Seamless steel tube and preparation method thereof

Abstract

The invention provides a seamless steel pipe and a preparation method thereof, and belongs to the technical field of alloy steel pipes, and the preparation method comprises the following steps: S1, taking a solid pipe as a steel billet which comprises the following components in percentage by mass: 0.20-0.23% of C, 0.50-0.55% of Si, 0.87-0.92% of Mn, 0.04-0.06% of Mo, 0.18-0.22% of Cr, 0.05-0.08% of Ni, 0.008-0.012% of Ti, 0.01-0.015% of rare earth element, less than or equal to 0.016% of P, less than or equal to 0.007% of S and the balance of Fe and inevitable impurities; punching the steel billet to obtain a pipe billet; s2, soaking the tube blank at 1260-1280 DEG C for 25-30 minutes, then carrying out periodic tube rolling to form a pierced billet, and controlling the finish rolling temperature at 870 + / -10 DEG C; s3, cooling liquid is sprayed inside and outside the pierced billet which moves forwards in a rotating mode, and the outer spraying flow is 1.6-2 times of the inner spraying flow; and S4, tempering, straightening and air cooling are conducted, and the steel plate is obtained. The cooling liquid comprises the following components in percentage by mass: 2-2.4% of phosphate, 1.5-1.8% of an iron ion chelating agent, 3.5-4% of citric acid and the balance of water. The tensile strength and wear resistance of the product are improved through high silicon content, and meanwhile, the surface smoothness of the product is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy steel pipes, and in particular relates to a seamless steel pipe and a preparation method thereof. Background Art

[0002] Seamless steel pipe is a steel pipe without joints, which is made by perforating a whole round steel. Seamless steel pipe can be made of different materials, including ordinary carbon structural steel, high-quality carbon structural steel, low alloy steel, alloy steel, stainless acid-resistant steel, etc. The main production process of hot-rolled seamless steel pipe includes tube blank preparation and inspection, tube blank heating, perforation, tube rolling, steel pipe reheating, sizing, heat treatment, finished tube straightening, finishing, inspection and other steps. As an indispensable material in modern industry, the optimization of production process and quality control of seamless steel pipe are the key to producing high-quality products.

[0003] The components of seamless steel pipes include a variety of materials and chemical compositions, which determine the performance and application areas of seamless steel pipes. For example, silicon can react with oxygen in steel to generate stable silicate compounds, thereby removing oxygen from steel, improving the purity of steel, and reducing the generation of defects such as pores and inclusions, thereby improving the quality of steel, including tensile strength and wear resistance.

[0004] However, when the silicon content is too high, it will significantly increase the oxidation tendency of the steel, making it easier for the steel to produce oxide scale during the heating process, affecting the surface finish and causing the surface quality of the steel to deteriorate. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a seamless steel pipe and a preparation method thereof, which improves the tensile strength and wear resistance of the product by high silicon content while improving the surface finish of the product.

[0006] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a method for preparing a seamless steel pipe, comprising the following steps:

[0007] S1. A solid tube is used as a steel billet, wherein the composition thereof includes, by mass percentage, C: 0.20-0.23%, Si: 0.50-0.55%, Mn: 0.87-0.92%, Mo: 0.04-0.06%, Cr: 0.18-0.22%, Ni: 0.05-0.08%, Ti: 0.008-0.012%, rare earth elements: 0.01-0.015%, P≤0.016%, S≤0.007%, and the rest is Fe and unavoidable impurities; and the steel billet is punched to obtain a tube billet;

[0008] S2, heat the tube blank at 1260-1280℃ for 25-30min, then perform periodic tube rolling to form a rough tube, and control the final rolling temperature at 870±10℃;

[0009] S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside, with the external spray flow rate being 1.6-2 times the internal spray flow rate;

[0010] S4, finally tempering, straightening and air cooling are performed to obtain a seamless steel pipe;

[0011] The components of the coolant include 2-2.4% of phosphate, 1.5-1.8% of iron ion chelating agent, 3.5-4% of citric acid and the balance of water in terms of mass percentage.

[0012] Furthermore, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1.

[0013] Further, in S3, the rotational advancement includes a rotational speed of 20-30 r / min and an advancement speed of 3-4 m / min.

[0014] Furthermore, in S3, the external spray flow rate is 2600-2800m 3 / h, internal spray flow rate is 1450-1600m 3 / h.

[0015] Furthermore, the phosphate includes sodium tripolyphosphate and / or sodium hexametaphosphate.

[0016] Furthermore, the iron ion chelating agent is disodium ethylenediaminetetraacetate.

[0017] Furthermore, the preparation method of the coolant is as follows: accurately weigh phosphate, iron ion chelating agent, citric acid and water according to mass percentage; add 40-60% of water in a container, and then add the weighed phosphate, iron ion chelating agent, and citric acid in sequence, and stir with a stirrer to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution; add the remaining amount of water to the mixed solution, continue stirring to ensure that all components are fully mixed; filter through filter paper or a filter to remove possible solid impurities to obtain a coolant.

[0018] Furthermore, in S4, the tempering equipment is a tempering heating furnace, the tempering temperature is 550±10°C, and the heating time is not less than 6h.

[0019] In a second aspect, the present invention provides a seamless steel pipe produced by the above-mentioned preparation method.

[0020] This application has the following beneficial effects:

[0021] 1. The present invention adopts high silicon content (0.50-0.55%). Silicon can react with oxygen in steel to generate stable silicate compounds, thereby removing oxygen in steel. This process can improve the purity of steel and reduce the generation of defects such as pores and inclusions. Silicon atoms can be dissolved in ferrite to produce solid solution strengthening. At the same time, silicon can also promote the formation of carbides, thereby improving the quality of steel (tensile strength and wear resistance).

[0022] In addition, the homemade coolant of the present invention is used to spray the rough pipe inside and outside, and the external spray flow rate is greater than the internal spray flow rate, forming an internal and external flow rate difference. On the one hand, the use of the coolant that forms the flow rate difference can more effectively remove defects such as powdering, pressing, and spots on the steel surface caused by high-temperature oxidation; on the other hand, the coolant uses the removal of sufficient oxide scale induced by high-content silicon as the treatment basis, which can achieve better surface treatment effects and is more conducive to improving the surface finish of the product and improving the surface quality.

[0023] 2. In the preparation of the coolant of the present invention, phosphate has the ability to soften and peel off oxide scale, and can react with iron oxide to form iron phosphate that is easily soluble in water, thereby removing oxide scale and improving surface finish. Phosphate can also form a protective film on the surface of the steel pipe to isolate air and moisture and reduce further oxidation; the iron ion chelating agent can combine with the iron ions in the iron oxide to form a stable water-soluble complex, thereby removing the oxide scale, and its effect on the steel itself is relatively weak, and it will not cause damage to the steel pipe substrate. It can remove the surface oxide scale without damaging the substrate and improve the surface finish; citric acid has a good metal cleaning effect and can effectively remove the oxide scale on the surface of the steel pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 , a comparative trend chart of wear loss quality test data of products obtained in Examples 1-5 of the present invention and Comparative Examples 1-11;

[0025] Figure 2 , a comparative trend chart of tensile strength test data of products obtained in Examples 1-5 of the present invention and Comparative Examples 1-11;

[0026] Figure 3 , a comparative trend chart of the surface roughness test data of the products obtained in Examples 1-5 of the present invention and Comparative Examples 1-11. DETAILED DESCRIPTION

[0027] The present application is further described in detail below with reference to the embodiments.

[0028] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0029] Example 1: (1) Prepare a coolant as follows: According to the mass percentage, accurately weigh 2.2% sodium tripolyphosphate, 1.6% disodium ethylenediaminetetraacetic acid, 3.7% citric acid and 92.5% water. Add 50% of the amount of water into the agitator, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, and use the agitator to stir at a speed of 130r / min for 20min to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5min to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0030] Among them, sodium tripolyphosphate (industrial grade) was purchased from Putian Jiahuang Chemical Co., Ltd. Disodium ethylenediaminetetraacetic acid was purchased from Changzhou Tianheng Industry and Trade Co., Ltd. Citric acid was citric acid monohydrate, purchased from Suzhou Zhuosheng Environmental Protection Technology Co., Ltd.

[0031] (2) A method for preparing a seamless steel pipe, comprising the following steps:

[0032] S1. Use solid pipe as steel billet, the composition of which includes C: 0.21%, Si: 0.52%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched, and the through hole diameter is 90mm to obtain a tube billet. In the continuous casting process of the steel billet in this step, the billet drawing speed is controlled at 0.75m / min, and the superheat is controlled at 22°C. If the superheat exceeds 40°C, continuous casting will no longer be performed.

[0033] S2. Send the tube blank into the annular furnace, heat it to 1270℃, soak it for 28min, and then perform periodic tube rolling to form a rough tube, with the final rolling temperature of 870℃. Periodic tube rolling can be based on the deformation characteristics of forging, rolling and extrusion. The high-temperature metal is always in a three-dimensional compressive stress state during the rolling deformation process, which is conducive to suppressing the cracks of the deformed metal, improving the comprehensive performance of the steel pipe, and making the rolled steel pipe have a better organizational structure than other rolling methods.

[0034] S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m 3 / h, internal spray flow rate is 1500m 3 / h.

[0035] S4. Use a conventional tempering heating furnace to perform tempering heating treatment, the tempering temperature is 550°C, and the heating time is 6 hours. Then straighten and air cool (both are existing technologies and will not be described in detail) to obtain a seamless steel pipe.

[0036] Example 2: The difference between this example and Example 1 is that: (1) Prepare a coolant, and the preparation method is as follows: According to the mass percentage, accurately weigh 2% sodium tripolyphosphate, 1.5% disodium ethylenediaminetetraacetic acid, 3.5% citric acid and 93% water. Add 40% of the amount of water to the container, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, use a stirrer to stir at a speed of 130r / min for 20min, ensure that each chemical substance is completely dissolved and mixed evenly, and obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5min to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0037] Example 3: The difference between this example and Example 1 is that: (1) Prepare a coolant, and the preparation method is as follows: According to the mass percentage, accurately weigh 2.4% of sodium tripolyphosphate, 1.8% of disodium ethylenediaminetetraacetic acid, 4% of citric acid and 91.8% of water. Add 60% of the amount of water to the container, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, use a stirrer to stir at a speed of 130r / min for 20min, ensure that each chemical substance is completely dissolved and mixed evenly, and obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5min, ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0038] Embodiment 4: The difference between this embodiment and embodiment 1 is that: (2) a method for preparing a seamless steel pipe comprises the following steps:

[0039] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.2%, Si: 0.5%, Mn: 0.87%, Mo: 0.04%, Cr: 0.18%, Ni: 0.05%, Ti: 0.008%, rare earth elements: 0.01%, P: 0.012%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is punched to obtain a tube billet.

[0040] S2. The tube billet is sent into a ring furnace, heated to 1260°C, and uniformly heated for 25 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 860°C.

[0041] S3, cooling the rotating pipe by spraying coolant inside and outside. The rotating pipe includes a rotating speed of 20r / min and a forward speed of 3m / min. The external spray flow rate is 2600m 3 / h, internal spray flow rate is 1450m 3 / h.

[0042] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0043] Embodiment 5: The difference between this embodiment and embodiment 1 is that: (2) a method for preparing a seamless steel pipe comprises the following steps:

[0044] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.23%, Si: 0.55%, Mn: 0.92%, Mo: 0.06%, Cr: 0.22%, Ni: 0.08%, Ti: 0.012%, rare earth elements: 0.015%, P: 0.013%, S: 0.005%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is punched to obtain a tube billet.

[0045] S2. Send the tube blank into the annular furnace, heat it to 1280℃, soak it for 30min, and then perform periodic tube rolling to form a rough tube, with the final rolling temperature being 880℃.

[0046] S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside. The rotating and advancing includes a rotating speed of 30r / min and a forward speed of 4m / min. The external spraying flow rate is 2800m 3 / h, internal spray flow rate is 1600m 3 / h.

[0047] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 560℃, and the heating time is 6h. Straightening and air cooling are performed to obtain seamless steel pipes.

[0048] Comparative Example 1: The difference between this comparative example and Example 1 is that the high-content silicon is replaced by the low-content silicon, that is, Si: 0.52% is replaced by Si: 0.32; and the coolant is replaced by water.

[0049] Specifically, a method for preparing a seamless steel pipe comprises the following steps:

[0050] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.21%, Si: 0.32%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched to obtain a tube billet.

[0051] S2. The tube billet is sent into a ring furnace, heated to 1270°C, and uniformly heated for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 870°C.

[0052] S3, use internal and external spraying water to cool the rotating and advancing waste pipe. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m 3 / h, internal spray flow rate is 1500m 3 / h.

[0053] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0054] Comparative Example 2: The difference between this comparative example and Example 1 is that the high-content silicon is replaced by the low-content silicon, that is, Si: 0.52% is replaced by Si: 0.25; and the coolant is replaced by water.

[0055] Specifically, a method for preparing a seamless steel pipe comprises the following steps:

[0056] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.21%, Si: 0.25%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched to obtain a tube billet.

[0057] S2. The tube billet is sent into a ring furnace, heated to 1270°C, and uniformly heated for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 870°C.

[0058] S3, use internal and external spraying water to cool the rotating and advancing waste pipe. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m3 / h, internal spray flow rate is 1500m 3 / h.

[0059] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0060] Comparative Example 3: The difference between this comparative example and Example 1 is that the high-content silicon is replaced by the low-content silicon, that is, Si: 0.52% is replaced by Si: 0.32.

[0061] Specifically, a method for preparing a seamless steel pipe comprises the following steps:

[0062] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.21%, Si: 0.32%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched to obtain a tube billet.

[0063] S2. The tube billet is sent into a ring furnace, heated to 1270°C, and uniformly heated for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 870°C.

[0064] S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m 3 / h, internal spray flow rate is 1500m 3 / h.

[0065] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0066] Comparative Example 4: The difference between this comparative example and Example 1 is that the high-content silicon is replaced by the low-content silicon, that is, Si: 0.52% is replaced by Si: 0.25.

[0067] Specifically, a method for preparing a seamless steel pipe comprises the following steps:

[0068] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.21%, Si: 0.25%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched to obtain a tube billet.

[0069] S2. The tube billet is sent into a ring furnace, heated to 1270°C, and uniformly heated for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 870°C.

[0070] S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m 3 / h, internal spray flow rate is 1500m 3 / h.

[0071] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0072] Comparative Example 5: The difference between this comparative example and Example 1 is that the coolant is replaced by water.

[0073] Specifically, a method for preparing a seamless steel pipe comprises the following steps:

[0074] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.21%, Si: 0.52%, Mn: 0.89%, Mo: 0.05%, Cr: 0.2%, Ni: 0.07%, Ti: 0.01%, rare earth elements: 0.012%, P: 0.01%, S: 0.006%, and the rest is Fe and unavoidable impurities. Among them, the rare earth elements include lanthanum (La) and cerium (Ce), and the mass ratio of the two is 1:1. The steel billet is centrally punched to obtain a tube billet.

[0075] S2. The tube billet is sent into a ring furnace, heated to 1270°C, and uniformly heated for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with a final rolling temperature of 870°C.

[0076] S3, use internal and external spraying water to cool the rotating and advancing waste pipe. The rotating and advancing includes a rotating speed of 25r / min and a forward speed of 3.5m / min. The external spraying flow rate is 2700m 3 / h, internal spray flow rate is 1500m 3 / h.

[0077] S4. Use a tempering heating furnace for tempering heating treatment, the tempering temperature is 550℃, and the heating time is 6h. Then straighten and air cool to obtain a seamless steel pipe.

[0078] Comparative Example 6: The difference between this comparative example and Example 1 is that in the preparation of the coolant, disodium ethylenediaminetetraacetate is replaced by citric acid.

[0079] Specifically, (1) prepare a coolant, and the preparation method is as follows: accurately weigh 2.2% sodium tripolyphosphate, 5.3% citric acid and 92.5% water according to mass percentage. Add 50% of the amount of water into the blender, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, and use the blender to stir at a speed of 130r / min for 20 minutes to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5 minutes to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0080] Comparative Example 7: The difference between this comparative example and Example 1 is that in the preparation of the coolant, sodium tripolyphosphate is replaced by citric acid.

[0081] Specifically, (1) prepare a coolant, and the preparation method is as follows: according to the mass percentage, accurately weigh 1.6% of disodium ethylenediaminetetraacetate, 5.9% of citric acid and 92.5% of water. Add 50% of the amount of water into the blender, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetate and citric acid in turn, and use the blender to stir at a speed of 130r / min for 20 minutes to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5 minutes to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0082] Comparative Example 8: The difference between this comparative example and Example 1 is that in the preparation of the coolant, disodium ethylenediaminetetraacetate and sodium tripolyphosphate are replaced by citric acid.

[0083] Specifically, (1) prepare a coolant, and the preparation method is as follows: accurately weigh 7.5% citric acid and 92.5% water according to the mass percentage. Add 50% of the amount of water into the blender, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, and use the blender to stir at a speed of 130r / min for 20 minutes to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5 minutes to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0084] Comparative Example 9: The difference between this comparative example and Example 1 is that in the preparation of the coolant, disodium ethylenediaminetetraacetate is replaced by sodium tripolyphosphate.

[0085] Specifically, (1) prepare a coolant, and the preparation method is as follows: accurately weigh 3.8% sodium tripolyphosphate, 3.7% citric acid and 92.5% water according to mass percentage. Add 50% of the amount of water into the blender, and then add the weighed sodium tripolyphosphate, disodium ethylenediaminetetraacetic acid and citric acid in turn, and use the blender to stir at a speed of 130r / min for 20 minutes to ensure that each chemical substance is completely dissolved and mixed evenly to obtain a mixed solution. Add the remaining amount of water to the mixed solution, and continue to stir at a speed of 130r / min for 5 minutes to ensure that all components are fully mixed. Use a filter to filter to remove possible solid impurities to obtain a coolant.

[0086] Comparative Example 10: The difference between this comparative example and Example 1 is that the external spray flow rate is equal to the internal spray flow rate, and both are 1500m 3 / h.

[0087] Comparative Example 11: The difference between this comparative example and Example 1 is that the external spray flow rate is equal to the internal spray flow rate, and both are 2700m 3 / h.

[0088] Test example: Test object: Products obtained in Examples 1-5 and Comparative Examples 1-11.

[0089] Test items: 1. Wear resistance; 2. Tensile strength; 3. Surface quality.

[0090] Test basis: 1. Wear resistance - wear test conditions: On the wear tester, set the disc speed to 400r / min, the maximum torque to 14N·m, test for 20min, and test the wear loss mass; the smaller the wear loss mass, the better the wear resistance.

[0091] 2. Tensile strength: refer to GB / T228.1 "Tensile test of metallic materials Part 1: Room temperature test method" for tensile strength test.

[0092] 3. Surface quality: Test surface roughness-GB / T 1031-2009. The smaller the value, the better the surface finish and the higher the surface quality.

[0093] Test results: See Table 1.

[0094] Table 1. Test data of the experimental example

[0095] Wear loss mass / g Tensile strength / MPa Surface roughness Ra / μm Example 1 0.019 805 3.19 Example 2 0.018 793 3.14 Example 3 0.017 811 3.14 Example 4 0.017 802 3.16 Example 5 0.020 795 3.21 Comparative Example 1 0.024 764 3.45 Comparative Example 2 0.027 749 3.16 Comparative Example 3 0.023 769 3.86 Comparative Example 4 0.028 752 3.68 Comparative Example 5 0.019 801 4.47 Comparative Example 6 0.019 801 3.45 Comparative Example 7 0.019 803 3.58 Comparative Example 8 0.020 798 4.21 Comparative Example 9 0.019 807 3.41 Comparative Example 10 0.021 791 3.59 Comparative Example 11 0.017 813 3.51

[0096] Result analysis: Analyze examples 1-5 and combine the data in Table 1 and Figure 1-3 It can be seen that the wear loss mass of the product obtained by the present invention is as low as less than 0.02g, the tensile strength is as high as more than 793MPa, and the surface roughness Ra is as low as less than 3.21μm, indicating that the products obtained in Examples 1-5 of the present invention have good wear resistance, high tensile strength and excellent surface quality.

[0097] Analyze Example 1 and Comparative Examples 1-5 and combine the data in Table 1 and Figure 1-3 It can be seen that when the silicon content is high (Si: 0.52%), the wear resistance and tensile strength of the product are significantly better than those of the low silicon content (Si: 0.32%, 0.25%). Moreover, when the silicon content is high (Si: 0.52%), replacing the water used for cooling with the coolant of the present invention can significantly reduce the surface roughness of the product, that is, improve the surface finish and improve the surface quality. When the silicon content is low (Si: 0.32%, 0.25%), replacing the water used for cooling with the coolant of the present invention will cause the surface roughness of the product to increase instead of decrease, that is, cause the surface finish to decrease, resulting in poor surface quality. The inventor believes that this is because when the silicon content is low, the oxide scale on the surface of the steel is less or non-existent. Due to the lack of sufficient oxide scale removal targets, the chemical components in the coolant do not have enough iron oxide to react with it to form soluble compounds or complexes, causing these chemical components to directly react with the surface of the steel, resulting in increased surface roughness and decreased surface finish.

[0098] Analyze Example 1 and Comparative Examples 5-9 and combine the data in Table 1 and Figure 1-3 It can be seen that the high silicon content (Si: 0.52%) ensures excellent tensile strength and wear resistance of the product. In the preparation of the coolant used for cooling, under the premise of the presence of citric acid, the participation of disodium ethylenediaminetetraacetic acid and sodium tripolyphosphate can significantly reduce the surface roughness of the product, and there is a synergistic effect between the two.

[0099] Analyze Example 1 and Comparative Examples 10-11 and combine the data in Table 1 and Figure 1-3It can be seen that the high content of silicon (Si: 0.52%) ensures that the tensile strength and wear resistance of the product are excellent. When the cooling liquid is sprayed inside and outside, (Comparative Example 10) the external spray flow rate is equal to the internal spray flow rate and is 1500m 3 / h, that is, the internal and external spray cooling is carried out at the same speed and the cooling speed is reduced. As a result, the wear resistance and tensile strength of the product are slightly reduced, while the surface roughness is significantly increased. (Comparative Example 11) The external spray flow rate is equal to the internal spray flow rate and is 2700m 3 / h, that is, the internal and external spray cooling is carried out at the same speed and the cooling speed is increased. As a result, the wear resistance and tensile strength of the product are slightly improved, and the surface roughness is significantly increased. This shows that when the coolant of the present invention is combined with the internal and external spray cooling, a certain flow difference is formed between the external spray flow rate and the internal spray zero flow rate, that is, a certain speed difference is formed between the external surface cooling speed and the internal surface cooling speed, which is more conducive to reducing the surface roughness of the product and improving the surface finish and surface quality of the product.

[0100] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0101] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a seamless steel pipe, characterized in that: The steps include: S1. A solid tube is used as a steel billet, wherein the composition thereof includes, by mass percentage, C: 0.20-0.23%, Si: 0.50-0.55%, Mn: 0.87-0.92%, Mo: 0.04-0.06%, Cr: 0.18-0.22%, Ni: 0.05-0.08%, Ti: 0.008-0.012%, rare earth elements: 0.01-0.015%, P≤0.016%, S≤0.007%, and the rest is Fe and unavoidable impurities; and the steel billet is punched to obtain a tube billet; S2, heat the tube blank at 1260-1280℃ for 25-30min, then perform periodic tube rolling to form a rough tube, and control the final rolling temperature at 870±10℃; S3, cooling the rotating and advancing waste pipe by spraying coolant inside and outside, with the external spray flow rate being 1.6-2 times the internal spray flow rate; S4, finally tempering, straightening and air cooling are performed to obtain a seamless steel pipe; The components of the coolant include 2-2.4% of phosphate, 1.5-1.8% of iron ion chelating agent, 3.5-4% of citric acid and the balance of water in terms of mass percentage.

2. The method for preparing a seamless steel pipe according to claim 1, characterized in that: The rare earth elements include La and Ce, and the mass ratio of the two is 1:

1.

3. The method for preparing a seamless steel pipe according to claim 1, characterized in that: In S3, the rotational advancement includes a rotational speed of 20-30 r / min and an advancement speed of 3-4 m / min.

4. The method for preparing a seamless steel pipe according to claim 1 or 3, characterized in that: In S3, the external spray flow rate is 2600-2800m 3 / h, internal spray flow rate is 1450-1600m 3 / h.

5. The method for preparing a seamless steel pipe according to claim 1, characterized in that: The phosphate includes sodium tripolyphosphate and / or sodium hexametaphosphate.

6. The method for preparing a seamless steel pipe according to claim 1, characterized in that: The iron ion chelating agent is disodium ethylenediaminetetraacetate.

7. The method for preparing a seamless steel pipe according to claim 1, 5 or 6, characterized in that: The preparation method of the coolant is as follows: accurately weighing phosphate, iron ion chelating agent, citric acid and water according to mass percentage; adding 40-60% of water into a container, and then adding the weighed phosphate, iron ion chelating agent and citric acid in sequence, stirring and mixing to obtain a mixed solution; adding the remaining amount of water into the mixed solution, continuing to stir, filtering, and obtaining the coolant.

8. The method for preparing a seamless steel pipe according to claim 1, characterized in that: In S4, the tempering equipment is a tempering heating furnace, the tempering temperature is 550±10℃, and the heating time is not less than 6h.

9. A seamless steel pipe, characterized in that: The method is prepared according to any one of claims 1 to 8.

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