High temperature resistant Ni-Cr alloy

Abstract: The invention provides a heat and corrosion resistant alloy having, by weight percent, 55-65% nickel, 19-25% chromium, 1-4.5% aluminum, 0.045-0.3% yttrium, 0.15-1% titanium, 0.005-0.5% carbon, 0.1-1.5% silicon, 0-1% manganese, at least 0.005% total magnesium, calcium and/or cerium, less than 0.5% total magnesium and/or calcium, less than 1% cerium, 0.0001-0.1% boron, 0-0.5% zirconium, 0.0001-0.1% nitrogen, 0-10% cobalt and balance, iron and incidental impurities.

Description: This invention is related to the field of Ni-Cr-Fe alloys and particularly to alloys used in high temperature (1200°C) applications. BACKGROUND OF THE INVENTION Ni-Cr-Fe alloys such as INCONEL® alloy 601 have historically been used for general-purpose engineering applications requiring heat and corrosion resistance. (INCONEL is a registered trademark of the Inco family of companies.) In addition, INCONEL alloy 601 has excellent resistance to thermal cycle fatigue in combination with high temperature oxidation resistance. Commercial uses of INCONEL alloy 601 include thermal processing equipment, chemical processing applications, petrochemical applications, pollution control applications and turbine engine components. INCONEL alloy 601 has been widely used as a roller alloy for applications within high temperature kilns used in firing of ceramic tiles. In high temperature kilns used for firing ceramics, rollers are typically exposed to oxidizing conditions at temperatures as high as 1000°C or 1165°C. At such high temperatures, roller alloys have a tendency to slowly fail due to gradual oxidation. At increased temperatures of about 1200°C, oxidation rate and spalling rate increase unacceptably. It is the object of this invention to provide a Ni-Cr-Fe alloy with improved resistance to oxidation at 1200°C. SUMMARY OF THE INVENTION The invention provides a heat and corrosion resistant alloy as defined in the accompanying claims. DESCRIPTION OF THE DRAWINGS Figure 1 is a plot of mass change versus time for various alloys in an air atmosphere at 1165°C. Figure 2 is a plot of mass charge versus time for various alloys in an air atmosphere at 1200°C. DESCRIPTION OF PREFERRED EMBODIMENT The invention provides a Ni-Cr-Fe-Al alloy with improved high temperature cyclic oxidation resistance. A nickel-base alloy containing a combination of chromium, yttrium, silicon and aluminum has been found to dramatically improve oxidation resistance at 1200°C. The 1200°C temperature is particularly useful for kilns used for firing lead-free frits. INITIAL TEST A total of six test heats of Ni-Cr-Fe alloys were cast into 10 kg ingots. Ingot 7 originated from a commercial heat. Chemical compositions of the test heats expressed in weight percent are given below in Table 1. (All compositions in this specification are expressed in weight percent unless specifically indicated.) TABLE 1 Ingot numbers 1-6 represent experimental heats; and Ingot number 7 represents an alloy within the commercial range of INCONEL alloy 601. The ingots were machined, dressed and forged at 1140°C into 50.8 mm round bars. The round bars were annealed at 1175°C for 30 minutes. Test coupons were machined from forged bar into plates having approximate dimensions of 15 mm x 20 mm x 3 mm. Plates were pierced with a 3 mm diameter hole for attaching the coupon to a jig. All oxidation test specimens were polished with silicon carbide paper to a 240 grade finish. Following recordation of sample size, all test samples were degreased and dried in hot air. The test specimens were given a cyclic oxidation test of 168 hours in a 1200°C air atmosphere furnace followed by a 20 minutes cooling cycle. Results from the cyclic oxidation test are given below in Table 2. WEIGHT CHANGE (mg/cm²) INGOT NUMBER / SAMPLE NUMBER Exposure Time (h) 1 2 3 4 5 6 7 025 0.21 0.17 0.23 0.26 0.25 0.17 0.20 168 -5.93 -5.60 -10.30 -10.06 -10.86 -1.86 -4.14 335 -11.04 -12.75 -18.29 -10.26 -20.16 -5.32 -8.04 500 -15.65 -14.91 -23.17 -10.23 -29.32 -9.99 -3.00 666 -21.15 -22.24 -33.49 -10.22 -40.03 -14.41 -19.10 832 -26.89 -27.91 -42.49 -10.27 -49.13 -19.73 -26.22 1000 -34.99 -34.02 -51.98 -10.34 -57.86 -25.33 -36.67 The above sample numbers correspond to the ingot numbers of Table 1. From the above high temperature experiment it was determined that the composition of ingot 4 at 1200°C provided the best oxidation resistance. Scale integrity was found to increase with decreased amounts of titanium. Segregation of yttrium rich phases at the alloy/scale interface was found to increase scale adhesion and may have an effect in modifying alloy oxidation mechanism leading to improved oxidation resistance. The tightly adherent scale layer of high yttrium sample number 4 was found to provide an effective barrier for preventing internal oxidation. In addition, the increased aluminum content of sample number 4 was believed to also contribute high temperature stability of the oxide scale. From the above results, a commercial heat of Ni-Cr-Fe-Al alloy (Alloy A) having the ranges of Table 3 was prepared. ELEMENT MAXIMUM AIM MINIMUM ACTUAL C 0.050 0.040 -- 0.032 Si 0.79 0.70 0.50 0.78 Mn 1.00 0.25 0.10 0.31 P .015 -- -- 0.010 S .015 -- -- 0.001 Al 3.00 2.70 2.50 2.63 Co 1.00 -- -- 0.02 Cr 23.00 21.00 20.00 20.59 Cu 0.50 -- -- <0.01 Fe 18.0 BAL -- 14.9 Mg 0.019 0.017 0.01 0.015 Mo 0.50 -- -- <0.01 Nb 0.30 -- -- <0.01 Ni 63.00 60.0 58.0 60.25 Ti 0.25 0.23 0.21 0.26 B (ppm) 60 34 30 40 Y 0.15 0.13 0.10 0.08 V 0.10 -- -- 0.03 W 0.10 -- -- <0.05 N 0.1 -- -- 0.033 The invention of Alloy A provided a Ni-Cr-Fe-Al alloy with improved high temperature (1200°C) oxidation resistance. A combination of chromium, yttrium, silicon and aluminum was found to dramatically improve oxidation resistance. The improved Ni-Cr-Fe-Al alloy had only a slight decrease in hot ductility in comparison to commercial INCONEL alloy 601. To verify and optimize the compositional ranges for Alloy A, a series of test heats was prepared and analyzed. EXAMPLE The first series of tests containing the compositions listed below in Table 4 was prepared. The series of 12.5 kg cast ingots were machined, dressed and then forged at about 1150°C to 15 mm thick slabs. Each slab was then hot rolled at about 1150°C in stages to produce 4 mm thick hot band. Each sample was final annealed for 30 minutes at 1177°C and air cooled to room temperature. Prior to oxidation testing, the specimens were ground on silicon carbide paper to a 240 grade finish as previously provided for the samples of Table 1. TABLE 4 In the initial series of cyclic oxidation tests, the alloys of Table 4 were exposed to a repetitive thermal cycle of 20 minutes heating followed by 10 minutes cooling in an air atmosphere with the resulting weight changes provided in Table 5. WEIGHT CHANGE FOR ALLOYS AFTER THERMAL CYCLING AT PEAK TEMPERATURES OF 1100 AND 1200°C IN AIR Weight Change mg/cm² at Peak Temperature of Heat No. 1100°C 1200°C 8 -2.3 -379.8 9 +0.9 -254.7 10 +2.2 -629.2 11 -180.1 -483.6 12 -3.0 -286.8 13 +0.2 -158.4 14 -9.0 -411.2 15 -74.4 -302.5 16 -231.9 -539.2 17 -188.5 -435.7 Alloy A -121.7 -213.4 Alloy 601 -47.4 -370.6 The examples of Table 5 on average were slightly poorer than alloy 601 at 1100°C. However, alloys of the invention provided some improvement in cyclic oxidation at 1200°C. It is believed that results of Table 5 would be improved if the stable oxide were formed by an initial oxidation treatment at a temperature of at least 1100°C prior to testing. The alloys of Table 4 were then exposed to an air atmosphere for one week periods followed by a 20 minute room temperature air cooling. Results of the one week cycle tests are provided in Table 6. WEIGHT CHANGE FOR ALLOYS AFTER SIX WEEKLY EXPOSURES AT TEMPERATURES OF 1050, 1165 AND 1200°C IN AIR Weight Change, mg/cm² at Temperatures Shown Heat. No. 1050°C 1165°C 1200°C 8 +0.2 -3.4 -5.0 9 +0.3 -2.7 -2.8 10 +0.7 -1.2 +3.6 11 -4.4 -7.7 -9.2 12 +0.4 -2.6 -3.6 13 +0.5 -2.6 -3.6 14 +0.5 -2.5 -3.1 15 -2.6 -8.9 -8.9 16 -3.0 -12.5 -17.2 17 -0.9 -9.3 -10.1 Alloy A -7.7 -11.5 -10.5 Alloy 601 -0.7 -18.0 -34.8 At temperatures of 1050°C alloys of the invention provided a mixed effect upon the longer cycle duration tests. However, at 1165°C and 1200°C, oxidation resistance was dramatically improved. Figures 1 and 2 illustrate this improvement. The alloys of the invention initially oxidize at a greater rate than alloy 601. An advantage to the alloys is the steady state low oxidation rate achieved after/during the first week of exposure. For optimum results, the alloy should be held at a temperature of at least 1100°C for sufficient time to enable the stable adherent oxide to form prior to service. Oxidation penetration was also tested for alloys of the invention and alloy 601. Oxidation penetration test result data are given below in Table 7. OXIDE PENETRATION MEASUREMENTS OF ALLOY A AND RELATED ALLOYS AFTER EXPOSURE FOR SIX WEEKLY CYCLES IN AIR AT TEMPERATURES SHOWN Maximum Depth of Oxidation mm at Temperatures of Heat No. 1050°C 1165°C 1200°C 8 0.03 0.10 0.12 9 0.06 0.30 0.35 10 0.14 0.50 0.60 11 0.05 0.20 0.18 12 0.02 0.10 0.10 13 0.03 0.10 0.09 14 0.04 0.15 0.20 15 0.02 0.10 0.09 16 0.03 0.08 0.10 17 0.04 0.08 0.12 Alloy A 0.05 0.04 0.05 Alloy 601 0.08 0.14 0.17 Data of Table 7 indicate good resistance to oxide penetration for alloys of the invention. From the above test the ranges below in Table 8 were determined to define ranges of the alloy of the invention. Element Broad Intermediate Narrow Nickel 55-65 57.5-62.5 57.5-62.5 Chromium 19-25 19-22 19.5-21 Aluminum 1-4.5 2.5-4.0 2.7-3.5 Yttrium 0.045-0.3 0.05-0.15 0.05-0.07 Titanium 0.15-1 0.15-0.75 0.3-0.75 Iron Bal. Bal. 10-18 Carbon 0.005-0.5 0.01-0.3 0.01-0.15 Silicon 0.1-1.5 0.5-1 0.5-1 Manganese 0-1 0-1 0-0.5 Magnesium 0.005-0.5 0.005-0.2 0.005-0.2 Calcium 0.005-0.5 0.005-0.2 0.005-0.2 Boron 0.0001-0.1 0.001-0.05 0.001-0.01 Zirconium 0-0.5 0-0.4 0-0.2 Nitrogen 0.0001-0.2 0.001-0.1 0.001-0.05 Cobalt 0-10 0-5 0-1 Cerium 0-1 0-1 0-1 Copper 0-0.5 Molybdenum 0-0.5 Niobium 0-0.3 Vanadium 0-0.1 Tungsten 0-0.1 Pb,Sn,Sb,Bi,P,S, O (total) 0-0.1 Nickel in an amount of 55-65% provides workability, fabricability and general oxidation resistance to the alloy. Chromium in an amount of 19-25% provides oxidation resistance. Oxidation resistance is insufficient at less than 19% chromium. At chromium levels above 25%, deleterious chromium phases may form. Initial testing has indicated that chromium levels above 20% have a neutral effect and do not contribute additional oxidation resistance. Aluminum is beneficial to oxidation properties and increased aluminum is believed to contribute to adherence of the oxide scale. Aluminum in an amount of at least 1% or most advantageously at least 2.7% provides high temperature oxidation resistance. Aluminum is limited to 4.5% (preferably 3.5%) to limit adverse hot workability effects. Yttrium in an amount of at least 0.045% and preferably at least 0.05% contributes to stabilizing the oxide. Yttria was not readily visible with optical microscopy in the samples tested. Excess yttrium (above 0.3%) is believed to adversely affect hot workability and welding properties. Most advantageously yttrium is limited to 0.07%. Titanium is added as a reactive element to combine with nitrogen and carbon. At least 0.15% titanium is added for tying up nitrogen. Excess titanium above 1% adversely affects oxidation resistance and workability. Iron acts as an inexpensive substitute for nickel. Most advantageously at least 10% iron is present to lower the cost of the alloy. Furthermore, iron is most advantageously limited to 20 or 18% to limit reduction of nickel's beneficial properties. Carbon in an amount of 0.005% or preferably 0.01% provides adequate grain size control. An upper limit of 0.5% carbon or preferably 0.2% carbon is maintained to limit excessive carbide formation that ties up useful elements and to limit grain boundary embrittlement. At least 0.1% silicon and advantageously 0.5% silicon is added for oxidation resistance. Silicon is limited to 1.5% or preferably 1% to limit weldability and workability problems. Manganese adversely impacts oxidation resistance. Manganese is limited to 1% and most advantageously manganese is limited to 0.5%. At least 0.005% total magnesium, calcium and/or cerium are added for improved malleability and deoxidation. Total magnesium and/or calcium is limited to 0.5% and most advantageously 0.2% to minimize adverse effects upon weldability and workability. Boron in an amount of 0.0001% or preferably 0.001% provides improved malleability. Boron is limited to 0.1% to minimize adverse effects upon malleability and weldability. Advantageously, boron is limited to 0.05% and most advantageously boron is limited to 0.01% or 0.006%. Zirconium may optionally be added for malleability and grain size control. Zirconium reacts with nitrogen to form nitrides that inhibit grain growth at elevated temperature. Zirconium is limited to 0.5% and most advantageously 0.2% to limit adverse effects upon weldability and workability. Similarly, nitrogen is added to provide an effective amount of grain growth resistance. Nitrogen, typically is provided in sufficient quantity as an impurity of raw materials. A quantity of at least 0.0001% nitrogen or 0.001% nitrogen provides resistance against grain growth. Most advantageous grain growth control may be obtained by maintaining a level of at least 0.03% nitrogen. Alternatively, grain growth may be controlled by limiting stored energy in the alloy by additional annealing steps between deformation processes. Nitrogen is limited to 0.2% to avoid excess internal oxidation of beneficial elements. Nitrogen is advantageously limited and most advantageously to 0.1% and 0.05% respectively. Cerium in an amount up to 1% may optionally be added as a magnesium substitute or for additional oxidation resistance. However, with the chromium, aluminum, silicon and yttrium ranges of the invention cerium is not necessary for oxidation resistance. Cobalt is acceptable in quantities up to 10% and acts as a substitute for nickel. Advantageously, cobalt is limited to 5% and most advantageously cobalt is maintained below 1%. Due to the relatively high cost of cobalt, cobalt is preferably not deliberately added. Copper, molybdenum, niobium, vanadium and tungsten are advantageously held to the limits of Table 8 to improve appearance of the alloy. Most advantageously, copper, molybdenum, niobium, vanadium and tungsten are held as low as commercially practical. Lead, tin, antimony, bismuth, phosphorous, sulfur and oxygen are all incidental impurities maintained at levels as low as commercially practical. Most advantageously, the total lead, tin, antimony, bismuth, phosphorous, sulfur plus oxygen level is maintained below 0.1%. The alloy of the invention was tested to provide acceptable mechanical properties. Initial welding tests indicated a tendency for solidification cracking linked to increased yttrium content. However, the tests were not performed on alloys of the invention. Alloys of the invention are readily fabricated in seamless tubes by conventional extrusion or extrusion and cold working techniques. The tubes are then cut into short length rollers especially useful for kilns having operating temperatures around 1200°C. The oxide formed at high temperature is extremely adherent and less prone to discoloration of ceramics than conventional alloy 601. The adherent scale is especially useful for white ceramics.

Claims: A heat and corrosion resistant alloy comprising, in weight percent, 55-65% nickel, 19-25% chromium, 1-4.5% aluminium, 0.045-0.3% yttrium, 0.15-1% titanium, 0.005-0.5% carbon, 0.1-1.5% silicon, 0-1% manganese, at least 0.005% total of at least one element selected from the group consisting of magnesium, calcium and cerium, less than 0.5% total magnesium plus calcium, less than 1% cerium, 0.0001-0.1% boron, 0-0.5% zirconium, 0.0001-0.2% nitrogen, 0-10% cobalt, 0-0.5% copper, 0-0.5% molybdenum, 0-0.3% niobium, 0-0.1% vanadium, 0-0.1% tungsten and balance iron and incidental impurities. The alloy of claim 1 wherein said chromium is 19-22%, said aluminium is 2.5-4.0%, said yttrium is 0.05-0.15%, said titanium is 0.15-0.75% and said silicon is 0.5-1%. The alloy of claim 1 or claim 2, wherein said carbon is 0.01-0.3%, said magnesium is 0.005-0.2%, said boron is 0.001-0.05% and said nitrogen is 0.001-0.1%. The alloy of claim 1, wherein said nickel is 57.5-62.5%, said chromium is 19-22%, said aluminium is 2.5-4%, said yttrium is 0.05-0.15%, said titanium is 0.15-0.75%, said carbon is 0.01-0.3%. said silicon is 0.5-1%, said magnesium and calcium is less than 0.2% total, said boron is 0.001-0.05%, said zirconium is 0-0.4% and said cobalt is 0-5%. The alloy of claim 4 wherein said chromium is 19.5-21%, said aluminium is 2.7-3.5%, said yttrium is 0.05-0.07% and said titanium is 0.3-0.75%. The alloy of claim 4 or claim 5, wherein said carbon is 0.05-0.15%, said magnesium is 0.005-0.2%, said boron is 0.001-0.01% and said nitrogen is 0.001-0.05%. The alloy of any one of claims 1 to 6 wherein said iron is less than 20%. The alloy of claim 7, wherein the said iron is 10-18%. The alloy of claim 1, wherein said nickel is 57.5-62.5%, said chromium is 19.5-21%, said aluminium is 2.7-3.5%, said yttrium is 0.05-0.07%, said titanium is 0.3-0.75%, said silicon is 0.5-1%, said manganese is 0-0.5%, said total of manganese plus calcium is less than 0.2%, said boron is 0.001-0.01%, said zirconium is 0-0.2%, said nitrogen is 0.001-0.05%, said cobalt is 0-1% and said iron is 10-18%. The alloy of any one of claims 1 to 9, wherein said alloy contains less than 0.1% total lead, tin, antimony, bismuth, phosphorus, sulfur and oxygen as impurities. The alloy of any one of claims 1 to 10, wherein said nitrogen is at least 0.03%. Use of the alloy of any one of claims 1 to 11 to make articles that are exposed, in use, to high temperatures, particularly in kilns. Articles that are exposed, in use, to high temperatures, particularly components of kilns, made from the alloy of any one of claims 1 to 11.

Inventors: CHAN WAI-YAN, ELLIOTT IAN CHRISTOPHER, FARR NORMAN CHARLES, CHAN, WAI-YAN, ELLIOTT, IAN CHRISTOPHER, FARR, NORMAN CHARLES
Applicants: INCO ALLOYS LTD, INCO ALLOYS LIMITED
Application year: 1992
Main classification: C22C19
IPC codes: C22C19