Manufacturing method of UNS N06690 alloy seamless heat exchange tube

Abstract

The invention discloses a manufacturing method of a UNS N06690 alloy seamless heat exchange tube, which belongs to the technical field of material processing, and comprises the following steps of: (1) performing peeling, PT inspection, shearing, centering, grinding, heating, perforating, water cooling and inspection on a round steel material; (2) carrying out acid pickling on the hot-punched blank, and then carrying out incoming material inspection and inner and outer surface grinding; (3) two-pass intermediate product cold rolling is carried out, and after cold rolling, intermediate product deoiling, intermediate product heat treatment, intermediate product straightening, intermediate product pipe cutting, acid pickling, intermediate product grinding and repairing and intermediate product inspection are carried out; (4) carrying out finished product cold rolling; (5) deoiling a finished product; (6) performing heat treatment on a finished product; (7) straightening a finished product; (8) carrying out finished product ultrasonic eddy current, water pressure and pipe cutting, sampling during pipe cutting, and carrying out physical and chemical tests; and (9) the obtained steel pipe is subjected to the procedures of finished product surface inspection, size inspection, cleaning, mark spraying and finishing and finally packaged and warehoused, and the product produced through the method is high in one-time inspection qualification rate and high in yield.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a heat exchange tube, in particular to a method for manufacturing a UNS N06690 alloy seamless heat exchange tube, and belongs to the technical field of material processing. Background Art

[0002] N06690 is a high-temperature corrosion-resistant alloy, mainly composed of nickel, chromium, iron and other elements. It has excellent resistance to stress corrosion cracking, good metallurgical stability and excellent processing characteristics. It is an ideal material for the heat transfer tubes of the steam generator of the pressurized water reactor of nuclear power plants. For thin-walled tubes of this type of alloy, hot extrusion / hot perforation combined with cold rolling is generally used for forming at home and abroad. At present, domestically produced N06690 alloy seamless heat exchange tubes have problems such as low first-time inspection pass rate, low material yield rate, low dimensional accuracy, and poor internal and external surface quality.

[0003] Patent CN115921573B discloses a method for manufacturing a UNS N10276 Hastelloy seamless heat exchange tube, which discloses: (i) subjecting the UNS N10276 hot extruded billet to incoming material inspection and grinding and repairing the inner and outer surfaces of the billet, specifically: subjecting the hot extruded billet to initial inspection + grinding and repairing + re-inspection, and subjecting the re-inspection to PT sampling; (ii) subjecting the billet obtained in step (i) to three passes of intermediate product cold rolling, and after each pass of cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, inspected and ground; (iii) subjecting the third pass of the steel pipe obtained in step (ii) to finished product cold rolling; (iv) subjecting the steel pipe obtained in step (iii) to finished product degreasing; (v) subjecting the steel pipe obtained in step (iv) to finished product heat treatment; (vi) subjecting the steel pipe obtained in step (v) to finished product straightening; (vii) subjecting the steel pipe obtained in step (vi) to finished product ultrasonic eddy current and water pressure treatment. , cutting the pipe, taking samples for physical and chemical tests when cutting the pipe; (viii) subjecting the steel pipe obtained in step (vii) to finished product surface inspection, cleaning, spraying and finishing processes, and finally packaging and warehousing; the products produced by this method have a high one-time inspection pass rate, high material yield rate, high dimensional accuracy, good internal and external surface quality, stable organizational performance, strong practicality, and are conducive to batch production; however, the intermediate product inspection and grinding in this patent are only simple grinding, the treatment is uneven, and it is easy to produce rough polishing marks, resulting in slight polishing marks on the surface of the finished product after cold rolling. The metallographic structure is not checked during the entire process, and the mechanical properties such as flaring and flattening and intergranular corrosion performance cannot be guaranteed. In addition, one-time degreasing is adopted when degreasing the finished product, which leads to incomplete degreasing and the risk of nitriding.

[0004] Based on this, developing a manufacturing method for N06690 alloy seamless heat exchange tubes that can overcome the above-mentioned difficulties, and developing N06690 alloy seamless heat exchange tubes with a high one-time inspection pass rate, high yield rate, high dimensional accuracy, good inner and outer surface quality, and physical and chemical properties that meet standard technical requirements has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0005] The technical problem to be solved by the present invention is to propose a method for manufacturing a UNSN06690 alloy seamless heat exchange tube in view of the shortcomings of the above-mentioned prior art. The products manufactured by this manufacturing method have a high one-time inspection pass rate, a high yield rate, high dimensional accuracy, good inner and outer surface quality, stable organizational performance, strong practicality, and are conducive to batch production.

[0006] The technical solution of the present invention to solve the above technical problems is:

[0007] A method for manufacturing a UNS N06690 alloy seamless heat exchange tube specifically comprises the following steps:

[0008] (I) UNS N06690 round steel is peeled, PT tested, sheared, centered, ground, heated, pierced, water cooled, and tested. The piercing temperature is 1120-1130°C, the heating time is 180 minutes, and the insulation time is 20 minutes.

[0009] (ii) The UNS N06690 hot-pierced billet is pickled, and the pickled billet is subjected to incoming material inspection and internal and external surface grinding and repairing, specifically: the hot-pierced billet is subjected to initial inspection + grinding and repair + re-inspection, and the endoscope is used for each re-inspection, and PT is performed on a random basis;

[0010] (iii) cold rolling the tube blank obtained in step (ii) to obtain an intermediate product, and after cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, ground and inspected, wherein:

[0011] When the intermediate product is cold rolled, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm. The value is an integer multiple of 0.05, where D represents the outer diameter and S represents the wall thickness.

[0012] The specific process of degreasing the intermediate product is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection;

[0013] The heat treatment of the intermediate product is carried out in a roller hearth furnace. The atmosphere in the furnace is a slightly oxidizing gas. The heat treatment temperature is 1070±10℃ and the holding time is ≥ wall thickness × 2min.

[0014] (iv) cold rolling the steel tube obtained in step (iii);

[0015] When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75;

[0016] When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm;

[0017] (5) degreasing the steel pipe obtained in step (4);

[0018] The specific steps of degreasing finished pipes are: soaking in alkali cylinder → soaking in hot water cylinder → wiping the outer surface → hitting the inner wall with wool felt balls → inspection → soaking in aerospace kerosene cylinder for 24 hours → soaking in alkali cylinder → soaking in hot water cylinder → wiping the outer surface → hitting the inner wall with wool felt balls → inspection;

[0019] (6) subjecting the steel pipe obtained in step (5) to finished product heat treatment;

[0020] The finished product heat treatment is carried out in a bright furnace with a pure hydrogen atmosphere;

[0021] When heat treating finished products, the heat treatment temperature is controlled to be 1070±10℃, and the holding time is ≥ wall thickness × 2.5min;

[0022] (7) straightening the steel pipe obtained in step (6);

[0023] (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical tests when cutting the pipe;

[0024] (IX) The steel pipe obtained in step (VIII) is subjected to finished product surface inspection, dimension inspection, cleaning, spray marking and finishing processes, and finally packaged and stored.

[0025] The technical solution further defined in the present invention is:

[0026] Furthermore, in the aforementioned method for manufacturing the UNS N06690 alloy seamless heat exchange tube, in the step (iii) of degreasing the intermediate product, the components of the solution in the alkali cylinder are controlled to be degreased in the alkali cylinder in a mass ratio of: degreasing agent (alkali powder): water = 1:7, the alkali cylinder temperature is 70-80°C, and the alkali cylinder immersion time is 40-60min;

[0027] When degreasing the acid cylinder, the components of the solution in the acid cylinder are controlled to be calculated by mass percentage as follows: HF: 1%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components is 100%. The acid cylinder temperature is 60°C and the pickling time is 40-60min.

[0028] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tube, when straightening the intermediate product in step (iii), the straightening control speed is ≤8m / min, the curvature after straightening is ≤1.0mm / m, and the outer diameter deviation after straightening is ±0.02mm.

[0029] Technical effect: The present invention stipulates the requirements for straightening speed, straightness and the deviation range of outer diameter after straightening, so as to ensure the curvature while avoiding the risks of iron rod straightening scratches and marks, thereby ensuring the straightening quality. Strictly stipulating the deviation range of outer diameter after straightening can effectively avoid the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0030] In the manufacturing method of the aforementioned UNS N06690 alloy seamless heat exchange tube, during the pickling of the intermediate product in step (iii), the components of the solution in the acid cylinder are calculated by mass ratio as follows: HF: 5-8%, HNO3: 10-15%, and the balance is tap water, the sum of the above components is 100%, the acid cylinder temperature is controlled to be: 60°C, the pickling time is 5-8h, and after pickling for 5 hours, the cylinder needs to be opened every 30 minutes to observe the inner and outer surfaces. Pickling is stopped when the inner and outer surfaces show uniform and slight oxide scale to avoid excessive pickling and affect subsequent work.

[0031] Technical effect: The present invention provides a method for pickling intermediate products in the first and second passes, including strictly controlling the ratio of the acid cylinder, temperature and time to ensure the pickling quality. Conventional N06690 pickling often lacks acid to avoid over-acidification, resulting in excessively thick scales, low internal and external polishing efficiency, and low pass rate of one endoscopic inspection after polishing, requiring multiple rework and repairs. However, the N06690 intermediate product tube washed out by this method has only slight uniform scales on the inner and outer walls, and has no tendency to over-acidification, high internal and external polishing efficiency, and high pass rate of one endoscopic inspection, which greatly reduces the cost of manual polishing, improves production efficiency, and shortens the entire intermediate product production cycle.

[0032] In the manufacturing method of the aforementioned UNS N06690 alloy seamless heat exchange tube, during the grinding and inspection of the intermediate product after the first cold rolling in step (iii), the grinding and repair adopts the method of local spot grinding after internal and external polishing, the external polishing adopts the method of flap wheel external polishing, the internal polishing adopts the method of internal polishing with a cross polishing head automatic internal polishing machine made of sandpaper, the local spot grinding adopts a polishing machine equipped with a patterned impeller, and the inspection adopts visual inspection + endoscope one by one; during the grinding and inspection of the intermediate product after the second pass, the grinding and repair adopts the method of local spot grinding after internal and external polishing, the external polishing adopts the method of belt polishing machine, the internal polishing adopts the method of artificial sandpaper internal polishing, the local spot grinding adopts a polishing machine equipped with a soft-edged patterned impeller, and the inspection adopts visual inspection + endoscope one by one. After the internal and external grinding and inspection, the tubes that have passed the inspection are randomly inspected for metallographic structure according to the frame number to ensure that there is no metallographic precipitation before circulated. The aforementioned UNS In the manufacturing method of N06690 alloy seamless heat exchange tube, when the finished tube is degreased once in step (V), the solution in the alkali cylinder is calculated by mass ratio of degreasing agent: water = 1:6.5, the alkali cylinder temperature is 40-60°C, the alkali cylinder immersion time is 30-60min, the hot water cylinder temperature is 70-80°C, the hot water cylinder immersion time is 10-20min, after the hot water cylinder is taken out of the cylinder, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, and the number of times is 3- 5 times; after the first degreasing, transfer to the aerospace kerosene cylinder and soak for 24 hours for the second degreasing. The mass ratio of the solution in the alkali cylinder for the second degreasing is, degreaser: water = 1:6.5, alkali cylinder temperature: 40-60℃, alkali cylinder soaking time: 20-40min, hot water cylinder temperature: 70-80℃, hot water cylinder soaking time: 5-10min. After the hot water cylinder is out of the cylinder, wipe the outer surface with cotton cloth soaked in acetone, and beat the inner wall with wool felt until it is clean, 2-4 times.

[0033] Technical effect: The present invention provides a process for high value-added nickel-based products, especially small-diameter heat exchange tubes with crystal corrosion requirements, which includes a primary degreasing process followed by kerosene cylinder immersion and a secondary degreasing process, which helps to improve the final degreasing quality of the finished product. The residual oil molecules that are difficult to remove after kerosene cylinder immersion and cold rolling are similarly dissolved for 24 hours and then subjected to secondary degreasing, which can greatly improve the degreasing quality of the finished product and avoid the presence of some residual oil, oil spots, oil film and the like due to unclean degreasing, which leads to the risk of nitriding in the heat treatment of the finished product, and ultimately leads to the risk of unqualified metallographic structure, mechanical properties and crystal corrosion properties of the finished product. The secondary degreasing process and the finished product heat treatment are combined in a pure hydrogen atmosphere, which helps to improve the final physical and chemical properties of the high value-added nickel-based alloy small-diameter heat exchange tube.

[0034] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tube, a plastic roller straightener is used for straightening the finished tube in step (seven), the straightener speed is controlled to be ≤10m / min, the curvature after straightening is ≤0.5mm / m, and the outer diameter deviation after straightening is ±0.01mm.

[0035] Technical effect: The present invention specifies the straightening machine model, straightening speed, straightness and outer diameter deviation range after straightening. The finished product straightening specifies the use of a plastic roller straightening machine, and specifies the straightening speed ≤ 10m / min. While ensuring the curvature, the risk of iron rod straightening scratches and marks can be avoided, thereby ensuring the quality of the finished product straightening. Strictly specifying the outer diameter deviation range after straightening of the finished product can effectively avoid the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0036] In the aforementioned method for manufacturing the UNS N06690 alloy seamless heat exchange tube, the first ultrasonic qualified rate in step (eight) is ≥96%, and the first eddy current qualified rate is 100%.

[0037] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tube, the surface inspection in step (IX) includes visual inspection and dimensional inspection, with a qualified rate of ≥95%, and the dimensional accuracy of the finished tube is controlled as follows: outer diameter ±0.05mm, wall thickness ±0.05mm, the inner and outer surfaces of the finished tube are smooth, and the inner and outer wall roughness Ra≤0.8.

[0038] In the aforementioned method for manufacturing the UNS N06690 alloy seamless heat exchange tube, the finished tube obtained by room temperature tensile test has the following characteristics: yield strength of 280-320 MPa, tensile strength of 640-680 MPa, and elongation after fracture ≥55%.

[0039] The beneficial effects of the present invention are:

[0040] The present invention adopts three cold rolling passes, wherein the first and second passes are intermediate cold rolling passes, and the cold rolling deformation is controlled at 55%-65%, and the third pass is finished cold rolling pass, and the cold rolling deformation is controlled at 60%-70%. The multi-pass rolling is performed to fully break the crystal grains, and a finer grain size can be obtained after heat treatment. The first and second intermediate cold rolling passes ensure the surface quality by strictly controlling the feed amount ≤3mm / time, and the deformation is more uniform by controlling the Q value ≥1.10, thereby improving the dimensional accuracy; similarly, the finished cold rolling ensures the surface quality and dimensional accuracy by strictly controlling the feed amount ≤2mm / time and controlling the Q value ≥0.75.

[0041] The present invention provides a method for degreasing intermediate products in steps 1 and 2, including strictly controlling the ratio of the solution in the alkali cylinder and the acid cylinder, the temperature and time to ensure the degreasing quality and avoid the risk of carburization during heat treatment, and provides a method for degreasing finished products in steps 3, which uses alkali cylinder degreasing, water cylinder soaking, acetone wiping the outer surface and acetone soaked cloth strips to clean the inner wall. Strictly control the ratio of the alkali cylinder, the temperature and time, and the inner and outer wall cleaning methods to ensure the degreasing quality of the finished pipe and ensure that there is no risk of nitriding during the bright heat treatment of the finished product.

[0042] The present invention stipulates that the solution heat treatment of the intermediate products of the 1st and 2nd passes is carried out in a roller hearth furnace, the atmosphere in the furnace is slightly oxidizing, the heat treatment temperature is 1070±10°C, the cold rolling work hardening is eliminated, the seamless pipe is guaranteed to have good plasticity, and the subsequent cold rolling forming is convenient; the insulation time of the intermediate products of the 1st and 2nd passes is ≥ wall thickness × 2min, generally the nearest integer is taken, the insulation time is slightly longer, the oxide scale is more uniform and loose, and the oxide scale is easy to be removed by pickling; the solution heat treatment of the finished product of the 3rd pass is carried out in a bright furnace, the atmosphere in the furnace is pure hydrogen, the heat treatment temperature is 1070±10°C, and the insulation time of the finished product is ≥ wall thickness × 2.5min, the purpose is to obtain good organization and comprehensive mechanical properties while ensuring the brightness of the surface color of the heat exchange tube and the consistency of the overall color.

[0043] The present invention provides a method for grinding and repairing hot perforated billets and intermediate steel pipes. The purpose of retesting and sampling the hot perforated billets is to avoid residual cracks on the outer surface. The purpose of endoscopes for hot perforated billets is to more accurately and efficiently treat the inner wall defects and avoid the inner wall defects from being transferred to the next cold rolling process and causing the defects to extend. The purpose of endoscopes for intermediate products is to ensure the inner wall quality of the finished cold-rolled products and reduce the risk of endoscope failure due to ultrasonic internal damage and inner wall defects, thereby improving the final ultrasonic qualified rate, surface inspection qualified rate and final yield rate.

[0044] Compared with the prior art, the present invention adds equipment and methods for grinding intermediate products. Belt polishing is used in the previous step before the finished product, which is more uniform than the external polishing by the flap wheel, and will not produce rough polishing marks that lead to slight polishing marks on the surface of the finished product after cold rolling. Metallographic inspection is carried out on the incoming intermediate products before the cold rolling of the finished product, and in order to ensure the degreasing quality, the finished product is degreased once and then immersed in a kerosene cylinder for 24 hours and then degreased twice, both of which are to ensure that there is no risk of nitriding after the heat treatment of the finished product, and to ensure the metallographic structure while also ensuring the mechanical properties such as expansion and flattening and intergranular corrosion resistance.

[0045] The method of the present invention solves the problems of low first-time inspection pass rate, low material yield rate, low dimensional accuracy and poor inner and outer surface quality by strictly limiting the process optimization of UNS N06690 alloy seamless heat exchange tubes. The products produced by the method have high first-time inspection pass rate, high material yield rate, high dimensional accuracy, good inner and outer surface quality, stable mechanical properties, strong practicality, and are conducive to batch production.

[0046] The N06690 alloy seamless heat exchange tube prepared by the method of the present invention has a first ultrasonic qualified rate of ≥96%, a first eddy current qualified rate of 100%, a first table inspection (visual inspection + size inspection) qualified rate of ≥95%, and a comprehensive first inspection qualified rate (ultrasonic qualified rate×eddy current qualified rate×table inspection qualified rate) of ≥91%.

[0047] The yield rate of the N06690 alloy seamless heat exchange tube prepared by the method of the present invention (round steel→finished tube) is ≥78%; the prepared N06690 alloy seamless heat exchange tube can meet the following dimensional accuracy: outer diameter ±0.05mm, wall thickness ±0.05mm; the prepared seamless heat exchange tube has smooth inner and outer surfaces, and the color is consistent, and the inner and outer wall roughness Ra≤0.8; its room temperature tensile test: yield strength 280-320Mpa, tensile strength 640-680MPa, elongation after fracture ≥55%. DETAILED DESCRIPTION

[0048] The present invention will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for manufacturing a UNS N06690 alloy seamless heat exchange tube, the finished product specification is φ25×3×7864mm, and the technical requirements must meet both ASME SB163-2021 and NB / T47019.9-2021 standards, specifically comprising the following steps:

[0051] (I) UNS N06690 Yongxing round steel is peeled, PT tested, cut, centered, ground, heated, perforated, water cooled and tested. The perforation temperature is 1120-1130℃, the perforation specification is φ95×12mm, the heating time is 180min, and the insulation time is 20min.

[0052] (ii) The UNS N06690 hot-pierced billet is pickled, and the pickled billet is subjected to incoming material inspection and internal and external surface grinding and repair. The hot-pierced billet is subjected to initial inspection + grinding and repair + re-inspection. During the re-inspection, endoscopes are used one by one, and PT is performed on random inspections. Specifically, the defects of the billet and its grinding and repairing methods are preliminarily characterized. For the hot-piercing defects on the outer surface of the billet, spot grinding + external polishing is performed on it. For the defects of the inner burrs and transverse cracks on some billets, internal polishing is performed on them. After the billet is ground, it is re-inspected. During the re-inspection, random inspections are performed for PT. Only qualified products can be circulated, and unqualified products are re-grinded;

[0053] (iii) subjecting the tube blank obtained in step (ii) to two passes of intermediate product cold rolling, and after each pass of cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, ground (local spot grinding after internal and external polishing) and inspected (endoscope for each product), wherein:

[0054] When the intermediate product is cold rolled, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm. The value is an integer multiple of 0.05, where D represents the outer diameter and S represents the wall thickness;

[0055] The specific process of degreasing the intermediate product is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection;

[0056] The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing atmosphere, a heat treatment temperature of 1070±10℃, and a holding time ≥ wall thickness × 2min (rounded to an integer);

[0057] (iv) cold rolling the steel tube obtained in step (iii);

[0058] When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75;

[0059] When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm;

[0060] (5) degreasing the steel pipe obtained in step (4);

[0061] The specific steps of degreasing finished pipes are: soaking in alkali tank → soaking in clean water tank → wiping the outer surface → taping the inner wall with cloth → inspection;

[0062] (6) subjecting the steel pipe obtained in step (5) to finished product heat treatment;

[0063] The finished product heat treatment is carried out in a bright furnace with a pure hydrogen atmosphere;

[0064] When the finished product is heat treated, the heat treatment temperature is controlled to be 1070±10℃, and the holding time is ≥ wall thickness×2.5min (take the integer);

[0065] (7) straightening the steel pipe obtained in step (6);

[0066] (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical tests when cutting the pipe;

[0067] (IX) The steel pipe obtained in step (VIII) is subjected to finished product surface inspection, dimension inspection, cleaning, spray marking and finishing processes, and finally packaged and stored.

[0068] In this embodiment, when formulating the cold rolling process of UNS N06690 seamless heat exchange tube, the cold rolling deformation of intermediate products and finished products is strictly controlled, and a reasonable rolling speed and a relatively small feed amount are selected to ensure the quality of the inner and outer surfaces. The uniformity of the structure in the wall thickness direction is ensured by controlling the Q value, thereby improving the dimensional accuracy and improving the inner wall quality. The specific cold rolling parameters are shown in Table 1 below, and the technical requirements for dimensional accuracy and actual dimensions are shown in Table 2. It can be seen from Table 2 that the dimensional accuracy of the intermediate product tubes and finished tubes of each pass meets the internal control requirements, and the dimensional accuracy of the finished tubes is much higher than the standard requirements for Class I heat exchange tubes in ASME SB163-2021 and NB / T47019.1-2021 standards.

[0069] Table 1 UNS N06690 cold rolling parameters

[0070]

[0071] Table 2 UNS N06690 technical requirements dimensional accuracy and actual measured dimensions

[0072]

[0073] The specific process of degreasing the intermediate product of the UNS N06690 alloy seamless heat exchange tube in this embodiment is: degreasing in an alkali cylinder → rinsing → soaking in a hot water cylinder → degreasing in an acid cylinder → rinsing → inspection. The main control requirements for degreasing the intermediate product are shown in Table 3; the specific steps for degreasing the finished product tube are: soaking in an alkali cylinder → soaking in a hot water cylinder → wiping the outer surface → hitting the inner wall with wool felt balls → inspection → soaking in an aerospace kerosene cylinder for 24 hours →

[0074] Soak in alkali tank → Soak in hot water tank → Wipe outer surface → Beat inner wall with wool felt ball → Inspect. The main control requirements for degreasing finished pipes are shown in Table 4. The inner and outer surfaces of the pipes degreased according to the above method are clean and free of oil stains, and there is no risk of nitriding during heat treatment.

[0075] Table 3 Main control requirements for UNS N06690 intermediate product degreasing process

[0076]

[0077] Table 4 Main control requirements for degreasing process of UNS N06690 finished pipe

[0078]

[0079] Table 4 shows that the finished product pipes are transferred to the aerospace kerosene tank for 24 hours after degreasing. After the secondary degreasing, the technicians confirm the degreasing quality of the inner and outer surfaces before heat treatment. The outer surface is wiped with a white cloth strip to show no blackening phenomenon. The inner wall is inspected by endoscope to confirm that there is no oil stain, oil spot or oil film. The heat treatment of the intermediate products of the UNS N06690 alloy seamless heat exchange tubes in this embodiment is carried out in a roller hearth furnace with an oxidizing atmosphere; the heat treatment of the finished products is carried out in a bright furnace with a pure hydrogen atmosphere. The heat treatment system is shown in Table 5.

[0080] 5UNS N06690 heat treatment system

[0081]

[0082] It can be seen from Table 5 that the solution heat treatment of the intermediate product is carried out in a roller hearth furnace. The atmosphere in the furnace is slightly oxidizing. There are 6 temperature zones in the furnace. The first three temperature zones T01-T03 are heating zones, and the last three temperature zones T04-T06 are insulation zones. The heat treatment temperature is 1070°C, and the insulation time is 14min and 9min respectively. The cooling method is water cooling. The finished product heat treatment is bright heat treatment. The atmosphere in the furnace is pure hydrogen. There are 5 temperature zones in the furnace. T01-T02 is the heating zone, T03-T05 is the insulation zone, the heat treatment temperature is 1070°C, the insulation time is 8min, and the cooling method is water jacket cooling.

[0083] The straightening parameters of the intermediate and finished products of the UNS N06690 seamless heat exchange tubes in this embodiment are shown in Table 6. By specifying the straightening machine model, straightening speed, straightness and outer diameter deviation range after straightening, especially the straightening of finished products, it is specified that a plastic roller straightening machine is used, and the straightening speed is specified to be ≤10m / min. While ensuring the curvature, the risk of iron rod straightening scratches and marks can be avoided, thereby ensuring the quality of finished product straightening. Strictly specifying the outer diameter deviation range after straightening, especially after straightening of finished products, can effectively avoid the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0084] Table 6 UNS N06690 straightening parameters

[0085]

[0086] In this embodiment 1, the requirements for cutting the intermediate products and finished products of the UNS N06690 alloy seamless heat exchange tubes are shown in Table 7. By strictly controlling the amount of flattening and strictly following the middle cutting method, the middle position must be manually measured and marked before cutting the tube, and visual inspection is not allowed. This can reduce the risk of the intermediate products and finished products being under-lengthened, and improve the final product inspection pass rate and the final yield rate.

[0087] Table 7 UNS N06690 pipe cutting requirements

[0088]

[0089] In this embodiment 1, the main control requirements for pickling of the intermediate product of UNS N06690 alloy seamless heat exchange tube are shown in Table 8 below, including strict control of the ratio of the acid tank, temperature and time to ensure the quality of pickling. Conventional N06690 pickling often lacks acid to avoid over-acidification, resulting in excessively thick oxide scales, low internal and external polishing efficiency, and low pass rate of one endoscopic inspection after polishing, requiring multiple rework and repair. However, the N06690 intermediate product tube washed out by this method has only slight and uniform oxide scales on the inner and outer walls, and has no tendency to over-acidification, high internal and external polishing efficiency, and high pass rate of one endoscopic inspection, which greatly reduces the cost of manual polishing, improves production efficiency, and shortens the entire intermediate product production cycle.

[0090] Table 8 Main control requirements for the pickling process of UNS N06690 intermediate products

[0091]

[0092] In this embodiment 1, the inspection and grinding and repairing requirements for the perforated billets and intermediate product tubes of UNS N06690 seamless heat exchange tubes are shown in Table 9 below. The re-inspection and random inspection of the hot perforated billets is to avoid that there are no cracks remaining on the outer surface. The endoscope of the hot perforated billets is to treat the inner wall defects more accurately and efficiently to avoid the inner wall defects from flowing to the next cold rolling process and causing the defects to extend. The endoscope is performed one by one during the grinding and repair of the intermediate products in the 1st and 2nd passes to ensure the inner wall quality of the finished cold rolling, reduce the risk of endoscope failure due to ultrasonic internal damage and inner wall defects, thereby improving the final ultrasonic qualified rate, surface inspection qualified rate and final yield rate.

[0093] Table 9 UNS N06690 grinding and repairing operation requirements

[0094]

[0095] In the above Table 9, when the intermediate product is ground and inspected after the first cold rolling, the grinding is carried out by polishing inside and outside and then spot grinding. The outer polishing is carried out by a flap wheel, and the inner polishing is carried out by an automatic inner polishing machine with a cross polishing head made of sandpaper. The local spot grinding is carried out by a polishing machine equipped with a patterned impeller, and the inspection is carried out by visual inspection + endoscope one by one;

[0096] During the second pass of intermediate product grinding and inspection, the grinding is carried out by internal and external polishing followed by local spot grinding. The external polishing is carried out with a belt polishing machine, the internal polishing is carried out with artificial sandpaper, and the local spot grinding is carried out with a grinder equipped with a soft-edged impeller. The inspection is carried out visually + through an endoscope one by one. After the internal and external grinding and inspection, the metallographic structure of the pipes that have passed the inspection is randomly inspected according to the frame number to ensure that there is no metallographic precipitation before arrangement for circulation.

[0097] In this embodiment 1, the ultrasonic, eddy current, water pressure, visual and dimensional inspection results of the finished UNS N06690 alloy seamless heat exchange tube are shown in Table 10. It can be seen from Table 10 that the ultrasonic, eddy current and water pressure qualified rates of the N06690 alloy seamless heat exchange tube produced by the production method are as high as 96.71%, and the qualified rates of eddy current and water pressure are both 100.00%, and the qualified rate of dimensional inspection is also 100.00%. The dimensional accuracy is much higher than the dimensional accuracy specified in ASME SB163-2021 and NB / T47019.9-2021 standards, the visual inspection qualified rate is as high as 95.97%, and the one-time inspection qualified rate is as high as 93.55%.

[0098] Table 10: Ultrasonic, eddy current, water pressure, visual and dimensional inspection of finished UNS N06690 pipes

[0099]

[0100] In this embodiment 1, the yield rate of UNS N06690 alloy seamless heat exchange tubes is shown in Table 11. The hot-punched billet round steel is 83.92 tons, and the final finished product φ25×2.1×7864mm has 5150 pieces in storage and weighs 66.82 tons, with a yield rate of up to 79.62%.

[0101] Table 11 UNS N06690 yield rate

[0102]

[0103] The test method for room temperature tensile properties of finished tubes is ASTM E8, and the test results are shown in Table 12. From Table 12, it can be seen that the N06690 alloy seamless heat exchange tubes manufactured by this method have excellent mechanical properties, with a yield strength of 282-318Mpa under 39 furnace batch numbers, which is higher than the ASME SB163-2021 standard requirement of ≥240Mpa, a stable tensile strength of 641-678Mpa, higher than the standard requirement of ≥586Mpa, and a post-break elongation of ≥55%, which is much higher than the standard requirement of ≥30%.

[0104] Table 12 Room temperature tensile properties of UNS N06690 finished pipe

[0105]

[0106] According to the test requirements of GB / T 242-2007, the expansion test results of all 39 batches of N06690 alloy tubes are: no cracks. According to the test requirements of GB / T 246-2017, the flattening test results of all 39 batches of N06690 alloy tubes are: no cracks.

[0107] According to the requirements of the technical agreement, all batches of N06690φ25×3 steel pipes were subjected to crystal corrosion tests according to GB / T 15260-2016B method. The results of the crystal corrosion tests are shown in Table 2.15 below.

[0108] Table 13 UNS N06690 crystal corrosion test results

[0109] Crystalline rot test Test solution Test cycle Test results GB / T 15260-2016 Method B <![CDATA[Cu-CuSO4-16%H2SO4]]> 24 hours Flattening test without cracks

[0110] The present invention solves the problems of low first-time inspection pass rate, low material yield rate, low dimensional accuracy and poor inner and outer surface quality by strictly limiting the process optimization of UNS N06690 alloy seamless heat exchange tubes. It can be seen from Tables 10-13 that the products produced by the method have a high first-time inspection pass rate, a high material yield rate, high dimensional accuracy, good inner and outer surface quality, stable mechanical properties, strong practicability, and are conducive to batch production.

[0111] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for manufacturing a UNS N06690 alloy seamless heat exchange tube, characterized in that: The specific steps include: (I) UNS N06690 round steel is peeled, PT tested, sheared, centered, ground, heated, pierced, water cooled and tested. The piercing temperature is 1120-1130℃, the heating time is 180min, and the holding time is 20min. (ii) The UNS N06690 hot-pierced billet is pickled, and the pickled billet is subjected to incoming material inspection and internal and external surface grinding and repairing. Specifically, the hot-pierced billet is subjected to initial inspection + grinding and repair + re-inspection. During the re-inspection, each endoscope is used and PT is randomly inspected; (iii) subjecting the tube blank obtained in step (ii) to two passes of intermediate product cold rolling, and after each pass of cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, ground and inspected, wherein: When the intermediate product is cold rolled, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm; The specific process of degreasing the intermediate product is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection; The intermediate product heat treatment is carried out in a roller hearth furnace, the atmosphere in the furnace is a slightly oxidizing gas, the heat treatment temperature is 1070±10°C, and the holding time is ≥ wall thickness×2min; (iv) cold rolling the steel tube obtained in step (iii); When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75; When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm; (5) degreasing the steel pipe obtained in step (4); The specific steps of degreasing finished pipes are: soaking in alkali cylinder → soaking in hot water cylinder → wiping the outer surface → hitting the inner wall with wool felt balls → inspection → soaking in aerospace kerosene cylinder for 24 hours → soaking in alkali cylinder → soaking in hot water cylinder → wiping the outer surface → hitting the inner wall with wool felt balls → inspection; (vi) subjecting the steel pipe obtained in step (v) to finished product heat treatment; The finished product heat treatment is carried out in a bright furnace with a pure hydrogen atmosphere; When heat treating finished products, the heat treatment temperature is controlled to be 1070±10℃, and the holding time is ≥ wall thickness × 2.5min; (VII) straightening the steel pipe obtained in step (VI); (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical tests when cutting the pipe; (IX) The steel pipes obtained in step (VIII) are subjected to finished product surface inspection, dimension inspection, cleaning, spray marking and finishing processes, and finally packaged and stored.

2. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (iii) of degreasing the intermediate product, when degreasing the alkali cylinder, the components of the solution in the alkali cylinder are controlled to be in the following mass ratio: degreasing agent: water = 1:7, the alkali cylinder temperature: 70-80°C, and the alkali cylinder soaking time: 40-60min; When degreasing the acid cylinder, the components of the solution in the acid cylinder are controlled to be calculated by mass percentage as follows: HF: 1%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components is 100%. The acid cylinder temperature is 60°C and the pickling time is 40-60min.

3. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: When straightening the intermediate product in the step (iii), the straightening control speed is ≤8m / min, the curvature after straightening is ≤1.0mm / m, and the outer diameter deviation after straightening is ±0.02mm.

4. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: When the intermediate product is pickled in step (iii), the components of the solution in the acid cylinder are calculated by mass ratio: HF: 5-8%, HNO3: 10-15%, and the balance is tap water. The sum of the above components is 100%. The temperature of the acid cylinder is controlled at 60°C and the pickling time is 5-8h.

5. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (iii), when the intermediate product is ground and inspected after the first cold rolling, the grinding is carried out by polishing the inside and outside and then spot grinding. The outer polishing is carried out by a flap wheel, the inner polishing is carried out by an automatic inner polishing machine with a cross polishing head made of sandpaper, the local spot grinding is carried out by a polishing machine equipped with a patterned impeller, and the inspection is carried out by visual inspection + endoscope one by one During the second pass of intermediate product grinding and inspection, the grinding is carried out by internal and external polishing followed by local spot grinding. The external polishing is carried out with a belt polishing machine, the internal polishing is carried out with artificial sandpaper, and the local spot grinding is carried out with a grinder equipped with a soft-edged impeller. The inspection is carried out visually + through an endoscope one by one. After the internal and external grinding and inspection, the metallographic structure of the pipes that have passed the inspection is randomly inspected according to the frame number to ensure that there is no metallographic precipitation before arrangement for circulation.

6. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: When the finished pipe is degreased once in the step (V), the mass ratio of the solution in the alkali cylinder is as follows: degreasing agent: water = 1:6.5, the temperature of the alkali cylinder is 40-60°C, the soaking time of the alkali cylinder is 30-60min, the temperature of the hot water cylinder is 70-80°C, the soaking time of the hot water cylinder is 10-20min, after the hot water cylinder comes out of the cylinder, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, the number of times is 3-5 times, after the first degreasing, it is transferred to the aerospace kerosene cylinder and soaked for 24h before secondary degreasing, the mass ratio of the solution in the alkali cylinder for secondary degreasing is as follows: degreasing agent: water = 1:6.5, the temperature of the alkali cylinder is 40-60°C, the soaking time of the alkali cylinder is 20-40min, the temperature of the hot water cylinder is 70-80°C, the soaking time of the hot water cylinder is 5-10min, after the hot water cylinder comes out of the cylinder, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, the number of times is 2-4 times.

7. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (VII), when the finished tube is straightened, the control speed of the straightening machine is ≤10m / min, the curvature after straightening is ≤0.5mm / m, and the outer diameter deviation after straightening is ±0.01mm.

8. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (eight), the first ultrasonic qualified rate is ≥96%, and the first eddy current qualified rate is 100%.

9. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: The surface inspection in step (IX) includes visual inspection and dimensional inspection, with a pass rate of ≥95%. The dimensional accuracy of the finished tube is controlled as follows: outer diameter ±0.05mm, wall thickness ±0.05mm, the inner and outer surfaces of the finished tube are smooth, and the inner and outer wall roughness Ra≤0.

8.

10. The method for manufacturing the UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: The room temperature tensile test of the manufactured finished pipe shows the following results: yield strength 280-320 MPa, tensile strength 640-680 MPa, and elongation after fracture ≥55%.

Images