JPH0114992B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a high-strength, high-toughness nickel base material that exhibits good stress corrosion cracking resistance and hydrogen cracking resistance in a corrosive environment, particularly in an environment containing one or more of hydrogen sulfide, carbon dioxide, and chloride ions. Concerning the manufacturing method of alloy materials. Conventionally, metal parts that require high strength and high corrosion resistance, such as structural materials for equipment in oil wells, chemical industries, geothermal power generation, etc., have been strengthened by (solid solution strengthening) + (cold working strengthening). Most of the methods were aimed at increasing the strength, so it was difficult to increase the strength of metal parts with complex or special shapes that could not be subjected to cold working using the conventional methods described above. . On the other hand, a conventionally known means of increasing strength that can be applied to members with special shapes is to add Ti and Al or Nb to the alloy composition to increase Ni ₃
This is to precipitate an intermetallic compound (γ' phase) mainly composed of (Ti, Al) or an intermetallic compound (γ'' phase) mainly composed of Ni ₃ Nb. As for Inconel-718,
There are Ni-based alloys such as Inconel-750 (trade name), but conventional alloys have low Cr and high Ti, so Ni ₃ Ti
precipitated and the corrosion resistance deteriorated. For example, Inconel
718 etc. are γ′ and γ″ precipitation-strengthened Ni-based alloys due to the addition of Nb, Ti, and Al, and are mainly precipitation strengthened by the γ″ phase, but because they contain a considerable amount of Ti and Ni ₃ Ti precipitates, their corrosion resistance is poor. It wasn't necessarily good. By the way, materials that are used in environments containing one or more of hydrogen sulfide, carbon disulfide, and chlorine ions, such as oil wells, chemical industries, and geothermal power generation environments, have excellent strength and toughness. Corrosion resistance, namely stress corrosion cracking resistance and hydrogen cracking resistance, is required. In the case of materials used as structural materials in such applications, it is desirable to increase the strength of materials that are relatively easy to form, such as plates or tubes, by cold working.
For joints, piping, etc. that have special shapes that cannot be subjected to cold working, the strength must be increased by precipitation strengthening. however,
According to the results of the research conducted by the present inventors, conventional precipitation-strengthened alloys such as those mentioned above, which are mostly γ′ precipitation-strengthened Ni-based alloys due to the addition of Ti and Al, inherently have poor corrosion resistance. I found out that. For example, the alloy disclosed in Japanese Patent Application Laid-open No. 57-203741 as an alloy with good stress corrosion cracking resistance contains γ′-Ni ₃ (Ti, Al) and γ″−Ni ₃ Nb
The two intermetallic compounds mainly precipitate, but due to the large amount of Ti added, overaging is likely to occur, and when the intermetallic compound η-Ni ₃ Ti is precipitated as an overaging precipitation phase, corrosion resistance, especially hydrogen cracking resistance, is significantly reduced. to degrade. In order to improve this corrosion resistance, it is necessary to strictly limit the heat treatment conditions and aging treatment conditions. Furthermore, as a similar alloy, the one described in JP-A-57-123948 is also known, but this also has poor corrosion resistance due to the addition of a large amount of Ti. Ti
As can be seen from the fact that a lower limit value is set for the amount of addition, it is intended to precipitate Ni ₃ (Ti, Al). Therefore, in the book, the inventors published the patent application No. 58-109422.
In this issue, we discuss the drawbacks in corrosion resistance and stability of Ti-added γ′ precipitation-strengthened Ni-based alloys, namely γ′-
We have solved the problem of deterioration of corrosion resistance of T-added alloys where Ni ₃ Ti precipitates (the same is true for Ti and Nb composite additions).
A method was disclosed that solved the problem by selecting the composition of the Ni-based alloy and specifying the conditions for hot working, heat treatment, and aging treatment. As a result of further research, the present inventors found that by adding Nb and Al in combination to the above-mentioned prior invention, it has various strengths, ductility, and toughness, and is resistant to stress corrosion cracking. The present invention was completed based on the discovery that a material with extremely excellent hardness and hydrogen cracking resistance could be obtained, and that the precipitation strengthening of the γ′ or γ″ phase could be promoted by adding Co if necessary, thereby shortening the aging time. Here, the gist of the present invention is as follows: C: 0.050% or less, Si: 0.50% or less, Mn: 2.0% or less, Ni: 45-60%, Cr: 18-27%, Ti: 0.40%. Below, at least one of Mo: 2.5-5.5% and W: 11% or less (however, 2.5%≦Mo+1/2W≦5.5%), Al: 0.3-2.0%, P: 0.015% or less, Nb: 2.5-5.0 % and Ta: at least one of 2.0% or less (however, 2.5%≦Nb+1/2Ta≦5.0%), S: 0.0050% or less, N: 0.030% or less, Cu: 2.0% or less and Co:
2.0% or less of at least one species, and/or
REM: 0.10% or less, Mg: 0.10% or less, Ca: 0.10
% or less and Y: at least one type of 0.20% or less,
After hot working an alloy with a composition consisting of Fe and the remainder incidental impurities at 1200 to 800°C with a reduction in area of 50% or more,
After holding at 1200℃ for 3 minutes to 5 hours, cool at a cooling rate faster than air cooling (however, between 900 and 500℃,
℃/min or higher), then 500~
This is a method for producing a precipitation-strengthened nickel-based alloy with excellent stress corrosion cracking resistance and hydrogen cracking resistance, which comprises performing an aging treatment at 750° C. for 1 to 200 hours once or twice or more. Furthermore, in another embodiment of the present invention, the alloy composition is Ni: 40 to 60%, Al: 2.0% or less, Co:
Contains more than 2.0% and less than 15%. That is, according to the present invention, one or both of hydrogen sulfide, carbon dioxide, and chlorine ions
For example, parts that have good stress corrosion cracking resistance and hydrogen cracking resistance in oil well, chemical industry, and geothermal power generation environments, and that cannot be subjected to cold working due to their special shape, such as valve bodies for oil wells. In order to obtain high strength even when used in applications, we have created an alloy composition that is higher in Cr than before, with less Ti added, and mainly contains Nb and Al. By applying these in combination, it is possible to obtain a precipitation-strengthened Ni-based alloy that exhibits extremely good corrosion resistance, high strength, and high toughness. Therefore, according to one feature of the present invention, as a method for improving the corrosion resistance of conventional precipitation-strengthened Ni-based alloys,
Based on the above knowledge, the amount of Ti added is suppressed compared to the conventional method, the addition of Nb and Al is the main content, and the γ′ and γ″ phases, which are intermetallic compounds of Ni ₃ Nb or Ni ₃ (Nb, Al), are added. In order to achieve precipitation strengthening, heat treatment conditions and aging conditions are specified in order to effectively carry out precipitation strengthening.According to another feature of the present invention, by adding Co, the γ′ phase and γ It promotes precipitation strengthening of the ``cobalt'' phase and shortens the aging time, and the addition of Co does not cause deterioration in corrosion resistance. The reason why the alloy composition and processing conditions are limited as described above in the present invention will be explained in more detail below. (1) Chemical composition Ni...The alloy in the present invention is basically an austenite matrix in which γ' phase or γ'' phase, which is an intermetallic compound of Ni ₃ (Nb, Al) or Ni ₃ Nb, precipitates and strengthens through aging. It is said that
The ductility of σ, μ, P, Laves phases, etc. depends on the balance of the amount of Cr, Mo, Fe, and Co added.
A sufficient amount of Ni is required to stabilize the austenite matrix so as not to form intermetallic compounds (hereinafter referred to as TCP phase) that are unfavorable for toughness and corrosion resistance.
%. However, if Co is contained in an amount exceeding 2.0%, Ni≧40% is sufficient. Also Ni
If Ni exceeds 60%, the hydrogen cracking resistance will deteriorate significantly, so it is desirable that Ni≦60%, but preferably within a range that satisfies both strength and toughness.
50%≦Ni≦55%. Cr: Improves corrosion resistance together with Mo. For this purpose, a content of 18% or more is required, but if it exceeds 27%, hot workability deteriorates and TCP phases are more likely to be generated. Preferably Cr is 22-27
%. Mo, W...In coexistence with Cr, the pitting corrosion resistance is particularly improved. This effect becomes noticeable when Mo2.5% or more is added, but as with Cr, adding a large amount makes it easier to form a TCP phase.
It is desirable to add Mo5.5% or less. W shows the same effect as Mo, but to obtain the same effect
It is necessary to add twice the amount of Mo. Therefore, at least a portion of the required amount of Mo may be replaced with W at that ratio. If W is added in an amount exceeding 11%, the above-mentioned intermetallic compounds are likely to be formed similarly to Mo, so it is limited to 11% or less. Therefore, in the present invention, Mo:
At least one type of 2.5 to 5.5% and W: 11% or less (however, 2.5%≦Mo+1/2W≦5.5%)
Add. Outside these ranges, corrosion resistance will not be improved sufficiently and ductility and toughness will deteriorate. Ti...If Ti exceeds 0.40%, it will precipitate as Ni ₃ Ti, significantly deteriorating corrosion resistance, especially hydrogen cracking resistance, so Ti should be 0.40% or less, but it is preferable to stably obtain hydrogen cracking resistance. teeth,
Ti: 0.20% or less. Al...Al has a deoxidizing effect and also has a deoxidizing effect as well as Nb _.
It precipitates as (Nb, Al) and contributes to an increase in strength. Precipitation strengthening behavior changes depending on the balance of addition amount with Nb. If only the deoxidizing effect is considered, Al should be less than 0.30%, but Ni ₃ (Nb,
In order to obtain effective precipitation strengthening as Al)
Al 0.3% or more is required. On the other hand, since adding a large amount of Al promotes TCP phase formation, the Al content was set to 2.0% or less. Nb, Ta...Nb is Ni ₃ Nb or N ₃ (Nb,
Al) precipitates and contributes to increased strength. Al
The precipitation strengthening behavior changes depending on the balance of the amount of Nb added, but the effect of adding Nb is
It becomes noticeable when it exceeds 2.5%, and on the other hand, when it exceeds 5.0%, hot workability decreases and TCP phase tends to be generated. Outside these ranges, there is no effect on increasing strength, but rather the ductility and toughness deteriorate. Because Ta exhibits the same effect as Nb,
Although a part of Nb may be replaced with Ta, the effect of the addition is approximately 1/2 that of Nb. Therefore, in the present invention, Nb: 2.5 to 5.0% and Ta:
2.0% or less of at least one species 2.5%≦Nb+1/
Add within the range of 2Ta≦5.0%. C... hinders precipitation strengthening and also 0.050%
If it exceeds this, the amount of inclusions such as NbC and TiC will increase and ductility, toughness, and corrosion resistance will deteriorate. Preferably C≦0.020%, but when C≦0.010%, ductility,
Toughness and corrosion resistance are further improved. Si, Mn...Si and Mn are added as deoxidizing agents and desulfurizing agents, respectively, but if Si exceeds 0.50%, TCP phase tends to be generated, so Si: 0.50%
The following shall apply. Considering weldability, Si≦0.10%
is preferred. Furthermore, the same applies to Mn.
It is desirable that Mn≦2.0%, but preferably Mn≦
It shall be 0.80%. P, S... P, S decreases hot workability due to grain boundary segregation and also deteriorates corrosion resistance.
PP≦0.015%, S≦0.0050%, preferably,
To further improve machinability during delivery, S≦
It shall be 0.0010%. N...N increases the amount of inclusions and causes anisotropy in material properties, so N≦0.030%,
In order to further dramatically improve ductility and toughness, preferably N≦0.010%. Fe...A suitable amount is required to promote precipitation strengthening depending on the balance with the amount of Ni added, and the remainder of the alloy composition is Fe, excluding incidental impurities. Preferably, 3.0%≦Fe≦25%. however,
Co: 3.0≦Fe≦20% when adding more than 2.0%
That's fine. Cu, Co...Effective in improving corrosion resistance, but the effect is saturated when it exceeds 2.0%, so Cu, Co
≦2.0%. However, when actively utilizing precipitation strengthening by adding Co, Co should be added in excess of 2.0%, and depending on the balance with the amount of Ni and Fe added, the precipitation of γ′ or γ″ phase can be promoted and the strength can be increased. Plan.
This effect becomes noticeable when Co: exceeds 2.0%, but 15%
If the content exceeds 2.0%Co≦15%, TCP phase tends to be generated. REM, Mg, Ca, Y... These elements improve hot workability by adding at least one kind of trace amount, but they are 0.10%, 0.10%, 0.10% respectively.
If the upper limits of 0.20% and 0.20% are exceeded, low-melting compounds tend to be produced and processability deteriorates. B...B is added for the purpose of improving hot workability and toughness, and is added in an amount of 0.10% or less if necessary. Others...Sn, Zn, Pb, etc. do not affect the properties of the alloy obtained by the present invention in trace amounts, so up to 0.10% of each is allowed as impurities, but if this upper limit is exceeded, workability or corrosion resistance deteriorates. (2) Hot working When Nb is added as in the present invention,
There is a tendency for low melting point compounds to be generated at grain boundaries during solidification, so it is necessary to limit the heating temperature and processing temperature range during hot processing. When the starting temperature of hot working exceeds 1200°C, weakening of grain boundaries is observed. On the other hand, if the finishing temperature is less than 800°C, processing becomes difficult. In the present invention, therefore,
Temperature range from 1200 to 800℃, preferably from 1150 to
Hot processing is performed at 850℃. Furthermore, Nb, Mo, etc. tend to cause macro-segregation during solidification, and if such segregation remains in products, it becomes a factor in deterioration of toughness and corrosion resistance in thick-walled materials. For this reason, the degree of hot working from the ingot to the product is set to 50% or more in area reduction rate to prevent macro segregation of Nb, Mo, etc. (3) Heat treatment In order to effectively precipitate the γ′ phase or γ″ phase due to aging, complete solution treatment is necessary, so in the present invention, prior to aging,
3 at 1000℃~1200℃, preferably 1050~1150℃
After holding for 5.0 minutes, cool at a cooling rate faster than air cooling. During cooling, the brittle phase tends to precipitate particularly between 900℃ and 500℃, so the temperature range between 900℃ and 500℃ is
Precipitation of such brittle phases is suppressed by cooling at a cooling rate of 10°C/min or more. ( ₄ ) Aging treatment The alloy obtained by the _present invention has high strength, good ductility, toughness and Provides corrosion resistance. Precipitation strengthening behavior due to aging varies depending on the solution treatment conditions and the amounts of Nb and Al added, as well as the amounts of Ni, Co, and Fe, but precipitation becomes noticeable at aging temperatures of 500°C or higher. However, high-temperature aging exceeding 750°C results in overaging, resulting in a decrease in strength and toughness due to agglomeration and coarsening of the γ′ or γ″ phase or the formation of TCP phase.The selection of aging time also varies depending on the aging temperature.Effectiveness Precipitation strengthening can be obtained in 1 to 200 hours, but sufficient strength can be obtained even in 5 to 20 hours.Stable strength, ductility,
In order to obtain toughness and corrosion resistance, it is desirable that the γ′ phase or γ″ phase be finely and uniformly dispersed and precipitated in the austenite base of the matrix.
Aging treatment at 600°C to 750°C is preferred. In addition, in the case where the aging treatment is performed two or more times in the present invention, the aging treatment after the second stage may be performed by cooling to around room temperature after the previous aging treatment and then reheating, or From the aging treatment temperature,
The aging treatment may be performed by directly heating or cooling (at a rate higher than furnace cooling) to the next aging treatment temperature. In either case, there is no noticeable difference in strength, toughness, or corrosion resistance. Thus, according to the method of the present invention, the mechanical property is 0.2% proof stress ≧63 Kgf/mm ² (preferably ≧77
Kgf/mm ² ), elongation ≧20%, aperture ≧30% and impact value ≧5Kgf-m/cm ² (preferably ≧10Kgf-m/
cm ² ) and excellent corrosion resistance, that is, stress corrosion cracking resistance and water cracking resistance. The alloy obtained by the present invention is
High strength can be obtained by precipitation strengthening of the γ′ phase or γ″ phase, so even products with special shapes such as valve bodies for oil country tubular goods, to which strengthening methods such as cold working cannot be applied, can have good strength and strength. It is possible to produce products with toughness and corrosion resistance.Next, the present invention will be further explained based on Examples.In this specification, "%" means "% by weight" unless otherwise specified. . Example 1 For each alloy having the chemical composition shown in Table 1 below, precipitation-strengthened nickel-based alloys were produced under the hot working conditions, heat treatment conditions, and aging treatment conditions shown in Table 2. The mechanical properties and corrosion resistance test results of the obtained alloy are also summarized in Table 2. The tensile test was conducted using a test rod with a diameter of 3.5 mm and a gage distance of 20.0 mm. The impact value was determined by a Charpy impact test using a test piece measuring 5.0 mm x 10 mm x 55 mm with a 2.0 mm V-notch. The test temperature was 0°C. Corrosion resistance is 25% in stress corrosion cracking test
NaCl − 0.5% CH ₃ COOH − 15 atm H ₂ S − 10 atm
It was evaluated using a solution of CO ₂ (PH=2) and tested at 250°C. Regarding the hydrogen cracking test,
Under NACE conditions (5% NaCl−05% _CH3COOH−
1atm H ₂ S) using carbon steel coupler,
Test specimens with R0.25U notches were used at 25°C. In Table 2, "0" indicates that no cracks were present, and "X" indicates that cracks occurred. Comparative examples are Nos. 25 to 30, which are within the composition range of the alloy used in the method of the present invention, but outside the hot working, heat treatment, and aging treatment conditions, and Nos. 25 to 30, where the processing conditions are within the range. However, Nos. 31 to 36 show those with different alloy components. In the comparative examples, one or more of strength, ductility, toughness, and corrosion resistance were not good. Nos. 37 to 44 are shown for comparison with the alloy obtained by the method of the present invention with respect to conventional precipitation-strengthened alloys containing Ti and Al. Many of these conventional alloys have good strength, but their corrosion resistance deteriorates due to their nature.On the other hand, in order to improve such corrosion resistance, strength must be sacrificed, and there are cannot be obtained. Example 2 For each alloy having the chemical composition shown in Table 3 below, precipitation-strengthened nickel-based alloys were produced under the hot working conditions, heat treatment conditions, and aging treatment conditions shown in Table 4. The mechanical properties and corrosion resistance test results of the obtained alloys are also summarized in Table 4. The test method was the same as that described in Example 1. Comparative examples are Nos. 21 to 26, which are within the composition range of the alloy used in the method of the present invention, but outside the hot working, heat treatment, and aging treatment conditions. However, Nos. 27 to 33 show those with a small amount of Co added. In Comparative Examples Nos. 21 to 26, none of the strength, ductility, and toughness was good. In addition, for Nos. 27 to 33, which are examples of the present invention,
Compared to the alloy of the present invention when a large amount of Co is added, the aging treatment time required to obtain the same level of strength is longer. Nos. 34 to 41 are shown for comparison with the alloy obtained by the method of the present invention with respect to conventional precipitation-strengthened alloys containing Ti and Al. Many of these conventional alloys have good strength, but their corrosion resistance has deteriorated due to their nature, and in order to improve such corrosion resistance, strength must be sacrificed. cannot be obtained. In this way, by limiting the composition range of the alloy and the conditions of hot working, heat treatment, and aging treatment as in the present invention, it is possible to achieve excellent corrosion resistance, that is, stress corrosion cracking resistance and hydrogen cracking resistance. A material with high strength and high toughness can be obtained. In particular, by adding an appropriate amount of Co, the aging treatment time can be shortened compared to the conventional method.

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[Table] *: Outside the scope of the present invention

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[Table] *: Outside the scope of the present invention

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[Table] *: Outside the scope of the present invention

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[Table] *: Outside the scope of the present invention

Claims (1)

[Claims] 1 C: 0.050% or less, Si: 0.50% or less, Mn: 2.0% or less, Ni: 45-60%, Cr: 18-27%, Ti: 0.40% or less, Mo: 2.5-5.5 % and W: at least one of 11% or less (however, 2.5%≦Mo+1/2W≦5.5%), Al: 0.3 to 2.0%, P: 0.015% or less, Nb: 2.5 to 5.0% and Ta: 2.0% or less At least one of the following (however, 2.5%≦Nb+1/2Ta≦5.0%), S: 0.0050% or less, N: 0.030% or less, Cu: 2.0% or less and Co:
2.0% or less of at least one species, and/or
REM: 0.10% or less, Mg: 0.10% or less, Ca: 0.10
% or less and Y: at least one type of 0.20% or less,
After hot working at 1200 to 800℃ with an area reduction rate of 50% or more, an alloy with a composition consisting of Fe and the remaining incidental impurities is heated to 1000 to 800℃.
After holding at 1200℃ for 3 minutes to 5 hours, cool at a cooling rate faster than air cooling (however, between 900 and 500℃,
℃/min or higher), then 500~
A method for producing a precipitation-strengthened nickel-based alloy with excellent stress corrosion cracking resistance and hydrogen cracking resistance, which comprises performing an aging treatment at 750°C for 1 hour to 200 hours once or twice or more. 2 C: 0.050% or less, Si: 0.50% or less, Mn: 2.0% or less, Ni: 40-60%, Cr: 18-27%, Ti: 0.40% or less, Mo: 2.5-5.5% and W: 11 % or less (however, 2.5%≦Mo+1/2W≦5.5%), Al: less than 0.3%, P: 0.015% or less, Nb: 2.5 to 5.0%, and Ta: 2.0% or less (but , 2.5%≦Nb+1/2Ta≦5.0%), S: 0.0050% or less, N: 0.030% or less, Co: more than 2.0%, 15% or less, and if necessary, Cu: 2.0% or less, and/
or B: 0.10% or less, and/or REM:
0.10% or less, Mg: 0.10% or less, Ca: 0.10% or less, and Y: 0.20% or less, and the balance is incidental impurities and Fe. After hot processing, 1000 ~
After holding at 1200℃ for 3 minutes to 5 hours, cool at a cooling rate faster than air cooling (however, between 900 and 500℃,
℃/min or higher), then 500~
A method for producing a precipitation-strengthened nickel-based alloy with excellent stress corrosion cracking resistance and hydrogen cracking resistance, which comprises performing an aging treatment at 750°C for 1 hour to 200 hours once or twice or more. 3 C: 0.050% or less, Si: 0.50% or less, Mn: 2.0% or less, Ni: 40-60%, Cr: 18-27%, Ti: 0.40% or less, Mo: 2.5-5.5% and W: 11% At least one of the following (2.5%≦Mo+1/2W≦5.5%), Al: 0.3 to 2.0%, P: 0.015% or less, Nb: 2.5 to 5.0%, and Ta: 2.0% or less (but , 2.5%≦Nb+1/2Ta≦5.0%), S: 0.0050% or less, N: 0.030% or less, Co: more than 2.0%, 15% or less, and if necessary, Cu: 2.0% or less, and/
or B: 0.10% or less, and/or REM:
0.10% or less, Mg: 0.10% or less, Ca: 0.10% or less, and Y: 0.20% or less, and the balance is incidental impurities and Fe, and the alloy has a cross-section reduction rate of 50% or more at 1200 to 800℃. After hot processing, 1000~
After holding at 1200℃ for 3 minutes to 5 hours, cool at a cooling rate faster than air cooling (however, between 900 and 500℃,
℃/min or higher), then 500~
A method for producing a precipitation-strengthened nickel-based alloy with excellent stress corrosion cracking resistance and hydrogen cracking resistance, which comprises performing an aging treatment at 750°C for 1 hour to 200 hours once or twice or more.