Austenitic Fe—Cr—Ni alloy for high temperature

Abstract

An austenitic alloy for high temperature use, particularly for use in resistance heating elements. The alloy includes primarily the elements Fe, Ni, and Cr, and it has the following main composition, given in weight %, Ni 38-48, Cr 18-24, Si 1.0-1.9, C <0.1, and the balance Fe. The alloy provides good hot form stability, good oxidation resistance, and a relatively high electrical resistance coupled with a low change in resistance as a function of temperature.

Claims

1. An FeNiCr alloy for high temperature use between 950 C. and 1100 C. having a composition consisting of: Ni 42-46 weight-%; Cr in an amount between (0.1Ni+23) and (0.2667Ni+36) (weight-%); Si in an amount between 0.8 and (0.0133Ni+2.2) (weight-%); N <0.15 weight-%; Ce 0.01-0.04 weight-%; C <0.1 weight-%; impurities up to 1 weight-% (total); and Fe balance.

2. The alloy according to claim 1, wherein the amount of C in the composition is 0.02 weight-%.

3. The alloy according to claim 1, wherein the amount of Ni in the composition is 44-46 weight-%.

4. An FeNiCr alloy for high temperature use between 950 C. and 1100 C. having a composition consisting of: Ni 42-46 weight-%; Cr in an amount between (0.1Ni+23) and (0.2667Ni+36) (weight-%); Si in an amount between 0.8 and (0.0133Ni+2.2) (weight-%); N <0.15 weight-%; Ce 0.01-0.04 weight-%; C <0.1 weight-%; Al <0.6 weight-%; Mn <1 weight-%; S <50 wt ppm; elements belonging to the group Ti, Zr, Hf, Y, rare earth elements (Lantanoid group), Ca, Mg and Ta less than 0.5 weight-% in total; elements belonging to the group Mo, Co, Ta, W less than 5 weight-%; elements belonging to the group Nb and V less than 0.4 weight-%; impurities up to 1 weight-% (total); and Fe balance.

5. The alloy according to claim 4, wherein the amount of C in the composition is 0.02 weight-%.

6. The alloy according to claim 4, wherein the amount of Ni in the composition is 44-46 weight-%.

7. The alloy according to claim 4, wherein the amount of Al in the composition is 0.02 to 0.6 weight-%.

8. The alloy according to claim 7, wherein the amount of Si in the composition is 1.0 to 1.5 weight-%.

9. The alloy according to claim 8, wherein the amount of C in the composition is 0.02 weight-%.

10. An FeNiCr alloy for high temperature use between 950 C. and 1100 C. having a composition consisting of: Ni 42-46 weight-%; Cr in an amount between (0.1Ni+23) and (0.2667Ni+36) (weight-%); Si in an amount between 0.8 and (0.0133Ni+2.2) (weight-%); N <0.15 weight-%; Ce 0.01-0.04 weight-%; C <0.1 weight-%; Mn less than 2 weight-%; Al, Ca, Ti, Zr, Hf, Ta, Nb, V, Mg, W and rare earth elements together are less than approximately 7 weight-%; impurities up to 1 weight-% (total); and Fe balance.

11. The alloy according to claim 10, wherein the amount of Si in the composition is 1.0 to 1.5 weight-%.

12. The alloy according to claim 10, wherein the amount of C in the composition is 0.02 weight-%.

13. The alloy according to claim 10, wherein the amount of Ni in the composition is 44-46 weight-%.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a test setup for measuring deformation of a heating coil;

(2) FIG. 2 is a graph showing linear relationships between Si content and Ni content for an alloy in accordance with the invention and in comparison with existing alloys;

(3) FIG. 3 is a graph showing linear relationships between Cr content and Ni content for an alloy in accordance with the invention and in comparison with existing alloys;

(4) FIG. 4 is a graph showing additional linear relationships between Si content and Ni content for an alloy in accordance with the invention and in comparison with existing alloys; and

(5) FIG. 5 is a graph showing additional linear relationships between Cr content and Ni content for an alloy in accordance with the invention and in comparison with existing alloys.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) It is Important that the Content of C is Below 0.1 wt %.

(7) Eight test melts were cast, hot rolled, and cold drawn to wire according to standard practice with chemical composition according to Table 2.

(8) TABLE-US-00002 TABLE 2 Chemical Composition of Test Melts Melt # 1 2 3 4 5 6 7 8 Ni 45.5 44.2 44.3 44.8 35.0 35.0 35.3 35.2 Cr 25.4 25.3 14.9 15.0 26.5 24.8 15.0 15.0 Si 2.64 1.10 3.69 1.18 2.72 1.16 3.06 1.13 Al 0.08 0.13 0.14 0.16 0.12 0.13 0.14 0.13 N 0.04 0.05 0.02 0.02 0.04 0.04 0.04 0.02 C 0.07 0.06 0.09 0.07 0.08 0.10 .010 0.08 S 0.001 0.002 0.001 0.002 0.003 0.002 0.002 0.002 P 0.007 .0008 0.006 0.006 0.008 0.009 0.006 0.006 Other <1 <1 <1 <1 <1 <1 <1 <1 Fe Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal.

(9) The wires were coiled into helixes and mounted on sample holders. These were exposed to a high temperature, 950 C., by means of a laboratory furnace for 168 hours. Deformation of the helixes was measured by means of a micrometer screw according to the setup in FIG. 1.

(10) Since these products are working at a high temperature, the oxidation life and in particular the cyclic oxidation life is an important design factor. In order to evaluate this property a cyclic oxidation test was performed. The sample wires were heated by passing electric current through them and the wires were exposed to a 2 minutes on/2 minutes off cycle. The time to burn off was recorded and the results were grouped according to performance.

(11) A combination of the deformation performance that occurs from relatively small applied forces, such as gravity acting on, e.g., suspended heater coils, and oxidation performance at high temperature, is therefore an object of the present invention.

(12) The results indicate that not only the level of each element, but in addition the relative contents of the base elements Nickel, Chromium, and Silicon, have a surprisingly large impact on performance.

(13) TABLE-US-00003 TABLE 3 Results from Deformation and Oxidation Test. Melt # 1 2 3 4 5 6 7 8 Sag + + + + Life + + + + + designates a better than average result.

(14) It has now been found that the relation between these elements has to be within a narrow range that is given on the one hand by sufficient deformation performance and on the other hand by adequate oxidation performance. Only in this narrow band of compositions was the optimum compromise achieved that gave the working solution.

(15) An alloy in accordance with the invention has the main composition (in wt %) of Ni ranging from 38 to 48. The Cr level is larger than Cr=0.1 Ni+24
and is smaller than Cr=0.1667Ni+30.

(16) At the same time, the Si level is larger than Si=1.0
and is smaller than Si=0.01Ni+1.9.

(17) In FIGS. 2 and 3 the above-mentioned Si content and Cr content are shown by means of graphs, where alloys in accordance with the invention are compared with existing alloys.

(18) The alloy can also contain up to 5% Co as a substitute for Ni and Mn up to 2%. Further, it contains Al up to 0.6%, and preferably above 0.03%, and R.E., Y, and Ca up to a level of 0.2% in total. C should be <0.1 and N in a range up to 0.15%, preferably above 0.03%. Nitride and carbide formers such as Ti, Zr, Hf Ta, Nb, and V can be added up to a total level of 0.4% but are not necessary to benefit from the advantages of the invention. The remainder consists of iron and various elements originating from the raw materials and the production process, up to a total level of <2%.

(19) A specific example of an alloy according to the invention contains (in wt %) Ni 39-41, Cr 20-22, Si 1-1.5, N 0.15, Ce 0.01-0.04, C <0.1, impurities up to 2%, and Fe the balance.

(20) Another example of an alloy in accordance with the invention having further improved oxidation performance due to the higher Ni content, but with otherwise comparable properties, is Ni 44-46, Cr 20-22, Si 1-1.5, N <0.15, Ce 0.01-0.04, C <0.1, impurities up to 2%, and Fe the balance.

(21) Preferred embodiments are as follows, with the composition in weight %. In FIGS. 4 and 5 the below-mentioned Si content and Cr content are shown by means of graphs, where alloys in accordance with the invention are compared with existing alloys.

(22) An alloy comprising Ni 38-48, Cr between 0.1Ni+23 and 0.2667Ni+36, Si between 0.8 and 0.0133Ni+2.2, and Fe the balance.

(23) An alloy comprising Ni 40, Cr 21, Si 1.2, N <0.15, Ce 0.03, C <0.1, impurities up to 2%, and Fe the balance.

(24) An alloy comprising Ni 45, Cr 21, Si 1.2, N <0.15, Ce 0.03, C <0.1, impurities up to 2%, and Fe the balance.

(25) Another alloy that is preferred comprises Ni 38-48, Cr larger than Cr=0.1Ni+24 and smaller than Cr=0.1667Ni+30, Si larger than Si=1.0 and smaller than Si=0.01Ni+1.9, C <0.1, Al up to 0.6, and Fe the balance.

(26) The alloy can also contain up to 5% Co as substitute of Ni Mn up to 2, Al up to 0.3, R.E., Y and Ca up to a level of 0.2% in total, C <0.1, N <0.15, Ti, Zr, Hf, Ta, Nb, and V up to a total level of 0.4, <50 wt ppm S, various elements originating from the raw materials and the production process up to a total level of <2, and Fe the balance

(27) An alternative is: 38-48 Ni, 18-22 Cr, 1.0-1.5 Si, Al <0.6, <0.1 C, N <0.15, <1 Mn, <50 wt ppm S, <0.5 in total sum of elements belonging to the group Ti, Zr, Hf, Y, Rare Earth Elements (Lantanoid group), Ca, Mg, Ta, <5 totally of elements belonging to the group Mo, Co, Ta, W, <0.4 totally of elements belonging to the group Ti, Zr, Hf, Ta, Nb, and V, <1 of other elements arising from impurities in the melting process, and Fe the balance.

(28) Further preferred embodiments are an alloy comprising, Ni 39-41, Cr 20-22, Si 1-1.5, Mn 0.5 C 0.02, N <0.15, Ce 0.01-0.04, impurities up to 2%, and in that Fe is the balance.

(29) And an alloy comprising, Ni 44-46, Cr 20-22, Si 1-1.5, Mn 0.5, C 0.02, N <0.15, Ce 0.01-0.04, impurities up to 2%, and in that Fe is the balance.

(30) Table 4 below is a comparison of commercially available alloys with alloys in accordance with the invention.

(31) TABLE-US-00004 Alloys Ni Cr Si Other 353MA 35 25 1.5 N 0.17 Incoloy DS 37 18 2.3 Incoloy 800 32 21 0.5 Incoloy 617 52 22 0.5 Al 1.2 Haynes HR-120 37 25 0.6 Nb 0.7 Nikrothal 80 80 20 1.35 Nikrothal 60 57.5 16 1.5 Nikrothal 40 37 20 2 Nikrothal 30 30 21 2 Nikrothal 20 21 25 2.3 Invention ex 1 40 21 1.3 Invention ex 2 45 21 1.2

(32) The alloy 353MA is produced by Outokumpo Oyj, Espoo, Finland. The alloy Incoloy is produced by Special Metals Corp., Huntington, W. Va., USA. The Haynes alloy is produced by Haynes International, Inc., Kokomo, Ind., USA. Nikrothal is produced by the assignee.

(33) As is apparent from the above, the present invention fulfills the objects mentioned in the opening part of the present application.