RU2791029C1 - Nickel alloy with good corrosion resistance and high tensile strength and method for production of semi-products - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to the production of semi-products of a nickel alloy with high resistance to hydrogen embrittlement and high mechanical properties. A method for the production of a semi-product of a nickel alloy containing, wt.%: Ni 50-55, Cr 17-21, Mo > 0-9, W 0-9, Nb 1-5.7, Ta > 0-4.7, Ti 0.1-3.0, Al 0.4-4.0, Co no more than 3.0, Mn no more than 0.35, Si no more than 0.35, Cu no more than 0.23, C 0.001-0.045, S no more than 0.01, P 0.001-0.02, B 0.001-0.01, the rest is Fe, and usual impurities caused by production, when following ratios are met: Nb+Ta 1-5.7, Al+Ti > 1.2-5, Mo+W 3-9, includes vacuum induction melting (VIM) and casting into ingots, annealing of ingots to relieve stresses in a temperature range from 500 to 1250°C for up to 110 hours. Then, ingots are processed in the process of electroslag remelting (ESR) and/or vacuum arc remelting (VAR), and, if necessary, the alloy is remelted in the process of electroslag remelting or vacuum arc remelting. Remelted ingots are subjected to homogenizing annealing in a temperature range from 500 to 1250°C for up to 150 h. Then, annealed ingots are subjected to hot and cold deformation to obtain a semi-product, at least one annealing per solid solution is performed in a temperature range from 900 to 1150°C for 0.1 to 60 h, followed by cooling in air, in mobile annealing atmosphere, in inert gas, in water, in polymer, or in oil.

EFFECT: semi-product has following properties: a coefficient of elongation at break during the test in acid gas is more than 75%, with a yield strength in air > 100 thousand pounds/in² (ksi).

13 cl, 37 dwg, 8 tbl

Description

The invention relates to a nickel alloy with high resistance to hydrogen embrittlement and very good mechanical properties.

Age-hardenable nickel alloys have long been used in the oil and gas industry where higher strength is required. In this application, good corrosion resistance is required, in particular in an atmosphere containing H ₂ S and Cl, in combination with good mechanical properties. Yield strength, notched impact strength and strength are additional important criteria when choosing a material. Prior art examples are shown in Table 1.

Suitable materials for this application include, among others, Alloy 718, which has the following chemical composition (in wt.%): 18.5% chromium, < 0.1% carbon, 18% iron, 0.9% titanium, 0.6 % aluminum, 3% molybdenum, 5% niobium + tantalum, the rest is nickel and due to melting impurities. Increasing demands on this material necessitate the development of a new nickel alloy with improved properties.

Alloy 718 is the material of choice for applications requiring the highest mechanical strength. The temperature during application does not exceed about 200°C. The material has good anti-corrosion properties against hydrogen embrittlement and stress corrosion cracking, as well as high mechanical strength. Due to the representative use of Alloy 718, this alloy is considered the basis for improvement or new development.

Table 1. Prior Art Examples

No. of the Universal Designation System for Metals and Alloys (UNS) NO7718 NO6625 NO7716 NO9925 NO5500 NO7725 Material name Alloy 718 Alloy 625* Alloy 625 Plus Alloy 925 Alloy
K-500* Alloy 725 Chemical composition WITH Max. 0.045 Max. 0.10 Max. 0.030 Max. 0.025 Max. 0.25 Max. 0.030 Mn Max. 0.35 Max. 0.50 Max. 0.20 Max. 1.00 Max. 1.5 Max. 0.35 Cr 17.0 - 21.0 20.0 - 23.0 19.0 - 22.0 19.5 - 23.5 19.0 - 22.5 Ni 50.0 - 55.0 rest 59.0 - 63.0 42.0 - 46.0 63.0 - 70.0 55.0 - 59.0 Mo 2.80 - 3.30 8.0 - 10.0 7.0 - 9.5 2.50 - 3.50 7.00 – 9.50 P Max. 0.010 Max. 0.015 Max. 0.015 Max. 0.020 Max. 0.02 Max. 0.015 Cu Max. 0.23 1.50 - 3.00 rest Al 0.40 - 0.60 Max. 0.40 Max. 0.35 0.10 - 0.50 2.30 - 3.15 Max. 0.35 Ti 0.80 - 1.15 Max. 0.40 1.0 - 1.6 1.90 - 2.40 0.35 - 0.85 1.00 - 1.70 Nb 4.75 - 5.50 3.15 - 4.15 2.75 - 4.00 0.08 - 0.50 2.75 - 4.00 B Max. 0.0060 Max. 0.006 Fe rest Max. 5.0 5 min. 22 Max. 2.0 rest

(API Standard 6ACRA *NACE MR 0175).

Alloy 718 is a deformable and age hardenable nickel-chromium alloy developed by H. Eiselstein and patented in 1962 US Patent No. 3,046,108. Alloy 718 has a good combination of high strength properties with good ductility over a wide temperature range. The material was developed for the aviation industry, and a few years later was introduced to the oil and gas industry due to the combination of good corrosion resistance and good mechanical properties.

US 3,160,500 discloses a matrix-hardened nickel-chromium alloy that subsequently led to Alloy 625, which has a combination of good mechanical properties over a wide temperature range and high fracture and stress resistance at elevated temperature. Due to its attractive combination of strength and corrosion resistance, this material has found wide application. High levels of chromium and molybdenum provide good corrosion resistance and strength, while iron and niobium provide additional strength. Aluminum and titanium additions serve primarily metallurgical purposes and are kept low to improve weldability. The alloy has the following composition: 21.44 - 21.68% Cr, 0.02 - 0.03% C, 0.11 - 0.12% Mn, 0.04 - 0.11% Si, 8.83 - 9 .1% Mo, up to 5.32% W, 4.19 - 4.35% Nb, 0.16 - 0.23% Al, 0.13 - 0.20% Ti, 1.92 - 6.89% Fe, up to 0.02% Mg, the rest is Ni.

DE 10 2015 016 729 A1 describes a method for producing a nickel-based alloy, wherein

- an electrode is made in a vacuum induction furnace,

- to reduce stress and overage the electrode is subjected to heat treatment in an oven in the temperature range from 400 to 1250°C for 10-336 hours,

- in air or in an oven, depending on the dimensions, in particular the diameter, the electrode is cooled to a temperature in the range from room temperature to less than 1250°C, in particular to less than 900°C,

- then the cooled electrode is remelted by vacuum arc remelting at a remelting speed of 3.0 to 10.0 kg/min to obtain a vacuum arc remelting ingot,

- the resulting ingot of vacuum-arc remelting is subjected to heat treatment in a furnace in the temperature range from 400 to 1250 ° C for 10 - 336 hours,

- depending on the size, in particular on the diameter, the vacuum-arc remelted ingot obtained is cooled in air or in a furnace to a temperature in the range from room temperature to less than 1250°C, in particular to less than 900°C,

- this vacuum arc remelted ingot is remelted again at a remelting rate of 3.0 to 10 kg/min,

- the remelted ingot of vacuum-arc remelting is subjected to heat treatment in the temperature range from 400 to 1250 ° C for 10 - 336 hours,

- then the ingot of vacuum-arc remelting by hot and/or cold deformation is brought to the desired size and shape of the product.

The nickel-based alloy may have the following composition:

max 0.25% C, max 0.15% S, 17-32% Cr, 45-72% Ni, max 1% Mn, max 1% Si, max 3.25% Ti, max 5.5% Nb, not more than 5% Cu, not more than 25% Fe, not more than 0.03% P, not more than 3.15% Al, not more than 0.6% V, not more than 0.12% Zr, not more than 28% Co, not more than 0.02% B, and impurities due to production.

Alloy 625 plus was developed from Alloy 625 and Alloy 718. Alloy 625 plus is a high strength alloy alternative to Alloy 625, with similar corrosion resistance provided by higher titanium content.

The use of the age-hardenable alloy called Alloy 925 is very similar to Alloy 718. They are used in oil source rods and pipes, gas source structural parts, valves, drill collars, connecting components and packers. Alloy 925 is used when strength requirements are somewhat lower than Alloy 718.

Niccoros Alloy K-500 (NO5500) is a nickel-copper alloy that can age-harden through the formation of a gamma phase. It is used in the offshore industry, not heavily burdened with hydrogen sulfide. Sour gas corrosion resistance and mechanical strength are lower than Alloy 718 and Alloy 925.

Alloy 725 has high mechanical strength similar to Alloy 718 and corrosion resistance similar to Alloy 625.

The content and presence of age hardening phases have a noticeable and direct effect on the resistance to hydrogen embrittlement. According to the literature, materials that do not contain precipitate phases, and therefore are not age-hardened, have markedly better resistance to hydrogen embrittlement compared to age-hardenable materials containing precipitate phases.

The invention is based on the object of providing an alloy based on Alloy 718 which, in addition to improved resistance to acid gas and hydrogen embrittlement, would also have higher yield strength and higher strength, with a lower proportion of delta and gamma'' phases and a higher fraction of the gamma phase.

It is also the object of the invention to provide a process for producing an alloy based on Alloy 718, whereby a higher yield strength and higher strength can be achieved, while providing a low proportion of delta and gamma phases and a higher proportion of gamma phase.

The first task is solved by means of a nickel alloy having the composition (wt.%):

Ni: 50 - 55%

C: 17 - 21%

Mo: >0 – 9%

W: 0 - 9%

Nb: 1 - 5.7%

Ta: >0 - 4.7%

T: >0 – 3.0%

Al: 0.4 - 4.0%

Co: no more than 3.0%

Mn: no more than 0.35%

Si: no more than 0.35%

Cu: no more than 0.23%

C: 0.001 - 0.045%

S: no more than 0.01%

P: 0.001 - 0.02%

B: 0.001 - 0.01%,

the rest is Fe and the usual production-related impurities,

the following relations are satisfied:

Nb + Ta: 1 - 5.7% ... (1)

Al + Ti: > 1.2 - 5% ... (2)

Mo + W: 3 - 9% ... (3),

where: Nb, Ta, Al and Ti express the concentration of the respective elements in wt.%.

Preferred developments of the nickel alloy according to the invention are given in the respective dependent claims.

The second problem is solved, on the one hand, by a method for obtaining powder from a nickel-based alloy, in which

- the alloy is smelted in a vacuum induction furnace,

- the melt is kept for 5 minutes to 2 hours for homogenization,

- in a closed spraying plant with supplied gas, a dew point from -10°С to 120°С is created,

- the melt is injected through the nozzle into the gas flow at a gas flow rate of 2 to 150 m ³ /min,

- hardened powder particles are collected in a hermetically sealed container, while

- the particle size is from 5 to 250 microns,

- powder particles have a spherical shape,

- the powder contains gas inclusions with a pore area of 0.0 to 4% (pores >1 µm) of the total surface of the evaluated objects,

- the apparent density of the powder is from 2 to the density of the alloy, which is about 8 g/cm ³ ,

- powder packaging is carried out hermetically in an atmosphere of protective gas containing argon.

On the other hand, the second problem is also solved due to the method of obtaining a nickel alloy of the following composition (in wt.%):

Ni: 50 - 55%

Cr: 17 - 21%

Mo: >0 – 9%

W: 0 - 9%

Nb: 1 - 5.7%

Ta: >0 - 4.7%

Ti: >0 - 3.0%

Al: 0.4 - 4.0%

Co: no more than 3.0%

Mn: no more than 0.35%

Si: no more than 0.35%

Cu: no more than 0.23%

C: 0.001 - 0.045%

S: no more than 0.01%

P: 0.001 - 0.02%

B: 0.001 - 0.01%,

the rest: Fe and common industrial impurities,

the following relations are satisfied:

Nb + Ta: 1 - 5.7% ... (1)

Al + Ti: > 1.2 - 5% ... (2)

Mo + W: 3 - 9% ... (3),

where Nb, Ta, Al and Ti express the concentration of the respective elements in wt.%, in which the alloy is smelted in a vacuum induction (VIM) furnace and cast into ingots, these vacuum induction melting ingots are subjected to stress relief annealing in the temperature range from 500 to 1250 °С for up to 110 hours, then the ingots are processed by electroslag remelting (ESR) and/or vacuum arc remelting (VAR), the remelted ingots are subjected to homogenizing annealing in the temperature range of 500–2500°С for up to 150 h, then the annealed ingots are subjected to hot and / or cold deformation to obtain a semi-finished product, and, if necessary, at least one intermediate annealing is carried out in the temperature range of 900 - 1150 ° C for a time of 0.1 to 60 h, followed by cooling in air, in a movable annealing atmosphere, inert gas, water, polymer or oil.

Alternatively, the problem is also solved by a method for producing a nickel alloy of the following composition (wt.%):

Ni: 50 - 55%

Cr: 17 - 21%

Mo: >0 – 9%

W: 0 - 9%

Nb: 1 - 5.7%

Ta: >0 - 4.7%

Ti: 0.1 - 3.0%

Al: 0.4 - 4.0%

Co: no more than 3.0%

Mn: no more than 0.35%

Si: no more than 0.35%

Cu: no more than 0.23%

C: 0.001 - 0.045%

S: no more than 0.01%

P: 0.001 - 0.02%

B: 0.001 - 0.01%,

the rest: Fe and common industrial impurities,

the following relations are satisfied:

Nb + Ta: 1 - 5.7% ... (1)

Al + Ti: >1.2 – 5% … (2)

Mo + W: 3 - 9% ... (3),

where: Nb, Ta, Al and Ti express the concentration of the respective elements in wt.%, in which the alloy is smelted openly and then processed in a vacuum oxygen decarburization (VOD) plant or in an argon oxygen decarburization (AOD) plant and cast into ingots, these ingots, if necessary, are subjected to stress relief annealing in the temperature range from 500 to 1250°C for up to 110 h, then at least one, in particular two-time, vacuum-arc remelting is carried out, the remelted ingots are subjected to homogenized annealing in the temperature range from 500 to 1250°C for up to 150 h, then the annealed ingots are subjected to hot and cold deformation to obtain a semi-finished product, then at least one solid solution annealing is carried out in the temperature range from 900 to 1150°C for a time of 0.1 - 60 h followed by cooling in air, in a mobile annealing atmosphere, inert gas, water, polymer or oil.

Preferred variants of the development of these methods according to the invention are given in the respective dependent claims on the method.

Through alternative smelting processes, the following combinations can be achieved:

VIM / (ESR or VAR) / if necessary (ESR or VAR)

EF (electric oven) / (VOD or AOD) / VAR/VAR.

The alloy according to the invention can preferably be used for the following types of products:

- rod,

- wire,

- band,

- sheet,

- longitudinally welded pipe,

- seamless pipe,

- powder.

Semi-finished products/structural parts are preferably used in the oil and gas and chemical industries.

The presence of any precipitation phases was analyzed and studies were carried out to better understand the interaction between the hydrogen atom and the crystal structure when the hydrogen atom occupies different positions in the unit cell. The calculation of the preferred places for trapping hydrogen along the phase boundaries or in the matrix material is made, taking into account the enthalpy energy of hydrogen when this place is occupied. Based on these results, multiple tensile tests were carried out to investigate bond relationships between metal atoms near phase boundaries.

According to the present invention, the presence of a hydrogen atom in the most stable position at the gamma/gamma' interface has no effect on the tensile strength compared to a system without the presence of hydrogen atoms (FIG. 1). In contrast, when the hydrogen atom occupies the most stable position at the gamma/gamma'' phase boundary, significant atom displacement occurs and the system exhibits a lower tensile strength compared to the system without a hydrogen atom (Fig. 2), which indicates that hydrogen embrittlement may occur. The delta phase, which is not present in representative amounts in Alloy 718 for oil and gas applications, does not significantly affect the mechanical properties (FIG. 3).

Alloy 718 is available in three different grades to meet different yield strength requirements. The 120K option has a minimum yield strength of 120,000 pounds per square inch (ksi) provided by age hardening at 774 to 802°C. The 140K option has a minimum yield strength of 140 ksi provided by age hardening at 760 - 802°C. 150K is a variant produced by two-stage aging hardening at the first temperature from 700 to 750°C and a second temperature of 600 to 659°C, which has a minimum required yield strength of 150 ksi.

Different heat treatment methods are capable of producing different microstructures (FIG. 4) which were examined for comparison with hydrogen embrittlement behavior. The gamma' phase is isolated in the form of point particles, while the gamma'' phase has an acicular shape.

A lower ratio between the mass fractions of gamma'/gamma'' phases creates the most unfavorable behavior in relation to hydrogen embrittlement, while a higher ratio between the mass fractions of gamma'/gamma'' phases provides better resistance to hydrogen embrittlement. This information is shown in Table 2.

Hydrogen embrittlement resistance was tested using cathodic gradual loading tests according to NACE Publication 3948, 2014. medium (0.5 M sulfuric acid solution at 40°C with a current density of 5 mA/cm ² to achieve cathodic polarization) and determined the ratio of relative elongation at break between aggressive and inert media. The higher elongation at break could explain why the resistance to hydrogen embrittlement was also higher.

The particle size of gamma' and gamma'' precipitates can also affect the mechanical and anti-corrosion properties of nickel alloys.

Typical conditions that cause hydrogen embrittlement to occur are material contacts with atomic or molecular hydrogen in combination with material stresses.

The addition of alloying elements to Alloy 718 nickel alloy, which is widely used in the oil and gas industry, has the following reasons.

Iron is effective in reducing the cost of the metal, but due to the deterioration of the material properties, it should not be overused for alloying.

Chromium is used to improve strength at room temperature and at the same time to provide overall corrosion resistance. In combination with carbon, chromium forms carbides that increase strength at high temperatures.

In general, it should be noted that the resistance to pitting corrosion in chlorine-containing environments increases with increasing molybdenum content. As the molybdenum content increases, the resistance to stress corrosion at high temperatures also improves. If necessary, molybdenum can be replaced by tungsten.

The austenitic matrix from the gamma phase is hardened by aging as a result of intermetallic precipitates of gamma ', ordered face-centered cubic phase of Ni ₃ (Al/Ti), and gamma '' - tetragonal Ni ₃ Nb phase, therefore aluminum, titanium and niobium are used as alloying additives . If necessary, niobium can be replaced by tantalum. Due to the cost of the metal, niobium is preferably used. Increasing the amount of aluminum and titanium should lead to more gamma', and decreasing the amount of niobium limits the formation of gamma''.

The delta phase is the equilibrium phase of the precipitation hardening gamma'' phase (Ni ₃ Nb) and, according to a possibly applicable specification, can only be present in the microstructure in very small quantities, since it adversely affects the mechanical and anti-corrosion properties. The formation of a delta phase is prevented by solution annealing at a temperature above the solvus temperature of the delta phase.

In reducing atmospheres, hydrogen is able to permeate the material, which can lead to hydrogen embrittlement. The presence of hydrogen atoms in the crystal structure of the material leads to a weakening of bonds between atoms. This causes a loss of tensile strength and can lead to failure of the material under mechanical loading.

The nickel alloy according to the invention, at sufficiently high contents of titanium, aluminum, molybdenum and niobium, and in combination with a certain heat treatment, is characterized by excellent resistance to hydrogen embrittlement, and at the same time:

• good durability

• good resistance to stress corrosion cracking and pitting

• good phase stability

• good processing ability.

The nickel content is between 50% and 55%, with the following preferred ranges:

- 51 – 55%

- 52 - 55%

- 53 - 55%.

Lower nickel contents can be replaced by cobalt, but due to the cost of the metal, nickel is preferably used.

Cobalt is contained in the alloy in an amount of not more than 3%. Preferred content would be:

- 0.01 - 1%

- 0.01 - no more than 0.8%

- 0.01 - no more than 0.6%

- 0.01 - no more than 0.4%.

The content range of the element chromium is from 17 to 21%, with the following ranges preferably being given:

- 17 - 20%

- 17 - 19%

- 18 - 19%.

The molybdenum content ranges from >0 to 9%, and in this case, depending on the application of the alloy, the preferred molybdenum contents can be:

- 0.01 - 8.5%

- 0.1 - 8.0%

- 3 – 8%

- 3 – 7%

- > 3.3 - 9%

- 3.75 - 9%.

If necessary, the element molybdenum may be replaced, at least in part, by tungsten, provided that tungsten is not used as an independent element within the specified limits. Combinations of Mo + W are also possible, but depending on the application. In this case, tungsten can be used at a content of 0 to 9%. Preferably, tungsten can be used in the alloy in the following ranges:

- >0 – 9%

- 0.001 - 9%

- 0.01 - 9%

- 0.1 - 9%

- 19%

- 18

- 3 – 7%

- 3 – 8%

- >3.3 - 9%.

The content of niobium is from 1 to 5.7%, while, depending on the scope of application, the preferred content of the element can be set within the following limits:

- 2 - 4.5%

- 2 – 4%

- 2 - 3.5%.

The titanium content is >0 to 3.0%. Preferably, the titanium content of the alloy can be set within the following ranges:

- 0.5 - 3.0%

- 1.0 - 3.0%

- 1.0 - 2.0%

- >1.15 - 3%

- 1.18 - 3%.

The same is true for the element aluminum, which may be contained in the alloy in an amount of from 0.4 to 4.0%. Alternatively, the following ranges are also possible:

- 0.6 - 4.0%

- 0.6 - 1.5%

- 0.8 - 4%

- 0.9 - 4.0%

- 1.0 - 4.0%

- 1.0 - 3.3%

- 1.5 - 3.0%.

The manganese element is present in the alloy in an amount of not more than 0.35%.

The silicon element is present in the alloy in an amount of not more than 0.35%.

Copper is contained in the alloy in an amount of not more than 0.23%.

Carbon is contained in the alloy in an amount of not more than 0.045%. Preferably, the carbon content of the alloy can be set within the following ranges:

- 0.001 - no more than 0.035%

- 0.001 - no more than 0.025%

- 0.001 - no more than 0.015%.

The maximum sulfur content in the alloy is allowed in the amount of 0.01%.

In addition, the alloy contains phosphorus in an amount of 0.001 to 0.02%. Another preferred content is 0.001 - 0.015%.

The boron content is between 0.001 and 0.01%, alternatively the following ranges are also acceptable:

- 0.003 - 0.01%

- 0.005 - 0.01%

The rest is iron and impurities due to production.

The following ratio between niobium and tantalum must be observed in order to provide a sufficient but limited content of gamma '' phase precipitates:

Nb + Ta = 1 - 5.7%,

where Nb and Ta express the concentration of the respective elements in wt.%.

Preferred content ranges can be set:

Nb + Ta = <4.75%

Nb + Ta = 1 - 4.75%

Nb + Ta = 1 - 5.0%

Nb + Ta = 2 - 4%

Nb + Ta = 2 - 3.5%

Nd + Ta = 1.6 - 4%

Nb + Ta = 1 – 4%.

In addition, the following relation must be observed in order to ensure sufficient stability of the gamma phase:

Al + Ti \u003d\u003e 1.2 - 5%,

where Al and Ti express the concentration of the respective elements in wt.%.

The following preferred ranges can be set:

Al + Ti = 1.5 - 5%

Al + Ti = 1.8 - 5%

Al + Ti = 1.8 - 3.5%

Al + Ti = >1.95%

Al + Ti = >1.95 - 5%.

The ratio Mo + W = 3 – 9% can take place. If necessary, and in this case, the restriction can be applied:

Mo+W=>3.3%

Mo + W = >3.3 - 9%.

If the formation of this phase is envisaged, then the following relationship must be observed:

Ti / Al >2 or

Al/Ti>2,

where Al and Ti express the concentration of the respective elements in wt.%.

The alloy according to the invention is preferably smelted and cast in a vacuum induction furnace (VIM) followed by electroslag remelting (ESR) or vacuum arc remelting (VAR). If necessary, the alloy is re-subjected to electroslag remelting (ESR) or vacuum arc remelting (VAR).

As a possible variant, the alloy according to the invention is open-smelted followed by a vacuum oxygen decarburization (VOD) or an argon oxygen decarburization (AOD) treatment followed by two vacuum arc remelting (VAR) treatments.

The produced alloy ingots are subjected to heat treatment, if necessary, at a temperature of from 500 to 1250°C for an annealing duration of up to 150 hours, after which they are subjected to hot and/or cold deformation to obtain the desired semi-finished product, such as in the form of billets, bars, wire, sheets , strips and foils, if necessary, with intermediate annealing at a temperature of 800 to 1270 ° C for 0.05 h to 100 h. If necessary, the surface of the material in the intervals and / or at the end (including repeatedly) can be subjected to chemically and/or mechanically (eg by roughing, turning, grinding) for cleaning purposes. Then, if necessary, solid solution annealing is carried out in the temperature range from 970 to 1150 ° C for 0.1 h to 60 h, if necessary in a protective gas atmosphere, for example, argon or hydrogen, followed by cooling in air, with necessary, in a mobile annealing atmosphere, in an inert gas, in water, in a polymer or in oil.

After that, if necessary, annealing for hardening by aging is carried out in the temperature range from 600 to 900°C for 0.1 h to 60 h, if necessary, in two stages with additional annealing for hardening by aging at 550–900°C for from 0.1 h to 60 h.

Annealing for hardening by aging is carried out in the temperature range from 600 to 900°C for 0.1 h to 60 h, and the following optimal ranges can be applied:

- 600 - 800°С for 0.1 h to 60 h

- 600 - 750°С for 0.1 h to 60 h

- 700 - 900°C for 0.1 h to 60 h

- 750 - 900°C for 0.1 h to 60 h.

If necessary, the specified aging hardening annealing is carried out with a two-stage hardening by aging, while the subsequent annealing for hardening by aging is carried out at 550 - 900 ° C for 0.1 h - 60 h, while the following optimal ranges can be set:

- 1st stage hardening by aging in the temperature range from 600 to 800°C for 0.1 h to 60 h, 2nd stage hardening by aging in the temperature range from 550 to 750°C for 0.1 h to 60 h;

- 1st stage hardening by aging in the temperature range from 600 to 800°C for 0.1 h to 60 h, 2nd stage hardening by aging in the temperature range from 800 to 900°C for 0.1 h to 60 h;

- 1st stage hardening by aging in the temperature range from 750 to 900°C for 0.1 h to 60 h, 2nd stage hardening by aging in the temperature range from 550 to 750°C for 0.1 h to 60 h;

- 1st stage hardening by aging in the temperature range from 750 to 900°C for 0.1 to 60 h, 2nd stage hardening by aging in the temperature range from 750 to 900°C for 0.1 h to 60 h.

If necessary, chemical and/or mechanical cleaning of the surface of the material (eg peeling, turning, grinding) can be carried out in between and/or after the last annealing.

The alloy according to the invention is also well processed and used in the form of bars, wires, strips, sheets, longitudinally welded pipes and seamless pipes.

If necessary, the alloy can be obtained and applied in the form of a powder (for example, for additive manufacturing methods). In this case, the powder is produced in a VIGA (Vacuum Induction Gas Atomizer) powder atomizer or by other means, selected or filtered to the desired powder particle size range.

Preferably, the alloy according to the invention can be used in applications where hydrogen-containing media are present, such as downhole completion tools, packers, mud rolls, hangers, valves, thrust brackets, vessels, magnetic logging probe body material (logging while drilling) and etc.

Due to the combination of chemical composition with heat treatment, the alloy according to the invention should preferably contain a gamma'/gamma'' ratio of more than 1.3, preferably more than 1.5. Thanks to this combination, it is also possible to achieve yield strengths in excess of 120 ksi.

Carried out calculations / tests

The phases formed in the equilibrium state were calculated for different alloy variants using the JMatPro Thermotech program. The database for nickel alloys from Thermotech was used as a database for calculations. The phase contents, particle sizes and expected mechanical properties (e.g. yield strength, tensile strength, hardness) were calculated using the "heat treatment" mode of the JmatPro software when a material of the appropriate chemical composition was annealed at different temperatures for age hardening.

Description of properties

The alloy according to the invention must have, in addition to excellent resistance to hydrogen embrittlement, the following properties at the same time:

• good strength

• good resistance to stress corrosion cracking and pitting

• good phase stability

• good processing ability.

In the nickel-chromium-aluminum-iron-titanium-niobium system, different ligature contents can form different phases, for example, gamma ', gamma '', delta and eta phases. Tables 3.1 and 3.2 show the results of calculations of the equilibrium fractions of the first calculated chemical compositions. All calculations were performed for the aging hardening temperature of 790°C.

Chemical compositions LV1, 8, 9 and 39 are examples of alloys not in accordance with the present invention.

Based on the above results, the proportions of equilibrium phases were calculated depending on temperature for other chemical compositions of interest. To determine the temperature at which precipitates are optimized and therefore improved mechanical properties are achieved, calculations were carried out with different aging hardening temperatures. The calculation results are shown in Table 4 and in Fig. 5 for chemistry LB250643. For the chemical composition LB250643, the temperature of 690°C is the peak temperature.

Table 4. Phase Precipitation and Corresponding Mechanical Properties According to Age Hardening Temperature in Model Alloy

Chemical
compound
charge
LB 250643 C 0.01 N 0.005 Cr 18.47 Ni 53.68 Mo 3.05 Ti 1.22 Nb 3.51 Fe* 19.32 P 0.003 Al 0.62 B 0.004 Ta 0.01 co 0.01 Cu 0.01 Mn 0.01 Si 0.02 hardening by aging 650°C/6h 670°C/6h 690°C/6h 710°C/6h 730°C/6h 750°C/6h Temperature 650 670 690 710 730 750 Yield strength [ksi] 144 158 164 159 154 146 Tensile strength [ksi] 192 202 206 203 200 194 Hardness [Rockwell] 37 40 41 40 39 38 γ' [%] 12 13 13 12 12 eleven γ' size (nm) 17.66 18.38 18.34 18.41 18.72 19.54 γ'' [%] 3.14 4.31 4.16 4.00 3.80 3.57 γ'' size (nm) 11.45 13.62 18.21 23.76 31.42 40.61 Fraction γ'/γ'' 3.82 3.02 3.13 3.00 3.16 3.08

Similar calculations were made for all other chemical compositions (diagrams in Figs. 11a – 11ab). To determine the optimal temperature of the precipitates, experiments were carried out using various increasing temperatures.

It should be noted that the calculated temperature may deviate from the experimental temperatures.

Properties at other chemical compositions of interest are listed, along with their peak temperatures, in Tables 5.1, 5.2 and 5.3.

If necessary, the alloy can be produced and used in powder form. Since the machinability of the alloy does not play a role in additive manufacturing methods, the presence of a wide gap in the aluminum content is noted in the chemical composition. For additive manufacturing methods, the powder may have a higher aluminum content, up to 4%. Possible chemical compositions for the powder alloy are shown in Table 6.

Table 5.3. Chemical compositions, mechanical properties and fractions of precipitation phases in alloy variants at peak temperature (3rd part)

Elements LB P01 LB P02 LB P03 LB P04 LB P05 LB P06 C 0.011 0.011 0.011 0.011 0.011 0.011 N 0.005 0.005 0.005 0.005 0.005 0.005 Cr 18.5 18.5 18.5 18.5 18.5 18.5 Ni 54 54 54 54 54 54 Mo 3.05 3.05 3.05 3.05 3.05 3.05 Ti 0.95 0.95 0.95 0.95 0.95 0.95 Nb 5 3.5 5 3.5 5 4.2 Fe* rest rest rest rest rest rest P 0.003 0.003 0.003 0.003 0.003 0.003 Al 1.2 1.2 1.8 1.8 1.5 1.2 B 0.002 0.002 0.002 0.002 0.002 0.002 Ta 0.01 0.01 0.01 0.01 0.01 0.01 co 0.01 0.01 0.01 0.01 0.01 0.01 Cu 0.01 0.01 0.01 0.01 0.01 0.01 Mn 0.01 0.01 0.01 0.01 0.01 0.01 Si 0.03 0.03 0.03 0.03 0.03 0.03 Peak temp. [°C] 690 690 690 670 690 690 YS [ksi] 172 134 142 88 163 158 TS [ksi] 212 186 191 152 206 202 Hardness
[according to Rockwell] 42 36 37 25 41 40 Gamma' [%] 16.41 17.34 24.62 24.03 20.83 16.31 Gamma'' [%] 6.2 1.7 2.5 0 5.0 4.2 Fraction γ'/γ'' 2.66 10.02 9.77 100 4.21 3.88

Table 6. Possible powder compositions

Elements LB P07 LB P08 LB P09 LB P10 LB P11 LB P12 LB P12 LB P12 C 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 N 0.012 0.012 0.012 0.012 0.012 0.012 0.012 0.012 Cr 18.5 18.5 18.5 18.5 18.5 18.5 18.5 18.5 Ni 54 54 54 54 54 54 54 54 Mo 3.05 3.05 3.05 3.05 3.05 3.05 3.05 3.05 Ti 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.5 Nb 5 4.2 3.5 5 4.2 3.5 3.5 3.5 Fe* rest. rest. rest. rest. rest. rest. rest. rest. P 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 Al 2.5 2.5 2.5 3.5 3.5 3.5 4 4 B 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 Ta 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 co 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Cu 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Mn 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Si 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02

According to the results of these calculations, by increasing the content of niobium from about 3.5 to 5%, the proportion of the gamma '' phase can be doubled if the content of titanium and aluminum is kept constant. If the aluminum and niobium (tantalum) contents are kept constant and the titanium content is increased, then more gamma phase is formed, and an improvement in mechanical properties is expected. With an increase in the aluminum content, more gamma 'phase can be released in combination with the same or less content of titanium and niobium (compared to Alloy 718).

With an extremely low content of niobium (tantalum) (<1%) and a constant content of aluminum (≈0.6%), the gamma '' phase is not formed and, therefore, according to the calculations, the mechanical properties are not satisfactory.

Fluctuations in the content of molybdenum, tungsten, boron and phosphorus do not have a direct and significant effect on the precipitation of gamma 'and gamma '' phases.

In FIG. 5, 6 are phase diagrams showing the separation of the gamma' phase at temperatures below 919°C and the gamma'' phase at temperatures below 880°C with the chemical composition LB250643 (with a high content of titanium and aluminum in combination with a low content of niobium (tantalum)) .

The phase diagram in Fig. 5 shows the calculation of the formation of precipitation phases at temperatures below 919°C and takes into account only thermodynamic stability. Therefore, the gamma phase is not taken into account in this phase diagram. The delta phase is thermodynamically the most stable phase of the release, but due to the kinetics of the release, it forms slowly. The content of this phase with this composition is essentially absent according to thermodynamic calculations.

The TTT (time, temperature, conversion) diagram for LB250643 chemistry is shown in FIG. 6. In this case, the presence of the gamma '' phase is now taken into account. As expected, the delta and this phases precipitated after longer annealing at the age-hardening temperature, therefore, the precipitation of these phases is affected by the duration of the aging-hardening annealing. And although no difference was noted between numerical tensile tests of the gamma / delta system with and without the presence of hydrogen, however, the overall characteristic of the gamma / delta phase boundaries can be critical due to the low atomic binding energy. Therefore, the duration of annealing during hardening by aging should be limited to no more than 60 hours to avoid the formation of the delta phase.

The content of boron and phosphorus does not affect the proportion of gamma 'or gamma '' phases. A change in the content of aluminum, niobium (tantalum) and titanium directly affects the formation of gamma 'and gamma '' phases.

To understand the quantitative formation of phases hardened by aging, calculations were carried out in relation to the chemical composition of LB250643. The calculations for the corresponding chemical composition were carried out at a temperature of the first stage of aging hardening of 650°C (below the peak temperature). This was followed by the second stage of hardening by aging at varying temperatures. Similar calculations were performed for the peak temperature as the temperature of the first stage of age hardening and at 730°C (above the peak temperature) as the temperature of the first stage of age hardening, while the temperature in the second stage was varied in steps of 20 degrees. The results are shown in Table 7 and in FIG. 7.

It should be noted that the duration of hardening by aging affects the phase fractions. An example for the chemical composition of LB250643 is shown in FIG. 8. This figure shows an isothermal diagram for a given chemical composition under age hardening at 650°C, with the maximum gamma' phase being reached after about 7 hours. If the temperature is raised to 730°C, the time to reach the maximum proportion of the gamma phase is shortened. In FIG. 9 is an isothermal diagram for a given age hardening chemistry at 730°C.

The difference between calculated and experimental peak temperatures is expected and known. In order to find out what deviation will occur at given composition limits, the peak temperature was confirmed through heat treatment and hardness testing. A diagram with experimentally established hardness indices for the chemical composition of LB250643 is shown in Fig. 10. With a given chemical composition, the deviation is 80°C, this difference must be taken into account when planning the heat treatment.

Table 7. Age hardening phase fraction and mechanical properties after different two-stage age hardening for composition LB250643

Temperature at the 1st stage 650 650 650 650 650 650 650 650 Temperature at the 2nd stage 550 570 590 610 630 670 690 710 γ' after the 1st stage (%) 12 12 12 12 12 12 12 12 Size γ' after 1st stage (nm) 19 19 19 19 19 18 18 19 γ' after 2nd stage (%) 1.8 2.4 2.2 2.1 1.9 1.4 1.1 0.8 Size γ' after 2nd stage (nm) 19 19 19 19 19 18 18 19 γ'' after the 1st stage (%) 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 Size γ'' after 1st stage (nm) 12 12 13 13 14 19 23 28 γ'' after the 2nd stage (%) 0.6 0.9 1.2 1.5 1.4 1.2 1.0 0.9 Dimension γ'' after 2nd stage (nm) 12 12 13 13 14 19 23 28 Yield strength (ksi) 156 159 161 162 163 167 163 158 Tensile strength (ksi) 201 203 204 205 205 208 205 202 Hardness (Rockwell) 39 40 40 40 40 41 40 40 Total Gamma’ 32.3 33.2 32.9 32.7 32.5 31.9 31.6 31.4 Total Gamma'' 15.9 16.4 17.1 17.8 18.5 22.8 26.9 32.4 Share γ’/γ’’ 2.040 2.023 1.918 1.843 1.759 1.397 1.172 0.968 Temperature at the 1st stage 690 690 690 690 690 690 690 690 Temperature at the 2nd stage 530 550 570 590 610 630 650 670 γ' after the 1st stage (%) 13 13 13 13 13 13 13 13 Size γ' after 1st stage (nm) 19 19 19 19 19 19 19 19 γ' after 2nd stage (%) 1.1 1.4 1.3 1.1 0.9 0.9 0.5 0.3 Size γ' after 2nd stage (nm) 19 19 19 19 19 19 19 19 γ'' after the 1st stage (%) 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 Size γ'' after 1st stage (nm) 19 19 19 19 19 20 21 23 γ'' after the 2nd stage (%) 0.2 0.4 0.5 0.5 0.5 0.4 0.3 0.1 Dimension γ'' after 2nd stage (nm) 19 19 19 19 19 20 21 23 Yield strength (ksi) 175 176 176 176 174 172 169 165 Tensile strength (ksi) 213 214 215 214 213 211 209 207 Hardness (Rockwell) 42 42 42 42 42 42 41 40 Total Gamma’ 32.9 33.4 33.2 32.9 32.7 32.6 32.1 31.9 Total Gamma’’ 23.0 23.3 23.6 23.7 23.8 24.2 25.1 27.1 Share γ’/γ’’ 1.433 1.434 1.406 1.388 1.373 1.348 1.278 1.178 Temperature at the 1st stage 730 730 730 730 730 730 730 730 Temperature at the 2nd stage 570 590 610 630 650 670 690 710 γ' after the 1st stage (%) 12 12 12 12 12 12 12 12 Size γ' after 1st stage (nm) 20 20 20 19 19 19 19 19 γ' after 2nd stage (%) 2.0 1.8 1.7 1.5 1.3 1.0 0.7 0.4 Size γ' after 2nd stage (nm) 20 20 20 19 19 19 19 19 γ'' after the 1st stage (%) 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 Size γ'' after 1st stage (nm) 32 33 33 33 33 34 35 38 γ'' after the 2nd stage (%) 0.3 0.5 0.6 0.7 0.6 0.5 0.4 0.2 Dimension γ'' after 2nd stage (nm) 32 33 33 33 33 34 35 38 Yield strength (ksi) 167 167 167 166 165 162 159 154 Tensile strength (ksi) 208 208 208 208 207 205 202 199 Hardness (Rockwell) 41 41 41 41 41 40 40 39 Total Gamma’ 33.7 33.4 33.2 33.0 32.7 32.3 32.0 31.9 Total Gamma'' 36.4 36.9 37.5 37.9 37.8 38.2 39.4 41.9 Share γ’/γ’’ 0.924 0.905 0.885 0.870 0.864 0.846 0.813 0.760

Experimental data

To confirm the mechanisms of hydrogen embrittlement, laboratory experiments were carried out with laboratory melts with chemical compositions LB250646, LB250647, LB250650, LB250642. These melts were tested for slow loading under cathodic polarization according to NACE publication 3948, 2014. The results are shown in Table 8.

Table 8. Results of slow loading tests using 4 chemistries (LB250646 comparative, LB250647 without Nb, LB250650 without Al, LB250642 with low Nb).

Composition Test condition Sample No. Elongation at break Time to break Rm (%) Coefficient, (%) min Coefficient, (%) MPa Coefficient, (%) LB250646 inert environment A1 20.3 - 4657 - 1109 - Aggressive environment A2 13.2 65 3295 71 1118 101 Aggressive environment A3 13.2 65 3448 74 1092 98 Aggressive environment A4 13 64 3375 72 1062 96 Average 65 72 98 LB250647 inert environment IN 1 40.9 - 9098 - 535 - Aggressive environment AT 2 44.9 110 9283 102 586 110 Aggressive environment AT 3 44.8 110 9442 104 487 91 Aggressive environment AT 4 43 105 9039 99 513 96 Average 108 102 99 LB250650 inert environment C1 17.8 - 4222 - 1108 - Aggressive environment C2 9.3 52 2524 60 1094 99 Aggressive environment C3 10 56 2450 58 1088 98 Aggressive environment C4 7.8 44 2055 49 1038 94 Average 51 55 97 LB250642 inert environment D1 30.5 - 6343 - 973 - Aggressive environment D2 28.4 93 5934 94 937 96 Aggressive environment D3 26.2 86 5838 92 882 91 Aggressive environment D4 31 102 6213 98 895 92 Average 94 95 93

Slow loading tests support the theoretical mechanism that the presence or predominance of gamma'' is detrimental to the resistance of a material to hydrogen embrittlement, since niobium-free or low (i.e., gamma'-dominant) alloys do not fully or almost do not have a predisposition to hydrogen embrittlement, which is confirmed by higher coefficients of elongation at break.

Gamma-only charge (LB250650 without aluminium) has the worst resistance to hydrogen embrittlement.

Therefore, the stated limits for the alloy according to the invention can be separately substantiated as follows.

Iron reduces cost and thus should be used. Therefore, 12% is the lower limit of iron content. However, iron should not be added excessively due to the deterioration of the material properties. Therefore, 24% should be considered the upper limit. If necessary, iron can be replaced by cobalt.

The minimum 17% chromium content increases strength at room temperature and at the same time provides overall corrosion resistance. In combination with carbon, chromium carbides are formed, which are able to increase strength at high temperatures. Too high chromium content deteriorates the phase stability of the alloy and promotes the formation of harmful phases, which adversely affects the ductility and toughness, and therefore the content of chromium in the amount of 21% is the upper limit.

Higher molybdenum contents increase pitting resistance in chlorinated environments. With an increase in the minimum content of molybdenum from 0.001 to 3%, the resistance to stress corrosion cracking at elevated temperatures also increases. The upper limit is considered to be 9%, since the addition of molybdenum significantly affects the cost of the metal.

Tungsten can be used as a substitute for molybdenum and is then also limited to >0 to 9%.

A combination of molybdenum and tungsten is also possible, with the proportion of tungsten set to at least 0.01%.

The formation of the intermetallic gamma phase released during hardening by aging increases with an increase in the amount of Al + Ti. Therefore, a minimum aluminum content of 0.4% is necessary. If the aluminum content is too high, then aggregation and coarsening of the gamma phase occurs along the grain boundaries, as a result of which the mechanical properties sharply decrease and the hot workability deteriorates. For powder alloy for additive manufacturing methods, the aluminum content can be set higher, since the corresponding processes dispense with hot deformation. Therefore, the aluminum content is limited to 4.0%.

Titanium is combined with aluminum and nickel to form the gamma phase, and it helps to increase the strength of the alloy as a result of precipitation. However, if titanium is added in excess, an eta phase may form, causing mechanical properties to deteriorate. Therefore, titanium is added in an amount up to 3.0%.

Niobium (or tantalum) stabilizes the gamma phase and increases strength. Therefore, its minimum content should be 1%. However, niobium (or tantalum) is involved in the formation of the gamma phase, which is detrimental to the resistance to hydrogen embrittlement, and therefore must be controlled. For this reason, the content of niobium (or tantalum) is limited to 1 to 5.7%.

Boron and phosphorus have the ability to suppress excessive accumulation of hydrogen along the boundaries of phases and grains. This may reduce the sensitivity to hydrogen embrittlement. However, segregations along the phase boundaries and grains are too pronounced when boron and phosphorus are used in excessive amounts, and the effect of reducing hydrogen embrittlement is lost. Processability may also be limited, and therefore boron is limited to 0.001% to no more than 0.01%, phosphorus is limited to 0.001 to no more than 0.02%.

Cobalt can replace nickel, it improves properties at elevated temperatures. The alloy may contain up to 3% cobalt.

The carbon content is limited to not more than 0.045%, since this element at this content reduces the workability due to excessive formation of carbides.

Copper is limited to no more than 0.23%, since this element reduces the oxidation resistance.

The rest of the alloy is nickel (50 - 55%), it should be borne in mind that the remainder contains small amounts of impurities that do not significantly change the properties of the alloy. Therefore, impurities such as sulfur may be present in a total amount of 0.01%. Manganese and silicon are limited to content not exceeding 0.35%.

Heat treatment planning is essential to control and simulate phase precipitation. Therefore, the limits of the heat treatment parameters of the alloy according to the invention can be justified separately as follows.

The precipitation phases for the possible limits of the chemical composition are formed at temperatures below 970 ° C and therefore the alloy is subjected to solution annealing for 0.1 min to 60 h in order to transfer all phases into solution, taking into account the dimensions of the product. The solution annealing temperature is limited to a maximum value of 1150° C. in order to limit grain growth. To exclude the formation of precipitates after solid solution annealing, it is proposed to carry out rapid cooling in a mobile annealing atmosphere, inert gas, water, polymer, or oil.

Subsequently, age hardening annealing is carried out to form precipitation phases and to achieve good mechanical properties. To do this, the material is annealed at 600 to 900° C. for 0.1 hour to 60 hours. Longer age hardening periods lead to precipitation of delta and eta phases and should be avoided.

If necessary, hardening by aging can be carried out in the second stage at a temperature of from 550 to 900°C for 0.1 h to 60 h.

The temperature of hardening by aging is selected depending on the purpose. Age hardening processes that optimize mechanical properties are used in applications where excellent mechanical properties are required. Age hardening processes that optimize the gamma/gamma phase ratio are used when excellent resistance to hydrogen embrittlement is required.

Single step age hardening results in higher gamma'/gamma'' phase ratios and lower mechanical properties.

Two-stage age hardening can lead to different structures with different mechanical properties depending on the selected temperatures in the first and second stages.

If the temperature in the first stage is equal to the mentioned peak temperature, then the age hardening results in excellent mechanical properties, although the ratio of gamma'/gamma'' phases is calculated to be less.

The two-stage age hardening at a first temperature above the peak temperature results in average mechanical properties. The proportions of the gamma'/gamma'' phases are smaller in this case, i.e. this results in lower resistance to hydrogen embrittlement.

If the temperature in the first stage is below the peak temperature, and the temperature in the second stage is less than the temperature in the first stage, then the mechanical properties will be lower than those that can be achieved with one-stage age hardening. However, the ratio of gamma'/gamma'' phases can be higher, and thus this heat treatment can be used in applications where higher requirements for resistance to hydrogen embrittlement are the main goal. On the other hand, excellent mechanical properties can also be achieved when the temperature in the first stage is below the peak temperature and the temperature in the second stage is above the first temperature. The ratio of the proportions of gamma ' / gamma '' phases is maintained at the same level.

It is also necessary to take into account the duration of hardening by aging. For low temperature age hardening, longer time hardening times are required so that all precipitation can occur, while for high temperature age hardening, short time hardening times are sufficient.

By the alloy according to the invention or by the heat treatment according to the invention (solution annealing and age hardening annealing), the following properties can be achieved: elongation at break when tested in sour gas (NACE publication 3948) exceeds 75%, preferably exceeds 90% , at a yield strength in air > 100 ksi, preferably > 120 ksi.

Brief description of the drawings

Fig. 1 – energy versus elongation in the numerical tensile test of the gamma/gamma’ system without (black line) and with (red line) the presence of a hydrogen atom.

Fig. 2 – energy versus tension in the numerical tensile test of the gamma/gamma’’ system without (black line) and with (red line) a hydrogen atom.

Fig. 3 - energy versus tension in a numerical tensile test of the gamma/delta system without (black line) and with (red line) a hydrogen atom.

Fig. 4 – SEM images of the material represented by 120K, 140K, 150K variants of Alloy 718 alloy.

Fig. 5 - mechanical properties depending on the temperature of hardening by aging of the alloy composition LB250643.

Fig. 5' - phase diagram of the alloy composition LB250643

Fig. 6 - diagram "time, temperature, transformation" of the alloy composition LB250643.

Fig. 7 - calculated mechanical properties after two-stage hardening by aging hardening of an alloy of chemical composition LB250643.

Fig. 8 is an isothermal diagram of the LB250643 alloy with aging hardening at 650°C. The proportion of the gamma phase is shown by red circles, the proportion of the gamma phase is shown by blue rectangles.

Fig. 9 is an isothermal diagram of an alloy of the chemical composition LB250643 during aging hardening at 730°C. The proportion of the gamma phase is shown by red circles, the proportion of the gamma phase is shown by blue rectangles.

Fig. 10 - experimental curve of hardness depending on the temperature of hardening by aging of an alloy of chemical composition LB250643.

Fig. 11a - 11ab - mechanical properties depending on the temperature of hardening by aging of different variants of the alloy.

Claims (75)

1. A method for obtaining a semi-finished product from a nickel alloy containing, wt.%: Ni: 50–55 Cr: 17–21 Mo: >0–9 W: 0–<9 Nb: 1–<5.7 Ta: >0–4.7 Ti: 0.1–3.0 Al: 0.4–4.0 Co: no more than 3.0 Mn: no more than 0.35 Si: no more than 0.35 Cu: no more than 0.23 C: 0.001–0.045 S: no more than 0.01 P: 0.001–0.02 B: 0.001–0.01, the rest is Fe and normal production-related impurities, when the following relations are fulfilled: Nb+Ta: >1–5.7 … (1) Al+Ti: >1.2–5 … (2) Mo+W: 3–9 … (3), where Nb, Ta, Al, Ti, Mo and W are the content of the corresponding elements, wt.%, including: - smelting in a vacuum induction (VIM) furnace and casting into ingots, - subjecting said VIM ingots to stress relief annealing in the temperature range from 500 to 1250°C for up to 110 hours, - then processing these ingots in the process of electroslag remelting (ESR) and/or vacuum arc remelting (VAR), and, if necessary, the alloy is remelted in the process of electroslag remelting or vacuum arc remelting, - subjecting the remelted ingots to homogenizing annealing in the temperature range from 500 to 1250°C for up to 150 hours, - then subjecting the annealed ingots to hot and cold deformation to obtain a semi-finished product, - at least one annealing per solid solution in the temperature range from 900 to 1150°C for 0.1 to 60 hours, followed by cooling in air, in a mobile annealing atmosphere, inert gas, in water, in a polymer or in oil, wherein the semi-finished product obtained has the following properties: an elongation at break during the acid gas test of more than 75%, preferably more than 90%, with a yield strength in air > ¹⁰⁰ ksi, preferably 120 ksi. 2. A method for obtaining a semi-finished product from a nickel alloy containing, wt.%: Ni: 50–55 Cr: 17–21 Mo: >0–9 W: 0–<9 Nb: 1–<5.7 Ta: >0–4.7 Ti: 0.1–3.0 Al: 0.4–4.0 Co: no more than 3.0 Mn: no more than 0.35 Si: no more than 0.35 Cu: no more than 0.23 C: 0.001–0.045 S: no more than 0.01 P: 0.001–0.02 B: 0.001–0.01, the rest is Fe and normal production-related impurities, when the following relations are fulfilled: Nb+Ta: >1–5.7 … (1) Al+Ti: >1.2–5 … (2) Mo+W: 3–9 … (3), where Nb, Ta, Al, Ti, Mo and W are the content of the corresponding elements, wt.%, including: - open smelting and then processing in a vacuum oxygen decarburization (VOD) plant or in an argon oxygen decarburization (AOD) plant and subsequent casting into ingots, - if necessary, subjecting said ingots to stress relief annealing in the temperature range from 500 to 1250°C for up to 110 hours, - then the implementation of at least one, in particular, two-time, vacuum-arc remelting (VAR), - subjecting the remelted ingots to homogenized annealing in the temperature range from 500 to 1250°C for up to 150 hours, - then subjecting the annealed ingots to hot deformation and cold deformation to obtain a semi-finished product, - then the implementation of at least one annealing per solid solution in the temperature range from 900 to 1150°C for 0.1 to 60 h, followed by cooling in air, in a mobile annealing atmosphere, inert gas, in water, in a polymer or in oil, wherein the semi-finished product obtained has the following properties: an elongation at break during the acid gas test of more than 75%, preferably more than 90%, with a yield strength in air > 100 ksi, preferably 120 ksi. 3. Method according to claim 1 or 2, characterized in that the chromium content is 17-20% by weight, preferably 17-19% by weight. 4. The method according to any one of paragraphs. 1-3, characterized in that the content of molybdenum and/or tungsten is 3-8 wt.%, preferably 3-7 wt.%. 5. The method according to any one of paragraphs. 1-4, characterized in that it has the following ratio between niobium and tantalum: Nb+Ta = 2–4.5 wt.%, in particular, Nb+Ta = 2–4 wt.%, where Nb and Ta are the content of the corresponding elements, wt.%. 6. The method according to any one of paragraphs. 1-5, characterized in that the titanium content is 0.5-3.0 wt.%, preferably 1.0-3.0 wt.%, more preferably 1.0-2.0 wt.%. 7. The method according to any one of paragraphs. 1-6, characterized in that the aluminum content is 0.6-2.5 wt.%, preferably 0.6-2.0 wt.%, more preferably 0.6-1.5 wt.%. 8. The method according to any one of paragraphs. 1-7, characterized in that the carbon content is from 0.001 to not more than 0.035 wt.%, preferably from 0.001 to not more than 0.025 wt.%. 9. The method according to any one of paragraphs. 1-8, characterized in that it has the following ratio between aluminum and titanium: Al+Ti = 1.4–4 wt.%, preferably Al+Ti = 1.6–4 wt.%, where Al and Ti are the content of the corresponding elements, wt.%. 10. The method according to any one of paragraphs. 1-9, characterized in that after annealing the semi-finished product to a solid solution, aging is carried out at a temperature of 600 to 900°C for 0.1 to 60 h, preferably at a temperature of 600 to 850°C for 0.1 to 60 h, most preferably at 600 to 750°C for 0.1 to 60 h, or at 700 to 900°C for 0.1 to 60 h, or at 750 to 900° C for 0.1 to 60 hours. 11. The method according to any one of paragraphs. 1-10, characterized in that after annealing the semi-finished product to a solid solution, two-stage aging is carried out, and at the first stage, aging is carried out at a temperature of 600 to 900 ° C for 0.1 to 60 h, and at the second stage, at a temperature of 550 up to 900°C for 0.1 to 60 hours, preferably at a temperature of 550 to 750°C for 0.1 to 60 hours or at a temperature of 800 to 900°C for 0.1 to 60 hours , or at a temperature of 750 to 900°C for 0.1 to 60 hours. 12. Application of the method according to any one of paragraphs. 1-11 to obtain a semi-finished product in the form of a rod, wire, strip, sheet, longitudinally welded pipe, seamless pipe. 13. Application of the method according to any one of paragraphs. 1-11 to obtain a semi-finished product for structural elements for the oil and gas industry or for the chemical industry.

Images