Seamless steel tube suitable for low-temperature environment and preparation method thereof

Abstract

The invention provides a seamless steel pipe suitable for a low-temperature environment and a preparation method thereof, and belongs to the technical field of seamless steel pipes, the preparation method comprises the following steps: S1, taking a solid pipe as a steel billet, and punching the steel billet to obtain a pipe billet; s2, the pipe blank is evenly heated for 25-30 min at 1220-1260 DEG C, and then a pierced billet is formed through periodic pipe rolling; and S3, the pierced billet is immersed in quenching liquid with the temperature of 20 + / -5 DEG C, quenching treatment is conducted for 55 + / -5 s, then the pierced billet is conveyed into a tempering furnace for tempering treatment, the pierced billet is discharged out of the furnace and air-cooled to the room temperature, and the seamless steel tube suitable for the low-temperature environment is obtained. The quenching liquid is prepared from the following components in parts by weight: 5 to 8 parts of sodium chloride-nano silicon carbide powder, 2.5 to 3 parts of activated polyvinyl alcohol liquid, 2.5 to 3.2 parts of antioxidant, 0.6 to 0.9 part of antirust agent and 82 to 90 parts of water. The hardness of the seamless steel tube is enhanced, and the impact resistance of the seamless steel tube in a low-temperature environment is improved.

Description

Technical Field

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

[0002] Seamless steel pipe is a steel pipe made by punching a whole round steel bar without welds on the surface. The production process of seamless steel pipe includes multiple steps, such as tube blank preparation and inspection, tube blank heating, perforation, tube rolling, tube reheating, sizing, heat treatment, straightening, inspection, etc. Among them, quenching liquid is used in the heat treatment process, especially after the steel pipe is reheated, the purpose is to change the microstructure of the steel pipe through rapid cooling, thereby improving its hardness and strength, but it may also affect its toughness and impact resistance.

[0003] In existing quenching liquids, sodium chloride can increase the cooling rate of the quenching liquid in the high temperature zone. Through rapid cooling, the austenite phase in the steel is transformed into the martensite phase, thereby increasing the hardness and strength of the steel. However, at the same time, due to the increased cooling rate in the high temperature zone, it will lead to the accumulation of internal stress in the steel and increase the inhomogeneity of the structure, thereby increasing the brittleness of the steel. This brittleness is particularly obvious in low temperature environments, which will further reduce the toughness of the steel, reduce the impact resistance of the steel, and make the steel more susceptible to fracture or damage. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the present invention provides a seamless steel pipe suitable for low temperature environment and a preparation method thereof, which can enhance the hardness of the seamless steel pipe while improving its impact strength in low temperature environment.

[0005] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a method for preparing a seamless steel pipe suitable for a low temperature environment, comprising the following steps:

[0006] S1. A solid tube is used as a steel billet, wherein the composition thereof includes, by mass percentage, C: 0.21-0.23%, Si: 0.48-0.53%, Mn: 0.86-0.92%, V: 0.05-0.07%, Cr: 0.21-0.25%, Ti: 0.007-0.01%, Ni: 0.05-0.08%, P≤0.015%, S≤0.008%, and the rest is Fe and unavoidable impurities; and the steel billet is punched to obtain a tube billet;

[0007] S2, the tube blank obtained in S1 is heated at 1220-1260°C for 25-30 minutes, and then subjected to periodic tube rolling to form a rough tube, and the final rolling temperature is controlled at 850±10°C;

[0008] S3, immerse the rough pipe obtained in S2 in a quenching liquid with a temperature of 20±5℃, quench for 55±5s, and then transport it to a tempering furnace for tempering. After the tempering is completed, take it out of the furnace and air cool it to room temperature to obtain a seamless steel pipe suitable for a low temperature environment;

[0009] The quenching liquid comprises the following components by weight: 5-8 parts of sodium chloride-nano silicon carbide powder, 2.5-3 parts of activated polyvinyl alcohol liquid, 2.5-3.2 parts of antioxidant, 0.6-0.9 parts of rust inhibitor and 82-90 parts of water.

[0010] Furthermore, the preparation method of the sodium chloride-nano silicon carbide powder is as follows:

[0011] A1. By weight, 3-4 parts of anhydrous glucose, 2-3 parts of silicon dioxide and 4-5 parts of sodium chloride were put into a nylon ball mill, agate balls were added, and the mixture was ball milled at a speed of 200-300 r / min for 2-3 hours on a planetary ball mill to obtain a mixed material;

[0012] A2. Put the mixture obtained in A1 into a graphite crucible, and place it in a high-temperature furnace. Under an argon atmosphere, heat it to 1500-1700°C, keep it warm for 1.5-2.5 hours, and then cool it to room temperature with the furnace to obtain sodium chloride-nano silicon carbide powder.

[0013] Furthermore, in A1, the particle size of silicon dioxide is 200-300 mesh.

[0014] Further, in A2, the temperature is increased at a rate of 8-10°C / min.

[0015] Furthermore, the preparation method of the activated polyvinyl alcohol liquid is as follows: add 100 parts of water by weight to the agitator, start stirring, the stirring speed is 90-100r / min, then add 35-40 parts of polyvinyl alcohol, continue stirring for 20-30 minutes, heat to 85-90°C, keep warm for 3-5 minutes, then add 1-1.5 parts of sodium dodecyl sulfate, continue stirring for 8-10 minutes, and cool to room temperature to obtain the activated polyvinyl alcohol liquid.

[0016] Furthermore, the preparation method of the quenching liquid is as follows: according to weight parts, activated polyvinyl alcohol liquid, antioxidant and rust inhibitor are added into water, stirred at a stirring speed of 350-400r / min for 25-30min, then the stirring speed is reduced to 150-180r / min, and then sodium chloride-nano silicon carbide powder is added, and stirring is continued for 7-10min to obtain the quenching liquid.

[0017] Furthermore, in S3, the specific operation of the tempering treatment is: firstly heating to 600-630°C, keeping the temperature for 35±5min, then cooling to 380-410°C, keeping the temperature for 25±5min.

[0018] Furthermore, the antioxidant includes tert-butylhydroquinone and ethanol, and the mass ratio of the two is (2-3):9.

[0019] Furthermore, the rust inhibitor is boric acid.

[0020] In a second aspect, the present invention provides a seamless steel pipe suitable for low temperature environments, which is produced by the above-mentioned preparation method.

[0021] This application has the following beneficial effects:

[0022] 1. In the quenching liquid used in the preparation process of the seamless steel pipe suitable for low-temperature environment of the present invention, activated polyvinyl alcohol liquid is added, and sodium chloride is prepared into sodium chloride-nano silicon carbide powder and then added, which can not only improve the hardness of the product, but also work synergistically, synergistically improve the impact resistance of the product at room temperature and low temperature, and synergistically reduce the impact absorption energy reduction rate of the product in a low-temperature environment, so as to ensure that the product of the present invention is more suitable for use in a low-temperature environment.

[0023] 2. The present invention prepares sodium chloride into sodium chloride-nano silicon carbide powder for use, and slows down the release rate of sodium chloride in the quenching liquid to achieve the slow release of sodium chloride. On the one hand, sodium chloride can play a role continuously and stably in the quenching process, ensuring that the hardness improvement effect of the obtained product will not be significantly reduced; on the other hand, it helps to control the cooling rate in the quenching process, avoid excessive internal stress and structural inhomogeneity caused by too fast and uneven cooling, thereby weakening the negative impact on the impact resistance and even improving the impact resistance.

[0024] The invention prepares polyvinyl alcohol into activated polyvinyl alcohol liquid for use, thereby improving surface activity and optimizing film-forming effect, thereby further improving the impact resistance of the obtained product; if sodium chloride is directly added, it will first excessively / concentratedly adhere to the surface of the hot quenching part in the quenching liquid, produce gas at high temperature and cause impact and damage, affecting the film-forming stability and integrity of the activated polyvinyl alcohol liquid during the quenching process, resulting in the weakening of the effect of improving the impact resistance; while the addition of sodium chloride-nano silicon carbide powder can play the role of slow release of sodium chloride, thereby improving the hardness of the obtained product and synergizing with the activated polyvinyl alcohol liquid, not only without destroying the film-forming effect, but also uniformly improving the cooling speed, promoting the rapid formation and stability of the protective film on the surface of the quenching part, thereby better playing the protective role and synergistically improving the impact resistance of the obtained product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , a comparative trend chart of hardness test data of products obtained from Examples 1 to 9 of the present invention and Comparative Examples 1 to 5;

[0026] Figure 2 , a comparative trend chart of the impact absorption energy test data of the products obtained in Examples 1 to 9 of the present invention and Comparative Examples 1 to 5 at room temperature (25° C.) and at low temperature (-70° C.);

[0027] Figure 3 , a comparative trend chart of the impact absorption energy reduction rate of the products obtained in Examples 1 to 9 of the present invention and Comparative Examples 1 to 5 at low temperature (-70°C) compared to that at room temperature (25°C). DETAILED DESCRIPTION

[0028] The present application is further described in detail below with reference to the embodiments.

[0029] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0030] Example 1: (1) Preparation of sodium chloride-nano silicon carbide powder, the preparation method is as follows:

[0031] A1. By weight, 3.5 parts of anhydrous glucose, 2.5 parts of silicon dioxide and 4.5 parts of sodium chloride were put into a nylon ball mill, agate balls were added, and the mixture was ball milled at a speed of 250 r / min for 2.5 h on a planetary ball mill to obtain a mixed material.

[0032] Among them, anhydrous glucose (superior grade, density 1.56g / cm 3 ) was purchased from Guangzhou Guangjia Chemical Co., Ltd. Silicon dioxide (300 mesh) was purchased from Guangzhou Yingke Chemical Technology Co., Ltd. Sodium chloride (industrial grade, 100 mesh) was purchased from Weifang Chengyang Chemical Co., Ltd.

[0033] A2. Put the mixture obtained in A1 into a graphite crucible and place it in a high-temperature furnace. Under an argon atmosphere, heat it to 1600°C at a rate of 9°C / min, keep it warm for 2 hours, and then cool it to room temperature with the furnace to obtain sodium chloride-nano silicon carbide powder.

[0034] (2) Prepare activated polyvinyl alcohol liquid, the preparation method of which is as follows: add 100 parts of water by weight into a stirrer, start stirring at a stirring speed of 95 r / min, then add 38 parts of polyvinyl alcohol, continue stirring for 25 minutes, raise the temperature to 88°C, keep warm for 4 minutes, then add 1.2 parts of sodium dodecyl sulfate, continue stirring for 9 minutes, and cool to room temperature to obtain activated polyvinyl alcohol liquid.

[0035] Among them, polyvinyl alcohol (PVA-203, content ≥99%, brand KURARAY) was purchased from Guangzhou Kuraina New Materials Co., Ltd. Sodium dodecyl sulfate (K12) was purchased from Jinan Runhui Chemical Co., Ltd.

[0036] (3) An antioxidant is prepared by mixing tert-butyl hydroquinone and ethanol in a mass ratio of 2:9, and stirring at a constant speed of 220 r / min for 20 minutes to obtain an antioxidant. Tert-butyl hydroquinone has a low solubility in water. By mixing with ethanol, the dispersibility and uniformity of tert-butyl hydroquinone in the solution can be improved, which helps it to play a better role in subsequent applications.

[0037] Among them, tertiary butylhydroquinone (TBHQ) was purchased from Yancheng Hengyuyuan Chemical Products Co., Ltd. Ethanol was purchased from Jinan Century Tongda Chemical Co., Ltd.

[0038] (4) preparing a quenching liquid, wherein the preparation method is as follows: by weight, 2.7 parts of activated polyvinyl alcohol liquid, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added into 86 parts of water, and the mixture is stirred at a stirring speed of 360 r / min for 28 minutes, and then the stirring speed is reduced to 170 r / min, and then 6 parts of sodium chloride-nano silicon carbide powder are added, and stirring is continued for 8 minutes to obtain a quenching liquid.

[0039] The sodium chloride-nano silicon carbide powder, activated polyvinyl alcohol solution and antioxidant are prepared from (1), (2) and (3) above, respectively. Boric acid is used as the rust inhibitor, which plays a certain role in slowing down or preventing the metal oxidation process in the quenching liquid. It is purchased from Jinan Xinjinshuo New Materials Co., Ltd.

[0040] (5) A method for preparing a seamless steel pipe suitable for a low temperature environment, comprising the following steps:

[0041] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.22%, Si: 0.5%, Mn: 0.88%, V: 0.06%, Cr: 0.23%, Ti: 0.009%, Ni: 0.07%, P: 0.01%, S: 0.005%, and the rest is Fe and unavoidable impurities. The steel billet is punched, and the through hole diameter is 80 mm to obtain a tube billet.

[0042] S2. The tube blank obtained in S1 is sent into a ring furnace, heated at 1240°C for 28 minutes, and then subjected to periodic tube rolling to form a rough tube, with the final rolling temperature being 852°C.

[0043] S3. Immerse the rough pipe obtained in S2 in a quenching liquid with a temperature of 20°C. After quenching for 55 seconds, transport it to a tempering furnace for tempering. The specific operation of the tempering treatment is to first heat it to 610°C, keep it warm for 35 minutes, then cool it to 390°C and keep it warm for 25 minutes. After the tempering is completed, take it out of the furnace and air-cool it to room temperature to obtain a seamless steel pipe suitable for low-temperature environment.

[0044] Example 2: The difference between this example and Example 1 is that: (1) sodium chloride-nano silicon carbide powder is prepared, and the preparation method thereof is as follows:

[0045] A1. Put 3 parts of anhydrous glucose, 2 parts of silicon dioxide and 4 parts of sodium chloride into a nylon ball mill by weight, add agate balls, and mill on a planetary ball mill at a speed of 200 r / min for 2 h to obtain a mixed material.

[0046] A2. Put the mixture obtained in A1 into a graphite crucible and place it in a high-temperature furnace. Under an argon atmosphere, heat it to 1500°C at a rate of 8°C / min, keep it warm for 1.5 hours, and then cool it to room temperature with the furnace to obtain sodium chloride-nano silicon carbide powder.

[0047] Example 3: The difference between this example and Example 1 is that: (1) sodium chloride-nano silicon carbide powder is prepared, and the preparation method thereof is as follows:

[0048] A1. Put 4 parts of anhydrous glucose, 3 parts of silicon dioxide and 5 parts of sodium chloride into a nylon ball mill by weight, add agate balls, and mill on a planetary ball mill at a speed of 300 r / min for 3 hours to obtain a mixture.

[0049] A2. Put the mixture obtained in A1 into a graphite crucible and place it in a high-temperature furnace. Under an argon atmosphere, heat it to 1700°C at a rate of 10°C / min, keep it warm for 2.5 hours, and then cool it to room temperature with the furnace to obtain sodium chloride-nano silicon carbide powder.

[0050] Example 4: The difference between this example and Example 1 is that: (2) Prepare activated polyvinyl alcohol liquid, and its preparation method is as follows: Add 100 parts of water by weight to the agitator, start stirring, the stirring speed is 90r / min, then add 35 parts of polyvinyl alcohol, continue stirring for 20 minutes, raise the temperature to 85°C, keep warm for 3 minutes, then add 1 part of sodium dodecyl sulfate, continue stirring for 8 minutes, and cool to room temperature to obtain activated polyvinyl alcohol liquid.

[0051] Example 5: The difference between this example and Example 1 is that: (2) Prepare activated polyvinyl alcohol liquid, and its preparation method is as follows: Add 100 parts of water by weight to the agitator, start stirring, the stirring speed is 100r / min, then add 40 parts of polyvinyl alcohol, continue stirring for 30 minutes, raise the temperature to 90°C, keep warm for 5 minutes, then add 1.5 parts of sodium dodecyl sulfate, continue stirring for 10 minutes, and cool to room temperature to obtain activated polyvinyl alcohol liquid.

[0052] Example 6: The difference between this example and Example 1 is that: (4) quenching liquid is prepared, and its preparation method is as follows: by weight, 2.5 parts of activated polyvinyl alcohol liquid, 2.5 parts of antioxidant and 0.6 parts of rust inhibitor are added to 82 parts of water, and stirred at a stirring speed of 350 r / min for 25 minutes, and then the stirring speed is reduced to 150 r / min, and then 5 parts of sodium chloride-nano silicon carbide powder are added, and stirring is continued for 7 minutes to obtain the quenching liquid.

[0053] Example 7: The difference between this example and Example 1 is that: (4) quenching liquid is prepared, and its preparation method is as follows: by weight, 3 parts of activated polyvinyl alcohol liquid, 3.2 parts of antioxidant and 0.9 parts of rust inhibitor are added to 90 parts of water, and stirred at a stirring speed of 400 r / min for 30 minutes, and then the stirring speed is reduced to 180 r / min, and then 8 parts of sodium chloride-nano silicon carbide powder are added, and stirring is continued for 10 minutes to obtain the quenching liquid.

[0054] Embodiment 8: The difference between this embodiment and embodiment 1 is that: (5) A method for preparing a seamless steel pipe suitable for a low temperature environment comprises the following steps:

[0055] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.22%, Si: 0.5%, Mn: 0.88%, V: 0.06%, Cr: 0.23%, Ti: 0.009%, Ni: 0.07%, P: 0.01%, S: 0.005%, and the rest is Fe and unavoidable impurities. The steel billet is punched, and the through hole diameter is 80 mm to obtain a tube billet.

[0056] S2. The tube blank obtained in S1 is sent into a ring furnace, heated at 1220°C for 25 minutes, and then subjected to periodic tube rolling to form a rough tube, with the final rolling temperature being 847°C.

[0057] S3. Immerse the rough pipe obtained in S2 in a quenching liquid with a temperature of 25°C. After quenching for 60 seconds, transport it to a tempering furnace for tempering. The specific operation of the tempering treatment is to first heat it to 630°C, keep it warm for 30 minutes, then cool it to 410°C, and keep it warm for 20 minutes. After the tempering is completed, take it out of the furnace and air-cool it to room temperature to obtain a seamless steel pipe suitable for low-temperature environment.

[0058] Embodiment 9: The difference between this embodiment and embodiment 1 is that: (5) A method for preparing a seamless steel pipe suitable for a low temperature environment comprises the following steps:

[0059] S1. A solid tube is used as a steel billet, and its composition by mass percentage includes C: 0.22%, Si: 0.5%, Mn: 0.88%, V: 0.06%, Cr: 0.23%, Ti: 0.009%, Ni: 0.07%, P: 0.01%, S: 0.005%, and the rest is Fe and unavoidable impurities. The steel billet is punched, and the through hole diameter is 80 mm to obtain a tube billet.

[0060] S2. The tube blank obtained in S1 is sent into a ring furnace, heated at 1260°C for 30 minutes, and then subjected to periodic tube rolling to form a rough tube, with the final rolling temperature being 859°C.

[0061] S3. Immerse the rough pipe obtained in S2 in a quenching liquid with a temperature of 15°C. After quenching for 50 seconds, transport it to a tempering furnace for tempering. The specific operation of the tempering treatment is to first heat it to 600°C, keep it warm for 40 minutes, then cool it to 380°C and keep it warm for 30 minutes. After the tempering is completed, take it out of the furnace and air-cool it to room temperature to obtain a seamless steel pipe suitable for low-temperature environment.

[0062] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the quenching liquid, the sodium chloride-nano silicon carbide powder and the activated polyvinyl alcohol liquid are deleted.

[0063] Specifically, a quenching liquid is prepared, and its preparation method is as follows: by weight, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added to 86 parts of water, and stirred at a stirring speed of 360 r / min for 28 minutes, and then the stirring speed is reduced to 170 r / min, and stirring is continued for 8 minutes to obtain a quenching liquid.

[0064] Comparative Example 2: The difference between this comparative example and Example 1 is that in the preparation of the quenching liquid, the activated polyvinyl alcohol liquid is deleted, and 6 parts of sodium chloride-nano silicon carbide powder are replaced by 2 parts of sodium chloride.

[0065] Specifically, a quenching liquid is prepared, and its preparation method is as follows: by weight, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added to 86 parts of water, and stirred at a stirring speed of 360 r / min for 28 minutes, and then the stirring speed is reduced to 170 r / min, and then 2 parts of sodium chloride are added, and stirring is continued for 8 minutes to obtain a quenching liquid.

[0066] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the quenching liquid, the activated polyvinyl alcohol liquid is deleted.

[0067] Specifically, a quenching liquid is prepared, and its preparation method is as follows: by weight, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added to 86 parts of water, and stirred at a stirring speed of 360 r / min for 28 minutes, and then the stirring speed is reduced to 170 r / min, and then 6 parts of sodium chloride-nano silicon carbide powder are added, and stirring is continued for 8 minutes to obtain a quenching liquid.

[0068] Comparative Example 4: The difference between this comparative example and Example 1 is that sodium chloride-nano silicon carbide powder is deleted in the preparation of the quenching liquid.

[0069] Specifically, a quenching liquid is prepared, and its preparation method is as follows: by weight, 2.7 parts of activated polyvinyl alcohol liquid, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added to 86 parts of water, and stirred at a stirring speed of 360 r / min for 28 minutes, then the stirring speed is reduced to 170 r / min, and stirring is continued for 8 minutes to obtain the quenching liquid.

[0070] Comparative Example 5: The difference between this comparative example and Example 1 is that in the preparation of the quenching liquid, 6 parts of sodium chloride-nano silicon carbide powder are replaced by 2 parts of sodium chloride.

[0071] Specifically, a quenching liquid is prepared, and its preparation method is as follows: by weight, 2.7 parts of activated polyvinyl alcohol liquid, 2.7 parts of antioxidant and 0.8 parts of rust inhibitor are added to 86 parts of water, and stirred at a stirring speed of 360 r / min for 28 minutes, then the stirring speed is reduced to 170 r / min, and then 2 parts of sodium chloride are added, and stirring is continued for 8 minutes to obtain a quenching liquid.

[0072] Test example: Test objects: Example 1-Example 9 and Comparative Example 1-Comparative Example 5.

[0073] Test items: 1. Hardness; 2. Impact resistance.

[0074] Test content: 1. Hardness test: measure Brinell hardness (HBW).

[0075] 2. Impact resistance test: refer to GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials" for impact energy test (impact absorption energy of V-notch specimen under 2mm pendulum blade);

[0076] ①At room temperature (25℃), impact absorption energy K 常温 ;

[0077] K 常温 The larger the value, the better the impact resistance of the product at room temperature;

[0078] ②At low temperature (-70℃), impact absorption energy K 低温 ;

[0079] K 低温 The larger it is, the more suitable the product is for use in low temperature environments;

[0080] ③Calculate the impact absorption energy reduction rate Δη=(K 常温 -K 低温 ) / K 常温 *100%;

[0081] The smaller Δη is, the more stable the product's impact resistance is, the less it is affected by cooling, and the better its low-temperature resistance is.

[0082] Test results: See Table 1.

[0083] Table 1. Test data of the experimental example

[0084]

[0085] Result analysis: Analyze Example 1-Example 9 and combine the data in Table 1 and Figure 1-Figure 3 It can be seen that the hardness of the product obtained by the present invention is as high as 247HBW or more, and the impact absorption energy at room temperature (25°C) is as high as 59.7J or more, and the small impact absorption energy at low temperature (-70°C) is as high as 56.9J or more. The impact absorption energy reduction rate at low temperature compared with that at room temperature is as low as 4.9% or less, indicating that the product obtained by the present invention has high hardness and excellent impact resistance at both room temperature and low temperature environments, and is suitable for use in low temperature environments.

[0086] Analyze Example 1 and Comparative Examples 1-5 and combine the data in Table 1 and Figure 1-Figure 3 By comparing Comparative Example 1 and Comparative Example 2, it can be seen that the addition of sodium chloride in the quenching liquid used in the preparation process of the product of the present invention (seamless steel pipe) can improve the hardness of the product, but at the same time, it will also lead to a decrease in the impact resistance of the product and an increase in the impact absorption energy reduction rate of the product in a low temperature environment.

[0087] From the comparison of Comparative Examples 1, 2 and 3, it can be seen that in the quenching liquid used in the preparation process of the product of the present invention, sodium chloride is prepared into sodium chloride-nano silicon carbide powder and then added, which can maintain the effect of improving the hardness of the obtained product. At the same time, the decline in the impact resistance of the obtained product can be significantly weakened, and the impact absorption energy decline rate of the obtained product in a low temperature environment can be reduced.

[0088] From the comparison between Comparative Example 1 and Comparative Example 4, it can be seen that the addition of activated polyvinyl alcohol liquid to the quenching liquid used in the preparation process of the product of the present invention can improve the impact resistance of the product, and at the same time, can also reduce the impact absorption energy decrease rate of the product in a low temperature environment.

[0089] From the comparison of Comparative Examples 1, 4 and 5, it can be seen that in the presence of activated polyvinyl alcohol solution in the quenching liquid used in the preparation process of the product of the present invention, adding sodium chloride can improve the hardness of the obtained product, but at the same time, it will also weaken the improvement of the impact resistance of the obtained product.

[0090] By comparing Comparative Examples 1, 4, 5 and Example 1, it can be seen that in the quenching liquid used in the preparation process of the product of the present invention, in the presence of activated polyvinyl alcohol solution, sodium chloride is prepared into sodium chloride-nano silicon carbide powder and then added, which can not only maintain the effect of improving the hardness of the product, but also work synergistically, synergistically improve the impact resistance of the product, and synergistically reduce the impact absorption energy decrease rate of the product in a low temperature environment, so as to ensure that the product of the present invention is more suitable for use in a low temperature environment.

[0091] 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.

[0092] 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 suitable for low temperature environment, 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: 0.21-0.23%, Si: 0.48-0.53%, Mn: 0.86-0.92%, V: 0.05-0.07%, Cr: 0.21-0.25%, Ti: 0.007-0.01%, Ni: 0.05-0.08%, P≤0.015%, S≤0.008%, and the rest is Fe and unavoidable impurities; and the steel billet is punched to obtain a tube billet; S2, the tube blank obtained in S1 is heated at 1220-1260°C for 25-30 minutes, and then subjected to periodic tube rolling to form a rough tube, and the final rolling temperature is controlled at 850±10°C; S3, immerse the rough pipe obtained in S2 in a quenching liquid with a temperature of 20±5°C, quench for 55±5s, and then transport it to a tempering furnace for tempering. After the tempering is completed, take it out of the furnace and air cool it to room temperature to obtain a seamless steel pipe suitable for a low temperature environment; The quenching liquid comprises the following components by weight: 5-8 parts of sodium chloride-nano silicon carbide powder, 2.5-3 parts of activated polyvinyl alcohol liquid, 2.5-3.2 parts of antioxidant, 0.6-0.9 parts of rust inhibitor and 82-90 parts of water.

2. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: The preparation method of the sodium chloride-nano silicon carbide powder is as follows: A1. Put 3-4 parts of anhydrous glucose, 2-3 parts of silicon dioxide and 4-5 parts of sodium chloride into a ball mill by weight, and mill at a speed of 200-300 r / min for 2-3 hours to obtain a mixture; A2. Place the mixture obtained in A1 in a high temperature furnace, heat it to 1500-1700°C under argon atmosphere, keep it warm for 1.5-2.5 hours, and then cool it to room temperature with the furnace to obtain sodium chloride-nano silicon carbide powder.

3. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 2, characterized in that: In A1, the particle size of silicon dioxide is 200-300 mesh.

4. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 2, characterized in that: In A2, the temperature was increased at a rate of 8-10°C / min.

5. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: The preparation method of the activated polyvinyl alcohol liquid is as follows: 100 parts of water are added to a stirrer by weight, stirring is started at a speed of 90-100 r / min, and then 35-40 parts of polyvinyl alcohol are added, stirring is continued for 20-30 minutes, the temperature is raised to 85-90° C., and the temperature is kept for 3-5 minutes, and then 1-1.5 parts of sodium dodecyl sulfate are added, stirring is continued for 8-10 minutes, and the activated polyvinyl alcohol liquid is obtained.

6. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: The preparation method of the quenching liquid is as follows: according to weight parts, activated polyvinyl alcohol liquid, antioxidant and rust inhibitor are added into water, stirred at a stirring speed of 350-400r / min for 25-30min, then the stirring speed is reduced to 150-180r / min, and then sodium chloride-nano silicon carbide powder is added, and stirring is continued for 7-10min to obtain the quenching liquid.

7. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: In S3, the specific operation of the tempering treatment is: firstly heat up to 600-630°C, keep warm for 35±5min, then cool down to 380-410°C, keep warm for 25±5min.

8. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: The antioxidant includes tert-butylhydroquinone and ethanol, and the mass ratio of the two is (2-3):

9.

9. The method for preparing a seamless steel pipe suitable for a low temperature environment according to claim 1, characterized in that: The rust inhibitor is boric acid.

10. A seamless steel pipe suitable for low temperature environment, characterized in that: The method is prepared according to any one of claims 1 to 9.

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