JPS6363608B2 - - 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, mining of oil and natural gas in a harsh corrosive environment containing corrosive components such as humid hydrogen sulfide, carbon dioxide, 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 (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, and the Ni content is reduced to 30%. ~60
%, and when the Cr content is 15 to 30%, _H2S - _CO2 , which is extremely corrosive, even if it is a cold-worked material.
- A surface film that exhibits excellent resistance to stress corrosion cracking in a Cl ^- oil well environment, especially in a harsh environment of 200°C or higher, can be obtained. (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) Cu: 2% or less and Co: 2 as alloy components
% or less, the corrosion resistance is further improved. (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,
Empirical formula: 260logC (%) +
The lower limit temperature (℃) calculated at 1300 and the same empirical formula: 16Mo (%) + 10W (%) + 10Cr (%) + 777
The carbide is completely dissolved by heat treatment at a temperature between the upper limit temperature (℃) calculated for 2 hours or less, and the total thickness is reduced by 10 to 60% after solid solution. It is necessary to perform temporary processing. 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 S: 0.0007% for the purpose of further improving hot workability.
Below, sol.al: 0.5% or less, Ni: 30-60%, Cr:
Contains 15-30%, Mo: 12% or less and W: 24
% or less, and if necessary, N: 0.05 to 0.3%, Cu: 2% or less,
Co: 2% or less, rare earth elements: 0.10% or less, Y:
1.20% or less, Mg: 0.10% or less, Ti: 0.5% or less,
and Ca: 0.10% or less, and the remainder is Fe and unavoidable impurities.
) and satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%. , the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. In particular, the present invention is characterized by a method for manufacturing high-strength oil country tubular goods having excellent stress corrosion cracking resistance. Next, in the method for manufacturing oil country tubular goods of this invention,
The reason why the component composition, solution treatment conditions, and wall thickness reduction rate during cold working are limited as described above will be explained below. A Component (a) C The lower the C content, the more the precipitation of carbides will be suppressed, so solution treatment can be carried out at a lower temperature, which is more effective in increasing the strength after cold working. It acts on 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 maintain stress corrosion cracking susceptibility to a certain 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 Although the Ni component has the effect of improving the stress corrosion cracking resistance of tube sheets, if its content is less than 30%, the desired excellent stress corrosion cracking resistance cannot be secured; Even if the content exceeds 60%, no further improvement effect on stress corrosion cracking resistance appears, so the content was determined to be 30 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 15%. 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 15%. On the other hand, if the S content exceeds 30%, deterioration of hot workability cannot be avoided no matter how much the S content is reduced, so the upper limit was set at 30%. (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: 12% and W: 24% are contained, the environmental temperature is 200℃ or higher H ₂ S—CO ₂
- In the corrosive environment of Cl ^- , no further improvement effect appeared, and in consideration of economic efficiency, the respective contents were determined to be Mo: 12% or less and W: 24% or less. Also, regarding the content of Mo and W,
The conditional expression: Mo (%) + 1/2W (%) is specified because the atomic weight of W is about twice that of Mo, and the effect is about 1/2, which is equal. If it is less than 8%, the desired stress corrosion cracking resistance cannot be obtained, especially under the above-mentioned adverse environment of 200°C or higher.On the other hand, even if this value is increased beyond 12%, as mentioned above, it is substantially unnecessary. Since the amount of Mo and W contained is uneconomical, the value of Mo (%) + 1/2 W (%) was set at 8 to 12%. (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 to further improve hot workability, so they can be used as needed when hot working 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 series and Cr-Ni-Mo-W series steels are melted, cast, forged and hot-rolled into a plate with a thickness of 7 mm, and then this plate is heated at a temperature of 1000°C. After being held for 30 minutes and subjected to water-cooling solution treatment, cold working was applied at a processing rate of 22% to improve strength. Width: 10mm×
A test piece with a length of 75 mm was cut out, and this test piece was heated at 10 atm using the three-point support beam jig shown in Figure 2, with a tensile stress equivalent to 0.2% proof stress being applied to the test piece S. _H2S
and in a 20% NaCl solution (temperature: 300 °C) saturated with _H2S and _CO2 with 10 atm of _CO2 .
A stress corrosion cracking test of 1000 hours immersion was carried out.
After the test, the presence or absence of cracks in the test piece was observed. Based on these results, the inventors independently set a conditional expression: Cr (%) + 10Mo
It has become clear that there is a relationship between (%) + 5W (%) and Ni content with respect to stress corrosion cracking resistance, as shown in Figure 1. In addition, in Figure 1, ○ marks indicate no cracking;
The x marks indicate the occurrence of cracks.
From the results shown in Figure 1, Cr (%) + 10Mo
(%) + 5W (%) value is less than 110%, and Ni
It is clear that if the content is less than 30%, the desired excellent stress corrosion cracking resistance cannot be obtained. In addition, in the alloy of this invention, B, Sn, Pb, and Zn are each contained at 0.1 as unavoidable impurities.
Even if the content is within the range of % or less, the properties of the alloy of the present invention will not be impaired in any way. B. Solution Treatment Conditions and Cold Working Conditions The high strength of the oil country tubular goods of this invention is ensured not only by the inclusion of alloy components but also by performing cold working after completely solutionizing carbides. It is something. In this case, complete solid solution of carbide is
Lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W (%) + 10Cr (%) +
It is measured by holding the temperature between the upper limit temperature (℃) calculated by 777 for 2 hours or less, but the formula for calculating the lower limit temperature above is: 260logC (%)
And upper limit temperature calculation formula: 16Mo (%) + 10W
(%) + 10Cr (%) + 777 was determined empirically based on numerous test results. Below the above lower limit temperature, carbides cannot be completely dissolved, and undissolved carbides remain. remains and stress corrosion cracking susceptibility increases.On the other hand, if the solution treatment temperature is increased beyond the above upper limit temperature or the holding time is extended beyond 2 hours, the crystal grains become coarse. The solution treatment temperature and holding time were determined as described above because the desired high strength could not be obtained by subsequent cold working. In addition, in this invention, as described above, cold working is performed after the solution treatment to improve the strength.
If this cold working is performed with a wall thickness reduction rate of less than 10%, the desired strength cannot be secured, whereas if cold working is performed with a wall thickness reduction rate of more than 60%, ductility and toughness will deteriorate. Because of this, the wall thickness reduction rate for cold working was set at 10 to 60%. By applying the above component composition and manufacturing conditions, we manufacture oil country tubular goods that have high strength with a 0.2% proof stress of 85 Kgf/mm ² or more, as well as excellent ductility and toughness, as well as excellent stress corrosion cracking resistance. It is possible to do so. 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: 500 mm 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, and then the billet is hot extruded to form a billet with a diameter of 60 mmφ x wall thickness: A 4 mm raw tube is formed, and then subjected to solution treatment and cold working under the solution treatment conditions (cooling after treatment is water cooling in both cases) and wall thickness reduction rate shown in Table 1. Inventive alloy tube materials 1 to 29, comparative alloy tube materials 1 to 8, and conventional alloy tube materials 1 to 4 were manufactured, respectively. Comparative alloy tube materials 1 to 8 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
29, comparative alloy pipe materials 1 to 8, 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: 300°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. This result is compared to the presence or absence of cracking during hot forging, the tensile test results, and

【table】

【table】

【table】

[Table] The results are shown in Table 2 along with 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. 8 is inferior in at least one of hot workability, stress corrosion cracking resistance, and strength, whereas alloy tube materials 1 to 29 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 cracking resistance, so they can be used in petroleum and natural products in harsh environments where these properties are required. It exhibits extremely excellent performance not only in gas extraction, but also when used as geothermal well pipes.

[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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 30%, one or two of Mo: 12% or less and W: 24% or less, and the rest is Fe. It has a composition (weight% or more) consisting of unavoidable impurities, and Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, For alloys that satisfy the conditions, the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 30%, one or two of Mo: 12% or less and W: 24% or less, and further Cu: 2 %
One or two of the following and Co: 2% or less
It has a composition (more than % by weight) containing seeds and the rest is Fe and unavoidable impurities, and Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/ 2W (%) ≦ 12%, the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 30%, one or two of Mo: 12% or less and W: 24% or less, and further rare earth elements: A composition containing one or more of the following: 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 inevitable impurities. (more than weight%) and satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12% , the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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.
Contains Al: 0.5% or less, Ni: 30 to 60%, Cr: 15 to 30%, one or two of Mo: 12% or less and W: 24% or less, and further Cu: 2 %
One or two of the following and Co: 2% or less
Species, 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 (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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: 30-60
%, Cr: 15 to 30%, Mo: 12% or less, W: 24% or less, and the remainder is Fe and unavoidable impurities (weight%). Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, 260logC (%) Lower limit temperature (℃) calculated by +1300 and 16Mo (%) +10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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: 30-60
%, Cr: 15 to 30%, Mo: 12% or less and W: 24% or less, and 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, calculate the alloy that satisfies the following conditions: Cr (%) + 10Mo (%) + 5W (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, using 260logC (%) + 1300 lower limit temperature (℃) and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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: 30-60
%, Cr: 15 to 30%, Mo: 12% or less and W: 24% or less, 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 (%) ≧110%, 8%≦Mo (%) + 1/2W (%)≦12%, the lower limit temperature (℃) calculated by 260logC (%) + 1300 and 16Mo (%) + 10W
(%) + 10Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (℃) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance. 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: 30-60
%, Cr: 15 to 30%, Mo: 12% or less and W: 24% or less, and 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 (%) ≧ 110%, 8% ≦ Mo (%) + 1/2W (%) ≦ 12%, the lower limit temperature (℃) calculated by 260logC (%) + 1300, 16Mo (%) + 10W
(%) + 10 Cr (%) + 777 After solution treatment at a temperature between the upper limit temperature (°C) calculated by holding for 2 hours or less, cold working at a wall thickness reduction rate of 10 to 60%. A method for manufacturing high-strength oil country tubular goods with excellent stress corrosion cracking resistance.