US2120562A - Refractory material and process of making same - Google Patents

Description

Patented Julie I4, 1938 2,120,562

REFRACTORY MATERIAL AND PROCESS OF MAKING SAIWE Clemens A. Laise, Tenafly, N. 1., assignor to Eisler Electric Corporation, Union City, N. J.,' a corporation of Delaware No Drawing. Application Octoberll, 1934,

Serial No. 747,891

16 Claims. (Cl. 75-137) The present invention relates to hard metal material suitable to be used in the extruding compositions, to methods of working such hard steps hereinafter set forth. The carbidized alloy metal compositions, and to processes for producmay betreated by breaking it up into an abrasive ing compositions of this description that are metallic powder suitable for directly forming adapted for working into shapes suitable for hard metal members without the formation of 5 UNITED STATES PATENT OFFICE various commercial uses. the extrusion material or the practice of the ex- Such shapes may take many forms. Among truding steps. others may be specifically mentioned the form Under the processes of the prior art, it seemed V of borers for oil-well drilling, sand blast nozzles, to be necessary to produce shapes such as above tips for cutting tools, nibs for wire-drawing dies, described, which might take the forms of polyg- 10 high resistance insulators for radio circuits and onal, fluted or cylindrical rods or of tubes, by parts and contacts for all types of mechanical machining the same or by pressing or molding and electrical apparatus subject to extreme wear various types of hard metal compositions into and tear. I the forms desired, or by first putting the material It is an advantage also that the material of into cylindrical form d u sequently shap 15 the invention is practically non-corrosive and e sa eue, o to the extreme hardmay consequently 'be employed for many uses ness of such materials, it was very difiicult to mawhere materials of the prior art are damaged chine or cut shapes so made, once they were by corrosion, tarnish or rust, or by electrolytic ed- This was Particularly e after the action. Y

I am aware that there are a number of procment which usually ac'dompanied the pp c esses' for producing hard metal compositions, of pressure-. some of which include in the composition some of It is n Qbl 0f e P es inVehtiOn t prothe basic elements mentioned in the present in- Vide a material and a method of v p g the vention. 'In the past, however, it has been cus- Same that Will p t of as y forming and 25 tomary, in making such hard metal compositions, cutting into the desired Shape d Size, and first to provide a finely divided carbid of l. which material and method greatly increase the fractory metal; then to press and sinter such Variety Shapes into which hard metal carbide into a form or shape. The resulting positions may be processedform or shape was naturally of a rather brittle The invention COmDIBhGHdS a material D 30 and porous character but extremely hard. Therecially adapted for th P p above mentioned, fore, in order to add toughness to the article the steps of preparing this material, the steps of ,so produced, it was necessary to impregnate it shaping the material so prepared into the desired with a cementing metal. This cementing metal forms and the steps of hardening the shapes so 3 was introduced into the pressed and sintered carformed into a usable, commercial condition. The bide form or shape, generally either by mixing achievement of these ends is among the objects the cementing metal in finely divided form with of the invention. the carbide before pressing and sintering, or else More specifically, the invention 'comprehends first pressing and sintering the carbide, and then an extrusion material, process and product. The

40 dipping the shape or form into a molten bath of extrusion material may be generally described as 40 cementing metal. a refractory metal composition in plasticstate;

In contradistinction to these methods and the process includes the mixing and alloying, and other similar processes of the prior art, the presthe carbidizing of. a refractory and a base metal ent invention comprehends the mixing, before and the extrusion, drying, baking, cutting and carbidization,- of a refractory metal or metals hardening of this material; and the product may 45 with a base metal or metals, both in very finely be represented by shaped members resulting from divided form. I have discovered that if such a the application of the process to the said mamixture' is then heated to a temperature just beterial. low that of the sintering temperature of the low- To accomplish these ends a mixture is prematerial had been subjected to the heat treat- 20 est melting point metal in the mixture, there is pared comprising very finely divided refractory 50 a relatively rapid combination or alloying of the metals and. base metals. The refractory metals metal contained in the mixture. This alloy is should for best results consist of a-mixture of then very readily carbidized at surprisingly low' any two or more of the following: Tungsten, temperatures as hereinafter set forth, and subtantalum, titanium, zirconium, chromium, thorisequently treated in such a manner to form a um or rhenium, etc. In fact, any carbide form- 55 cedure.

ing metals having a melting point above 1500 C. may be'used. These or some of these metals of such refractory nature are then in proper cases mixed with one or more of such other metals having a melting point of 900 C. or above, as. iron, manganese, nickel, cobalt, silver, copper, etc., also in very finely divided state.

I have discovered that it is possible to produce a remarkable change by intimately mixing and milling finely divided refractory metal powders such as tungsten and molybdenum, etc., with base metal powders such as iron, nickel or cobalt, without heating the mixture to the lowest melting point of any of its constituents. To produce this result constitutes the first step in the pro- The mixtureof powders above mentioned is heated in a hydrogen atmosphere in a suitable gas or electric furnace at a temperature of 700 C. to 900 C. and preferably at temperatures just under the melting pointsof the base metal constituents for a period of several hours. Under this treatment a light sintering takes place permitting subsequent crushing and sieving; but more than this, an apparent absorption of some of the elements into others takes place, thus forming substantially homogeneous particles having the characteristics of alloys. For instance, copper and nickel will readily intimately intermix in this manner so that a" red 50% mixture, after heattreating will result in a white or silvery powder no longer resembling the original mixture and having characteristics of an alloy. Similarly, tungsten or cobalt, or tungsten and nickel, may be intimately intermixed and alloyed in the powder form. This preliminary intimate intermixing, alloying and sintering stage is, therefore, an important step in my process, as it greatly facilitates the preparation of the material with which the subsequent extrusion step is carried out.

The next step is the formation of carbides from these intimate mixtures or alloys of metal powders. The sintered alloy metal powders consistmg of refractory metals intimately admixed with base metals, preferably of the iron group, are carbidized by uniformly mixing carbon or carbon and boron, also in fine division, with them in order to form a combination of such alloys with nonmetallic elements such as carbon and boron and to facilitate theformation of' carbides or borides or both. Such sintered powders can be carbidized at temperatures much lowerthan merely the powdered mixtures of the same composition. 'I'hus, I find to carbldize tungsten powder in itself requires a temperature of 200 C. to 400 C. higher than when I carbidiz'e a. sintered tungsten-nickel alloy powder containing 70% tungsten and 10% nickel. The amount of carbon should be calculated to provide an amount sufficient to cause the carbide-forming metals to absorb .the normal atomic ratio of carbon to metal to give the desired carbide molecule. The carbon may, however, be added during the heat treatment which follows by heating in an atmosphere of carbonaceous gas. For facility of explanation I shall refer hereinafter to carbides" with the understanding that what is said of. carbides applies equally to borides or carbides and borides. 1

In order to effect carbidization, the alloyed metal powders and carbon are subjected to a heat treatment at a temperature elevated to or almost to the sintering temperature of the mixture and below the melting point thereof, say 1200 C. to i400 C., for a period of from two to six hours.

pores or voids.

This operation is carried out in a hydrogen, carbonaceous or reducing atmosphere. The result is either a still finely divided product consisting of carbides, or borides, or, in a case where both carbon and boron are added, of both carbides and borides of the alloyed metals in the mix. Where the temperature of the heat treat- ,ment is sufliciently high, the powdered metal carcarbidized alloy, however, may be crushed orground to form an abrasive metallic powder which may be used to produce hard metal members by other methodsthan by the extrusion process herein described.

From this carbidized or boridized fine alloy powder thus prepared, the extrusion material of the present invention is formed and its formation constitutes the next step.

The nature of this extrusion material is determined by the requirements necessitated by the conditions of the extruding procedure which will be described hereafter and, to a certain extent, by atmospheric conditions.

The formation of the extrusion material is best begun by forming a, suitable paste which may act as a binder for the finely divided alloy carbide. This paste may consist of starch, water and ammonia, in the proportions of grams of starch to 825 cc. of water to 75 cc. of ammonia. In place' of the foregoing paste, organic binding materials, such as a caramel solution, gum arabic, or a casein solution, or mineral binders, such as silicates or mineral colloids may be used. In any case the quantity of paste must be such as to render the mixture sufiiciently viscous so that the extruded mass will hold together into a compact body having a smooth surface and free from If the mixture of alloy carbides and paste contains an improper quantity of paste, the extruded pieces may show minute cracks on the surface. In this case the pieces must be broken up and remixed'with the proper proportion of paste until the proper consistency for yielding dense, smooth-surfaced products is attained.

The paste may be mixed by the use of any standard heavy duty mixing equipment and should be carried out until a thorough intermixture of ingredients into a plastic mass is obtained. A suitable consistency hasbeen obtained by mixing refractory carbide powders and a starch paste compounded as above described in the proportion of about grams starch binder to 1 kilogram of carbide. The consistency of the composition may vary slightly under varying atmospheric conditions, but a mixture of the correct consistency may be produced under any given set of conditions by a suitable variation in the amount of binder material. In some cases the paste may be rolled between or under suitable rolls of standard rolling mills so as to render the powders exceedingly fine and the paste hard and plastic so that it must be extruded with the aid of hydraulic pressure.

Extrusion is accomplished by placing this plastic mass obtained as above outlined in an ex.

truding apparatus and forcing the composition and cobalt. This may be still further hardened through an orifice of suitable shape under hydraulic or other pressure, in excessof one hundred pounds per square inch. Channels or plates of plaster of Paris or glass may be provided adjacent the extrusion nozzles in order to carry the extruded forms as they are produced. The extrusion equipment should be kept clean and free from. imperfections in order to avoid the formation of scores and faults in the extruded products.

The next step in the formation of the shaped members of hard metal composition characterizing the final product comprises drying the extruded shapes preferably at room temperature and under a slightly humid atmosphere for a period of two or three days or longer.

They are then cut to the desired lengths and baked in a sintering furnace in order to carbonize the binding material with which the plastic mass was formed. A temperature of 500 to 700 C. for about one hour or less has been found sufficient to carbonize the binding and plasticizing material. The extruded members may be packed in carbon boats surrounded by lamp black during this baking treatment, during which a reducing atmosphere may be maintained to advantage. I

The final step comprises a further heat treatment for bonding together the particles into a uniform, homogeneous, strong. compact. wearresisting body. The carbonized members produced by the baking treatment are again packed in carbon boats, surrounded by lamp black, and then heated inan electric furnace at a temperature of 1400" to 1500 C This operation is carried out from, 5 to 30 minutes, depending upon the shape and size of the extruded members. Preferably a carbonaceous or hydrogenous atmosphere is maintained in the furnace during this compacting and hardening step.

During the cohesion and adhesion of the particles together under the conditions of the final compacting and hardening step, a considerable shrinkage of the original extruded product takes place, ranging from 10 to 30%. Shrinkage in length is generally about 22% and in diameter about 27%, although small pieces manifest considerably less shrinkage. Uniformity in shrinkage is facilitated by maintaining as smooth a surface as possible on the extruded members.

An example of the composition of my novel product is as follows:

v Per cent Refractory metal (such as tung sten)- 92.5 to 57.5 Iron .25 to' 5 Chromium and thorium .25 to 2.5 'Carbon and boron 5.0 to 10.0 Cobalt and nickel "a 2.0 to 25.0

The composition of the starting material is ad- ,iusted with reference to the additions and losses taking place during the processing, and also with the purpose in mind for which the, .end product is to be used. If the final composition is to be exce'edingly hard, the metallic constituents should be held to a refractory metal content above 90% and a basemetal content below 10%. If, on the other hand, the composition is to be extremely tough,.the base metal content is increased above 10% or 12% and the refractory metal content proportionately reduced.

A more specific composition for a superior wear-resisting material comprises in its final stage a compact homogeneous body composed of a carbidized alloy oftungsten, chromium, iron.

. group through the incorporation of to 1% of thorium. The final body consists of approximately the following composition:

Cobalt (and/or nickel) 13.5

In cases where a combined carbidizing and boridizing effect is desired, I may add powders of boron suboxide or boron nitride or other suitable boron compounds to the original mixture before the heat treating. and alloying step, or immediately prior to carbidizing. In this case the total carbon and boron in the composition should not exceed about 15%.

By the above extrusion process I produce extruded metallic bodies which are not only exceedingly hard but also exceedingly tough,.the hardness exceeding on the "A Rockwell hardness scale, and the tensile strength exceeding 200,000 lbs. per square inch. At the same time my composition is exceedingly compact and dense. The harder and more compactthe paste is before extrusion the more dense and pore-free is my composition. In fact, .before extruding, my paste may even be rolled between metallic rolls so as to make the powders exceedingly fine and the paste exceedingly hard so that it must be extruded on a hydraulic or power press.

Having thus described my invention, what I claim is:

1. An extrusion material comprising in a finely divided state a carbidized alloy of two or more refractory metals of the group consisting of tungsten, tantalum, titanium, zirconium, chromium, thorium and rhenium, and a metal of the consisting of iron, nickel, cobalt, manganese, silver and copper, in intimate admixture with a paste containing carbonizable material, said paste being present in said mixture in quantity sufiicient to impart 'to the whole the capability of being extruded through an orifice in the form of a dense, coherent body.

2. An extrusion material comprising a carbidized alloy of tungsten and another refractory metal with a base metal, said metals being in powdered form and in intimate. admixture with a' paste consisting of carbonizable binding material and water, said paste being present in quantity suflicient to impart to the whole the capability of being extruded through an orifice in the form of a dense, smooth, coherent body.

3. An extrusion material comprising a finely divided carbidized alloy of tungsten and another refractory metal with a base metal, said finely divided carbidized'alloy being in intimate admixture with a paste containing carbonizable binding material .and water.

4. The method of making hard metal members comprising intimately intermixing finely divided powders of one or more refractory-metals of the group consisting of tungsten, tantalum, titanium,

zirconium, chromium; thorium and rhenium,

ganese, nickel, cobalt, silver and copper, sintering and alloying said mixture and then carbidizing the same, finely dividing the carbidized product,

.thoroughly mixing therewith a paste of carbonizable material and thereby forming said carbidiz'ed material into a plastic mass. extruding said mass into a shape of the desired form, drying the same and cutting the dried shapes ap-' powders of one or more refractory metals of the group consisting of tungsten, tantalum, titanium, zirconium, chromium, thorium and rhenium, with finely divided powders of one or more base metals of the group consisting of iron, manganese, nickel, cobalt, silver and copper, sintering and alloying said mixture and then carbidizing the same, finely dividing the carbidized product and forming a plastic mass thereof, extruding said mass into a shape of the desired form, drying the same and cutting the dried shapes approximately to. size, carbonizing said shapes and finally firmly cohering the carbonized product.

6. The method of making hard metal members comprising intimately intermixing finely divided powders of oneor more refractory metals of the group consisting of tungsten, tantalum, titanium, zirconium, chromium, thorium and rhenium, with finely divided powders of one or more base metals of the group consisting of iron, manganese, nickel, cobalt, silver and-eopper, sintering andalloying said mixture and then carbidizing the same, finely dividing the carbidized product and forming a plastic mass thereof, extruding said mass into a shape, carbonizing said shape and-finally baking the carbonized product under reducing conditions.

7. The method of making hard metal members comprising intimately intermixing powders of a refractory metal with powders of a base metal, sintering and alloying said mixture and then carbidizing the same, finely dividing the carbidized product and forming a plastic mass thereof, extruding said mass into a shape of the desired form, drying the same and cutting the dried shapes approximately to size, carbonizing said shapes and finally firmly cohering the carbonized product. o

8. The' method of making hard metal members comprising intimately intermixing powders of a refractory metal with powders of a base metal, sintering, alloying and carbidizing the mixture, comminuting the carbidized product, forming the same into a plastic mass, extruding said mass, drying the extruded shape, carbonizing the same and finally baking the product under reducing conditions.

9. The method of making hard metal members comprising intimately intermixing powders of a refractory metal with powders of a base metal, sintering, alloying and carbidizing the mixture, comminuting the carbidized product, forming the same into a plastic mass, extruding said mass, drying the extruded shape, carbonizing the same and finally bonding together the carbide particles by heat.

10. The method of making hard'metal members comprising intimately intermixing powders of :3.

refractory metal with powders of a base metal, sintering, alloying and carbidizing the mixture, comminuting the carbidized product, forming the same into a plastic mass, extruding said mass and then finishing the extruded mass into a hard member of the desired size and shape.

11. The process of making hard metal members which includes the steps of forming a plastic mass of carbidized alloy particles and then extruding the said mass.

12. The process which comprises intimately intermixing refractory metal powders with base metal powders, alloying and carbidizing said mixture, comminuting said carbidized product, then mixing the same with a binder into a plastic mass, extruding the mass, drying the same, and

- then firmly uniting the mass by heating the same under reducing conditions.

13. The process of making hard metal members which comprises mixing, in finely divided form, one or more refractory metals adapted to form carbides and having melting points materially higher than 1500 C. with one or more metals also in finely divided state having melting points :above 900 C., alloying said metals by heating said mixture to a temperature of 700 C. to 900 C.,

and rhenium with finely divided metals of the group consisting of iron, nickel, cobalt, manganese, silver and copper, alloying the finely divided metals in the mixture by heating the same to a temperature slightly below the melting point of. the metal or metals of the said second group in the mixture, carbidizing the metals thus alloyed, comminuting said carbides, plasticizing the comminuted product, and then forming the-desired member from said plastic mixture. 15. The method of forming hard metal compositions which comprises intimately mixing and milling the finely divided metal powders, in dry state, of two or more refractory metals of the group consisting of tungsten, tantalum, titanium, zirconium, chromium, thorium, and rhenium, and one or more metals of the group consisting of iron, nickel, cobalt, manganese, silver and copper; then heating the mixture to a temperature below the melting point of the metal or metals of the second group and thereafter carbidizing the alloy so formed.

16. The method of forming hard metal compositions which comprises intimately mixing and milling in dry state one or more refractory metal powders with one or more base metal powders, alloying said metals by heating to a temperature below the melting pointof the base metal or metals, and thereafter carbidizing the alloys so formed.

CLEMENS A. LAISE.