Seamless steel tube for elastic casing centralizer and manufacturing method thereof

Abstract

The invention relates to a seamless steel pipe for an elastic casing centralizer and a manufacturing method of the seamless steel pipe. The seamless steel pipe comprises the following chemical components: 0.60%-0.75% of C, 1.10%-1.40% of Si, 1.30%-1.80% of Mn, 0.20%-0.50% of Cr, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.08%-0.20% of Ti, 0.02%-0.05% of Re and the balance of Fe and impurities. The production process mainly controls the processes of heating, perforating, rolling and cooling after rolling. Through the design of chemical components and the control of rolling and cooling process parameters in the production process, the produced seamless steel pipe has high strength and hardness, certain toughness and good wear resistance, is particularly suitable for manufacturing the centralizer, and is beneficial to prolonging the service life of the centralizer.

Description

Technical Field

[0001] The invention relates to the technical field of high-strength and high-wear-resistant steel pipe production, and in particular to a seamless steel pipe for a casing elastic centralizer and a manufacturing method thereof. Background Art

[0002] The centralizer is an oil extraction tool used in oilfield pumping wells. Its main function is to support and stabilize the pumping rod in the oil well to ensure the normal operation of the oil well. The main functions of the pumping rod centralizer are as follows:

[0003] (1) Improve stability: The sucker rod centralizer helps to improve the stability of the sucker rod and prevent it from swinging or twisting during the operation of the oil well, thereby reducing the risk of oil well accidents.

[0004] (2) Extending service life: Reducing the vibration and friction of the sucker rod by using the sucker rod centralizer helps to extend the service life of the sucker rod and reduce equipment failures caused by wear.

[0005] (3) Improve production efficiency: The sucker rod straightener is used to keep the sucker rod in good condition during use, ensuring the normal production operation of the oil well, thereby improving production efficiency and the oil recovery rate of the oil well.

[0006] The sucker rod centralizer (abbreviated as centralizer) needs to withstand large friction and impact forces during service, so the material used to manufacture the centralizer (usually seamless steel pipe) is required to have high wear resistance and impact resistance.

[0007] The Chinese patent application with application publication number CN104294156A discloses "an economical and excellent processing performance high carbon wear-resistant steel pipe and production method". The steel pipe composition is: C 0.60%-0.72%, Si 0.10%-0.30%, Mn0.50%-1.20%, Ca 0.0030-0.0070%, Cr 0.60-0.86%, Als 0.015%-0.050%, P≤0.015%, S≤0.008%. It adopts the welded pipe process, that is, the steel is rolled into a steel strip and then made into a welded pipe. The hot-rolled steel strip is obtained by controlled rolling and controlled cooling and annealing after rolling to change the structure, which is completely different from the production process of seamless steel pipes.

[0008] The Chinese invention patent with the authorization announcement number CN107630165B discloses "A NM600 high-strength wear-resistant pipe and its manufacturing process". The wear-resistant pipe composition is C 0.69% to 0.75%, Si 0.20% to 0.40%, Mn 1.00% to 1.15%, Cr 0.12% to 0.20%, V 0.030% to 0.050%, P≤0.025%, S≤0.020%, Al≤0.010%; it is designed with high carbon and high manganese to obtain tempered martensite structure, which is easy to form cracks during quenching. To avoid cracking, the thickness of the hardened layer needs to be thinned. Although the pure martensite structure has high hardness, it has poor toughness and poor crack resistance. Under the condition of impact load, the wear resistance of the steel pipe is poor.

[0009] The Chinese patent application with application publication number CN111020370A discloses "a single-layer wear-resistant seamless steel pipe for concrete pump trucks and its manufacturing method". The chemical composition of the wear-resistant seamless steel pipe is as follows by weight: C 0.50%-0.69%, Si 0.15%-0.35%, Mn 0.60%-1.00%, Cr 0.25-0.50%, Ti 0.010-0.030%, P≤0.025%, S≤0.020%, and the balance is Fe. The inner surface hardened structure of the seamless steel pipe is a mixed structure of martensite and troostite, and the thickness of the hardened structure is greater than 2mm. However, the toughness of the steel pipe matrix is ​​poor, which limits the thickness of the hardened structure. The martensite content in the mixed structure is relatively high, resulting in poor wear resistance. Summary of the invention

[0010] The present invention provides a seamless steel pipe for a casing elastic centralizer and a manufacturing method thereof. Through chemical composition design and control of rolling and cooling process parameters in the production process, the produced seamless steel pipe has high strength, hardness and certain toughness, good wear resistance, is particularly suitable for manufacturing centralizers, and is beneficial to increasing the service life of the centralizer.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A seamless steel pipe for a casing elastic centralizer, the chemical composition of the seamless steel pipe is as follows by weight: C 0.60%-0.75%, Si 1.10%-1.40%, Mn 1.30%-1.80%, Cr 0.20%-0.50%, P≤0.025%, S≤0.020%, Ti 0.08%-0.20%, Re 0.02%-0.05%, and the balance is Fe and unavoidable impurities.

[0013] Furthermore, the structure of the finished seamless steel pipe is fine pearlite + a small amount of ferrite, the volume fraction of the fine pearlite is ≥95%, and the interlamellar spacing of the fine pearlite is 80-150nm.

[0014] Furthermore, the yield strength of the finished seamless steel pipe is greater than 758 MPa, the tensile strength is greater than 965 MPa, the elongation is greater than 10%, the longitudinal impact energy at 20°C is greater than 14 J, and the hardness value is greater than 300 HB.

[0015] A method for manufacturing a seamless steel pipe for a casing elastic centralizer, wherein the seamless steel pipe is manufactured using a seamless steel pipe production line, and the following process is controlled:

[0016] 1) Heating: The temperature of the heating section is controlled at 1220-1240°C, and the temperature of the soaking section is controlled at above 1230°C;

[0017] 2) Perforation: The perforator roll speed is controlled at 600-650rpm, and the feed angle is controlled at 8.5°-9.0°;

[0018] 3) Rolling: Ensure that the final rolling temperature of seamless steel pipes with wall thickness <8mm is ≥730℃, and the final rolling temperature of seamless steel pipes with wall thickness ≥8mm is 820℃~960℃;

[0019] 4) Cooling after rolling:

[0020] For seamless steel pipes with a wall thickness of less than 8mm, they are heated in a medium frequency induction furnace at a heating speed of 1 to 1.5m / s to 820℃ to 960℃, and then sent to a cooling bed for air cooling to room temperature;

[0021] For seamless steel pipes with a wall thickness of 8mm≤<16mm, they are directly sent to the cooling bed for air cooling to room temperature;

[0022] For seamless steel pipes with a wall thickness of 16mm≤≤25mm, an accelerated cooling method is adopted. A cooling device is installed after the sizing unit to reduce the temperature of the seamless steel pipe to 450-650℃ at a cooling rate of 2-5℃ / s, and then the pipe is sent to the cooling bed for air cooling to room temperature.

[0023] Furthermore, the cooling medium for accelerating the cooling of the steel pipe is water mist, or a mixture of compressed air and water mist.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Through the design of chemical composition and the control of rolling and cooling process parameters in the production process, the seamless steel pipe produced has high strength, hardness and certain toughness, good wear resistance, and is particularly suitable for the manufacture of centralizers, and is beneficial to increasing the service life of the centralizers. DETAILED DESCRIPTION

[0026] The seamless steel pipe for elastic casing straightener of the present invention has the following chemical compositions by weight percentage: C 0.60% to 0.75%, Si 1.10% to 1.40%, Mn 1.30% to 1.80%, Cr 0.20% to 0.50%, P≤0.025%, S≤0.020%, Ti 0.08% to 0.20%, Re 0.02% to 0.05%, and the remainder is Fe and unavoidable impurities. The structure of the seamless steel pipe is fine pearlite + a small amount of ferrite, the volume fraction of the fine pearlite is ≥95%, and the interlamellar spacing of the fine pearlite is 80 to 150nm. The yield strength of the seamless steel pipe is greater than 758MPa, the tensile strength is greater than 965MPa, the elongation is greater than 10%, the longitudinal impact energy at 20°C is greater than 14J; and the hardness value is greater than 300HB.

[0027] The reasons for the composition design of the seamless steel pipe for the casing elastic centralizer described in the present invention are as follows:

[0028] C: is the most economical and effective element for improving the hardness of steel. A certain amount of C can ensure the strength and hardenability of steel. In order to ensure the hardness of pearlite in the seamless steel pipe, the present invention controls the C content to 0.60% to 0.75%.

[0029] Si: It is an element that plays a beneficial role in improving the oxidation resistance and thermal strength of steel, and can inhibit the decomposition of carbides. If the Si content is too low, the effect is not obvious, and if the Si content is too high, it will have an adverse effect on the recrystallization grain growth and hot working plasticity of steel. In order to take into account both strength and toughness, the present invention controls the Si content to 1.10% to 1.40%.

[0030] Mn: It is the main hardenability element and can refine the interlamellar spacing of pearlite. In the present invention, the Mn content is controlled within 1.30% to 1.80%.

[0031] Cr: can improve hardenability and form certain carbides to enhance the hardness and wear resistance of steel. The present invention controls the Cr content to 0.20% to 0.50%.

[0032] Ti: can form MC type carbides, prevent grain growth, and provide a good original structure for forming fine pearlite grains. Dispersed MC type carbides can also improve the wear resistance of steel. The present invention controls the Ti content to 0.08% to 0.20%.

[0033] Re: can change the morphology of inclusions, purify molten steel, reduce inclusions in steel, improve the quality of ingots, and refine grains. The present invention controls the Re content to 0.02% to 0.05%.

[0034] P and S are harmful elements in steel. Too high a content of P and S will affect the toughness of the steel. In the present invention, the upper limit of the P content is controlled at 0.025%, and the upper limit of the S content is controlled at 0.020%.

[0035] The seamless steel pipe for the casing elastic centralizer of the present invention is manufactured by a conventional seamless steel pipe production line, which mainly includes the following processes:

[0036] 1. Billet heating: The seamless steel pipe described in the present invention is high carbon steel. The heating temperature of the ring furnace is 30℃~40℃ lower than that of ordinary 20# steel. However, the temperature drops rapidly after leaving the furnace, and the deformation resistance is large. Therefore, the furnace temperature of the heating section is controlled at 1220℃~1240℃, and the temperature of the soaking section (furnace exit temperature) is controlled at above 1230℃, which is beneficial to uniform heating of the billet and control of grain growth.

[0037] 2. Punching: Increase the speed of the punching machine roller to 600-650rpm, control the feed angle at 8.5°-9.0°, increase the punching speed, and control the cooling water volume of the guide roller to reduce the temperature drop of the capillary tube.

[0038] 3. Continuous rolling and fixed diameter reduction: Since the temperature of the rough tube drops quickly, it is required to turn down the high-pressure water descaling water and the frame cooling water. It is only necessary to ensure the cooling effect of the rolls and avoid pouring cooling water onto the rough tube.

[0039] 4. Rolling: Ensure that the final rolling temperature of seamless steel pipes with wall thickness <8mm is ≥730℃, and the final rolling temperature of seamless steel pipes with wall thickness ≥8mm is 820℃~960℃;

[0040] 5. Cooling after rolling: Different cooling process paths are formulated according to the different wall thickness of seamless steel pipes; the details are as follows:

[0041] The seamless steel pipe of the present invention is designed with a high carbon content, and the temperature drop of the seamless steel pipe is relatively fast. For seamless steel pipes with a wall thickness of less than 8 mm, the final rolling temperature is generally less than 820°C, and a medium frequency induction furnace is required for heating. The heating speed is 1 to 1.5 m / s, and the seamless steel pipe is heated to 820°C to 960°C, and then sent to a cooling bed for air cooling to room temperature.

[0042] For seamless steel pipes with a wall thickness of 8 to 16 mm (excluding 16 mm), they can be directly sent to the cooling bed for air cooling to room temperature.

[0043] For seamless steel pipes with a wall thickness of 16 to 25 mm, a cooling device is installed after the sizing unit, and the temperature of the seamless steel pipe is reduced to 450 to 650 ° C by accelerated cooling, and then sent to the cooling bed for air cooling to room temperature. The cooling rate during accelerated cooling is controlled at 2 to 5 ° C / s, and the cooling medium is water mist or a mixture of compressed air and water mist. After the outer surface temperature of the steel pipe is reduced to 450 to 650 ° C by accelerated cooling, the inner wall of the steel pipe is continuously heated and warmed up, and the temperature is finally controlled at 820 to 960 ° C.

[0044] The steel tube structure obtained by the above method is uniform and fine pearlite + a small amount of ferrite, and the interlamellar spacing of the fine pearlite is 80-150nm. The uniform and fine pearlite structure can improve the strength and toughness of the steel, and improve the hardness and wear resistance of the steel.

[0045] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

[0046] [Example]

[0047] In this embodiment, the manufacturing method of the seamless steel pipe for the casing elastic centralizer is as follows:

[0048] The molten steel is smelted in a converter, refined outside the furnace, vacuum treated and continuously cast to obtain billets. The billets are heated in a ring furnace at a temperature of 1220°C to 1240°C, and the furnace temperature is controlled at 1230°C. After heating, the billets are rolled into shape by a piercing mill, a tube rolling mill and a sizing mill to ensure that the final rolling temperature of the steel pipe is between 820°C and 960°C.

[0049] Post-rolling cooling Different cooling process paths are formulated according to the different wall thickness of seamless steel pipes:

[0050] 1. For seamless steel pipes with a wall thickness of less than 8 mm, if the final rolling temperature is less than 820°C, it is necessary to heat and keep warm in a medium frequency induction furnace. In this embodiment, the heating speed of the seamless steel pipe in the medium frequency induction furnace is 1-1.5 m / s. After the seamless steel pipe is heated to 820°C-960°C, it is sent to the cooling bed for air cooling to room temperature.

[0051] 2. For seamless steel pipes with a wall thickness of 8 to 16 mm (excluding 16 mm), they can be directly sent to the cooling bed for air cooling to room temperature.

[0052] 3. For steel pipes with a wall thickness of 16 to 25 mm, a cooling device is installed after the sizing unit. Accelerated cooling is used to reduce the surface temperature of the seamless steel pipe to between 450 and 650 °C. The cooling rate is controlled at 2 to 5 °C / s, and then the pipe is sent to the cooling bed for air cooling to room temperature.

[0053] In this embodiment, the cooling medium used for accelerated cooling of the seamless steel pipe is water mist.

[0054] The chemical composition of the steel in each embodiment is shown in Table 1, and the specifications, rolling and cooling process parameters, and mechanical properties of the finished product of the seamless steel pipe produced in each embodiment are shown in Table 2.

[0055] Table 1 Chemical composition of steel (wt%)

[0056] Example C Si Mn Cr Ti Re P S 1 0.62 1.21 1.54 0.33 0.12 0.03 0.012 0.010 2 0.69 1.34 1.42 0.41 0.12 0.03 0.012 0.010 3 0.73 1.14 1.58 0.26 0.08 0.02 0.014 0.011 4 0.68 1.32 1.67 0.22 0.16 0.02 0.010 0.013 5 0.74 1.22 1.31 0.23 0.18 0.03 0.010 0.009 6 0.71 1.16 1.39 0.33 0.08 0.04 0.016 0.012 7 0.75 1.38 1.71 0.44 0.11 0.04 0.010 0.010

[0057] Table 2 Seamless steel pipe specifications, rolling and cooling process parameters, and finished product mechanical properties

[0058]

[0059] The structure of the seamless steel pipe obtained in Example 1-7 is fine pearlite + a small amount of ferrite, the volume fraction of the fine pearlite is ≥95%, and the interlamellar spacing of the fine pearlite is 80-150nm.

[0060] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A seamless steel pipe for a casing elastic centralizer, characterized in that: The chemical composition of the seamless steel pipe is calculated by weight percentage: C 0.60%~0.75%, Si 1.10%~1.40%, Mn 1.30%~1.80%, Cr 0.20%~0.50%, P≤0.025%, S≤0.020%, Ti 0.08%~0.20%, Re 0.02%~0.05%, and the balance is Fe and unavoidable impurities.

2. A seamless steel pipe for casing elastic centralizer according to claim 1, characterized in that: The structure of the finished seamless steel pipe is fine pearlite + a small amount of ferrite, the volume fraction of fine pearlite is ≥95%, and the interlamellar spacing of fine pearlite is 80-150nm.

3. The seamless steel pipe for casing elastic centralizer according to claim 1, characterized in that: The yield strength of the finished seamless steel pipe is >758MPa, the tensile strength is >965MPa, the elongation is >10%, the longitudinal impact energy at 20℃ is >14J, and the hardness value is >300HB.

4. The method for manufacturing a seamless steel pipe for a casing elastic centralizer according to any one of claims 1 to 3, characterized in that: The seamless steel pipe is manufactured by a seamless steel pipe production line, and the following process is controlled: 1) Heating: The temperature of the heating section is controlled at 1220-1240°C, and the temperature of the soaking section is controlled at above 1230°C; 2) Perforation: The perforator roll speed is controlled at 600-650rpm, and the feed angle is controlled at 8.5°-9.0°; 3) Rolling: Ensure that the final rolling temperature of seamless steel pipes with wall thickness <8mm is ≥730℃, and the final rolling temperature of seamless steel pipes with wall thickness ≥8mm is 820℃~960℃; 4) Cooling after rolling: For seamless steel pipes with a wall thickness of less than 8mm, they are heated in a medium frequency induction furnace at a heating speed of 1 to 1.5m / s to 820℃ to 960℃, and then sent to a cooling bed for air cooling to room temperature; For seamless steel pipes with a wall thickness of 8mm≤<16mm, they are directly sent to the cooling bed for air cooling to room temperature; For seamless steel pipes with a wall thickness of 16mm≤≤25mm, an accelerated cooling method is adopted. A cooling device is installed after the sizing unit to reduce the temperature of the seamless steel pipe to 450-650℃ at a cooling rate of 2-5℃ / s, and then the pipe is sent to the cooling bed for air cooling to room temperature.

5. The method for manufacturing a seamless steel pipe for a casing elastic centralizer according to claim 4, characterized in that: The cooling medium for accelerating cooling of the steel pipe is water mist, or a mixture of compressed air and water mist.

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