A low alloy fatigue-resistant wireline coring drill pipe and its preparation method

Abstract

The present invention discloses a low-alloy, fatigue-resistant pipe for rope coring drill pipe and a method for preparing the same. The pipe comprises, by weight, 0.26% ≤ C ≤ 0.32%, 0.15% ≤ Si ≤ 0.25%, 1.3% ≤ Mn ≤ 1.7%, 0.30% ≤ Cr ≤ 0.40%, 0.01% ≤ Al ≤ 0.025%, P ≤ 0.015%, and S ≤ 0.009%, with the remainder being Fe and unavoidable impurities. The pipe produced by the present invention has a metallographic structure of fine, uniform tempered troostite and lamellar ferrite, with a grain size of 9.0. The pipe exhibits excellent mechanical properties and fatigue resistance, and features a limited number of alloying elements and a low alloy content, significantly reducing production costs. The pipe can effectively meet the requirements of rope coring drilling technology and has broad market prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of material metallurgy, and in particular to a low-alloy fatigue-resistant rope coring drill pipe and a preparation method thereof. Background Art

[0002] Wireline coring drilling technology originated in oil drilling. It uses drill pipe to obtain rock cores without lifting the drill bit. It is widely used in geological prospecting, coalfield exploration, and other fields. Wireline coring drill pipe features "three highs and one low": high penetration rate, long diamond drill bit life, high tool utilization, and low labor intensity. The drill pipe is the most important and valuable component of the entire drilling tool set. Its quality directly impacts the advantages of wireline coring drilling and is crucial for accurately acquiring geological data and controlling drilling costs.

[0003] By the 1990s, my country had completed tens of millions of meters of rope core drilling, and rope core drilling technology gradually became dominant in geological core drilling. However, due to the limitations of seamless steel pipe performance and quality, as well as the range of drill pipe sizes at the time, conventional rope drill pipes often experienced breakage and stripping, deformation of the female thread into a bell-shaped shape, high flushing fluid circulation resistance, and high pump pressures when drilling holes exceeding 1500m.

[0004] To address these issues, Chinese technical personnel have conducted extensive experimental research and have made considerable progress. In recent years, they have successfully developed XJY850, a high-strength wireline drill pipe for deep drilling exceeding 2,000 meters. Furthermore, based on the XJY850 pipe, improvements have been made to its chemical composition, manufacturing process, and heat treatment methods to improve its hardenability, toughness, fatigue resistance, abrasion resistance, and impact resistance, further enhancing the overall performance of wireline coring pipes. Consequently, 30CrMo and 42CrMoA pipes have been developed. However, with the rising prices of precious alloying elements such as Cr and Mo, the manufacturing costs of 42CrMoA and 30CrMo have increased significantly. Therefore, the challenge of producing low-cost pipes that meet the comprehensive performance requirements for wireline coring has become a bottleneck in wireline coring drilling technology. Summary of the Invention

[0005] In order to reduce the manufacturing cost of existing rope coring pipes while meeting the comprehensive mechanical performance requirements of rope coring pipes, the present invention provides a low-alloy fatigue-resistant rope coring drill pipe and a preparation method thereof.

[0006] To solve the above technical problems, the technical solutions provided by the embodiments of the present invention are:

[0007] A low-alloy anti-fatigue rope coring drill pipe has the following components by weight: 0.26%≤C≤0.32%, 0.15%≤Si≤0.25%, 1.3%≤Mn≤1.7%, 0.30%≤Cr≤0.40%, 0.01%≤Al≤0.025%, P≤0.015%, S≤0.009%, and the balance is Fe and unavoidable impurities.

[0008] Compared with the prior art, the low-alloy fatigue-resistant wireline coring drill pipe provided by the present invention is based on Cr-Mo steel. By controlling the C content to 0.26%-0.32%, increasing the Mn content to 1.3%-1.7%, and adding an appropriate amount of Al as an alloying element and deoxidizing element, the Cr content is effectively reduced and the addition of Mo is omitted. This not only effectively reduces the manufacturing cost of the wireline coring drill pipe, but also ensures that the wireline coring drill pipe has good comprehensive mechanical properties.

[0009] The alloy component system of the rope coring drill pipe in the present invention is simple, no precious alloy elements such as Mo, Nb, and V are added, and the Cr content is greatly reduced, belonging to the category of low-alloy steel, which significantly reduces the production cost of the rope coring drill pipe. Moreover, the above-mentioned components are combined with each other in specific proportions, and the prepared rope coring drill pipe can reach XYJ850 steel grade, has excellent mechanical properties and fatigue resistance, can better meet the use requirements of rope coring drilling technology, and has broad market prospects.

[0010] Furthermore, the microstructure is tempered troostite and lamellar ferrite, and the grain size is 9.0.

[0011] The present invention also provides the above-mentioned low-alloy fatigue-resistant wireline coring drill pipe, comprising the following steps:

[0012] A continuous cast round billet having the same chemical composition as the low-alloy fatigue-resistant rope coring drill pipe is heated in an annular furnace, perforated to produce a rough pipe, the rough pipe is rolled to obtain a rough pipe, the rough pipe is heated, subjected to micro-tension reduction, and cooled on a walking cooling bed to obtain a rolled steel pipe;

[0013] The rolled steel pipe is subjected to heat treatment and straightening to obtain the low alloy fatigue resistant wireline coring drill pipe.

[0014] The method for preparing a low-alloy fatigue-resistant rope coring drill pipe provided by the present invention has a simple preparation process and is easy to produce in practice.

[0015] Furthermore, the heating temperature of the rough pipe is 1000°C-1100°C.

[0016] Preferably, the heat treatment process includes the following steps: heating the rolled steel pipe to 880℃-890℃ and keeping it warm once, and then performing a quenching treatment; then heating the steel pipe to 850℃-880℃ and keeping it warm twice, and then performing a second quenching treatment; then heating the steel pipe to 510℃-530℃ and keeping it warm three times, straightening it, and air cooling it.

[0017] Further preferably, in the heat treatment process, the time of the first insulation is 35 min-40 min.

[0018] Further preferably, in the heat treatment process, the secondary insulation time is 35 min-40 min.

[0019] Further preferably, in the heat treatment process, the three insulation times are 55 min-60 min.

[0020] Preferably, in the heat treatment process, the quenching time of the primary quenching treatment and the secondary quenching treatment is 5s-10s, and the quenching water temperature is 15°C-30°C.

[0021] In the present invention, the rolled steel pipe is first heated at 880°C-890°C and then quenched to obtain lamellar martensite. Then, it is heated in a two-phase region at 850°C-880°C. After the martensite carbon is demelted, the transformed ferrite inherits the orientation of the lamellar martensite and maintains the lamellar characteristics, forming a parallel strip structure with austenite and ferrite spaced apart from each other. After quenching, martensite is formed between the ferrite strips and grows in phase to form a martensite + ferrite strip structure. At the same time, due to the transformation of austenite to martensite, the volume expands, causing the ferrite to undergo plastic deformation, inducing high-density dislocations in the ferrite, strengthening the ferrite, and forming a structure in which the tough phase lamellar ferrite surrounds the strengthening phase fibrous martensite. This morphological structure plays an important role in improving the strength of the steel. During the tensile process, the lamellar ferrite and lamellar martensite can deform synergistically, giving it excellent plasticity during stretching. During impact, the soft phase ferrite can prevent crack propagation and increase the crack propagation work, which significantly contributes to the improvement of the steel's strength and toughness. Finally, tempering is carried out at 510℃-530℃, where the lamellar martensite transforms into tempered troostite while still retaining its lamellar properties. Ultimately, a microstructure of lamellar tempered troostite + lamellar ferrite is formed, which plays a crucial role in significantly improving the mechanical properties and fatigue resistance of the steel.

[0022] At the same time, the preferred heat treatment method can also refine the material structure, control the precipitation amount and size of carbides, obtain a fine and uniform microstructure, and ensure the comprehensive mechanical properties of the steel.

[0023] Preferably, in the heat treatment process, the first quenching treatment and the second quenching treatment are both performed by internal spraying and external showering, wherein the flow rate of the internal spraying water is 150m 3 / h-500m 3 / h, the flow rate of external water is 1500m 3 / h-2000m 3 / h.

[0024] The preferred internal and external water flow rates of the present invention are conducive to ensuring uniform quenching and ensuring that the lamellar martensite structure in the quenched steel pipe reaches more than 98%. The preferred quenching time and water temperature are also conducive to further ensuring uniform quenching.

[0025] Preferably, the continuous casting round billet is made by subjecting steelmaking raw materials to electric arc furnace melting, ladle refining and continuous casting processes.

[0026] Furthermore, in the electric arc furnace smelting process, the steelmaking raw material smelted in the electric arc furnace is 100% ordinary scrap steel.

[0027] Furthermore, in the ladle refining process, the basicity of the refined slag is controlled to be 4.5-6.0.

[0028] Furthermore, in the ladle refining process, aluminum particles, calcium carbide and silicon carbide are used for diffusion deoxidation, and the refining time of the white slag is 20 minutes to 35 minutes.

[0029] In the ladle refining process, by controlling the basicity of the refining slag and the refining time of the white slag, harmful elements such as P and S in the molten steel can be effectively removed, while preventing the slag from reacting to form non-metallic inclusions in the later stage of refining.

[0030] Preferably, in the continuous casting process, crystallizer electromagnetic stirring and end electromagnetic stirring are adopted, wherein the crystallizer stirring adopts a (6-8)s-(2-3)s-(6-8)s alternating stirring mode, and the end electromagnetic stirring adopts a (9-11)s-(2-4)s-(9-11)s alternating stirring mode, the electromagnetic stirring current is 350A-400A, and the frequency is 3HZ-6HZ.

[0031] The electromagnetic stirring method of the above-mentioned crystallizer can improve the solidification quality of the ingot and the homogenization of the composition structure, and prevent the problem of structural segregation in the steel.

[0032] The beneficial effects of adopting the above technical solution are:

[0033] The present invention adopts precise chemical composition design and unique preparation process, so that the purity of molten steel is high, the inclusions are small and dispersed, and the metallographic structure is fine and uniform tempered troostite and lamellar ferrite, and the grain size can reach 9.0 grade. As a result, the prepared steel has excellent mechanical properties and fatigue resistance, and the types of alloy elements are small, the alloy content is low, and the production cost is significantly reduced. It has broad application prospects in the field of rope coring drilling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram of the original austenite grain size of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0035] Figure 2 This is a metallographic structure diagram of a low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0036] Figure 3 This is a yield strength distribution diagram of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0037] Figure 4 This is a tensile strength distribution diagram of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0038] Figure 5 This is the elongation distribution diagram of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0039] Figure 6 This is a distribution diagram of the 0°C impact properties of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0040] Figure 7 This is a hardness distribution diagram of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention;

[0041] Figure 8 This is a diagram showing the fatigue resistance of the low-alloy fatigue-resistant wireline coring drill pipe prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] In order to better illustrate the present invention, further examples are given below.

[0044] Example 1

[0045] An embodiment of the present invention provides a low-alloy fatigue-resistant wireline coring drill pipe, the chemical composition of which is:

[0046] C 0.26%, Si 0.20%, Mn 1.7%, Cr 0.31%, Al 0.02%, P 0.009%, S 0.004%, and the balance is Fe and inevitable impurities.

[0047] The preparation steps of the above-mentioned low alloy fatigue-resistant wireline coring drill pipe are as follows:

[0048] S1, the steelmaking raw materials are subjected to 80t electric arc furnace melting, ladle refining, and continuous casting processes to produce continuous casting round billets with the same chemical composition as the above-mentioned pipes;

[0049] S2, the continuous casting round billet is heated in an annular furnace and perforated to form a rough pipe, the rough pipe is rolled by a three-roll continuous rolling mill to obtain a rough pipe, the rough pipe is removed from the pipe by a three-stand pipe remover, heated in a supplementary heating furnace, reduced by micro-tension, and cooled on a walking cooling bed to be rolled into a rolled steel pipe with an outer diameter of 114.3 mm and a wall thickness of 6.3 mm;

[0050] S3, heat treating and straightening the seamless steel pipe to obtain a low-alloy fatigue-resistant wireline coring drill pipe.

[0051] Among them, in the electric arc furnace smelting process, the steelmaking raw materials smelted in the electric arc furnace are 100%.

[0052] During the ladle refining process, the basicity of the refining slag is controlled at 6.0.

[0053] In the ladle refining process, aluminum particles, calcium carbide and silicon carbide are used for diffusion deoxidation, and the refining time of white slag is 35 minutes.

[0054] During the continuous casting process, an electromagnetic stirrer is used to electromagnetically stir the molten steel in the crystallizer. The electromagnetic stirring of the crystallizer adopts a 7s-2s-7s alternating stirring mode, and the end crystallizer adopts a 10s-3s-10s alternating stirring mode. The current of the electromagnetic stirring is 380A and the frequency is 4HZ.

[0055] During the rolling process, the rough pipe is heated to 950℃ in the supplementary heating furnace.

[0056] The heat treatment process includes the following steps: heating the rolled steel pipe to 885°C and holding it for 38 minutes, followed by a primary quenching treatment; then heating the steel pipe to 865°C and holding it for 37 minutes, followed by a secondary quenching treatment; then heating the steel pipe to 520°C and holding it for 59 minutes, followed by straightening and air cooling;

[0057] The first quenching treatment and the second quenching treatment are both carried out by internal spraying and external showering, wherein the flow rate of the internal spraying water is 290m 3 / h, the flow rate of external water is 1800m 3 / h; the quenching time is 7s, and the quenching water temperature is 20℃.

[0058] Example 2

[0059] An embodiment of the present invention provides a low-alloy fatigue-resistant wireline coring drill pipe, the chemical composition of which is:

[0060] C 0.28%, Si 0.25%, Mn 1.4%, Cr 0.38%, Al 0.025%, P 0.008%, S 0.002%, and the balance is Fe and inevitable impurities.

[0061] The preparation steps of the above-mentioned low alloy fatigue-resistant wireline coring drill pipe are as follows:

[0062] S1, the steelmaking raw materials are subjected to 80t electric arc furnace melting, ladle refining, and continuous casting processes to produce continuous casting round billets with the same chemical composition as the above-mentioned pipes;

[0063] S2, the continuous casting round billet is heated in an annular furnace and perforated to form a rough pipe, the rough pipe is rolled by a three-roll continuous rolling mill to obtain a rough pipe, the rough pipe is removed from the pipe by a three-stand pipe remover, heated in a supplementary heating furnace, reduced by micro-tension, and cooled on a walking cooling bed to be rolled into a rolled steel pipe with an outer diameter of 89.5 mm and a wall thickness of 5.5 mm;

[0064] S3, heat treating and straightening the seamless steel pipe to obtain a low-alloy fatigue-resistant wireline coring drill pipe.

[0065] Among them, in the electric arc furnace smelting process, the steelmaking raw materials smelted in the electric arc furnace are 100%.

[0066] During the ladle refining process, the basicity of the refining slag is controlled at 4.5.

[0067] In the ladle refining process, aluminum particles, calcium carbide and silicon carbide are used for diffusion deoxidation, and the refining time of white slag is 30 minutes.

[0068] During the continuous casting process, an electromagnetic stirrer is used to electromagnetically stir the molten steel in the crystallizer. The electromagnetic stirring of the crystallizer adopts a 7s-2s-7s alternating stirring mode, and the end crystallizer adopts an 11s-3s-11s alternating stirring mode. The current of the electromagnetic stirring is 350A and the frequency is 3HZ.

[0069] During the rolling process, the rough pipe is heated to 920℃ in the supplementary heating furnace.

[0070] The heat treatment process includes the following steps: heating the rolled steel pipe to 880℃ and holding it for 40 minutes, followed by a primary quenching treatment; then heating the steel pipe to 850℃ and holding it for 40 minutes, followed by a secondary quenching treatment; then heating the steel pipe to 530℃ and holding it for 55 minutes, followed by straightening and air cooling;

[0071] The first quenching treatment and the second quenching treatment are both carried out by internal spraying and external showering, wherein the flow rate of the internal spraying water is 150m 3 / h, the flow rate of external water is 1500m 3 / h; the quenching time is 5s, and the quenching water temperature is 15℃.

[0072] Example 3

[0073] An embodiment of the present invention provides a low-alloy fatigue-resistant wireline coring drill pipe, the chemical composition of which is:

[0074] C 0.32%, Si 0.15%, Mn 1.3%, Cr 0.35%, Al 0.01%, P 0.011%, S 0.005%, and the balance is Fe and inevitable impurities.

[0075] The preparation steps of the above-mentioned low alloy fatigue-resistant wireline coring drill pipe are as follows:

[0076] S1, the steelmaking raw materials are subjected to 80t electric arc furnace melting, ladle refining, and continuous casting processes to produce continuous casting round billets with the same chemical composition as the above-mentioned pipes;

[0077] S2, the continuous casting round billet is heated in an annular furnace and perforated to form a rough pipe, the rough pipe is rolled by a three-roll continuous rolling mill to obtain a rough pipe, the rough pipe is removed from the pipe by a three-stand pipe remover, heated in a supplementary heating furnace, reduced by micro-tension, and cooled on a walking cooling bed to be rolled into a rolled steel pipe with an outer diameter of 95 mm and a wall thickness of 10 mm;

[0078] S3, heat treating and straightening the seamless steel pipe to obtain a low-alloy fatigue-resistant wireline coring drill pipe.

[0079] Among them, in the electric arc furnace smelting process, the steelmaking raw materials smelted in the electric arc furnace are 100%.

[0080] During the ladle refining process, the basicity of the refining slag is controlled at 5.0.

[0081] In the ladle refining process, aluminum particles, calcium carbide and silicon carbide are used for diffusion deoxidation, and the refining time of white slag is 20 minutes.

[0082] During the continuous casting process, an electromagnetic stirrer is used to electromagnetically stir the molten steel in the crystallizer. The electromagnetic stirring of the crystallizer adopts a 7s-2s-7s alternating stirring mode, and the end crystallizer adopts a 10s-3s-10s alternating stirring mode. The current of the electromagnetic stirring is 400A and the frequency is 6HZ.

[0083] During the rolling process, the rough pipe is heated to 980℃ in the supplementary heating furnace.

[0084] The heat treatment process includes the following steps: heating the rolled steel pipe to 890°C and holding it for 35 minutes, followed by a primary quenching treatment; then heating the steel pipe to 880°C and holding it for 35 minutes, followed by a secondary quenching treatment; then heating the steel pipe to 510°C and holding it for 60 minutes, followed by straightening and air cooling;

[0085] The primary quenching treatment and the secondary quenching treatment are both carried out by internal spraying and external showering, wherein the flow rate of the internal spraying water is 500m 3 / h, the flow rate of external water is 2000m 3 / h; the quenching time is 10s, and the quenching water temperature is 30℃.

[0086] According to the requirements of GB-T 16950-2014, samples were randomly taken from the pipes for rope coring drill pipes prepared in Examples 1 to 3 to analyze their yield strength, tensile strength, elongation, 0°C longitudinal impact energy, hardness, non-metallic inclusions, grain size, and metallographic structure; the results are shown in Tables 1 and 2. Figure 1-Figure 2 shown.

[0087] Table 1 Mechanical properties statistics

[0088] Inspection items Standard requirements Number of samples Minimum Maximum average value CPK value <![CDATA[Yield strength Rp 0.2 / MPa]]> ≥850 119 921 993 950 2.18 <![CDATA[Tensile strength R m / MPa]]> ≥950 119 970 1054 1004 1.69 Elongation / % ≥14 119 16.5 24.5 17.5 1.67 Longitudinal Charpy impact energy / J ≥54 119 79 104 89 3.52 Hardness / HRC 28-33 119 29 33 31.8 0.69

[0089] As can be seen from the table, the pipes produced by the above method have a yield strength of 921-993 MPa, a tensile strength of 970-1054 MPa, an elongation of 16.5%-24.5%, and a full-scale longitudinal Charpy impact energy at 0°C of 79-104 J. The average yield strength is 950 MPa, with a Cpk value of 2.18 (>1.33); the average tensile strength is 1004 MPa, with a Cpk value of 1.69 (>1.33); the average elongation is 17.5%, with a Cpk value of 1.67 (>1.33); and the average full-scale longitudinal Charpy impact energy at 0°C is 89 J, with a Cpk value of 3.52 (>1.33).

[0090] Table 2 Non-metallic inclusion rating statistics

[0091]

[0092] The results show that the total non-metallic inclusions of the pipes for wireline coring drill pipes prepared in Examples 1-3 are 0.5, the grain size is 9.0, and the metallographic structure is tempered troostite and lamellar ferrite.

[0093] According to the provisions of the national standard "Rotational Bending Method for Fatigue Testing of Metal Materials", a PQ-6 rotary full fatigue testing machine was used to test the fatigue resistance of the pipe for rope coring drill pipe prepared in Example 1 at room temperature, with a rotation speed of 3000 r / min and the sample subjected to symmetrical cyclic stress (R = -1).

[0094] When the stress drops to a certain limit value, the SN curve approaches a horizontal line, that is, when the stress does not exceed the limit value, the fatigue life can be increased infinitely. This limit value is the fatigue limit of the material. The test life reaches 1.0×10 7 The fatigue limit data of the pipe for rope coring drill pipe prepared in Example 1 are shown in Table 3. The fatigue curve is shown in Figure 8 As shown (the numbers in the brackets in the figure indicate the number of "out-of-bounds" specimens under the corresponding stress).

[0095] Table 3 Fatigue limit data

[0096]

[0097]

[0098] In summary, the rope coring pipe provided by the present invention has excellent mechanical properties through precise composition design and process control. In addition, the alloy composition is simple, Mo is excluded, the Cr content is greatly reduced, and the production cost is significantly reduced. Therefore, the pipe has broad application prospects in the field of rope coring drilling.

[0099] In summary, the pipe prepared by the present invention has excellent metallurgical properties, low harmful element content, fine and uniform microstructure, and reliable mechanical properties. It can be widely used in the drilling and production of shale gas reservoirs and has broad market prospects.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low alloy fatigue resistant wireline coring drill pipe, characterized in that: Its composition by weight percentage is: 0.26%≤C≤0.32%, 0.15%≤Si≤0.25%, 1.3%≤Mn≤1.7%, 0.30%≤Cr≤0.40%, 0.01%≤Al≤0.025%, P≤0.015%, S≤0.009%, the balance is Fe and inevitable impurities; its microstructure is strip-shaped tempered troostite and strip-shaped ferrite, and the grain size is 9.0 grade; The low alloy fatigue-resistant rope coring drill pipe is prepared by the following method: A continuous cast round billet having the same chemical composition as the low-alloy fatigue-resistant rope coring drill pipe is heated in an annular furnace, perforated to produce a rough pipe, the rough pipe is rolled to obtain a rough pipe, the rough pipe is heated, subjected to micro-tension reduction, and cooled on a walking cooling bed to obtain a rolled steel pipe; The rolled steel pipe is subjected to heat treatment and straightening to obtain the low alloy fatigue resistant wireline coring drill pipe; The continuous casting round billet is produced by subjecting steelmaking raw materials to electric arc furnace melting, ladle refining and continuous casting processes; in the ladle refining process, the basicity of the refined slag is controlled to be 4.5-6.0; aluminum particles, calcium carbide and silicon carbide are used for diffusion deoxidation, and the refining time of the white slag is 20 minutes to 35 minutes; The heat treatment process includes the following steps: heating the rolled steel pipe to 880℃-890℃ and holding it once, and then performing a quenching treatment; then heating the steel pipe to 850℃-880℃ and holding it twice, and then performing a second quenching treatment; then heating the steel pipe to 510℃-530℃ and holding it three times, and then straightening and air cooling; In the heat treatment process, the time of the first heat preservation is 35min-40min; In the heat treatment process, the secondary insulation time is 35min-40min; In the heat treatment process, the three insulation times are 55min-60mi.

2. A method for preparing the low alloy fatigue-resistant wireline coring drill pipe according to claim 1, characterized in that: The steps include: A continuous cast round billet having the same chemical composition as the low-alloy fatigue-resistant rope coring drill pipe is heated in an annular furnace, perforated to produce a rough pipe, the rough pipe is rolled to obtain a rough pipe, the rough pipe is heated, subjected to micro-tension reduction, and cooled on a walking cooling bed to obtain a rolled steel pipe; The rolled steel pipe is subjected to heat treatment and straightening to obtain the low alloy fatigue resistant wireline coring drill pipe.

3. The method for preparing a low alloy fatigue-resistant wireline coring drill pipe according to claim 2, characterized in that: In the heat treatment process, the first quenching treatment and the second quenching treatment are both carried out by internal spraying and external showering, wherein the flow rate of the internal spraying water is 150m 3 / h-500m 3 / h, the flow rate of external water is 1500m 3 / h-2000m 3 / h.

4. The method for preparing a low alloy fatigue-resistant wireline coring drill pipe according to claim 3, characterized in that: In the heat treatment process, the quenching time of the primary quenching treatment and the secondary quenching treatment is 5s-10s, and the quenching water temperature is 15°C-30°C.

5. The method for preparing a low alloy fatigue-resistant wireline coring drill pipe according to claim 2, characterized in that: In the continuous casting process, crystallizer electromagnetic stirring and end electromagnetic stirring are adopted. Among them, the crystallizer stirring adopts the alternating stirring mode of (6-8)s-(2-3)s-(6-8)s, and the end electromagnetic stirring adopts the alternating stirring mode of (9-11)s-(2-4)s-(9-11)s. The current of electromagnetic stirring is 350A-400A, and the frequency is 3HZ-6HZ.

Images