US2841511A - Metal alloy and its manufacturing process - Google Patents

Description

July 1, 1958 i H. BIBRING 2,841,511

METAL ALLOY AND ITS MANUFACTURING PROCESS Filed Sept. 14, 1953 Fig- 2 400 200 300 400 58c 600 700 Goo Sou 4on0 -lxillllLlllll United States Patent METAL ALLOY AND ITS MANUFACTURING PROCESS Herv Bibring, Mendon, France, assignor to Oflice National dEtudes et de Recherches Aeronautiques, Chatillon-sous-Bagneux, France Application September 14, 1953, Serial No. 379,779 Claims priority, application France September 16, 1952 20 Claims. (Cl. 148-2) The present invention relates to a metal alloy and to its manufacturing process.

Numerous metal alloys, containing cobalt, nickel, chromium, molybdenum, have been proposed for high temperature service, and attempts have been made to prevent the creep and oxidation thereof at high working temperatures.

These alloys have made it possible to develop techniques as regards cases where prolonged service is not indispensable, but have not contributed to resolve the problems which arise in the construction of apparatus comprising members enduring high temperature service over long periods of time. After a few hundred hours, in fact, the creep ratio of these alloys increases rapidly, said members becoming unserviceable.

The explanation of this evolution, as generally admitted, is that the precipitation having caused the structural hardening is carried on; this corresponds to the coalescence or globulation of the dispersed phase, and, perhaps, also to its crystallographic rearrangement.

Castrefractory alloys are also known, which present interesting mechanical properties as regards high temperature service, but these show dilatometrical anomalies at working temperatures, this prohibiting certain applications and are liable to cause perturbations during operation.

The invention, in one of its objects, aims to provide a cast metal alloy presenting very small creep at high temperature, and which is constant in ratio, even afterv a very long time of service.

Another object of the invention is to provide a metal alloy in which super-ageing phenomena will not appear, which is thus capable of constituting the material used for manufacturing operating members associated in mechanical assemblies designed for long high temperature service without replacement.

A further object of the invention is to provide an alloy devoid of dilatometrical anomalies in the contemplated field of application.

It is also an object of the invention to prevent the appearance of any undesirable fragile phases in the alloy, either prior to, or during its utilization.

A still further object of the invention is to provide an alloy formed by the combination of components which are currently available in industry.

It is another object of the invention to provide cast alloy having excellent pouring features and which, consequently, enables the production of cast pieces by the lost wax process. 1 1

It is another object of the invention to provide an alloy giving cast pieces directly usable without mechanical treatment after the casting.

The invention also enables the production of an unoxidizable corrosion resisting alloycapable of a specular olish. p It is also an object of the invention to provide an alloy possessing good welding properties without observing any special precautions, either as regards auto-welding or as regards welding to other'metals or ferrous alloys.

The invention aims also at a process for the elaboration of an alloy such as defined above.

The invention, in this respect, aims to provide a process which enables the production of pieces presenting good dimensional stability.

The alloy according to the invention, while utilizing the above mentioned structural hardening to the 'best advantage, using improved means, hereinafter more fully described, utilizes also another hardening process which, in essence, is not evolutive with time, the alloy acquiring thus high mechanical assistance properties at high temperatures extending over a long period of time.

According to the invention, the hardening, instead of being caused by the heterogeneousness introduced by the presence of a precipitate of a determined phase into a matrix in a different phase, is caused also by the heterogeneousness procured -by the simultaneous presence of two allotropic forms of the same metal or same metallic compound, the change from one form to the other taking place without any transformation in composition, and, accordingly, without diffusion through a martensitic type of mechanism, which is not dependent on the operational time of service.

In this respect, the alloy according to the invention is characterized by the fact that it includes simultaneously and in a clearly defined proportion, in the vicinity of one by preference, cobalt, or a cobalt solid solution on the one hand, in a face-centered cubic lattice crystal form, de-' nominated a form, or perhaps a stable modification of the latter, and, on the other hand, in a compact hexagonal lattice form, or [3 form.

It is thought that the heterogeneousness, procured by the fine precipitation of the B hexagonal form into the face-centered cubic lattice matrix a, through the martensitic type of mechanism, contributes to the good performance the alloy at high temperature, the precipitation of A the [3 form into the a type matrix causing a strained condition which contributes to the hardening.

The alloy includes substances in proportions such that the transformation from one form to the other, although sufficiently slowed down, will lead, at the operating temperature, to a relative or type and 13 type percentagesuch as will be most profitable, preferably of the above mentioned value. 1

The cobalt-base alloy according to the invention comprises, as regards substances propitious for a structure formation, nickel, iron, carbon, and, as propitious substances for the 5 structure, chromium and molybdenum.

According to the invention, the a-genous action of nitrogen, always present, and which would be dilficult to control, is avoided by the presence of zirconium, with or without titanium. 1

The undesirable mutual reactions between the above mentioned substances are also avoided by the addition of zirconium, with or without titanium.

The proportions in the above specified substances may be varied, but within very narrow limits, inorder to meet the various requirements mentioned in the preceding paragraphs, and, also, owing to the fact that several of these intervene in other manners in the alloy, as this will be.

3 planes, enabling thus to pass from one crystalline system to another.

(b) The action is completed at the end of the elaboration stage, by subjecting the alloy to a permanent deformation, under heat, which causes a partial change from the or form to the {3 form, this change resulting in a relative proportion of oz and [3 of a stable nature, probably due to the appearance during the plastic deformation of a stable modification of the a form. The alloy according to'the invention retains a large grain dendritic appearance crystallization, this type of structure ensuring not only a better resistance to creep, but also, as proved by'tests,'exce1lent wear-resisting properties at high temperature (repeated alternating stresses);

The large grain dendritic segregation is developed by the fusion technique, by carefully selecting the casting and mould temperatures, and by adopting a composition such that the liquidus and the solidus areas will be sufliciently far apart. To retain this segregation, the alloy will not, theoretically, be subjected to any subsequent mechanical working or shaping.

The alloy according to the invention is also characterized by its relatively high. percentage of carbon, higher, theoretically, than 0.6%, by weight.

The presence of a relatively high percentage of carbon, reducing the cooling speed of the alloy and decreasing the first crystallization temperature, enables the results in a growth of the grains to proceed faster than the solidification. This high percentage of carbon, moreover, ensures the absence of dilatometrical anomalies in the alloy by suppressing any changes in the course of heating, since it widens the stability zone of the oa'form, which is stable at high temperature.

It procures also a dense carburic pattern to the alloy, this being propitious to a good performance at high temperature.

The invention makes also provision for adding nickel in such proportions that it will not only play its part in helping to the formation of the a structure, but also,

owing to the increase of the solubility area of the Cr into the Co, it avoids the formation of hard and brittle compounds in the alloy, such as Co Cr in spite of the fact that the Co proportion is higher than 40%, and that a Cr proportion sufiicient for conferring good oxidation resisting properties to the alloy and for favouring the appearance of the 5 form.

According to the invention, the nickel percentage goes with pair with a dependent carbon percentage, which compensates the effect resulting of the Ni addition as shown by the liquidus and solidus being brought nearer to each other, the carbon and nickel being present, in this view, advantageously in equi-atomic quantities.

Zirconium and titanium, even in slight amounts, oppose to the'oxidation of the type known as catastrophic oxidation, which could be caused by the presence of molyb denum.

Zirconium and titanium, moreover, stabilize the chromium and molybdenum percentage in the matrix, in spite of the presence of a noticeable amount of carbon, since they show a greater affinity for this substance than Cr and Mo.

Further, zirconium and titanium fix the nitrogen in the form of nitrides or cyanides, and prevent this element, always present, from acting in an uncontrollable manner on the stabilization of the or form.

which occurs at various temperaturesextending over a P wide scale and at different moments covering a long period of time.

The mechanical properties of the alloy according to the invention are thus increased by a hardening process similar to the one utilized in some known types of alloys, but the hardening in the present case is carried out in an extremely more efiicient manner with respect to the operational time, and also with respect to the variety of the operating temperatures.

To this result contributes also the evolution dilferent relatively to time, and according to the various temperatures, of the different intermetallic precipitates or carbides in which enter the elements introduced in the alloy, and, namely, chromium, molybdenum, carbon, zirconium and titanium.

The invention includes a series of alloys wherein the component elements percentages are comprised within the following limits:

proportions ensuring remarkable high temperature creep properties would have to be close to the following values:

Co 9 Cr 6 Mo 1 Ni l the C atomic proportion may vary within limits com prised between one half and one time that of Ni.

Changes may be made in the above given atomic proportions to meet any particular requirement. For instance, if it is desired that the alloy be possessed with special oxidation resisting properties, the percentage of carbon will be decreased, whereas the proportion of the first four elements will remain practically unchanged.

The carbon percentage may be reduced to 0.3%, the

loss of creep properties not being so important in this case.

An alloy of this type, having a small percentage of carbon, permits namely to cover large surfaces free of defects such as tears, contraction cracks or clinks.

If the alloy is to include tungsten, the atomic proportions must be proximate of the values given below:

Co 9 Cr Mo 1.5 W 0.75 Ni 2.5 C 1 EXAMPLE I The composition of the alloy is (percent by weight):

Co 50' Cr -a 28 Mo m. 10 Ni a- 6 C 1 Zr 01 Ti N 03 Si 1 Mn 1 Fe to complete Figure 1 shows the creep curve lot this alloy at 750 C. under a stress of 18.1 kg./mm. and the-creep curves A and B of the twoforged nickelbase-alloys currently with an alloy according to the invention, the creep characteristics of the latter remaining unchanged respectively to time; the figure shows clearly that applying a pro-strain to nimonic type alloys (curves A and B) would refer to the useful part of the curve and, accordingly, would limit their service time.

By way of example, an elongation of approximately 0.35% (point M on the figure) may be obtained under the conditions experimented and illustrated on curve I, (750 C. and 18.1 kg./mm. after 200 hours of service, but the alloy may, with advantage, be subjected to an equivalent deformation in a. much reduced time, by modifying the operating conditions:

Thus an elongation of app. 0.4% is obtained:

In 10 hours at 790 C. with 18 kg./mm.

In 2 hours at 830 C. with 18 kg./mm.

In 35 mins. at 870 C. with 18 kg./mm. and also In mins. at 750 C. with 42 kg./mm.

D on Figure 2, represents the differential dilatometrical curve on the alloy between and 1000 C. respectively to a Pyros test piece (curve obtained by means of a photo-recording Chevenard differential dilatometer).

The true expansion of the alloy is obtained by adding the Pyros test piece expansion to the differential expansion read on the curve for the same temperature.

This curve D is perfectly reversible. The aspect of the curve does not change, even following prolonged high temperature treatment.

The specific weight of the alloy at 20 C. is 8 g./cm.

The mean expansion factor is 18.2 X 10" between 20 and 900 C.

The electrical resistivity at 20 C. is 88 microhms cm./cm.

The alloy is non-magnetic.

The modulus of elasticity at 1000 C. is 14,480 kg./mm.

The fatigue limit, at 730 C., for an undulated stress between 2.5 and kg./mm. with a pulsation of 32 c./s.

is higher than 3 x 10" reversals.

A high temperature tensile strength test shows at 815 C.:

Breaking load: 44 kg./mm.

Limit of proportionality: 32 kg./mm.

Elongation: 14.2 kg./mm.

EXAMPLE II The alloy has the following composition (percent by weight).

6 This alloy possesses also excellent creep-properties. Curve II on Figure 3 shows the creep curve of this alloy at 730 C. with a stress of 10.5 kg./mm.

Curve 1' represents the creep curve of the alloy given in Example I under the conditions defined above.

The alloy according to Example II shows also a very steady differential dilatometrical curve. It is represented on Figure 2 by reference D EXAMPLE III The alloy composition is as follows (percent by weight): Co I 39 Cr 25 Mo 10 W 10 Ni 10 C 1 Zr 0.1 Ti 0.3 Si 1 Mn 1 Fe to complete The creep curve of this alloy, drawn under the same conditions than for Example II, is shown in III, Figure 3.

Elaboration of the alloy The alloy is obtained by casting, and the following Co, Ni, Mo, Cr, Zr, Ti, Mn, Si.

Carbon may be introduced in the form of carburized parent alloy, by conventional means. i a

When fusion is carried out by means of an induction furnace, it will be advantageous to introduce the carbon by means of graphite, immediately after the titanium.

The pouring is carried out at 1500 C. The alloy is poured in pre-heated moulds, a suitable temperature for this being from 800 to 1050 C., depending on the desired grain size.

The alloy is maintained at the Working temperature for twenty-four hours, in order to cause the structural hardening on one hand, and, on the other hand, to facilitate the partial allotropic transformation from a to B.

The alloy is then permitted to cool slowly. Pieces obtained at this stage present already very interesting high temperature mechanical characteristics, and may be utilized as they are.

The remarkable properties of the alloy, however, may be further increased by a high temperature deformation before being put into service. This prior strainmay take place with advantage with the piece under service conditions. If necessary, this prior strain will be followed by a final truing-up operation.

In a modification, this prior deformation can be obtained rapidly by subjecting the piece to more severe mechanical or thermal conditions than those met in the contemplated application, as mentioned in Example I.

When manufacturing a piece having a determined dimension of an alloy according to the invention, it may be cast with a dimension slightly smaller than the dimension corresponding to service, the piece being ultimately subjected to the above definedtreatment so as to bring it to the said predetermined dimension.

The alloy according to the invention has remarkable smelting properties, and it can be reliedupon for the precise fabrication of pieces having various and complex shapes designed for long service operation at high temperatures. Its fluent pouring, for instance, permits the fabrication, by means of a precision pouring process (lost-wax process), of a turbine wheel and blade assembly in one single piece, free from defects.

What is claimed is: i V

1. A cast refractory metal alloy having substantially the following composition:

Percent Co 50 Cr 28 Mo 10 Ni 6 C 1 Zr ()1 Ti 03 Si Mn 1 Fe the remainder 2. A cast refractory metal alloy having substantially the following composition;

Percent Co 55 Cr 27 Mo 7 Ni C 1 Zr 0.2 Ti 0.2 Si 1 Mn 1 Fe the remainder 3. A cast refractory metal alloy having substantially the following composition:

Percent Co 39 Cr 25 Mo W 10 Ni 10 C 1 Zr 0.1 Ti 0 3 Si 1 Mn 1 Fe the remainder 4. A cast cobalt base refractory metal alloy containing by weight in excess of approximately 40% cobalt, from 20% to 35% chromium, from 5% to 20% molybdenum, from 0 to tungsten, from 3% to 15% nickel, from 0.6% to 1.2% carbon, from 0 to 0.5% titanium, from 0.05% to 0.3% zirconium, less than 3% of silicon and manganese and iron, said iron being present and constituting the remainder of said alloy, said cobalt being present in both the alpha and beta allotropic forms thereof.

5. A cast cobalt base refractory metal alloy as recited in claim 4 in which said carbon and said nickel are present in equi-molecular quantities.

6. A cast cobalt base refractory metal alloy as recited in claim 4 in which the cobalt, chromium, molybdenum, nickel and carbon atomic proportions are substantially 9:611:121.

7. A cast cobalt base refractory metal alloy as recited in claim 4 in which the atomic proportions of cobalt, chromium, molybdenum, tungsten, nickel and carbon are substantially 9:6.5:1.5:0.75:2.5:1.

8. A cast cobalt base refractory metal alloy as recited in claim 4 in which said alpha and said beta allotropic forms of cobalt are present in approximately equal proportions.

9. A cast cobalt base refractory metal alloy containing by weight in excess of approximately 40% cobalt, from to chromium, from 5% to 20% molybdenum, than 0 to 15 tungsten, from 3% to 15% nickel,

from 0.6% to 1.2% carbon, from 0 to 0.5% titanium, from 0.05 to 0.3% zirconium, less than 3% of silicon and manganese and iron, said iron being present and constituting the remainder of said alloy, said cobalt being present in both the alpha and beta allotropic forms thereof, said alloy having been maintained at a temperatures between about 800 C. and about 1050 C. for a prolonged period of time.

10. A cast cobalt base refractory metal alloy as recited in claim 9 in which said alloy is maintained at the said temperature for about 24 hours.

11. A cast cobalt base refractory metal alloy as recited in claim 9 in which said heat-treated alloy is drawn about 0.35%.

12. A cast cobalt base refractory metal alloy as recited in claim 9 in which said alloy is drawn after the same is cast and during the cooling thereof.

13. A cast cobalt base refractory metal alloy as recited in claim 9 in which said alloy is drawn at a temperature of about 750 C. to about 870 C.

14. A cast cobalt base refractory metal alloy as recited in claim 9 in which said heat-treated alloy is mechanically drawn to permanently deform the same.

15. A process of producing a cast cobalt base refractory metal alloy characterized by small creep of constant ratio at high temperature comprising admixing in amounts by weight in excess of approximately 40% cobalt, from 20% to 35% chromium, from 5 to 20% molybdenum, from 0 to 15% tungsten, from 3% to 15% nickel, from 0.6% to 1.2% carbon, from O to 0.5% titanium, from 0.05 to 0.3% zirconium, less than 3% of silicon and manganese and iron, said iron being present and constituting the remainder of said alloy, casting said mixture, and maintaining said cast mixture at a temperature between about 800 C. and about 1050 C. for a prolonged period of time.

16. A process as recited in claim 15 in which said heat treated alloy is drawn about 0.35% at a temperature of about 750 C. to about 870 C.

17. A process as recited in claim 15 in which said heat-treated alloy is mechanically drawn to permanently deform the same.

18. A process as recited in claim 15 in which said mixture is cast into preheated molds and maintained at a temperature between about 800 C. and about 1050 C. and in which said cast mixture is maintained in said molds at said temperature for a prolonged period of time.

19. A process as recited in claim 18 in which said alloy is maintained in said molds at said temperature for about 24 hours.

'20. A process as recited in claim 15 in which said heat-treated cast alloy is mechanically drawn at a temperature of about 750 C. to about 870 C.

References Cited in the file of this patent UNITED STATES PATENTS 119,682 Yeilding Oct. 33, 1871 1,417,638 Sowers May 30, 1922 1,517,354 Gillett Dec. 21, 1924 1,830,550 Kerekgyarto Nov. 3, 1931 2,090,044 Hassenbrush Aug. 17, 1937 2,299,871 Baird Oct. 27, 1942 2,486,576 Savage Nov. 1, 1949 2,515,775 Eprernian July 18, 1950 2,617,725 Owens Nov. 11, 1952 2,684,299 Binder July 20, 1954 OTHER REFERENCES Materials and Methods, June 1946, page 1562. Journal of Metals, vol. 188, pages 154-161, January 1950.

Claims (1)

15. A PROCESS OF PRODUCING A CAST COBALT BASE REFRACTORY METAL ALLOY CHARACTERIZED BY SMALL CREEP OF CONSTANT RATIO AT HIGH TEMPERATURE COMPRISING ADMIXING IN AMOUNTS BY WEIGHT IN EXCESS OF APPROXIMATELY 40% COBALT, FROM 20% TO 35% CHROMIUM, FROM 5 TO 20% MOLYBDENUM, FROM 0 TO 15% TUNGSTEN, FROM 3% TO 15% NICKEL, FROM 0.6% TO 1.2% CARBON, FROM 0 TO 0.5% TITANIUM, FROM 0.05% TO 0.3% ZIRCONIUM, LESS THAN 3% OF SILICON AND MANGANESE AND IRON, SAID IRON BEING PRESENT AND CONSTITUTING THE REMAINDER OF SAID ALLOY, CASTING SAID MIXTURE, AND MAINTAINING SAID CAST MIXTURE AST A TEMPERATURE BETWEEN ABOUT 800*C. AND ABOUT 1050*C. FOR A PROLONGED PERIOD OF TIME.

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