US2048167A

US2048167A - Nickel-chromium-iron-titanium alloys

Info

Publication number: US2048167A
Application number: US73930A
Authority: US
Inventors: Norman B Pilling; Paul D Merica
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1936-04-11
Filing date: 1936-04-11
Publication date: 1936-07-21
Anticipated expiration: 1953-07-21

Description

Patented July 21, 1936 UNITED STATES PATENT OFFICE NICKEL-CHROMIUM-IRON-TITANIUM ALLOYS Norman B. Pilling, Westfield, N. J., and Paul D.

Merica, New York, N. Y., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application April 11, 1938, Serial No. 73,930

27 Claims. (Cl. 14831) This invention relates to improved nickel-chrotion to the metal nickel, all of which behave submium-iron-titanium alloys. stantially similarly, and which behavior will be Hitherto it has been proposed to utilize the described more in detail below. No exceptions to metal titanium as a deoxidizing agent for alloy this definition have as yet beenencountered, al-

steels and the like in which the residual content though the degree of hardening displayed by dif- 5 of titanium contemplated was very small, usually ferent combinations of base alloy and hardening less than .1 percent. It has been further proposed agent, of course, vary somewhat in degree. In to use titanium as a toughening agent or grain re one such series, viz., iron-nickel-chromium-titafiner in which cases the alloy may have some 1 nium, the hardening characteristics were dispercent of titanium retained, although several displayed in alloys having ranges of nickel content 10 closures specify ranges of titanium for such purvarying from substantially 6 to 98 percent. poses up to 10 percent. It is an object of the The preferred hardening agents comprehended present invention to provide improved hardenable within the spirit and scope of this invention are nickel alloys by combining with a suitable alloy, titanium, aluminum, and zirconium, and it is apreferred to as the base alloy, quantities of titaniparent that the hardening characteristics herein um and titanium-like elements. disclosed may be properties or functions of the ho- It is a further object of this invention to conrun and the titanium groups of the periodic classiier hardening properties upon particular base flcation of the elements according to Mendeleefl. alloy compositions chosen to provide other de- Of these hardening agents titanium has been sirable properties, whereby not only the hardness found to be the more useful from the standpoint 20 but the elastic strength and breaking strength of of developing physical properties of engineering the base alloy is increased without materially value combined with practical working qualities. changing its other characteristic properties. For the purpose of illustration, in order to It is a still further object of this invention to moreclearly set forth the novel features of the alloy a suitable hardening agent with a nickelpresent invention, the characteristics of iron- 25 bearing base material and subject the resulting nickel base alloys alloyed with titanium as a alloy to a particular heat treatment to develop hardening agent will be discussed. Nickel-iron and control increased strength properties. These alloys which include from about 25 percent to and other desirable advantages of the present insubstantially 100 percent nickel in their compovention will be set forth and described in the sition are soft and relatively unaffected in hard- 30 accompanying specification, certain preferred ness by heat treatment. Titanium is soluble in compositions being given by way of example only, these alloys and, if completely dissolved therein, for, since the underlying principles may be applied the resulting ternary alloys retain substantially to other specific compositions, it is not intended the original soft character. Ifasuflicient amount 36 to be limited to those herein shown except as such of titanium be added, however, the resulting alloys limitations are clearly imposed by the appended are soft only when cooled rather rapidly from a claims. high temperature; if reheated to some lower tem- The present invention comprehendsawide variperature range, or allowed to cool rather slowly ety of base alloy compositions and three preferred through this range, a substantial rise in hardness 40 hardening agents, as will be described more in occurs. A still further increase in titanium con- 0 detail hereinafter. The preferred base alloy tent causes the alloys to become increasingly hard, which is particularly amenable to the proposed even when subjected to rapid cooling from high treatment may be defined as nickel-bearing solid temperatures, yet these alloys change somewhat solutions having the face-centered cubic lattice in hardness with heat treatment. These charactype of crystalline structure. The claim for this teristics in a series of iron-nickel alloys contain- 4 broad definition is predicted on experimental work ing 35 percent nickel and varying amounts of tiwith six distinct alloy series of this type in additanium are shown in the following table:

Number 1 2 a 4 5 a 1 Perwnt titanium z o .49 1. a1 2. 20 a. is 4. oo o. 71 Brine 1oo0 C-mr cool 132 131 131 151 118 268 393 700 C 3 hrs. water quenched 132 138 107 307 327 371 380 Tha desirable range of titanium to be added to this particular base is from substantially l percent, at which point hardening begins, to about 4 percent, at which point the malleability of the alloys becomes impaired. The hardened alloys in common with iron-nickel alloys generally are characterized by their toughness, resistance to attack by non-oxidizing acids, ferro-magnetism and high electrical resistivity. With an increase in the nickel content of the base alloy, the desirable range of titanium, as just defined, remains substantially the same up to '75 percent nickel content, but the capacity for hardening displayed by the alloys under consideration, steadily diminishes with increase innickel content up to 99% with a range of about 150 to 225 Brinell hardness units. Within the range of '15 to 96 percent nickel content, the minimum titanium content necessary to develop hardening, increases from about 1 percent to somewhat more than 4 percent, the amount being roughly proportional to the excess of nickel over '75 percent. Within this range the hardness difierential developed by heat treatment is from about 75 to substantially Brinell units.

Titanium when added to many other nickel alloys of the face centered cubic lattice type previously noted, permits the formation of alloys having hardening characteristics similar to the iron-nickel-titanium alloys described. Among these other base alloys may be mentioned: Ironnickel-copper; iron-nickel-chromium; iron-nickel-manganese; nickel-copper; nickel-chromium, and nickel metal. The following table shows several malleable alloys exemplifying this fact, the hardness numbers being expressed in Brlnell sea Bggglnlllfilrg-{g goc am quanch)-- 154 155 112 151 at a (600 Q,t mp 218 256 3 183 In the case of aluminum, the content of this element necessary to develop suitable hardening response varies from about 2.5 to substantially 6 percent, the latter percentage marking the I approximate upper limit of forgeability. A preferred range is from 5.0 to 5.5 percent.

When titanium is used as an alloying element, the use of commercial ferro-titanium may introduce appreciable quantities of aluminum and silicon into the metal, both of which elements will appear in the resulting alloy. This content of aluminum is not harmful and it has now been found in fact that the useof even higher contents of aluminum in combination with titanium as hardening agents offers certain advantages, notably in accelerating the rate at which the 40 43 30 35 23.3 18.4 15.3 35.5 93 so 20 ,20 14 35 5s 31 05 00 c0 51 1.2 9 12 3 12 19 3.0 1.1 64 10 10 7.9 11.8 14.5 8.0 3.0 2.3 2.3 2.5 2.3 "2.5 "3.0 "3.13- ""Z "i Bolt (1000 50. waterquench)---- 121 151 159 154 153 152 120 194 300 164 17s 45 Hard (temperad600-700 c. 231 211 302 315 315 304 234 250 234 317 321 200 215 The ranges of the several elements in addition to titanium, may be extended as follows: copper .5-90%, chromium 13-30%, nickel 2-99%, and iron 2-90%, the titanium being replaceable, under the conditions discussed more in detail hereinafter, by from .5-10% of titanium-like metals such as aluminum and/or zirconium. These elements may be associated with each other in any desired amounts to give compositions having certain specified characteristics.

The preferred range of titanium is substantially from 1 to 4 percent. This range is determined approximately by the first appearance of hardening and the substantial disappearance of hot malleability. When it is desired to retain good hot and cold working properties in order to permit shaping by forging, hot rolling, cold rolling, drawing, or plastic deformation generally, full advantage cannot be taken of the maximum titanium content. In such cases it is preferable to employ titanium contents ranging from 2.2 to 3.2 percent for alloys having a low carbon content and in which the base is nickel-iron, nickelcopper-iron, and nickel-chromium-iron. It will, of course, be understood that in case of castings where workability is not a factor to be considered, a much greater range of titanium is hardening reaction occurs. As an example of this discovery, the nickel-iron-titanium alloy including 34.8 percent nickel, 2.2 percent titanium, and 0.3 percent aluminum, showed no appreciable hardening when air-cooled from 1000 degrees centigrade. A similar alloy including 34 percent nickel, 2.5 percent titanium, and 1.9 percent aluminum increased in hardness about 110 Brinell units on air-cooling. Both alloys hardened to about 320 Brinell units when furnace cooled. It will also be appreciated that by the use of hardening agents in multiple as herein described, it is possible to secure marked economies in manufacture due to the ability to use cheaper addition materials without in any way sacrificing the good results desired in the finished product.

The diversity of base compositions amenable to hardening by titanium and aluminum has been described. No common alloying elements in amounts less than 2 percent have been found to interfere with this hardening characteristic with the exception of aluminum and carbon. The effect of aluminum when combined with titanium has just been described. Since carbon forms an inert titanium carbide, its presence with titanium is highly detrimental. This is-due 75'.

to the fact that although thetotal titanium content may be great enough to indicate vigorous hardening, the alloy is, in fact, devoid of hardening response. Itis' highly. desirable, therefore, to keep the carbon content as low as is metallurgically feasible. Alloys of this type have been produced with as little asv .01 percent carbon, yet melts containing as much as 0.40 percent carbon have been produced which dis-' played good hardening properties, although an inefliciently high titanium. content in the alloy was necessary. a

It is considered to be within the scope of this invention to provide, in addition to the major elements of composition, such other elements as are commonly used, in metallurgy to aid in refining, purifying, degas'ifying, and otherwise treating the alloy to insure its production in sound. tough, malleable form. These auxiliary elements are:

The nature and quantity of these accessory elements is determined by the nature of the base alloy in question.

Many characteristics of the hardening action. developed by titanium and its equivalents, as described hereinbefore suggest that it is of the socalled "precipitation" 'type, and that nickel, in association with titanium and/or aluminum, is withdrawn from solid solution concurrently with the rise in hardness on heat treatment. 01 course, this is only a possible theory and it is to be understood that we are not bound to this theory.

To bring the alloys under consideration into the softest working condition, the heat treatment required in all cases is a not too slow cooling from above a minimum temperature. Most efllcient results are obtained when this minimum temperature is exceeded, but the temperature margin by which it is exceeded is not of very great importance, the upper limit usually being that atwhich an undesirable coarsening in grain size occurs. The minimum softening temperature varies directly with increase in content of the hardening element or elements, and also varies to some exentire group of alloys herein described respond;

well to a range of softening temperatures varying from 900 deg. C. to 1050 degaC. The rate of cooling required to avoid hardening is not,

great, and air cooling will usually prove fast enough, although cooling in water or in oil is permissible.

Where it is desired to heat treat the alloys in order to harden them, the treatment is much more variable. Variations in composition of the base metal, and of the hardening elements effect both the temperature at which the desired hardeningis most efiectively produced, and also the rate at which it occurs. In all cases hardening occurs overa: considerable range of temperatures, and the lower the temperatureat which thiscan be carried out, the greater will be the hardness ultimately developed. Since the rate of hardening diminishes as the temperature is decreased, an 5 optimum hardening temperature may be appropriately designated.

With a hardening treatment which includes holding the alloy at a fixed temperature for several hours, the preferred hardening temperature is substantially ,700 deg. C. for alloys in which titanium is the hardening element, and about 600 deg. C. when aluminum or zirconium is the hardening element. It is to be noted that when chromium does not exceed about 5 percent, good hardening may be produced by furnace cooling from the softening range. When the chromium content exceeds this value, the hardening reaction proceeds slugglshly, and considerably more time is required in order to develop full hardness. High chromium alloys containing up to chromium may show very little hardening on furnace cooling.

When it is desired to develop the maximum hardness of a given alloy, it has been found ad- 25 vantageous to carry out the hardening operations in several steps at progressively lower temperatures and preferably with the duration of heating increasing at the lower temperatures. The temperature range in which this incremental hardening may be carried out is from the minimum softening temperature above described, down to about 500 0. As a particular example, an alloy of a composition including Percent N15! Cr 6.7 Ti 2.6 Fe s Balance having an, initial Brinell hardness of 148 hardened to 290 Brinell after twenty-four hours of treatment at 700 deg. C. When an incremental hardening heat treatment was given to this alloy, a hardness of 340 Brinell units was secured, the particular treatment included heating at 750 C. for two hours, followed by heat treatment at about 600 C. for five hours, and at about 600 C. for twenty-three hours.

On the other hand. for the purpose of improv- 5 ing toughness and ductility of the hardened alloy, the termination of the hardening operation may include the step of reheating to a temperature higher than the last preceding step, but still within the range of temperature in which the particular alloy is hardenable.

A further example may be given in which the hardening characteristics as described hereinabove are combined with martensitic hardening of the type commonly observed in air-hardening steels. This combination occurs in marginal austenitic nickel-content ferrous alloys of the nickel, nickel-chromium, nickel-copper, nickelmanganese and related series in which the iron content is up to about 10 percent lower than that 65 at which martensite ceases to be a constituent, under ordinary conditions of cooling.

A loys of the aforesaid type when heat treated develop a strengthening precipitate, accompanied'by a change in composition of the residual I are two examples of alloys in which the eifect is characterized by intense hardening. I

Brinell hardness number 0 Al m or In 1000 C. I

' water Tempered quenched 15.7 10.3 2.7 .iB 143 420 In 8.2 2.7 .03 1.8 150 v 498' expansivity in nickel-iron alloys, a slight adjustment of composition may be necessary in the hardened alloy. This adjustment generally involves a small increase in nickel content.

It will now be appreciated that there has been provided an improved process for producing high strength alloys of the solid solution type containing nickel, which'are initially soft and workable, which process comprehends the use otsuitable amounts of hardening agents such-as titanium, aluminum and/or zirconium. It is to be noted further that the hardenable alloys comprehended within the spirit and scope of the present invention are adapted for a wide variety of uses, and more particularly for use in structures which can economically be made by plastic deformation such-as drawing, pressing, etc., such formed articles being adapted to being suitably hardened by a heat treatment as set forth. Furthermore. the present invention has been described in con- Pro Ult. Elong. Red. Izod No. Ni Cu Cr Tl Fe Temper lim t strength percent area ft lbs psi psi 2 percent 3L1 8.0 2.5 1381... Scit 24,800 87,600 37.5 65.1 Hard 110, 000 192, 000 16. 0 33. 0

21.7 0.3 2.4 Bal Soft-.-" 34,600 87,800 35.0 59.8 v I Hard. 71, 400 158,000 22.0 47. s

16.5 12.4 2.7 B3]... Soft--- 24.000 88.000 48 68 102 Hard (0) '66, 000 130, 000 36 62 74 Hardfli)- 80, 000 M50, 000 22 18 50 in) 700 0. Temp.

0) Incremental Temp.

In addition to exhibiting these high physical properties at room temperatures, the high strength and elastic properties shown may be retained at high temperatures, provided that the base alloy is of a suitable type; iron-nickelchromium is appropriate, and the titanium alloy I with this base shows excellent strength proper- 90,000 psi FL. 125,000 psi ULT. 25% Elong. in 2" 12% Red. area Such alloys are particularly suited for purposes involving considerable heat and load such as obtalned in steam and internal combustion tur-' bines, as well as in many chemical processes, a particular example being that of tube stills and like apparatus which may be used in oil-cracking and oil refining.

Many alloys, in particular steels, exist which have hardness and tensile properties equal to or even excelling the alloys of the present type. The advantage of the latter lies in the unique fact that the present hardening elements may add hardening properties to particular base alloys without detriment to their other distinctive properties, thus affording a combination of strength with other special qualities not previously possible. For example, the addition of titanium to austenitic nickel-chromium steels imparts hardness and high elastic properties without interfering with the valuable corrosion and heat resisting qualities of the latter. In particular'cases in which a property is closely aslociatedwith a specific nickel content, e. g. low

junction with various compositions the nickel content of which may be applied to any of the alloys disclosed herein. Thus, specific nickel alloys containing about6% and about 15% are referred to on pages 2 and 12, respectively, butthese nickel contents or variations thereof within the scope of the present invention-may be used in any of the present alloys. For example, a nickel alloy containing about 10% nickel, about 87% copper and about 3% titanium when in a soft condition resulting from quenching in water from 900 C. had a Brinell hardness number of and when in a hard condition resulting from reheating to a temperature of about 600 C. to about 700 C. had a Brinell hardness number of l83.

This is a continuation in part application of our application, Serial No. 356,870, filed April 15, 1929, for Titanium alloys.

What is claimed is:

l. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufficiently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufiiciently high and for a period of time suflicient to obtain a substantial increase in the hardness of the alloy.

2. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufiiciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufllciently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

3. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufllciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a period of time sufficient to'obtain a substantial increase in the hardness of the alloy.

4. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time and 'at a sufllciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufficient period of time and at a sufilciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

5. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufficient period of time and at a sufiiciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufiicient period of time and at a sufficiently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

6. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suificient period of time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

7. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufficient period of time at a sufilciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial increase in the hardness of the alloy.

- 8. A hard nickel-chromium-ironalloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4%. titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sumcient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy. and cooling the alloy from the aforesaid tempera- 5 ture to about 500 C. at a rate sufilciently slow to cause a substantial increase in the hardness of the alloy.

9. A hard nickel-chromium-iron alloy containing about 2% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial increase in the hardness of the alloy.

10. A hard nickel-chromi'Im-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sufilcient to obtain a substantial increase in the hardness of the alloy.

11. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% titanium, .and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

12. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufiiciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time suflicient to obtain a substantial increase in the hardness of the alloy.

13. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufficient period of time and at a sufilciently high temperature 65 between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suflicient period of time and at a sufliciently high tem- 70 perature below 750 C. to obtain a substantial increase in the hardness of the alloy.

14. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 75 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sumcient period of time and at a sumciently hightemperature between 750 C. and the melting point to dissolve at least a portion or the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy tor a sumcient period of time and at a suilicien'tly high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

15. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% of titanium, and iron constituting substantially the balance of the alloy. said alloy being age hardened by heating for a suilicient period 0! time and at a-sufliciently high temperature between 750 C. and the. melting point to dissolve at least a portion of titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy (or a sumcient period of time and at a suiiiciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

16. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for asuihcient period of time at a suiliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial increase in the hardness of the alloy. 7 17. A hard nickel-chromium-iron alloy containing about 20 to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufflcient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial increase in the hardness of the alloy.

'18. A hard nickel-chromium-iron alloy containing about 20% to about 50% nickel, about 3% to about 30% chromium, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sumcient period of time at a suiiiciently high temperature between 750 C. and the melting point 01 the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate suiliciently slow to cause a substantial increase in the hardness of the alloy.

19. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substantially the balance oi the alloy. said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufllciently high to cause titanium togo into solution, quenching the alloy and reheating to a temperature below that of the initial heatingbut suniciently high and for a period or time sutiicient to obtain a substantial increase in the hardness of the alloy.

20. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% of titanium, and iron constituting substantially the balance of the alloy,'said alloy being age hardened by heating for a sumcient period of time and at a sufliciently high temperature between 750 C. and the melting point of the 10 alloy to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suiiicient period of time and at a sunlciently high temperature below 750 C. to obtain a substantial 15 increase in the hardness of the alloy.

21. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 10% titanium, and iron constituting substango cause at least a portion or the titanium to disg solve in the alloy, and cooling the alloy from the aforesaid temperature to about500 C. at a rate sufllciently slow to cause a substantial increase in the hardness of the alloy.

22. A hard nickel-chromium-iron alloy con- 30 taining about 10% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but suflicient- 1y high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time suflicient to obtain a substantial increase in the hardness of the alloy.

23. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30% chromium, at least 1% to about 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suiiicient period 01' time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating thealloy for a suflicient period of time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness oi the alloy.

24. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30%chromium, at least 1% to about 4% titanium, and iron constituting substantially the 00 least a portion of the titanium to dissolve in the 05 alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufficientlyslow to cause a substantial increase in the hardness of the alloy.

25. A hard nickel-chromium-iron alloy con- 70 taining about 10% to about 50% nickel, about 3% to about 30% chromium, 2.2% to about 3.2% titanium, and iron constituting substantially the balance 01' the alloy, said alloy being age hardened by heating the alloy to an elevated tempera- 75.

ture below its melting point but sufficiently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a period of time sufilcient to obtain a substantial increase in the hardness of the alloy.

26. A hard nickel-chromium-iron alloy containing about 10% to about 50% nickel, about 3% to about 30% chromium, 2.2% to about 3.2% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time and at a suificiently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufiicient period of time and at a sufficiently high temperature below 750 C. to oband the melting point of the alloy to cause at least 10 a portion of the titanium to dissolve in the alloy. and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufllciently slow to cause a substantial increase in the hardness of the alloy.

NORMAN B. FILLING. PAUL D. MERICA.