EP0549286A1

EP0549286A1 - High temperature resistant Ni-Cr alloy

Info

Publication number: EP0549286A1
Application number: EP92311611A
Authority: EP
Inventors: Ian Christopher Elliott; Wai-Yan Chan; Norman Charles Farr
Original assignee: Inco Alloys Ltd
Current assignee: Inco Alloys Ltd
Priority date: 1991-12-20
Filing date: 1992-12-18
Publication date: 1993-06-30
Anticipated expiration: 2012-12-18
Also published as: ES2073873T3; DE69202965T2; ATE123819T1; EP0549286B1; DE69202965D1

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

FIELD OF INVENTION

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 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 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 poaching 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.
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.

TABLE 3

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 ingot 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 atmosphere with the resulting weight changes provided in Table 5.
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 result 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. Result of the one week cycle tests are provided in Table 6.
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.
Data of Table 7 indicate good resitance to oxide penetration for alloys of the invention.
From he above test the ranges below in Table 8 were determined to define ranges of the alloy of the invention.
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 0.29 carbon is maintained to limit excessive carbide formation that ties up useful element 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 is an impurity that adversely impacts oxidation resistance. Advantageously, manganese is limited to 1% and most advantageously manganese is limited to 0.5%. Most advantageously, at least 0.005% total magnesium, calcium and/or cerium are added for improved malleability and deoxidation. Total magnesium and/or calcium is advantageously 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 effect 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 an impurity acceptable in quantities up to 10% that 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.
While in accordance with the provisions of the statute, there is illustrated and described herein specific embodiments of the invention. Those skilled in the art will understand that changes may be made in die form of the invention covered by the claims and the certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

Claims

1. A heat and corrosion resistant alloy consisting essentially of, in weight percent, about 55-65% nickel, about 19-25% chromium, about 1-4.5% aluminum, 0.045-0,3% yttrium, about 0.15-1% titanium, about 0.005-0.5% carbon, about 0.1-1.5% silicon, about 0-1% manganese, at least about 0.005% total of at least one element selected from the group consisting of magnesium, calcium and cerium, less than about 0.5% total magnesium plus calcium, less than about 1 % cerium, about 0.0001-0.1 % boron, about 0-0.5 % zirconium, about 0.0001-0.2% nitrogen, about 0-10% cobalt and balance iron and incidental impurities.

2. The alloy of claim 1 wherein said chromium is about 19-22 %, said aluminum is about 2.5-4.0 %, said yttrium is about 0.05-0.15 %, said titanium is about 0.15-0.75% and said silicon is about 0.5-1 %.

3. The alloy of claim 1 wherein said carbon is about 0.01-0.3%, said magnesium is about 0.005-0.2%, said boron is about 0.001-0.05% and said nitrogen is about 0.01-0.1 %.

4 A heat and corrosion resistant alloy consisting essentially of, in weight percent, about 57.5-62.5% nickel, about 19-22% chromium, about 2.5-4% aluminum, about 0.05-0.15% yttrium, about 0.15-0.75% titanium, about 0.01-0.3% carbon, about 0.5-1% silicon, about 0-1% manganese, at least about 0.005% total at least one element selected from the group consisting of magnesium, calcium and cerium, less than about 0.2% total magnesium plus calcium, less than about 1 % cerium, about 0.001-0.05% boron, about 0-0.4% zirconium, about 0-5% cobalt and balance iron and incidental impurities.

5 The alloy of claim 4 wherein said chromium is about 19.5-21%, said aluminum is about 2.7-3.5 %, said yttrium is about 0.05-0.07% and said titanium is about 0.3-0.75%.

6. The alloy of claim 4 wherein said carbon is about 0.05-0.15%, said magnesium is about 0.005-0.2 %, said boron is about 0.01-0.01 % and said nitrogen is about 0,001-0.05%.

7 The alloy of any one of claims 1 to 6 wherein said iron is less than about 20%, e.g. 10-18%.

8 The alloy of claim 4 wherein said alloy includes about 0-0.5 % copper, about 0-0.5% molybdenum, about 0-0.3% niobium, about 0-0.1% vanadium and about 0-0.1% tungsten.

9 A heat and corrosion resistant alloy consisting essentially of about 57.5-62.5% nickel, about 19.5-21% chromium, about 2.7-3.5 aluminum, about 0.05-0.07% yttrium, about 0.3-0.75% titanium, about 10-18% iron, about 0.5-1% silicon, about 0-0.5% manganese, at least about 0.005% total at least one element selected from the group consisting of magnesium, calcium and cerium, less than about 0.2% total magnesium plus calcium, less than about 1% cerium, about 0.001-0.01 % boron, about 0-0.2% zirconium, about 0.001-0.05% nitrogen, about 0-1% cobalt and incidental impurities.

10 The alloy of claim 9 wherein said alloy includes about 0-0.5% copper, about 0-0.5 % molybdenum, about 0-0.3 % niobium, about 0-0.1 % vanadium and about 0.01% tungsten.

11 The alloy of claim 9 wherein said alloy contains less than about 0.1% total lead, tin, antimony, bismuth, phosphorous, sulfur and oxygen.

12 The alloy of claim 9 wherein said nitrogen is at least 0.03%.