DE1533291A1 - Chrome-nickel alloy - Google Patents

Description

.ng. G. Eichenberq, _o - ■ „ _nrr

ι ue IJ ⁴ Da5seldorf, the .1.8, ..... J-UlI ... 19.6.6

Dl.-lng. M. oauerland ceaiienaiiee η

Patent attorneys Λ C ο ο O η 'j

Bank account:

fsdie Bank AG., Düsseldorf branch
Postal check account: Essen 8734
Telephone number 432732

send in correspondence also , r characters:

International Nickel Limited, Thames House, Millbank,

London, S. W ₀₁ , England

"Ohrom-Nickel Alloy"

The invention relates to Ohrom nickel alloys. which have a high creep rupture strength at elevated temperatures, i.e. which are able to withstand high stresses withstand over long periods of time without breaking.

In the most widely used for this purpose alloys, the good heat resistance depends on the formation of A Aussoheidungsphasen from the nickel and titanium and / or aluminum and are generally of the formula Ni a (Ti, Al) form corresponding gamma-prime phase. Other known alloys contain niobium and, although less effectively, are strengthened by a niocel-niobium annealing phase, while both types are present in still other phases. In all these alloys, however, the carbon content is very low, i.e. below 0.2 ^ or even lower, in order to prevent the formation of carbides of the additional elements at the expense of the required

to prevent liohen intermetallic phase. 90985 1/0839

July 18, 1966 at RChxom ^ Ji.iclcftl.mLeeieiyungi !. Sheet ..... ^ S *

The service life of the aforementioned alloys decreases with increasing temperature. Lies is partly on one Loss of strength of the basic structure, mainly however, on the instability of the intermetallic phase, which leads to a coarsening of the grain, thereby reducing its ability loses to solidify the alloys and possibly tends to loosen. At temperatures above 900 ° 0 it also falls the service life of the best alloys hardened by intermetallic phases is greatly reduced.

Another disadvantage of containing titanium and aluminum Alloys consists in that they harden very strongly when they cool down from the temperature of the hot working. Thus, for example, sheets made from these alloys have to be quenched after rolling to make them soft enough for • To keep in further processing by cold forming. However, it is very difficult to use metal sheets, especially large areas To quench metal sheets without warping them. In addition, the strongest alloys, i.e. those with the highest titanium and aluminum contents are not used in the same way as sheet metal, because the increase in hardness with the titanium and aluminum content becomes stronger and these steels also through an extraordinarily strong quenching cannot be kept sufficiently soft.

The underlying the invention task was zn eliminate the aforementioned disadvantages of high-temperature alloys Le _T. The invention is based on the

909851/0839

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surprising plague that the disadvantages in question duroh the use of niobium and carbon as hardening additives to nickel-chromium alloys "fix ·

The alloys according to the invention therefore contain 2 to 6 * Kiob, 0.3 to 0.5 * carbon and 19 to 33 * chromium. If the Ohrom content is below 24 *, the alloys must also Contain molybdenum in a minimum amount that corresponds to the formula

* Mo «5/8 (24 - * Cr)

corresponds, the alloys preferably containing at least 1 * molybdenum. If the chromium content is below 30 *, the result is the maximum molybdenum content can be derived from the equation

* Mo - 3.5 + 0.5 (30 - * Cr),

while in alloys with more than 30 * chromium the molybdenum content must not exceed 3f5 *. The alloys contain also 0 to 0.01 * boron and 0 to 0.1 * zirconium, the remainder, apart from impurities and deoxidation residues, Nickel.

The hardening phases that develop in such alloys remain effective and undissolved for a long time even at temperatures at which the gamma phase of the chromium-nickel alloys, which are hardened by titanium and aluminum goes into solution; it was thus possible to establish that the hardening phases not completely in solution even at temperatures slightly below the melting point of the alloy went. Thus, the alloys of the invention keep theirs

909851/0 8 39

.1JBL *. «Lull .1.9.6.6 ... an lOhromrHifiicel ^ Leglerung .. '!. sheet

high strength at temperatures of 90O ⁰ C and more, at which the known alloys lose their strength rapidly, although the alloys do not have as great a strength as some known alloys hardened by intermetallic phases at temperatures below 90O ⁰ C ₈ In addition The alloys according to the invention do not harden as quickly and thoroughly on cooling from high temperatures as the alloys hardened by the gamma phase.

Despite the relative insolubility of the hardening phases at high temperatures, a sufficient part for a much later precipitation can be dissolved during subsequent hardening at lower temperatures, so that the alloys according to the invention require a heat treatment consisting of solution annealing and hardening for optimum creep strength. The higher the temperature of the solution heat treatment, the better the fatigue strength after hardening. Preferably, therefore, the temperature of the solution heat treatment is at least 1 125 ⁰ C, for example 1150 ⁰ C or even 125O ⁰ C, but the annealing temperature should of course not be so high that the alloys begin to melt ready. The annealing time is usually 0.5 to 8 hours, although longer annealing times can also be used if necessary.

The alloys can be made from solution heat treatment at any conventional cooling rate either directly up to the curing temperature or up to

909851/0839

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to a lower temperature, generally down to room temperature, be cooled, which in the latter case is followed by reheating to the aging temperature.

After cooling from the solution heat treatment to room temperature, the hardness of the alloy is if they are in the form of 16 mm thick billets or sheets, generally low enough to allow billet machining and sheet metal working to be carried out within a short time. The cooling rate hardly affects the hardness, but it is preferable for optimal creep rupture strength rapidly cooling the alloys from the solution heat treatment temperature, for example by quenching in water.

The curing is preferably carried out at 750 to 1060 ° 0, for example at 850 ⁰ C, specifically 1 to 48 hours. The aging time depends on the temperature and is at 850 ⁰ O generally 16 hours.

The results of numerous tests with alloys of different compositions are shown below Tables are compiled and show that it is important with regard to a suitable combination of properties is that the contents of each alloy element are within the limits of the present invention. The test alloys were melted in air and deoxidized with usual amounts of magnesium or calcium, poured into blocks that were up to

909851/0839

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Billets with a diameter of 16 mm were forged down. O were prepared from the billets after a two-hour solution heat treatment "at 115o ⁰ cut with subsequent cooling in air samples, the final 16 hours were cured at 85O ⁰ C for.

The creep rupture strength was determined at 900 ⁰ C and the Kerbsehlagzähigkeit Charpy at room temperature after a 1000-hour offsets annealing at 850 ⁰ C to reduce the tendency to brittle fracture.

The niobium makes a major contribution to the creep rupture strength of the alloys. In this respect, a niobium content of at least 2 $ is required for adequate creep strength, the alloy according to the invention preferably containing at least 2.5 μg or even better at least 3> 5 # niobium. However, an increase in the niobium content above 6 # leads to a sharp drop in the creep strength , whereby at the same time the notch bottom toughness of the alloys decreases somewhat with increasing niobium content

The effect of different niobium contents is shown in Table I, the values of which relate to alloys with nominally 30? <Chromium and 0.4 # carbon with different niobium and eolybdenum contents and a corresponding residual nickel content. The alloys 2, 3, 5 and 6 fall under the invention, while the niobium-free alloy 1 and the alloys 4 and 7, each containing Ii * niobium, are outside the invention.

909851/0839

For writing dated ... 1 & *. July 19.6.6 .. to ~ ... -.gOhronuNi oVel ^ Itagiexuiig ^ sheet 3 «..

Nb Mon
(Ji) 4.72 k "/ mm ² Tabel Service life
(Hours) - 900 ⁰ C Notched bottom • O 0 Service life
(Hours) ! I. 167 strain toughness
(kgm / cm) Legie
tion 3 0 - - Creep test
- 900 ⁰ C 3.15 kg / mm ² - 1 5 0 151 strain 2063 4.15 2 7th 0 492 _ - 26th 1.90 3 2.5 2.5 98 18th 2145 - - 4th 5 2.5 - 23 ^ 1063 * 30th 3.46 ι 5 7th 2.5 654 51 - > 0.7 1.04 6th 86 mm - - 7th 27 23

* m The experiment was canceled because of the very low creep speed.

The carbon is of great importance in the alloys according to the invention, since it is an important shell plays in the control of curing and solidification. Increased with an increase in the carbon content above 0.2ji the service life is extraordinarily strong, while at the same time the notch toughness drops and in the case of carbon held by over 0.53 * is insufficient. This gives can be clearly seen from the results of the pollutants in Table II, which are based on alloys with different carbon, niobium and molybdenum content, each with 30 # chromium content, the remainder niobium relate. Alloys 2, 3, 5 and 6 according to the invention were for the purpose of comparison with those not included in the Invention falling alloys 8 to 12 are listed, the carbon of which is either too high or too low.

909851/0839

For the letter from ..1.8. * ..._ J.U11 ..-. 1.9.6..6 .. to ".i! JahresOm ^ Nickßl-- _: Jiegl.er.ung." Bian

C. Nb Mc Table II Creep test 3.15 kg / mm ^{2-900 0} C I. (*) W. - 900 ⁰ C Service life strain Carving 0.2 2.9 4.72 kg / mm ² strain (Hours) tenacity o Legie 0.4 3.0 Service life - _ (kgm / om) tion 0.2 5.1 (Hours) 32 - 5.89 8th 0.4 5 (*) 95 18th - - 4.15 2 0.6 5 0 151 31 - - 2.42 9 0.2 3.0 0 131 23 - - 1.90 3 0.4 2.5 0 492 41 61 48 - 0 0.2 5.1 0 95 - 2145 30th 6.40 '11 0.4 5 0 - - - - 3.46 5 2, - 26th - - - - 12th 2, 92 27 .1.04 6th 2, 654 2, , 7 , 5 ,8th , 5

In order to ensure the advantageous strengthening by niobium and carbon, the contents of chromium and Molybdenum can be matched to one another. Chromium contributes Creep rupture strength of the alloys, so that in the absence of molybdenum the alloys contain at least 24 $ chromium should. In addition, chromium also promotes corrosion resistance, so that in terms of the best possible Corrosion resistance the chromium content should be relatively high, i.e. at least 28 #. On the other hand, falls with increasing chromium content, the notched impact strength of the alloys decreases, so that in view of the best possible notch impact strength it is important to keep the chromium content below 25 # to keep. Alloys with a high chromium content are also difficult to deform and if the chromium content exceeds 33 # no longer forgeable.

909851/0839

COPY

... IB. «July. 19 6.6 .. to ".GliE.Qm-Ni.QJtsl-I.figi.e.rung.". _ Sheet ... SL ...

However, it was surprisingly found that that molybdenum, although the creep rupture strength is niob-free alloys not improved, in niobhal fig alloys according to the invention is very effective. If the chromium content is below 24 # i, the alloys must contain molybdenum, so that regardless of the chromium content, the molybdenum content is preferably at least 1ji. Supplement chromium and molybdenum in their effect, so that with increasing chromium content the required for a certain creep strength increases Molybdenum content correspondingly reduced Too high molybdenum content, however, leads to a decrease in the creep rupture strength, thus the maximum content falls as the chromium content increases, in accordance with the equation

JiMo «3.5 + 0.5 (30 - JiCr),

until the maximum content of molybdenum is 3.5 # for chromium contents of 30fi and more. Optimal creep strength results when the chromium and molybdenum contents are matched to one another in accordance with the following equation:

JiMo - 3.5 + 0.4 (30 - JiCr).

The change in the creep rupture strength and notch bottom toughness in the case of changing chromium and molybdenum contents results from the table III Test results that look at alloys with 0.4ji carbon relate. A comparison of alloys 1 and 14, both of which do not come under the invention, shows the efficiency

90985I / 083 0 · CO? V

For writing of ... IS .. July 196.6 ... to. !!. GlirflmrllXGlceL ^ IifigisrUllg ". Leaf ... Ar.

AO

the absence of molybdenum in the absence of niobium. However, alloys 3, 6, 15 and 17-20 show the effect of increasing molybdenum contents with chromium contents of 3096 and 20 # o The last-mentioned alloys are also included With the exception of alloy 15, which, in view of its chromium content of 3096, contained too much molybdenum, and the alloy 17, which only contained $ 20 chromium and no molybdenum, among those Invention. Each of these alloys had poor temporal strength. The effect of different chromium contents alone results from a comparison of alloys 3, 16 and 17.

Table-III

Cr Man Mon 4.72 kg / mi Creep test 3.15 Wmm ² - 900 ⁰ C Notched bar (#) (*) Service life α ² - 900 ⁰ C Service life strain toughness p energy 30th 0 0 (Hours) strain (Hours) (kgm / om) xng 30th 0 4-, 9 - 167 - 1 30th 5 0 - 118 24 3.29 30th 5 2.5 492 • 2063 26th 1.90 3 30th 5 5 654 22nd - - - 6th 25th 5 0 105 27 - - - 5 20th 5 0 431 - - - 5.19 6th 20th 5 2.5 103 38 - - 9.70 7th 20th 5 5 - 41 - - 7.96 8th 20th 5 7.5 675 - - 5.02 9 743 30th - - 2.60 O 26th

From Table III it can be seen that alloy 6 has the best creep rupture strength, so that the invention

909851/083 9

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appropriate alloy preferably 28 to 32 ° C chromium, 4 »5 to 5.55 * ITiob, 2 to 3 * molybdenum, 0.35 to 0.45 # carbon, Has nickel in it. A very beneficial combination of Corrosion resistance and creep rupture strength have alloys with 24 to 33 # chromium, 2 to 6) ί niobium, 1 to 3.5 # Molybdenum, 0.3-0.5 # carbon, the remainder nickel.

In order to form a niobium-rich strengthening phase, it is essential that the alloy contain both niobium and carbon. Probably the good creep strength of the alloys according to the invention results at 90O ⁰ C and more from the presence of Miobkarbid (NbC) in a finely dispersed form with or without Nickelniobid (Ni, Nb) ₀ Frequently, the phase Cr ₂₅ Cg before, which also with the The niobium-rich phase can cooperate in strengthening the alloys, although this phase alone is not very effective at high temperatures. The importance of the presence of a niobium-rich phase emerges from the test results of Table IV, in which the alloys 21, 22 and 14, which are niobium-free and therefore do not come under the invention, are _{hardened by Cr 2} -Cg alone and in comparison to that Alloy according to the invention 3 • have a relatively low long-term strength. All of the alloys in Table IV contained 30% chromium and 0.43% carbon.

909851/0839 'COPY

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Table IV Zeitstandyersueh

3.15 kg / mm ² ~ 9OQ ⁰ O alloy Nb Mo W tool life, elongation, precipitation phases (#) (#) (#) (hours) (#)

0 0 2063 26 NbO, Ni, Nb

^Cr 23 ° 6 ⁵

21 O O 5 b , 0 187 38 Cr ₂₅ C ₆ 22nd O 2, 9 2 , 5 479 10 ^Or 23 ° 6 14th O 4, O 118 24 ^Cr 23 ° 6

Are solidified in Gregeneatz to the legieningeni the intermctellisohe by titanium- and aluminum-containing phases, which is de Zeitstandfestiglreit: erfindUiigsgemäßen alloys duroh the addition of boron or zirconium did not improve, but these elements may also gersber.eiifalls in contents of up to 0.01 boron and # / or o _f i $ zirioidum, "for example 0.0059 ^ boron and 0.03 # zirconium are present. Nevertheless, such additions impair the weldability of the alloys, so that with sheet metal or other welding materials the alloys are preferably free of boron and zirconium.

In the alloys according to the invention, the tungsten is not an equivalent of the molybdenum, so that a tungsten additive no positive effects and often both with regard to the creep strength and also with regard to the notched impact strength is harmful. This can be seen from Table V, in which alloy 3 according to the invention, apart from the 2.6 # WoIf-

909851/0839

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ram, identical alloy, and alloy 6, which contains 2.5 # molybdenum, is compared. From the experimental values shows that the tool life and notch toughness is greatly reduced by tungsten, bo that the alloys according to the invention contain no tungsten.

! Table Y
Creep failure

Nb
(#) Mon
(*) W.
(#) 4.72 k «/ mm ² - 90O ⁰ O Carving
toughness p
(kgm / om) Legie
tion 5 - Q Service life
(Hours) strain 1.90 3 5.1 - 2.6 492 23 1.04 23 5 2.5 - 50 40 1.04 6th 654 27

In addition, it was found that tantalum is also no equivalent in the alloys according to the invention of niobium is and the replacement of part of niobium by the same atomic percentage of tantalum reduces the creep rupture strength to an extraordinary degree · This is evident from the test results of Table VI, in which alloy 6 is compared to an alloy of the same type however, the 2.5J * Kiob were replaced by 59 * Tantalum. .

909851/0839

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153329 '

Nb
W) !Tabel VI ) 00 ° C 5
2.5 mung *
Time trial 27
34 Legie
tion ¹ Sat week
W) W) 4.72 k "/ mm ² - J 6th
24 - 2.5
5 2.5 Service life De:
(Hours) ( 654
78

Me alloys according to the invention should be more contain no tantalum, although it is an impurity in the amount usually found in commercial niobium Bind, that is to say, niobium weighed in amounts of up to about 10 $ fl <& i » can.

Both SijTfiii and Kc "bait impair the lateral stability of the alloy. Ä / ia deeper reasons the maximum contents of BiBeE" Dai 3 ^ iind for JZo calt should be 25 ^, or the alloys iron - and be cobalt-free. Silicon has a negative impact on the weldability of the alloys. For this reason, the silicon content is no more than Q}) fi , while alloys where good weldability is not important, silicon up to 0 _t 5? F or auoh Vf * baw. May contain £ 2. Ale pollution can? uoh up to 1? ί manganese are present.

With a view to facilitating hot working, the alloys according to the invention should be low

909851/08 3 9

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J €

Residual levels of magnesium or calcium, for example up to 0.0353 * included. Such levels are generally after deoxidation with the elements in question following air melting, but it is also present in vacuum melting it is advantageous to add magnesium or calcium to the alloy before casting.

The good corrosion resistance of an alloy according to the invention results from an experiment in which a test piece of alloy 3 was immersed up to halfway in a bath of a mixture of 25% sodium chloride and 75 ^{% sodium sulfate at 90O 0 C for sixteen hours.} The weight loss of the sample was only 14 mg / cm.

The advantageous properties of the alloys according to the invention make possible their use at high, d.ho 900 ⁰ C for rising temperatures in the form of sheets and sheets of manufactured articles. However, the alloys according to the invention are also suitable as material for objects for which both high strength and good corrosion resistance at high temperatures are required, i.e. for example for parts of heat treatment furnaces, furnace belts, for example wire ties, troughs for holding objects during heat treatment and the like.

909851/0839

Claims (5)

International Nickel Limited, Thames House, Milltank, 3a == S8SaSB3BS33aB3> aMSSSS = 3a3 = 3S3S = S = a3SSS33am London, S.W. 1, England Claims; 1, chromium-nickel alloy with 2 to 6% niobium, 0.3 to 0.5% carbon, 19 to 33% chromium, with chromium contents below 24% a molybdenum content of at least «/" 5/8 (24 -% Cr) _7% and with chromium contents of at most »30% from 0 to / "3t5 + 0.5 (30 -% Cr) J7% as well as with chromium contents of over 30% 0 to 3.53 * molybdenum, 0 to 0.01Ji boron and 0 to 0.1% Zirconium, the remainder including impurities caused by the fusion process Niokel. 2. Alloy according to claim 1 with 24 to 33% chromium, 2 to 6% Job, 1 to 3.5% molybdenum and 0.3 to 0.5% carbon, Remainder including impurities caused by the melting Hiekel. 3 · Alloy according to claims 1 and 2, characterized by at least 3 * 5% niobium. 4 · Alloy according to claims 1 to 3 _t characterized by at least 28% chromium. 5. Alloy according to claims 1 to 4 with 28 to 32% chromium, 909851/0839 Sheet _ .. <fcfer ... 4.5 to 5.596 niobium, 2 to 39 * molybdenum, 0.35 to 0.453 * coals substance, remainder including impurities caused by fusion Nickel. 909851/0839