Method for improving low-temperature performance and welding quality of welding seam of 25Cr2Ni3Mo steel impeller

Abstract

The invention provides a method for improving the low-temperature performance and the welding quality of a 25Cr2Ni3Mo steel impeller welding seam, and belongs to the technical field of impeller machining. The method comprises the steps that a cover disc and a shaft disc are subjected to pre-heat treatment including normalizing treatment and tempering treatment; welding of the impeller: preheating the cover disc and the shaft disc, performing shielded metal arc welding by adopting an optimized V840 welding material, and performing post-heat treatment on the welded impeller after welding; the welded impeller is subjected to stress relief treatment including stress relief-normalizing treatment in vacuum heat treatment equipment; and the welded impeller is subjected to performance heat treatment including quenching treatment and tempering treatment. According to the method provided by the invention, the problems of poor low-temperature toughness and poor welding seam quality of the 25Cr2Ni3Mo steel impeller in the welding process can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of impeller processing, and in particular to a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld. Background Art

[0002] 25Cr2Ni3Mo steel is a commonly used material for impellers in low-temperature compressors. It is widely used in ethylene compressors, propylene compressors, ammonia compressors, etc. The operating temperature range is -50℃ to -115℃.

[0003] The existing compressor forming method is still mainly based on milling and welding impellers, that is, the blades are milled on the shaft disk or cover disk and then welded to the corresponding cover disk and shaft disk. The conventional welding material is V840 welding rod. After welding, the impeller not only has poor low-temperature toughness, but is also prone to cracking, which directly affects the quality of the impeller.

[0004] Therefore, there is an urgent need for a method to improve the low-temperature performance and welding quality of the 25Cr2Ni3Mo steel impeller weld, so as to solve the problem of poor low-temperature toughness and poor weld quality of the 25Cr2Ni3Mo steel impeller during the welding process. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for improving the low-temperature performance and welding quality of the 25Cr2Ni3Mo steel impeller weld, so as to solve the problem of poor low-temperature toughness and poor weld quality of the 25Cr2Ni3Mo steel impeller during the welding process.

[0006] To solve the above technical problems, the present invention provides a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld, comprising the following steps:

[0007] Performing preliminary heat treatment including normalizing and tempering on the cover disc and the shaft disc;

[0008] Impeller welding: After preheating the cover plate and shaft plate, use optimized V840 welding materials for arc welding. After welding, perform post-heat treatment on the welded impeller.

[0009] The welded impeller is subjected to stress relief treatment including stress relief and normalizing treatment in a vacuum heat treatment equipment;

[0010] The welded impeller is subjected to a performance heat treatment including quenching and tempering.

[0011] Furthermore, the normalizing treatment in the preliminary heat treatment includes: charging the cover plate and the shaft plate into a furnace at ≤500°C, heating to 880-900°C and holding the temperature for 0.6*effective thickness / 30+1h, then air-cooling to room temperature, and the holding time is not less than 2h;

[0012] The tempering treatment in the preliminary heat treatment includes: charging the cover plate and the shaft plate into a furnace at ≤350°C, heating to 660-690°C, holding the temperature for 0.9*effective thickness / 30+1h, and then air-cooling to room temperature for no less than 3h.

[0013] Furthermore, the effective thickness is the effective thickness of the cover disc and the shaft disc.

[0014] Furthermore, the preheating temperature is 200-250°C, and the post-heating temperature is 250-350°C.

[0015] Furthermore, the optimized V840 welding material includes, by mass percentage, a Ni content of 3.0-4.0%, a Mn content of 0.4-0.9%, a Cr content of 1.8-2.5%, and the contents of S and P are controlled at ≤0.008%.

[0016] Preferably, the Ni content is 3.25-3.5%, the Mn content is 0.5-0.7%, and the Cr content is 2.0-2.3%.

[0017] Furthermore, the welding parameters of the arc welding include current controlled at 100-145A, voltage controlled at 23-26V, welding speed controlled at 13-17cm / min, and interlayer temperature controlled at 200-350°C.

[0018] Furthermore, the stress relief-normalizing treatment step includes:

[0019] Place the welded impeller into a vacuum heat treatment device, place it in a furnace at room temperature, heat it to 660-690°C at a rate of 1-3°C / h, and then keep it warm for 5-10 hours;

[0020] Then, heat up to 850-890°C at a rate of 1-3°C / h and keep warm for 2-7h;

[0021] Finally, 1.1-1.5 Bar nitrogen is introduced into the vacuum heat treatment equipment to cool it to 50-60°C, and then it is taken out of the furnace and air-cooled.

[0022] Furthermore, the quenching treatment of the performance heat treatment includes charging the welded impeller after stress relief and normalizing treatment into a furnace at 500°C, heating it to 840-880°C at a rate of ≤100°C / h, keeping it at that temperature for 2-7h, then taking it out of the furnace and oil cooling it to 200-300°C and then oil cooling it in air;

[0023] The tempering treatment of the performance heat treatment comprises charging the welded impeller after quenching treatment into an air furnace at ≤350°C, heating it to 560-640°C at a speed of ≤70°C / h, keeping it at that temperature for 3-10 hours, and then cooling it to room temperature in air.

[0024] The present invention provides a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld. The method comprises first performing a preliminary heat treatment, including normalizing and tempering, on the cover disc and shaft disc. Then, during impeller welding, the cover disc and shaft disc are preheated and then arc welded using optimized V840 welding consumables. After welding, the welded impeller is post-heated. The welded impeller is then subjected to stress relief treatment, including stress relief and normalizing, in a vacuum heat treatment apparatus. Finally, the welded impeller is subjected to a performance heat treatment, including quenching and tempering. This method effectively improves the low-temperature performance and welding quality of the 25Cr2Ni3Mo steel welded impeller weld, ensuring the weld remains intact and free of weld cracking after welding. This method effectively addresses the issues of poor low-temperature toughness and weld quality associated with 25Cr2Ni3Mo steel impellers during welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart of a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] See also Figure 1 The embodiment of the present invention provides a method for improving the low temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld, comprising the following steps:

[0027] Step 1) performing a preliminary heat treatment including normalizing and tempering on the cover disc and the shaft disc.

[0028] Among them, the normalizing treatment in the preliminary heat treatment process includes: the cover plate and the shaft plate are loaded into the furnace at ≤500℃, heated to 880-900℃ and kept warm for 0.6*effective thickness / 30+1h, and then air-cooled to room temperature, and the holding time is not less than 2h.

[0029] Among them, the tempering treatment in the preliminary heat treatment process includes: the cover plate and the shaft plate are loaded into the furnace at ≤350°C, heated to 660-690°C for a holding time of 0.9*effective thickness / 30+1h, and then air-cooled to room temperature for a holding time of not less than 3h.

[0030] Among them, the effective thickness is the effective thickness of the cover plate and the shaft plate, that is, when the cover plate is normalized and tempered, the effective thickness described in the holding time is the effective thickness of the cover plate, and when the shaft plate is normalized and tempered, the effective thickness described in the holding time is the effective thickness of the shaft plate.

[0031] Before welding the impeller, the cover and shaft disc undergo preliminary heat treatment, including normalizing and tempering. This, on the one hand, reduces structural defects generated during the forging process, such as overheated coarse-grained microstructure, Widmanstätten structure, and banded microstructure, thereby improving the overall material performance. It also stabilizes the metallographic structure of the weldment, reducing deformation and cracking caused by stress changes during use, thereby ensuring the stability of the workpiece's size and shape. Furthermore, this preliminary heat treatment further improves the uniformity of the parent material structure of the impeller cover and shaft disc, providing a guarantee for subsequent impeller welding.

[0032] Step 2) Welding of the impeller: After preheating the cover plate and the shaft plate, use optimized V840 welding material to perform arc welding. After welding, the welded impeller is post-heat treated.

[0033] The preheating temperature of the cover and shaft disc after preliminary heat treatment is 200-250°C. Preheating the cover and shaft disc before welding can reduce the cooling rate of the weld joint, thereby facilitating the escape of diffused hydrogen in the weld metal and preventing hydrogen-induced cracks. It can also reduce the temperature difference between the weld zone and the entire weldment, reducing welding stress and providing a guarantee for preventing weld cracks.

[0034] The current V840 welding consumables contain 2.0-2.8% Ni, 0.08-1.6% Mn, and 0.5-1.0% Cr. To improve the low-temperature performance and weld quality of the 25Cr2Ni3Mo steel impeller weld, the composition of the V840 welding consumables was optimized. The Ni content was increased to 3.0-4.0% and the Mn content was optimized to 0.4-0.9%. Since the reduction in Mn content necessitated the addition of Cr to increase strength, the Cr content was optimized to 1.8-2.5%. Furthermore, the S and P contents were reduced to ≤0.008%.

[0035] More optimally, the Ni content in the optimized V840 welding material is controlled within a range of 3.25-3.5%, the Mn content is controlled within a range of 0.5-0.7%, and the Cr content is controlled within a range of 2.0-2.3%.

[0036] Among them, the welding parameters for arc welding after preheating the cover plate and the shaft plate include: current controlled at 100-145A, voltage controlled at 23-26V, welding speed controlled at 13-17cm / min, and interlayer temperature controlled at 200-350℃.

[0037] At the same time, the welded impeller requires post-heat treatment at a temperature of 250-350°C. Post-heating after welding can reduce the cooling rate of the weld, promote hydrogen escape, and avoid hydrogen-induced cracking. It also slows the cooling rate of the weld joint, preventing the formation of hardened structures, thereby reducing the occurrence of cold cracking and delayed cracking, and preventing cracking during the welding process. It also reduces residual stress in the weld joint, preventing the occurrence of cold cracking or reheating cracking.

[0038] The present invention can make the structures of the weld and the heat-affected zone uniform and refine the grains through preheating before welding and heating after welding, thereby reducing the residual stress of the weld joint.

[0039] Step 3) The welded impeller is subjected to stress relief treatment including stress relief and normalizing treatment in a vacuum heat treatment device.

[0040] Among them, the steps of stress relief-normalizing treatment include:

[0041] Place the welded impeller into a vacuum heat treatment device, place it in a furnace at room temperature, heat it to 660-690°C at a rate of 1-3°C / h, and then keep it warm for 5-10 hours;

[0042] Then, heat up to 850-890°C at a rate of 1-3°C / h and keep warm for 2-7h;

[0043] Finally, 1.1-1.5 Bar nitrogen is introduced into the vacuum heat treatment equipment to cool it to 50-60°C, and then it is taken out of the furnace and air-cooled.

[0044] Due to the localized uneven heat input during the welding process, the internal temperature field, stress field, and microstructural state of the workpiece change rapidly, which can easily lead to uneven elastic-plastic deformation, thereby generating various stresses during the welding process. Post-weld stress relief treatment through stress relief and normalizing can reduce the internal stress generated during welding, prevent deformation or cracking of the workpiece, improve the resistance of the weld joint to brittle fracture, and avoid delayed cracking. In addition, normalizing treatment is also performed after stress relief to improve the metallographic structure of the weld location, making the structure more uniform and further reducing the risk of weld cracking. At the same time, performing the stress relief and normalizing treatment in a vacuum heat treatment device can also promote the degassing effect of the vacuum heat treatment on hydrogen and oxygen, improving the quality of the weld and reducing the risk of cracking.

[0045] Step 4) performing a performance heat treatment including quenching and tempering on the welded impeller.

[0046] Among them, the quenching treatment of performance heat treatment includes loading the welded impeller after stress relief and normalizing treatment into a furnace at 500℃, heating it to 840~880℃ at a rate of ≤100℃ / h, keeping it warm for 2~7h, then taking it out of the furnace and oil cooling it to 200~300℃ and then oil cooling it in air.

[0047] Among them, the tempering treatment of the performance heat treatment includes charging the welded impeller after quenching treatment into an air furnace at ≤350°C, heating it to 560-640°C at a rate of ≤70°C / h, keeping it warm for 3-10h, and then air cooling it to room temperature.

[0048] By performing a performance heat treatment including quenching and tempering on the welded impeller after stress relief treatment in a vacuum heat treatment device, the mechanical properties of the welded impeller can be made to meet the use requirements.

[0049] The present invention provides a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld. Through the above-mentioned processing method, the final 25Cr2Ni3Mo steel welded impeller can have a complete weld after welding without cracking while meeting high weld yield strength requirements and low-temperature impact energy of the weld and heat-affected zone, thereby greatly improving the low-temperature performance and welding quality of the 25Cr2Ni3Mo steel impeller weld.

[0050] The following is a detailed description of a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld provided by the present invention through examples and comparative examples.

[0051] Example 1

[0052] The impeller is manufactured with a diameter of 450 mm and a material of 25Cr2Ni3Mo. The yield strength of the weld must be ≥685 MPa, and the impact energy of the weld and heat-affected zone at -105°C, Kv2, must be ≥27 J.

[0053] 1. Preparatory heat treatment of impeller cover and shaft disc before welding

[0054] The impeller cover and shaft disc are normalized and tempered.

[0055] Normalizing treatment: Place the cover plate and shaft plate in a furnace at 180℃, heat to 880℃ and keep warm for 2h, then air cool to room temperature;

[0056] Tempering treatment: After normalizing treatment, the cover plate and shaft plate are loaded into the furnace at 150℃, heated to 680℃ and kept warm for 3 hours, and then air-cooled to room temperature.

[0057] 2. Welding of impeller

[0058] The cover plate and shaft plate need to be preheated at 220℃;

[0059] Welding material composition: 0.085% C, 0.8% Mn, 0.45% Si, 2.2% Cr, 3.4% Ni, 1.1% Mo, 0.004% S and 0.006% P.

[0060] The impeller is welded by arc welding with the current controlled at 110A, the voltage controlled at 24V, the welding speed at 14cm / min, the interlayer temperature at 240℃, and post-heating at 300℃ after welding.

[0061] 3. Stress relief of impeller

[0062] Stress relief-normalizing treatment: Place the welded impeller into a vacuum device, load it into a furnace at room temperature, heat it to 680°C at a rate of ≤2°C / h, keep it warm for 6 hours, then heat it to 860°C at a rate of 2°C / h again, keep it warm for 3 hours, then introduce 1.1 Bar nitrogen into the vacuum device and cool it to 50°C, then take it out of the furnace and air cool it.

[0063] 4. Performance heat treatment

[0064] Quenching treatment: put the impeller after stress relief and normalizing treatment into furnace at 180℃, heat it up to 850℃ at a rate of 80℃ / h, keep it at that temperature for 2h, then take it out of furnace and cool it in oil to 200℃ and then cool it in air;

[0065] Tempering treatment: the quenched impeller is charged into the furnace with air at 120℃, heated to 640℃ at a rate of 40℃ / h, kept at this temperature for 3h, and then air-cooled to room temperature.

[0066] The mechanical properties of the weld and heat-affected zone of the welded impeller obtained in the embodiment of the present invention are shown in Table 1.

[0067] Table 1 Mechanical properties of weld and heat affected zone

[0068]

[0069] After welding, the weld is intact and there is no cracking.

[0070] Example 2

[0071] The impeller is φ600mm in diameter and made of 25Cr2Ni3Mo. The weld yield strength requirement is ≥735Mpa, and the impact energy of the weld and heat-affected zone at -70℃ Kv2 is ≥27J.

[0072] 1. Preparatory heat treatment of impeller cover and shaft disc before welding

[0073] The impeller cover and shaft disc are normalized and tempered.

[0074] Normalizing treatment: the cover plate and the shaft plate are placed in a furnace at 180°C, heated to 890°C and kept warm for 2.5 hours, then air-cooled to room temperature;

[0075] Tempering treatment: After normalizing treatment, the cover plate and shaft plate are loaded into the furnace at 150℃, heated to 680℃ and kept warm for 4 hours, and then air-cooled to room temperature.

[0076] 2. Welding of impeller

[0077] The cover plate and shaft plate need to be preheated at 220℃;

[0078] Welding material composition: 0.085% C, 0.8% Mn, 0.45% Si, 2.2% Cr, 3.4% Ni, 1.1% Mo, 0.004% S and 0.006% P.

[0079] The impeller is welded by arc welding with the current controlled at 120A, voltage controlled at 25V, welding speed at 15cm / min, interlayer temperature at 260℃, and post-heating at 310℃ after welding.

[0080] 3. Stress relief of impeller

[0081] Stress relief-normalizing treatment: Place the welded impeller into a vacuum device, load it into a furnace at room temperature, heat it to 690°C at a rate of ≤2°C / h, keep it warm for 7 hours, then heat it again to 865°C at a rate of 1°C / h, keep it warm for 4 hours, then introduce 1.2 Bar nitrogen into the vacuum device and cool it to 55°C, then take it out of the furnace and air cool it.

[0082] 4. Performance heat treatment

[0083] Quenching treatment: put the impeller after stress relief and normalizing treatment into the furnace at 160℃, heat it up to 845℃ at a rate of 60℃ / h, keep it at that temperature for 2h, then take it out of the furnace and cool it in oil to 220℃ and then cool it in air;

[0084] Tempering treatment: the quenched impeller is charged into the furnace with air at 140°C, heated to 610°C at a rate of 30°C / h, kept at this temperature for 3h, and then air-cooled to room temperature.

[0085] The mechanical properties of the weld and heat-affected zone of the welded impeller obtained in the embodiment of the present invention are shown in Table 2.

[0086] Table 2 Mechanical properties of weld and heat affected zone

[0087]

[0088] After welding, the weld is intact and there is no cracking.

[0089] Example 3

[0090] The impeller with a diameter of φ800mm is manufactured using 25Cr2Ni3Mo as the material. The weld yield strength requirement is ≥800Mpa, and the impact energy of the weld and heat-affected zone at -70℃ Kv2 is ≥27J.

[0091] 1. Preparatory heat treatment of impeller cover and shaft disc before welding

[0092] The impeller cover and shaft disc are normalized and tempered.

[0093] Normalizing treatment: Place the cover plate and shaft plate in a furnace at 180℃, heat to 900℃ and keep warm for 3 hours, then air cool to room temperature;

[0094] Tempering treatment: After normalizing treatment, the cover plate and shaft plate are loaded into the furnace at 150℃, heated to 680℃ and kept warm for 5 hours, and then air-cooled to room temperature.

[0095] 2. Welding of impeller

[0096] The cover plate and shaft plate need to be preheated at 230°C;

[0097] Welding material composition: 0.085% C, 0.8% Mn, 0.45% Si, 2.2% Cr, 3.4% Ni, 1.1% Mo, 0.004% S and 0.006% P.

[0098] The impeller is welded by arc welding with the current controlled at 110A, the voltage controlled at 25V, the welding speed at 14cm / min, the interlayer temperature at 250℃, and post-heating at 300℃ after welding.

[0099] 3. Stress relief of impeller

[0100] Stress relief-normalizing treatment: Place the welded impeller into a vacuum device, load it into a furnace at room temperature, heat it to 680°C at a rate of ≤1°C / h, keep it warm for 6 hours, then heat it to 855°C at a rate of 1°C / h again, keep it warm for 4 hours, then introduce 1.3 Bar nitrogen into the vacuum device and cool it to 60°C, then take it out of the furnace and air cool it.

[0101] 4. Performance heat treatment

[0102] Quenching treatment: put the impeller after stress relief and normalizing treatment into the furnace at 150℃, heat it up to 840℃ at a rate of 50℃ / h, keep it at that temperature for 2.5h, then take it out of the furnace and cool it in oil to 200℃ and then cool it in air;

[0103] Tempering treatment: the quenched impeller is charged into a furnace with air at 130°C, heated to 590°C at a rate of 45°C / h, kept at this temperature for 5h, and then air-cooled to room temperature.

[0104] The mechanical properties of the weld and heat-affected zone of the welded impeller obtained in the embodiment of the present invention are shown in Table 3.

[0105] Table 3 Mechanical properties of weld and heat affected zone

[0106]

[0107] After welding, the weld is intact and there is no cracking.

[0108] Comparative Example

[0109] The impeller is φ700mm in diameter and made of 25Cr2Ni3Mo. The weld yield strength requirement is ≥735Mpa, and the impact energy of the weld and heat-affected zone at -50℃ Kv2 is ≥27J.

[0110] 1. Welding of impeller

[0111] The cover plate and shaft plate need to be preheated at 220℃;

[0112] Welding material composition: 0.09% C, 1.2% Mn, 0.40% Si, 1.0% Cr, 2.8% Ni, 0.60% Mo, 0.03% S and 0.03% P.

[0113] The impeller is welded by arc welding with the current controlled at 120A, the voltage controlled at 24V, the welding speed at 15cm / min, the interlayer temperature at 260℃, and post-heating at 320℃ after welding.

[0114] 2. Stress relief of impeller

[0115] Stress relief: Place the welded impeller into an electric furnace at room temperature, heat it to 680°C at a rate of 60°C / h, then keep it warm for 5 hours and take it out of the furnace for air cooling.

[0116] 3. Performance heat treatment

[0117] Quenching treatment: put the stress-relieved impeller into the furnace at 160℃, heat it up to 850℃ at a rate of 80℃ / h, keep it at that temperature for 2.5h, then take it out of the furnace and cool it in oil;

[0118] Tempering treatment: the quenched impeller is charged into the furnace with air at 140℃, heated to 610℃ at a rate of 40℃ / h, kept at this temperature for 5h, and then air-cooled.

[0119] The mechanical properties of the weld and heat-affected zone of the welded impeller obtained in the comparative example of the present invention are shown in Table 4.

[0120] Table 4 Mechanical properties of weld and heat affected zone

[0121]

[0122] After welding, the weld fusion line appears in dot and linear form.

[0123] Comparison of Examples 1-3 with the comparative example shows that the present invention provides a method for improving the low-temperature performance and welding quality of a 25Cr2Ni3Mo steel impeller weld. The method comprises first performing a preliminary heat treatment including normalizing and tempering on the cover disc and shaft disc; then, during impeller welding, preheating the cover disc and shaft disc before arc welding using optimized V840 welding consumables; and post-heating the welded impeller after welding. The welded impeller then undergoes stress relief treatment including stress relief and normalizing in a vacuum heat treatment apparatus; and finally, a performance heat treatment including quenching and tempering on the welded impeller. This method effectively improves the low-temperature performance and welding quality of the welded 25Cr2Ni3Mo steel impeller, ensuring that the weld remains intact and free of weld cracking after welding. This method effectively resolves the issues of poor low-temperature toughness and weld quality associated with 25Cr2Ni3Mo steel impellers during welding.

[0124] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller welds, characterized in that: The steps include: Performing preliminary heat treatment including normalizing and tempering on the cover disc and the shaft disc; Impeller welding: After preheating the cover plate and shaft plate, use optimized V840 welding materials for arc welding. After welding, perform post-heat treatment on the welded impeller. The welded impeller is subjected to stress relief treatment including stress relief and normalizing treatment in a vacuum heat treatment equipment; The welded impeller is subjected to a performance heat treatment including quenching and tempering.

2. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The normalizing treatment in the preliminary heat treatment includes: charging the cover plate and the shaft plate into a furnace at ≤500°C, heating to 880-900°C and holding the temperature for 0.6*effective thickness / 30+1h, then air-cooling to room temperature, and the holding time is not less than 2h; The tempering treatment in the preliminary heat treatment includes: charging the cover plate and the shaft plate into a furnace at ≤350°C, heating to 660-690°C, holding the temperature for 0.9*effective thickness / 30+1h, and then air-cooling to room temperature for no less than 3h.

3. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 2, characterized in that: The effective thickness is the effective thickness of the cover disc and the shaft disc.

4. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The preheating temperature is 200-250°C, and the post-heating temperature is 250-350°C.

5. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The optimized V840 welding material includes, by mass percentage, a Ni content of 3.0-4.0%, a Mn content of 0.4-0.9%, a Cr content of 1.8-2.5%, and the contents of S and P are controlled at ≤0.008%.

6. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 5, characterized in that: The Ni content is 3.25-3.5%, the Mn content is 0.5-0.7%, and the Cr content is 2.0-2.3%.

7. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The welding parameters of the arc welding include current controlled at 100-145A, voltage controlled at 23-26V, welding speed controlled at 13-17cm / min, and interlayer temperature controlled at 200-350°C.

8. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The step of stress relief-normalizing treatment comprises: Place the welded impeller into a vacuum heat treatment device, place it in a furnace at room temperature, heat it to 660-690°C at a rate of 1-3°C / h, and then keep it warm for 5-10 hours; Then, heat up to 850-890°C at a rate of 1-3°C / h and keep warm for 2-7h; Finally, 1.1-1.5 Bar nitrogen is introduced into the vacuum heat treatment equipment to cool it to 50-60°C, and then it is taken out of the furnace and air-cooled.

9. The method for improving the low temperature performance and welding quality of 25Cr2Ni3Mo steel impeller weld according to claim 1, characterized in that: The quenching treatment of the performance heat treatment comprises charging the welded impeller after stress relief and normalizing treatment into a furnace at 500°C, heating it to 840-880°C at a rate of ≤100°C / h, keeping it at that temperature for 2-7h, then cooling it with oil to 200-300°C and then cooling it with oil and air; The tempering treatment of the performance heat treatment comprises charging the welded impeller after quenching treatment into an air furnace at ≤350°C, heating it to 560-640°C at a speed of ≤70°C / h, keeping it at that temperature for 3-10 hours, and then cooling it to room temperature in air.

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