US2170432A - Hard metal tool alloy - Google Patents

Description

,ivaasa No Drawing. Application July 27.- 1937, many Paul Schw' N. Y., a corporation of No. 155,919. in Ge 8 Claims.

This invention refers to a hard metal tool alloy and method of producing the same.

This invention forms a continuation in part of my copending application Ser. #727,781, filed May 26, 1934, and of my copendlng application Ser. #743,717, filed September 12, 1934, and issued into Patent #2,122,157, which were in turn copending with my'application Ser. #656,103, filed February 10, 1933, and issued into Patent #1,959,879, and my application Ser. #625,042, filed July- 27, 1932, and issued into Patent No. 2,091,017, which were in turn copending with my application Ser. #452,132, filed May 13, 1930.

It is an object of the invention to increase the hardness of such hard metal tool alloys without impairing their toughness.

It is another object of the invention to increase the resistance of such hard metal tool alloys against mmhanical wear and chemical effects such as of the oxygen of the surrounding air, or moisture, or a cooling liquid such as water.

It is a further object of the invention to increase the hardness of the alloy without impairing its toughness and size of hard particles contained therein.

It is another object of the invention to adjust the heat conductivity oi the hard metal tool alloy without impairing its hardness or resistance against oxidation.

It is still another object of the invention to increase the speed at which hard alloys of this kind can be used for cutting, drilling, milling, and other machining purposes.

This and other objects of the invention will be more clearly understood when the specification proceeds.

Hard metal tool alloys of the type referred to have been made of tungsten carbide and auxiliary metal taken substantially from the iron the heat.

The present invention particularly refers to a tool alloy comprising a consolidated product containing at least two carbides for instance, of tungsten, molybdenum (i. e. an element of the sixth group of the periodical system), boron (i. e. an element 01' the third group of the periodical system), silicon, titanium, zirconium (i. e. an element of the fourth group of the periodiair cal system). and vanadium (i. e. an element of the flfth group of the periodical system) which are obtained essentially or entirely in the form of mixed crystals by heating to a sufficient extent and the usual cementing auxiliary metal amounting to about 3 to 22% of one or more metals of the'groupcontaining'nickel, cobalt and chromium. A mixed crystal is a homogeneous solid solution of two (or more) substances capable of dissolving one in the other.

Experiments have shown and science has given the rule that the hardness of the mixed crystals is a function of the proportion in which the carbides are present in the mixed crystal, and that this function possesses a mammum. It is particularly advantageous to choose for use in the present invention crystals which lie in, or close to this range of maximum hardness. Let me take first experiments made for instance with the series MozC, W2C and Co, let me increase the amount of MozC while decreasing the amount of W2C, adding always 10% Co; then (1) 90% W2C and 0% M030 and 10% Co give a Rockwell hardness of 55; (2) 81% W2C and 9% M026 and 10% Co give a Rockwell hardness of 62; (3) 72% W20 and 18% MozC and 10% Go give a Rockwell hardness of 57,5: while (4) with 63% W30 and 27% M020 and 10% Co the material is brittle. By these few tests it is possible to ascertain by experiment the hardest mixed (W0), 40 to 20% molybdenum carbide and 10% additional metal. When the additional metal is cobalt the hardness varies between 65 to 69 Rockwell for the composition range given. By way of comparison it may be stated that the Rockwell hardness of an alloy containing 90% tungsten monocarbide and 10% colbalt is 60, whilst that of an alloy 01 90% molybdenum carbide and 10% cobalt is 51.

Let me take new the rules given by the science based on the investigations of Kurnakow and Zemczuzny in the Zeitschrlft filr anorganische Chemie" 1908, volume 60, page 1, and 1910, volume 68', page 123, referred to in the standard book of Reinglass "Chemische Technologie cler Legierungen, second edition, pages 52, 53, and in the Metallund Legierungsk-unde" of Dr. M. v. Schwarz, Professor of the College at Munich, second edition (1929), page 49. There is referred to the investigations of Kurnakow and verbatim said: In an uninterrupted series of mixed crystals the curve of hardness increases with the concentration gradually up to a flat maximum, which lies mostly at the simple atomic composition. If Schwarz says atomic composition", it is to be considered that he mentions metals and not chemical combinations as carbides. If such combinations are to be taken, then instead of atoms, existing only for the pure metals, are to be taken the molecules" being equivalent for compounds to the atoms of the single pure metal. I 1

Furthermore, the science says, that the maximum does not always lie at simple molecular proportions. If one carbide exceeds another carbide materially in hardness, then the maximum of hardness is shifted in favour of the harder carbide in the mixed crystal and consequently two (or three) molecules of the harder (or exceedingly harder) carbide form together with one molecule of the softer carbide the mixed crystal of greatest hardness. In other words, the carbides are to be present approximately in integer number ratios of their molecular weights, the higher ratio applying to the relatively harder carbide, if one of the composed carbides is harder than the other. Lastly, if building up a curve of hardness of mixed crystals depending on the content of the respective carbides, then the maximum of the curve is flat and does not form a tip so that mixed crystals of about greatest hardness are practically also obtained if deviating about 5% to 10% to both sides from the theoretical molecular proportion corresponding to greatest hardness.

If I mention,'therefore, in the appended claims proportions of carbides suitable to yield mixed crystals of approximate greatest hardness, I mean the theoretical ratio of molecular proportions to be calculated according to the rules of science given above, including a range of about 10% to both sides of that theoretical ratio.

Let me take again the example of 10% auxiliary metal and a mixed crystal of molybdenumcarbide and tungsten-carbide. It is to observe that tungsten-carbide exceeds in hardness the molybdenum-carbide. Therefore the maximum of hardness is not to be obtained at a simple molecular proportion, but I have to take two molecules of tungsten-carbide and one molecule of molybdenum-carbide to form a mixed crystal of greatest hardness. Tungsten-monocarbide (WC) has a molecular weight of 196, molybdenum -carbide (MozC) of about 204 and are therefore about equal. Therefore the of carbide have to be made of two molecules of tungstenmonocarbide and one molecule of molybdenumcarbide. It means that about 60% tungstencarbide, about 30% molybdenum-carbide per weight are to be chosen for the mixed crystals,-

while the balance of-10% is formed by the amtiliary metal. The experiments show that the maximum hardness is present at about 27% molybdenum-carbide and therefore 63% tungsten-carbide, if 10% cobalt as auxiliary metal is present.

does not form a tip but is quite flat, so that 5 to 10% variation to both sides of the theoretical maximum is ppssible. Therefore 6% tungstencarbide more or less and 3% molybdenum-carbide more or less are allowable and the results shown are absolutely in conformity with the theory.

Let me take an alloy having 10% auxiliary metal and therefore 90% carbide. Let me furthe fourth group).

The theory says. that the maximum.

ther take'that tungsten-carbide and titaniumcarbide are to be mixed to form the hardest.

mixture. Then we have to divide these 90% in the proportion of 602196, it means we have to take about 20% (on weight) titanium-carbide,

about 70% tungsten-carbide and about 10% auxiliary metal.

Let me take molybdenum-carbide and titanium-carbide. Titanium-carbide is exceedingly hard, at least harder than molybdenum-carbide,

, and is furthermore very light. Consequently the periodical system. Then the correct molecular proportion will be 1:2 because tungsten-carbide exceeds in hardness. Consequently the alloy will contain 10% auxiliary metal, about 76% tungsten-carbide and about 14% vanadium-carbide,

corresponding to the molecular weight of 196 of tungsten-carbide (WC) and 63 of vanadiumcarbide (VC).

Let me take vanadium-carbide (carbide of the fifth group) and titanium-carbide (carbide of the fourth group). Considering that titaniumcarbide exceeds in hardness vanadium-carbide,

- the molecular proportion is to be chosen with 1:2

and consequently the hard metal will contain 10% auxiliary metal, about 60% titanium-carbide and about 30% vanadium-carbide in order to remain within the range of hardest mixed crystals formed by these carbides.

Let me take titanium-carbide (TiC) and zirconium-carbide (ZrC) both carbides of the fourth group of the periodical system. Considering that titanium-carbide exceeds in hardness zirconiumcarbide, the maximum of hardness of the mixed crystals is to be expected in the proportion one zirconium-carbide and two titanium-carbide. Considering that the molecular weight of airconium-carbide is 103 and of titanium-carbide 60, I get an alloy of 10% auxiliary metal, about 40% zirconium-carbide and about 50% titaniumcarbide.

Let me take, as last example, boron-carbide (of the third group) and titanium-carbide (of Boron-carbide is known as the hardest carbide and consequently a little harder than titanium-carbide. The boron-carbide is investigated as BsC with a molecular weight of '78. Taking that the hardness of both carbides is about the same, the mixed crystal has to be made of equal proportions of the molecules, it means in the proportion 78:60. Consequently an alloy will contain 10% auxiliary metal, about 50% boron-carbide and about 40% titaniumcarbide.

I showed by the examples given that either one molecule 01' each carbide is to be taken, or two molecules of one carbide and only one molecule of the other, or three molecules of one carbide and again one of the other, I must touch the pos-' sibility that also two molecules of one carbide and three of the other carbides, are to be taken to form the hardest mixed crystal. There may be exceptionally also the medium-proportion of 3:2.

' In the examples given, 10% auxiliary metal is chosen only for the sakeof uniformity. But the amount of auxiliary metal e. g. of the iron group and chromium can vary between about 3% and 22%. The amount may be smaller if heavy mixtures of carbides (e.g. tungsten, molybdenumcarbide) are concerned and larger if lighter mixtures of carbides (e. g. with titanium-carbide) are concerned.

But I have also found that mixed crystals of two or more carbides of the elements of the fourth group, f, i. a nnxed crystal of titanium-carbide and zirconium-carbide, are capable of forming very hard and particularly for polishing usable crystals.

As a consequence of the considerations presented, the following compositions meet my invention regarding the use of the approximately hardest mixed crystal; to vanadiumcarbide, 85 to 65% tungsten-carbide, 5 to 20% I auxiliary metal; 50 to 70% titanium-carbide, 40

to 20% vanadium-carbide, 5 to 20% auxiliary metal; 3 to 50% titanium-carbide, 60 to 40% boron-carbide, 5 to 20% auxiliary metal; 15 to 25% titanium-carbide, 75 to 55% tungsten-carbide, 5 to 20% auxiliary metal.

Such solid solutions are cemented by auxiliary metals such as nickel. cobalt and chromium singly or in suitable mixtures. Thereby the fine grain imparted to the powdered carbide is substantially maintained and a desirable toughness of the alloy or tool obtained. I

For special purposes, e. g. for finest cuts or polishing mixtures of titanium-carbide andmolybdenum-carbide in about equal proportions forming substantially mixed crystals of great hardness according, to the theory and nickel up to 9 and 15% and chromium up to l and 2% as auxiliary metals has been proved.

But I have found also good results by forming substantially mixed crystals of about 30 to 15% molybdenum-carbide (M020) of the sixth group, and about 65 to 70% titanium-carbide (TiC) of the fourth group, adding hereto as auxiliary I metals 8 to 15% nickel and 0 to 7% chromium.

Within this range the-optimum e. g. for high speed work seems ,to be at about 8 to 10% nickel and up to 1 to 2% chromium.

Generally, according to this part of myinvention, substantially mixed crystals formed of one or more carbides of one or more elements of the sixth group of the periodical system, and one or more carbides of one or more elements of the fourth group of the periodical system, cemented by one or more auxiliary metals of the sixth or eighth group of the periodical system, or both,

such as :.zhromium, nickel, cobalt, are usable. In these cases the carbides of the fourth group present their advantages e. g. of high resistance against oxidation at elevated temperature, great hardness and relatively small specific weight.

Any suitable known method may be used for the production of the mixed crystals; The car bides, e. g. of tungsten and molybdenum, can be suitably comminuted, mixed and heated up to about 1600 to 2000 C. for about 1 to 2 hours until mixed crystals are formed in substantial amount, which latter are then mixed with the auxiliary metal in powdered form, and the whole is molded and sintered at a temperature of about 1400', to 1600" C, It is also possible to mix oxides e. g. of molybdenum and tungsten in finely div'ided form with additions of suitably pulverized and molybdenum carbide in substantial amounts are obtained.

Another of'jpreparing'the mixed crysmetal can be carbonized in the presence of carbon containing gases already from 800 0., and tungsten metal already from about 1000 C., so that the treatment in question will be made at about 1000 C. The intimate mixture of carbides of molybdenum and tungsten is nowto be transformed in mixed crystals. For this purpose the temperature has to be elevated again up to about 1600 to 2000 C. After this preparation of mixed crystals the alloying. has to be done. For this purpose the selected auxiliary metal or metals are to be added in the wanted quantity, the whole is to be intimately mixed and then to be sintered. If the mixed crystals are too coarse, then the mixed crystals are suitable to be pulverized and to be mixed with the auxiliary metal and then to be sintered. Before or while sintering, the molding of the powder so obtained takes place, preferably under pressure.

But my invention is not limited to any special process of producing carbides, transforming them essentially or entirely into mixed crystals, and also not to any method of consolidating such mixture to or in any shape adapted for the use intended, say as a tool element. I

In particular the tool or alloy according to my invention may be produced by mixing the carbides and auxiliary metal which are to be contained in the tool alloy, in as finely divided a form as possible, shaping and pressing, if desired, the mixture, and thereupon sintering it. Sintering may be performed e. g. by electrical induction heating, if desired, in vacuo.

For producing e. g. molybdenum-carbide the following way has been proved as most conveninet. Metallic molybdenum and carbon are mixed in the proportion corresponding to the theoretical values, needed for producing the combination MoQC. This mixture is powdered and then heated in a reducing atmosphere up to about 1400 to 1600 C. Hereby the combinationv is produced containing about 5.9% C. the rest being Mos.

Titanium-carbide can be formed in arr equal way for metallic titanium and carbon. An advantage consists however, therein to use titaniumoxide (T102) powdering and then mixing it with carbon, heating the mixture till the carbon is combined with the titanium while the oxygen of the titanium-oxide is expelled in the form of gaseous carbon-monoxide. The product is again mixed with additional carbon and heated up. The treatment is finished if no further carbonmonoxide or titanium-oxide evaporates. Accordingly e. g. about parts titanium-oxide and 33 electrical induction (high frequency-treatment).

The titanium-carbide obtained in such a way is free of oxygen and contains up to about20% carbon.

In similar ways zirconium-carbide, silicon-carbide, boron-carbide, a. s. 0. could be produced.

Whatever be the procedure in the formation of the mixed crystals in any case a body is obtained which is superior in hardness-to the elements or carbides alone.

An electric furnace can be employed for effecting the heating and sintering; the sintering may also be carried out by means of high frequency currents. In some cases particularly good results are obtained by carrying out the heating or sintering in a vacuum. i

The carbides prepared according to the invention areextremely hard but require additions, as mentioned before, to increase the toughness of the alloy. As such addition use may be made of one or more of the auxiliary metals such as nickel, cobalt, chromium, either separately or in suitable admixture, and containing sometimes a few per cent (1 to 10%) of carbide as forming one or more (or all) constituents of the mixed crystals.

As I stated already in my copending application Serial Number 452,132, also ferrovanadium may be used as auxiliary metal. Ferrovanadium contains about 20% iron and melts like iron or cobalt between about 1450 to 1500 C. I suggested in the above mentioned application to add such an auxiliary metal, like ferrovanadium, in amounts up to about 10%. Consequently such a hard metal according to my copending application comprises up to about 10% auxiliary metal melting between about 1450 and 1500 C., and about 90% carbide. If choosing the range of hardest mixed crystals formed e. v g. by WC and M020, as mentioned in my application referred .to hereinbefore, then immediately according to the general science existing prior to my invention as reproduced hereinbefore, the proportion of the carbide contained can be calculated, namely WC about 60% and MOaC about 30%, and the range of such carbide satisfying the science to form hardest mixedcrystals lies between about 10% over and below these figures, 1. e. between about'54% and 66% WC, 27% and 33% MOaC, balance auxiliary metal like ferrovanadium (on an average 10%).

The mixed crystals of carbides produced are,

V if needed, powdered again and intimately mixed with the chosen auxiliary metal or metals. Suitable proportions are already mentioned before. The mixtures are then preformed by pressingin suitable moulds to a shape similar to the desired shape. There is to be taken into calculation the shrinking which takes place during the following treatment.

The preforming in the moulds may be done also under elevated pressure, up to several atmospheres per square centimeter, say up to 50 and '75 atmospheres and higher.

The body so preformed and advantageously still under pressure is now to be sintered. It is done by electrical current led through the body itself or around the body through the mould. Any other kind of heating is applicable.

The temperature of the body is to be elevated to about 1400 to 1600 C. and this heat-treatment to be continued about one or more hours, or parts of them, till the wanted structure of the body is obtained.

In case, however, difficult forms of the body are to be produced not obtainable by usual moulds, or in case sharp edges are desired, or angles difficult to manufacture in such a way, so that the mechanical working or finishing of the hard metal body is needed after sintering, then the following ways are preferable.

The pressed and preformed body is to be sub- I mitted to sintering temperatures as mentioned before, but such sintering has-to be done only in a short period of time, say 1 to 5 to minutes so that the particles are sufficiently fritted together to withstand mechanical treatment with-- this body of sufficient cohesion whereupon the sintering is possible without any further interruption.

Surprising results have been further achievedby adding oxide of metals or metalloids not being reducible by hydrogen and not, or only at high temperatures, forming carbides. Such oxides are presented by alumina, silicon, the earth alkalis,

v the group comprising zirconium and the group comprising the rare earth metals. Especially the addition of alumina in the finest divided form in relatively small amounts, say up to about 0.5% has caused the formation of most suitable alloys of the herein mentioned various compositions.

Generally, the body according to my invention is consolidated by using auxiliary metals of the kind and in the amount as mentioned before and treating it at elevated temperature, say in the range up to about 1400 to 1600 C.

When I refer in the appended claims to car-- bide of elements selected from the third, fourth, fifth and sixth group of the periodical system, I mean. carbides adapted for'use in hard tool elements, having a suitable hardness and not being dissolved by water or other liquid employed for cooling or similar purposes at operation temperatures. Such carbides are boron-carbide (belonging to the third group) titanium-carbide, siliconcarbide, zirconium-carbide, thorium-carbide (belonging to the fourth group), vanadium-carbide, niobium-carbide, tantalum-carbide (belonging to the fifth group), and tungsten-carbide, molybdenum-carbide and chromium-carbide (belonging to the sixth group).

When I refer in the appended claims to formation of mixed crystals in a substantial amount by heat treatment, I mean thereby a minimum amount of about 10% as disclosed in my co-pending application No. 743,717, filed September 12, 1934, andissued into Patent 2,122,157.

It is quite difficult to mention any minimum amounts of carbide to be present. Nevertheless, the minimum amount of carbide to be present and forming part of a mixed crystal according to the invention, has to be substantial, and as a minimum about 1% by weight of the alloy.

Tool alloys prepared according to theinvention are, as a rule, not used for the production of the entire tool, but merely for the part of the tool which in practice is used directly for cutting,

drilling, etc. and which is subject to wear.

From the above description it appears that the carbides to be cemented by auxiliary metal may either be transformed into mixed crystals entirely or in substantial amount before a substantial amount of auxiliary metal is added, or.

substantial amount. In the first case, mixed crystals are formed by heat treatment and thereupon powdered before the auxiliary metal is admixed. In the latter case, the carbides are to be powdered to as finely divided a form as possible,

then mixed with auxiliary metal and shaped and,

sintered. In view of this extremely fine powdered form mixed crystal formation occurs in the presence of auxiliary metal during normal or extended sintering. Growth of crystals (recrystallization) is either prevented by the presence of auxiliary metal or can be prevented through addition of traces of alumina, silica, etc.,

.as explained hereinabove. It has also been found that mixed crystals resist recrystallization to a large extent. Thereby finest grain of carbides present in the alloy including mixed crystals is retained, and a tough and very eflicient, clean cutting material is obtained.

If carbides highly resistant to oxidation are combined with mixed crystals and other carbides less resistant to oxidation, the resistivity of those mixed crystals against oxidation surpasses that of the carbides of originally lower resistivity. However, it has been found that the mere presence of carbide of higher resistance to oxidation in finely divided form close to carbides of lower resistivity sufflces to increase that resistance against oxidation for the entire alloy beyond the more than 2.6% carbon and being present in finely divided form and proportions suitable to yield mixed crystals of approximately greatest hardness, such mixed crystals formed in a substantial amount by heat treatment.

2. A cemented hardmetal composition sintered by heat treatment, for tool elements and other working appliances, consisting substantially of auxiliary metal essentially of the iron group in amounts from about 3% to 22% and two hard carbides of elements selected from the third, fourth, fifth, and sixth group of the periodical system, said carbides as finely divided as possible and present in substantial amount approximately in integer number ratio of their molecular weights so as to produceapproximately hardest mixed crystals, said ratio consistingv of 1:1 to 1:3, the equal ratio being applied if the two hard carbides-are of substantially equal hardness, the higher ratio being applied if the carbides considerably differ as to hardness so that the amount of the substantially harder carbide in the mixed crystal exceeds that of the less hard carbide, such mixed crystals formed in substantial amount by heat treatment.

3. A cemented hard metal composition sintered by heat treatment consisting substantially of two hard carbides of elements of the fifth group ofthe periodical system, these carbides being present in proportions adapted to yield approximately hardest mixed crystals in substantial amounts, and auxiliary metal taken essentially from. the iron group in amounts from about 3% to 22%, such mixed crystals formed by heat treatment in substantial amount, including a minimum of about 10%.

4. A cemented hard metal composition sintered by heat treatment consisting substantially of a hard carbide of an element of the third group and of a hard carbide of an element of the sixth group .of the periodical system, these carbides being present in substantial amounts in proportions adapted to form approximately hardest mixed crystals, and auxiliary metal essentially of the iron group in amounts from about 3% to 22%, said mixed crystals formed by heat treatment in substantial amount, including a minimum of about 10%.

5. A cemented hard metal composition sintered by heat treatment, for tool elements and other working appliances, consisting substantially of two hard carbides of different elements selected from the third, fourth, fifth, and sixth group of the periodical system, and auxiliary metal essentially of the iron group in amounts of about 3% to 2. the minimum amount of a selected carbide to be 1%, said carbides being present in finely divided state and forming mixed crystals by heat treatment in substantial amount, including a minimum of about 10%.

6. A cemented hard metal composition sinteredby heat treatment, for tool elements and other working appliances, consisting substantially of auxiliary metal essentially of the iron group .in amounts from about 3% to about 22%, and

two hard carbides of elements selected from the group consisting of titanium, tantalum, columbium, and tungsten, the mlnimumamount of a selected carbide to be 1%, said carbides present in finely divided state and forming mixed crystals by heat treatment in substantial amount, including a minimum of 10%, the hardness'of said-mixed crystals exceeding that of either carbide contained therein.

7. A cemented hard metal composition sintered by heat treatment, for tool elements and other working appliances, consisting substantially of two hard carbides of difi'erent elements selected from the third, fourth, fifth and sixth group of the periodical system, and auxiliary metal essentially of the iron group in amounts of about 3% to 22%, the minimum amount of a selected carbide to be 1%, said carbides being present in finely divided state and forming mixed crystals by heat treatment in substantial amount, including a minimum of about 10, the hardness of said mixed crystals exceeding that of either carbide contained therein.

8. A cemented hard I metal composition sintered by heat treatment, for tool elements and other working appliances, consisting substantially of two hard carbides of different elements selected from the third, fourth, fifth and sixth group of the periodical system, and auxiliary metal essentially of the iron group in amounts of about 3% to 22%, the minimum amount of a selected carbide to be 1%, said carbides being present in as finely divided a state as possible and forming mixed crystals by heat treatment in substantial amount, includiing a minimum of about 10%, the hardness of said mixed crystals exceeding that of either carbide contained therem