A high-temperature alloy seamless pipe with low residual stress and preparation method thereof

Abstract

The invention discloses a high-temperature alloy seamless pipe with low residual stress and a preparation method thereof. The high-temperature alloy seamless pipe with low residual stress comprises the following components by mass percentage: C: 0.03-0.12%, Mn: 1.0-2.1%, Cr: 14-17%, Ni: 35-38%, Mo: 1.5-3.5%, Nb: 0.5-1.5%, W: 0.5-2.0%, B: 0.004%, Y: 0.1-0.2%, Zr: 0.05-0.1%, and the balance is Fe and inevitable impurities. By designing the alloy composition, vacuum induction smelting → vacuum consumable remelting → homogenization treatment → forging blanking → hot extrusion pipe making → surface finishing → infiltration layer, a high-temperature alloy seamless pipe with low residual stress and excellent organizational stability at high temperature is obtained.

Description

Technical Field

[0001] The invention relates to the field of manufacturing of iron-nickel-based high-temperature alloy seamless pipes, and more specifically to a high-temperature alloy seamless pipe with low residual stress and a preparation method thereof. Background Art

[0002] As one of the most cutting-edge nuclear power technologies in the world today, the sodium-cooled fast reactor is the main reactor type for my country to develop the fourth-generation advanced nuclear energy system, and is also an important strategic choice for China's nuclear energy technology to achieve a closed fuel cycle and sustainable development. At this stage, my country has built a sodium-cooled experimental fast reactor, of which a 600MW demonstration fast reactor project is under active construction. Due to the extremely harsh service conditions of the sodium-cooled fast reactor, which is in a harsh environment such as high temperature, corrosion, and irradiation for a long time, the selection standards for key structural materials of the sodium-cooled fast reactor are significantly higher than those of the second- and third-generation pressurized water reactors. At present, the materials used for key structural parts of the sodium-cooled fast reactor have not yet been domestically produced, which seriously restricts the long-term development of China's fast reactor project.

[0003] The moving guide tube in the sodium-cooled fast reactor system provides a channel for the control rod to drop. It has been in service for a long time in a high temperature, sodium, and irradiation environment. In order to ensure that the control rod can move up and down accurately, it is required that it cannot be deformed during long-term service. In the process of hot processing or cold processing of manufacturing structural parts, internal residual stress is inevitably caused. Under the interaction of static and dynamic loads during service, the residual stress can easily cause deformation of the structural parts. Therefore, low residual stress is an important prerequisite for ensuring that the deformation of the moving guide tube is small. In addition, the service life of the sodium-cooled fast reactor is as long as 40 to 60 years. The normal and stable operation of key components during the operation of the reactor is an important prerequisite for ensuring nuclear power safety. Therefore, the material is required to have good organizational and performance stability at high temperatures. Regarding the materials and related processes of various key structural parts of the sodium-cooled fast reactor, foreign countries have been in a state of technical blockade and there are few public reports. Publication No. CN111876690A provides an alloy moving guide tube and a manufacturing method for a sodium-cooled fast reactor control rod drive mechanism. The moving guide tube is prepared by hot extrusion + multi-pass cold rolling. Not only is the pipe making process longer, but multi-pass cold rolling is also likely to lead to large residual stress in the material, mixed crystal and other structural instability phenomena.

[0004] In view of the above situation, according to the service characteristics of the above-mentioned sodium-cooled fast reactor moving guide tube and the influence of W, Mo, Nb, W / Nb on the microstructure stability of the alloy at high temperature and the influence of the tube making process on the residual stress, it is necessary to develop a high-temperature alloy seamless tube with low residual stress and high microstructure stability to ensure that the sodium-cooled fast reactor moving guide tube has good microstructure and performance stability during long-term service. Summary of the invention

[0005] In view of the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide a high-temperature alloy seamless pipe with low residual stress and a preparation method thereof. By designing the alloy composition, vacuum induction smelting → vacuum consumable remelting → homogenization treatment → forging blanking → hot extrusion pipe making → surface finishing → infiltration layer, a high-temperature alloy seamless pipe with low residual stress and excellent organizational stability at high temperature is obtained.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a high-temperature alloy seamless pipe with low residual stress, comprising the following components in mass percentage: C: 0.03-0.12%, Mn: 1.0-2.1%, Cr: 14-17%, Ni: 35-38%, Mo: 1.5-3.5%, Nb: 0.5-1.5%, W: 0.5-2.0%, B: 0.004%, Y: 0.1-0.2%, Zr: 0.05-0.1%, and the balance is Fe and inevitable impurities.

[0008] Preferably, the composition of the low residual stress high temperature alloy seamless pipe satisfies: W / Nb is 0.5-0.8.

[0009] Preferably, at room temperature, the yield strength Rp of the low residual stress high temperature alloy seamless pipe is 0.2 ≥240MPa, tensile strength Rm≥550MPa, elongation A≥45%, impact energy KV2≥400J;

[0010] At 750°C, the yield strength Rp of the low residual stress high temperature alloy seamless pipe 0.2 ≥140MPa, tensile strength Rm≥270MPa, elongation A≥60%.

[0011] The second aspect of the present invention provides a method for preparing a high-temperature alloy seamless pipe with low residual stress as described in the first aspect of the present invention, comprising the following steps:

[0012] S1, vacuum induction smelting, using vacuum induction smelting and casting electrode rods, and then annealing and surface finishing the electrode rods;

[0013] S2, vacuum consumable remelting, performing vacuum consumable remelting on the electrode rod to obtain a consumable ingot;

[0014] S3, homogenization treatment, homogenization treatment of the consumable ingot, and then air cooling out of the furnace;

[0015] S4, forging and blanking, heating the consumable ingot after the treatment in step S3, and then taking it out of the furnace to forge it into a tube blank;

[0016] S5, hot extrusion pipe making, preheating the tube blank, and then heating it to 1150-1200°C, keeping it at this temperature for ≥1h, and then hot extruding it to obtain a rough tube, and adopting annular water cooling after extrusion;

[0017] S6, surface finishing, machining the inner and outer surfaces of the rough pipe;

[0018] S7, infiltration layer, the inner surface of the rough pipe is infiltrated with Cr and N to obtain the high-temperature alloy seamless pipe with low residual stress.

[0019] Preferably, in the step S1, during the annealing treatment, the annealing temperature is 1000-1100°C.

[0020] Preferably, in the step S2, during the vacuum remelting consumable process, the melting rate is 6.0-6.8 kg / min.

[0021] Preferably, in step S3:

[0022] During the homogenization process, the heating temperature is 1160-1220°C and the insulation time is ≥20h; and / or

[0023] During the homogenization process, the charging temperature of the consumable ingot is ≤500°C, and the heating rate is ≤100°C / h.

[0024] Preferably, in step S4:

[0025] During the heating process, the consumable ingot is first heated to 900-1000° C., kept at this temperature for 2-3 hours, and then heated to 1120-1200° C., and kept at this temperature for ≥2 hours; and / or

[0026] During the forging process, the forging deformation is 20-60%.

[0027] Preferably, in step S5:

[0028] During the preheating process, the preheating temperature is 750-900° C.; and / or

[0029] During the hot extrusion pipe making process, the extrusion speed is 160-180 mm / s.

[0030] Preferably, in the step S7, during the diffusion process, the treatment temperature is 1000-1150°C.

[0031] The composition design principles of the low residual stress high temperature alloy seamless pipe of the present invention are as follows:

[0032] Carbon: C is the most commonly used strengthening element in steel materials. It can form carbides such as M23C6 and MX with alloy elements, effectively pinning the lath boundaries and maintaining the performance of the material for a long time. However, too high C content is not good for processing and welding performance, so the carbon content is 0.03-0.12wt%.

[0033] Chromium: From the perspective of improving oxidation resistance, it is often hoped that the Cr content is as high as possible. However, when the Cr content is too high, delta-ferrite will appear in the material, reducing the material's long-term strength and toughness. Therefore, the chromium content is 14-17wt%.

[0034] Tungsten: The W element exists in two forms in steel. One is solid solution in the matrix to play a solid solution strengthening role, and the other is in the form of precipitation phase to play a precipitation strengthening role. However, W is an element that is easy to segregate in steel. The solidification segregation produced during industrial production is more serious and difficult to completely eliminate. Therefore, the tungsten content is controlled to 0.5-2.0wt%.

[0035] Molybdenum: Mo is similar to W, and also plays a role in solid solution strengthening and precipitation strengthening in steel. Related research shows that the combined addition of W and Mo has a better strengthening effect than adding W or Mo alone. When the Mo content is too low, it is not enough to achieve the above effects, and when the W+Mo content is too high, it is not only not conducive to performance improvement, but also causes high-temperature ferrite precipitation, thereby significantly reducing the hot working performance and mechanical properties of the alloy. Therefore, the molybdenum content is controlled to 1.5-3.5wt%.

[0036] Niobium: Nb and C elements mainly form MC phase. Related studies have shown that adding Nb can significantly improve the high temperature strength of the alloy. However, too much Nb is prone to precipitate large carbides due to element segregation; therefore, the niobium content is controlled to 0.5-1.5wt%.

[0037] Manganese: Mn has a deoxidizing effect and is also beneficial to the nitriding process; therefore, the manganese content is controlled to be 1.0-2.1wt%.

[0038] The present invention has the following beneficial effects:

[0039] 1. Short pipe making process: Abandoning the traditional hot extrusion + multi-pass cold rolling method, simplifying it to hot extrusion method;

[0040] 2. Low residual stress: high temperature hot extrusion (extrusion temperature> 1150℃) is adopted to make the deformed grains fully recrystallized during the thermal deformation process, which not only significantly reduces the deformation resistance, but also helps to reduce the residual stress; the annular water cooling method is adopted to make the inner and outer walls of the tube cool evenly, which can significantly reduce the residual stress; in addition, the surface infiltration layer treatment can not only improve the surface wear resistance and fatigue resistance, but also effectively reduce the residual stress generated during the tube making process;

[0041] 3. Excellent organizational stability: Adding Nb 0.5-1.5wt%, W 0.5-2.0wt%, and controlling W / Nb to 0.8-1.0 can significantly improve the organizational stability of the material at high temperatures; high-temperature hot extrusion (extrusion temperature > 1150°C) helps the microstructure such as grains to tend to balance and stabilize. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0043] Figure 1 It is a schematic diagram of the grain morphology of the high-temperature alloy seamless tube with low residual stress of the present invention;

[0044] Figure 2 It is a schematic diagram showing the variation of the cross-sectional shrinkage of the high-temperature alloy seamless pipe with low residual stress according to the present invention with temperature. DETAILED DESCRIPTION

[0045] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0046] The invention discloses a high-temperature alloy seamless pipe with low residual stress, comprising the following components by mass percentage: C: 0.03-0.12%, Mn: 1.0-2.1%, Cr: 14-17%, Ni: 35-38%, Mo: 1.5-3.5%, Nb: 0.5-1.5%, W: 0.5-2.0%, B: 0.004%, Y: 0.1-0.2%, Zr: 0.05-0.1%, and the balance is Fe and inevitable impurities; wherein the composition of the high-temperature alloy seamless pipe with low residual stress also satisfies: W / Nb is 0.5-0.8. The high-temperature alloy seamless pipe with low residual stress has a yield strength Rp of 0.03-0.12% at room temperature. 0.2 ≥240MPa, tensile strength Rm ≥550MPa, elongation A ≥45%, impact energy KV2 ≥400J; at 750℃, the yield strength Rp of the high temperature alloy seamless pipe with low residual stress 0.2 ≥140MPa, tensile strength Rm≥270MPa, elongation A≥60%.

[0047] The preparation process of the above-mentioned low residual stress high temperature alloy seamless pipe is as follows:

[0048] S1, vacuum induction smelting, using vacuum induction smelting and casting electrode rods, and then annealing and surface finishing the electrode rods;

[0049] The specific process is: according to the composition of the above-mentioned high-temperature alloy seamless tube with low residual stress, the electrode rod is proportioned, and then the electrode rod is smelted and cast by vacuum induction, and then the electrode rod is annealed, and the annealing temperature is kept at 1000-1100°C for 10-15h, and then the annealed electrode rod is surface finished;

[0050] S2, vacuum consumable remelting, performing vacuum consumable remelting on the electrode rod to obtain a consumable ingot;

[0051] The specific process is: the electrode rod is vacuum remelted for consumables, wherein the electrode rod shrinkage hole is installed downward, the melting rate is 6.0-6.8 kg / min, the vacuum setting value is 0.25 Torr, and finally the consumable ingot is smelted;

[0052] S3, homogenization treatment, homogenization treatment of the consumable ingot, and then air cooling out of the furnace;

[0053] The specific process is as follows: the consumable ingot is transferred into an annealing furnace for homogenization treatment, wherein the charging temperature of the consumable ingot is ≤500°C, during the homogenization treatment, the consumable ingot is heated to 1160-1220°C at a heating rate of ≤100°C / h (in a preferred embodiment, the heating temperature of the homogenization treatment is 1190-1220°C), and the holding time is ≥20h; then the ingot is taken out of the furnace and air-cooled;

[0054] S4, forging and blanking, heating the consumable ingot after the treatment in step S3, and then taking it out of the furnace and forging it into a tube blank;

[0055] The specific process is: the consumable ingot is first heated to 900-1000°C at a heating rate of ≤100°C / h and kept warm for 2-3h, and then heated to 1120-1200°C at a heating rate of ≤100°C / h and kept warm for at least 2h, wherein the charging temperature of the consumable ingot is ≤500°C; then the ingot is taken out of the furnace for forging to obtain a tube blank, wherein the forging deformation during forging is 20-60%.

[0056] S5, hot extrusion pipe making, preheating the tube blank, and then heating it to 1150-1200°C, keeping it at this temperature for ≥1h, and then hot extruding it to obtain a rough tube, and adopting annular water cooling after extrusion;

[0057] The specific process is: preheat the tube blank at 750-900℃, then heat it to 1150-1200℃ and keep it warm for at least 1h, then hot extrude it on the extruder to get the rough tube, and control the extrusion speed to 160-180mm / s; after the hot extrusion, use annular water cooling to cool the rough tube.

[0058] Through research, it is found that the dynamic recrystallization volume fraction of the low residual stress high-temperature alloy seamless tube increases with the increase of deformation temperature and decreases with the increase of strain rate. At the same deformation temperature, the size of the recrystallized grains becomes finer with the increase of strain rate; however, when the deformation temperature is 1150℃ and above, the dynamic recrystallization volume fraction at different strain rates reaches 100%, and when the strain rate is greater than 1S -1 The effect of strain rate on grain size can be ignored; therefore, combined with the actual working conditions of hot extrusion equipment, a hot extrusion process for the high-temperature alloy seamless pipe of the present invention was developed, and the extrusion temperature was controlled to be 1150-1200°C, and the extrusion rate was 160-180 mm / s.

[0059] S6, surface finishing, machining the inner and outer surfaces of the rough pipe;

[0060] S7, infiltration layer, the inner surface of the rough pipe is infiltrated with Cr and N to obtain the high-temperature alloy seamless pipe with low residual stress;

[0061] The specific process is: in the temperature range of 1000-1150℃, the inner surface of the above-mentioned rough pipe is treated with Cr and N, and finally a high-temperature alloy seamless pipe with low residual stress is obtained. The infiltration layer treatment can not only improve the surface wear resistance and fatigue resistance, but also effectively reduce the residual stress generated during the pipe making process.

[0062] Combination Figure 1 As shown, the low residual stress high temperature alloy seamless pipe prepared by the present invention has fine and uniform grains, which can well meet the requirement that the grain size range is not greater than level 3. Figure 2 As shown, the cross-sectional shrinkage of the high-temperature alloy seamless tube with low residual stress is greater than 40% at a high temperature of 800-1250°C, wherein at 1000-1250°C, the cross-sectional shrinkage of the high-temperature alloy seamless tube with low residual stress is ≥60%. It can be seen that the high-temperature alloy seamless tube with low residual stress has good plasticity.

[0063] The low residual stress high temperature alloy seamless pipe and its preparation method of the present invention are further introduced below with reference to specific examples.

[0064] Example 1

[0065] The preparation process of the high-temperature alloy seamless pipe with low residual stress in this embodiment is as follows:

[0066] (1) Vacuum induction smelting: According to the proportion of component A shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the electrode rod is annealed at 1020°C to 1030°C for 15 hours, and then the surface of the electrode rod is finished.

[0067] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610 mm; the melting rate is 6.0-6.8 kg / min, and the vacuum setting value is 0.25 Torr; the chemical composition of the consumable ingot is shown in Table 1;

[0068] (3) Homogenization treatment: The charging temperature of the consumable ingot is ≤500℃, and the alloy ingot is heated to 1210±10℃ at a heating rate of ≤100℃ / h, and the holding time is 24h; then the ingot is air-cooled after being taken out of the furnace.

[0069] (4) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1160℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. The ingot is taken out of the furnace for forging to obtain a tube billet of Φ346mm. The forging deformation is 50-60%.

[0070] (5) Hot extrusion pipe making: The tube blank is first preheated at 850 °C, then heated to 1180 °C and kept warm for 1 hour, and then hot extruded on an extruder at an extrusion speed of 170 mm / s. After hot extrusion, a rough tube with a specification of Φ194×46 mm is obtained, and annular water cooling is used after extrusion.

[0071] (6) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0072] (7) Infiltration layer: The inner surface of the rough pipe is infiltrated with Cr and N at a temperature of 1000-1150°C to obtain a high-temperature alloy seamless pipe with low residual stress.

[0073] Example 2

[0074] The preparation process of the high-temperature alloy seamless pipe with low residual stress in this embodiment is as follows:

[0075] (1) Vacuum induction smelting: According to the B component shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the electrode rod is annealed at 1050°C to 1060°C for 15 hours, and then the surface of the electrode rod is finished.

[0076] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610 mm; the melting rate is 6.0-6.8 kg / min, and the vacuum setting value is 0.25 Torr; the chemical composition of the consumable ingot is shown in Table 1;

[0077] (3) Homogenization treatment: The charging temperature of the consumable ingot is ≤500℃, and the alloy ingot is heated to 1210±10℃ at a heating rate of ≤100℃ / h, and the holding time is ≥24h; then the ingot is air-cooled after being taken out of the furnace.

[0078] (4) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1170℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. The ingot is taken out of the furnace for forging to obtain a tube billet of Φ346mm. The forging deformation is 50-60%.

[0079] (5) Hot extrusion pipe making: The tube blank is first preheated at 850°C, then heated to 1160°C and kept warm for at least 1 hour, and then hot extruded on an extruder at an extrusion speed of 180 mm / s. After hot extrusion, a rough tube with a specification of Φ194×46 mm is obtained, and annular water cooling is used after extrusion.

[0080] (6) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0081] (7) Infiltration layer: The inner surface of the rough pipe is infiltrated with Cr and N at a temperature of 1000-1150°C to obtain a high-temperature alloy seamless pipe with low residual stress.

[0082] Example 3

[0083] The preparation process of the high-temperature alloy seamless pipe with low residual stress in this embodiment is as follows:

[0084] (1) Vacuum induction smelting: According to the C component shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the electrode rod is annealed at 1050°C to 1060°C for 15 hours, and then the surface of the electrode rod is finished.

[0085] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610 mm; the melting rate is 6.0-6.8 kg / min, and the vacuum setting value is 0.25 Torr; the chemical composition of the consumable ingot is shown in Table 1;

[0086] (3) Homogenization treatment: The charging temperature of the consumable ingot is ≤500℃, and the alloy ingot is heated to 1200±10℃ at a heating rate of ≤100℃ / h, and the holding time is ≥30h; then the ingot is air-cooled after being taken out of the furnace.

[0087] (4) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1150℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. The ingot is taken out of the furnace and forged to obtain a tube billet of Φ346mm. The forging deformation is 50-60%.

[0088] (5) Hot extrusion pipe making: The tube blank is first preheated at 850°C, then heated to 1150°C and kept at this temperature for 1 hour, and then hot extruded on an extruder at an extrusion speed of 170 mm / s. After hot extrusion, a rough tube with a specification of Φ194×46 mm is obtained, and annular water cooling is used after extrusion.

[0089] (6) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0090] (7) Infiltration layer: The inner surface of the rough pipe is infiltrated with Cr and N at a temperature of 1000-1150°C to obtain a high-temperature alloy seamless pipe with low residual stress.

[0091] Example 4

[0092] The preparation process of the high-temperature alloy seamless pipe with low residual stress in this embodiment is as follows:

[0093] (1) Vacuum induction smelting: According to the A component shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the electrode rod is annealed at 1050°C to 1060°C for 12 hours, and then the surface of the electrode rod is finished.

[0094] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610 mm; the melting rate is 6.0-6.8 kg / min, and the vacuum setting value is 0.25 Torr; the chemical composition of the consumable ingot is shown in Table 1;

[0095] (3) Homogenization treatment: The charging temperature of the consumable ingot is ≤500℃, and the alloy ingot is heated to 1200±10℃ at a heating rate of ≤100℃ / h, and the holding time is ≥30h; then the ingot is air-cooled after being taken out of the furnace.

[0096] (4) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1180℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. After it is taken out of the furnace and forged, a tube with a specification of Φ346mm is obtained. The forging deformation is 50-60%.

[0097] (5) Hot extrusion pipe making: The tube blank is first preheated at 750°C, then heated to 1150°C and kept warm for 1 hour, and then hot extruded on an extruder at an extrusion speed of 160 mm / s. After hot extrusion, a rough tube with a specification of Φ194×46 mm is obtained, and annular water cooling is used after extrusion.

[0098] (6) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0099] (7) Infiltration layer: The inner surface of the rough pipe is infiltrated with Cr and N at a temperature of 1000-1150°C to obtain a high-temperature alloy seamless pipe with low residual stress.

[0100] Example 5

[0101] The preparation process of the high-temperature alloy seamless pipe with low residual stress in this embodiment is as follows:

[0102] (1) Vacuum induction smelting: According to the B component shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the electrode rod is annealed at 1050°C to 1060°C for 16 hours, and then the surface of the electrode rod is finished.

[0103] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610 mm; the melting rate is 6.0-6.8 kg / min, and the vacuum setting value is 0.25 Torr; the chemical composition of the consumable ingot is shown in Table 1;

[0104] (3) Homogenization treatment: The charging temperature of the consumable ingot is ≤500℃, and the alloy ingot is heated to 1200±10℃ at a heating rate of ≤100℃ / h, and the holding time is ≥40h; then the ingot is air-cooled after being taken out of the furnace.

[0105] (4) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1180℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. After it is taken out of the furnace and forged, a tube with a specification of Φ346mm is obtained. The forging deformation is 50-60%.

[0106] (5) Hot extrusion pipe making: The tube blank is first preheated at 900°C, then heated to 1190°C and kept warm for 1 hour, and then hot extruded on an extruder at an extrusion speed of 180 mm / s. After hot extrusion, a rough tube with a specification of Φ194×46 mm is obtained, and annular water cooling is used after extrusion.

[0107] (6) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0108] (7) Infiltration layer: The inner surface of the rough pipe is infiltrated with Cr and N at a temperature of 1000-1150°C to obtain a high-temperature alloy seamless pipe with low residual stress.

[0109] Comparative Example

[0110] The comparative example adopts vacuum induction smelting → vacuum consumable remelting → forging blanking → hot extrusion pipe making → cold rolling → surface finishing; the specific process is as follows:

[0111] (1) Vacuum induction smelting: According to the D component shown in Table 1, vacuum induction smelting and casting are used to obtain a Φ520 mm electrode rod; the surface of the electrode rod is finished.

[0112] (2) Vacuum consumable remelting: The electrode rod is vacuum consumable remelted into a consumable ingot of Φ610mm; the melting rate is 6.0~6.8kg / min.

[0113] (3) Forging: The charging temperature of the consumable ingot is ≤500℃. The consumable ingot is heated to 900-1000℃ at a heating rate of ≤100℃ / h and kept at this temperature for 2-3h. Then, it is heated to 1130℃ at a heating rate of ≤100℃ / h and kept at this temperature for ≥2h. The ingot is taken out of the furnace for forging to obtain a tube billet of Φ346mm. The forging deformation is 50-60%.

[0114] (4) Hot extrusion and cold rolling: preheat the tube at 900℃, then heat to 1150℃ and keep it at that temperature for 1 hour, then hot extrude the tube on the extruder at an extrusion speed of 150mm / s, and obtain a rough tube with a specification of Φ194×46mm. Then cold roll it to Φ180×40mm, and then carry out solution treatment: keep it at 1080℃ for 1h, and water cool it.

[0115] (5) Surface finishing: The inner and outer surfaces of the rough pipe obtained above are machined.

[0116] The mechanical properties of the low residual stress high temperature alloy seamless pipes prepared in Examples 1 to 5 of the present invention and the seamless pipes prepared in the comparative example are shown in Tables 2 and 3; the isotropic residual stresses are shown in Table 4.

[0117] Table 1 Chemical composition (wt%)

[0118] C Mn Cr Ni Mo Y B Zr Nb W Fe A 0.06 1.9 15 36 2.3 0.1 0.004 0.06 1.2 0.6 Remain B 0.05 1.7 15 36 2.4 0.1 0.004 0.06 1.2 0.8 Remain C 0.08 1.8 15 36 2.4 0.1 0.004 0.07 1.3 0.7 Remain D 0.06 1.5 16.6 36 3.4 0.001 0.0017 0.01 - - Remain

[0119] Table 2 Mechanical properties at room temperature

[0120]

[0121] Table 3 Mechanical properties at high temperature

[0122]

[0123] Table 4 Tangential residual stress

[0124]

[0125]

[0126] As shown in Table 2 and Table 3, at room temperature, 350°C and 750°C, the elongation of the high-temperature alloy seamless pipe with low residual stress in the embodiment is much higher than that of the seamless pipe in the comparative example, the yield strength and impact work of the high-temperature alloy seamless pipe with low residual stress in the embodiment are higher than those of the seamless pipe in the comparative example, and the tensile strength of the high-temperature alloy seamless pipe with low residual stress in the embodiment is equivalent to that of the seamless pipe in the comparative example; as shown in Table 4, the tangential residual stress of the high-temperature alloy seamless pipe with low residual stress in the embodiment is much lower than that of the seamless pipe in the comparative example.

[0127] In summary, the present invention abandons the traditional hot extrusion + multi-pass cold rolling method and simplifies it to hot extrusion pipe making; the residual stress of the low residual stress high-temperature alloy seamless pipe is low: high-temperature hot extrusion (extrusion temperature>1150°C) is adopted to make the deformed grains fully recrystallize during the thermal deformation process, which not only significantly reduces the deformation resistance, but also helps to reduce the residual stress; the annular water cooling method is adopted to make the inner wall and the outer wall of the pipe cool evenly, which can significantly reduce the residual stress; in addition, the surface permeation layer treatment can not only improve the surface wear resistance and fatigue resistance, but also effectively reduce the residual stress generated during the pipe making process; the low residual stress high-temperature alloy seamless pipe has excellent organizational stability: adding Nb 0.5~1.5wt%, W 0.5~2.0wt%, and controlling W / Nb to 0.5~0.8, which significantly improves the organizational stability of the material at high temperature; the use of high-temperature hot extrusion (extrusion temperature>1150°C) helps the microstructures such as grains to tend to balance and stabilize.

[0128] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A high temperature alloy seamless pipe with low residual stress, characterized in that: The invention comprises the following components by mass percentage: C: 0.03-0.12%, Mn: 1.0-2.1%, Cr: 14-17%, Ni: 35-38%, Mo: 1.5-3.5%, Nb: 0.5-1.5%, W: 0.5-2.0%, B: 0.004%, Y: 0.1-0.2%, Zr: 0.05-0.1%, and the balance is Fe and inevitable impurities. The composition of the low residual stress high temperature alloy seamless pipe meets the following requirements: W / Nb is 0.5 to 0.8, At room temperature, the yield strength Rp of the low residual stress high temperature alloy seamless pipe 0.2 ≥240MPa, tensile strength Rm≥550MPa, elongation A≥45%, impact energy KV2≥400J; At 750°C, the yield strength Rp of the low residual stress high temperature alloy seamless pipe 0.2 ≥140MPa, tensile strength Rm≥270MPa, elongation A≥60%, The low residual stress high temperature alloy seamless pipe is prepared by the following preparation method, comprising the steps of: S1, vacuum induction smelting, using vacuum induction smelting and casting electrode rods, and then annealing and surface finishing the electrode rods; S2, vacuum consumable remelting, performing vacuum consumable remelting on the electrode rod to obtain a consumable ingot; S3, homogenization treatment, homogenization treatment of the consumable ingot, and then air cooling out of the furnace; S4, forging and blanking, heating the consumable ingot after the treatment in step S3, and then taking it out of the furnace and forging it into a tube blank; S5, hot extrusion pipe making, preheating the tube blank, and then heating it to 1150-1200°C, keeping it at this temperature for ≥1h, and then hot extruding it to obtain a rough tube, and adopting annular water cooling after extrusion; S6, surface finishing, machining the inner and outer surfaces of the rough pipe; S7, infiltration layer, the inner surface of the rough pipe is infiltrated with Cr and N to obtain the high-temperature alloy seamless pipe with low residual stress.

2. A method for preparing a high-temperature alloy seamless pipe with low residual stress as claimed in claim 1, characterized in that: The following steps are involved: S1, vacuum induction smelting, using vacuum induction smelting and casting electrode rods, and then annealing and surface finishing the electrode rods; S2, vacuum consumable remelting, performing vacuum consumable remelting on the electrode rod to obtain a consumable ingot; S3, homogenization treatment, homogenization treatment of the consumable ingot, and then air cooling out of the furnace; S4, forging and blanking, heating the consumable ingot after the treatment in step S3, and then taking it out of the furnace and forging it into a tube blank; S5, hot extrusion pipe making, preheating the tube blank, and then heating it to 1150-1200°C, keeping it at this temperature for ≥1h, and then hot extruding it to obtain a rough tube, and adopting annular water cooling after extrusion; S6, surface finishing, machining the inner and outer surfaces of the rough pipe; S7, infiltration layer, the inner surface of the rough pipe is infiltrated with Cr and N to obtain the high-temperature alloy seamless pipe with low residual stress.

3. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In the step S1, during the annealing treatment, the annealing temperature is 1000-1100°C.

4. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In the step S2, during the vacuum consumable remelting process, the melting rate is 6.0-6.8 kg / min.

5. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In step S3: During the homogenization process, the heating temperature is 1160-1220°C and the insulation time is ≥24h; During the homogenization process, the charging temperature of the consumable ingot is ≤500°C, and the heating rate is ≤100°C / h.

6. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In step S4: During the heating process, the consumable ingot is first heated to 900-1000° C., kept at this temperature for 2-3 hours, and then heated to 1120-1200° C., and kept at this temperature for ≥2 hours; During the forging process, the forging deformation is 20-60%.

7. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In step S5: During the preheating process, the preheating temperature is 750-900°C; During the hot extrusion pipe making process, the extrusion speed is 160-180 mm / s.

8. The method for preparing a high-temperature alloy seamless pipe with low residual stress according to claim 2, characterized in that: In the step S7, during the diffusion process, the treatment temperature is 1000-1150°C.

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