Nickel-based alloy

Abstract

A nickel-based alloy having the following in weight percent (wt.%): C up to 0.05, Si up to 1.0, Mn 0.5 - 1.5, P up to 0.03, S up to 0.03, Cr 31.5 - 36.0, Mo 7.0 - 10.0, N 0.08 - 0.18, Cu up to 0.4, Fe 2.0 - 6.5, Optionally, Al up to 0.30, Optionally, either Ca or Mg, each up to 0.05, or REM up to 0.5, Optionally, B up to 0.0050, The balance of Ni and normally occurring impurities, in total up to 1.5 weight percent having the composition, wherein the composition satisfies the following Equation 1: E Ni ≥ 1.864 * E Cr - 24.0 (Equation 1) [wherein, E Cr = [wt.-% Cr] + [wt.-% Mo] + 1.5 * [wt.-% Si], and E Ni = [wt.-% Ni] + 30 * [wt.-% C] + 30 * [wt.-% N] + 0.5 * [wt.-% Mn] + 0.5 * [wt.-% Cu]] A nickel-based alloy satisfying the requirements.

Description

[Technical Field]

[0001] This invention generally relates to nickel-based alloys intended for use in highly corrosive environments. This disclosure further generally relates to methods for manufacturing nickel-based alloy objects. [Background technology]

[0002] Nickel-based alloys are important to modern industry because they can withstand a variety of harsh operating conditions, including corrosive environments, high temperatures, high stress, and combinations of these factors. Therefore, nickel-based alloys can be used in applications where the properties of today's austenitic stainless steels are insufficient to meet the requirements.

[0003] However, nickel-based alloys with high Cr and Mo content tend to form undesirable intermetallic phases, though not to the same extent as austenitic stainless steels. These phases may already be formed during solidification, primarily by microsegregation. Intermetallic phases can negatively affect both the mechanical properties and corrosion resistance of nickel-based alloys. It is known that the content of intermetallic phases in nickel-based alloys can be reduced by certain methods, such as remelting and dipping. Common remelting techniques include vacuum arc remelting (VAR) and electroslag remelting (ESR). However, such processes are very expensive. To reduce manufacturing costs, it is desirable to use conventional metallurgical methods used in the production of austenitic stainless steels.

[0004] A well-known example of a nickel-based alloy is Alloy 625 (UNS N06625), which is used in a variety of applications due to its excellent corrosion resistance and mechanical properties. Alloy 625 is typically composed of Mn ≤ 0.5 wt%, Cr 20.0-23.0 wt%, Co ≤ 1.0 wt%, Mo 8.0-10.0 wt%, Nb + Ta 3.15-4.15 wt%, Fe ≤ 5.0 wt%, and Ni at least 58 wt%. However, this alloy does not possess sufficient properties to withstand harsher environments.

[0005] Another previously known example of a nickel-based alloy is G-35 (UNS N06035), which was developed to withstand the phosphoric acid used in the "wet process" of fertilizer production. This alloy also exhibits high resistance to localized attack by chlorides. G-35 is typically composed of Mn ≤ 0.5 wt%, Cr 32.25–34.25 wt%, Co ≤ 1.0 wt%, Mo 7.6–9.0 wt%, W ≤ 0.60 wt%, Cu ≤ 0.30 wt%, V ≤ 0.20 wt%, and Fe ≤ 2.0 wt%. However, this alloy is difficult to manufacture using conventional metallurgical processes in melting plants where iron contamination of the molten material is possible.

[0006] International Publication No. 2019 / 224287 A1 discloses an austenitic alloy containing 25-33.0 wt% Cr, 42.0-52.0 wt% Ni, 6.0-9.0 wt% and 0.07-0.11 wt% N, satisfying the condition ENi > 1.864 * ECr -19.92. The alloy exhibits good corrosion resistance, has a low content of intermetallic phases after solidification, and can be manufactured by conventional metallurgical methods. While the alloy performs very well in many applications, there may be applications requiring even higher resistance to localized corrosion. [Overview of the Initiative]

[0007] The purpose of this disclosure is to provide a nickel-based alloy that can be manufactured by conventional metallurgical methods (i.e., methods that do not require special processing steps such as remelting), has excellent corrosion resistance even in highly corrosive environments, and forms only a small amount of intermetallic phase during solidification.

[0008] According to this disclosure, a nickel-based alloy having the following composition in weight percent (wt.%) is provided. C 0.05 or less, Si 1.0 or less, Mn 0.5~1.5, P 0.03 or less, S 0.03 or less, Cr 31.5~36.0, Mo 7.0~10.0, N 0.08~0.18, Cu 0.4 or less, Fe 2.0~6.5, Optionally, set Al to a maximum of 0.30. Selectively, either Ca or Mg, up to a maximum of 0.05, or REM, up to a maximum of 0.5. Optionally, set B to a maximum of 0.0050. The remaining Ni and normally occurring impurities total a maximum of 1.5% by weight. Having the composition, In the formula, the composition is as follows: E Ni ≥1.864* ​​E Cr -24.0 (Equation 1) [In the formula, E Cr =[wt.-% Cr]+[wt.-% Mo]+1.5*[wt.-% Si], and E Ni =[wt.-% Ni]+30*[wt.-% C]+30*[wt.-% N]+0.5*[wt.-% Mn]+0.5*[wt.-% Cu]] A nickel-based alloy that meets the requirements.

[0009] Surprisingly, it has been found that by using the nickel-based alloys described herein, high corrosion resistance, particularly high pitting corrosion resistance, can be achieved while reducing the amount of intermetallic phase during solidification. Furthermore, the nickel-based alloys described herein exhibit high yield strength and high ductility. Moreover, the nickel-based alloys described herein can be manufactured by conventional metallurgical processes.

[0010] The nickel-based alloys described herein are suitable for a variety of applications involving highly corrosive environments, such as the chemical process industry (including the petrochemical industry). For example, the nickel-based alloys described herein can be used in heat exchangers, process tubes, and / or piping in the chemical process industry. Given their excellent properties, they can also be used in components that use seawater as a cooling medium. The nickel-based alloys described herein can also be used in other components configured for seawater cooling, and optionally, in one or more aggressive solutions present on the process side of the component.

[0011] Furthermore, the present invention provides a method for manufacturing an object of nickel-based alloy as described herein. This method is - Casting a molten material having the above-mentioned composition to obtain a cast alloy, - Optionally, heat-treating the cast alloy, - Hot working (and optionally heat treatment) of cast alloys, - Optionally, heat-treating a hot-worked alloy, - Selectively performing hot working (and selectively heat-treating) on ​​an alloy and cold working on that alloy. - Optionally, heat-treating a cold-worked alloy. Includes. [Brief explanation of the drawing]

[0012] [Figure 1] The amount of intermetallic phase formed during the solidification of the experimental alloy is shown as a function of 1.864*ECr-ENi. [Figure 2] Shows the critical pitting temperature (CPT) of the test alloy measured at a potential of 600 mV versus SCE using 4.5 M MgCl2 pH 5 as the electrolyte in accordance with ASTM G150. [Figure 3] Shows the general corrosion rate of the test alloy measured in 20% H2SO4 at a temperature of 93°C in accordance with ISO 18069.

Mode for Carrying Out the Invention

[0013] The present invention will be described in more detail below with reference to embodiments. However, the present invention is not limited to the exemplary embodiments described herein and can be modified within the scope of the appended claims.

[0014] When a range is disclosed in the present disclosure, each end value of the range is included in such range unless otherwise explicitly disclosed separately. Similarly, when an open range is disclosed, a single end value of the open range is also included in the open range unless otherwise explicitly disclosed separately.

[0015] The present invention provides an austenitic nickel-based alloy. The austenitic nickel-based alloy can exist in any possible product form without departing from the present disclosure. For example, the austenitic nickel-based alloy can exist as an ingot, billet, bloom, bar, tube, pipe, rod, strip, plate, sheet, hollow, fitting, flange, or wire (such as welding wire), but other product forms are also conceivable.

[0016] The austenitic nickel-based alloy of the present invention, even if it contains iron, ensures that the product form has acceptable properties such as corrosion resistance and mechanical properties.

[0017] Surprisingly, it has been found that using the austenitic nickel-based alloys described herein allows for the achievement of extremely high corrosion resistance while avoiding the formation of large amounts of intermetallic phases during solidification from (primary) melting. Austenitic nickel-based alloys also possess mechanical properties, making them suitable as alternatives to conventional nickel-based alloys. Furthermore, since the austenitic nickel-based alloys described herein can be manufactured by conventional metallurgical processes, there is no need to remelt them to obtain the desired properties. The term "conventional metallurgical processes" refers to processes that include steps such as melting, casting, hot working, and cold working, but do not include special steps such as remelting and prolonged diffusion heat treatment operations.

[0018] The austenitic nickel-based alloy according to this disclosure has the following composition in weight percent (wt.-%). C 0.05 or less, Si 1.0 or less, Mn 0.5~1.5, P 0.03 or less, S 0.03 or less, Cr 31.5~36.0, Mo 7.0~10.0, N 0.08~0.18, Cu 0.4 or less, Fe 2.0~6.5, Optionally, set Al to a maximum of 0.30. Selectively, either Ca or Mg, up to a maximum of 0.05, or REM, up to a maximum of 0.5. Optionally, set B to a maximum of 0.0050. The remaining Ni and normally occurring impurities total a maximum of 1.5% by weight. Having the composition, In the formula, the composition is as follows: E Ni ≥1.864* ​​E Cr -24.0 (Equation 1) [In the formula, E Cr=[wt.-% Cr]+[wt.-% Mo]+1.5*[wt.-% Si], and E Ni =[wt.-% Ni]+30*[wt.-% C]+30*[wt.-% N]+0.5*[wt.-% Mn]+0.5*[wt.-% Cu].

[0019] As is evident from the above, the austenitic nickel-based alloys described herein contain a relatively high amount of iron compared to conventionally known nickel-based alloys designed for very aggressive environments, such as G-35. Surprisingly, by selecting the composition to satisfy the requirements of Equation 1 above, it was found that, despite the relatively high iron content, the amount of intermetallic phase formed during solidification was significantly reduced, resulting in good thermal stability. Compared to conventional nickel-based alloys designed for very harsh environments, a higher iron content in the alloy has the advantage of significantly reducing manufacturing costs. For example, the alloys can be manufactured using equipment used for steel production without requiring remelting or other specific process steps that increase manufacturing costs.

[0020] According to the embodiment, the composition of the austenitic nickel-based alloy can further satisfy the requirement that PRE (wherein PRE = [wt.-% Cr] + 3.3 * [wt.-% Mo] + 16 * [wt.-% N]) is 61.0 or higher. To further improve pitting corrosion resistance, the composition of the austenitic nickel-based alloy can satisfy the requirement that PRE is 63.0 or higher.

[0021] The importance of various alloying elements in austenitic nickel-based alloys is briefly described below. All percentages of the chemical composition are given in weight percent (wt.-%) unless expressly disclosed otherwise. The upper and lower limits of the individual components of the composition may be freely combined within the broadest range described in the claims unless expressly disclosed otherwise.

[0022] Carbon (C): 0.05% or less Carbon is not an element intentionally added to the alloys described herein, but may be present as a result of the raw materials and processes used. However, if the carbon content is too high, chromium carbide may precipitate at the grain boundaries, potentially reducing corrosion resistance. Therefore, the carbon content of the alloys described herein is 0.05% or less. The risk of chromium carbide formation is further reduced by the reduced carbon content. Therefore, carbon may instead be present in an amount of 0.03% or less.

[0023] Since carbon is merely an impurity in the alloys described herein, there is no critical lower limit for the presence of carbon. However, in some cases, carbon may be present in concentrations of 0.005% or more.

[0024] Silicon (Si): 1.0% or less Silicon is an element frequently added as an oxygen scavenger. However, if the silicon content is too high, unwanted intermetallic phases such as the sigma phase may precipitate, potentially reducing hot workability. Therefore, the silicon content of the alloys described herein is 1.0% or less. To further reduce the risk of intermetallic phase formation, the silicon content may be 0.50% or less, or even 0.30% or less.

[0025] Lower content is also possible, but the silicon content of the alloys described herein may be 0.10% or more, according to one alternative. According to the embodiment, the Si may be in the range of 0.10 to 0.50%, for example, 0.10 to 0.30%.

[0026] Manganese (Mn): 0.5~1.5% Manganese is an element used to bond sulfur by forming MnS, thereby increasing the hot ductility of alloys. Mn is also an effective deoxidizer. Furthermore, Mn is an element that stabilizes austenite. Mn may also contribute to increased deformation hardening during cold working. Therefore, the alloys described herein contain 0.5% or more of Mn. To further increase deformation hardening during cold working, according to embodiments, Mn may be present in amounts of 0.60% or more, and even 0.85% or more.

[0027] However, if the amount of Mn is too high, it can not only reduce the strength of the alloy but also reduce its hot workability. Therefore, the alloys described herein contain 1.5% or less of Mn. According to the embodiments, Mn can be present in an amount of 1.30% or less, for example, 1.20%.

[0028] Phosphorus (P): 0.03% or less Although phosphorus is not an element that is intentionally added, it can be present as an impurity. It is well known that when present in excessive amounts, phosphorus (P) adversely affects hot workability and hot crack resistance. Therefore, in the alloys described herein, phosphorus may be present in amounts of 0.03% or less without substantially adversely affecting the properties.

[0029] Sulfur (S): 0.03% or less Like phosphorus, sulfur is an impurity element in the alloys described herein, and excessive amounts can reduce hot workability. S may be acceptable in amounts of 0.03% or less without substantially adversely affecting the properties of the alloy. Lower amounts of S are preferable, and therefore the S content may be limited to 0.02% or less.

[0030] Chromium (Cr): 31.5-36.0% Chromium is a very important element because it contributes to corrosion resistance in the sense of both pitting corrosion resistance and crevice corrosion resistance. Furthermore, Cr contributes not only to general corrosion resistance but also to stress corrosion cracking resistance. To achieve the desired corrosion resistance, the alloys described herein contain 31.5% or more Cr. For the purpose of further enhancing corrosion resistance, according to embodiments, the alloy may contain 32.0% or more Cr, or 32.5% or more Cr.

[0031] However, if the chromium content is too high, the risk of intermetallic phase formation, such as the sigma phase, increases, which can lead to reduced corrosion resistance and decreased brittleness. Therefore, the chromium content of the alloys described herein is 36.0% or less. According to the embodiments, the chromium content is 35.0% or less.

[0032] Molybdenum (Mo): 7.0~10.0% Molybdenum has the effect of stabilizing the passive film formed on the surface of austenitic nickel-based alloys, and is an element that greatly contributes to improving pitting corrosion resistance. Mo can also contribute to improving resistance to crevice corrosion. To obtain the desired corrosion resistance, the alloys described herein contain 7.0% or more of Mo. To further improve corrosion resistance, the alloys may contain 7.5% or more of Mo, and even 8.0% or more of Mo.

[0033] However, too much Mo can negatively affect hot workability. Furthermore, excessively high molybdenum content increases the risk of intermetallic phase formation, such as sigma phases, which can lead to reduced corrosion resistance and decreased brittleness. Therefore, the alloys described herein contain 10.0% or less Mo. According to embodiments, the alloys described herein may contain 9.5% or less Mo, or 9.0% or less Mo.

[0034] Nitrogen (N): 0.08~0.18% Nitrogen is an effective element for increasing strength through solid solution hardening and may also improve structural stability. Furthermore, nitrogen contributes to pitting corrosion resistance. Nitrogen may also contribute to deformation hardening during cold working of alloys. To achieve the desired contributions to strength and pitting corrosion resistance, the alloy contains 0.08% or more of N. To further improve strength and pitting corrosion resistance, according to the embodiment, the alloy may contain 0.10% or more of N.

[0035] However, too much nitrogen can negatively affect hot workability and lead to the formation of chromium nitrides, which negatively impact mechanical and corrosion properties. Therefore, the alloy contains 0.18% or less of N. The alloy of the present invention can contain 0.17% or less of N. The alloy of the present invention can contain 0.15% or less of N.

[0036] Copper (Cu): 0.4% or less The alloys described herein may contain copper, for example, to improve corrosion resistance to sulfuric acid or phosphoric acid. Copper may also be present as a result of the raw materials used in the manufacture of the alloy. Once copper is present in an austenitic alloy, it is extremely difficult to remove, and if such alloys are used as raw materials in the manufacture of the alloys described herein, copper will inevitably be present. High levels of Cu may risk resulting in reduced hot workability of the alloy. Therefore, the Cu content is 0.4% or less.

[0037] Furthermore, high levels of Cu are undesirable because, as mentioned above, removing Cu is difficult, and this can cause problems when attempting to recycle the alloys described herein. Therefore, the upper limit for Cu may alternatively be 0.25% or less.

[0038] Copper may be present in amounts such as, for example, at least 0.01%, at least 0.02%, or at least 0.05%. The presence of 0.10% or more of Cu may further improve the corrosion resistance of the alloy.

[0039] Iron (Fe): 2.0-6.5% Iron is not a critical element for obtaining desirable alloy properties such as corrosion resistance, and is generally considered an unnecessary element in nickel-based alloys intended for use in highly corrosive environments. However, to enable a cost-effective manufacturing process while obtaining desired thermal stability and corrosion resistance, the alloys described herein contain 2.0% or more Fe. As mentioned above, given the composition that satisfies the requirements of Formula 1, such a high presence of iron is permissible in the alloys described herein. A higher amount of Fe in the alloy allows for even easier manufacturing. Therefore, according to the embodiment, the iron content of the alloy may be equal to 2.5%, but advantageously it may be 3.0% or more.

[0040] Therefore, the alloys defined above or below primarily contain iron in order to enable the cost-effective manufacture of the alloys of the present invention.

[0041] However, if the iron content is too high, the alloying elements that contribute to the desired corrosion resistance will decrease. Furthermore, if the iron content is too high, the risk of intermetallic phase formation, such as the sigma phase, increases, leading to reduced corrosion resistance and decreased brittleness. This increased risk of intermetallic phase formation inevitably results in a decrease in the amount of nickel in the alloy due to the higher amount of iron. The amount of nickel in the alloy has a significant impact on the risk of intermetallic phase formation, as is clear from the requirements of Equation 1 above. Therefore, the alloys described herein contain 6.5% or less of Fe. According to embodiments, iron is present in amounts of 6.0% or less, and even 5.5% or less.

[0042] Aluminum (Al), optionally, up to 0.30% In the manufacturing process for austenitic alloys, aluminum may be added, for example, for deoxygenation purposes. The alloys described herein may contain, for example, up to 0.30% or up to 0.10% of Al. However, in some cases, Al may be present in amounts of 0.001% or more.

[0043] Calcium (Ca) or magnesium (Mg) or REM: Selectively, up to 0.05% Ca or Mg and up to 0.5% REM. Calcium, magnesium, and REM are examples of elements that may be added during the manufacturing process, for example, to improve hot ductility or machinability. The alloys described herein may optionally contain either Ca or Mg in an amount of up to 0.05%. Alternatively, the alloys described herein may optionally contain up to 0.5% REM. However, in some cases, these elements may be present individually in an amount of at least 0.0005%.

[0044] Boron (B): Optionally, 0.0050% or less. Another example of an element that may be added during the manufacturing process is boron (B), which is sometimes used in austenitic alloys as a grain refiner or to improve hot ductility. The alloys described herein may contain B in amounts of 50 ppm or less, or 30 ppm or less. However, in some cases, boron may be present at least 0.0005%.

[0045] Typical impurities: up to 1.5% in total The alloys described herein may contain, in addition to the elements already identified and discussed above, a total of up to 1.5% of commonly occurring impurities. In this disclosure, commonly occurring impurities are considered to be impurities arising from the manufacturing process and / or the raw materials used. Here, commonly occurring impurities include both impurities and trace elements. The amount of commonly occurring impurities is appropriately 1.0% or less in total, according to the embodiments.

[0046] For example, the alloys described herein may contain commonly occurring impurities belonging to the group consisting of niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), and vanadium (V). In the alloys of the present invention, the content of elements belonging to the group can be limited to a maximum of 0.2% by weight each and a total of 0.5% by weight or less in order to reduce the risk of unintended intermetallic phase formation. To further reduce the risk of unintended intermetallic phase formation, elements belonging to the group consisting of niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), and vanadium (V) may be present in amounts of a maximum of 0.1% each and a total of 0.3% or less.

[0047] Furthermore, the alloys described herein may additionally or alternatively contain cobalt (Co) and / or tungsten (W) as impurity elements. Co and W are examples of elements commonly found in austenitic alloys and may therefore be present in the raw materials used in the manufacture of the alloys described herein. The normally occurring impurities belonging to the group consisting of Co and W may be limited to a maximum of 0.5% each, or a maximum of 0.3% each.

[0048] Another example of a possible impurity is tin (Sn), which may be present in amounts of less than 0.1%.

[0049] Nickel (Ni) As stated above, the alloys described herein contain nickel as the remainder. For example, nickel may be present in an amount of at least 50%. To further improve the properties, nickel may be present in an amount of at least 51.0%.

[0050] Manufacturing method The austenitic nickel-based alloys described herein can be manufactured, for example, by conventional metallurgical methods without requiring remelting, and can be processed into desired product forms depending on the intended use.

[0051] More specifically, the nickel-based alloys described herein can be produced by preparing a molten material having the above-described composition, and subsequently casting the molten material into a casting alloy. A molten material having the intended composition is produced, for example, in a process using an EAF (electric arc furnace), and then subjected to AOD (argon oxygen decarburization) and optionally final adjustment. The molten material is cast, for example, into an ingot, billet, or bloom.

[0052] If necessary, the cast alloy may be subsequently heat-treated. For example, the cast alloy may be optionally homogenized.

[0053] The cast alloy may then be subjected to hot working. In some cases, the hot working may be carried out until the final product form is reached. However, in most cases, the hot working is carried out to an intermediate product form. An intermediate product form means a product form that is intended to be subjected to cold working and / or other processing steps to reach the final product form intended herein. The hot working may be carried out by forging and / or rolling and / or extrusion.

[0054] Hot-worked alloys can then be optionally subjected to heat treatment. Such heat treatment may include, for example, annealing for the purpose of recrystallization and / or melting.

[0055] Subsequently, the hot-worked (and optionally heat-treated) alloy can be subjected to cold working. For example, cold working can be carried out by pilgering, rolling, or drawing. According to one alternative, cold working can be carried out to the final desired product form.

[0056] Cold-worked alloys can be subjected to optional heat treatment as needed. For example, cold-worked alloys can be subjected to solution heat treatment or stress relaxation treatment.

[0057] Depending on the application of the alloy described herein, it may be subjected to further steps after cold working and, if applicable, after subsequent heat treatment. Examples of such steps include, but are not limited to, straightening and / or machining.

[0058] It should be noted that the term "heat treatment" as used above may include one or more consecutive heat treatment steps without departing from this disclosure.

[0059] The final product may take the form of rods, tubes, pipes, strips, plates, sheets, hollow bodies, fittings, flanges, wires, etc., but other forms are also possible. In many of the intended applications of the alloys described herein, the product form can be selected from the group consisting of tubes, rods, and welding wires. Such welding wires can be used, for example, in welding processes to join other parts containing the alloys described herein.

[0060] characteristics The austenitic nickel-based alloys described herein contain less than 0.8 volume percent of intermetallic phase after solidification. This is a result of the composition of the austenitic nickel-based alloys, which includes both the specified ranges of individual elements and a composition that satisfies the requirements of Formula 1 above. In fact, it has been found that intermetallic phase content of 0.6 volume percent or less can be achieved despite the high alloying element content of the alloys described herein.

[0061] Furthermore, the alloys described herein may exhibit a critical pitting temperature (CPT) of at least 88°C, for example, at least 92°C, when measured according to ASTM G150 using 4.5 M MgCl2 pH5 as the electrolyte and a potential of 600 mV relative to a saturated calomel electrode (SCE). Typically, the CPT increases with increasing PRE, and it was found that when the composition of the alloys described herein was selected such that the PRE was 63.0 or higher, a CPT of 98°C or higher was obtained, as measured according to ASTM G150 using 4.5 M MgCl2 pH5 as the electrolyte and a potential of 600 mV relative to a saturated calomel electrode (SCE). The pitting temperature was measured on samples with all surfaces wet-polished using P600 paper.

[0062] Furthermore, because the alloys described herein have a relatively high iron content, they can be manufactured using far more cost-effective methods compared to conventional nickel-based alloys designed for highly corrosive environments. In fact, conventional metallurgical processes, and the same equipment used for stainless steel production, may result in iron contamination.

[0063] Furthermore, the austenitic nickel-based alloys described herein, after solution heat treatment at room temperature, exhibit a yield strength (Rp0.2) exceeding 320 MPa and an elongation exceeding 35%, as measured according to ISO 6892-1. In fact, it has been found that after solution heat treatment, yield strengths exceeding 350 MPa and elongation exceeding 50% can be obtained.

[0064] Experimental results Ten different experimental alloys, numbered A through J below, were manufactured by melting each alloy in a high-frequency induction furnace to obtain 270 kg of molten material. The molten material was cast into ingots using a 9-inch diameter mold. After the molten material solidified, the mold was removed and the ingots were rapidly cooled in water. For comparison, alloy X, corresponding to G-35 (UNS N06035), was manufactured using the same method. The compositions of the manufactured experimental alloys A through J and alloy X are shown in Table 1.

[0065] For the purpose of investigating the amount of intermetallic phases formed during solidification, samples were taken from the top of the ingot, prepared for metallographic examination, and etched using Murakami etchant. The occurrence of intermetallic phases was investigated using an optical microscope (LOM) and image analysis. The percentage of intermetallic phases was measured by image analysis applied to a total of 20 randomly selected image fields at a magnification of 200x.

[0066] The results of the investigation of the amount of intermetallic phases formed during solidification are presented in Table 1 and shown in Fig. 1. As is clear from the results, when 1.864*E Cr -E Ni exceeds 25, the amount of intermetallic phases increases rapidly. Therefore, in order to make the amount of intermetallic phases less than 0.8% by volume, 1.864*1.864*E Cr -E Ni needs to be 24.0 or less. In fact, when the criteria of Equation 1 are met, as the results show, the amount of intermetallic phases formed during solidification can be 0.6% by volume or less. Table 1 Chemical composition after heating TIFF2026516861000002.tif93170* Comparison, outside the scope of the claims

[0067] After samples were taken to investigate the amount of intermetallic phases formed during solidification, the ingot was hot forged, hot rolled, and then cold rolled to a sheet with a final thickness of 7 mm. The cold rolled 7 mm sheet was then solution heat treated at a temperature of 1175 °C to 1200 °C.

[0068] For the purpose of comparing corrosion resistance, commercially available Alloy 625 was also obtained and the following corrosion tests were performed.

[0069] The pitting corrosion resistance of alloys A - G and J, and Alloy X was tested in all solution heat treated states. More specifically, in accordance with ASTM G150, the critical pitting temperature (CPT) was determined at a potential of 600 mV vs. SCE (saturated calomel electrode) with 4.5 M MgCl2 pH 5 as the electrolyte. For comparison, Alloy 625 (UNS N06625) was also tested in a solution heat treated state following the same procedure.

[0070] For experimental alloys A-G and J, resistance to general corrosion in sulfuric acid was tested under solution heat treatment conditions. For comparison, Alloy 625 and Alloy X were also tested under solution heat treatment conditions using the same procedure. General corrosion was measured according to ISO 18069 at a temperature of 93°C with 20% H2SO4, and the test specimens were activated with 26% hydrochloric acid at room temperature before each test period.

[0071] The results of the above corrosion resistance tests are shown in Table 2. Furthermore, Figure 2 shows the critical pitting temperature of the tested alloy, and Figure 3 shows the typical corrosion of the tested alloy. Table 2 Results of corrosion resistance tests TIFF2026516861000003.tif105170* Comparison, outside the scope of claims

[0072] As is clear from the results shown in Table 2, the experimental alloys according to this disclosure exhibit a CPT (Critical Point Threshold) of over 92°C. This is significantly higher than the CPT values ​​of the tested Alloy 625 and Alloy X (equivalent to G-35).

[0073] Furthermore, considering that the alloys described herein were tested with higher concentrations of MgCl2 in the electrolyte and exhibited equivalent or higher critical pitting temperatures, they demonstrate higher resistance to pitting corrosion compared to the experimental results disclosed in International Publication No. 2019 / 224287.

[0074] Furthermore, the results shown in Table 2 indicate that selecting a composition such that the PRE is 63.0 or higher can achieve a CPT of at least 98°C.

[0075] The results shown in Table 2 indicate that the experimental alloys according to this disclosure exhibit significantly higher resistance to general corrosion in sulfuric acid compared to Alloy 625. While their resistance to general corrosion is considerably superior to that of Alloy X (equivalent to G-35), Alloy A exhibits corrosion resistance comparable to that of Alloy X.

[0076] Furthermore, tensile tests were performed on alloys A-J and X at room temperature in a solution-heat-treated state, according to ISO 6892-1. The results of the tensile tests are shown in Table 3. Table 3 Results of Tensile Tests TIFF2026516861000004.tif98170* Comparison, outside the scope of claims

[0077] As is clear from the results shown in Table 3, all experimental alloys exhibited a yield strength Rp0.2 exceeding 320 MPa and an elongation exceeding 35% after solution heat treatment. This indicates that this alloy possesses even greater mechanical properties and is suitable as a replacement for known nickel-based alloys for use in highly corrosive environments. In fact, the results show that a yield strength exceeding 350 MPa and an elongation exceeding 50% can be obtained after solution heat treatment.

Claims

1. Nickel-based alloys, expressed in the following weight percentages (wt.%): C 0.05 or less, Si 1.0 or less, Mn 0.5-1.5, P 0.03 or less, S 0.03 or less, Cr 31.5-36.0, Mo 7.0-10.0, N 0.08-0.18, Cu 0.4 or less, Fe 2.0~6.5, Selectively, set Al to a maximum of 0.

30. Selectively, either Ca or Mg, up to a maximum of 0.05, or REM, up to a maximum of 0.

5. Optionally, set B to a maximum of 0.0050. The remaining Ni and normally occurring impurities total a maximum of 1.5% by weight. Having the composition, In the formula, the composition is as follows: E Ｎｉ ≥ 1.864 * E Ｃｒ -24.0 (Formula 1) [In the formula, E Ｃｒ = [wt.-% Cr] + [wt.-% Mo] + 1.5 * [wt.-% Si], and E Ｎｉ 1000000000000000000000000000000000000000030000000000000000000000000000000000000005 ll    Lo li Lo rags +       !” 000000000000000000000000000500000000000000020 A nickel-based alloy that meets the requirements.

2. The nickel-based alloy according to claim 1, wherein Ni is present in an amount of at least 50% by weight.

3. The nickel-based alloy according to claim 1 or 2, wherein Cr is present in an amount of 32.0 to 35.0% by weight.

4. A nickel-based alloy according to any one of claims 1 to 3, wherein Mo is present in an amount of 7.5 to 9.5% by weight.

5. A nickel-based alloy according to any one of claims 1 to 4, wherein N is present in an amount of 0.10 to 0.17% by weight.

6. A nickel-based alloy according to any one of claims 1 to 5, wherein Fe is present in an amount of 2.5 to 6.0% by weight.

7. A nickel-based alloy according to any one of claims 1 to 6, wherein Mn is present in an amount of 0.60 to 1.30% by weight.

8. A nickel-based alloy according to any one of claims 1 to 7, wherein Cu is present in an amount of 0.01 to 0.25% by weight.

9. A nickel-based alloy according to any one of claims 1 to 8, wherein Si is present in an amount of 0.50% by weight or less.

10. A nickel-based alloy according to any one of claims 1 to 9, wherein the amount of commonly occurring impurities belonging to the group consisting of Nb, Ti, Ta, Zr, and V is limited to a maximum of 0.2% by weight each and a total of 0.5% by weight or less, and / or the amount of commonly occurring impurities belonging to the group consisting of Co and W is limited to a maximum of 0.5% by weight each, or a maximum of 0.3% by weight each.

11. A nickel-based alloy according to any one of claims 1 to 10, wherein the composition satisfies the requirement that PRE [wherein PRE = [wt. -% Cr] + 3.3 * [wt. -% Mo] + 16 * [wt. -% N]] is 61.0 or greater.

12. Use of the nickel-based alloy according to claims 1 to 11 in components used in the chemical process industry and / or components used for seawater cooling, wherein the component is optionally a heat exchanger component, a process tube component, or a piping component.

13. A method for producing a nickel-based alloy object according to any one of claims 1 to 11, - Casting a molten material having the above composition to obtain a cast alloy, - Optionally, heat-treating the cast alloy, - Hot working of cast alloys, - Selectively heat-treating a hot-worked alloy, - Optionally, cold working a hot-worked alloy, - Selectively heat-treating a cold-worked alloy A method that includes this.

14. The method according to claim 13, wherein the object is selected from the group consisting of rods, tubes, pipes, strips, plates, sheets, hollow bodies, fittings, flanges, or wires.

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