS N0 Drawing. Application filed December 21, 1931, Serial No. 582,490, and in Canada June 26, 1931.

The present invention relates to a process of treating iron-bearing metals and alloys in their molten state with an alloy of lithium and a metal of the. alkali group, including alkali, and/or alkaline earth groups and/or rare earth group and to the improved products resulting from such a process.

Heretofore, a great variety of scavengers and improvers of metals and alloys have been proposed. Of these scavengers and improvers, the more important were manganese, silicon, aluminum, magnesium, metallic lithium, metallic calcium, etc. From an industrial point of view manganese, silicon, aluminum, magnesium, have been the most important, but the art was attempting to obtain better and more satisfactory results than those obtained by the use of these substances. 'ith this object in view, those skilled in the art were attempting to find improved scavengers. Metallic lithium and metallic calcium were proposed, but it was found that these metals had short-comings and disadvantages when used on an industrial scale. The more serious disadvantages were that the molten metal and alloy under oing treatment was not cleaned com lete y, did not possess the desired improver properties and usually was contaminated with impurities or contained blow holes. In other words, when lithium or in fact some other metal of the alkali group or alkaline earth group was added to a molten bath of metal these disadvantages were encountered which in many cases not only counter-balanced any advantages but actually over-balanced any advantages. For instance, in the treating of steel or steel alloys, the temperature of the molten bath was such as to cause a quick volatilization of lithium with the consequence that the treatment only partly occurred or that an excessive amount of lithium had to be used in order to obtain the desired results. From a practical point of view, it was found that the use of these metals was not wholly economical and satisfactory on an industrial scale. Various suggestions have been made for remedying the shortcomings and disadvantages noted hereinabove with respect to prior scavengers including metallic lithium and metallic calcium and/or processes of using the same, but as far as is known, no scavenger and/or improver and/or process of using the same has been proposed which is wholly satisfactory and practical when used on an industrial scale.

1t is an object of the present invention to provide a process of treating iron-bearing metals and alloys in their molten state so as to obtain the benefits resulting from lithium treatments without the disadvantage noted hereinabove.

It is a further object of the invention to provide a simple, economical and thoroughly satisfactory process of treating iron-bearing metals and alloys in their molten state with active lithium-bearing substances so as to improve the characteristics thereof.

It is another object of my invention to provide a process of treating molten metals and molten alloys with an active lithium alloy of a metal of the alkali group or alkaline earth group or rare earth group which is capable of being carried into commercial practice on an industrial scale in the ferrous and the non-ferrous industries, which is also capable of producing greater effects than provided by the same amount of lithium and the like.

Other objects and advantages of the invention will become apparent from the following description.

Broadly stated, my invention contemplates the treatment of molten iron-bearing metals and alloys with an active lithium alloy of a metal of the alkali group or alkaline earth group or rare earth group in which the lithium is so bonded that the loss thereof through volatilization and the like is materially reduced. At the same time, the lithium alloy can function actively to effect improvements in the properties and qualities of the metallic substance under treatment. I have found that in carrying my invent-ion into practice, that lithium alloys containing members of the alkali or alkaline earth families such, for example, as calcium, barium, strontium, magnesium, lanthanum, cerium, sodium or potassium or relatively stable compositions of lithium and silicon or of mixtures of the foregoing substances can be utilized in the included is diminished thereby.

treatment of metals and alloys in their molten state so as to effect improvements in the properties and qualities in the metals or alloys treated.

' The following examples are given for illustrative urposes and for a better understanding 0? carrying my invention into practice.

A. Cast iron general It is well known, that cast iron has to serve many purposes which have different requirements. In all cast irons, however one of the most important improvements which the art has been attempting to make is an increase in the tensile strength of the cast iron, combined with a good density, a good machinability, etc. From a practical and commercial point of view, it is essential that the improved cast iron does not cost much more than ordinary cast iron. If the cost of the improved cast iron is too high then it is unavailable economically.

At the present time conventional improved cast irons are made generally by the use of two distinct methods; (1) an alloying method and (2) a heat treatment method of the molten metal.

In the first method, alloying elements such as nickel, chromium, etc., are added either singly or in combination 1n addition to silicon, etc. If nickel is added, for instance, oxides of nickel are formed to a considerable extent and the benefit of the alloying element Moreover, there seems to be some doubt as to the efiect of nickel on the dispersion of graphite. In some cases, the dispersion effect can be observed whereas in other cases it cannot be observed. In the same way, the addition of the other alloying metals have limitations. Since the alloying effect of these additions, such as nickel or chromium is diminished by the gases, oxygen, and other impurities present in the molten metal, it is possible to greatly improve the effect of nickel and chromium by treating molten cast iron with the present improved lithium alloy.

The second method of producing improved cast iron contemplates overheating the cast iron while in a molten condition. This overheating efi'ects a better dispersion of the graphite but has a detrimental effect of increasing the oxygen contained in the molten metal. As is well known, when oxygen is present in cast iron, the density is considerably decreased. In other words, the cast iron is somewhat porous and cannot be dependent upon for structural engineering purposes. For example, a cast iron containing 0.06 to 0.08% of oxygen has a slightly higher tensile strength than a cast iron without oxygen, but the density of the im roved cast iron is decreased about 0.02 to aiiout 0.03 points or units. This decrease in density is detrimental to the cast iron and limits the uses thereof.

When cast iron is treated according to the process of the present invention, it has been found that the cast iron has a very fine and I even distribution of the graphite; that some of the free carbon has combined with the metal without making the cast iron too hard for machining purposes; that the gases and oxygen have been practically removed; that the crystal structure of the cast iron has been decidedly improved as shown by photomicrographs; that a general improvement of the mechanical properties have been effected (see following tables). Among the improvements in cast iron treated with the present improved lithium alloy the following may be noted; the cast iron is sound, has a higher tensile strength than untreated metal from the same heat and has. a very good machinability. The test pieces of cast iron produced by the present invention, for example, turned on the lathe to give better and larger chips in spite of the fact that -cast iron produced by the present invention has a higher hardness than ordinary cast iron. Moreover, the untreated cast iron was found to have hard spots. By the use of the present process and the present improved lithium alloy, the hard spots are eliminated and uniform cast iron with uniform hardness is produced.

A comparison of the fractures of cast iron bars treated with the present improved lithium alloy and those untreated shows that cast iron produced by the present invention has a finer grain structure than the other one and is of a lighter color which means that the graphite is broken up in finer particles and distributed more uniformly and, furthermore, that to some extent there is less graphitic carbon present.

The casting properties of the molten metal were improved. After the present improved lithium alloy was added to molten cast iron in a bull ladle, the temperature increased and the fluidity was much better than that of untreated cast iron.

B. Cast iron made in a cupola Photomicrographs of specimen clearly show the improvement in cast iron when treated with the present lithium alloy. For purposes of comparison, photomicrographs of a corresponding cast iron which has been untreated were taken. For instance, photomicrographs (#223) were taken from a bar of ordinary gray cast iron which did not have any steel scrap added thereto and which was made in a cupola. The unetched and etched photomicrographs show large flakes of graphite at the grain boundaries. It is well known that when the graphite occurs in large fiakes at the boundary a weak cast iron results.

Some ordinary cast iron of the same heat which had been treated with the present lithium alloy was made up in the form of test bars to form for examp e, a specimen (#226) The photomicrographs of this specimen show the improvement in the metal. The graphite flakes are broken up and finely distributed throughout the mass of cast iron. A comparison of the photomicrographs makes itself evident that beneficial improvements are effected by the use of the present lithium alloy.

Tests were made on ordinary gray cast iron and the same cast iron treated with the present lithium alloy and the following Table I gives the results of these tests. It should be noted that no addition was made to the cast iron, not even of the usual steel scrap.

The foregoing tests as well as the following tests on cast iron were made on a tensile bar and not on a so-called arbitration bar. It is to be noted that if an arbitration bar, which is the usual commercial practice, were used, higher figures for tensile strength would, of course, have been obtained.

A cast iron containing nickel and steel scrap is usually recommended as a good product. If, however, nickel cast iron is treated with the present lithium alloy, then more accentuated improvements are obtained as shown by photomicrographs taken of test specimens and data obtained in testing specimens. For instance, ordinary untreated cast iron containing 40% steel scrap and 1% nickel showed a tensile strength of 26,000 :fjz/sq. in. The photomicrograph disclosed large graphite flakes and large white areas of ferrite and phosphide eutectic. On the other hand, the same cast iron from the same cupola when treated with the present lithium alloy showed a tensile strength of about 30,000 #/sq. in. and the photomicrograph disclosed a fine distribution of graphite and white areas.

0. Cast iron made in an electric arc furnace Cast iron was made in an electric arc furnace with plain gray iron scrap with no addition even of steel scrap by heating the furnace up to 2800 F. and holding it at this temperature for about fifteen minutes. From this heat cast iron specimens were made which were untreated and cast iron specimens were made which were treated with the present lithium alloy.

The aforesaid specimens were subjected to tests and Table II shows the results of these tests:

Photomicrographs showed that an untreated specimen (#232) had many hard spots and showed non-uniformity of material whereas photomicrographs showed that treated specimens (#233 and #234) possessed a uniform structure, and that there was an excellent distribution of the graphite in the form of very fine particles. Tests demonstrated that the treated specimens exhibited excellent machinability.

Ordinary untreated gray cast iron of a high grade containing no addition of steel scrap, etc. produced by the overheating method shows tensile strength of about 23,000 to about 25,000 #/sq. in. The ordinary cast iron mentioned above had a. tensile strength still higher than the best of the usual commercial gray cast iron. The foregoing table demonstrates that cast iron, when treated with the present lithium alloy, gives far greater tensile strength than the best of the untreated ordinary cast iron. Thus improvements of the order of about 12 to 18% over the best ordinary cast iron without even using nickel or chromium or steel scrap have been obtained by the use of the present invention.

D. Carbon steel Table III Tensile Brinell Carbon strength hardness Remarks #/Sr 111. Number U 3. 50,000..." 98.5"... Untreated (somewhat dirty).

(B) .3.. 70,000.. 119 Treated (clean) from same heat as (A) 40-45000 #/sq. in. yield point. Z033.000,000 modulus r. elasticity. About 35% elongation. About 45% reduction of area.

2075.... Untreated (good quality) elastic limit 30,000 lbs/sq. in. Itlnnga7tion 3%. Reduction of area (D) .5 108,000.... 2075.... Treated (good quality) elastic ,6 limit 53,000 lbs/sq. in. Elongation 7%. Reduction of area (A) to (D) tested in the annealed condition Photomicrographs of the aforesaid specimens demonstrated that the improved carbon steel embodying the present invention had a better structure, fewer inclusions, a more uniform pearlitic constitution, etc., than ordinary untreated carbon steel.

E. Alloy steels Various types of nickel-chromium and chromium steels were treated with the present lithium alloy. In general, the treatment resulted in the increase of temperature of the molten metal; better fluidity of the molten bath of metal; better castings; improved crystal structure; cleaner metal; superior metal regarding physical and mechanical properties and an increase in corrosion resistance. All tests were carried out on a comparative basis between untreated metal and the same metal when treated in accordance with the present invention.

Photomicrographs of improved alloy steels embodying the present invention will clearly show to one skilled in the art the improvements obtained by the use of the present lithium alloy. These improvements include better structure, fewer and smaller inclusions,

practically complete freedom from impurities at grain boundaries. etc.

Various nickel-chromium steels which had been treated in accordance with the present invention were subjected to tests. The following Tables IV, V and VI show the results of these tests Table IV Tests on a steel containing 18% Cr and 8% Ni and treated with 0.02% Lithium-Alkali Alloy (Li-Ca) Tests on a steel containing 18% Cr and 8% Ni and Treated with 0.04% present lithium Alkali-Alloy (Li-Ca) Par Par Brinell Elastic- Tensile cent cent yg Hard- Size limit strength elongareducness #/sq. in. 5/80. in. tion tion in numin 2" area e Ce ber 'Nori;.1he values for the two larger sizes would be in tact still higher because due to a mistake in the mill the ingots were not cropped at all. Therefore, these sizes had a detect known as pipes.

Table VI Nickel chromium steels, comparative figures as obtainable (mm the industries (A) Radiator shells, as used for Ford automobiles, (18% Cr 8% Ni steel) #Iaq. in. Tensile strength 90, 000 Elastic limit v 000 (B) Allegheny wire (average quality of 18% Cr 8% Ni steel) 42/: in. .005" Diam. 92. 000 tansfie strength 48,000 elastic limit 0.01" Diam 117,000 tensile strength 60,000 elastic limit 0.01 Diam 143,000 tensile strength 75,000 elastic limit Allegheny strip (Cold rolled from .078 gauge down to .049 gauge 157,850 #/sq. in. tensile strength 153,460 #/sq. in. yield point (C) Krupp-Nirosta KA2 hot rolled sheet steel #Iaq. in. 111,000 tensile strength 56,000 elastic limit n) Bethlehem steel (18% c: and 8%Ni when cold drawn from to 174,000 #/sq. in. tensile strength 167.000 it/sq. in. yield point 302 BHN hardness.

ment with the present alloy. The tests showed the following results:

Table VII (18% Cr 8% Ni steel) as cast Property Untreated Treated Tensile strength per sq. in 01900 #/Sq. in. 72350 tt/sq. in. Elongation in 2" 18% 20% Brinell hardness number 134. 5 181. 5

Example 1V 0. 1

In the treatment of iron or steel, for instance the molten metal is contained in a suitable crucible such as a graphite crucible or in a bull ladle or in an ingot mold. To the molten mass I add in any appropriate manner, an active lithium alloy, for example, an alloy of lithium and calcium in an amount sufiicient to effect improvements in the prop-- erties of the iron or steel. In practice, I have found that up to about 2 parts of an alloy of lithium and calcium having about 50% lithium content are capable of effectively treating about 100 parts of molten steel or steel alloys.

The addition of the active lithium alloy to the molten metal is preferably effected by plunging the selected amount of active lithium alloy into the molten material in a crucible by any appropriate means such as an inverted cup with side openings or ports or the like. By adding the active lithium alloy to the molten metal in the aforesaid manner, I am able to effect a thorough distribution of the lithium alloy throughout the molten mass and to effect the proper treatment of said metal to improve the properties and qualities therebetter and denser castings.

When iron and/or steel and/or alloys thereof are treated with one of my active lithium-bearing alloys, the molten mass has a better fluidity and consequently, can be cast very much better than heretofore and gives In addition, the physical properties of the iron or steel or metal or alloy treated are improved. For instance, there is an increased hardness and corrosive resistance of the metal thus treated and the finished product is relatively or practicallyfree from blow holes, oxygen, sulphur and the like.

Example N0. 2

When steel or a steel alloy is used for the production of castings, I add to about 100 parts of molten iron prior to casting enough of a lithium alloy such as a lithium-calcium alloy or a mixture of lithium alloys having such a composition as to give a lithium content up to about 1%. The lithium alloy is preferably added in the form of a solid briquette, block, lump or the like which is 1ntroduced into the body and preferably the lower portion of the molten mass of iron by means of an inverted cup or other appropriate instrumentality. The lithium alloy thus added, improves the crystal structure of the steel; combines with gases, such as oxygen and nitrogen, and also with such detrimental substances as sulphur and phosphorus; increases the fiuidity of the molten steel and produces denser and sounder castings than produced heretofore. In practice, I prefer in some instances to add the lithium alloy in. a mass which is surrounded by or coated with iron silicide. By adding the lithium alloy in this manner, the procedure is facilitated. If it is desired, a lithium-calcium alloy can be silicided and then the silicided lithium alloy used for the treatment of the molten metal or alloy.

Instead of steel or iron in the examples given above. nickel or alloys thereof or copper or alloys thereof can be treated by the addition of the lithium alloy to the molten metallic mass. substance is added to the molten mass to give the latter a lithium content up to about 1.0%.

In some instances, I prefer to employ an alloy of lithium with the metal or alloy to be treated. For example, if steel is to be treated, I use an active lithium alloy containing iron. The lithium alloys should prefer- Sufiicient lithium-bearing pbly be silicided or reacted with silicon prior 0 use.

The amount of lithium alloy added to the molten metallic mass depends upon a number of variables as one skilled in the art will readily understand. For example, the percentage of lithium in the lithium alloy will determine in part how much of the substance is to be used. Then again the amount of impurities and gases in the molten metal or alloy and the improvement to be given to the metal or alloy will also have to be taken into account in determining the amount of lithium-bearing substance to be used.

It will be observed that the present inventlon provides a process which can be utilized on an industrial scale to produce successful and satisfactorv results which are acceptable to those skilled in the art.

It will be further observed that the present invention provides a method for the production of improved metals and alloys which not only can be carried out on a laboratory scale but which also can be carried out on an industrial scale. When carrying the invention out on an industrial scale the preferred addition of the lithium alloy is an amount within the range of about 0.005% to about 0.05%.

It will also be noted that the present inventlon provides a process by the use of which the disadvantages inherent in the sole use of lithium alone or other member of the alkali group or the alkaline earth group alone are avoided and unexpected advantages are obtained from the use of lithium alloys of metals of the alkali group or the alkaline earth group. The lithium in alkali alloys contemplated by my invention is exceedingly' active and have an activity which could not be predicted from the prior use of lithium alone of other metals of the alkali or alkaline earth groups alone.

Although I have herein described specific illustrative examples of my invention which included specific substances, percentages and the like, it is to be observed that the invention is not to be limited thereto but the scope and spirit thereof is to be determined by the appended claims. For instance, when in the specification and claims, I use the term lithium-alkali alloy it is intended to mean lithium alloy of a metal of the alkali group or alkaline earth group or rare earth group. Similarly, when the term alkali is used, it is intended to refer to alkali group, alkaline earth group or rare earth group.

The present application is a continuation in part of my co-pending application, Serial No.467.625.filed July 12,1930, entitled Processes of treating molten metals and alloys with compositions containing lithium and products resulting from such treatment.

What is claimed is:

1. The process of treating iron and/or steel and/or alloys thereof in their molten state to improve the properties thereof, whichcomprises treating said iron and/or steel and/or alloys thereof while in a molten state with a lithium-alkali alloy.

2. The process set forth in claim 1 in which the lithium-alkali alloy contains lithium and calcium.

3. The process set forth in claim 1 in which up to about 2 parts of the lithium-alkali alloy is used to about 100 parts of iron and/ or steel and/or alloys thereof.

4. The process of treating iron and/or steel and or alloys thereof in their molten state to improve the properties thereof which comprises dipping a solid body of an active lithium-alkali alloy into a molten mass of iron and/or steel and/or alloys thereof to be treated and stirring the thus treated molten mass to effect a thorough distribution of said lithium-alkali alloy.

5. The process of treating iron and/or steel and/or alloys thereof in their molten state to improve the properties thereof which comprises adding a briquette containing an active lithium-alkali alloy to the lower portion of a molten mass of iron and/or steel and/or alloys thereof to be treated and causing a thorough mixing of said lithium alloy in said molten iron and/or steel and/or alloys thereof.

6. The process of treating iron and/or steel and/or alloys thereof in their molten state to improve the properties thereof which comprises adding a lithium-calcium alloy to a molten mass of iron and/or steel and/or alloys thereof to 'be treated and stirring said molten mass to effect a treatment of the various parts of said mass with said lithium calcium alloy.

7. The process of treating iron and/or steel and/or alloys thereof in their molten state to improve the properties thereof which comprises dipping a block of lithium-calcium alloy into the lower portion of a molten mass of the iron and/or steel and/or alloys to be treated and effecting a distribution of said lithium-calcium alloy substantially throughout said mass.

8. The process of treating iron and/or steel and/or alloys thereof in their molten state to improve the properties thereof which comprises adding a lithium alloy containing an alkali metal to a molten mass of metal or alloy to be treated and stirring said molten mass to effect a treatment of the various parts of said mass with said lithium alloy containing an alkali metal.

9. The process set forth in claim 8 in which the lithium alloy is coated with lithium.

10. The improved iron and/or steel and/or alloy thereof which comprises an iron and/ or steel and/or alloy thereof resulting from the treatment thereof in a molten state with a lithium-alkali alloy.

11. The improved iron and/or steel and/or