Centrifugal casting method of steel for high-strength corrosion-resistant composite sucker rod

Abstract

The invention belongs to the technical field of steel for sucker rods, and particularly relates to a centrifugal casting method for high-strength corrosion-resistant composite steel for a sucker rod. A sucker rod needs to bear a large tensile load in a working environment and is easily corroded by salt and alkali, so that the sucker rod is mostly prepared from a composite steel material in the prior art to meet working condition requirements. The invention provides a centrifugal casting process of steel for a high-strength corrosion-resistant composite sucker rod, which is characterized in that a stainless steel pipe is used as an outer layer, and molten steel of inner-layer low-alloy structural steel is injected into a preheated centrifugally rotating stainless steel pipe for centrifugal casting. Through verification, the composite steel for the sucker rod prepared by the process has good mechanical properties, corrosion resistance and fatigue resistance, and is expected to obtain longer service life when being used as the steel for the sucker rod.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel for sucker rods, and particularly relates to a preparation method of high-strength and corrosion-resistant composite steel for sucker rods based on centrifugal casting. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or any form of implication that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] As a key component in oil extraction, sucker rods are subjected to complex mechanical loads for a long time. During the reciprocating motion up and down, sucker rods are subjected to periodic tensile-compressive loads, which easily cause fatigue failure of the material. Deep-well sucker rods bear their own weight + the weight of the liquid column, resulting in a large tensile load on the sucker rods. The oil well environment is usually harsh, and the service environment of sucker rods is complex, so that sucker rods are subjected to a strict corrosion environment for a long time. High-H2S oil wells cause hydrogen embrittlement and sulfide stress corrosion cracking. H2S reacts with steel to form FeS, and hydrogen atoms penetrate into the grain boundaries, resulting in embrittlement. In wells with a CO2 partial pressure > 0.05 MPa, a loose FeCO3 film is formed on the steel surface, and the local pitting corrosion rate can reach 5 - 8 mm / a. Some oil wells also contain a high concentration of brine, making sucker rods vulnerable to corrosion by brine and microorganisms. Brine accelerates electrochemical corrosion, and the metabolites of sulfate-reducing bacteria cause a local decrease in pH value, inducing ulcer-like corrosion pits. Therefore, sucker rods need to have high mechanical properties and corrosion resistance. Traditional single-metal sucker rods (such as carbon steel, alloy steel) are prone to failure due to corrosion fatigue or surface damage. Although stainless steel has good corrosion resistance, its price is expensive, and its mechanical properties cannot meet the requirements of the working conditions. To improve the service life, the bimetallic composite structure (high-strength inner layer + corrosion-resistant outer layer) has become the mainstream solution, but there are significant defects in the existing preparation technologies. For example, in traditional explosion welding or rolling composite processes, the bonding strength of the interface between dissimilar metals is insufficient. Processes such as surfacing and spraying require multiple processes, and the material utilization rate is low, the process is complex, and the cost is high.

[0004] Centrifugal casting is a casting process that uses the action of centrifugal force to achieve material forming. In this process, by rotating the mold or workpiece, the molten metal is evenly distributed and fills the mold under the action of centrifugal force, thereby forming the required shape and structure. In the late 1940s, centrifugal casting was initially developed, but the technology was not perfect, and it was only beginning to be applied to the industrial production of composite roller sleeves of several materials. By the mid-1970s, centrifugal casting technology had developed and was gradually used in industry. In addition to the advantages of centrifugal casting, the centrifugal casting composite technology can meet the higher requirements for materials of composite centrifugal composite castings because different materials are used for the inner and outer layers. The centrifugal casting process has the advantages of high production efficiency, high yield, refined crystal grains of the casting structure, and high strength, and is widely used in products in various industries. Centrifugal casting is widely used in the manufacture of high-performance components such as turbine blades and engine components in the aerospace field. In the automotive industry, centrifugal casting is used to manufacture key components such as exhaust valves and turbochargers. Centrifugal casting is also commonly used in the manufacture of corrosion-resistant chemical equipment such as composite pipes and pump casings.

[0005] Centrifugal casting has many advantages compared with traditional casting processes. Using centrifugal casting technology to prepare bimetallic composite steel pipes can simplify the production process flow without using sand cores, improve production efficiency, and reduce production costs. It can significantly improve the filling ability of liquid metal and improve the filling conditions. It can reduce or even eliminate the riser system and reduce metal consumption. In the process of centrifugally casting alloy steel liquid on the inner wall of a stainless steel pipe, the inner layer of molten metal solidifies directionally, which is conducive to the discharge of gas, oxides, inclusions, etc. in the liquid metal in the mold, and under the action of centrifugal force, they are distributed on the inner side of the inner layer of metal, which is convenient for subsequent removal. During the centrifugal casting process, an external force is applied to the unfrozen metal liquid to force the unfrozen metal to flow, that is, by using the method of dynamic effect, it can promote the transformation of columnar crystals into equiaxed crystals, control the organizational structure, refine the crystal grains, and improve the feeding conditions for the solidification of the casting, making the structure of the casting dense and improving the mechanical properties. The inner surface of the outer layer of stainless steel pipe remelts, and the interface with the inner layer of metal is metallurgical bonding, improving the bonding strength. Summary of the Invention

[0006] This patent uses centrifugal casting technology to shorten the manufacturing process flow and obtain steel for sucker rods with excellent performance, good quality and low cost.

[0007] In the first aspect of the present invention, a centrifugal casting method for high-strength and corrosion-resistant composite sucker rod steel is provided. The composite sucker rod steel is of a tubular structure, and from the surface layer to the inside, it is successively a stainless steel layer and a low-alloy structural steel layer with metallurgical bonding; the centrifugal casting method for the composite sucker rod steel is as follows: Select a stainless steel pipe of appropriate size as the outer mold for centrifugal casting. Pickle the inner surface of the stainless steel pipe, preheat the stainless steel pipe to 480 - 600 °C in an inert gas atmosphere, and fix it in a horizontal centrifugal casting device. Pour low alloy structural steel molten metal into the centrifugally rotating stainless steel pipe. The centrifugal casting temperature is 1400 - 1600 °C, and the centrifugal rotation speed is 800 - 1000 r / min until the inner low alloy structural steel layer is formed.

[0008] The thickness of the steel for the above-mentioned composite sucker rod is preferably 5 - 7 mm, more preferably 5 - 6 mm. The feasible thickness ratio of the stainless steel layer to the low alloy structural steel layer is 0.5 - 2:3 - 5.5, and the more preferred thickness ratio is 2:5.

[0009] Among them, the optional materials for the stainless steel layer include but are not limited to austenitic stainless steel and ferritic-austenitic stainless steel; the optional materials for the low alloy structural steel layer are such as chromium-molybdenum stainless steel. In a preferred embodiment of the present invention, the stainless steel layer is made of austenitic stainless steel, in which C does not exceed 0.07, and each of Mn and Si does not exceed 0.6. Excessive C will increase the pitting tendency and the density of carbide precipitation; Mn can partially replace nickel (Ni) to stabilize the austenite structure, and Si can significantly improve the strength, hardness and high-temperature oxidation resistance of the steel by strengthening ferrite and promoting the formation of a dense oxide film, but excessive Mn and Si will affect the formation of the inner low alloy structural steel. It has been verified that the austenitic stainless steel within the above dosage range can balance the processing performance and corrosion resistance.

[0010] The steps for pickling the inner surface of the stainless steel pipe are as follows: Mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:4 - 8 to obtain a pickling solution, and use the pickling solution to pickle the inner wall of the stainless steel pipe. The pickling method is such as spraying or dipping, and more preferably the dipping method.

[0011] In the centrifugal casting process, the stainless steel pipe is preheated to 480 - 600 °C by the lower support roller and maintained at a rotation speed of 800 - 1000 r / min. Heat the low alloy structural steel molten metal to 1400 - 1600 °C and pour it into the rotating stainless steel pipe. Wait for 15 - 30 min until the inner low alloy structural steel layer is formed; when the temperature drops to 800 °C - 950 °C, introduce argon for cooling, and the temperature drops to 600 - 500 °C within 5 min to obtain the steel for the above-mentioned composite sucker rod.

[0012] Furthermore, the steel for the above-mentioned composite sucker rod also includes subsequent treatment processes such as precision rolling and quenching and tempering.

[0013] In the prior art, composite steel is generally prepared by methods such as surfacing, composite rolling, explosion welding, spraying, etc. The above-mentioned centrifugal casting process provided by the present invention drives the melt gradient (element gradient distribution at the phase and interface) through centrifugal force. The advantages of this process and structure are as follows: 1) Under the action of centrifugal force, substances with low density in the melt, such as oxides and impurities, will gradually accumulate on the inner wall of the tube. High-quality molten steel solidifies adjacent to the stainless steel tube, facilitating subsequent mechanical removal of impurities.

[0014] 2) When the high-temperature molten steel contacts the stainless steel tube wall, remelting occurs at the stainless steel contact interface. Since stainless steel is rich in alloying metal elements such as Cr, Cr will diffuse under the driving force of the chemical concentration gradient, and then be gradient-distributed at the interface, and a good metallurgical bond is formed at the interface.

[0015] In the second aspect of the present invention, there is provided steel for a composite sucker rod prepared by the method described in the first aspect.

[0016] In the third aspect of the present invention, there is provided the application of the steel for a composite sucker rod described in the first aspect in the field of oil exploitation.

[0017] The above composite sucker rod provided by the present invention is applied as a hollow sucker rod for exploiting high pour-point, high-viscosity or high-wax-content crude oil; based on the hollow structure of the above composite sucker rod, hot water, hot oil, chemical reagents or cables can be injected into the wellbore.

[0018] In one embodiment, the steel for the composite sucker rod is used for hot washing and wax removal technology. Through the hollow structure, hot washing media (such as hot water and hot oil) are injected above the wax deposition point in the well to melt the paraffin condensed on the inner walls of the sucker rod and the tubing, thereby reducing the load of the pumping unit, improving the working efficiency of the oil pump, enhancing the lifting capacity of the oil production system, and also solving the problem of the inspection pump cycle caused by wax deposition in the oil well.

[0019] In another embodiment, the steel for the composite sucker rod is used for diluting crude oil above the pump. Dilute oil is incorporated into the heavy crude oil at the bottom of the well through the hollow structure of the sucker rod. After the two crude oils are mixed, the viscosity is reduced, so that the mixed oil can be smoothly lifted to the ground to realize the exploitation of heavy crude oil.

[0020] In yet another embodiment, the steel for the composite sucker rod is used for electrothermal oil production technology. A cable is lowered into the wellbore through the hollow structure, so that the hollow sucker rod string and the cable form a closed loop, and an electromagnetic "skin effect" is generated on the surface of the rod body of the hollow sucker rod, becoming a heat source to carry out daily wax removal of the oil well, and smoothly realizing the lifting of crude oil by using the temperature sensitivity of heavy crude oil, ensuring the normal production of the oil well.

[0021] Compared with the prior art, the beneficial effects of the present invention are: Compared with the existing steel for sucker rods, the unique features of the present invention are as follows: By using the centrifugal casting method, low-alloy structural steel is used as the inner layer, and a stainless steel pipe is used as the outer layer. Through the control of the melt gradient distribution driven by centrifugal force, the alloy steel liquid is directly solidified and formed on the inner wall of the stainless steel pipe. The utilization rate of the metal liquid is high, and it is formed in one step without the need for a sand core, with high efficiency, especially suitable for the preparation of rotary parts. It improves the interfacial bonding strength of the composite layer, optimizes the microstructure of the matrix, promotes the transformation of dendritic crystals into equiaxed crystals through dynamic effects, reduces segregation, improves its mechanical properties, has a continuous gradient transition of materials, high performance, and small interfacial stress concentration. It can prepare composite materials with a large cladding thickness, making full use of the material characteristics and complementarity.

[0022] Through centrifugal casting, the grains of the inner low-alloy structural steel matrix can be refined, the dendritic crystals are broken and refined, and defects such as shrinkage cavities are reduced, improving the strength and fatigue resistance of the matrix. The outer stainless steel can provide good corrosion resistance. The finally prepared composite steel for sucker rods has high strength, good corrosion resistance, high bonding strength, long service life, and low price. It simplifies the process flow, saves materials, and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0024] Figure 1 It is a schematic structural diagram of the high-strength and corrosion-resistant composite steel for sucker rods described in Embodiment 1; Wherein, 1 is the stainless steel layer, 2 is the low-alloy structural steel layer, and 3 is the cavity; Figure 2 It is a schematic structural diagram of the centrifugal casting device described in Embodiment 1; Wherein, 1 is stainless steel, 2 is low-alloy structural steel, 41 is the motor, 42 is the lower support roller, 43 is the upper support roller, and 44 is the molten steel storage device. DETAILED DESCRIPTION OF THE INVENTION

[0025] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] In order to enable those skilled in the art to more clearly understand the technical solutions of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

[0028] Example 1 In this embodiment, a steel for high-strength corrosion-resistant composite sucker rods and its centrifugal casting method are provided. The structure of the composite sucker rod steel is as Figure 1 shown, which is a hollow tubular shape. From the surface layer to the center of the circle, there are stainless steel 1 and low-alloy structural steel 2 in sequence, and the two are metallurgically bonded. 3 is the cavity. Specifically, stainless steel 1 is austenitic stainless steel, and its chemical composition is shown in Table 1. Its thickness is 2 mm and its inner diameter is 14 mm; low-alloy structural steel 2 is chromium-molybdenum alloy steel (30CrMo), and its thickness is 5 mm.

[0029] Table 1 Chemical composition of austenitic stainless steel in Example 1 The above-mentioned steel for high-strength corrosion-resistant composite sucker rods adopts a centrifugal casting process, which is realized by a horizontal centrifugal casting device. The setting method is as Figure 2 shown. The horizontal centrifugal casting device includes a motor 41, a lower support roller 42, an upper support roller 43, and a molten steel storage device 44. Among them, the lower support roller 42 and the upper support roller 43 are used to support the outer mold of centrifugal casting. When the lower support roller 42 rotates, it drives the outer mold to rotate together. The motor 41 drives the rotation of the lower support roller 42, and technicians can adjust the rotation speed of the outer mold through the motor 41. The above-mentioned molten steel storage device 44 is used to heat and hold the molten steel for injecting into the outer mold. The specific preparation process is as follows: 1. Select an austenitic stainless steel pipe with a thickness of 2 mm and an inner diameter of 14 mm as the outer mold of centrifugal casting, and fix it through the upper support roller 43 and the lower support roller 42; mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:5 to obtain an acid pickling solution, and use the acid pickling solution to impregnate and pickle the inner wall of the austenitic stainless steel pipe to remove impurities and oxides.

[0030] 2. Place the pickled austenitic stainless steel pipe obtained above in an argon atmosphere and preheat it to 600 °C. Refine chromium molybdenum alloy steel (30CrMo) to molten steel through an electroslag crucible furnace, heat the molten steel to 1400 - 1600 °C, and inject the above molten steel into the pickled austenitic stainless steel pipe through the molten steel storage device 44.

[0031] 3. Adjust the motor 41 to make the rotational speed of the austenitic stainless steel pipe 800 r / min. After injection, cool down the centrifugal casting equipment, naturally cool for 15 min, and wait for the inner layer of metal to solidify. When the temperature drops to 800 °C, introduce argon for cooling, and the temperature drops to 500 °C within 5 min to obtain the steel pipe.

[0032] 4. According to the required use dimensions, perform precision rolling on the above steel pipe, then remove the impurities on the inner wall of the steel pipe by mechanical processing, and finally perform quenching and tempering treatment to obtain the steel for the high-strength corrosion-resistant composite sucker rod.

[0033] In this embodiment, the mechanical properties of the above composite sucker rod steel are tested according to GB / T228.1, and its yield strength is 800 MPa and the tensile strength is 932 MPa.

[0034] The neutral salt spray experiment is carried out according to ISO 9227∶2017: Control the pH of the NaCl droplet to be 6.5 - 7.2. Keep the test environment temperature at (35 ± 1) °C, conduct a 300-hour neutral salt spray test, and light rust spots appear on the stainless steel surface. Calculate its corrosion rate through the mass change, and the calculated corrosion rate is 0.0013 mm / a.

[0035] Take a sine wave with a frequency f = 10 Hz and a stress ratio R = 0.1, and the number of cycles is greater than 1×10 6 times, and conduct a corrosion fatigue test at room temperature. Through the fatigue test results at different stroke frequencies, it is predicted that its service life can reach 2.7 million times.

[0036] Example 2 In this embodiment, another kind of steel for high-strength corrosion-resistant composite sucker rod is provided. The difference from Example 1 is that: the stainless steel 1 is austenitic stainless steel with a thickness of 0.5 mm, and the low-alloy structural steel 2 is chromium molybdenum alloy steel (30CrMo) with a thickness of 5.5 mm; the chemical composition of the austenitic stainless steel is shown in Table 2; Table 2 Chemical composition of austenitic stainless steel in Example 2 In the centrifugal casting process: 1. Select an austenitic stainless steel tube with a thickness of 2 mm and an inner diameter of 14 mm as the outer mold for centrifugal casting; mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:4 to obtain an acid pickling solution, and use the acid pickling solution to pickle the inner wall of the austenitic stainless steel tube to remove impurities and oxides.

[0037] 2. Place the pickled austenitic stainless steel tube obtained above in an argon atmosphere and preheat it to 480 °C. Refine the chromium-molybdenum alloy steel (30CrMo) to obtain molten steel through an electroslag crucible furnace, and inject the molten steel into the pickled austenitic stainless steel tube through the molten steel storage device 44.

[0038] 3. Adjust the motor 41 to make the rotational speed of the austenitic stainless steel tube 1000 r / min. After injection, cool down the centrifugal casting equipment, and naturally cool for 30 min. Wait for the inner layer of metal to solidify. When the temperature drops to 950 °C, introduce argon for cooling, and the temperature drops to 600 °C within 5 min to obtain a steel pipe.

[0039] 4. Same as Example 1.

[0040] In this example, the mechanical properties of the above composite sucker rod steel were tested according to GB / T228.1. The yield strength was tested to be 790 MPa and the tensile strength was 942 MPa according to GB / T228.1.

[0041] The neutral salt spray experiment was carried out according to ISO 9227∶2017: Control the pH of the NaCl droplet to be 6.5 - 7.2. Keep the test environment temperature at (35 ± 1) °C, and conduct a 300-hour neutral salt spray test. Shallow rust spots appeared on the stainless steel surface, and its corrosion rate was calculated through the mass change, and the calculated corrosion rate was 0.001 mm / a.

[0042] Take a sine wave with a frequency f = 10 Hz and a stress ratio R = 0.1, and the number of cyclic times is greater than 1*10 6 times, and conduct a corrosion fatigue test at room temperature. Through the fatigue test results at different stroke frequencies, it is predicted that its service life can reach 2.9 million times.

[0043] Example 3 In this example, another kind of high-strength and corrosion-resistant composite sucker rod steel is provided. The difference from Example 1 is that: Stainless steel 1 is austenitic stainless steel with a thickness of 2 mm, and low-alloy structural steel 2 is chromium-molybdenum alloy steel (30CrMo) with a thickness of 3 mm; the chemical composition of the austenitic stainless steel is shown in Table 3; Table 3 Chemical composition of austenitic stainless steel in Example 3 In the centrifugal casting process: 1. Use the above austenitic stainless steel pipe as the outer mold for centrifugal casting; mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:8 to obtain an acid pickling solution, and use the acid pickling solution to pickle the inner wall of the austenitic stainless steel pipe to remove impurities and oxides.

[0044] 2. Place the pickled austenitic stainless steel pipe obtained above in an argon atmosphere and preheat it to 520 °C. Refine chromium molybdenum alloy steel (30CrMo) to obtain molten steel through an electroslag crucible furnace, and inject the above molten steel into the pickled austenitic stainless steel pipe through a molten steel storage device 44.

[0045] Steps 3 and 4 are set the same as in Example 1.

[0046] In this example, the above steel for composite sucker rods was subjected to mechanical tests in accordance with GB / T228.1. The yield strength was tested to be 803 MPa and the tensile strength was 954 MPa in accordance with GB / T228.1.

[0047] The neutral salt spray experiment was carried out in accordance with ISO 9227∶2017: Control the pH of the NaCl droplet to be 6.5 - 7.2. Keep the test environment temperature at (35 ± 1) °C, conduct a 300-hour neutral salt spray test, and a relatively light rust spot appears on the stainless steel surface. Calculate its corrosion rate through the mass change, and the calculated corrosion rate is 0.002 mm / a.

[0048] Take a sine wave with a frequency f = 10 Hz and a stress ratio R = 0.1, and the number of cycles is greater than 1×10 6 times, and conduct a corrosion fatigue test at room temperature. Through the fatigue test results at different stroke frequencies, it is predicted that its service life can reach 3 million times.

[0049] Example 4 In this example, another kind of steel for high-strength and corrosion-resistant composite sucker rods is provided. The difference from Example 1 is that stainless steel 1 is a ferritic-austenitic duplex stainless steel pipe, and its chemical composition is shown in Table 4, and low-alloy structural steel 2 is 25CrMo.

[0050] Table 4 Chemical composition of duplex stainless steel in Example 4 In the centrifugal casting process: 1. Select a ferritic-austenitic duplex stainless steel pipe with a thickness of 2 mm and an inner diameter of 14 mm as the outer mold for centrifugal casting; mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:8 to obtain an acid pickling solution, and use the acid pickling solution to pickle the inner wall of the duplex stainless steel pipe to remove impurities and oxides.

[0051] 2. Place the pickled duplex stainless steel pipe in an argon atmosphere and preheat it to 520 °C. Refine the chromium molybdenum alloy steel (25CrMo) to obtain molten steel through an electroslag crucible furnace, and inject the molten steel into the pickled duplex stainless steel pipe through the molten steel storage device 44.

[0052] Steps 3 and 4 are set the same as in Example 1.

[0053] In this embodiment, the steel for the composite sucker rod is subjected to mechanical tests in accordance with GB / T228.1. The yield strength is tested to be 880 MPa and the tensile strength is 1011 MPa according to GB / T228.1.

[0054] The neutral salt spray test is carried out in accordance with ISO 9227∶2017: Control the pH of the NaCl droplet to be 6.5 - 7.2. Keep the test environment temperature at (35 ± 1) °C and conduct a 300-hour neutral salt spray test. Shallow rust spots appear on the stainless steel surface, and its corrosion rate is calculated through the mass change, and the calculated corrosion rate is 0.0003 mm / a.

[0055] Take a sine wave with a frequency f = 10 Hz and a stress ratio R = 0.1, with the number of cycles greater than 1 * 10^6 times, and conduct a corrosion fatigue test at room temperature. Through the fatigue test results at different stroke frequencies, it is predicted that its service life can reach 2.65 million times.

[0056] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A centrifugal casting method for steel used in high-strength corrosion-resistant composite sucker rods, characterized in that, The steel for the composite sucker rod is of tubular structure, and from the surface layer to the inside, there are a metallurgically bonded stainless steel layer and a low alloy structural steel layer in sequence; the centrifugal casting method of the steel for the composite sucker rod is as follows: Select a stainless steel pipe with appropriate size as the outer die for centrifugal casting, pickle the inner surface of the stainless steel pipe, preheat the stainless steel pipe to 480 - 600 °C in an inert gas atmosphere and fix it in a horizontal centrifugal casting device, pour the low alloy structural steel melt into the centrifugally rotating stainless steel pipe, the centrifugal casting temperature is 1400 - 1600 °C, the centrifugal speed is 800 - 1000 r / min, and wait for the inner low alloy structural steel layer to be formed.

2. The centrifugal casting method of the steel for high-strength corrosion-resistant composite sucker rods according to claim 1, characterized in that, The thickness of the steel for the composite sucker rod is preferably 5 - 7 mm, and more preferably 5 - 6 mm.

3. The centrifugal casting method of the steel for high-strength corrosion-resistant composite sucker rods according to claim 1, characterized in that, The feasible thickness ratio of the stainless steel layer to the low alloy structural steel layer is 0.5 - 2:3 - 5.5, and the preferred thickness ratio is 2:

5.

4. The centrifugal casting method of the steel for high-strength corrosion-resistant composite sucker rods as described in claim 1, characterized in that, The material of the stainless steel layer includes but is not limited to austenitic stainless steel and ferritic-austenitic stainless steel; the material of the low alloy structural steel layer is chromium-molybdenum stainless steel.

5. The centrifugal casting method of the steel for high-strength corrosion-resistant composite sucker rods as described in claim 1, characterized in that, The steps of pickling the inner surface of the stainless steel pipe are as follows: Mix nitric acid, hydrofluoric acid and water in a volume ratio of 1:1:4 - 8 to obtain a pickling solution, and use the pickling solution to pickle the inner wall of the stainless steel pipe. The pickling method is spraying or dipping, and preferably dipping.

6. The centrifugal casting method of the steel for high-strength and corrosion-resistant composite sucker rods as described in claim 1, characterized in that, In the centrifugal casting process, the stainless steel pipe is preheated to 480 - 600 °C by the lower support roller and maintained at a speed of 800 - 1000 r / min, the low alloy structural steel melt is heated to 1400 - 1600 °C and poured into the rotating stainless steel pipe. Wait for 15 - 30 min for the inner low alloy structural steel layer to be formed; when the temperature drops to 800 °C - 950 °C, introduce argon for cooling, and the temperature drops to 600 - 500 °C within 5 min to obtain the steel for the composite sucker rod.

7. The centrifugal casting method of the steel for high-strength corrosion-resistant composite sucker rods according to claim 6, characterized in that, The steel for the composite sucker rod also includes subsequent treatment processes such as precision rolling and quenching and tempering.

8. The steel for the composite sucker rod prepared by the method according to any one of claims 1 - 7.

9. The application of the steel for the composite sucker rod according to claim 8 in the field of oil exploitation.

10. The application according to claim 9, wherein The composite sucker rod is applied as a hollow sucker rod in the exploitation of high pour point, high viscosity or high wax content crude oil; based on the hollow structure of the composite sucker rod, hot water, hot oil, chemical reagents are injected into the well or a cable is passed through; Further, the steel for the composite sucker rod is used for hot washing to remove wax. Through the hollow structure, a hot washing medium is injected above the wax deposition point in the well to melt the paraffin condensed on the inner walls of the sucker rod and the tubing; Further, the steel for the composite sucker rod is used for diluting above the pump. Through the hollow structure of the sucker rod, light oil is incorporated into the heavy oil at the bottom of the well. After the two crude oils are mixed, the viscosity is reduced, and thus the mixed oil is lifted to the ground to realize the exploitation of heavy oil; Further, the steel for the composite sucker rod is used for the electric heating oil production process. Through the hollow structure, a cable is lowered into the well, so that the hollow sucker rod string and the cable form a closed loop and become a heat source.

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