US3298801A - Powder metallurgical addition agent - Google Patents

Description

United States Patent POWDER METALLURGICAL ADDITION AGENT Charles B. Goodrich, Charles E. Manilla, Cecil L.

Ramsey, Richard H. Hanewald, all of Huntington, W.

Va., assignors to The International Nickel Company,

Inc., New York, N.Y., a corporation of Delaware NoDrawingL Filed Mar. 29, 1966, Ser. No. 538,197

r 3 Claims. (Cl. 29-182) The present invention is directed to a novel nickelmagnesium briquetted agent produced by powder metallurgical methods and to the method for producing the said briquetted agent.

The use of various melted and cast alloys containing nickel and magnesium, which are employed industrially as deoxidizing alloys for the treatment of molten nickel and other metals and f0l"tl'l introduction of magnesium into molten cast iron for the production of ductile iron, has long been known. For example, a nickel-magnesiumcarbon alloy having special utility for the purpose of intrcducing magnesium into molten cast iron is described in US. Patent No. 2,529,346 and a nickel-magnesium-silicon alloy useful for the same purpose is described in US. Patents No. 2,563,859 and No. 2.690.392. The alloys as described in the aforementioned US. Patents have been prepared ,by melting and casting the alloys into slabs and crushing the slabs to provide lumps of material which vary considerably. in size and shape and grading the crushed product to provide the lump size ranges desired in the iron foundry. The crushing operation employed to produce the alloys in graded particulate form within the desired sizerange, e.g., Vs inch or inch or larger lumps, has always resulted in the production of a substantial quantity of fine material. These fines have been found to be of little use for the foundry production of ductile iron since the ,fines oxidize rap-idly in contact with the molten iron with the result that they are ineffective for the purpose of introducing magnesium in the molten cast iron. Accordingly, these fine materials have been segregated from the desired product and have been remelted to recover the nickel content thereof with accompanying substantial loss of the magnesium content. The production of fines as aforedescribed has resulted in a substantial uneconomic loss of material. Efforts to render the fine material useful for the purpose of introducing magnesium into molten cast iron such as by briquetting, etc., have not solved the problem as it is found that the fine material is hard and is difficult to briquette. Thus, the fine material will not adhere when cold pressed. Endeavors to agglomerate the fine material through the use of binders and the like have also been unavailing. It would accordingly be desirable to provide a method for preparing alloys of nickel and magnesium which would not be accompanied by the undesirable production of fines and, in addition, it would be desirable to provide an addition alloy containing magnesium which would readily be produced in forms having closely controlled size and which would be more effective for the purpose of introducing the magnesium content thereof into molten cast iron or into other molten metallic materials.

"We have now found a powder metallurgical method whereby a nickel-magnesium alloy can be produced without attendant production of fines, which method provides a nickel-magnesium product having a closely controlled size and shape and having improved utility from the stand point. of increasing the addition efficiency of the magnesium content thereof into molten cast iron.

, It is an object of the present invention to provide a powder metallurgy method for the production of an addition material containing nickel and magnesium.

It is a further object'of the invention to provide by powder metallurgy means an addition agent containing nickel and magnesium which provides improved results from the standpoint of magnesium introduction when it is employed for the purpose of introducing magnesium into molten ferrousmelts.

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

Broadly stated, the method provided in accordance with the invention comprises blending fine nickel powder having a particle size not exceeding about 10 microns with magnesium powder having a particle size of at least about 40 microns but not greater than about 1000 microns, cold pressing the blended powder mixture into a coherent form,

sintering the pressedmaterial at a temperature of at least about 950 F. but not exceeding about 1200 F. in a protective atmosphere, and cooling the sintered material at a rate exceeding about 2 F. per minute to provide a sintered agent containing nickel and magnesium, having a porosity of about 20% to about 50%, and an average pore size of about 50 to about 500 microns. The resulting sintered material contains at least about 4% up to about 20% magnesium, e.g., about 10% to about 17% mag nesium, has a porosity of about 20% to about 50% and a crushing strength of at least about 12,000 pounds per square inch (p.s.i.). The sintered material containing about 4% to about 20% magnesium in briquetted form has substantial sterngth, withstands normal commercial handling and-is particularly useful for the introduction of magnesium into molten cast iron. Advantageously, the sintered briquettes have a surface area to volume ratio of at least about 8 to 1 when used to introduce magnesium into molten cast iron.

In preparing the briquetted nickel-magnesium addition material contemplated in accordance with the invention, it is important to employ a nickel powder having a particle size not exceeding about 10 microns, e.g., about 3 to about 7 microns, as the pressing operation is then facilitated and green briquettes of high green strength are produced. Carbonyl nickel powder having a particle size not exceeding about 7 microns is a satisfactory starting material particularly in view of the high purity of this powder including the almost complete absence of sulfur and oxygen therefrom. The oxygen content of the nickel powder should not exceed about 0.75% as it is found that greater amounts of oxygen interfere with the sintering operation and with magnesium recovery when the sintered material is added to molten cast iron. The initial powder mixture may contain up to about 25% of iron powder having a particle size not exceeding about microns. More advantageously, from the standpoint of reactivity, etc., the iron content does not exceed about 15%. The iron powder may be carbonyl iron, reduced iron oxide, etc. It is preferred that the magnesium powder employed in the initial powder blend have a particle size of at least about 200 microns since it is found that the use of finer magnesium powders results in final sintered agents having a finer average pore size and less desirable addition characteristics.

Provided the foregoing precautions are observed in the selection of the powder to form the initial powder blend, it is found that the powder blend presses readily at ambient temperatures to form dense briquettes and other forms which may readily be handled. The resulting briquettes are then sintered in a protective atmosphere, e.g., hydrogen, argon or other essentially nitrogen-free atmosphere which will prevent oxidation of the magnesium-bearing briquettes. It has been found that magnesium will form nitrides when heated in a nitrogen-containing atmosphere. These nitrides will react with water vapor to form magnesium oxide and ammonia. The sintering temperature should exceed approximately 950 F. .as this ,is the melting temperature of the lowest melting eutectic formed in the nickel-magnesium binary system. A sintering temperature of about 1000 F. is satisfactory. The time of sintering should be sufficient to cause substantially complete liquid-phase sintering throughout the entire cross section of the briquette. Sintering times of about one to about three hours, e.g., about one hour per inch of cross section, are satisfactory. The sintering operation results in the formation of a liquid phase and the formation of a porous sintered structure. It is found that the sintered material should be cooled from the sintering temperature at a rate of at least about 2 F. per minute, e.g., 5 F. per minute or faster, as otherwise cracking of the material sintered at 1000 F. may occur. The sintered briquettes are characterized by high crushing strength, e.g., the briquettes will withstand a compressive load of at least about 12,000 p.s.i. before crushing. This high strength permits shipment of the briquettes produced in accordance with the invention by usual commercial means without encountering undesirable size degradation leading to the uneconomic production of fines, and accompanying loss of material.

The sintering operation is essential in accordance with the concepts of the present invention in order to provide agents, e.g., briquetted agents, having the special controlled porosity and quiet introduction characteristics when the briquettes are employed for the purpose of introducing magnesium into cast iron. Thus, it is found that when green (unsintered) briquettes, i.e., briquettes which have been formed by isotati-c pressing at ambient temperatures, are employed for the aforementioned purpose they have insufficient strength, generate excessive fines during handling, are considerably more reactive in contact with molten cast iron, and give a lower magnesium recovery in cast iron than do briquettes sintered as taught herein. Illustrative data are set forth in Table III hereinafter.

When the briquetted and sintered agents are employed for the purpose of introducing magnesium into molten cast iron by the commonly-employed practice wherein the magnesium-containing agent is placed at the bottom of a ladle and molten cast iron to be treated (at a temperature of about 2500 F. to about 2750 F., or even 2850 F. e.g., 2650 F.) is poured thereover, it is particularly advantageous for purposes of minimizing reactivity to provide the agents in a form which will not fioat to the surface of the molten cast iron. In order to accomplish this objective, the briquetted and sintered agents :are produced in a physical form such that the ratio of surface area to volume is at least 8 to 1. To illustrate the foregoing, a series of sintered 85% nickel-15% magne- :siurn agents having surface area to volume ratios from 9.5 to 1 to 4.26 to 1 was prepared by mixing fine carbonyl nickel powder with magnesium powder having a particle size in the range minus 20 mesh, plus 70 mesh (Tyler), 'isostatically pressing the mixture to the various briquette :sizes and sintering the resulting briquettes at 1000 F. in hydrogen. The resulting briquettes were then employed to treat 150 pound batches of molten cast iron having the same composition in each instance by ladling the molten cast iron at a temperature of about 2750 F. upon about 1.2 pounds of the sintered briquettes. Data pertaining to these tests are set forth in the following Table I.

An advantageous means for producing briquettes in accordance with the invention comprehends the use of rubber molds wherein the initial powder mix is molded under isostatic pressure to the desired final size having regard for the shrinkage which takes place during pressing and sintering. For example, a plurality of shaped cavities canbe punched in a rubber disc having the desired thickness. One end of the cavities can be sealed off by vulcanizing a rubber sheet on one side of the rubber disc to provide a plurality of cup-like cavities in the disc. The disc or a plurality of discs can be filled with powder and stacked in a rubber casing so as to permit isostatic pressing of a number of briquettes simultaneously at a commercial production rate. If desired, billets can be pressed from the initial powder mixture and-the sintered billet can be crushed to lump form, although this technique provides an undesired loss of material in the form of fines.

In order to give those skilled in the art a better understanding of the advantages of the invention, the following illustrative examples are given.

Example I A series of powder blends containing fine carbonyl nickel powder of about 5 micron particle size and magnesium powder of minus 20, plus 70 mesh particle size with hydrogen-reduced iron powder of minus 325 mesh size as an optional addition was prepared and briquettes were pressed isostatically therefrom at about 30,000 psi. pressure using rubber briquette molds. The resulting green briquettes were sintered at about 1000 F. in hydrogen. The resulting briquettes were porous and quite strong in each instance. The compositions of the resulting briquettes are set forth in Table II. In Table II, the briquettes made .of'Alloys 1 through 5 were 1 inch in diameter by about /8 inch thick and had a'surface area to volume ratio of about 6.3 to 1 while the briquettes made of Alloys 6 through 10 were about 0.65 inch in diameter by about 1 inch thick and had a surface area to volume ratio of about 8.14 to 1.

TAB LE II Alloy iitagunsin in, Iron.

No. Percent Percent NorE.The balance in each case is nickel.

TABLE III Tapping Percent Percent Percent Alloy Tempera- Magnesium Magnesium Magnesium Comments No. ture, F. Added I Recovered Recovery 2, 790 0.076 0.067 88 Slight floating. 2, 775 0. 077 0. 060 77 Dissolved. 2, 750 0.095 0. 075 79 Slight floating. 2, 750 0. 135 0. 076 56 Floated. 2, 760 0. 126 0. 059 47 Extremely active. 2, 700 0. 139 0. 096 09 Dissolved. 2, 750 0. 127 0. 072 57. 6 o. 2, 750 0. 130 0. 071 54. 6 Floatod. 2, 700 0. 138 0. 051 37 Do. 2, 700 0. 142 0. 099 69. 7 Dissolved.

*Green (nnsintered) briquettes.

It is to benoted that the green (unsintered) briquette made of the Alloy No. composition was extremely active and gave a low magnesium recovery as compared to the sintered briquette made of the comparable Alloy No. 4 composition. Furthermore, it is to be noted that the briquettes made of the Alloy No. 8 and Alloy No. 9 compositions, which contained 20% and 25% iron, re-

. spectively, floated and gave materially lower magnesium recoveries than did the briquettes of the Alloy No. 6 and Alloy No. 10 compositions which contained 10% and 0% iron, respectively.

Example ll size of about 300 to 400 microns and a porosity of about 30%. The briquettes had a surface area to volume ratio of about 8.14 to 1. The sintered briquettes were employed on a commercial foundry scale for the production of ductile iron. The molten cast iron was prepared in an induction furnace and contained about 3.58% carbon, about 2.36% silicon, about 0.1% manganese, about 0.011% sulfur, about 0.005% phosphorus and the balance essentially iron. About 300 pounds of molten iron at a temperature between 2800 F. and 2850 F. were poured over about 3 /2 pounds of the briquettes held in the bottom of a ladle. The briquettes did not float. The iron was inoculated with about 0.15% silicon as a graphitizing inoculant and was poured to provide ductile iron castings. The last iron poured from the ladle contained about 0.058% magnesium.

' The briquettes provided in accordance with the present invention are useful not only for the purpose of introducing magnesium into cast iron but also for the purpose of introducing magnesium into melts of other metals, e.g., nickel, copper, ferrous-base metals, etc., for deoxidation, desulfurization, alloying and other purposes.

When the briquettes provided in accordance with the invention are employed for the purpose of treating molten cast iron, they contain nickel, magnesium and optionally iron as described hereinbefore. Carbon in amounts of up to about 2% may be introducedinto the briquettes without harmfully affecting. reactivity thereof with respect to molten cast iron. Copper in amounts up to about 15% or about 20% does not adversely afliect the addition characteristics of the briquettes with respect to cast iron. Although copper is an undesirable constituent in ductile iron, copper-containing briquettes may be employed in treating other types of molten metals. The addition of silicon powder in elemental form to an initial powder mixture results in foaming of the resulting briquettes during sintering. Silicon as a pre-alloyed powder with nickel and magnesium can be introduced into the briquette in amounts up to about 15 or 20% but such an expedient is uneconomic.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A sintered briquette having high crushing strength, containing about 4% to about 20% magnesium, up to about 25% iron, with the balance essentially nickel, having a porosity of about 20% to about 50% and an average pore size of about 50 to about 500 microns.

2. A briquette according to claim 1 having a crushing strength of at least about 12,000 p.s.i.

3. A briquette according to claim 1 containing not more than about 15% iron and having a surface area to volume ratio of at least about 8 to 1.

References Cited by the Examiner FOREIGN PATENTS 527,579 7/ 1956 Canada.

References Cited by the Applicant UNITED STATES PATENTS 1,555,978 10/1925 Hunt. 2,485,760 10/ 1949 Millis et al. 2,555,014 5/1951 Strauss. 2,610,912 9/1952 Millis et al. 2,757,082 7/1956 Busby et al. 2,826,497 3/ 1958 Gagnebin et al. 2,988,444 6/ 1961 Hururn.

CARL D. QUARFORTH, Primary Examiner.

REUBEN EPSTEIN, Examiner.

A. J. STEINER, Assistant Examiner.

Claims (1)

1. A SINTERED BRIQUETTE HAVING HIGH CRUSHING STRENGTH, CONTAINING ABOUT 4% TO ABOUT 20% MAGNESIUM, UP TO ABOUT 25% IRON, WITH THE BALANCE ESSENTIALLY NICKEL, HAVING A POROSITY OF ABOUT 20% TO ABOUT 50% AND AN AVERAGE PORE SIZE OF ABOUT 50 TO ABOUT 500 MICRONS.