Nickel chromium alloy

Abstract

A nickel chromium alloy comprising 0.4 to 0.6% carbon, 28 to 33% chromium, 15 to 25% iron, 2 to 6% aluminum, up to 2% silicon, up to 2% manganese, up to 1.5% niobium, up to 1.5% tantalum, up to 1.0% tungsten, up to 1.0% titanium, up to 1.0% zirconium, up to 0.5% yttrium, up to 0.1% nitrogen, and nickel, has a high oxidation and carburization stability, long-term rupture strength and creep resistance. This alloy is particularly suited as a material for components of petrochemical plants and for parts, for example tube coils of cracker and reformer furnaces, pre-heaters, and reformer tubes, as well as for use for parts of iron ore direct reduction plants.

Claims

1. A nickel-chromium alloy, comprising: 0.4 to 0.6% carbon by weight, 28 to 33% chromium by weight, 17 to 22% iron by weight, 3 to 4.5% aluminum by weight, 0.01 to 1% silicon by weight, 0.01 to 2% manganese by weight, 0.01 to 1.0% niobium by weight, 0.01 to 0.6% tungsten by weight, 0.001 to 0.5% titanium by weight, 0.001 to 0.3% zirconium by weight, 0.001 to 0.3% yttrium by weight, and 0.001 to 0.1% nitrogen by weight, remainder nickel with melt-induced impurities.

2. The alloy of claim 1, said alloy further comprising: 0.01 to 0.5% molybdenum by weight.

3. The alloy of claim 2, said alloy further comprising: 0.01 to 0.5% tantalum by weight.

4. The alloy of claim 1, wherein said alloy comprises 0.01 to 0.5% manganese by weight.

5. The alloy of claim 1, wherein said alloy comprises 0.06 to 0.11% zirconium by weight.

6. The alloy of claim 5, said alloy further comprising: 0.01 to 0.06% cobalt by weight.

7. A nickel-chromium alloy, comprising: 0.4 to 0.6% carbon by weight, 28 to 33% chromium by weight, 17 to 22% iron by weight, 3 to 4.5% aluminum by weight, 0.01 to 1% silicon by weight, 0.01 to 2% manganese by weight, 0.01 to 1.0% niobium by weight, 0.01 to 0.5% molybdenum by weight, 0.001 to 0.5% titanium by weight, 0.001 to 0.3% zirconium by weight, 0.001 to 0.3% yttrium by weight, and 0.001 to 0.1% nitrogen by weight, remainder nickel with melt-induced impurities.

8. The alloy of claim 7, said alloy further comprising: 0.01 to 0.5% tantalum by weight.

9. The alloy of claim 7, wherein said alloy comprises 0.01 to 0.5% manganese by weight.

10. The alloy of claim 7, said alloy further comprising: 0.01 to 1.5% tantalum by weight, and 0.01 to 1.0% tungsten by weight.

11. The alloy of claim 7, said alloy further comprising: 0.01 to 1.0% tungsten by weight, and 0.06 to 0.11% zirconium by weight.

12. The alloy of claim 11, said alloy further comprising: 0.01 to 0.06% cobalt by weight.

13. A nickel-chromium alloy, comprising: 0.4 to 0.6% carbon by weight, 28 to 33% chromium by weight, 17 to 22% iron by weight, 3 to 4.5% aluminum by weight, 0.01 to 1% silicon by weight, 0.01 to 2% manganese by weight, 0.01 to 1.0% niobium by weight, 0.01 to 0.5% tantalum by weight, 0.001 to 0.5% titanium by weight, 0.001 to 0.3% zirconium by weight, 0.001 to 0.3% yttrium by weight, and 0.001 to 0.1% nitrogen by weight, remainder nickel with melt-induced impurities.

14. The alloy of claim 13, said alloy further comprising: 0.01 to 0.6% tungsten by weight.

15. The alloy of claim 13, wherein said alloy comprises 0.01 to 0.5% manganese by weight.

16. The alloy of claim 13, said alloy further comprising: 0.01 to 1.0% tungsten by weight.

17. The alloy of claim 13, said alloy further comprising: 0.01 to 1.0% tungsten by weight, and 0.06 to 0.11% zirconium by weight.

18. The alloy of claim 17, said alloy further comprising: 0.01 to 0.06% cobalt by weight.

19. A nickel-chromium alloy, comprising: 0.4 to 0.6% carbon by weight, 28 to 33% chromium by weight, 17 to 22% iron by weight, 3 to 4.5% aluminum by weight, 0.01 to 1% silicon by weight, 0.01 to 2% manganese by weight, 0.01 to 1.0% niobium by weight, 0.001 to 0.5% titanium by weight, 0.001 to 0.3% zirconium by weight, 0.001 to 0.3% yttrium by weight, 0.001 to 0.1% nitrogen by weight, and nickel with melt-induced impurities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows weight change of various alloys as a function of the number of annealing cycles according to the present invention.

(2) FIG. 2 shows weight gains of various alloys after carburizing treatment.

(3) FIGS. 3a and 3b show long-term rupture strength of various alloys as a function of service life.

(4) FIG. 4 shows a comparison of creep resistance of various alloys.

(5) FIGS. 5 and 6 show surface micrographs with and without conditioning according to the invention.

(6) FIGS. 7 and 8 show metallographic cross-sections of surface regions.

(7) FIGS. 9 and 10 show aluminum concentration as a function of depth following various processing steps.

(8) FIG. 11 shows an REM top view of the conventional sample.

(9) FIG. 12 shows in a metallographic cross-section a continuous aluminum-containing oxide layer after three cracking cycles.

(10) FIG. 13 shows in a metallographic cross-section a uniform aluminum-containing oxide layer protecting the material.

(11) FIGS. 14 and 15 show micrographs of a near-surface zone.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(12) As shown in the diagram of FIG. 1, the alloy 9 according to the invention does not exhibit any interior oxidation even after more than 200 cycles of 45-minute annealing at 1150 C. in air, whereas the two comparison alloys 12 and 13 already undergo an increasing weight loss due to the catastrophic oxidation after only a few cycles.

(13) The alloy 9 is also distinguished by a high carburizing stability; because the alloy 9 has, due to its small weight gain, after all three carburizing treatments according to the diagram of FIG. 2 the smallest weight gain compared to the conventional alloys 12 and 13.

(14) Moreover, the diagrams of FIGS. 3a and 3b show that the long-term rupture strength of the nickel alloy 11 according to the invention is in an important range still superior over that of the comparison alloys 12 and 13. The alloy 15, which is not part of the invention because its iron content is too low, is an exception, having significantly inferior oxidizing, carburizing and coking stability.

(15) The diagram of FIG. 4 finally shows that the creep resistance of the alloy 11 is significantly better than that of the comparison alloy 12.

(16) In addition, in a series of simulations of a cracking operation, several tube sections made of a nickel alloy according to the invention where inserted in a laboratory system to perform heat-up experiments under different gas atmospheres and different heat-up conditions, followed by a 30-minute cracking phase at a temperature of 900 C., in order to investigate and evaluate the initial phase of catalytic coking, or the tendency for catalytic coking.

(17) The data and the results of these experiments with samples of the alloy 11 from Table I are summarized in Table II. They show that the respective gas atmosphere in conjunction with temperature control according to the invention is associated with a significant reduction of the already low catalytic coking.

(18) Examples of the surface properties of the tube interior of furnace tubes having the composition of the alloy 8, which is part of the invention, can be seen from FIGS. 5 and 6. FIG. 6 (Experiment 7 in Table II) shows the superiority of the surface after conditioning according to the invention compared to FIG. 5 which relates to a surface that was not conditioned according to the invention (Table II, Experiment 2).

(19) In the FIGS. 7 (alloy 14) and 8 (invention), regions near the surface are shown in a metallographic cross-section. The samples were heated to 950 C. and then subjected to 10 cracking cycles of 10 hours each in an atmosphere of water vapor, hydrogen and hydrocarbons. After each cycle, the sample tubes were burned out for one hour to remove the coke deposits. The micrograph of FIG. 7 shows in form of dark regions the large-area and hence also large-volume result of an interior oxidation on the interior tube side with a conventional nickel chromium cast alloy as compared to the micrograph of the FIG. 8 of the alloy 9 according to the invention, which virtually did not experience any interior oxidation, although both samples with subjected in an identical manner to multiple cyclical treatments of cracking, on one hand, and removal of the carbon deposits, on the other hand.

(20) The experiments show that samples from conventional alloys experience strong interior oxidation on the interior tube side, originating from surface defects. As a result, small metallic centers with a high nickel content are produced on the interior tube surface, on which a significant amount of carbon in form of carbon nanotubes is formed (FIG. 11).

(21) Conversely, Sample 9 from an alloy according to the invention does not exhibit any nanotubes following the same 10-fold cyclical cracking and thereafter storage in a coking atmosphere, which is the result of an essentially continuous sealed, catalytically inert aluminum-containing oxide layer. Conversely, FIG. 11 shows an REM top view of the conventional sample shown in FIG. 7 in a polished section; catastrophic oxidation and therefore catastrophic generation of catalytic coke in the form of carbon nanotubes is here observed due to the missing protective layer.

(22) In a comparison of the diagrams of FIGS. 9 and 10, the stability of the oxide layer on an alloy according to the invention is particularly clearly demonstrated by the shape of the aluminum concentration as a function of depth of the marginal zone following ten cracking phases accompanied by an intermediate phase where the coke deposits were removed by burning out. Whereas according to the diagram of FIG. 9 the material is depleted of aluminum in the region near the surface due to the local failure of the protective cover layer and subsequently strong interior aluminum oxidation, the aluminum concentration in the diagram of FIG. 10 is still approximately at the initial level of the cast material. This shows clearly the significance of a continuous, sealed and in particular firmly adhering interior aluminum-containing oxide layer in the tubes according to the invention.

(23) The stability of the aluminum-containing oxide layer was also investigated in extended time tests in a laboratory system under process-like conditions. The samples of the alloys 9 and 11 according to the invention were heated in water vapor to 950 C. and then each subjected three times to 72-hour cracking at this temperature; they were then each burned out for four hours at 900 C. FIG. 12 shows the continuous aluminum-containing oxide layer after the three cracking cycles and in addition, how the aluminum-containing oxide layer covers the material even across chromium carbides in the surface. It can be seen that chromium carbides residing at the surface are completely covered by the aluminum-containing oxide layer.

(24) As clearly shown in the micrograph of FIG. 13, the material is protected by a uniform aluminum-containing oxide layer even in disturbed surface regions, where primary carbides of the basic material have accumulated and which are therefore particularly susceptible to interior oxidation. As can be seen, oxidized former MC-carbide is overgrown by aluminum-containing oxide and hence encapsulated.

(25) FIGS. 14 and 15 show in the micrographs of the zone near the surface that interior oxidation has not occurred even after the extended cyclic time tests, which is a result of the stable and continuous aluminum-containing oxide layer.

(26) Samples of the alloys 8 to 11 according to the invention were used in these experiments.

(27) Overall, the nickel chromium iron alloy according to the invention, for example as a tube material, is differentiated by a high oxidation and corrosion stability, and more particularly by a high long-term rupture strength and creep resistance, after the interior surface is removed under mechanical pressure and a subsequent multi-step in situ heat treatment for conditioning the interior surface.

(28) In particular, the outstanding carburizing stability of the material should be mentioned, which is caused by rapid formation of a substantially closed and stable oxide layer or Al.sub.2O.sub.3-layer, respectively. This layer also substantially suppresses in steam-cracker and reformer tubes the generation of catalytically active centers accompanied by risk of catalytic coking. These material properties are still retained even after large number of significantly prolonged cracking cycles, in conjunction with burning out the deposited coke.

(29) TABLE-US-00001 TABLE I (Weight %) Alloy C Si Mn P S Cr Mo Ni Fe W Co Nb Al Ti Hf Zr Y Ta Ce 1 0.44 0.30 0.02 0.002 0.003 29.50 0.20 46.90 18.20 0.07 0.40 0.68 3.05 0.15 0.15 0.06 2 0.44 0.30 0.02 0.002 0.003 29.60 0.15 46.75 17.90 0.07 0.30 0.67 3.18 0.16 0.60 0.06 3 0.49 0.02 0.01 0.010 0.004 30.80 0.01 51.60 12.50 0.08 0.01 0.64 3.58 0.10 0.06 0.004 0.01 0.005 4 0.42 0.03 0.03 0.007 0.005 26.70 0.02 46.10 Residue 0.07 0.01 0.69 2.24 0.08 0.05 0.004 0.01 5 0.20 0.01 0.01 0.010 0.003 30.40 0.01 52.30 Residue 0.07 0.01 0.52 3.17 0.12 0.06 0.004 6 0.38 0.11 0.01 0.006 0.003 29.75 0.05 44.50 19.70 0.03 0.05 0.68 4.25 0.19 0.20 0.06 7 0.48 0.11 0.01 0.007 0.003 30.35 0.05 44.00 19.40 0.38 0.05 0.69 4.05 0.13 0.04 8 0.47 0.59 0.13 0.006 0.002 29.50 0.07 42.70 20.72 0.09 0.06 0.80 4.54 0.18 0.06 0.24 9 0.44 0.16 0.09 0.006 0.002 30.35 0.07 42.20 Residue 0.03 0.01 0.78 3.17 0.1 0.07 0.013 10 0.50 1.43 0.17 0.006 0.002 30.10 0.01 Residue 19.20 0.05 0.05 0.78 4.00 0.15 0.07 0.18 11 0.42 0.07 0.09 0.007 0.003 30.30 0.02 Residue 21.20 0.04 0.01 0.77 3.28 0.23 0.11 0.15 12 0.45 1.85 1.26 0.007 0.003 35.02 0.01 45.70 14.85 0.01 0.05 0.81 0.10 0.20 0.05 0.01 13 0.44 1.72 1.23 0.010 0.005 25.02 0.01 34.40 Residue 0.04 0.01 0.84 0.13 0.10 0.02 14 0.45 0.14 0.06 0.01 0.003 25.7 0.02 57.50 11.40 0.04 0.01 0.53 3.90 0.15 0.05 0.04 15 0.44 0.05 0.19 0.01 0.002 30.4 0.07 55.27 10.71 0.05 0.09 0.10 2.40 0.14 0.05 0.024

(30) TABLE-US-00002 TABLE II Relative coverage of Gas composition during heat- surface with catalytic Test up phase Temperature curve during heat-up phase coke* 1 100% air From 150 C. to 875 C., 50 C./h; 40 h hold at 875 C. 1.4% 2 100% water vapor 1.1% 3 70% water vapor From 150 C. to 600 C., 50 C./h; 40 h hold at 600 C.; 1.2% 30% methane from 600 C. to 875 C., 50 C./h; 4 3% water vapor 0.37% 97% methane 5 3% water vapor 0.26% 97% methane (+H.sub.2S-shock**) 6 3% water vapor 0.08% 97% ethane (+H.sub.2S-shock**) 7 3% water vapor 0.05% 97% ethane *This value was determined by counting the coke fibers on a specified tube surface. **After reaching the operating temperature 1 h treatment with 250 ppm sulfur (H.sub.2S) in water vapor.