US2116923A

US2116923A - Process of heat-treating alloys

Info

Publication number: US2116923A
Application number: US721943A
Authority: US
Inventors: John W Bolton
Original assignee: Lunkenheimer Co
Current assignee: Lunkenheimer Co
Priority date: 1933-11-01
Filing date: 1934-04-23
Publication date: 1938-05-10
Anticipated expiration: 1955-05-10

Description

Wlay 10 938. J, w. BGL-[QN 2,116,923

PROCESS oF HEAT TREATING ALLoYs original Filed Novv. 1, 1935 HTTO/BIVE VS Patented May 10, 1938 UNITED STATES PATENT OFFICE Lunkenheimer Company,

corporation of Ohio Cincinnati, Ohio. a

Original application November 1, 1933, Serial Divided and this application April 23, 1934, Serial N0. 721,943

7 Claims.

alloy and a method of making it, which results in an increase in fluidity and a decrease in shrinkage or contraction cavity formation tendency in copper and nickel base alloys.

It is a further object to provide a modification of grain structure, especially in the elimination of loose coarse grain or excessive dendritism in copper or nickel base alloys.

A further object is the prevention of brittleness and the reduction of the liability of cracking during heat treatments of such alloys.

The objectief this invention is to add calcium or certain compounds or alloys thereof to various alloys of copper and nickel and of copper, nickel and silicon for the accomplishment of the foregoing objects.

In particular it is the object of this invention to permit of a nickel, copper, or nickel, copper and silicon alloy to be cast with high initial hardness and then softened for machining purposes by heating to a high temperature and then quickly quenching. Thereafter, the original hardness is restored by heating or aging at a temperature somewhat below the quenching tem- ,0: perature. i

If sufficiently drastic quenching to get maximum machinability is employed, it has been found that cracking will likely result so that the manufacturer is unable to safely employ quenching treatments to get `maximum machinability.

While such alloys are machinable within a certain range, yet the present invention, by the addition of calciumy or certain compounds or alloys including, permits the castings to be quenched to produce greater softness and better machinability with the result that ordinary machine operations through 'a wide range can be performed upon this alloy and there, has opened up a large number of manufacturing operations and consequent uses for this alloy which werenot hitherto open to it. K The addition of calcium minimizes the tendency towards crackingand permits of the economical production `of parts made from such age-hardened copper, nickel and silicon-alloys, together with a grain refinement which is very marked.

I It is a further object to provide for the addition of a small percentage of calcium within the alloy so that the range of retained calcium for ordinary purposes is 0.2 to 0.5 per cent., and for this purpose 0.1 to 1.0 `per cent. of calcium is added to the alloy initially in the mix.

The following indicates the results obtained with the use of retainedcalcium:

(a) It increases the fluidity in copper base, copper-nickel base, and copper-nickel base alloys to which silicon has been added. This action is not conned to alloys withage-hardening properties. For example, this action appears in alloys of 90% copper and 10% nickel and alloys of 62% copper, 4% tin, 34% nickel which alloys do not have much age-hardening possibilities. It also increases the fluidity of the copper-nickel silicon age-hardening alloys. The fluidity increase is not due to a deoxidation effect, as it -increases the fluidity of already carefully deoxidized alloys. The advantages of increased fluidity for successful pouring of intricate castings is well known.

It is beneficial in elimination of shrinkage or con- 25 traction cavities formation. t

(b) It refines the grain size of various alloys within the above classication. This claim is not confined to alloys of copper-nickel and silicon,

although it cannot be fairly said to hold in`-all alloys of copper base nickel nickel base.

(c) It minimizes the tendency toward red shortness of various alloys of the above types.

base, and copper This benet is not necessarily conned to" age-.`

hardening alloys. For example, the red "short tendencies of Monel metal nickel 35% copper) are well known and myexperiments have shown that the calcium addition will benefit this-because the heat treating` troubles of` noncalcium modified copper-nickel-silicon alloys, and others `mentioned herein, are due to the same causaa red short range. Grain refinement and prevention of red shortness in these alloys enable .me to employ more drastic quenching media, and hence to obtain a softer, more machinable .alloy after this treatment. i It is probable that similar lbenefit would be `obtained in `any other agehardening alloys which have a tendency toward cracking. In none of the alloys doescalciumin itselfappearto increase hardness. I

Any equivalent analysis might be used within theV scope of this invention, but I have usedfthis as typical forillust'rative purposes.` f Referring;to"thef'drawirlg; i

` rograph etched and magnified iive diameters with oblique illumination employed; the cross section shown in the drawing is -based upon the macrograph as photographed.

Figure 2 is a similar view showing the use of calcium as in formula (b) The drawing is based upon a macrograph showing the grain size as cast using the same etchant, a bar of the same size as in Figure 1 with the same magniiication and the same oblique illumination; it will be noted that the general grain size of Figure 1 is about twice that of Figure 2 and illustrates the benecial eiect of calcium on the grain size of (as cast) alloys.

Figure 3 is an illustration of a cross section of the specimen of Figure 1 which has been oilquenched. The same etchant and illumination were utilized as in Figure l, but with a magnifica-` tion of 'T1/2 diameters. The grain structure of this composition without calcium is apparent.

Figure 4 is a similar view of the specimen4 shown in Figure 2 using calcium and treated in the same manner as the specimen in Figure 3.

Figure 5 is a reproduction of a photograph of a macrograph showing the composition of the specimen shown in Figure 1 which has been water-quenched. The magnication is six diameters and a Silverman illuminator was used for the detection of the intercrystalline crystal cracks, one of which is very apparent, and the coarse grain size also is apparent. 'I'he grain boundaries are located where the orientation of the small primary dendrites change.

Figure 6 is a similar view of the same specimen in which the grain boundaries are more clearly dened for the purpose of illustration with black ink lines.

Figure 7 shows the structure of Figure 2 that has been water-quenched and photographed in the same Way as that of Figure 5. The fine uniform grain size and freedom from cracks are quite apparent.

Figure 8 is a similar view of the composition of a specimen of Monel metal (65% nickel and 35% copper) with the addition of calcium.

It will be understood that this drawing is based upon actual macrographs and photographs of the etched specimens and is as near as it is possible to reproduce such photographs in a drawing. y

This is a division of application Ser. No. 696,- 162, filed November 1, 1933.

'I'he alloy of this invention may be produced with high resistance to wear, high hardness, resistance to galling or seizing, high strength and a marked resistance to corrosion under conditions of high temperature, high pressure water, and high steam or air pressures. In the presence of corrosive materials, such as dilute sulphuric acid, and the presence of various alkaline substances, such as sodium hydroxide, it is practically immune to attack.

This alloy is one that Amay be cast and heattreated so that it will have a relatively low hardness for machining or forming purposes, and

ananas 'I'he base of this alloy may either be copper or nickel or both or a combination of copper, nickel and silicon. To this combination of copper and nickel, or copper, nickel and silicon is added calcium in amounts ranging from 0.1 to 1.0 per cent. ,By calcium is meant metallic calcium, alloys oi calcium with copper, nickel, manganese, magnesium, beryllium, zirconium, or other metals, compounds of calcium, such as silicides, or other commonly used materials containing calcium, such as calcium-manganese-silicon or calcium-ferro-silicon. In short, it is of no importance how the calcium is added so long as the requisite amount is added.

'I'he addition of calcium improves the properties of the alloy, modifies the grain structure and improves the ability to heat treat the alloy in order to get the most economic use of the machine.

As a typical alloy there may be selected an alloy consisting of from 1.75 to 3.25 per cent. silicon, the balance being copper and nickel in varying ratios but approximately equal ratios preferably. To this alloy is added from 0.1 to 1.0 per cent. of calcium. Y

After casting this alloy it is softened by quenching in any suitable medium, such as air, water or oil, from a temperature approximately 1350 to 1600 degrees Fahrenheit. I hold such a temperature for about forty-iive minutes or more, according to the requirements of heat penetration and the time necessary for partial and ranges from 150 to 190 Brinell. About 170 Brinell is preferred and it is possible by the addition of the calcium to get a Brinell as low as this in order to give the most satisfactory machinability for work in the shop.

After the machine work has been performed, the parts that have been machined are subjected to an aging treatment at from 900 to 1200 degrees Fahrenheit for approximately eight' hours. 'I'he parts are then cooled in the air or in the furnace as desired.

The result of this aging treatment is to recover or increase the initial hardness. The grain renement is very marked as a. result of the addition of the calcium. The calcium does not disappear in the ultimate alloy but remains substantially in the proportion of from 0.2 to 0.5 per cent.

It will be understood that this effect is also secured in a somewhat different manner and degree with the use of nickel and copper alloys Without the addition of silicon but the silicon, nickel and copper alloy has been selected purely as illustrative because of the practical experience with this combination on an extensive scale and because of the marked change in this alloy upon the addition of calcium.

The result of the aging treatment is to increase the hardness from 250 to 350 Brinell while at the same time retain an appreciable ductility in the alloy.

The exact properties desired can be secured by vthe use of this composition of alloy, first casting it, then heat-treating it to increase ductility and obtain reduction of hardness, machining it and then recovering or increasing hardness by age-hardening it without affecting the machine work and without pronounced distortion, shrinkage or cracking. In short, the resulting product is ready for use, with possibly a slight finish which sometimes is desired.

It will be understood that the resulting alloy such as described herein has the light silver or white color of alloys containing large percentages of nickel and is only slightly darkened by the nal heat-treatment.

Under conditions which are extremely severe, as encountered by valve seats, disks and like structures, the alloy develops unique mechanical properties of resistance to galling or seizing, and high strength. It is produced at a much lower cost than any material such as stainless steel of equivaient hardness and can be handled in a machine shop without diculty, -due to its controllable hardness. It does not lose its hardness at working temperature as in valves at 500 degrees Fahrenheit, whereas such products as stainless steel will lose as much as 50 `points Brlnell hardness under similar circumstances.

It will be understood that the reduction of hardness after the first heat-treatment of this cast alloy enables rapid machining on automatic or semi-automatic machine tools with accompanying economies of production.

A modification of the alloy by the addition of calcium results in the improvement of the casting properties, the grain structure and the ability to heat-treat to get the most economical machining. The entire appearance of the alloy is changed from one that has a rather large rough grain structure to one that has a very fine smooth and uniform grain structure when calcium is added. In addition, cracking of the alloy is avoided with consequent perfection in the resulting product.

It will be understood that it is desired to comprehend within this invention and the scope of the claims thereof such equivalent materials and' proportions as may be found necessary to adapt this invention to the varying conditions met in actual practice and this invention is not limited to these specific materials and proportions.

'I'he silicon confers age-hardening properties and the calcium the properties of improving casting, refining grain structure, prevention of cracking and fissures, and increasing the ability to heat-treat to get the most economical machining properties. By calcium I include any means or method of incorporating calcium in the mix. It will be further understood that calcium silicon and calcium copper have proved convenient materials for the purpose of this invention. but there' is no intention to limit the invention to these materials. The amounts of 0.1 to `1.0 per cent. indicate the practical boundaries of the percentage of calcium but it will be understood that a variation from those amounts may be had without completely destroying the merits of the invention but simply reducing the maximum success of the invention. For instance, calcium over one per cent. tends to reduce the ductility of the alloy which, for most purposes, is undesirable.

It will be understood that this effect is secured in a somewhat different manner and degree in other alloys whose major components are copper or nickel or copper and nickel. I have described specifically the effect of calcium addition to age-hardening alloys of copper nickel and silicon because in these alloys all the effects described in this description are combined with great advantage to the casting properties of such alloys and to their `most economical production. I do not limit myself to incorporation of calcium to such alloys, but include also other age-hardening copper or nickel or copper and nickel base alloys, and to alloys which do not possess appreciable age-hardening properties. For example, the addition of calcium, as above specified, to a. nonage-hardening alloy, copper and 10% nickel. very markedly increases its fluidity and improves the grain structure.

'Ihe addition of calcium as above specified to an alloy, 62% copper, 4% tin and 34% nickel (an alloy with slight age-hardening properties) confers marked fluidity, benefits casting properties and minimizes tendency toward red shortness (brittleness at elevated temperatures) sometimes noticed in conditions of manufacture and service.

In short, the addition of calcium in such manner that metallic calcium is retained within the structure of the alloys described in the following claims results in the benefits described. 'I'he addition of calcium as above specified, does not materially change the hardness or ultimate strength of such alloys, but improves their castability, their grain size, and their ductility at elevated temperatures.

Calcium addition dissipated'by oxidation effects does not produce these results. The calcium must be retained in the structure of the final alloy. For this reason full benefit is attained only by addition to fully deoxidized alloys or an excess of calcium must be added to compensate for any dissipation by oxidation.

I especially' comprehend within my invention the employment of retained calcium as an agent for preventing intergranular brittleness in agehardening alloys. I comprehend within my invention nickel or copper base alloy castings of high initial hardness, then softened for machining purposes by heating to ahigh temperature; and then quickly quenching. Thereafter, according to the method I comprehend within this invention, the original hardness is restored by heating or aging at a temperature somewhat below the quenching temperature. In the event that calcium is used, the calcium is retained in the alloy and does not disappear.

The addition of calcium or certain compounds or alloys thereof permits the castings to be quenched to produce greater softness and better machinability, without cracking, with the result that ordinary machine operations, through a wide range, can be performed upon this alloy, opening up a large -number of manufacturing operations` and .consequent uses for this alloy which were hitherto not opened to it. The addition of calcium minimizes the tendency towards cracking. It permits of age-hardened alloys with a marked refinement of grain.

I comprehend within my invention an alloy that is practically immune to attack in the presence of such corrosive materials as dilute sulphuric acid and in the presence of various alkaline substances, such as sodium hydroxide. The alloy has high resistance to wear, high hardness, resistance to galling or seizing, high strength and a marked resistance to corrosion under conditions of high temperature, high water pressure, steam or air pressures.

The silicon confers age-hardening properties and calcium the properties of improving the casting, refining grain structure and prevention of cracking and fissures, with an increase in the ability to heat-treat in order to get the most economical machining properties.

It will be understood that I desire to compre- 7| hend within my invention such modifications as may be necessary to adapt it to varying conditions and uses.

Having thus fully described my invention, what I claim as new and desire t secure by Letters Patent, is:

1. In a method of manufacturing an alloy, casting the alloy with from 1.75 -to 3.25 per cent. silicon, from 0.1 to 1.0 per cent. calcium and with the balance substantially nickel and copper in approximately equal ratios, reducing its hardness by heating it at from 1350 to 1600 degrees Fahrenheit, quenching it, machining it, and restoring or increasing its hardness by heat-aging it at from 900 to 1200 degrees Fahrenheit.

2. In a method of producing a cast machine alloy of calcium, silicon, nickel and copper in which the ultimate product is of greater hardness than is feasible to freely machine, casting the alloy with silicon from 1.75 to 3.25 per cent., adding in the alloy before casting calcium from 0.1 to 1.0 per cent., heating and quenching the alloy to reduce its hardness, machining it, and then age-hardening it to restore or increase its hardness without distorting, cracking or injuring the machine Work which has been performed thereon.

3. In a method of producing a cast alloy of calcium, nickel and copper in which the ultimate product is of greater hardness than is feasible to freely machine, casting the alloy with calcium from 0.1 to 1.0 per cent., heating and quenching the alloy to reduce its hardness, machining it, and then age-hardening it to restore or increase its hardness without distorting, cracking or injuring the machine Work which has been performed thereon.

4. In a method of manufacturing an alloy, casting the alloy with from 0.1 to 1.0 per cent. calcium and with the balance substantially nickel and copper in approximately equal ratios, reducing its hardness by heating it at from 1350 to 1600 degrees Fahrenheit for forty-ve minutes or more, quenching it, machining it, and restoring or increasing its hardness by heat-aging it at from 900 to 1200 degrees Fahrenheit.

5. In a method of treatment of an age hardening alloy comprising from 1.75 to 3.25 per cent silicon and with nickel and copper in approximately equal ratios, consisting of the addition thereto of a modifying elementin the amounts of 0.1 to 1.0 per cent of calcilun and casting the alloy; retaining the calcium in the alloy; and thereafter heat treating the alloy to insure controllable hardness, while retaining the calcium to insure an .alloy without cracks and of the requisite hardness.

6. In a method of treatment of age hardening non-ferrous alloys comprising approximately half nickel and half copper with an addition of 1.75 to 3.25 per cent silicon and the addition of 0.1 to 1.0 per cent calcium, the step of casting the alloy; the step of reducing the alloys hardness by heating it and quenching it; the step of machining it to a desired. form While thus softened; and the step of restoring or increasing its hardness byvheat treating it, while throughout all of said steps retaining the calcium in the alloy and utilizing the calcium to maintain grained renemerit and eliminate cracking of the alloy.

7. In a method of manufacturing an alloy, casting the alloy with approximately half nickel and half copper, with an addition of 1.75 to 3.25 per cent silicon and the additionv of 0.1 to 1.0 per cent calcium, reducing the hardness of the alloy by heating it from approximately 1350 to 1600 degrees Fahrenheit, quenching it, machining it, and restoring or 'increasing its hardness by heat ageing it at from approximately 900 to 1200 degrees Fahrenheit while retaining the calcium as a modifying element in the alloy.

JOHN W. BOLTON.