JPS6363609B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing high-strength oil country tubular goods having excellent stress corrosion cracking resistance. In recent years, due to the deterioration of the energy situation, there has been a marked tendency for oil and natural gas wells to become deeper.
Deep wells over 6000m deep, some over 10000m deep, have appeared. Furthermore, due to similar circumstances, the extraction of oil and natural gas in a harsh corrosive environment containing humid hydrogen sulfide and other corrosive components such as carbon dioxide gas and chlorine ions is becoming untenable. As oil and natural gas are drilled in such harsh environments, the oil country tubular goods used in this process are now required to have high strength and excellent corrosion resistance, especially stress corrosion cracking resistance. . As a general anti-corrosion measure for oil country tubular goods, it is known to introduce a corrosion suppressant called an inhibitor, but this method is often not effective for use in, for example, offshore oil wells. From this point of view, consideration has recently begun to be given to the use of high-grade corrosion-resistant high-alloy steels such as stainless steel and Incoloy and Hastelloy (both trade names) for the production of oil country tubular goods. Regarding the corrosion behavior of H ₂ S―CO ₂ ―Cl ^- in an oil well environment, the details have not yet been fully elucidated, and furthermore, it does not have the high strength required for oil country tubular goods for deep wells. is the current situation. Therefore, from the above-mentioned point of view, the present inventors investigated deep wells and severe corrosive environments, especially H ₂ S―CO ₂ -
As a result of conducting research to manufacture oil country tubular goods with high strength and excellent stress corrosion cracking resistance that can sufficiently withstand oil drilling in the Cl ^- oil well environment, we found that (a) H ₂ S―CO ₂ - The main type of corrosion in a Cl ^- environment is stress corrosion cracking, but the behavior of stress corrosion cracking in this case is completely different from that of general austenitic stainless steel. In other words, whereas general stress corrosion cracking is deeply related to the presence of Cl ^- , in the oil well environment mentioned above, the influence of H ₂ S is greater than that of Cl ^- . (b) Steel pipes used for practical use as oil country tubular goods are generally
Cold working is performed to improve strength, but cold working significantly reduces the resistance to stress corrosion cracking. (c) The elution rate (corrosion rate) of steel in an H ₂ S—CO ₂ —Cl ⁻ environment depends on the contents of Cr, Ni, Mo, and W, and is affected by the surface film made of these components. Corrosion resistance is maintained and these components are
It also increases its resistance to stress corrosion cracking, with Mo being 10 times more effective than Cr, and Mo being 10 times more effective than W.
It has twice the effect of
Mo and W satisfy the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%, and the Ni content is 35%. ~60
%, and the Cr content is 22.5 to 35%, H ₂ S—, which is extremely corrosive, even if it is a cold-worked material.
It is possible to obtain a surface film that exhibits excellent resistance to stress corrosion cracking in a CO ₂ - Cl ^- oil well environment, especially in a harsh environment of 150°C or less. (d) Ni has the effect of increasing stress corrosion cracking resistance not only on the surface film but also on the structure. (e) When N is included as an alloy component in the range of 0.05 to 0.3%, the strength of the pipe material is further improved. (f) If the S content as an unavoidable impurity is reduced to 0.0007% or less, the hot workability of the pipe material will be significantly improved. (g) When the P content as an unavoidable impurity is reduced to 0.003% or less, the susceptibility to hydrogen cracking significantly decreases. (h) When containing Cu as an alloy component: 2% or less,
Further improvement in corrosion resistance. (i) Rare earth elements: 0.10% or less as alloy components;
Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5%
When one or more of the following and Ca: 0.10% or less is contained, hot workability is further improved. (j) However, in order to ensure the desired high strength,
First, to the alloy of the above composition, preferably 1050 ~
When heated to a temperature within the temperature range of 1250℃ to completely dissolve intermetallic compounds and carbides, 1000℃
Wall thickness reduction rate is 10% or more at below, finishing temperature 800
By performing hot working at temperatures above ℃, we aim to refine the crystal grains without precipitation of intermetallic compounds or carbides that cause deterioration in corrosion resistance.The formation of these fine crystal grains gives the pipe material high strength and high Toughness is imparted, and subsequently 10 to 60%
It is necessary to perform cold working at a wall thickness reduction rate of , and to strengthen this process. The findings shown in (a) to (j) above were obtained. Therefore, this invention was made based on the above knowledge, and includes C: 0.05% or less, Si: 1.0%.
% or less, Mn: 2.0% or less, P: 0.030% or less, preferably for the purpose of further improving hydrogen cracking resistance, P: 0.003% or less, S: 0.005% or less, preferably for the purpose of further improving hot workability. So S: 0.0007%
Below, sol.Al: 0.5% or less, Ni: 35-60%, Cr:
Contains 22.5-35%, Mo: less than 4% and W:
Contains one or two of less than 8%, and further includes N: 0.05 to 0.3%, Cu: 2% or less, Co: 2% or less, rare earth elements: 0.10% or less,
One or two of Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5% or less, and Ca: 0.10% or less
Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1.5%≦Mo(%)+1/2W(%)<4% This method is characterized by the production of high-strength oil country tubular goods with excellent stress corrosion cracking resistance by hot working under the following conditions and then cold working at a wall thickness reduction rate of 10 to 60%. It is. Next, in the method of this invention, the component composition,
The reason why the hot and cold working conditions were limited as described above will be explained. A Component (a) C The lower the C content, the more the precipitation of carbides will be suppressed, so the thermal temperature during hot working can be lowered, and this will be more effective in increasing the strength after cold working. It works. Therefore, it is desirable that the C content be as low as possible, but if the C content exceeds 0.05%, intergranular stress corrosion cracking tends to occur, so the upper limit was set at 0.05%. (b) Si Si is a necessary component as a deoxidizing component, but
If the content exceeds 1.0%, hot workability will deteriorate, so the upper limit value should be set.
It was set at 1.0%. (c) Mn Mn component has a deoxidizing effect like Si,
Furthermore, since this component has almost no effect on stress corrosion cracking resistance, its upper limit was set at a rather high value of 2.0%. (d) P The P component as an unavoidable impurity has the effect of increasing stress corrosion cracking susceptibility when its content exceeds 0.030%.
It is necessary to set it at 0.030% to keep stress corrosion cracking susceptibility to a low level. It has also been found that as the P content is reduced, hydrogen cracking resistance rapidly improves after reaching 0.003%. If necessary, the P content is preferably 0.0030% or less. (e) S The S component as an unavoidable impurity has the effect of deteriorating hot workability when its content exceeds 0.005%, so the upper limit value must be set.
It is necessary to set it at 0.005% to prevent deterioration of hot workability. In this way, the S component has the effect of deteriorating hot workability when its content increases, but by decreasing its content, 0.0007
On the contrary, if the S content is reduced to 0.0007% or less, hot workability will be further improved, so if hot workability under severe conditions is required, it is desirable to reduce the S content to 0.0007% or less. . (f) Al Al is effective as a deoxidizing component like Si and Mn, and even if it is included up to 0.5% in sol.Al content, it will not impair the properties of the pipe material. .0.5 in Al content
% or less. (g) Ni Ni has the effect of improving the stress corrosion cracking resistance of pipe materials, but if its content is less than 30%, the desired excellent stress corrosion cracking resistance cannot be secured; Even if the content exceeds 35%, no further improvement in stress corrosion cracking resistance will be obtained, and the content was set at 35% to 60%, taking economic efficiency into consideration. (h) Cr The Cr component is a component that significantly improves stress corrosion cracking resistance when coexisting with Ni, Mo, and W components, but hot workability is not improved even if its content is less than 22.5%. On the contrary, in order to secure the desired stress corrosion cracking resistance, the content of Mo and W must be increased by that amount, which is economically disadvantageous, so the lower limit The value was set at 22.5%. On the other hand, if its content exceeds 35%,
Since deterioration of hot workability cannot be avoided no matter how much the S content is reduced, the upper limit was set at 35%. (i) Mo and W As mentioned above, these components have an equal effect on improving stress corrosion cracking resistance when coexisting with Ni and Cr, but each
Even if Mo: 4% or more and W: 8% or more are contained, the environmental temperature is 150℃ or less H ₂ S-CO ₂
- In a corrosive environment of Cl ^- , no further improvement effect was observed, and in consideration of economic efficiency, the respective contents were determined to be less than 4% for Mo and less than 8% for W. In addition, regarding the content of Mo and W, the conditional expression: Mo (%) + 1/2 W (%) specifies that the atomic weight of W is approximately twice that of Mo,
In terms of effectiveness, it becomes equal at about 1/2, so if this value is less than 1.5%, the desired stress corrosion cracking resistance cannot be obtained, especially under the above-mentioned adverse environment of 150℃ or less. Even if it is 4% or more, as mentioned above, it will contain substantially unnecessary amounts of Mo and W, which is not economical, and from this point of view,
The value of Mo (%) + 1/2 W (%) was set at 1.5 to less than 4%. (j) N Since the N component has the effect of improving strength through solid solution strengthening, it is included as necessary when particularly high strength is required, but if the content is 0.05
If the content is less than 0.3%, the desired strength improvement effect cannot be obtained; on the other hand, if the content exceeds 0.3%,
Since melting and ingot making are difficult, its content was set at 0.05 to 0.3%. (k) Cu and Co These components have a uniform effect of improving the corrosion resistance of pipe materials, and Co has a solid solution strengthening effect. However, if Cu exceeds 2%, hot workability will deteriorate, while Co content will not improve further even if it exceeds 2%. each value
Cu: 2% and Co: 2% were set. (l) Rare earth elements, Y, Mg, Ti, and Ca These components have a uniform effect that further improves hot workability, so they are necessary when hot workability is carried out under severe conditions. Rare earth elements: 0.10
%, Y: 0.20%, Mg: 0.10%, Ti: 0.5%,
If the content exceeds 0.10% of rare earth elements and
Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5
% or less, and Ca: 0.10% or less. (m) Cr (%) + 10Mo (%) + 5W (%) Figure 1 shows stress corrosion cracking resistance under severe corrosive environments. Cr (%) + 10Mo (%) + 5W
(%) and the relationship between Ni content. That is, Cr-Ni-Mo system, Cr-
Ni-W steel and Cr-Ni-Mo-W steel are melted, cast, and forged to form a slab with a thickness of 50 mm, which is then heated to 1200°C and hot rolled. In this hot rolling, when the plate thickness reaches 10 mm, the temperature reaches 1000°C, and the processing rate is increased to 30°C from now until the finishing temperature of 900°C.
The steel plate was hot-rolled to a thickness of 7 mm, then cold-worked to a working rate of 22% to improve strength, and the resulting steel plate was rolled perpendicular to the rolling direction to a thickness of 2 mm x width. A test piece of : 10 mm x length: 75 mm was cut out, and a tensile stress equivalent to 0.2% proof stress was applied to the test piece using the three-point support beam jig shown in Figure 2. atm H ₂ S and 10 atm
20% NaCl saturated with _H2S and _CO2 with _CO2
A stress corrosion cracking test was conducted by immersing the specimen in a solution (temperature: 150°C) for 1000 hours, and after the test, the presence or absence of cracking in the test piece was observed. Based on these results, the inventors independently set a conditional formula: Cr (%) + 10Mo (%) + 5W (%) and Ni
It has become clear that there is a relationship between the content and the stress corrosion cracking resistance shown in FIG. In addition, in Figure 1,
The ○ mark indicates no cracking, and the x mark indicates cracking. From the results shown in Figure 1, the values of Cr (%) + 10Mo (%) + 5W (%) are
It is clear that if the Ni content is less than 50% and the Ni content is less than 35%, the desired excellent stress corrosion cracking resistance cannot be obtained. In addition, in the pipe material of this invention, B, Sn, Pb, and Zn are each contained at 0.1% as inevitable impurities.
Even if the content is within the range of % or less, the characteristics of the pipe material of the present invention will not be impaired in any way. B. Hot working conditions The reason why the wall thickness reduction rate at temperatures below 1000℃ during hot working is set to be 10% or more is because this wall thickness reduction rate is 10%.
This is because if it is less than this, the degree of working is too low and it is not possible to sufficiently form fine crystal grains that are essential for imparting the desired high strength and excellent ductility to the pipe material. Furthermore, the reason why the finishing temperature was set at 800°C or higher is that if the finishing temperature is lower than 800°C, carbides, which cause corrosion resistance deterioration, will precipitate. In addition, when hot working, the heating temperature should be
It is desirable to set the temperature to 1050-1250°C, because if the heating temperature is less than 1050°C, the deformation resistance during hot working becomes too high and the working itself becomes difficult, and also undissolved intermetallic compounds and This is because carbides remain and cause deterioration of toughness and corrosion resistance, while heating temperatures exceeding 1250°C result in a significant decrease in hot deformability, making hot working not difficult. C Cold Working Conditions As mentioned above, in the method of the present invention, cold working is performed in a state where the crystal grains have been refined by hot working to improve strength. If it is less than 10%, it is not possible to secure the desired high strength, and on the other hand, if the wall thickness reduction rate is less than 60%.
If cold working exceeds 100%, the deterioration of ductility and toughness becomes significant, so the wall thickness reduction rate during cold working was set at 10% to 60%. By applying the above component composition and processing conditions, oil country tubular goods with high strength with a 0.2% proof stress of 85 Kgf/mm ² or more and excellent stress corrosion cracking resistance as well as ductility and toughness are manufactured. It can be done. Next, the method for manufacturing oil country tubular goods of the present invention will be specifically explained using examples and comparing with comparative examples. Example Molten metal having the composition shown in Table 1 was heated in a normal electric furnace and for the purpose of desulfurization and N addition.
Diameter: 50mm after melting using an Ar-oxygen decarburization furnace (AOD furnace) and, if necessary, an electroslag melting furnace (ESR furnace) for the purpose of dephosphorization.
It is cast into a φ ingot, and then hot forged at a temperature of 1200°C to create a diameter of 150mm.
A billet of φ is formed, and in this case, for the purpose of evaluating hot workability, it is observed whether or not cracks occur in the billet.
Hot extrusion processing is performed under the hot processing conditions shown in the table to form a raw tube with an outer diameter of 60 mmφ and a wall thickness of 4 mm.
Subsequently, the present invention alloy tube materials 1 to 27, comparative alloy tube materials 1 to 9, and conventional alloy tube materials 1 to 4 were prepared by cold working at the wall thickness reduction rates shown in Table 1. manufactured respectively. Comparative alloy tube materials 1 to 9 have a content of any one of the constituent components or one of the manufacturing conditions (indicated with an asterisk in Table 1) of the present invention. The tube material 1 was manufactured under conditions outside the range, and all conventional alloy tube materials have known compositions.
For JIS/SUS316, same 2 for JIS/SUS310S, same 3
The composition is equivalent to Incoloy 800, and the composition corresponding to Incoloy 4 is JIS/SUS329J1. Next, the resulting alloy tube materials 1 to 1 of the present invention
27, comparative alloy pipe materials 1 to 9, and conventional alloy pipe material 1
From ~4, cut out a test piece with a length of 20 mm,
Cut off a section corresponding to 60° along the length of this test piece, pass a bolt through this test piece as shown in the front view in Figure 3, tighten it with a nut, and attach it to the outside surface of the tube. A tensile stress equivalent to 0.2% proof stress is applied to the specimen S in this state, and H ₂ S
A stress corrosion cracking test was conducted by immersion in H ₂ S - 10 atm CO ₂ - 20% NaCl solution (liquid temperature: 150°C) at partial pressures of 0.1 atm, 1 atm, and 20 atm, respectively, for 1000 hours. The presence or absence of stress corrosion cracking was investigated. The results are shown in Table 2 together with the presence or absence of cracking during hot forging, the tensile test results, and the impact test results. In Table 2, the ○ mark indicates that no cracking occurred, while the x mark indicates that cracking occurred. From the results shown in Table 2, comparative alloy tube materials 1 to
No. 9 is inferior in at least one of hot workability, stress corrosion cracking resistance, and strength, whereas alloy tube materials 1 to 27 of the present invention are
Both have excellent hot workability and stress corrosion cracking resistance, and also have high strength and good hot workability, but have relatively low strength and poor stress corrosion cracking resistance. It is clear that this material has even better characteristics than conventional alloy tube materials 1 to 4, which are inferior. As mentioned above, oil country tubular goods manufactured by the method of the present invention have particularly high strength and excellent stress corrosion resistance.

【table】

【table】

【table】

[Table] Because it has corrosion resistance, it exhibits extremely excellent performance not only in oil and natural gas extraction in harsh environments where these characteristics are required, but also when used as geothermal well pipes. be.

[Brief explanation of drawings]

Figure 1 shows the stress corrosion cracking resistance of alloys.
A diagram showing the relationship between content and Cr (%) + 10Mo (%) + 5W (%), Figures 2 and 3 are diagrams showing the mode of stress corrosion cracking tests on plate-shaped and tubular specimens, respectively. .

Claims (1)

[Claims] 1 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, Ni: 35-60%, Cr: 22.5-35%
containing one or two of Mo: less than 4% and W: less than 8%, with the remainder consisting of Fe and unavoidable impurities (weight% or more),
And, Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%, the thickness of the alloy at 1000℃ or less Excellent stress corrosion cracking resistance characterized by hot working at a reduction rate of 10% or more and finishing temperature of 800°C or more, followed by cold working at a wall thickness reduction rate of 10 to 60%. A manufacturing method for high-strength oil country tubular goods. 2 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, Ni: 35-60%, Cr: 22.5-35%
contains one or two of Mo: less than 4% and W: less than 8%, and further contains Cu: 2%.
% or less and Co: 2% or less, with the remainder consisting of Fe and unavoidable impurities (weight %), and Cr (%) + 10Mo (%) + 5W (%)≧50%, 1.5%≦Mo(%)+1/2W(%)<4%, Thickness reduction rate at 1000℃ or less: 10% or more, Finishing temperature: 800 A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which is characterized by hot working under conditions of ℃ or higher, followed by cold working at a wall thickness reduction rate of 10 to 60%. 3 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, Ni: 35-60%, Cr: 22.5-35%
Contains one or two of Mo: less than 4% and W: less than 8%, further rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5 % or less, and Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (weight %), and Cr (%) + 10Mo (%) +5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%, Thickness reduction rate at 1000℃ or less: 10% or more, Finishing temperature: A method for producing high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which is characterized by hot working at a temperature of 800°C or higher, followed by cold working at a wall thickness reduction rate of 10 to 60%. 4 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, Ni: 35-60%, Cr: 22.5-35%
contains one or two of Mo: less than 4% and W: less than 8%, and further contains Cu: 2%.
% or less and Co: 2% or less, rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5% or less, and
Contains one or more of Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (weight%), and Cr (%) + 10Mo (%) + 5W (%) )≧50%, 1.5%≦Mo(%)+1/2W(%)<4%, Thickness reduction rate at 1000℃ or less: 10% or more, Finishing temperature: 800℃ or more A method for producing high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which is characterized by hot working under the following conditions and then cold working at a wall thickness reduction rate of 10 to 60%. 5 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, N: 0.05-0.3%, Ni: 35-60
%, Cr: 22.5 to 35%, Mo: less than 4% and W: less than 8%, and the remainder is Fe and unavoidable impurities (weight%). Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%. Stress corrosion cracking resistance characterized by hot working at a wall thickness reduction rate of 10% or more and a finishing temperature of 800°C or more, followed by cold working at a wall thickness reduction rate of 10 to 60%. A manufacturing method for high-strength oil country tubular goods with excellent properties. 6 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, N: 0.05-0.3%, Ni: 35-60
%, Cr: 22.5 to 35%, contains one or two of Mo: less than 4% and W: less than 8%, and further contains Cu: 2% or less and Co: 2% or less. Contains one or two types, with the remainder consisting of Fe and unavoidable impurities (weight %),
And, Cr (%) + 10Mo (%) + 5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%, the thickness of the alloy at 1000℃ or less Excellent stress corrosion cracking resistance characterized by hot working at a reduction rate of 10% or more and finishing temperature of 800°C or more, followed by cold working at a wall thickness reduction rate of 10 to 60%. A manufacturing method for high-strength oil country tubular goods. 7 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, N: 0.05-0.3%, Ni: 35-60
%, Cr: 22.5 to 35%, Mo: less than 4% and W: less than 8%, further containing rare earth elements: 0.10% or less, Y: 0.20%
Below, Mg: 0.10% or less, Ti: 0.5% or less, and
Contains one or more of Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (weight%), and Cr (%) + 10Mo (%) + 5W (%) ≧50%, 1.5%≦Mo (%) + 1/2W (%) <4%, Thickness reduction rate at 1000℃ or less: 10% or more, Finishing temperature: 800℃ or more A method for producing high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which is characterized by hot working under conditions and then cold working at a wall thickness reduction rate of 10 to 60%. 8 C: 0.05% or less, Si: 1.0% or less, Mn: 2.0%
Below, P: 0.030% or less, S: 0.005% or less, sol.
Al: 0.5% or less, N: 0.05-0.3%, Ni: 35-60
%, Cr: 22.5 to 35%, contains one or two of Mo: less than 4% and W: less than 8%, and further contains Cu: 2% or less and Co: 2% or less. 1 or 2 types, rare earth elements: 0.10% or less, Y: 0.20% or less, Mg: 0.10% or less, Ti: 0.5
% or less, and one or more of Ca: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (wt%), and Cr (%) + 10Mo (%) ) + 5W (%) ≧ 50%, 1.5% ≦ Mo (%) + 1/2W (%) < 4%, Thickness reduction rate at 1000℃ or less: 10% or more, Finishing temperature : A method for producing high-strength oil country tubular goods with excellent stress corrosion cracking resistance, which is characterized by hot working at a temperature of 800°C or higher, followed by cold working at a wall thickness reduction rate of 10 to 60%.