DE2050086A1 - Nickel zinc alloy - Google Patents

Description

Dipl.-Ing. H. Sauerland ■ Dn.-Ing. R. König Patentanwälte · 4odd Düsseldorf · CecifiehaMee% ■ Telephone 43373a

October 12, 1970 III / Fu. 26 196

International Nickel Limited, Thames House, Millbank,

London, SW 1, UK

"Nickel-Zinc Alloy"

Copper-nickel-zinc alloys are known to have various favorable properties, in particular good ductility, good mechanical properties including good strength and toughness and general corrosion resistance. Although copper-nickel-zinc alloys are used as a material for numerous objects such as tableware, medical instruments, scientific measuring instruments and electrical switches are known a need for alloys with higher strength and ductility.

The tensile strength of the alloy can be increased by cold deformation are increased, but this results in a considerable reduction in ductility, so that the fatigue strength is impermissibly low. A high fatigue strength combined with a high yield point is particularly important of great importance in materials for vibrating parts and springs. It also enables better Deformability a more extensive use of the alloy, in particular as a material for objects such as bowls, Bowls and pots.

In the copper-nickel-zinc system there is a face-centered cubic ÖC phase and various / J phases

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including a body-centered cubic ^ phase and a body-centered tetragonal ^ & ^ phase. Some of the silver-colored alloys are known as nickel-silver and can have either a single-phase oC or a two-phase ^^ / ^ σ structure. Although the term nickel-silver usually refers to alloys with 9 to 25% nickel, the <j £ - and the α phase can also be used in copper-nickel-zinc alloys with significantly more nickel and in copper-free nickel-zinc alloys. Alloys with 71% nickel and 29% zinc occur. In the case of two-phase alloys with one C- ^{and <} ^ · one ^ v phase, the phase boundary temperature, ie the temperature at which the cC -phase converts into a structure with a CO- and a / <f -phase, depends on the respective alloy composition.

The invention is based on the surprising finding that alloys with a phase boundary temperature for the conversion from the single-phase to the two-phase structure of 427 to 649 ⁰ C with a cold deformation in the single-phase area (<£ phase) and while maintaining the internal stress from the cold deformation after a Annealing at a temperature below the transition temperature, but at or above the recrystallization temperature, a fine-grain two-phase structure is obtained, which essentially consists of a finely dispersed and intergranular β phase in a base structure. Usually, the recrystallization temperature is the temperature at which recrystallization begins; it depends on the alloy composition and to a certain extent also on the degree of cold deformation. The annealing at or above the recrystallization temperature following the cold working leads to a recrystallization of the phase and a simultaneous precipitation of the / y phase, which blocks the grain growth of the recrystallized grain,

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The structure that is established in the process according to the invention has an average grain size of at most approximately 10 microns, but also from 1 to 5 microns if the process is controlled in a targeted manner. The grain size of the ^ phase is in the same order of magnitude as or below that of the ice. Korns.

The above-mentioned fine-grain two-phase structure can be produced in alloys within the content limits of 4 to 71% nickel, 29 to 40 # zinc and 0 to 2% lead, the remainder including impurities caused by the melting process in copper, which have the above-mentioned transformation temperatures determine for each alloy, but requires a considerable amount of work. The field covered by the invention alloys result in approximately from the example shown in the drawing ternary system copper-nickel-zinc, as well as, the line ABCD denotes the composition range of those alloys which have a transition temperature of 649 ⁰ C while the line AGFE those alloys with a transition temperature of 427 ° C. The coordinates of points A to G in the ternary system result as follows:

Table I.

Ni Zn Cu (90 A. 4th 37 59 B. 8th 39 53 C. 40 33 27 D. 67 33 0 E. 71 29 0 F. 40 29 31 σ 8th 36 56

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Although any alloy lying on or within the ABCDEF curve can be treated according to the invention, however, the nickel content is preferably only 8 to 4096 in accordance with the BCFGB curve in the ternary system. With nickel contents below 8%, the fluctuation range of the zinc content is extremely small and is only approx + 1.2% “Such tolerances can be achieved in practice difficult to adhere to. On the other hand, if the nickel content exceeds 40%, the zinc content must be adjusted also difficult because of its high vapor pressure at the melting temperature of such alloys.

An alloy with 8 to 20% nickel has good strength including fatigue strength and fatigue strength, For example, a yield strength of 45 to 62 kp / mm, as well as a soft and easily deformable at normal temperatures Structure, alloys with 20 to 35% nickel have a higher strength, for example a yield point from 62 to 72 kp / mm, but a little less good deformability, On the other hand, alloys with 33 to 40% nickel have the best corrosion resistance and excellent Yield strength of about 66 to 69 kp / mm. However, the alloy should contain at least 37% nickel, when it is used as a material for parts that are used under stress in an ammoniacal environment and should be resistant to stress corrosion cracking.

The lead is not one of the mandatory alloy components, but improves the machinability by up to 2%. However, if particularly good deformability at higher temperatures is important, the lead content should below OP5%, preferably below 0.015%.

In the ternary system shown in the drawing, the contents of lead and impurities were the copper added. Contaminants include deoxidation

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residues and desulphurizing agents as well as the usual accompanying elements of copper-nickel-zinc alloys, such as for example up to 0.1% titanium, up to 0.03% aluminum, up to 0.5% magnesium and up to 1% manganese. Iron, carbon and Silicon are harmful accompanying elements, which is why the alloy does not exceed 0.15% iron, maximum 0.05% Carbon and not more than 0.05% silicon, better still not more than 0.05% iron, 0.01% carbon and 0.01% each Should contain silicon. \ I the elements bismuth, Phosphorus, sulfur and tellurium can have adverse effects, which is why their maximum levels are 0.005% each should.

With regard to the fine-grained two-phase structure of the deformed alloy, it is important that the cold working starts with a structure which consists essentially of a homogeneous solid solution free of coarse components such as dendrites, segregations and precipitates has been melted in the usual way and cast into blocks, destroyed by hot deformation, for example extrusion or forging. Since the β phase normally separates out when the alloy is normally cooled in air with wall or block thicknesses of about 12 mm and more, the alloy normally has to be solution annealed before cold working. The solution heat treatment takes place advantageously from 10 minutes to 2 hours at 30 to 110 ^° C. above the transition temperature. If the alloy contains up to 20% nickel, the air cooling is usually fast enough for wall thicknesses up to about 12 mm. In the case of larger dimensions or nickel contents above 20%, the alloy should be cooled more quickly, for example quenched in water, in order to obtain a solid solution.

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In view of a fine-grain two-phase structure, the alloy must be given adequate internal stress or permanent elongation during cold working. The required degree of deformation, measured as the decrease in cross-section, varies depending on the temperature and duration of the subsequent recrystallization annealing and the respective nickel content of the alloy. In any case, cross-sectional reductions of 60% are preferable and larger cross-sectional reductions of, for example, 85% Jk are particularly advantageous.

The recrystallization annealing is preferably carried out at temperatures well above the recrystallization temperature of the <£ phase, but sufficiently below the transition temperature so that the f * phase precipitates in sufficient quantity to control the recrystallization of the a & grain in this way. Advantageously, the recrystallization annealing is performed 15 minutes to 24 hours at a temperature which is about 28 to 11O ⁰ C below the transition temperature. The structure according to the invention has good stability; accordingly, the annealing time can also exceed 24 hours and the cooling rate can be high or low, ie the alloy can also be cooled in air.

The invention is explained in more detail below on the basis of exemplary embodiments.

As part of the experiments, seven alloys were melted in air using electrolytic copper and nickel and at a temperature a little above the liquidus temperature, zinc pellets or a nickel-zinc master alloy added to the melts with a higher nickel content. After adding the zinc, the bath temperature was

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Temperature increased to the casting temperature, ie to about 83 ° above the liquidus temperature, and after adding 0.1% titanium, the melt was poured into molds. The ingots were homogenized for several hours at 815 to 87O ⁰ C and then either extruded or forged.

The compositions of the test alloys are shown in Table II below, whose alloys 1 to 4 contain less than 20% nickel and their alloys 5 to 7 contain more than 20% nickel. The alloys 1 to 4 were for one hour at 620 ⁰ C solution heat treated, water quenched, cold rolled with a draft of 85%, annealed for 24 hours at 480 ⁰ C and cooled in air. Alloys 5 to 7 were solution heat treated for one hour at 65O ⁰ C, water quenched, cold rolled with a draft of 82%, annealed for four hours at 55O ° C and cooled in air. The mechanical properties of the test alloys can also be found in Table II.

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2 O 5 Π Ο 8

Ni
(%) Cu
(96) Tabel II Stretch
limit ρ
(kB / mm) Tensile strength
speed ρ
(kp / mm) Deh
tion
(96) alloy 10.0
14.7 51.7
49.2 Zn
(96) 45.8
47.6 61.2
65.0 32
29 1
2 15.4 48.3 38.3
36.1 55.7 68.8 24 3 19.2 45.8 36.3 62.1 69.5 21st 4th 25.5 40.1 35.0 72.3 81.5 17th 5 30.2 36.7 34.4 67.5 83.5 26th 6th 38.1 30.1 33.1 67.6 89 28 7th 31.7

The strengthening pads of the alloys with the fine-grain two-phase structure are much higher than the strengths in the solution-annealed condition. So is the yield point of alloy 1 in the solution annealed condition only 18.5

ρ Ο

kp / mm and its tensile strength only 34.4 kp / mm, while the yield strength of alloy 7 in the solution-annealed

2
stood only 35.5 kp / mm with a tensile strength of 81.5

kp / mm.

The high fatigue strength can be seen in an experiment with alloy 3, which in a cyclical

Ο f. Ι

Bending load of 27.5 kp / mm not braöh.

In the case of a material for springs and others, it is more elastic Parts subject to stress should be the ratio of the 0.0196 and the O, O2? 6 yield point to the 0.2J6 yield point be high. For example, this is

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-9- 2ü5fiO86

Ratio of the 0.0196 yield point to the 0.296 yield point

of alloys 6 and 7 0.68: 1 to 0.87: 1 and that

Ratio of the 0.0296 yield strength to the 0.296 yield strength 0.85: 1 to 0.96: 1.

The strength that results from the fine-grain two-phase structure can be further increased by final cold forming, although this is at the expense of ductility. If the ductility is then to be increased again, for example in the case of a wire to be drawn in several passes, the recrystallization annealing can be repeated. Tentatively, the alloy was solution 3 for one hour at 620 ° C, cooled in air, cold worked, annealed for 24 hours at 480 ⁰ C for the purpose of recrystallization and the withdrawal of the f * phase and then cooled in air. Table III below shows the mechanical properties of alloy 3 after the aforementioned treatment, with ¹¹ KW "indicating cold rolling and ¹¹ RG" indicating recrystallization annealing and the hardness values referring to Rockwell 30T.

KW -ι + 2096 KW Tabel III Deh hardness KW H + 5096 KW Stretch train tion KW H + 7096 KW border" firm 00 KW H + RG Πςρ / nHB) ability ₂ (kp / mm) 18th 79 8OX 50.5 74 5 84 8096 79 95 3 85 8096 89 99 24 79 5096 55 69 KRG - RG h RG K RG

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A comparison of the upper and lower test data shows that after considerable cold working through a second recrystallization annealing can bring the alloy back into practically the same state, as after the original recrystallization or precipitation annealing. In practice this represents one significant advantage.

Experiments have also shown that the electrical conductivity of the deformed alloy is essentially nickel content comparable to that of nickel-silver is equivalent to.

The deformed alloy according to the invention has remarkable ductility at elevated temperatures. For example, a tensile specimen of alloy 5 with the fine-grain two-phase structure according to the invention was included a load with constant expansion rate of initially 0.6 mm per 25 mm and minute at 480 ° C a constriction-free Elongation of 3Ο55ί. In addition, the Elongation no grain growth. Another tensile specimen of the same alloy was tested in a similar manner at A80 ° C in stretched in such a way that the rate of stretching was gradually increased from 0.05 to 1.2 mm / min. It resulted a constriction-free elongation of about 300 # without breakage.

As already mentioned, the degree of deformation, the annealing temperature and the annealing time for recrystallization annealing must be adjusted to the composition of the alloy in order to obtain an optimal structure. Such a structure exists when the um phase is fully recrystallized, the whole structure is homogeneous and the R particles are finely dispersed _: and equiaxed at the grain boundaries, distributed over the entire <£, phase. But even such deformed alloys, which are not in all respects with the above

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2050Ü86

match, still own excellent technological Properties.

The structures found after various treatments can be classified as follows:

A very good

B fully recrystallized ct> phase, with a certain inhomogeneity due to concentrations of the β phase, "

C 80% of the ds, phase are recrystallized and a smaller part of the β phase is not equiaxed;

D <£ · phase fully recrystallized, / 3 phase not completely equiaxed;

E ct phase fully recrystallized, structure partially free of β- precipitates;

F dL phase not recrystallized, ß phase to the Slip lines and the grain boundaries;

G as F, but with stronger concentrations of the phase;

The structures according to A to D can be considered satisfactory, so that all alloys with such structures fall under the invention, while alloys with structures according to E to G are outside the invention. In Table IV below, the structures of alloys 1 to 3 are different, taking into account different ones Reductions in cross-section during cold rolling and different annealing temperatures and times during recrystallization annealing marked.

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alloy 96 KW Tabel 6th IV 2 425 ⁰ C 2 480 ⁰ C 24 Glows enroe rature G 37O ⁰ C G 6th 24 C. 6th A. 1 72 Glow time 2 A. 24 A. C. C. A. A. A. 1 85 ' G A. G A. A. A. A. A. A. 1 96 A. - A. - A. A. E. A. B. 2 72 A. G A. E. F. D. E. - A. O 2 85 - G - A. A. A. A. B. A. CD 2 96 F. - E. - A. A. E. A. D. 3 72 F. . F. A. F. - E. D. - A. 3 85 - .Ot. - E. E. A. A. B. A. * · *
cn 3 96 F. G A. A. ^A. F. E.

O CD OO CD

The table above shows the significance of the degree of deformation. Good results show in fact with a deformation rate of at least 8596 and a 24-hour annealing at least 425 ⁰ C. In addition, Table IV shows that also the degree of deformation as well as the annealing temperature and / or time should increase with increasing nickel content.

From the alloy according to the invention, sheets, strips, blanks, rods, billets, wire and other rolled as well as Extrusion products are produced; it is particularly suitable as a material for tableware, for example Cutlery or forks, spoons, butter knives, bowls, pots, bowls and others commonly called Items designated as harnesses, as well as for springs, for example barometer springs, diaphragm springs and electric contact springs, keys for musical instruments, surgical and medical instruments and spurious Jewellery. In addition, the alloy can also serve as a carrier for plating with silver.

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Claims (9)

International Nickel Limited, Thames House, Millbank, London. S.W. 1, Great Britain claims: 1. Deformable nickel-zinc alloy, consisting of 4 to ^ 71% nickel, 29 to 40% zinc and O to 2% lead, the remainder Ψ Finally, copper impurities caused by the smelting process with a conversion temperature of theoC / cC + ß- conversion of 427 to 649 ° C, characterized by a fine-grained two-phase structure consisting essentially of finely dispersed and intercrystalline β-phase precipitated in a cC basic structure. 2. Alloy according to claim 1, characterized by one on or within the curve BCFGB lying composition. 3. Alloy according to claim 1 or 2, characterized in that the grain size of the <A and the β grain is below 5 microns. 4. Alloy according to one or more of claims 1 to 3, characterized by a nickel content of 10 to 20%. 5. Alloy according to one or more of claims 1 to 3, characterized by a nickel content from 33 to 40%. 6 (jl Process for the heat treatment of an alloy according to the Claims 1 to 5, characterized 109817/1 453 by cold deformation of the single-phase <C structure as well as a subsequent recrystallization and precipitation annealing 7. The method according to claim 6, characterized in that the recrystallization and precipitation annealing 30 bi
the alloy takes place. Divisional annealing 30 to 110 ° below the transformation temperature 8. The method according to claim 6 or 7, characterized in that that the alloy is solution annealed before cold working. 9. Use of an alloy according to claims 1 to 8 as a material for objects such as tableware, Cutlery, feathers, medical instruments, jewelry must have high strength and ductility. 109817 / U53 Blank page