JP2017503085A - Nickel-based alloys, methods and uses - Google Patents

Abstract

A method for producing a nickel-based alloy, comprising forging and solution treatment of a metal material having a predetermined composition, a first aging step at a high temperature and a step of cooling in air, and It is subjected to a second aging step at low temperature and a step of cooling in air, thereby obtaining a nickel-base alloy. As a result of these steps i) to v), the alloy comprises a hardened metal phase that is uniformly deposited throughout its crystal grains. The invention further relates to a nickel-base alloy and the use of this alloy. [Selection figure] None

Description

  The present invention relates to a nickel-base alloy having excellent corrosion resistance and mechanical properties and a method for producing the same.

[0001] In recent years, as energy demand has increased significantly, the oil extraction industry has encountered the problem of finding oil at increasing depths both on land and at the bottom of the sea.
[0002] At the same time, the size of the equipment has increased and the wall diameter or thickness has reached 18 inches (460 mm). This increase forced manufacturers to more than double the size of the starting ingot, after long and expensive homogenization heat treatments, if the chemical composition varies. Even so, it presents significant problems regarding the chemical homogeneity of the product.

[0003] Commercially available alloys known by the N07718, N07716, N07725 markings currently available on the market for use in the harshest environments have the following limitations:
-N07718 alloy can achieve good mechanical properties without damaging grain boundaries by many precipitation of harmful phases, and can be used at medium temperature and in the absence of elemental sulfur ;
-N07716 alloy is aged to obtain high mechanical properties, but has a microstructure with grain boundaries modified by significant phase precipitates, which precipitates are laboratory tested for intergranular corrosion Affects the behavior of the alloy at the same time, so the precipitates hinder its use in environments where HPHT (high pressure and high temperature) and nascent hydrogen may be present. It becomes very brittle.

  [0004] The equipment requirements of the petroleum extraction industry have markedly increased the mechanical properties of standard alloys (N07718, N07716, N07725) that primarily act on aging heat treatment, relative to commonly used alloy manufacturers. However, the aging heat treatment unfortunately does not affect the corrosivity of these alloys.

  [0005] Applicants have optimized VAR (vacuum arc remelting) recasting and thermal transformation processes to minimize chemical imperfections and repeated the processes using high performance machinery After years of research on making it tough, to satisfy the current demands of the oil and gas extraction industry, invalidate the microstructure and corrosion resistance, even for large parts It was concluded that it was necessary to obtain high mechanical properties depending on the chemical composition of the alloy.

[0006] Accordingly, the present invention, in the above spirit, proposes to provide a manufacturing method and a nickel-base alloy that can solve the problems indicated with respect to the prior art.
[0007] More specifically, the alloys according to the present invention may have some desirable features described below that have been considered to date to be substantially incompatible with each other.

[0008] The above objective is accomplished by a method for producing a nickel-base alloy that includes the following steps:
i) Forging and solution treatment of metal material;
ii) subjecting the product of step i) to a first aging step at high temperature;
iii) cooling the product of step ii) in air;
iv) subjecting the product of step iii) to a second aging step at low temperature;
v) Cooling the product of step iv) (preferably in air), thereby obtaining a nickel-base alloy.

[0009] As a result of steps i) to v), the hardened metal phase of the nickel-based alloy is precipitated in a uniform form in the crystal grains of the alloy.
[0010] In practice, in steps ii) and iv) the hardened metal phases (γ ′ and γ ″) are significantly precipitated, and the aging step is performed in such a way that the maximum precipitation rate of those phases is obtained. chosen.

  [0011] The hardened metal phase may continue to precipitate during the cooling step, but it is no longer at an optimal rate, while the carbide phase (also referred to herein as "carbide") Also, in some cases, undesired intermetallic phases may have a large precipitation rate during this process.

[0012] For this reason, the cooling steps shown above (which are followed by aging steps) are much faster than those conventionally used.
[0013] According to a particularly advantageous embodiment, as a result of steps i) to v), the nickel-base alloy comprises hardened phases γ ′ and γ ″ that are essentially precipitated at the location of the grain boundaries, and at least It includes carbides precipitated discontinuously along the boundaries of the crystal grains.

  [0014] Innovatively, according to the method described above, coupled with an appropriate analytical balance, the precipitation of carbides and unwanted phases at the grain boundaries is minimized, and within the grains of the alloy Since the uniform distribution of the hardened phase of the metal is promoted (especially outside the grain boundary region), at least presently used, even if not in non-existing form, in the alloys produced using the above method. It can be said that the phenomenon of intergranular corrosion is extremely limited compared to the alloys that are used.

  [0015] More specifically, by performing two aging treatments alternately and cooling after both, it is possible to adjust the rate of precipitate formation in each step of iii) and v). Furthermore, for each step of the process, only the precipitation of metal phases (ie γ ′ and γ ″) which is advantageous for the properties of the nickel-base alloy is activated.

  [0016] The metal material is expressed by weight percent, C = 0.030 or less, Si = 0.50 or less, Mn = 0.50 or less, Cr = 20.0 to 24.0, Ni = 55.0. ˜60.0, Mo = 5.5 to 7.0, S = 0.005 or less, P = 0.015 or less, Cu = 1.0 or less, Co = 1.0 or less, Al = 0.80 or less, Ti = 0.50-1.50, Nb = 4.0-5.5, and the remaining percentage of Fe. Preferably, Fe may be present in a percent of about 5-15 or about 5-12.

  [0017] Preferably, the metal material forged and solution-treated in step i) is expressed by weight percent, C = 0.222 or less, Si = 0.20 or less, Mn = 0.20 or less, Cr = 21.0-23, Ni = 57.0-59.0, Mo = 5.5-6.0, Al = 0.30-0.60, Ti = 0.70-1.0, Nb = 4.5-5.0, Fe = 5 as the minimum percentage.

  [0018] By way of example only, the material of the metal that has been forged and solution treated in step i), expressed in weight percent, is Ni = 58, Cr = 21.5, Mo = 5.8, Nb. = 4.8, Ti = 0.9, Al = 0.4, Fe = 8%.

  [0019] According to a possible embodiment, the metal material may consist exclusively of the above-mentioned elements, ie C, Si, Mn, Cr, Ni, Mo, S, P, in the indicated percentage. You may consist of Cu, Co, Al, Ti, Nb, and Fe.

  [0020] According to a variant embodiment, step i) comprises the sub-step of forging a metal blank at a temperature of approximately 1000-1160 ° C and then solution treating the blank at a temperature of approximately 1030-1080 ° C. Including.

[0021] Advantageously, the cooling step can be performed in water after the solution treatment sub-step and before step ii), or a similar type of quenching can be performed.
[0022] It is important to note that the product of step iii) itself already constitutes an industrially important product and has its own market.

  [0023] According to a possible aspect of the present invention, the method comprises the steps of separating the product of step iii) and performing a transformation on the first part of the separated product to produce the first final It can be said that it can include the steps of making a product (eg, a relatively low performance product) and / or storing the separated product.

  [0024] In other words, it is not necessary for all of the metal materials that have been subjected to forging and solution treatment after the start of the process to be products of step v), some of which are removed at the end of step iii) Can be modified as described above, or simply stored.

[0025] Thus, the manufacturing and logical advantages when compared to conventional alloys are obvious.
[0026] According to a preferred variant embodiment, the product of step iii) can be characterized by a yield strength of about 827 MPa or more as measured at ambient temperature.

  [0027] According to a further advantageous embodiment, the method sends the second part of the separated product in step iii) to step iv) (and then to step v)), whereby a nickel-base alloy A second product (e.g., a product with relatively high performance) may be included.

  [0028] For example, it can be said that as a result of an order for a nickel-base alloy, the separated and / or stored product may be subjected to step iv) at a different time than step iii).

  [0029] According to a preferred embodiment, after step v), the nickel-base alloy is characterized by a yield strength of approximately 950 to 970 MPa or more, preferably a yield strength of 970 MPa or more, as measured at ambient temperature. .

  [0030] It can be said herein that the terms "high" and "low" are interpreted as relative terms in the method or alloy itself, and not as absolute terms.

  [0031] Alloys with low performance are considered as such only in relation to high performance alloys, and preferably it is limited to yield strength parameters only. This does not mean that a “low” alloy according to this aspect may not be good when compared in relation to other factors, for example when compared in terms of corrosion resistance.

[0032] Similarly, the phrases "high temperature" and "low temperature" referred to above with respect to the aging process will have only a relative meaning.
[0033] With respect to step ii), this step is particularly used to minimize the precipitation of carbides and other undesirable phases at the grain boundaries.

  [0034] More specifically, according to a preferred embodiment, step ii) is carried out at a temperature of about 720-780 ° C. (defined as “high temperature”) for about 3-8 hours or about 3-6 hours. Can do. According to a further preferred embodiment, step iv) can be carried out at a temperature of about 600-640 ° C. (which is defined as “low temperature”) for about 4-10 hours.

  [0035] Preferably, one or both of the cooling steps iii) and / or v) can be carried out in air at room temperature, preferably at about the ambient temperature of the respective product.

  [0036] In the present invention, the term "ambient temperature" refers to the temperature outside of a strongly heated atmosphere in which the aging steps ii) and iv) are carried out (unless stated otherwise). Is understood to mean. In particular, the “ambient temperature” can be said to be the temperature outside the furnace used to perform the aging heat treatment described above, more precisely the temperature at the cooling plane located inside the production plant.

  [0037] To be more precise, the ambient temperature is the temperature of the production plant, which can vary greatly depending on the season in which the production takes place and / or the latitude of the production point at which the above method is carried out. .

[0038] The objects described above are also solved by a nickel-base alloy obtained by the following steps:
i) Forging and solution treatment of the metal material described above;
ii) subjecting the product of step i) to a first aging step at high temperature;
iii) cooling the product of step ii) in air;
iv) subjecting the product of step iii) to a second aging step at low temperature;
v) Cooling the product of step iv) (preferably in air), thereby obtaining a nickel-base alloy.

[0039] As a result of steps i) to v), the nickel-base alloy includes a hardened metal phase that is uniformly deposited throughout its crystal grains.
[0040] With regard to preferred or advantageous variants for the production of this alloy, the above explanations apply.

  [0041] According to a particularly advantageous embodiment, at the end of steps i) to v), the nickel-base alloy comprises hardened phases γ ′ and γ ″ that have precipitated essentially at the location of the grain boundaries, and at least The carbide | carbonized_material precipitated in the discontinuous form along the boundary of said crystal grain is included.

  [0042] More precisely, steps ii) and iv) involving step iii) promote the precipitation of the hardened phases γ ′ and γ ″ in a uniform form, and preferably in the fine form. And minimizing precipitated carbides and undesirable intermetallic phases at grain boundaries.

  [0043] The objects described above are also expressed in weight percent, C = 0.030 or less, Si = 0.50 or less, Mn = 0.50 or less, Cr = 20.0-24.0, Ni = 55. 0-60.0, Mo = 5.5-7.0, S = 0.005 or less, P = 0.015 or less, Cu = 1.0 or less, Co = 1.0 or less, Al = 0.80 or less , Ti = 0.50-1.50, Nb = 4.0-5.5, and the remaining percentage of Fe. This alloy essentially contains hardened phases γ ′ and γ ″, which are effectively uniformly (and preferably finely) precipitated at the location of the grain boundaries and is discontinuous at least at the grain boundaries mentioned above. It is characterized by containing carbides precipitated in

  [0044] For example, the alloy can be obtained using the method according to any embodiment described above. From this, even if not specifically indicated, preferred or advantageous variations of this alloy may include any manufacturing process that can be inferred from the above description.

  [0045] Advantageously, the alloys of the present invention can preferably be used to produce equipment and pipes for the chemical or petroleum industry.

It is a figure which shows the typical mechanical property of the bar material which carried out solution treatment. It is a figure which shows the typical mechanical property of the bar material ageed by solution treatment. It is a figure which shows the typical mechanical property of the bar material which carried out the solution treatment for two aging cycles. FIG. 5 shows typical analytical values for an alloy compared to AF.955. FIG. 2 shows typical mechanical properties of alloys compared to AF.955. It is a figure which shows the result of the tolerance test with respect to intergranular corrosion. It is a figure which shows the result of the tolerance test with respect to intergranular corrosion. It is a figure which shows the result of the test for determining a critical pitting temperature. It is a figure which shows the result of a SCC-NACE test. It is a figure which shows the result of the test of hydrogen embrittlement sensitivity. It is a figure which shows the structure | tissue of alloy AF.955. It is a figure which shows the structure | tissue of alloy N07718. It is a figure which shows the structure | tissue of alloy N07716.

[0046] Objects of the present invention will be described below based on non-limiting examples.
Example 1 : Means for carrying out the method
[0047] The metal material to which the present invention relates is preferably for obtaining a highly limited analytical range of composition to ensure strong desulfurization, complete deoxidation, and repeatability for mechanical and corrosive properties. Then, it is melted in an electric arc furnace and purified in AOD (argon / oxygen decarburization).

[0048] The purification process can be completed by at least one of the following operations:
-Further finishing of liquid steel in VIDP (induction vacuum degassing and casting);
-Source casting in a mold suitable for subsequent forging;
-Ingot source casting intended for subsequent remelting VAR or ESR (vacuum arc remelting or electroslag remelting).

  [0049] According to a variant, the ingot obtained after VAR remelting or ESR remelting can be subjected to a suitable homogenization heat treatment, and then subjected to a forging press (e.g. an entity for each cycle and Can be transformed into bloom by using two integrated fully automated manipulators that can be programmed for both deformation speeds.

  [0050] The bloom after intermediate grinding is a hydraulic press with four tuned hammers (eg, a dual arm manipulator and / or a new concept RCD (circular continuous deformation) rolling mill (these two devices) Can also be automated and programmed))) and can be transformed into billets or bars.

  [0051] Heat treatment equipment specially designed for long products (especially those having a length substantially greater than the width or thickness, such as pipes and bars), for grain uniformity Process in a narrow temperature range in order to give good controllability and avoid the precipitation of phases that are detrimental to corrosion resistance, especially in environments intended to use products made from alloys according to the invention Can make it possible.

  [0052] According to a preferred variant, the metal material, and thus the corresponding alloy according to the invention, can contain, on average, the basic elements in the following weight percentages: Ni = 58, Cr = 2. 5, Mo = 5.8, Nb = 4.8, Ti = 0.9, Al = 0.4, Fe = 8%.

Example 2 : Comparison between the nickel-base alloy of the present invention and a conventional alloy currently used
[0053] The nickel-base alloys of the present invention typically have the mechanical characteristics shown in FIG. 1 after thermal transformation in the temperature range of 1000-1160 ° C. and solution treatment in the range of 1030-1080 ° C.

  [0054] The nickel-base alloy of the present invention (referred to as “AF.955”) is subjected to aging for 3-8 hours at a temperature range of 720-780 ° C. after solution treatment as in the above paragraph, and When air-cooled (or equivalently cooled or rapidly cooled), it typically has the mechanical features shown in FIG. 2 and the intergranular corrosion and pitting resistance data shown in FIGS.

  [0055] Alloys air-cooled after second aging at 600-640 ° C. for 4-10 hours are resistant to the mechanical properties shown in FIG. 3 and the intergranular corrosion and pitting corrosion shown in FIGS. Shows tolerance.

  [0056] The results of the SCC corrosion test (stress corrosion cracking test) according to FIG. 9 (captured in an additional test) acknowledge the inclusion of the alloy in Nace Standard MR 0175 / ISO 15156-3 (2009).

[0057] The SSRT (Low Strain Rate Tensile Test) results in FIG. 10 show that the susceptibility of the alloy is reduced to the phenomenon of hydrogen embrittlement.
[0058] FIGS. 4 and 5 show the chemical composition and characteristic mechanical properties of the most commonly used alloys in many environments encountered in the oil and natural gas extraction industry.

[0059] For all alloys, grade 3 (Gr.3) differs from grade 3HS (Gr.3HS) only in the method of thermal aging treatment (temperature / time).
[0060] More specifically, for alloys according to the present invention, Grade 3 (Gr.3) is a nickel-based alloy that is subjected to a single aging step according to steps ii) and iii) described above and subsequent cooling. It is about. Conversely, the 3HS grade (Gr.3HS) relates to alloys that have also undergone a second aging and cooling step, ie, alloys that have also undergone steps iv) and v).

[0061] Figures 6, 7, 8, 9, and 10 provide information about the resistance capability of each material in a laboratory corrosion test when compared to the alloys of the present invention.
[0062] Further comparison of the characteristic microstructures (FIGS. 11A-11F for alloy AF.955; FIGS. 12A-12F for prior art alloy N07718; FIGS. 13A-13F for prior art alloy N07716;) The results of intergranular corrosion, pitting corrosion, SCC, and SSRT tests are based on this innovative analysis of alloying elements compared to the results obtained for conventional alloys with comparable nickel content (N07718, N07716). It clearly shows the improvement obtained by introducing the harmony of this and combining it with a thorough and innovative heat treatment method.

  [0063] With respect to the above-mentioned drawings, FIGS. 11A and 11B show the metallographic structure (100) of alloy AF.955 before step ii), ie, alloy AF.955 after forging and solution treatment of only the metal material. Times and 500 times magnification). FIGS. 11C and 11D show the metal structure (same magnification as above) of the product of step iii) above, ie the product after the first aging and subsequent air cooling steps. Finally, FIGS. 11E and 11F show the metallographic structure corresponding to that described above for alloy AF.955 at the end of step v).

  [0064] FIGS. 12A-12F and FIGS. 13A-13F show the microstructures of Alloy N07718 and Alloy N07716, respectively, corresponding to the drawings described above (after solution treatment, FIGS. 12A and 12B for Alloy N07718, and Alloy N07716). 13A and 13B; after the first type of aging for 3 grades of each alloy (FIGS. 12C, 12D and 13C, 13D); and for the 3HS grade of each alloy After the second aging (FIGS. 12E, 12F and 13E, 13F)).

  [0065] These improvements in structural resistance and corrosion resistance coupled with the high mechanical properties achieved without excessive aging heat treatment time, combined with the use of the alloy in any “sour” environment (considerably It would be advantageous to use even in deep locations (even in HPHT (high pressure high temperature) applications), and such use once had to be targeted by the user, and was similar to alloys N07718 and N07716 The optimum selection was not necessarily made with N07725.

[0066] Innovatively, the methods and nickel alloys of the present invention make it possible to brilliantly solve the drawbacks that have been said with respect to the prior art.
[0067] More specifically, the methods and nickel alloys of the present invention substantially eliminate metal phase precipitates (particularly carbides) at grain boundaries, and therefore, compared to the prior art, The phenomenon of corrosion at the grain boundaries is dramatically reduced (if not said to be substantially absent).

  [0068] In addition, the alloys of the present invention have greater mechanical resistance and tensile properties than previously compared alloys, particularly considerable corrosion resistance under stress in elongation and pinch point data. And extremely low hydrogen embrittlement, and the elongation in fracture properties is high enough to ensure safe use of the alloy in environments where initial hydrogen may be generated.

  [0069] As explained at the outset, none of the prior art alloys has been able to achieve such technical results so far, in particular products manufactured by being forged on an industrial scale Was about.

[0070] Advantageously, the nickel base alloy components and heat treatment and / or thermomechanical treatment for the present invention make the precipitation phenomenon of the hardened phase of the metal unique and characteristic.
[0071] Advantageously, in the method of the present invention, a clear temporal separation of the precipitated phases makes it possible to obtain different types of different alloys with significantly different performance.

  [0072] Nevertheless, this method makes it possible to achieve significant manufacturing cost savings, not only because of the general process that characterizes the production of various resulting alloys.

  [0073] In fact, there are currently two types of products in the market: products with Ys exceeding 120 KSi (MPa 827) and products with Ys exceeding 140 KSi (MPa about 966). Thus, using the method and alloy of the present invention, the above minimum level can be guaranteed with each of the products of step iii) and products of step v) that are part of the same manufacturing chain.

[0074] Finally, advantageously, even the length of cooling clearly affects the precipitation of the most useful phases due to mechanical properties such as resistance to corrosion and embrittlement of the alloy.
[0075] Although not desired to provide a scientific explanation of the phenomenon in any way, undesirable phases and carbides tend to precipitate at the grain boundaries. Therefore, it is technically important to minimize such precipitation and to ensure that these precipitates are not continuous at the grain boundaries. The presence or absence of precipitates at the grain boundaries affects the resistance to intergranular corrosion and hydrogen embrittlement, but has a more limited effect on the phenomenon of stress corrosion cracking.

[0076] Advantageously, even the product of step iii) has been found to be optimal for certain industrial applications.
[0077] Those skilled in the art can make modifications to the methods and nickel-base alloys described above to satisfy certain requirements and to replace one element with another functionally equivalent element.

[0078] Such modifications are also encompassed within the scope of protection defined by the claims.
[0079] In addition, each variation deemed to belong to a possible aspect can be understood as independent of the other aspects.

Claims (15)

A method for producing a nickel-based alloy, comprising the following steps:
i) Expressed in weight percent, C = 0.030 or less, Si = 0.50 or less, Mn = 0.50 or less, Cr = 20.0-24.0, Ni = 55.0-60.0, Mo = 5.5-7.0, S = 0.005 or less, P = 0.015 or less, Cu = 1.0 or less, Co = 1.0 or less, Al = 0.80 or less, Ti = 0.50 Forging and solution treatment of a metal blank containing 1.50, Nb = 4.0-5.5, and the remaining percentage of Fe;
ii) subjecting the product of step i) to a first aging step at high temperature;
iii) cooling the product of step ii) in air;
iv) subjecting the product of step iii) to a second aging step at low temperature;
v) cooling the product of step iv) in air, thereby obtaining a nickel-base alloy;
And after said steps i) to v), the hardened metal phase of the nickel-base alloy is precipitated in a uniform form in the crystal grains of the alloy.   After steps i) to v), the nickel-base alloy essentially comprises a hardened metal phase γ ′ and γ ″ precipitated at the location of the grain boundaries, and at least discontinuously along the grain boundaries. The method of claim 1 comprising a precipitated carbide phase.   And c) separating the product of step iii) and transforming the first portion of the separated product into an initial final product (eg, a lower performance product). 3. The method according to any one of 2.   Sending the second part of the separated product to step iv) and then to step v), thereby obtaining a second product of higher performance comprising the nickel-base alloy. The method in any one of 1-3.   The product of step iii) is characterized by a yield strength of approximately 827 MPa or more as measured at ambient temperature, and after step v), the nickel-base alloy is approximately 950 to 970 MPa as measured at ambient temperature. The method according to claim 1, characterized by the yield strength of   The metal material forged and solution treated in step i) is expressed by weight percent, C = 0.222 or less, Si = 0.20 or less, Mn = 0.20 or less, Cr = 21.0- 23, Ni = 57.0-59.0, Mo = 5.5-6.0, Al = 0.30-0.60, Ti = 0.70-1.0, Nb = 4.5-5. 6. A method according to any preceding claim comprising 0, Fe = 5 as a minimum percentage.   The metal material forged and solution treated in step i) is expressed as weight percent, Ni = 58, Cr = 21.5, Mo = 5.8, Nb = 4.8, Ti = 0.9. The method according to claim 1, comprising Al = 0.4 and Fe = 8%.   The process according to any of claims 1 to 7, wherein step ii) is carried out at a temperature of about 720-780C for about 3-8 hours or about 3-6 hours.   The process according to any of claims 1 to 8, wherein step iv) is carried out at a temperature of 600 to 640C for about 4 to 10 hours.   Step i) includes a sub-step of forging a metal material at a temperature of approximately 1000 to 1160 ° C. and then solution-treating the material at a temperature of approximately 1030 to 1080 ° C. The method according to claim 1, wherein a cooling step is carried out in water later before step ii).   Cooling steps iii) and v) are carried out in air at ambient temperature, ie at temperatures outside the heated atmosphere in which the aging steps ii) and iv) are carried out until the ambient temperature of the respective product is reached. The method according to claim 1. The following steps:
i) Expressed in weight percent, C = 0.030 or less, Si = 0.50 or less, Mn = 0.50 or less, Cr = 20.0-24.0, Ni = 55.0-60.0, Mo = 5.5-7.0, S = 0.005 or less, P = 0.015 or less, Cu = 1.0 or less, Co = 1.0 or less, Al = 0.80 or less, Ti = 0.50 Forging and solution treatment of a metal blank containing 1.50, Nb = 4.0-5.5, and the remaining percentage of Fe;
ii) subjecting the product of step i) to a first aging step at high temperature;
iii) cooling the product of step ii) in air;
iv) subjecting the product of step iii) to a second aging step at low temperature;
v) cooling the product of step iv) in air, thereby obtaining a nickel-base alloy;
The nickel-base alloy obtained by the method according to claim 1, wherein the nickel-base alloy includes a hardened metal phase uniformly precipitated over the entire crystal grains after steps i) to v).   After steps i) to v), the nickel-base alloy essentially comprises a hardened metal phase γ ′ and γ ″ deposited at the location of the grain boundaries and is discontinuous at least along the grain boundaries. The alloy of claim 12 comprising a carbide phase precipitated in form.   Expressed in weight percent, C = 0.030 or less, Si = 0.50 or less, Mn = 0.50 or less, Cr = 20.0-24.0, Ni = 55.0-60.0, Mo = 5 0.5 to 7.0, S = 0.005 or less, P = 0.015 or less, Cu = 1.0 or less, Co = 1.0 or less, Al = 0.80 or less, Ti = 0.50 to 1. A nickel-base alloy comprising a metal stock comprising 50, Nb = 4.0-5.5, and the remaining percentage of Fe (e.g., a nickel-base produced by the method of any of claims 1-11) Alloy), which essentially includes hardened phases γ ′ and γ ″ precipitated at non-crystalline grain boundaries, and carbides precipitated in a discontinuous manner at least along the boundaries of the crystal grains. The nickel-base alloy characterized by   Use of an alloy according to any of claims 12 to 14 for the manufacture of equipment or pipes for the chemical or petroleum industry.

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