GB2133419A - Nickel-based alloys - Google Patents

Abstract

Alloys having excellent corrosion resistance and stress corrosion cracking resistance as well as high strength, especially when subjected to environments containing highly concentrated H2S and CO2 and to high loads, such as are encountered in deep oil wells. The alloy comprises: C</=0.06% Mn</=1.20% Al: 0.1 SIMILAR 1.6% Al+Ti:1.5 SIMILAR 2.5% Mo</=15% Fe</=35% and Si</=0.7% Cr: 15.0 SIMILAR 25.0% Ti: 1.0 SIMILAR 1.6% W</=20% Mo+W</=25% Ni+Cu>/=30% (Cu: 0 SIMILAR 5%> and satisfies the conditions: Al+Tl: 1.5-2.5% Mo+W</=25% Ti/Al= 1.0 SIMILAR 10.00 Ni-(Cr+Mo+W)>/=3% [Ni-(Cr+Mo+W)]/(Al+Ti)=2 SIMILAR 16, and Cr+0.73Ni+5.35(Mo+W)+3.16Cu>/=50%. The alloys are subjected to hot working and to a precipitation treatment for precipitating gamma ' type intermetallic compound.

Description

SPECIFICATION Nickel-based alloys The present invention relates to nickel-based alloys displaying high resistance to corrosion and to stress corrosion cracking properties. These properties are desirable for materials subjected to atmospheres containing large amounts of hydrogen sulphide and carbonic acid gas together with high salt levels which conditions are very often encountered in deep oil wells.

In recent years, it has been necessary for the production of oil and gas to be performed at greater depths below ground, and hence under more and more severe conditions, so as to be able to meet the ever increasing consumption of energy throughout the world. Along with these trends, demands are increasing for steel materials used in deep oil wells, which involve severe corrosive media, to have excellent properties and particularly high strength and high resistance to corrosion and stress corrosion cracking.

Conventionally, for relatively mild environments containing only hydrogen sulphide of low concentration, CR-Mo alloy steels and 13Cr alloy steels and the like have been used. These alloy steels, however, are liable to corrosion and are highly susceptible to stress corrosion cracking when they are used in environments containing highly concentrated hydrogen sulphide and carbolic acid gas with high salt levels, where the alloys are also subjected to high load stresses due to the increased depth of oil wells. In order to overcome these prob!ems, two-phase steels have been developed and now used in these severe environments. Even these two-phase steels have been found often to be practically unusable in stiil deeper oil wells or in oil wells containing larger amounts of hydrogen sulphide.In particular, for oil wells where there is more than 1 atm hydrogen sulphide and the steels are subjected to a 2% yield stress (00.2) of more than 130 KSI, the two-phase steels cannot satisfactorily be used. As a simulation test method for such severe environments, the CR resistance and the SCC resistance are usually estimated in NACE solutions (1 atm. H2S+5% NaCI+0.5% CH3COOH) and in NSC solutions (80 atm. C02+9 atm. H2S+Sea water).

The present inventors have investigated the 00.2 strength, as well as the CR and SCC resistances, of various alloy steel compositions, in view of the above technical problems, and the novel alloy materials having oO,2 strength not lower than 130KSI and excellent CR and SCC resistances of this invention have resulted therefrom.

Accordingly, one aspect of this invention provides a Ni-based alloy comprising (by weight): C < 0.06% Si < 0.7% Mn < 1 .20% Cr:15.0~25.0% Al:0.1~1.6% Ti:1.0~1.6% Mo < 15% W < 20% Fe < 35% and Ni+Cu#30%(Cu:0~5%) with the balance being unavoidable impurities and the alloy satisfying the conditions: Al+Ti:1.5~2.5% MO+WS25% Ti/Al=1 .01 0.0 Ni-(Cr+Mo+W)#3% [Ni-(Cr+ Mo+W)]/(Al +Ti)=2 1 6, and Cr+0.73 Ni+5.35 (Mo+W)+3.16Cu250% said alloy being subjected to hot working and to a precipitation treatment for precipitating y' type intermetallic compound.

A further aspect of this invention provides a modification of the nickel-based alloy as defined above, which further comprises one or more of Ca, Zr and rare earth metals (REM) in amounts of not more than 0.1%.

The invention as just defined will now be described in greater detail, and certain specific embodiments thereof given, reference being made as necessary to the accompanying drawings, in which: Figure 1 is a graph showing the relation between the alloy content and the corrosion rate (CR/mdd) in Fe-X (X=alloying elements) alloy systems; Figures 2 (a), (b) and (c) are respectively a graph showing the relation between the Sr value [SR=Cr+0.73N1+5.35 (Mo+W+3.16Cu] and CR for various alloys; Figure 3 is a graph showing the effects on the strength 00.2 (KSI) by the content of Al+Ti in a 20Cr-42Ni-3Mo alloy system;; Figure 4 is a graph showing the relation between CR in NACE solution and cold working rate in Alloys No. 1, No. 8 and No. 9 according to the present invention, in comparison with reference Alloy No. 30; Figure 5 is a graph showing the correlation of the content of Al+Ti and the cold working rate with respect to the strength 0.2 (KSI) in a 20Cr--42Nii-3Mo alloy system, which is basically within the scope of the present invention; Figure 6 is a graph showing the relation between the SR value and the SCC resistance in NACE solution in various alloys; Figure 7 is a graph showing the relation between the y' precipitation treating conditions and the strength 0.2 in Alloy No. 2;; and Figure 8 is a graph showing the y' precipitation treating conditions for obtaining 00.2 > 1 in in Alloys No. 2 and No. 12.

The reasons for the various limitations in the alloy composition and the treatment for producting the y' type intermetallic compound precipitation in the alloy according to the present invention will now be explained.

When one of Cr, Mo or W is added singly to an iron matrix (Fe) the corrosion rate (CR) increases as the addition increases. On the other hand, when one of Ni or Cu is added singly to an iron matrix the corrosion rate decreases as the addition increases. These tendencies are illustrated in Figure 1, showing the relation between the contents of the alloying elements and the corrosion rate in the Fe-X (X=alloying elements) alloy system. However, when any one of these elements is added in combination with any other element or elements, then CR and SCC resistances are improved as the addition is increased.

These tendencies are illustrated in Figure 2, showing the relation between the Sr value and the CR value for various alloy compositions, wherein the horizontal axis, SR, represents the effects of alloying elements on Cr analyzed by the method of least squares when Ni, Cu, Cr, Mo and W are added in combination to the iron matrix. Thus the SR value is equal to [Cr+0.73 Ni+5.35 (Mo, W)+3.1 6CU]. The vertical axis represents the logarithm of the CR values. As illustrated, the CR resistance is improved as the SR value increases (increase of individual elements).Results of the precise analysis of these phenomena have revealed that when each alloying element is added singly to Fe, Ni, Cu, NiS and CuS respectively form on the alloy surface, which improved the CR and SCC resistances, but Cr, Mo and W do not form their sulphides, thus failing to form a protective film. It has been also found that when Ni and Cu are added in combination with Cr, Mo and W, NiS and CuS are formed on the surface, and Cr203, Cr(OH)3, MoO3 and W03 are formed beneath the sulphide layer, thus providing a double-layer protective film which can exhibit remarkable CR and SCC resistances in NACE and NSC solutions.

In the Fe-Ni system shown in Figure 1, as the Ni content increases, in the low-Ni zone the corrosion rate decreased, then increases, and then decreases again in the high-Ni zone. When Ni is added to Fe, the structure transforms from ferrite to martensite and then to austenite as the Ni addition increases. In the ferrite and austenite zones, the corrosion rate decreases as the Ni addition increases, but in the martensite zone, the corrosion rate increases as the Ni addition increases, because the lath distance becomes coarse. Ni and Cu improve the CR and SCC resistances through the same mechanism, and it has been found that when Ni and Cu are added in combination in an amount of not lower than 30% (Ni+Cu), the resultant CR and SCC resistances are excellent. However, the Cu addition should desirably be maintained at 5% or less from production requirements of Ni-based alloys.Thus in the present invention, the Cu content is limited to the range of from 0 to 5%.

As typical methods for strengthening austenite steels, solid solution treatment, carbide precipitation and intermetallic compound precipitation can be considered. Of these practices, the former two methods are practically unable to enhance the 00.2 strength up to 1 30 KSI. Various types of intermetallic compounds are known, such as FeNiCr, NiAI, NiTi. However, for increasing the strength without deteriorating other properties such as ductility, the y' phase composed of Ni3 (Al, Ti) is most effective. As a result, precise and extensive investigations have been made on the effects of the intermetallic compounds on the strength and on the CR and SCC resistances of Ni-base alloys.In alloys containing 25% or more Ni, it was found Al and Ti form the y' phase to increase the strength when Al is present in amounts of not less than 0.1% and Ti is present in amounts of not less than 1%. As the amount of Al+Ti increases, the strength 00.2 improves, but an excessive addition will only saturate in their effects, as will be understood from the relation between the amounts of Al+Ti and 00.2 shown in Figure 3. On the other hand, the hot workability significantly is lowered as these elements increase.

Therefore, the upper limits for each of Al and Ti are set at 1.6%, and at 2.5% in total.

Regarding the effects of cold working, the strength 0.2 improves as the cold working rate increased, but the CR resistance markedly deteriorates, as indicated by the relation between the corrosion rate in the NACE solution and the cold working rate as illustrated in Figure 4. Also the reliability of material quality is reduced and the productivity is lowered. Therefore, the cold working rate is limited to a rate not higher than 20%, and Al and Ti are added in a total amount (Al+Ti) required to assure a 00.2 value higher than 130 KSI. The lower limit of (Al+Ti) is set at 1.5% from the correlation with (Al+Ti) and the cold working rate as illustrated in Figure 5.

Ti is more effective than Al at increasing the lattice constance of y' and at strengthening the alloy, but an excessive addition of Ti will absorb N during the melting stage to form undesirable coarse TiN which deteriorates the alloy quality. Therefore, the ratio of Ti/AI is limited to the range of from 1.0 to 10.0.

Meanwhile, the lower limits of Ti and Al which are effective for they' precipitation strengthening are respectively 1% and 0.1% below which no y' is precipitated and hence no improvement of strength is expected.

Cr, Mo and W are effective at improving the CR and SCC resistances by forming oxides beneath the Ni (Cu)S film.

With regard to the CR and SCC resistances, Cr is about 1.4 times more effective than Ni, and Mo and W are about 7.3 times more effective than Ni when Ni, Cu, Mo, Cr and W are added in combination. Therefore, for the purpose of improving the CR and SCC resistances, it is more effective to increase the addition of Cr, Mo and W, but of these elements, Cr in particular tends to make unstable the austenite structure. Therefore, the upper limit of the Cr content is set at 25%. Furthermore, W and Mo have similar effects on the SR value, and one or both of these elements may be added, but for the reason set forth above, Mo is limited to the range of from 0 to 15%, W is limited to the range of from O to 20% and the upper limit of the total amount of Mo and W is set at 23%.Also, the amount of [Ni-(Cr+Mo+W)] is defined to be 3% or larger so as to assure the stabilitv of the austenite structure.

When Al and Ti are added, y' is produced and Ni is consumed thereby, so that it is necessary to increase the amount of Ni in the matrix so as to stabilize the austenite phase. For this purpose, the ratio of [Ni-(Cr+Mo+W)]/(Al+Ti) is defined to be not less than 2. Regarding its upper limit, it is defined to be not larger than 16, because even if the ratio exceeds 16, little additional effect is obtained on the stability but there are economic losses.

Cr is a useful element not only for the CR and SCC resistances, but also for various purposes in the production of alloys and their applications, and for these reasons its lower limit is set at 15%. As shown in Figure 2, the CR and SCC resistances can be adjusted by the formula: SR=Cr+0.73Ni+5.35(Mo+W)+3. 1 6Cu and when the SR value is not lower than 50, a satisfactory SCC resistance can be obtained, as will be understood from the relation between the SR value and the SCC resistance (tensile rupture elongation in NACE solution/tensile rupture elongation in air) as shown in Figure 6. Therefore, the lower limit of the SR value is set at 50.

In environments containing H2S, almost no contribution can be expected by Fe at improving the CR and SCC resistances, and a smaller Fe content is more desirable. However, from the economical point of view, the upper limit of Fe is set at 35%.

C tends to form carbides which are harmful to the CR and SCC resistances. Therefore, it is desirable to maintain the carbon content as low as possible and in the present invention, the upper limit is set at 0.06%.

Si and Mn are a source of non-metallic inclusions which damage the CR and SCC resistances.

However, these elements are added in the minimum amounts required for deoxidation and desulphurization of the alloy as well as for control of non-metallic inclusions, although it is desirable to maintain these elements as low as possible. Thus the upper limits of these elements are set at 0.7% for Si and 1.20% for Mn.

According to a modification of the present invention, Ca, Zr and rare earth metals (REM) are added to the above basic composition of the Ni-based alloy for the purpose of deoxidation and desulphurization as well as for the purpose of improving the hot workability. Particularly, when S is contained in amounts more than 0.005% as impurities, it is desirable to add these additional elements in amounts large enough to fix S and 0 contained in the alloy so as to improve the hot workability.

Small amounts of S and 0, of usually not more than 0.01% of S and not more than 0.05% of 0 are contained in Ni-base alloys of the type according to the present invention. For fixing such S and 0 contents, additions of Ca, Zr and rare earth metals each in amount not larger than 0.1% are enough.

Therefore, the upper limit of these elements, either singly or in combination, is set at 0.1%.

Regarding the y' precipitation treatment, the required treatment temperature depends on the content of Al+Ti, and in accordance with the Al+Ti content defined in the present invention an economical and effective temperature for precipitation of y' is within the range of from 700 to 850"C and a treating time ranging from one minute to five hours is required. One embodiment of the precipitation treatment is illustrated in Figure 7 wherein the relation between the treating conditions and the strength 00.2 in connection with the modified alloy composition according to the present invention is shown.With a precipitation temperature below 7000 C, a considerably long period of time is required for the precipitation of y', leading to great economical disadvantage and low production efficiency.

On the other hand, if the temperature exceeds 8500C, the precipitation becomes rapid and the treating time becomes shorter, but the problem is that if the treatment is performed for even only a little longer a rapid coarsening of they' precipitate is caused, so that it is quite difficult to control the strength. For these reasons, it is desirable to maintain the treatment temperature within the range of from 700 to 8500C, and to maintain the treating time in the range of from one minute to 5 hours, to ensure adequate strength control and also from the economical aspect.

The temperature and time which cause they' precipitation vary depending on the amount of Ti and Al, as shown in Figure 8. The most desirable treatment conditions for y' precipitation in the present invention lie within the zone defined by the area within the lines connecting (A) (B) (C) (D) (E) in Figure 8.

Regarding the production process for the Ni-based alloys according to the present invention, they can be produced by the same production process as for ordinary stainless steels, Ni-based heat resistant steels, and corrosion resistant steels, and they can be subjected to the y' precipitation treatment under their as-hot-worked condition after hot working or hot extrusion, or under their ascold-worked condition after cold working to not more than 20% after the hot working thereof.

Preferred Examples of this invention will now be set out, in comparison with reference alloys.

In the Table are shown alloy compositions according to the present invention and reference alloy compositions. Alloys No. 1 to No. 21 are within the scope of the present invention, and were prepared in a 30 kg furnace, subjected to hot working, then 20% cold working (*1 in the Table indicates "ashot-worked condition") and heat treatment at 7500C for 3 minutes. Alloys No. 1 to No. 9 are to demonstrate the effects of Cr, Mo and W, while No. 10 to No. 1 5 are to demonstrate the effects of Ni and Cu, and No. 16 to No. 21 are to illustrate the effects of Ti and Al. For comparison, tests were performed on marginal alloy compositions outside the scope of the present Invention. These compositions are illustrated by Alloys No. 22 to No. 30. As procured, these alloys were subjected to a solid solution treatment and had a low 00.2 value.Therefore, before testing, these alloys were given 20% cold working just as with the alloys of the present invention, and subjected to heat treatment at 7500C for 3 minutes.

The results of the tests are also shown in the Table, and it is clearly illustrated by the results that the marginal alloy compositions outside the scope of the present invention are inferior to the alloy compositions within the scope of the present invention, with respect to either the CR resistance, the SCC resistance, or the 0.2 strength. These facts clearly demonstrate the technical advantages of the present invention.

Thus, although Alloy No. 22 has an alloy composition within the scope of the present invention, its SR value is low and it shows inferior CR and SCC resistances. Alloys No. 23 and 28 show a high SR value and provide CR and SCC resistances as high as the alloys within the scope of the present invention, but their strength is low due to the absence of Al and Ti, essential for the y' precipitation.

Alloys No. 24 and No. 27, which utilize the intermetallic precipitation of Nb, are also inferior in their strength due to their lower Al and Ti contents. Alloy No. 25 has a lower SR value and a lower content of Al+Ti and thus is inferior to the alloys of the present invention with respect to the strength and the corrosion resistance. Alloys No. 26 and No. 29 have an alloy composition within the scope of the present invention, but the content of AI+Ti and the X, value lie outside the scope of the present invention so that their strengths are not satisfactory. Alloy No. 30 shows a high strength, and excellent CR and SCC resistances in the NACE solution but it is inferior with respect to the CR resistance in the NSC solution. Further, this steel has a higher content of Al+Ti and shows markedly inferior hot workability so that it is quite difficult to work this alloy into long pipe products. Therefore, Alloy No. 30 should be discriminated from the alloys according to the present invention.

Table Alloy compositions (Wt.%) and various properties

NACE solution Strength 90 C NACE*4 XCC*5 solution Ca,Zr @0.2 resis- 250 C No. C Si Mn Cr Ni Mo Cu W Al Ti REM Fe X1*2 Sr*3 (KSl) CR tance CR/mdd 1 0.032 0.60 1.18 20.5 33.1 1.20 4.9 --- 0.9 1.5 --- 34.0 4.8 66.6 150 1.89 0 28.6 2 0.018 0.65 1.00 19.0 43.8 2.50 2.3 1.0 0.3 1.3 --- 28.4 13.3 77.0 135 1.19 0 5.27 3 0.048 0.32 0.70 20.5 48.0 5.00 3.4 2.2 0.2 1.5 --- 18.3 11.9 104.8 148 0.12 0 1.48 4*1 0.030 0.10 0.25 18.8 58.5 -- -- 19.3 0.5 1.5 Zr0.02 0.8 10.2 164.8 153 0 0 11.0 Ga0.01 5 0.012 0.03 0.13 17.3 52.3 12.5 2.4 1.0 0.9 1.4 Zr0.01 11.9 9.3 135.3 155 0 0 0.92 Ca 0.01 REM0.02 6 0.008 0.05 0.18 15.4 62.1 9.8 --- 10.0 0.4 1.3 Zr 0.03 --- 15.8 166.7 14.10 0 0 3.6 Ca 0.02 7 0.025 0.25 0.30 20.3 56.7 14.9 --- --- 0.3 1.4 --- 5.9 12.6 141.4 144 0 0 0.5 8 0.003 0.42 0.56 18.3 55.3 11.5 4.3 5.2 0.3 1.3 --- 3.0 12.7 161.6 138 0 0 0.47 9 0.045 0.18 0.91 21.0 44.0 2.5 2.0 --- 0.5 1.1 --- 27.6 12.8 72.8 133 1.04 0 3.5 10 0.041 0.65 0.05 18.3 41.5 3.0 4.4 --- 0.6 1.2 --- 32.0 11.2 78.5 142 0.53 0 5.92 11 0.002 0.44 0.30 17.9 53.0 3.1 2.5 --- 0.6 1.5 --- 21.1 15.2 81.1 152 0.43 0 4.45 12*1 0.036 0.32 0.24 19.5 62.0 4.5 2.4 --- 0.9 1.5 --- 8.2 15.8 96.4 158 0.08 0 1.83 13 0.021 0.10 1.05 18.2 44.0 2.9 --- --- 0.4 1.2 --- 34.2 14.3 65.9 138 2.00 0 12.02 14 0.016 0.05 1.00 18.2 32.0 5.1 0.5 --- 0.2 1.5 --- 32.1 5.1 70.5 141 1.10 0 9.76 15 0.033 0.23 0.92 17.8 44.5 2.3 1.5 --- 0.5 1.1 --- 32.8 14.9 70.1 139 1.15 0 8.7 16 0.029 0.39 0.75 20.5 45.8 2.5 --- 1.8 0.2 1.4 --- 26.3 13.1 76.9 144 1.89 0 6.61 17 0.007 0.59 0.63 20.7 45.7 2.4 --- 2.0 0.4 1.4 --- 25.9 11.4 77.6 148 1.98 0 6.44 18*1 0.041 0.42 0.14 20.9 45.8 2.4 --- 2.0 0.8 1.4 --- 25.8 9.3 77.9 154 1.92 0 6.11 19 0.035 0.18 1.15 20.9 46.9 2.4 --- 1.9 0.9 1.5 --- 23.9 9.1 78.1 151 1.76 0 5.92 Table (cont.) Alloy compositions (wt. %) and various properties

NACE solution Strength 90 C NACE*4 XCC*5 solution Ca,Zr @0.2 resis- 250 C No. C Si Mn Cr Ni Mo Cu W Al Ti REM Fe X1*2 Sr*3 (KSl) CR tance CR/mdd 20 0.022 0.29 0.48 20.8 45.8 2.4 --- 1.9 0.8 1.4 --- 26.5 12.9 77.2 149 1.94 0 6.26 21 0.025 0.15 0.59 20.9 46.7 2.4 --- 1.9 0.8 1.5 --- 24.8 9.3 78.0 150 1.79 0 5.95 22 0.1 --- --- 15 26 1.3 --- --- 0.2 2.0 80.015 53 4.4 40.9 140 32.8 x 56.65 23 0.006 --- --- 15 62 16 --- 4 --- --- Co 2.5 6 --- 167.3 80 0 0 1.25 24 0.1 --- --- 21 60 9 --- --- 0.2 0.2 Nb+Ta3.5 5 75.0 112.9 100 0.01 0 1.14 25 0.05 --- --- 21 32 --- 0.38 --- 0.4 0.4 --- 45 13.7 45.6 105 19.89 x 12.6 26 0.05 --- --- 22 42 3 2.25 --- 0.1 0.9 --- 30 17.0 75.8 110 0.75 0 2.47 27 0.08 --- --- 19 57 3 0.15 --- 0.5 0.9 Nb+Ta5.0 13 25.0 77.1 115 0.65 0 5.99 28 0.1 --- --- 22 47 9 --- --- --- --- Co 2.5 19 --- 104.5 70 0.03 0 1.3 29 0.07 --- --- 22 56 9 --- --- 0.5 1.0 Co12.5 --- 16.6 111.0 120 0.02 0 1.00 30 0.06 0.20 --- 16 71 --- --- --- 0.7 2.5 Nb 0.1 7.5 17.1 67.8 148 2.19 0 15.17 No. 22:A-286 ; No. 23: Hastelloy C276 ; No, 24: Inconel 625 ; No. 25: Incoloy 800 ; No. 26: Incoloy 825 ; No. 27:Inconel 718 ; No. 28: Hastelloy X ; No. 29: Inconel 1617 ; No, 30: Inconel X 750 .

*1:@ precloltation treatment (700 C for 3 min.) was performed directly after hot working.

*2:X1[Ni-(Cr+Mo+W)]/(Al+Ti).

*3:Sr Cr+0.73 Ni+5.35(Mo+W)+3.16 Cu.

*4:CO2; 80 atm+H2S 9 atm in artificial sea water saturated with 80 atm, CO2+9 atm. HsS.

*5:O=No stress corrosion cracking ; x=Stress corrosion cracking observed.

Claims (1)

1. Claims

   1. A Ni-based alloy comprising (by weight): C#0.06% Si#0.7% Mn#1.20% Cr:15.0~25.0% Al:0.1~1.6% Ti:1.0~1.6% Mo < 1 5% W < 20% Fe < 35% and (Cu: 0~5%) Ni+Cu#30% with the balance being unavoidable impurities and the alloy satisfying the conditions: Al+Ti:1.5~2.5% MO+W < 25% Ti/Al=1.0~10.0 Ni-(Cr+Mo+W)#3% [Ni-(Cr+Mo+W)]/(Al+Ti)=2~16, and Cr+0.73 Ni+5.35 (Mo+W)+3.16 Cu#50% said alloy being subjected to hot working and to a precipitation treatment for precipitating y' type intermetallic compound.

   2. A Ni-based alloy according to claim 1, wherein the alloy is cold worked at a rate of not more than 20% before the y' type intermetallic compound precipitation treatment.

   3. A Ni-based alloy according to claim 1 or claim 2, wherein the precipitation treatment is conducted at a temperature in the range of from 700 to 8500C for a time ranging from one minute to 5 hours.

   4. A modification of the Ni-based alloy according to any of claims 1 to 3, which alloy further comprises one or more of Ca, Zr and rare earth metals in amounts of not more than 0.1%.

   5. A high strength Ni-based alloy substantially as hereinbefore described with reference to any oneofExamplesNos. 1 to 21.

   Superseded claim 1.

   New or amended claim: (filed on 24 January 1984.

   1. A Ni-based alloy comprising (by weight): C < 0.06% Si#0.7% Mn#1.20% Cr:15.0~25.0% Al:0.1~1.6% Ti:0.1~1.6% Mo#15% W < 20% Fe < 35% and Ni+Cu#30%(Cu:0~5%) with the balance being unavoidable impurities and the alloy satisfying the conditions: Al+Ti:1.5~2.5% MO+W#25% Ti/Al=1.0~10.0 Ni-(Cr+Mo+W)#3% [Ni-(Cr+Mo+W)]/(Al+Ti)=2~16, and Cr+0.73 Ni+5.35 (Mo+W)+3.16 Cu#50% said alloy being subjected to hot working and to a precipitation treatment for precipitating y' type intermetallic compound.