US1698936A - Alloy - Google Patents

Description

Patented Jan. 15, 1929.

UNITED STATES PATENT OFFICE.

PM O. CHESTERFIELD, OI DETROIT, MICHIGAN, ASSIGNOR T CHESTERFIELD METAL COMPANY, OF DETROIT, MICHIGAN, A CORPORATION 01" MICHIGAN.

ALLOY.

Il'o Drawing.

This invention relates to alloys, more particularly those designed for use in the production of high speed cutting tools.

This application is a continuation in part 5 of. my ap lications Serial No. 493,108, filed August 1 1921, and'Serial No. 628,801, filed March 22, 1923. 1

It is necessary that alloys for such purposes have the property of red-hardness so that a tool made therefrom may maintain its cutting edge after the same has become red hot.

In addition to heat resistance, the alloy must also possess abrasive hardness and for 16 this purpose should contain embedded 1n the metallic matrix hard crystals, usually metallic carbides.

Alloys of this general character are known comprising cobalt, chromium and k 20 tungsten. Both chromium and tungsten form carbides and of these the harder is tungsten carbide, so that the chef funct on of the tungsten is to give the alloy abrasive hardness.

While tungsten will give alloys abrasive hardness, the use of tungsten is attended with certain disadvantages not possessed by other metals.

Thus the melting point of tungsten is excessivel high being over 3000 C, so that alloys t ereof have to be made by dissolv ng the tungsten in the other molten constituents, like sugar dissolves in water, instead of by the admixture and mingling of molten tungsten with the other molten metals.

This renders the roduction of a homogeneous alloy more ifiicult. The temperature of formation of an alloy havlng large roportions of tungsten is also higher than 1s required to produce alloys of more easily fusible metals.

Further, the very high specific, gravity of tungsten (18.7) as'compared with that of nickel or cobalt (8.7) or chromium (6.0)

tends to produce segregation of the constituents of the alloy and hinders the production of a homogeneous alloy.

Moreover, the amount of tun sten re quired to give the desired degree oi abrasive hardness is higher than those of certam other metals.

The object of the present invention, therefore, is to provide an alloy containing a metal having the properties of nickel and I cobalt, and a metal capable'of forming a Application med Deoemcer 1, 1924. Serial No. 753,354.

hard carbide and having a iower melting point than tungsten.

Another object of the invention is to provide an alloy in which the desired abrasive hardness is produced by a smaller propor- 00 tlon of the hardening metal than is possible w1th tungsten.

Other and further important objects of the invention will hereinafter appear.

All of these three metals form hard carbides, thus titanium carbide is'harder than carborundum and will even scratch or score diamond.

These metals may be alloyed with cobalt and a small amount of carbon without substantial amounts of other metals. It is preferred, however, to employ either or both nickel and chromium in addition thereto.

While vanadium and chromium, for example, are similar in properties in so far as 7 they both form hard carbides, the hardening efi'ect of vanadium is much greater than that of chromium. The latter metal has a valu able toughening effect so that to obtain the best results the individual characteristics of these metals should be blended.

The same is true of nickel and cobalt. Alloys with nickel alone have a tendency to be hot-short while the cobalt alloys tend to be cold-short. A combination of the two metals gives an alloy having the desired toughness and strength under all conditions.

The chief function of the cobalt and nickel appears to be that of producing a strong, tough, heat resisting matrix for the carbides of the chromium group or other group of metals. Neither cobalt or nickel possess the affinity for carbon, that is possessed by chromium or vanadium for example, so that it is probable that there is little or no carbide of either cobalt or nickel in my alloys.

The amount of carbon b weight in my alloys is comparatively slig t, say 1.50%, but the proportion of carbide by volume may be over 10% of theentire alloy. This follows from the great differences in specific gravity of carbon and the metals with which it combines to form carbide. In view of this large .content of non-metallic compounds, the IN composition of the matrix is of great importance.

Ordinarily alloys made in accordance with this invention will consist of cobalt, nickel, chromium and either. titanium, vana- 11o dium or niobium with a small amount of carbon.

The percentage of these metals will usually be within the following limits:

Percent. Cobalt 25 to Nickel 10 to 20 Chromium 25 to 40 Vanadium, etc 10 to 25 The total amount of cobalt and nickel should be between 35 and In certain cases a wider range of propors tions may be employed such as those lying within the following percentages:

Per cent. Cobalt 15 to 55 Nickel 7 to' 30 Chromium 20 to 45 Vanadium, etc 4 to 30 The total amount of cobalt and nickel should be between 30 and As an example of a suitable alloy falling within the above limits the following may be given:

' Percent. Cobalt 37 Nickel 15 Chromium 36 Vanadium, etc 12 If the content of nickel is increased there should be a corresponding increase in the vanadium to maintain the desired hardness. This is exemplified by the following:

Percent. Cobalt 21 Nickel 28 Chromium 25 Vanadium 26 In some alloys the chromium may be omitted-thus Per cent.

Cobalt 40 Nickel 30 Vanadium 30 Further it may be found desirable to use onlyl'l cobalt and vanadium as in the following a oy:

Cobalt if??? Vanadium 25 p the metals forming the alloy, the latter on cooling will not contain free carbide crystals but only carbide in solid solution.

While carbide in solid solution has a hardening effect it is not the desired abrasive hardness which results from the presence of free carbide crystals. The carbon content of the alloy should, therefore, be high enough to provide a substantial proportion of free carbide crystals in'the alloy.

If the carbon is too hi h the alloy will contain in addition to carbide frce uncombined carbon in graphitic form. As a given amount of carbon will combine with different weights of different metals to form ourhides the amount of carbon which may be added before free graphitic carbon is formed in the alloy will depend upon the nature and proportions of the metals composing the al- 10 llsually the amount of carbon in the alloy will be between 1 and 2.5%, for example around 1.5%, although in some cases it may be as low as 0.5 or as high as 3.5%. It ,is desirable on the one hand to have enough carbon to produce free carbide crystals and on the other hand not enough to cause the formation of particles of graphitic carbon throughout the alloy, as the presence of graphltic carbon greatly reduces the strength of the alloy.

The carbon is most readily and accurately added as a carbide, such as the carbide of one of the metals forming the alloy as chromium.

In addition to a hardening element it is frequently advisable to use a de-oxidizer such as aluminum or boron. Further, the

hardening element and de-oxidizer may to advanta e be added simultaneously in the form ofioron carbide.

While my alloys consist essentially of the above metallic and non-metallic .in edients it will be understood that the ad ition or presence as impurities of small quantities of other metals, etc., such as iron, manganese or the like, will not change the general characteristics of m alloys.

In the process 0 forming the alloy the several ingredients in proper proportion are placed in a crucible preferabl together with some readily fusible materia such as glass, which will form a protecting layer over the alloy and so prevent oxidation.

The temperature employed for fusing the constituents may be from 1750 to 1950 C., according to conditions. As these alloys do not respond to heat treatment, as does steel, at least at a temperature below 1100 C., the alloy must be formed into the desired sha e by casting and then grinding instead of by forging;

To 0 tain the best results molds made of sand should not be employed since, such molds, even if brushed over with graphite owder, the bars are apt to be full of blow oles and too soft to make good lathe tools. Preferably the molds are conusing structed of graphite although cast iron may be used for th1s purpose 1f the surface is treated before use to prevent the hot metal adhering thereto. Such treatment may consist either in treatment with sulphuric acid or coating with carbon by the application of a smok flame thereto.

Grap ite is, however, much superior to cast iron as a material for molds. In the first place it is much easier to machine graphite than cast iron so that molds for casting special sizes and shapes can be more readily made. Then again, cast iron molds have to be repeatedly treated with sulphuric acid solution since the effect of the treatment soon wears off.

Further, cast iron molds, especially for small sizes of bars, chill the metal too rapidly. This chilling makesthe bars hard,

and, while hardness is a desideratum, it should be uniform throu hout the bar and chilling makes the outer layers harder than the center.

Now graphite has a lower specific heat per unit volume and also a much lower heat conductivity than cast iron. Consequently the rate of abstraction of heat from the cooling metal is far less in the case of graphite than in the case of iron molds.

I have also found that the hardness of bars cast with the above alloys vary according to the rate at which they cool so that a small bar, which necessarily cools more rapidly than a large one, is, other conditionsvbeing the same, harder. On the other hand, increasing the carbon content of the alloy increases its hardness. It has further been found that heat treatment of the alloy after casting does not appreciably change its hardness so that the alloy may be termed self-hardening.

To secure the best results it is necessary to hit the happy mean between too eat hardness, which means brittleness, an liability to flake or chip, and too little hardness, which means that a tool made therefrom will be too soft to cut for the desired length of-time or to cut hard metals.

This I accomplish by the present invention by var ing the amount of hardenin element, suc as boron carbide, added wit var ing dimensions of the bar to be cast.

or exam 1e, for a inch bar 0.56% boron carbi 6 may be used to advantage;

. for a inch bar 0.85% and for a inch bar 0.97%.

By so varying the content of boron oarbide the sum of the hardness due to chilling and the hardness due to the hardening element is maintained substantially uniform irrespective of the size of the bar cast.

If on casting a trial bar from any given melt the alloy appears to be too soft, small additions of tungsten may be added to the crucible to give the requisite hardness.

The above mentioned quantities of carbon, added as boron carbide, are considerably lower than the desired carbon contents of the bars for the reason that not only do the constituent commercial metals contain small amounts of carbon but also larger amounts of carbon are icked up from the crucible in which the 1510 is made, if an unlined graphide crucible e employed. i

As a result of the picklng u of carbon from the crucible it is desirab e to avoid heating the metal to too high a temperature or for too long a time 1n the crucible. Further, when remelting scrap along with a proportion of new metal the quantity of boron carbide added should be decreased to allow for the carbon already in the scrap.

group capable of forming a hard carbide and havlng a melting point between 1000 and 2100 C. with a small amount of carbon.

2. A high speed tool formed of a substantially non-ferrous alloy compring 15 to 55% cobalt, 7 to 30% nickel, 20 to 45% chromium and 4 to 30% of a metal not in the chromium group capable of forming a hard carbide and having a melting point between 1600 and 2100 C. with a small amount ofcarbon.

3. An alloy for high speed tools com rising 25 to 50% cobalt, 10 to 20% nicke 25 to 40% chromium, 10 to 25% vanadium with a small amount of carbon.

4. An alloy for hi h ing approximately 3 cobalt, 15% nickel, 36% chromium, 12% vanadium with a small amount of carbon.

In testimony whereof I have hereunto subscribed my name.

PERCY c. CHESTERFIELD.