A heat exchange tube, a preparation method thereof, and an application in a lead-bismuth fast reactor

Abstract

The present invention relates to the technical field of metal processing, and provides a heat exchange tube, a preparation method thereof, and an application in a lead-bismuth fast reactor. By weight percentage, the heat exchange tube comprises C: 0.14 - 0.25%, Si: 1.0 - 2.0%, Mn: ≤1.0%, Cr: 10.0 - 12.0%, W: 1.0 - 2.0%, V: 0.15 - 0.30%, Ta: 0.10 - 0.20%, Ti: ≤0.01%, Al: ≤0.01%, P: ≤0.005%, S: ≤0.005%, Co: ≤0.01%, Ni: ≤0.01%, Cu: ≤0.01%, Mo: ≤0.005%, Nb: ≤0.005%, B: ≤0.002%, and the balance is Fe and inevitable impurities; the heat exchange tube has a high grain size and low inclusions, has excellent high-temperature strength, and meets the requirements of the heat exchange tube for a lead-bismuth fast reactor.

Description

Technical Field

[0001] The present invention relates to the technical field of metal processing, and particularly relates to a heat exchange tube, a preparation method thereof, and an application in a lead-bismuth fast reactor. Background Art

[0002] The lead-bismuth fast reactor has excellent fuel conversion ability, can effectively improve the utilization rate of uranium resources, and greatly improve the sustainability of fuel. It is one of the main reactor types of the fourth-generation nuclear energy system. The heat exchange tube used in the lead-bismuth fast reactor operates for a long period at high temperature, and requires the heat exchange tube to have high room temperature and high temperature strength, high fatigue strength, high creep strength, and good long-term aging tissue stability.

[0003] Compared with austenitic steel and low alloy steel, martensitic steel with high temperature resistance, radiation resistance and liquid metal corrosion resistance, such as SIMP steel, has more excellent comprehensive service performance and service safety in the liquid lead-bismuth environment, and is a more suitable candidate material for preparing the heat exchange tube of the lead-bismuth fast reactor. However, due to the characteristics of high strength and low toughness of martensitic steel, its processing difficulty is high and the processing technology is immature. Therefore, there is no report on the high heat transfer performance martensitic steel heat exchange tube that can support the fourth-generation lead-bismuth fast reactor. It is found that even if the processing technology suitable for austenitic steel and low alloy steel is used to prepare the martensitic steel heat exchange tube, the various indexes of the obtained heat exchange tube, such as high temperature structure and mechanical stability, high dimensional accuracy and surface quality, etc., are difficult to meet the performance requirements of the fourth-generation lead-bismuth fast reactor. Summary of the Invention

[0004] The present invention provides a heat exchange tube, a preparation method thereof, and an application in a lead-bismuth fast reactor to solve the defect that it is difficult to meet the performance requirements of the fourth-generation lead-bismuth fast reactor when preparing the martensitic steel heat exchange tube by using the method of the prior art. The present invention realizes a heat exchange tube with excellent comprehensive performance such as low non-metallic inclusion level, mechanical properties, high dimensional accuracy, surface quality, etc. by optimizing the preparation method of the heat exchange tube, especially improving the cold rolling and heat treatment processes, and it fully meets the performance requirements of the heat exchange tube for the lead-bismuth fast reactor.

[0005] Specifically, in the first aspect, the present invention provides a heat exchange tube. By weight percentage, its components include: C: 0.14~0.25%, Si: 1.0~2.0%, Mn: ≤1.0%, Cr: 10.0~12.0%, W: 1.0~2.0%, V: 0.15~0.30%, Ta: 0.10~0.20%, Ti: ≤0.01%, Al: ≤0.01%, P: ≤0.005%, S: ≤0.005%, Co: ≤0.01%, Ni: ≤0.01%, Cu: ≤0.01%, Mo: ≤0.005%, Nb: ≤0.005%, B: ≤0.002%, and the balance is Fe and inevitable impurities;

[0006] The grain size of the heat exchange tube is grade 7 - 10, the microstructure is martensite, and there is no δ-ferrite;

[0007] The inclusions in the heat exchange tube satisfy: AH ≤ 0.5, AT ≤ 0.5, BH ≤ 0.5, BT ≤ 0.5, CH ≤ 0.5, CT ≤ 0.5, CH0.5, CT ≤ 1.0.

[0008] The inevitable impurities in the present invention refer to P with a content ≤ 0.005% and S with a content ≤ 0.005%.

[0009] The heat exchange tube in the present invention contains alloy elements. Among them, the C content is controlled at 0.14 - 0.25%, the Si content is controlled at 1.0 - 2.0%, which can effectively increase the inoculant dosage and thus improve the swelling resistance; the Mn content is controlled below 1.0%, increasing the strength and hardness of the steel while suppressing the appearance of δ-ferrite; the Cr content is controlled at 10.0 - 12.0%, improving the corrosion resistance, oxidation resistance and high-temperature strength, and having excellent thermal stability and radiation resistance, etc.; the W content is controlled at 1.0 - 2.0%, improving the high-temperature strength and creep resistance of the steel without increasing the ductile-brittle transition temperature; the V content is controlled at 0.15 - 0.30%, improving the strength and wear resistance of the steel without causing a decrease in toughness; the Ta content is controlled at 0.10 - 0.20%, enhancing the creep resistance, high-temperature strength and ability to resist radiation damage.

[0010] Meanwhile, the heat exchange tube of the present invention has a relatively fine grain size, which can balance the strength and ductility of the heat exchange tube, and the non-metallic inclusion level is at a relatively low level, thus ensuring the hot working and cold working properties of the heat exchange tube, and making its comprehensive properties such as plasticity, toughness, strength, fatigue performance, etc. reach the best effect, so as to meet the use requirements of the heat exchange tube for lead-bismuth fast reactors.

[0011] According to the heat exchange tube provided by the present invention, the inner surface roughness Ra of the heat exchange tube ≤ 1.6 μm, and the outer surface roughness Ra ≤ 1.6 μm;

[0012] And / or, the depth of the decarburized layer on the inner surface of the heat exchange tube is h1, and the depth of the decarburized layer on the outer surface of the heat exchange tube is h2, and h1 and h2 satisfy: h1 + h2 ≤ 0.3 mm;

[0013] Further preferably, h1 ≤ 0.2 mm; or, h2 ≤ 0.2 mm.

[0014] According to the heat exchange tube provided by the present invention, the ovality of the heat exchange tube ≤ 80% of the allowable deviation of the outer diameter; the wall thickness non-uniformity of the heat exchange tube ≤ 80% of the allowable deviation of the wall thickness.

[0015] Preferably, the outer diameter deviation of the heat exchange tube is ±0.1 mm.

[0016] Preferably, the wall thickness deviation of the heat exchange tube is ±0.2 mm.

[0017] The size deviation and surface roughness of the heat exchange tube of the present invention are extremely low, meeting the extremely high requirements for surface quality and dimensional accuracy of small-diameter thin-wall tubes used in lead-bismuth fast reactors.

[0018] According to the heat exchange tube provided by the present invention, the mechanical properties of the heat exchange tube are as follows:

[0019] At 25 °C, R m ≥586 MPa, R p0.2 ≥414 MPa, A≥20%;

[0020] At 100 °C, R m ≥586 MPa, R p0.2 ≥384 MPa, A≥20%;

[0021] At 200 °C, R m ≥584 MPa, R p0.2 ≥377 MPa, A≥20%;

[0022] At 300 °C, R m ≥577 MPa, R p0.2 ≥377 MPa, A≥20%;

[0023] At 400 °C, R m ≥534 MPa, R p0.2 ≥358 MPa, A≥20%;

[0024] At 500 °C, R m ≥441 MPa, R p0.2 ≥306 MPa, A≥26.5%;

[0025] At 525 °C, R m ≥410 MPa, R p0.2 ≥288 MPa, A≥28%.

[0026] Among them, R m represents the tensile strength, R p0.2 represents the yield strength, and A represents the elongation after fracture.

[0027] According to the heat exchange tube provided by the present invention, the outer diameter of the heat exchange tube is 10~20 mm, and the wall thickness is 1~3 mm.

[0028] In a second aspect, the present invention also provides a method for manufacturing the heat exchange tube as described above, including: cold rolling a raw tube; the cold rolling includes pre-cold rolling in more than 1 pass, first intermediate cold rolling in more than 2 passes, second intermediate cold rolling in more than 2 passes, and finish cold rolling in more than 1 pass; heat treatment is performed after cold rolling in each pass; the deformation amount in each pass of cold rolling is independently 35% to 50%;

[0029] The feed amount in the first intermediate cold rolling is 3 to 4 mm per pass, and the rolling speed is 40 to 50 times per minute;

[0030] The feed amount in the second intermediate cold rolling is 3 to 4 mm per pass, and the rolling speed is 65 to 70 times per minute;

[0031] The feed amount in the finish cold rolling is 3 to 4 mm per pass, and the rolling speed is 30 to 40 times per minute.

[0032] The raw tube is obtained by melting, forging, and processing an alloy with the above-described components.

[0033] The present invention uses cold rolling in more than 6 passes to form, controls the cold rolling deformation amount through a controller, fully breaks the grains, and can obtain a finer grain size after heat treatment, thereby taking into account the strength and ductility of the heat exchange tube. By controlling the feed amount and rolling speed in the pre-cold rolling and the first intermediate cold rolling, a seamless tube with good surface quality and high dimensional accuracy can be obtained; by controlling the feed amount and rolling speed in the second intermediate cold rolling, the surface quality and dimensional accuracy of the seamless tube are more excellent; by controlling the feed amount and rolling speed in the finish cold rolling, the surface quality and dimensional accuracy of the heat exchange tube reach the best level, thereby meeting the extremely high requirements for surface quality and dimensional accuracy of the small-diameter thin-walled tube for a lead-bismuth fast reactor.

[0034] According to the method for manufacturing the heat exchange tube provided by the present invention, the deformation amount in each pass of cold rolling in the pre-cold rolling is 40% to 45%;

[0035] The deformation amount in each pass of cold rolling in the first intermediate cold rolling is 40% to 50%, the outer diameter tolerance D is ±0.3 mm, and the wall thickness tolerance S is ±0.3 mm;

[0036] The deformation amount in each pass of cold rolling in the second intermediate cold rolling is 35% to 50%, the outer diameter tolerance D is ±0.2 mm, and the wall thickness tolerance S is ±0.2 mm;

[0037] The deformation amount in each pass of cold rolling in the finish cold rolling is 40% to 45%, the outer diameter tolerance D is ±0.1 mm, and the wall thickness tolerance S is ±0.2 mm.

[0038] According to the preparation method of the heat exchange tube provided by the present invention, during pre-cold rolling, a first solution heat treatment is carried out after cold rolling in each pass; the temperature of the first solution heat treatment is 740-780°C, the time is 10-40 min, and the cooling method is water-air cooling;

[0039] During the first intermediate cold rolling, a second solution heat treatment is carried out after cold rolling in each pass; the temperature of the second solution heat treatment is 740-780°C, the time is 10-40 min, and the cooling method is water-air cooling;

[0040] During the second intermediate cold rolling, a third solution heat treatment is carried out after cold rolling in each pass; the temperature of the third solution heat treatment is 740-780°C, the time is 15-20 min, and the cooling method is water jacket cooling under a protective gas;

[0041] During the finish cold rolling, normalizing heat treatment and tempering heat treatment are carried out after cold rolling in each pass; the temperature of the normalizing heat treatment is 1000-1100°C, the time is 15-30 min, and the cooling method is water jacket cooling under a protective gas; the temperature of the tempering heat treatment is 740-780°C, the time is 80-100 min, and the cooling method is water jacket cooling under a protective gas.

[0042] According to the preparation method of the heat exchange tube provided by the present invention, a forged martensitic steel tube blank is subjected to hot piercing to obtain a rough tube; generally, a solid round steel is used for the forged martensitic steel tube blank.

[0043] The rough tube is successively subjected to annealing treatment, straightening and pickling to obtain a first intermediate tube blank;

[0044] The first intermediate tube blank is subjected to 1 pass of pre-cold rolling, degreasing, first solution heat treatment, straightening and pickling to obtain a second intermediate tube blank; the first solution heat treatment is carried out in a continuous roller hearth furnace;

[0045] The second intermediate tube blank is successively subjected to 2 passes of the first intermediate cold rolling, and after cold rolling in each pass, degreasing, second solution heat treatment, straightening and pickling are carried out to obtain a third intermediate tube blank; the second solution heat treatment is carried out in a continuous roller hearth furnace;

[0046] The third intermediate tube blank is successively subjected to 2 passes of the second intermediate cold rolling, and after cold rolling in each pass, degreasing, third solution heat treatment, straightening and pickling are carried out to obtain a fourth intermediate tube blank; the third solution heat treatment is carried out in an ammonia decomposition heat treatment furnace;

[0047] The working principle of the ammonia decomposition heat treatment furnace in the present invention is mainly to heat liquid ammonia to 800-850°C, and under the action of a catalyst, ammonia is decomposed into a hydrogen-nitrogen mixed gas of hydrogen and nitrogen. This mixed gas can be used as a protective atmosphere for the heat treatment process of the steel tubes of the present invention.

[0048] The fourth intermediate tube blank is successively subjected to finish cold rolling, degreasing, normalizing heat treatment, tempering heat treatment, and straightening in 1 pass to obtain a finished tube; the normalizing heat treatment and / or the tempering heat treatment are carried out in a protective gas heat treatment furnace.

[0049] The working principle of the protective gas heat treatment furnace in the present invention is mainly to use a protective gas (such as hydrogen, nitrogen, etc.) during the heat treatment process to control the atmosphere in the furnace and prevent the steel pipe of the present invention from oxidizing at high temperatures.

[0050] The pure hydrogen protection bright heat treatment furnace in the present invention uses high-purity hydrogen as the protective atmosphere. Hydrogen has strong reducibility and can effectively prevent the oxidation of the metal surface at high temperatures. The workpiece is heated to the required temperature in the furnace, and hydrogen reacts with the oxide on the metal surface at high temperatures to reduce it to metal, thereby keeping the surface of the workpiece bright. After heating is completed, the workpiece is slowly cooled under hydrogen protection to avoid surface oxidation.

[0051] In a third aspect, the present invention also provides the application of the heat exchange tube as described above or the heat exchange tube prepared by the preparation method as described above in a lead-bismuth fast reactor.

[0052] Beneficial effects:

[0053] For the heat exchange tube, preparation method, and application in a lead-bismuth fast reactor provided by the present invention, on the one hand, the mechanical properties of the heat exchange tube are improved by using a tube blank with specific components. On the other hand, the present invention also adopts cold rolling forming with specific passes to fully break the grains, and finer grain sizes can be obtained after heat treatment, taking into account both the strength and ductility of the heat exchange tube. Moreover, the cold rolling feed rate and rolling speed are strictly controlled to make the surface quality and dimensional accuracy of the heat exchange tube reach the best level, and the level of non-metallic inclusions is effectively controlled, so that the finished heat exchange tube has good microstructure and high-temperature strength, fully meeting the usage requirements of the heat exchange tube for lead-bismuth fast reactors, thereby filling the domestic technical gap in the preparation process of martensitic steel heat exchange tubes for lead-bismuth reactors. Description of the drawings

[0054] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0055] Figure 1 It is a microstructural picture of the heat exchange tube of Embodiment 1 provided by the present invention.

[0056] Figure 2 It is a microstructural picture of the heat exchange tube of Comparative Example 1 provided by the present invention. Detailed implementation manners

[0057] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without any creative efforts shall fall within the protection scope of the present invention.

[0058] In an embodiment of the present invention, a heat exchange tube is first provided. By weight percentage, its components include: C: 0.14 - 0.25%, Si: 1.0 - 2.0%, Mn: ≤1.0%, Cr: 10.0 - 12.0%, W: 1.0 - 2.0%, V: 0.15 - 0.30%, Ta: 0.10 - 0.20%, Ti: ≤0.01%, Al: ≤0.01%, P: ≤0.005%, S: ≤0.005%, Co: ≤0.01%, Ni: ≤0.01%, Cu: ≤0.01%, Mo: ≤0.005%, Nb: ≤0.005%, B: ≤0.002%, and the balance is Fe and inevitable impurities;

[0059] The grain size of the heat exchange tube is 7 - 10 grades, the microstructure is martensite, and there is no δ-ferrite;

[0060] The inclusion levels of the heat exchange tube are: AH 0.5, AT 0.5, BH 0.5, BT 0.5, CH 0.5, CT 0.5, CH0.5, CT 1.0.

[0061] Preferably, the inclusion levels of the heat exchange tube are: AH 0, AT 0, BH 0, BT 0, CH 0, CT 0, CH 0.5, CT 0.5.

[0062] In a specific embodiment of the present invention, the grain size of the heat exchange tube is 7 - 10 grades, for example, it can be any value or any range composed of values among 7 grades, 8 grades, 9 grades and 10 grades.

[0063] In a specific embodiment of the present invention, the inner surface roughness Ra of the heat exchange tube ≤1.6 μm, and the outer surface roughness Ra ≤1.6 μm;

[0064] In a specific embodiment of the present invention, the decarburized layer depth of the inner surface of the heat exchange tube is h1, and the decarburized layer depth of the outer surface of the heat exchange tube is h2, and h1 and h2 satisfy: h1 + h2 ≤0.3 mm;

[0065] Further preferably, h1 ≤0.2 mm; or h2 ≤0.2 mm.

[0066] In a specific embodiment of the present invention, the ovality of the heat exchange tube ≤ 80% of the allowable deviation of the outer diameter; the wall thickness non-uniformity of the heat exchange tube ≤ 80% of the allowable deviation of the wall thickness.

[0067] In a specific embodiment of the present invention, the mechanical properties of the heat exchange tube are:

[0068] At 25 °C, R m ≥ 586 MPa, R p0.2 ≥ 414 MPa, A ≥ 20%;

[0069] At 100 °C, R m ≥ 586 MPa, R p0.2 ≥ 384 MPa, A ≥ 20%;

[0070] At 200 °C, R m ≥ 584 MPa, R p0.2 ≥ 377 MPa, A ≥ 20%;

[0071] At 300 °C, R m ≥ 577 MPa, R p0.2 ≥ 377 MPa, A ≥ 20%;

[0072] At 400 °C, R m ≥ 534 MPa, R p0.2 ≥ 358 MPa, A ≥ 20%;

[0073] At 500 °C, R m ≥ 441 MPa, R p0.2 ≥ 306 MPa, A ≥ 26.5%;

[0074] At 525 °C, R m ≥ 410 MPa, R p0.2 ≥ 288 MPa, A ≥ 28%.

[0075] In a specific embodiment of the present invention, the outer diameter of the heat exchange tube is 10 - 20 mm, and the wall thickness is 1 - 3 mm.

[0076] In a specific embodiment of the present invention, the outer diameter is 10 - 20 mm, for example, it can be any value or a range composed of any values among 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, and 20 mm.

[0077] In a specific embodiment of the present invention, the wall thickness is 1 - 3 mm, for example, it can be any value or a range composed of any values among 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm.

[0078] The embodiment of the present invention also provides a method for manufacturing the heat exchange tube as described above, including: cold rolling a raw tube; the cold rolling includes pre-cold rolling with more than 1 pass, first intermediate cold rolling with more than 2 passes, second intermediate cold rolling with more than 2 passes, and finish cold rolling with more than 1 pass; heat treatment is carried out after cold rolling in each pass; the deformation amount in each pass of cold rolling is independently 35-50%;

[0079] The feed amount of the first intermediate cold rolling is 3-4 mm per pass, and the rolling speed is 40-50 times per minute;

[0080] The feed amount of the second intermediate cold rolling is 3-4 mm per pass, and the rolling speed is 65-70 times per minute;

[0081] The feed amount of the finish cold rolling is 3-4 mm per pass, and the rolling speed is 30-40 times per minute.

[0082] In a specific embodiment of the present invention, the deformation amount in each pass of cold rolling is 35-50%, for example, it can be any value or a range composed of any values among 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% and 50%.

[0083] In a specific embodiment of the present invention, the feed amount of the first intermediate cold rolling is 3-4 mm per pass, for example, it can be any value or a range composed of any values among 3.0 mm per pass, 3.2 mm per pass, 3.4 mm per pass, 3.6 mm per pass, 3.8 mm per pass and 4.0 mm per pass.

[0084] In a specific embodiment of the present invention, the rolling speed is 40-50 times per minute, for example, it can be any value or a range composed of any values among 40 times per minute, 41 times per minute, 42 times per minute, 43 times per minute, 44 times per minute, 45 times per minute, 46 times per minute, 47 times per minute, 48 times per minute, 49 times per minute and 50 times per minute.

[0085] In a specific embodiment of the present invention, the feed amount of the second intermediate cold rolling is 3-4 mm per pass, for example, it can be any value or a range composed of any values among 3.0 mm per pass, 3.2 mm per pass, 3.4 mm per pass, 3.6 mm per pass, 3.8 mm per pass and 4.0 mm per pass.

[0086] In a specific embodiment of the present invention, the rolling speed is 65-70 times per minute, for example, it can be any value or a range composed of any values among 65 times per minute, 66 times per minute, 67 times per minute, 68 times per minute, 69 times per minute and 70 times per minute.

[0087] In a specific embodiment of the present invention, the feed rate of finished cold rolling is 3 - 4 mm / time, for example, it can be any value or the range composed of any values among 3.0 mm / time, 3.2 mm / time, 3.4 mm / time, 3.6 mm / time, 3.8 mm / time, and 4.0 mm / time.

[0088] In a specific embodiment of the present invention, the rolling speed is 30 - 40 times / min, for example, it can be any value or the range composed of any values among 30 times / min, 31 times / min, 32 times / min, 33 times / min, 34 times / min, 35 times / min, 36 times / min, 37 times / min, 38 times / min, 39 times / min, and 40 times / min.

[0089] In a specific embodiment of the present invention, the deformation amount of each pass of cold rolling during pre - cold rolling is 40 - 45%.

[0090] In a specific embodiment of the present invention, the deformation amount of each pass of cold rolling during the first intermediate cold rolling is 40 - 50%, the outer diameter tolerance D is ±0.3 mm, and the wall thickness tolerance S is ±0.3 mm.

[0091] In a specific embodiment of the present invention, the deformation amount of each pass of cold rolling during the second intermediate cold rolling is 35 - 50%, the outer diameter tolerance D is ±0.2 mm, and the wall thickness tolerance S is ±0.2 mm.

[0092] In a specific embodiment of the present invention, the deformation amount of each pass of cold rolling during finished cold rolling is 40 - 45%, the outer diameter tolerance D is ±0.1 mm, and the wall thickness tolerance S is ±0.2 mm.

[0093] In a specific embodiment of the present invention, after each pass of cold rolling during pre - cold rolling, a first solution heat treatment is carried out; the temperature of the first solution heat treatment is 740 - 780 °C, the time is 10 - 40 min, and the cooling method is water - air cooling.

[0094] In a specific embodiment of the present invention, the temperature of the first solution heat treatment is 740 - 780 °C, for example, it can be any value or the range composed of any values among 740 °C, 745 °C, 750 °C, 755 °C, 760 °C, 765 °C, 770 °C, 775 °C, and 780 °C.

[0095] In a specific embodiment of the present invention, the time of the first solution heat treatment is 10 - 40 min, for example, it can be any value or the range composed of any values among 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min.

[0096] In a specific embodiment of the present invention, a second solution heat treatment is performed after cold rolling in each pass during the first intermediate cold rolling; the temperature of the second solution heat treatment is 740-780°C, the time is 10-40 min, and the cooling method is water-air cooling.

[0097] In a specific embodiment of the present invention, the temperature of the second solution heat treatment is 740-780°C, for example, it can be any value or a range composed of any values among 740°C, 745°C, 750°C, 755°C, 760°C, 765°C, 770°C, 775°C, and 780°C.

[0098] In a specific embodiment of the present invention, the time of the second solution heat treatment is 10-40 min, for example, it can be any value or a range composed of any values among 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min.

[0099] In a specific embodiment of the present invention, a third solution heat treatment is performed after cold rolling in each pass during the second intermediate cold rolling; the temperature of the third solution heat treatment is 740-780°C, the time is 15-20 min, and the cooling method is water jacket cooling under a protective gas.

[0100] In a specific embodiment of the present invention, the temperature of the third solution heat treatment is 740-780°C, for example, it can be any value or a range composed of any values among 740°C, 745°C, 750°C, 755°C, 760°C, 765°C, 770°C, 775°C, and 780°C.

[0101] In a specific embodiment of the present invention, the time of the third solution heat treatment is 15-20 min, for example, it can be any value or a range composed of any values among 10 min, 15 min, and 20 min.

[0102] In a specific embodiment of the present invention, normalizing heat treatment and tempering heat treatment are performed after cold rolling in each pass during finish cold rolling; the temperature of the normalizing heat treatment is 1000-1100°C, the time is 15-30 min, and the cooling method is water jacket cooling under a protective gas; the temperature of the tempering heat treatment is 740-780°C, the time is 80-100 min, and the cooling method is water jacket cooling under a protective gas.

[0103] In a specific embodiment of the present invention, the temperature of the normalizing heat treatment is 1000-1100°C, for example, it can be any value or a range composed of any values among 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, and 1100°C.

[0104] In a specific embodiment of the present invention, the normalizing heat treatment time is 15 to 30 minutes, for example, it can be any value or a range composed of any values among 15 minutes, 20 minutes, 25 minutes, and 30 minutes.

[0105] In a specific embodiment of the present invention, the tempering heat treatment temperature is 740 to 780 °C, for example, it can be any value or a range composed of any values among 740 °C, 745 °C, 750 °C, 755 °C, 760 °C, 765 °C, 770 °C, 775 °C, and 780 °C.

[0106] In a specific embodiment of the present invention, the tempering heat treatment time is 80 to 100 minutes, for example, it can be any value or a range composed of any values among 80 minutes, 85 minutes, 90 minutes, 95 minutes, and 100 minutes.

[0107] In a specific embodiment of the present invention, the forged martensitic steel pipe billet is hot pierced to obtain a rough pipe; generally, the forged martensitic steel pipe billet uses solid round steel.

[0108] The rough pipe is successively annealed, straightened, and pickled to obtain a first intermediate pipe billet;

[0109] The first intermediate pipe billet is subjected to 1 pass of pre-cold rolling, degreasing, first solution heat treatment, straightening, and pickling to obtain a second intermediate pipe billet; the first solution heat treatment is carried out in a continuous roller hearth furnace;

[0110] The second intermediate pipe billet is successively subjected to 2 passes of first intermediate cold rolling, and after each pass of cold rolling, degreasing, second solution heat treatment, straightening, and pickling are carried out to obtain a third intermediate pipe billet; the second solution heat treatment is carried out in a continuous roller hearth furnace;

[0111] The third intermediate pipe billet is successively subjected to 2 passes of second intermediate cold rolling, and after each pass of cold rolling, degreasing, third solution heat treatment, straightening, and pickling are carried out to obtain a fourth intermediate pipe billet; the third solution heat treatment is carried out in an ammonia decomposition heat treatment furnace;

[0112] The fourth intermediate pipe billet is successively subjected to 1 pass of finish cold rolling, degreasing, normalizing heat treatment, tempering heat treatment, and straightening to obtain a finished pipe; the normalizing heat treatment and / or the tempering heat treatment are carried out in a protective gas heat treatment furnace.

[0113] In a specific embodiment of the present invention, the annealing treatment uses a roller hearth continuous heat treatment furnace, the furnace atmosphere is a slightly oxidizing atmosphere, the heat treatment temperature is 750 to 770 °C, the holding time is 40 to 60 minutes, and the cooling method is air cooling.

[0114] In a specific embodiment of the present invention, the pickling is carried out with a 5-10% sulfuric acid solution at 40-50°C. When pickling, the raw pipe should be inclined both when entering and leaving the tank. The pickling time is 80-170 min, and it is lifted once every 10 min, and the inner wall of the steel pipe is rinsed with high-pressure water.

[0115] In a specific embodiment of the present invention, before hot piercing, the forged martensitic steel pipe blank is also skived, and the skiving depth is 1.5-2.0 mm, and then it is cut to a fixed length on a band saw.

[0116] In a specific embodiment of the present invention, a centering hole with a diameter of Ф12±2 mm is drilled at one end of the forged martensitic steel pipe blank, and then hot piercing is carried out on a skew rolling piercing mill. The heating temperature is 1130-1170°C, the heating time is 100-120 min, the holding time is 10-15 min, the guide plate spacing is 79 mm, the roll spacing is 69 mm. After hot piercing, the raw pipe specification is Ф90×10 mm, and the cooling method is water cooling. The outer diameter deviation is controlled within ±3%, and the wall thickness deviation is controlled within ±10%.

[0117] In a specific embodiment of the present invention, the first intermediate pipe blank is also inspected and ground on the inner and outer surfaces, and then internally and externally polished.

[0118] In a specific embodiment of the present invention, the pre-cold rolling uses an LG110 rolling mill.

[0119] In a specific embodiment of the present invention, the first intermediate pipe blank is pre-cold rolled through an LG110 rolling mill, and is rolled to Ф76×6.5 mm in cooperation with the cold rolling pass and the mandrel.

[0120] In a specific embodiment of the present invention, for the straightening after the first solution heat treatment, the straightness is controlled to be ≤1.5 mm / m.

[0121] In a specific embodiment of the present invention, the second intermediate pipe blank is also inspected and ground on the inner and outer surfaces, and then internally and externally polished.

[0122] In a specific embodiment of the present invention, the first intermediate cold rolling uses an LG60 rolling mill.

[0123] In a specific embodiment of the present invention, the second intermediate pipe blank is cold rolled through an LG60 rolling mill for 2 passes, and is rolled to Ф57×5 mm and Ф38×4 mm respectively in cooperation with the cold rolling pass and the mandrel.

[0124] In a specific embodiment of the present invention, for the straightening after the second solution heat treatment, the straightness is controlled to be ≤1.5 mm / m.

[0125] In a specific embodiment of the present invention, the third intermediate pipe blank is also inspected, ground, and internally and externally polished on the inner and outer surfaces.

[0126] In a specific embodiment of the present invention, the second intermediate cold rolling is carried out using an LG30 rolling mill.

[0127] In a specific embodiment of the present invention, the third intermediate billet is cold rolled through an LG30 rolling mill for 2 passes, and is respectively rolled to Ф25×3.2mm and Ф19×2.6mm with the cooperation of cold rolling pass and mandrel.

[0128] In a specific embodiment of the present invention, for the straightening after the third solution heat treatment, the straightness is controlled to be ≤1.0mm / m.

[0129] In a specific embodiment of the present invention, the inner and outer surfaces of the fourth intermediate billet are also inspected, ground, and polished inside and outside.

[0130] In a specific embodiment of the present invention, the finished product cold rolling is carried out using an LD30 rolling mill.

[0131] In a specific embodiment of the present invention, the fourth intermediate billet is cold rolled through an LD30 rolling mill for 1 pass, and is rolled to Ф14×2mm with the cooperation of cold rolling pass and mandrel.

[0132] In a specific embodiment of the present invention, the normalizing heat treatment is carried out in a pure hydrogen-protected bright heat treatment furnace.

[0133] In a specific embodiment of the present invention, the tempering heat treatment is carried out in a pure hydrogen-protected bright heat treatment furnace.

[0134] In a specific embodiment of the present invention, for the straightening after the tempering heat treatment, the straightness is controlled to be ≤1.0mm / m.

[0135] In a specific embodiment of the present invention, degreasing is preferably completed within 48 hours after each cold rolling, and a special alkaline degreasing agent or acetone is used for degreasing. During the transfer process after degreasing, clean slings are required for lifting to prevent contamination during transportation.

[0136] In a specific embodiment of the present invention, rust prevention treatment is carried out after each pickling, non-destructive inspection, and final inspection. The passivation solution is a 20% sodium nitrite aqueous solution; the water-soluble rust inhibitor is selected from VpCI-377 or TKX-10 water-based rust inhibitor, and is prepared in a ratio of 1:10 (volume ratio: VpCI-377: distilled water) or 1:5 (volume ratio: TKX-10: distilled water).

[0137] In a specific embodiment of the present invention, the finished pipes are ultrasonically inspected one by one. According to the GB / T 5777 standard, the acceptance standard for ultrasonic flaw detection of the notch size is: a U-shaped groove with a length of 12.5mm and a depth of 0.1±0.02mm. Each pipe is ultrasonically detected.

[0138] In a specific embodiment of the present invention, the finished tube is cleaned as follows:

[0139] Outer surface cleaning: Wipe the outer surface of each finished tube with a cotton cloth dipped in acetone or alcohol until there are no color spots caused by oil stains and foreign matters on the outer surface, and finally wipe it clean with a dry white cotton cloth;

[0140] Inner surface cleaning: Blow a white wool felt plug dipped in acetone or alcohol into the hole of the finished tube with high-pressure nitrogen for cleaning until there are no color spots caused by oil stains and foreign matters on the surface of the cleaned wool felt plug, and finally dry it with a dry wool felt plug or white cotton cloth.

[0141] In a specific embodiment of the present invention, each finished cladding tube is sleeved and labeled by means of bar code identification. After labeling, both ends are firmly sealed with plastic plugs immediately, and each tube is sleeved with a pentachloroethylene plastic bag, and then the cladding tubes are bundled and placed in a wooden box.

[0142] The embodiment of the present invention also provides the application of the heat exchange tube as described above or the heat exchange tube prepared by the preparation method as described above in a lead-bismuth fast reactor.

[0143] The present invention will be described in more detail by the following specific cases for the heat exchange tube and its preparation method of the present invention and its application in a lead-bismuth fast reactor.

[0144] Example 1

[0145] A heat exchange tube provided in this embodiment comprises the following components by weight percentage: C: 0.22%, Si: 1.5%, Mn: 0.8%, Cr: 10.5%, W: 1.2%, V: 0.18%, Ta: 0.14%, Ti: 0.008%, Al: 0.005%, P: 0.002%, S: 0.002%, Co: 0.01%, Ni: 0.007%, Cu: 0.01%, Mo: 0.005%, Nb: 0.005%, B: 0.002%, and the balance is Fe and unavoidable impurities, and the sum of the above components is 100%.

[0146] The allowable deviation of the outer diameter of the heat exchange tube is ±0.1 mm, and the allowable deviation of the wall thickness is ±0.2 mm; the ovality ≤ 80% of the allowable deviation of the outer diameter; the wall thickness non-uniformity ≤ 80% of the allowable deviation of the wall thickness; the inner surface roughness Ra ≤ 1.6 μm, and the outer surface roughness Ra ≤ 1.6 μm.

[0147] The microstructure of the heat exchange tube is tempered martensite at high temperature, and there is no δ-ferrite; the grain size is grade 7; the depth of the decarburized layer on the inner surface of the heat exchange tube ≤ 0.2 mm, the depth of the decarburized layer on the outer surface ≤ 0.2 mm, and the sum of the two ≤ 0.3 mm. The mechanical property parameters are as follows:

[0148] R at 25 °Cm = 794 MPa, R p0.2 = 524 MPa, A = 24%;

[0149] R at 100 °C m = 758 MPa, R p0.2 = 491 MPa, A = 23%;

[0150] R at 200 °C m = 723 MPa, R p0.2 = 484 MPa, A = 24%;

[0151] R at 300 °C m = 696 MPa, R p0.2 = 477 MPa, A = 20%;

[0152] R at 400 °C m = 639 MPa, R p0.2 = 429 MPa, A = 20.5%;

[0153] R at 500 °C m = 497 MPa, R p0.2 = 354 MPa, A = 27.5%;

[0154] R at 525 °C m = 463 MPa, R p0.2 = 337 MPa, A = 28.5%.

[0155] After being tested by an optical microscope, the microstructural pictures of the heat exchange tube are as Figure 1 shown.

[0156] This embodiment also provides a preparation method of the above heat exchange tube, which specifically includes the following steps:

[0157] (1) Hot piercing: The forged martensitic steel round tube blank is peeled, and the peeling depth is 1.9 mm. Then it is cut to a fixed length on a band saw, and a centering hole is drilled at one end of the round tube blank. The diameter of the centering hole is Ф12 mm. Then hot piercing is carried out on an inclined rolling piercing mill. The heating temperature is 1150 °C, the heating time is 110 min, the holding time is 15 min, the guide plate spacing is 79 mm, the roll spacing is 69 mm. After hot piercing, the specifications of the rough tube are Ф90×10 mm, and the cooling method is water cooling. The outer diameter deviation is controlled within ±1.5%, and the wall thickness deviation is controlled within ±10%.

[0158] (2) Rough tube annealing: The rough tube obtained in step (1) is annealed. A roller hearth continuous heat treatment furnace is used, and the atmosphere in the furnace is a slightly oxidizing atmosphere. The heat treatment temperature is 760 °C, the holding time is 40 min, and the cooling method is air cooling.

[0159] (3) Pickling: Straighten the annealed raw tube obtained in step (2), cut off the head and tail defects and remove burrs, then pickle it with an 8% sulfuric acid solution at 45°C. The raw tube should be tilted when entering and leaving the tank. The pickling time is 120 minutes, and it is lifted once every 10 minutes. The inner wall of the steel tube is rinsed with high-pressure water, and the pickling quality is observed. When there is basically no scale on the inner and outer walls of the steel tube, it can be judged that the pickling is completed.

[0160] (4) Surface inspection and grinding: Inspect and grind the inner and outer surfaces of the steel tube obtained in step (3) to remove the slightly remaining scale and other defects on the surface, and then perform internal and external through polishing to obtain the first intermediate tube blank.

[0161] (5) Cold rolling and heat treatment are as follows:

[0162] (5.1) Cold roll the first intermediate tube blank obtained in step (4) with an LG110 rolling mill for 1 pass. Specifically: Roll it to Ф76×6.5mm with the cold rolling pass and mandrel. The cold rolling deformation is 43.53%. After cold rolling, degrease it and perform solution heat treatment in a continuous roller hearth furnace. The heat treatment temperature is 760°C, hold for 30 minutes, and the cooling method is water-air cooling. Then straighten it, control the straightness ≤1.5mm / m, and then perform pickling, internal and external surface inspection, grinding, and internal and external polishing to obtain the second intermediate tube blank.

[0163] (5.2) Cold roll the second intermediate tube blank with an LG60 rolling mill for 2 passes. Specifically: Roll it to Ф57×5mm and Ф38×4mm with the cold rolling pass and mandrel respectively. The cold rolling deformations are 42.45% and 47.69% respectively. The feed is 3mm / time, the rolling speed is 45 times / min, and the outer diameter and wall thickness tolerances are both controlled within D±0.3mm, S±0.3mm. After each cold rolling pass, degrease it and perform solution heat treatment in a continuous roller hearth furnace. The heat treatment temperature is 760°C, hold for 30 minutes, and the cooling method is water-air cooling. Then straighten it, control the straightness ≤1.5mm / m, and then perform pickling, internal and external surface inspection, grinding, and internal and external polishing to obtain the third intermediate tube blank.

[0164] (5.3) The third intermediate tube blank is cold-rolled in two passes using an LG30 rolling mill, specifically: rolled to Ф25×3.2 mm and Ф19×2.6 mm respectively in cooperation with the cold-rolling pass and mandrel. The cold-rolling deformation amounts are 48.71% and 38.88% respectively, the feed rate is 3 mm per pass, the rolling speed is 65 times per minute, and the outer diameter and wall thickness tolerances are both controlled within D±0.2 mm and S±0.2 mm. After cold-rolling in each pass, acetone is used for degreasing and solution heat treatment is carried out in an ammonia decomposition heat treatment furnace. The heat treatment temperature is 760 °C, the holding time is 20 min, the cooling method is water jacket cooling under protective gas, and then straightening is carried out, controlling the straightness ≤1.0 mm / m. Then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the fourth intermediate tube blank.

[0165] (5.4) The fourth intermediate tube blank is cold-rolled in one pass using an LD30 rolling mill, specifically: rolled to Ф14×2 mm in cooperation with the cold-rolling pass and mandrel. The cold-rolling deformation amount is 43.71%, the feed rate is 3 mm per pass, the rolling speed is 35 times per minute, and the outer diameter and wall thickness tolerances are controlled within D±0.1 mm and S±0.2 mm. After cold-rolling, acetone is used for degreasing and normalizing and tempering heat treatments are carried out in a pure hydrogen protection bright heat treatment furnace. The normalizing heat treatment temperature is 1050 °C, the holding time is 20 min, and the cooling method is water jacket cooling under protective gas; the tempering heat treatment temperature is 760 °C, the holding time is 90 min, and the cooling method is water jacket cooling under protective gas. Then straightening is carried out, controlling the straightness ≤1.0 mm / m. Then internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the finished tube, that is, the above-mentioned heat exchange tube.

[0166] Example 2

[0167] A heat exchange tube provided in this example is basically the same as that in Example 1, the difference is only that:

[0168] In this example, the obtained heat exchange tube has the following mechanical property parameters:

[0169] At 25 °C, R m = 748 MPa, R p0.2 = 512 MPa, A = 23%;

[0170] At 100 °C, R m = 721 MPa, R p0.2 = 488 MPa, A = 23%;

[0171] At 200 °C, R m = 707 MPa, R p0.2 = 455 MPa, A = 23%;

[0172] At 300 °C, R m = 687 MPa, R p0.2= 445 MPa, A = 20%;

[0173] R at 400 °C m = 619 MPa, R p0.2 = 401 MPa, A = 20%;

[0174] R at 500 °C m = 484 MPa, R p0.2 = 350 MPa, A = 26.5%;

[0175] R at 525 °C m = 459 MPa, R p0.2 = 333 MPa, A = 28%.

[0176] This embodiment also provides a preparation method for the heat exchange tube as described above, which is basically the same as that of Embodiment 1, except for step (5), specifically:

[0177] (5.1) The first intermediate tube blank obtained in step (4) is cold-rolled in 1 pass using an LG110 rolling mill, specifically: rolled to Ф76×6.5 mm with a cold rolling pass and a mandrel, and the cold rolling deformation is 43.53%. After cold rolling, degreasing is carried out and solution heat treatment is carried out in a continuous roller hearth furnace at a heat treatment temperature of 750 °C for 20 min, and the cooling method is water-air cooling. Then straightening is carried out, controlling the straightness ≤ 1.5 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the second intermediate tube blank.

[0178] (5.2) The second intermediate tube blank is cold-rolled in 2 passes using an LG60 rolling mill, specifically: rolled to Ф57×5 mm and Ф38×4 mm respectively with a cold rolling pass and a mandrel, and the cold rolling deformations are 42.45% and 47.69% respectively, the feed is 3.5 mm / time, the rolling speed is 40 times / min, and the outer diameter and wall thickness tolerances are both controlled within D±0.3 mm, S±0.3 mm. After each cold rolling pass, degreasing is carried out and solution heat treatment is carried out in a continuous roller hearth furnace at a heat treatment temperature of 750 °C for 20 min, and the cooling method is water-air cooling. Then straightening is carried out, controlling the straightness ≤ 1.5 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the third intermediate tube blank.

[0179] (5.3) The third intermediate tube blank is cold-rolled on an LG30 rolling mill in 2 passes, specifically: rolled to Ф25×3.2 mm and Ф19×2.6 mm respectively with the cold-rolling pass and mandrel, the cold-rolling deformation amounts are 48.71% and 38.88% respectively, the feed is 3.5 mm / time, the rolling speed is 65 times / min, and the outer diameter and wall thickness tolerances are both controlled within D±0.2 mm, S±0.2 mm. After each cold-rolling pass, acetone is used for degreasing and solution heat treatment is carried out in an ammonia decomposition heat treatment furnace. The heat treatment temperature is 750 °C, the holding time is 15 min, the cooling method is water jacket cooling under protective gas, and then straightening is carried out, controlling the straightness ≤1.0 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the fourth intermediate tube blank.

[0180] (5.4) The fourth intermediate tube blank is cold-rolled on an LD30 rolling mill in 1 pass, specifically: rolled to Ф14×2 mm with the cold-rolling pass and mandrel, the cold-rolling deformation amount is 43.71%, the feed is 3.5 mm / time, the rolling speed is 40 times / min, and the outer diameter and wall thickness tolerances are controlled within D±0.1 mm, S±0.2 mm. After cold-rolling, acetone is used for degreasing and normalizing and tempering heat treatments are carried out in a bright heat treatment furnace under pure hydrogen protection. The normalizing heat treatment temperature is 1030 °C, the holding time is 15 min, and the cooling method is water jacket cooling under protective gas; the tempering heat treatment temperature is 750 °C, the holding time is 80 min, and the cooling method is water jacket cooling under protective gas. Then straightening is carried out, controlling the straightness ≤1.0 mm / m, and then internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the finished tube, that is, the above heat exchange tube.

[0181] The non-metallic inclusion level of the heat exchange tube prepared in the above embodiment is tested: tested and rated according to GB / T 10561-2023, and the results are shown in Table 1 below:

[0182] Table 1

[0183]

[0184] As can be seen from Table 1, the measured value of the non-metallic inclusion content of the heat exchange tube of the present invention is lower than the standard requirement value. The level represents the purity of the heat exchange tube. The lower the level, the purer the steel quality. The non-metallic inclusion level is at a relatively low level, thus ensuring the hot working and cold working properties of the heat exchange tube and making its comprehensive properties such as plasticity, toughness, strength, and fatigue performance reach the best effect. If the non-metallic inclusion level is high, the processing performance of the obtained heat exchange tube is difficult to be applicable to the lead-bismuth fast reactor field.

[0185] The above indexes of the heat exchange tube prepared in the above embodiment meet the application requirements of lead-bismuth fast.

[0186] Comparative Example 1

[0187] A heat exchange tube provided in this comparative example is basically the same as that in Example 1, except that:

[0188] In this comparative example, the grain size of the heat exchange tube is Grade 6.5; and the mechanical property parameters are as follows:

[0189] R at 25 °C m = 756 MPa, R p0.2 = 485 MPa, A = 19.5%;

[0190] R at 100 °C m = 714 MPa, R p0.2 = 422 MPa, A = 19.5%;

[0191] R at 200 °C m = 703 MPa, R p0.2 = 401 MPa, A = 20%;

[0192] R at 300 °C m = 602 MPa, R p0.2 = 388 MPa, A = 19%;

[0193] R at 400 °C m = 584 MPa, R p0.2 = 356 MPa, A = 20.5%;

[0194] R at 500 °C m = 418 MPa, R p0.2 = 284 MPa, A = 25%;

[0195] R at 525 °C m = 399 MPa, R p0.2 = 218 MPa, A = 25.5%.

[0196] The heat exchange tube was tested by an optical microscope, and the microstructural pictures of the heat exchange tube are as Figure 2 shown.

[0197] This comparative example also provides a preparation method of the above heat exchange tube, which is basically the same as that in Example 1, except for step (5), specifically:

[0198] (5.1) The first intermediate tube blank obtained in step (4) is cold-rolled in one pass using an LG110 rolling mill. Specifically: it is rolled to Ф76×6.5 mm with the cold-rolling pass and mandrel, and the cold-rolling deformation is 43.53%. After cold-rolling, degreasing is carried out and solution heat treatment is carried out in a continuous roller hearth furnace. The heat treatment temperature is 760 °C, the holding time is 30 min, the cooling method is water-air cooling, then straightening is carried out, controlling the straightness ≤ 1.5 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the second intermediate tube blank.

[0199] (5.2) The second intermediate tube blank is cold-rolled in two passes using an LG60 rolling mill. Specifically: it is rolled to Ф57×5 mm and Ф38×4 mm respectively with the cold-rolling pass and mandrel, and the cold-rolling deformations are 42.45% and 47.69% respectively. The feed rate is 2.5 mm / time, the rolling speed is 60 times / min, and the outer diameter and wall thickness tolerances are both controlled within D±0.3 mm, S±0.3 mm. After each pass of cold-rolling, degreasing is carried out and solution heat treatment is carried out in a continuous roller hearth furnace. The heat treatment temperature is 790 °C, the holding time is 30 min, the cooling method is water-air cooling, then straightening is carried out, controlling the straightness ≤ 1.5 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the third intermediate tube blank.

[0200] (5.3) The third intermediate tube blank is cold-rolled in two passes using an LG30 rolling mill. Specifically: it is rolled to Ф25×3.2 mm and Ф19×2.6 mm respectively with the cold-rolling pass and mandrel, and the cold-rolling deformations are 48.71% and 38.88% respectively. The feed rate is 2.5 mm / time, the rolling speed is 60 times / min, and the outer diameter and wall thickness tolerances are both controlled within D±0.2 mm, S±0.2 mm. After cold-rolling, degreasing is carried out using acetone and solution heat treatment is carried out in an ammonia decomposition heat treatment furnace. The heat treatment temperature is 790 °C, the holding time is 20 min, the cooling method is water jacket cooling under protective gas, then straightening is carried out, controlling the straightness ≤ 1.0 mm / m, and then pickling, internal and external surface inspection, grinding, internal and external polishing are carried out to obtain the fourth intermediate tube blank.

[0201] (5.4) The fourth intermediate tube blank is cold-rolled on an LD30 rolling mill in one pass, specifically: rolled to Ф14×2 mm with a cold-rolled pass and a mandrel, the cold-rolled deformation amount is 43.71%, the feed amount is 2.5 mm / time, the rolling speed is 50 times / min, and the outer diameter and wall thickness tolerances are controlled within D±0.1 mm and S±0.2 mm. After cold rolling, it is degreased with acetone and normalized and tempered in a bright heat treatment furnace under pure hydrogen protection. The normalizing heat treatment temperature is 1050°C, the holding time is 35 min, and the cooling method is water jacket cooling under protective gas; the tempering heat treatment temperature is 790°C, the holding time is 90 min, and the cooling method is water jacket cooling under protective gas. Then it is straightened, with the straightness controlled to ≤1.0 mm / m, and then the inner and outer surface inspections, grinding, inner and outer polishing are carried out to obtain the finished tube, that is, the above heat exchange tube.

[0202] From Figure 1 and Figure 2 The comparison of the obtained microstructures shows that the microstructures of the heat exchange tubes in Example 1 and Comparative Example 1 are both martensite, but the grain size of the heat exchange tube in Example 1 is finer, the distribution of martensite lath bundles is more uniform, the carbides are finer and more dispersed.

[0203] The heat exchange tube of this comparative example has a low grain size and poor mechanical properties, and is not suitable for the lead-bismuth fast reactor field.

[0204] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a heat exchange tube, characterized in that: In terms of weight percentage, the components of the heat exchange tube include: C: 0.14-0.25%, Si: 1.0-2.0%, Mn: ≤1.0%, Cr: 10.0-12.0%, W: 1.0-2.0%, V: 0.15-0.30%, Ta: 0.10-0.20%, Ti: ≤0.01%, Al: ≤0.01%, P: ≤0.005%, S: ≤0.005%, Co: ≤0.01%, Ni: ≤0.01%, Cu: ≤0.01%, Mo: ≤0.005%, Nb: ≤0.005%, B: ≤0.002%, and the balance is Fe and unavoidable impurities; The grain size of the heat exchange tube is 7-10, and the microstructure is martensite without delta ferrite; The inclusion levels of the heat exchange tube are: AH 0.5, AT 0.5, BH 0.5, BT 0.5, CH 0.5, CT 0.5, CH0.5, CT 1.0; The inner surface roughness Ra of the heat exchange tube is ≤1.6 μm, and the outer surface roughness Ra is ≤1.6 μm; The depth of the decarburized layer on the inner surface of the heat exchange tube is h1, and the depth of the decarburized layer on the outer surface of the heat exchange tube is h2, and h1 and h2 satisfy: h1+h2≤0.3mm; The ovality of the heat exchange tube is ≤ 80% of the allowable deviation of the outer diameter; the uneven wall thickness of the heat exchange tube is ≤ 80% of the allowable deviation of the wall thickness; The preparation method of the heat exchange tube comprises: cold rolling a rough tube; the cold rolling comprises one or more pre-cold rolling, two or more first intermediate cold rolling, two or more second intermediate cold rolling and one or more finished cold rolling; heat treatment is performed after each cold rolling; the deformation amount of each cold rolling is independently 35-50%; The feed amount of the first intermediate cold rolling is 3~4mm / time, and the rolling speed is 40~50 times / min; The feed amount of the second intermediate cold rolling is 3~4mm / time, and the rolling speed is 65~70 times / min; The feed rate of finished cold rolling is 3~4mm / time, and the rolling speed is 30~40 times / min; During pre-cold rolling, a first solid solution heat treatment is performed after each cold rolling pass; the temperature of the first solid solution heat treatment is 740-780°C, the time is 10-40 minutes, and the cooling method is water-air cooling; During the first intermediate cold rolling, a second solution heat treatment is performed after each cold rolling pass; the temperature of the second solution heat treatment is 740-780°C, the time is 10-40 minutes, and the cooling method is water-air cooling; During the second intermediate cold rolling, the third solution heat treatment is performed after each cold rolling pass; the temperature of the third solution heat treatment is 740-780°C, the time is 15-20 minutes, and the cooling method is water jacket cooling under protective gas; During cold rolling of the finished product, normalizing heat treatment and tempering heat treatment are performed after each cold rolling pass; the temperature of the normalizing heat treatment is 1000-1100°C, the time is 15-30 minutes, and the cooling method is water jacket cooling under protective gas; the temperature of the tempering heat treatment is 740-780°C, the time is 80-100 minutes, and the cooling method is water jacket cooling under protective gas.

2. The method for preparing a heat exchange tube according to claim 1, characterized in that: The mechanical properties of the heat exchange tube are: R m ≥586MPa, R p0.2 ≥414MPa, A≥20%; R at 100℃ m ≥586MPa, R p0.2 ≥384MPa, A≥20%; R at 200℃ m ≥584MPa, R p0.2 ≥377MPa, A≥20%; R at 300℃ m ≥577MPa, R p0.2 ≥377MPa, A≥20%; R at 400℃ m ≥534MPa, R p0.2 ≥358MPa, A≥20%; R at 500℃ m ≥441MPa, R p0.2 ≥306MPa, A≥26.5%; R at 525℃ m ≥410MPa, R p0.2 ≥288MPa, A≥28%.

3. The method for preparing a heat exchange tube according to claim 1 or 2, characterized in that: The outer diameter of the heat exchange tube is 10-20 mm, and the wall thickness is 1-3 mm.

4. The method for preparing a heat exchange tube according to claim 1, characterized in that: The deformation of each cold rolling pass during pre-cold rolling is 40~45%; During the first intermediate cold rolling, the deformation of each cold rolling pass is 40~50%, the outer diameter tolerance D is ±0.3mm, and the wall thickness tolerance S is ±0.3mm; During the second intermediate cold rolling, the deformation of each cold rolling pass is 35~50%, the outer diameter tolerance D is ±0.2mm, and the wall thickness tolerance S is ±0.2mm; During the cold rolling of the finished product, the deformation of each cold rolling pass is 40~45%, the outer diameter tolerance D is ±0.1mm, and the wall thickness tolerance S is ±0.2mm.

5. The method for preparing a heat exchange tube according to claim 4, characterized in that: Hot-piercing the forged martensitic steel tube billet to obtain a rough tube; The rough tube is subjected to annealing treatment, straightening and pickling in sequence to obtain a first intermediate tube blank; The first intermediate tube blank is subjected to one pass of pre-cold rolling, degreasing, first solid solution heat treatment, straightening and pickling to obtain a second intermediate tube blank; the first solid solution heat treatment is carried out in a continuous roller hearth furnace; The second intermediate tube blank is subjected to two passes of first intermediate cold rolling in sequence, and degreasing, second solid solution heat treatment, straightening and pickling are performed after each pass of cold rolling to obtain a third intermediate tube blank; the second solid solution heat treatment is performed in a continuous roller hearth furnace; The third intermediate tube blank is subjected to two passes of second intermediate cold rolling in sequence, and degreasing, third solid solution heat treatment, straightening and pickling are performed after each cold rolling pass to obtain a fourth intermediate tube blank; the third solid solution heat treatment is performed in an ammonia decomposition heat treatment furnace; The fourth intermediate tube blank is subjected to one pass of finished cold rolling, degreasing, normalizing heat treatment, tempering heat treatment and straightening in sequence to obtain a finished tube; the normalizing heat treatment and / or the tempering heat treatment is carried out in a protective gas heat treatment furnace.

6. A heat exchange tube, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the heat exchange tube as claimed in claim 6 in a lead-bismuth fast reactor.

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