DE2027656A1 - Nickel Chromium Iron Alloy - Google Patents

Description

2027656 Dipl.-Ing. H. Sauerland · Dn.-lng. R. King

Patent Attorneys ■ Aoao Düsseldorf · Cecilienallee 7S -Telephone 43 2732

Our files; 25 843 June 3, 1970

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International Nickel Limited, Thames House, Millbank, London, S. W. 1, Great Britain

"Nickel-Chromium-Iron Alloy"

The invention relates to high-temperature nickel-chromium-iron alloys, especially a carbide-strengthened nickel-chromium-iron alloy.

Various processes, for example the reforming of hydrocarbons, take place at temperatures of 1000 ° and more; they require systems made of alloys that have sufficient strength and corrosion resistance at these temperatures. Alloys suitable for this purpose should have good casting properties and, in particular, should be capable of being cast in air so that the parts of the apparatus can be cast and they should also be weldable. During reforming, the hydrocarbons react with water vapor in the presence of a catalyst, forming a mixed gas of hydrogen and carbon monoxide, which is widely used under the name of synthesis gas to produce alcohol and as a hydrogen supplier in ammonia synthesis. The reforming takes place at high temperatures of, for example, 800 to 1000 ^° C

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under high pressure in so-called Reformierrohjreji from the outside by way of the incineration of fuel-containing fuels heated: turn.

Suitable materials for reforming pipes must therefore have a high level of resistance to smell and strength under high stress at high temperatures, and must retain adequate toughness even with prolonged exposure to heat. A suitable alloy must be able to withstand relatively low creep stress for a period of 10,000 hours or more. It is particularly important that the leadership in a given time for breaking load with increasing service life not z / u, falls rapidly. Finally, the alloy must be resistant to decarburization and corrosion by the exhaust gases of impure fuels, in particular to sulphurisation.

So far, reforming tubes were usually after Centrifugal casting using a steel with 25% chromium and 20% nickel. Most recently In time, an alloy, referred to below as A, made of 0.5% carbon, 26% chromium, 35% nickel, 5% tungsten and 5% cobalt, the remainder iron used. Higher In long-term tests, some showed creep strengths containing little or no iron Nickel alloys, however, due to their high Nickel content and the fact that the chromium and other alloying elements are not in the form of cheap Ferro alloys or also as nickel-chromium-Schwtt can be introduced are very expensive.

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The object on which the invention is based thus exists therein, an inexpensive alloy with higher creep rupture strength and adequate corrosion resistance to accomplish. These requirements are met by an alloy which, according to the invention, consists of 24 to 3196 chromium, 50 to 40% nickel, 10 to 27% cobalt with a total nickel and cobalt content of at least 45%, 3 to 7% tungsten, 0.3 to 0.7% carbon, 0.4 to 3% niobium and 0 to 1% zirconium, the remainder including smelting " pollution caused by pollution at least 12.5% iron consists.

In view of the advantageous technological properties, it is important to keep the individual alloy components within the aforementioned content limits to keep.

The high heat resistance of the alloy according to the invention is largely due to the presence of insoluble carbides, which is why carbon is an essential alloy component and the alloy contains g at least 0.3% _t but preferably at least 0.4% carbon. However, the carbon content should not exceed 0.7%, since higher carbon contents impair the weldability and notched impact strength.

With regard to the resistance to carburization and corrosion by the combustion gases, the alloy according to the invention must contain at least 24%, but advantageously at least 25% chromium. However, the chromium content must not exceed 31% and should preferably not exceed 28% in order to avoid embrittlement and to ensure good '

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Maintain weldability.

Nickel contributes to structural stability, strength and resistance to carburization at, which is why the nickel content is at least 30%, preferably at least 33%.

Cobalt also contributes to the creep rupture strength of the invention Alloy at its content is at least 10%, preferably at least 12.5%.

The upper limit for the total content of nickel and cobalt is primarily determined by the requirement to introduce as much iron as possible into the alloy in order to reduce its manufacturing costs as much as possible to keep it low. Accordingly, the nickel content must not exceed 40% and is preferably not more than 38%, while the cobalt content does not exceed 27% may and preferably does not exceed 20%. However, the creep rupture strength of the alloy falls with a nickel content exceeding about 35%, so that with regard to the highest creep strength a nickel content of 34 to 35% is preferable. The cobalt content is preferably 13 to 20%.

Tungsten is indispensable for a high creep rupture strength, so that the tungsten content is at least 3% and preferably at least 4%. Tungsten contents above 7% lead, apart from the result related cost increase, to structural instability, embrittlement and impairment of durability against oxidation and sulphurisation. The maximum salary for tungsten is therefore preferably 6%.

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Niobium is the most important additional element because it in long-term tests compared to similar, niobium-free alloys, the creep strength of the alloy is greatly increased. This is the case, for example from the diagram of FIG. 1, in which on a logarithmic scale the creep strength against the load is plotted for a number of alloys. Curve A refers to the one at the beginning mentioned niobium-free alloy A, while the curves "

B, C ₁ D and E refer to alloys according to the invention with 0.7%, 1%, 2% and 3% niobium with a basic composition of 26% chromium, 35% nickel, 15% cobalt, 5% tungsten and 0.5% carbon , Remainder iron. The advantageous effect of the mob is extremely surprising in that it has been shown that the niobium-containing alloys are significantly worse than the niobium-free alloys under conditions in which breakage occurs very quickly.

In order to achieve this favorable behavior, which occurs only after long-term exposure, the alloy according to the invention contains at least 0.4%, preferably at least 0.7% and, with particular advantage, at least 0.8% niobium. With increasing niobium content, however, the oxidation and / or sulphurization resistance of the alloy at high temperatures can be impaired, so that the niobium content does not exceed 3%, preferably 2%. ·

In addition to the elements mentioned, the alloy can contain up to 1 /) "zirconium, preferably 0.01 to 0.5% zirconium. Finally, HIe contains" at least

ΊΟ-'ί- / -If. 9 2 BAD ORLANAL

12y5%, preferably at least 15% iron, to the various To be able to introduce alloy components as ferro alloys.

The impurities of the alloy are manganese and nitrogen ,, The alloy can ■ although containing up to 2% silicon, but the silicon leads zn impaired Aufschweflungsbeständigkeitj the creep rupture strength and Gefügestafoilitätj, so that under prolonged exposure to heat is a risk of Yersprödung ₀ The silicon content exceeds therefore preferably not 1% and is advantageously at 0.13 to 0.17% <> manganese content up to 1% and Ge. hold on to nitrogen, which is introduced when melting under air, up to O ₉ 15% are sulässig®

The alloy can also contain tantalum due to the use of tantalum-containing scrap or a tantalum-containing niobium master alloy. However, the tantalum content should not be more than 10% of the niobium content ₀

Various impurities may ^ be entered containing scrap for example, titanium _D aluminum ₉ molybdenum or boron "by a chromium alloys Hickel-However, the contents of titanium and aluminum may be a total of 2% and should _s not exceed 5% preferably 0, since they _p although Titanium and aluminum increase elongation, react easily with oxygen and nitrogen and form non-metallic inclusions, which disadvantageously contaminate the cast structure. However, titanium, aluminum and zirconium can be used as deoxidizing agents

Tüi; . · ■ · /! η 02 BATH ORIGINAL

However, it should not exceed 0.5%. That too Boron present as an impurity can lead to oxide inclusions and the formation of low-melting phases lead, which is why the boron content is preferably 0 ,. 196 does not exceed.

Molybdenum impairs the resistance to oxidation and sulphurisation at high temperatures. It should therefore be present only λ as an impurity in amounts up to 296, provided that the total content of tungsten and twice the molybdenum content does not exceed 7%. However, the molybdenum content advantageously does not exceed 1%.

An alloy that contains 25 to 28% chromium, 33 to 38% nickel, 13 to 20% Cobalt, 4 to 6% tungsten, 0.4 to 0.6% carbon and 0.7 to 2% niobium, the remainder including melt-related Contains at least 15% iron.

"Furthermore, its technological f

Properties of an alloy according to the invention consisting of 25 to 27% chromium, 34 to 36% nickel, 14 to 16% cobalt, 4 to 5.5% tungsten, 0.4 to 0.55% carbon and 0.7 to 1.3 % Niobium, the remainder with the exception of the impurities caused by the melting, for example up to 1% manganese and at most 0.7%, preferably 0.3 to 0 _f 5% silicon, iron.

IM the invention on the basis of exemplary embodiments • explain were in a basic high frequency induction furnace The alloys listed in Table I are made from virgin raw materials

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melted, the melts of 0.2 to 0.5% manganese, 0.1 to 0.3% silicon and 0.02 to 0.05% calcium were added as a calcium silicide for deoxidation. The melts were cast at 1500 ⁰ C in the steel mold into billets, from which samples for creep and impact tests were identified. In the tests, the service life of the alloys was determined at 1000 C and a load of 1.8 to 2.1 kp / mm. Moreover, the notched impact strength as cast were the one hand and on the other hand is determined according to a 1000-hour calcination at 800 ⁰ C. Table I summarizes the alloy compositions and the test results including published data for conventional alloy A. The data in Table I clearly show the increase in the creep rupture strength with increasing niobium content up to 3% and the advantages of an increasing cobalt content.

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C. Cr Ki Fe (#) Table I. Co Nb Bela p kp / mm Time to stand firm 000 ⁰ C) Notched impact 1000h / ■ ro 4.5 stung 2.1 ability (1 Deh toughness kpm 800 ° C I. O (5ό) (%) (%) 00 bo 00 1.8. was standing tion GuB to D. Legie 0.52 25.7 34.5 rest 4.7 5.3 0.58 2.1 Time was standing 0.4 I. cn tion 1.8 (H) 20th CO 0.53 25.6 34.3 ti 4.9 5.2 1.0 2.1 47 41 0.4 0.4 1.8 84 33 1 0.50 25.4 34.3 » 4.7 5.2 2.0 2.1 29 25th 0.5 0.5 1.8 96 29 2 0.50 '- ?. »' - 34.3 It 4.5 5.2 2.8 2.1 21st 20th 0.6 0.4 1.8 135 35 0.54 26.0 34.2 ti 4.5 10.2 0.6 2.1 44 28 0.5 0.4 1.8 76 39 £ ■ 4 0.54 26.0 34.2 It 4.7 10.2 0.9 2.1 66 29 0.5 0.4 ^v ο 1.8 124 27 II 5 0.50 25.5 34.2 η 4.8 10.1 2.0 2.1 53 30th 0.5 0.4 ■ • ο 1.8 236 27 ^ 6 0.49 25.3 34.7 ti 4.5 10.3 2.6 2.1 42 20th 0.4 0.4 - * 1.8 210 25th CD "7 0.54 26.0 34.0 It 4.5 14.8 0.75 2.1 62 21st 0.6 0.4. to 1.8 153 19th ^ * S 0.52 25.5 34.0 ti 4.7 14.7 1.0 2.1 169 18th 0.7 0.5 1.8 415 27 9 0.50 25.5 34.8 η 4.8 15.0 1.9 2.1 58 23 0.7 0.5 1.8 466 29 10 0.50 25.1 34.5 η 5 14.9 2.8 2.1 77 —_ 0.6 0.5 1.8 465 24 11 0.5 25th 35 ti 15th , ι., 113 20th 0.7 635 12th 80 165

The advantageous effect of niobium on the service life without impairing the tensile elongation and notched impact strength in the as-cast state at room temperature can be seen in the results of further requests ₅ in which three centrifugally cast pipes with a stripping knife of 127 em and a wall thickness of 25 mm were examined "The three melts were deoxidized by adding 0.05% calcium in the form of calcium silicide and, with the exception of the carbon, niobium and zirconium contents shown in Table II, contained 35% nickel, 15% cobalt, 26% chromium and -5% tungsten, Remainder iron. The creep strengths, the elongation and the necking as well as the notched impact strengths of the three aforementioned alloys are shown in Table II below.

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Table II

'- ■ - ■■

Creep strength tensile test (20 C) notch

Ξ ¹ SSJ "" (1.8 kpM ² - 1000 ⁰ C) impact.

O tion η m. W- ,, ι r- ^ diixg—

co ^u " ^{μ ΛΧ Service} life Elongation Elongation (5.65 V'A) Constriction

13 0.52

sj 14 0.49 1.1

15 0.47 1.0 0.23

141 32 11.0 868 17th 10.7 544 21st 9.6

9.0 0.7 12.0 0.6 11.0 0.8

The alloy 14 had at 1OOO ° G and a load of 2.1 kgf / mm with an elongation of 20%, a service life of 295 hours and at 100O ⁰ C and a BeIastung of 1.6 kgf / mm an elongation of 12% and a service life of 1215 hours.

The calcium can also act as a deoxidizer through magnesium, for example through the addition of 0.04 to 0.06% magnesium can be replaced.

The alloy according to the invention is also suitable as a casting material for the production of reforming tubes and other parts of reforming plants advantageously also as a cast or wrought alloy for objects that are exposed to high stress and corrosion at high temperatures.

Parts made from the alloy of the invention can advantageously be subjected to stress-free annealing after welding.

In order to demonstrate the good corrosion resistance of the alloy according to the invention in comparison to the conventional alloy A, sulphurisation tests were carried out at various temperatures in a .75% Na ₂ SO ^ and. Salt bath containing 25% NaCl with the results compiled in Table III below. _; carried out. .-. r ^ · -

Tabel 111 4.2
456 240
442 alloy 14th
A- 1OSH1 // 1 Weight loss (mg / cm ² )
90O ⁰ C 1000OC 09?

Claims (6)

Patent claims: 1. Nickel-chromium-iron alloy, consisting of 0.3 to 0.7% carbon, 0.4 to 3% niobium, 3 to 7% Tungsten, 24 to 31% chromium, 30 to 40% nickel, 10 to 27% cobalt with a total hardness of nickel and cobalt of at least 45%, up to 1% Zirconium, the remainder including impurities from the smelting process, at least 12.5% iron. 2. Alloy according to claim 1, but which is 0.4 to 0.6% carbon, 0.7 to 2% niobium, 4 to 6% tungsten, 13 to 20% cobalt, 25 to 28% chromium and 33 to Contains 38% nickel. ' 3. Alloy according to claim 2, which, however, additionally | still contains 0.01 to 0.5% zirconium. 4. Alloy according to claim 1, but containing 0.4 to 0.55% carbon, 0.7 to 1.3% niobium, 4 to 5.5% Tungsten, 14 to 16% cobalt, 25 to 27% chromium and contains 34 to 36% nickel. 5. Use of an alloy according to one of the claims 1 to 4 as a material for cast and kneaded objects that have a high creep 1 0 9 S l 'ν / 1 ο 9 2 strength and corrosion resistance at high Must have temperatures » 6. Use of an alloy according to one of the claims 1 to 4 as a material for objects that, like reforming tubes, have a high creep rupture strength, Creep resistance and corrosion resistance at high temperatures as well as good Must have weldability, ■ ti ' 109812/1092