A 110 ksi high strength 13cr oil casing steel and method of manufacture

Abstract

The application discloses a 110ksi high-strength 13Cr oil casing which contains the following chemical elements in mass percentage except Fe and inevitable impurities: C: 0.15-0.22%, 0

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of steel and its manufacturing method, and more particularly to a kind of oil casing steel and its manufacturing method. BACKGROUND

[0002] CO2 corrosion is one of the serious corrosion often encountered in the development of oil and gas fields at home and abroad. In order to solve the problem of CO2 corrosion in oil and gas fields, API SPEC 5CT standard and ISO 13680 standard respectively introduce L80-13Cr and 13-5-2 110ksi super 13Cr martensitic stainless steel.

[0003] Among them, the strength of L80-13Cr oil casing is low, only 80 ksi, which can not meet the requirement of 5000 meters deep well for oil casing strength.

[0004] The alloy content of 13-5-2 110ksi super 13Cr oil casing is very high, especially containing about 5% Ni and 2% Mo, and the product price is more than twice of L80-13Cr, which limits the popularization and application of 13Cr oil casing in deep oil and gas field.

[0005] The Chinese patent document with publication number CN101144141A and publication date March 19, 2008, entitled "A kind of high strength 13Cr oil casing steel and its manufacturing method" develops an economic type of 110 ksi high strength 13Cr oil casing by adding 1% Ni and 0.5% Mo on the basis of L80-13Cr, aiming at reducing the cost of 110 ksi high strength 13Cr oil casing.

[0006] However, the cost of the above-mentioned patent is still high, and the users of oil and gas fields urgently need to use low-cost similar L80-13Cr chemical composition to heat treat 110 ksi high strength 13Cr oil casing. However, API SPEC 5CT standard clearly points out that L80-13Cr will be brittle when tempered at a temperature lower than 620℃, and its impact toughness is lower than 20J. Therefore, according to the existing technical level, the impact toughness of L80-13Cr chemical composition heat treated to 110 ksi high strength 13Cr oil casing is far lower than the standard requirement, which cannot guarantee the safety of 13Cr oil casing in deep oil and gas field. SUMMARY

[0007] One of the purposes of the present application is to provide a kind of 110 ksi high strength 13Cr oil casing steel, which can be designed with low-cost chemical composition to produce 110 ksi high strength 13Cr oil casing with impact toughness higher than 40J, so as to greatly reduce the production cost, meet the requirement of impact toughness, and guarantee the safety of 13Cr oil casing in deep oil and gas field.

[0008] To achieve the above object, the present application provides a 110 ksi high-strength 13Cr oil casing, which contains the following chemical elements in the mass percentage of:

[0009] C: 0.15-0.22%, 0

[0010] In addition, the chemical composition satisfies 1≤100[(Al-0.01)+(V-0.04)+N]≤10 and V≥2N, wherein each chemical element is substituted by the value before the mass percentage of the corresponding element.

[0011] Correspondingly, the present application also provides a 110 ksi high-strength 13Cr oil casing, which contains the following chemical elements in the mass percentage of:

[0012] C: 0.15-0.22%, 0

[0013] In addition, the chemical composition satisfies 1≤100[(Al-0.01)+(V-0.04)+N]≤10 and V≥2N, wherein each chemical element is substituted by the value before the mass percentage of the corresponding element.

[0014] In the 110 ksi high-strength 13Cr oil casing of the present application, the design principles of each chemical element are as follows:

[0015] C: In the 110 ksi high-strength 13Cr oil casing of the present application, C is an austenite forming element, and increasing the content of C can increase the strength of 13Cr, but too much C content will reduce the corrosion resistance and toughness of 13Cr, so the content of C is 0.15-0.22%.

[0016] Si: In the 110 ksi high-strength 13Cr oil casing of the present application, Si is an important deoxidizer in the steelmaking process, but too high Si has adverse effects on the toughness and corrosion resistance of 13Cr, so the present application controls 0

[0017] Mn: In the 110 ksi high-strength 13Cr oil casing described in the present application, Mn can increase the strength of 13Cr, but when the content of Mn is too high, the toughness decreases, so the content thereof is controlled to be 0.25-1.0% in the present application.

[0018] Cr: Cr is an important element for improving corrosion resistance in stainless steel. In order to have sufficient CO2 corrosion resistance, the content of Cr is required to be at least 12% in the present application, but when the content of Cr is too high, the risk of ferrite precipitation increases, which is not good for rolling and corrosion resistance of the product, so the content thereof is controlled to be 12-14% in the present application.

[0019] Al: In the 110 ksi high-strength 13Cr oil casing described in the present application, Al and Si are used for composite deoxidization to ensure deoxidization quality and improve the control level of inclusions, but when the content of Al is too high, the purity of the steel decreases, so the content thereof is controlled to be 0.01-0.04%.

[0020] N: In the 110 ksi high-strength 13Cr oil casing described in the present application, N is an element for stabilizing austenite, which can improve the quality of hot working of the steel pipe and increase the strength of the steel, but when the content of N exceeds 0.02%, the toughness decreases, so the content thereof is controlled to be 0.01-0.02%.

[0021] V: In the 110 ksi high-strength 13Cr oil casing described in the present application, V forms nitride with N, which can reduce the amount of solid solution N and increase the toughness. In addition, the addition of V can increase the strength of the steel. However, when V is added in excess, a large amount of carbonitride is formed after heat treatment, which leads to a decrease in toughness, so the content thereof is controlled to be 0.04-0.10% in the present application.

[0022] In addition, the chemical composition of the 110 ksi high-strength 13Cr oil casing described in the present application also satisfies 1≤100[(Al-0.01)+(V-0.04)+N]≤10 and V≥2N, wherein Al, V and N respectively represent the mass percentage of the corresponding element.

[0023] The above-mentioned synergistic relationship is the core technical feature of the present application. The present application simultaneously adds Al, N and V, and optimizes the ratio of Al, N and V through the above-mentioned formula, which can increase the strength of the steel and delay the precipitation of M 23 C6 type carbide, and ensure the control level of inclusions, so that the 13Cr oil casing with high strength and high toughness is finally obtained.

[0024] Further, in the 110 ksi high-strength 13Cr oil casing described in the present application, the mass percentage of each chemical element satisfies at least one of the following:

[0025] 0 0

[0026] 0 < Cu ≤ 0.25 %.

[0027] In some embodiments of the present application, at least one of Ni and Cu can be further selected to further improve the performance. Among them:

[0028] Ni: Ni can expand the austenite zone, while it can improve the corrosion resistance and toughness of 13Cr. But the present application also aims to reduce the cost of steel, so it is necessary to control the addition amount of Ni not too high, so the upper limit of its content is controlled to 0.5%.

[0029] Cu: Cu is an austenite stabilizing element, but if the content of Cu is too high, the hot workability will decrease significantly, so the present application can control the upper limit of its content to 0.25%.

[0030] Further, among other unavoidable impurities in the 110ksi high-strength 13Cr oil casing described in the present application: P ≤ 0.020%, and / or S ≤ 0.005%.

[0031] The main impurities in the present application are S and P, and if their content is too high, the toughness of the steel will decrease, so generally it is desirable to have as low content as possible under the circumstances allowed by the technical conditions. In some embodiments, P ≤ 0.020%, S ≤ 0.005%.

[0032] Further, in the 110ksi high-strength 13Cr oil casing described in the present application, the microstructure is tempered sorbite.

[0033] Further, the yield strength of the 110ksi high-strength 13Cr oil casing described in the present application is ≥ 758 MPa, and the full-size 0℃ impact toughness is > 40 J.

[0034] Further, the hardness of the 110ksi high-strength 13Cr oil casing described in the present application is ≤ 32 HRC.

[0035] Correspondingly, another object of the present application is to provide a manufacturing method for 110ksi high-strength 13Cr oil casing steel, which cooperates with the unique component design of the present application to produce 110ksi high-strength 13Cr oil casing with impact toughness higher than 40 J, thereby greatly reducing the production cost and meeting the requirements of impact toughness, ensuring the safety of 13Cr oil casing in deep oil and gas fields.

[0036] Based on the above-mentioned purposes of the present application, the present application also provides a manufacturing method for the 110ksi high-strength 13Cr oil casing described above, which comprises the steps of:

[0037] producing a steel pipe;

[0038] Quenching: After the steel pipe is cooled to room temperature, it is heated to 900℃-990℃ and then cooled to 350-400℃ at a cooling rate of 40-120℃ / s; then, it is cooled to room temperature from the intermediate temperature at a cooling rate of 1-10℃ / s.

[0039] Tempering.

[0040] The manufacturing method described in this invention employs a specially designed quenching and tempering process. The quenching is a two-stage cooling process, with a sufficiently rapid cooling rate of 40-120℃ / s in the high-temperature stage above 350-400℃. This process, combined with the unique Al, N, V ​​ratio and their synergistic relationships of this invention, not only improves the strength of the steel but also delays the degradation of M. 23 The precipitation of C6-type carbides ensures a controlled level of inclusions, guaranteeing sufficient toughness in the product. Simultaneously, the cooling rate in the low-temperature range below 350-400℃ is sufficiently slow, as slow as 1-10℃ / s, to prevent quenching cracking.

[0041] Using the above manufacturing method, high-strength 13Cr oil casing with a yield strength of over 758MPa and a full-size 0℃ impact toughness of over 40J can be produced without quenching cracking.

[0042] If the Al, N, V ​​ratio and their elemental synergy are used in accordance with the present invention, the strength after oil quenching and tempering reaches 758 MPa. However, if the cooling rate is too fast in the low temperature range below 350-400℃, which exceeds the scope of the present invention, quenching cracks will occur.

[0043] If the Al, N, V ​​ratio and their elemental synergy are used in this invention, but if air quenching is performed, the cooling rate of air quenching is too slow. Although quenching cracks will not occur, coarse carbides will still easily precipitate, resulting in a significant decrease in toughness. Therefore, after air quenching and tempering, the strength reaches 758 MPa. Although its impact toughness is higher than 20J, it still cannot meet the 40J standard requirements.

[0044] Furthermore, in the manufacturing method described in this invention, oil quenching is used in the quenching step.

[0045] Furthermore, in the manufacturing method described in this invention, the tempering temperature in the tempering step is 590–610°C.

[0046] The 110ksi high-strength 13Cr oil casing and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0047] Compared with the prior art, the 110ksi high-strength 13Cr oil casing of the present invention adopts a low-cost chemical composition design to produce a 110ksi high-strength 13Cr oil casing with an impact toughness higher than 40J, which meets the impact toughness requirements while significantly reducing costs.

[0048] In some embodiments, the 110ksi high-strength 13Cr oil casing of the present invention has a yield strength ≥758MPa and a full-size 0℃ impact toughness >40J.

[0049] In some embodiments, the hardness of the 110ksi high-strength 13Cr oil casing of the present invention is ≤32HRC. Detailed Implementation

[0050] The following will provide a further explanation and description of the 110ksi high-strength 13Cr oil casing and its manufacturing method according to the present invention, with reference to specific embodiments. However, this explanation and description do not constitute an undue limitation on the technical solution of the present invention.

[0051] Examples 1-6 and Comparative Examples 1-5

[0052] The 110ksi high-strength 13Cr oil casing pipes of Examples 1-6 of the present invention are prepared by the following steps:

[0053] (1) A steel pipe with a diameter of Φ114.3×6.88mm was obtained by conventional process. The chemical element composition of the steel pipes in each embodiment and comparative example is shown in Table 1.

[0054] (2) Quenching: After the steel pipe is cooled to room temperature, it is heated to 900℃-990℃ and then cooled to 350-400℃ at a cooling rate of 40-120℃ / s. Then, it is cooled to room temperature at a cooling rate of 1-10℃ / s.

[0055] (3) Tempering: The tempering temperature is 590-610℃.

[0056] The chemical composition design and related processes of the comparative oil casings in Comparative Examples 1-5 all contain parameters that do not meet the design requirements of this invention.

[0057] Table 1 lists the mass percentage of each chemical element in the 110ksi high-strength 13Cr oil casing of Examples 1-6 and the comparative oil casing of Comparative Examples 1-5.

[0058] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0059]

[0060] Note: In the table above, Al, V, and N in 100[(Al-0.01)+(V-0.04)+N] represent the mass percentage of the corresponding elements. The " / " in this column for Comparative Examples 3-5 indicates that the data in this column is not controlled.

[0061] Table 2 lists the specific process parameters for quenching and tempering of the 110ksi high-strength 13Cr oil casings of Examples 1-6 and the comparative oil casings of Comparative Examples 1-5.

[0062] Table 2.

[0063]

[0064]

[0065] To verify the effectiveness of this implementation, samples of the 110ksi high-strength 13Cr oil casing from Examples 1-6 and the control oil casing from Comparative Examples 1-5 were taken and observed, and their mechanical properties were tested. The observation results and mechanical property test results are listed in Table 3. The specific testing methods and means are as follows:

[0066] (1) Tensile test: According to API SPEC 5CT standard and ASTM A370 standard, tensile specimens were cut longitudinally along the pipe axis and subjected to tensile tests at room temperature to measure the tensile strength (R). m Yield strength (R) t0.6 ).

[0067] (2) Hardness test: According to API SPEC 5CT standard, a hardness test ring is cut from one end of the pipe for Rockwell hardness test. The Rockwell hardness test is performed according to ASTM E18 standard and uses the Rockwell scale C (HRC).

[0068] (3) Impact test: According to API SPEC 5CT standard, an impact specimen was cut from one end of the pipe for impact testing. The impact test was carried out according to ASTM E23 standard, and the impact toughness was measured.

[0069] Table 3 lists the mechanical property test results of the 110ksi high-strength 13Cr oil casing of Examples 1-6 and the comparative oil casing of Comparative Examples 1-5.

[0070] Table 3.

[0071]

[0072]

[0073] Note: The actual impact specimens are 5×10×55mm half-size impact specimens. The impact toughness values ​​in Table 3 have been converted to full size according to API standards. L-10-0℃ refers to a 0℃ longitudinal 10×10×55mm full-size impact specimen.

[0074] As can be seen from Table 3, the 110ksi high-strength 13Cr oil casings in Examples 1-6 all achieved a yield strength >758MPa on the basis of low-cost design, and their full-size 0℃ impact toughness >80J, hardness ≤32HRC, and no cracking occurred.

[0075] In contrast, although Comparative Example 1 adopted the Al, N, V ​​ratio and their synergistic relationship of the present invention, it experienced quenching cracking because of its faster cooling rate in the low temperature range below 350-400℃. Although its yield strength reached more than 758MPa after tempering, it experienced quenching cracking.

[0076] Although Comparative Example 2 adopted the Al, N, V ​​ratio and synergistic relationship of the present invention, the air quenching cooling rate was too slow. Although quenching cracks would not occur, coarse carbides would still easily precipitate, resulting in a significant decrease in toughness. Therefore, although the strength reached more than 758 MPa after air quenching and tempering, the impact toughness was still lower than the requirement of 40 J.

[0077] Comparative Example 3 did not meet the Al, N, V ​​ratio of the present invention, resulting in insufficient strength. It could not stably reach a strength of 758 MPa at the same tempering temperature, and due to the slow air quenching cooling rate, its full-size 0°C impact toughness was less than 20 J.

[0078] Comparative Example 4 does not meet the Al, N, V ​​ratio of the present invention, and the cooling rate is fast in the low temperature range below 350-400℃. Therefore, although the strength reached 758MPa, quenching cracks occurred.

[0079] Comparative Example 5 does not meet the Al, N, V ​​ratio of the present invention. Although its strength reaches more than 758 MPa, its full-size 0°C impact toughness is less than 40 J.

[0080] In addition, observation of the microstructure of Examples 1-6 shows that the microstructure of the 110ksi high-strength 13Cr oil casing in Examples 1-6 is tempered sorbite.

[0081] In summary, it can be seen that the 110ksi high-strength 13Cr oil casing of the present invention, through reasonable chemical composition design and optimized process, can produce 110ksi high-strength 13Cr oil casing with an impact toughness higher than 40J while reducing costs. This significantly reduces production costs, meets the requirements for impact toughness, and ensures the safety of 13Cr oil casing in deep oil and gas fields.

[0082] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0083] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A 110 ksi high strength 13Cr oil casing characterized in that, each of the chemical elements in mass percent: C: 0.15-0.22%, 0 Mn: 0.25-1.0%, Cr: 12-14%, Al: 0.01-0.04%, N: 0.01-0.02%, V: 0.04-0.10%; the balance being Fe and other unavoidable impurities; the chemical composition also satisfies 1≤100[(Al-0.01)+(V-0.04)+N]≤10 and V≥2N, wherein each of the chemical elements is substituted with the value before the mass percent of the corresponding element; 2. The 110 ksi high strength 13Cr oil casing of claim 1 wherein, the microstructure of the 110 ksi high-strength 13Cr oil casing is tempered sorbite, the yield strength thereof is ≥758 MPa, and the full-size 0°C impact toughness thereof is >40 J, and the hardness thereof is ≤32 HRC. each of the chemical elements in mass percent satisfies at least one of the following: 0 3. The 110 ksi high strength 13Cr oil casing of claim 1 wherein, 0 4. The method of manufacturing a 110 ksi high strength 13Cr oil casing of any one of claims 1-3, wherein, In other unavoidable impurities: P≤0.020%, and / or S≤0.005%. It comprises the steps of: producing a steel pipe; quenching: after heating the steel pipe cooled to room temperature to 900-990°C, cooling from 900-990°C to 350-400°C at a cooling rate of 40-120°C / s; then, cooling from the intermediate temperature to room temperature at a cooling rate of 1-10°C / s; 5. The production method according to claim 4, wherein tempering.

6. The production method according to claim 4, wherein In the quenching step, oil quenching is used for cooling. In the tempering step, the tempering temperature is 590-610°C.

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