A method for repairing a welded joint of P91 steel

Abstract

The present application relates to the technical field of welding repair, and discloses a P91 steel welded joint repair method, which comprises the following steps: S1, chiseling a repair welding groove on the weld of a workpiece; S2, performing repair welding in a multi-layer and multi-pass manner, wherein the welding material is ENiCrFe-3, the inter-pass temperature of the repair welding is 100-150 DEG C, and the welding line energy is 10-20 kJ / cm; and S3, knocking the repair welding part and the periphery of the workpiece after the repair welding, wherein the number of times of knocking is 4800-5200 times / min.The present application has the beneficial effects that: the P91 steel welded joint is repaired by the multi-layer and multi-pass repair welding manner, thereby effectively reducing the thermal stress residue; the post-welding internal stress can be reduced by knocking treatment after the repair welding, the optimization of the weld residual stress of the repair welding area of the welded joint, the microstructure and mechanical properties of the repair weld and the fusion zone are realized, and the reliability and service life in the subsequent service process are improved; and the present application also has the advantages of simple process, easy operation, low cost, high repair efficiency, energy saving and environmental protection, etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding repair, in particular to a P91 steel welding joint repair method. BACKGROUND

[0002] P91 steel is a modified martensitic heat-resistant steel, which reduces the content of C element on the basis of 9Cr-1Mo steel, further controls the content of S and P elements, and adds a small amount of V, Nb and N elements for alloying to obtain a steel grade. Because of its excellent high-temperature performance, it is widely used in the power industry. However, P91 steel inevitably produces cracks and other defects in the local welding joint during service, thereby reducing the reliability of the welded structure and affecting the safe and economic operation of the pipeline. Welding repair has the characteristics of high efficiency, low economic cost and easy operation, and is widely used in the power industry.

[0003] At present, Li Zhixin of Jilin University points out in the research on P91 steel welding process that before welding P91 steel, preheat to 200-250 DEG C, and then use multi-layer multi-pass welding process for welding, which is beneficial to reduce the tendency of welding cold crack. However, if this technology is used in local repair welding process, the influence of welding residual stress on the stability of welded structure is more prominent due to the influence of unbalanced thermal cycle, which will lead to different degrees of loss of microstructure and mechanical properties of welded joint weld metal and heat affected zone after welding repair, and reduce the reliability and service life in the subsequent service process. Even re-failure. SUMMARY

[0004] The technical problem to be solved by the present application is how to provide a P91 steel welding joint repair method, so that the welding residual stress of the repair welding area of the welding joint, the microstructure and mechanical properties of the repair welding seam and the fusion zone are optimized, and the reliability and service life in the subsequent service process are improved.

[0005] The present application solves the above technical problems by the following technical means:

[0006] The present application provides a P91 steel welding joint repair method, comprising the following steps:

[0007] S1, chisel a repair welding groove on the weld of the workpiece;

[0008] S2, repair welding is carried out by using multi-layer multi-pass repair welding method, the welding material is ENiCrFe-3, the interpass temperature of repair welding is 100-150 DEG C, and the welding line energy is 10-20 kJ / cm;

[0009] S3, knock the repair welding part and the periphery of the workpiece after repair welding, the knocking frequency is 4800-5200 times / min.

[0010] Beneficial effects: the application adopts the multi-layer and multi-pass repair welding mode, and under the conditions that the inter-pass temperature is 100-150 DEG C and the welding line energy is 10-20kJ / cm, the P91 steel welded joint is repair welded, so that the residual stress of the repair welded joint is effectively reduced; after the repair welding is completed, the post-welding internal stress is further reduced by knocking the repair welding part and the periphery, so that the optimization of the welding residual stress of the repair welding area of the welded joint, the microstructure and the mechanical property of the repair welding seam and the fusion zone are realized, and then the reliability and the service life in the subsequent service process are improved.

[0011] The repair method has the advantages of simple process, easy operation, low cost and high repair efficiency, and does not need post-welding heat treatment, but can reduce the post-welding stress by knocking, is especially suitable for repair welding of large-sized workpieces, and has the advantages of convenient operation, energy saving and environmental protection.

[0012] Preferably, the repair welding groove in S1 is a V-shaped groove with an angle of 55-60 DEG.

[0013] Preferably, the depth of the repair welding groove in S1 is not more than 75% of the wall thickness.

[0014] Beneficial effects: the P91 steel welded joint repair method has good repair effects on both large and small cracks.

[0015] Preferably, the inside of the repair welding groove is treated in S1, so that the inside of the groove is flat and clean.

[0016] Preferably, the repair welding part and the periphery are preheated to 100-150 DEG C before the repair welding in S2.

[0017] Preferably, the inter-pass temperature of the repair welding in S2 is 100 DEG C, and the welding line energy is 15kJ / cm.

[0018] Preferably, the diameter of ENiCrFe-3 in S2 is 3.2mm.

[0019] Preferably, ENiCrFe-3 in S2 comprises the following components in mass fraction: C 0.048%, Mn 7.32%, Si 0.69%, Cr 17%, Ni 65.2%, S 0.002%, P 0.011%, Cu 0.03%, Nb 2.04%, Ti 0.06%, Fe 7.5%, and the rest is Co.

[0020] Preferably, the number of times of knocking in S3 is 5000 times / min.

[0021] The second aspect of the application provides an application of the above-mentioned P91 steel welded joint repair method in the welding repair of special-shaped components in high-parameter thermal power plants.

[0022] The application has the advantages that:

[0023] 1. The application adopts the mode of multi-layer and multi-pass repair welding, under the conditions of 100-150 DEG C of interpass temperature and 10-20 kJ / cm of welding line energy, to repair the P91 steel welded joint, effectively reduces the residual stress of the repair welded joint; after the repair welding is completed, the post-weld internal stress is further reduced by knocking the repair welding part and the periphery, the optimization of the residual stress of the repair welding zone weld of the welded joint, the microstructure and mechanical properties of the repair weld and the fusion zone are realized, and then the reliability and service life in the subsequent service process are improved;

[0024] 2. The repair method has the advantages of simple process, easy operation, low cost and high repair efficiency, and does not need post-welding heat treatment, and the post-welding stress can be reduced by knocking, especially suitable for repair welding of large-sized workpieces, and has the advantages of convenient operation, energy saving and environmental protection;

[0025] 3. The P91 steel welded joint repair method has good repair effect on larger and smaller cracks. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The drawings are the appearance diagrams of the groove and the welded joint before and after the first welding of the test piece of Example 1 of the application.

[0027] Figure 2 The drawings are the appearance diagrams of the groove and the welded joint before and after the first welding of the test piece of Example 1 of the application.

[0028] Figure 3 The drawings are the appearance diagrams of the groove and the welded joint before and after the first welding of the test piece of Example 1 of the application.

[0029] Figure 4 The drawings are the appearance diagrams of the groove and the welded joint before and after the first welding of the test piece of Example 1 of the application.

[0030] Figure 5 The drawings are the metallographic macrographs of the welded joints after repair welding with different slotting depths in Test Example 1 of the application.

[0031] Figure 6 The drawings are the metallographic macrographs of the welded joints after repair welding with different interpass temperatures in Test Example 2 of the application.

[0032] Figure 7 The drawings are the metallographic micrographs of the repair welding zone weld metal after repair welding with different interpass temperatures in Test Example 3 of the application.

[0033] Figure 8 The drawings are the metallographic micrographs of the repair welding zone weld metal after repair welding with different welding line energies in Test Example 3 of the application.

[0034] Figure 9 The drawings are the metallographic micrographs of the repair welding zone weld metal after repair welding with different post-treatment methods in Test Example 3 of the application.

[0035] Figure 10 SEM and EDS characterization results of the weld metal in the repair welding area after repair welding at different interpass temperatures in Test Example 4 of the present application.

[0036] Figure 11 SEM and EDS characterization results of the weld metal in the repair welding area after repair welding at different interpass temperatures in Test Example 4 of the present application.

[0037] Figure 12 SEM and EDS characterization results of the weld metal in the repair welding area after repair welding at different interpass temperatures in Test Example 4 of the present application.

[0038] Figure 13 SEM and EDS characterization results of the weld metal in the repair welding area after repair welding at different interpass temperatures in Test Example 4 of the present application.

[0039] Figure 14 Metallographic structure photos of the fusion line between the repair welding area and the original weld area after repair welding at different interpass temperatures in Test Example 5 of the present application.

[0040] Figure 15 Line scanning energy spectrum graph of the RWZ fusion area after repair welding at different interpass temperatures in Test Example 6 of the present application.

[0041] Figure 16 Line scanning energy spectrum graph of the RWZ fusion area after repair welding at different interpass temperatures in Test Example 6 of the present application.

[0042] Figure 17 Room temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 8 of the present application.

[0043] Figure 18 Room temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 8 of the present application.

[0044] Figure 19 Room temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 8 of the present application.

[0045] Figure 20 High temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 9 of the present application.

[0046] Figure 21 High temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 9 of the present application.

[0047] Figure 22 High temperature tensile morphology graph of the repair welding area after repair welding at different interpass temperatures in Test Example 9 of the present application.

[0048] Figure 23The hardness curve distribution diagram after repair welding of the P91 steel plate in the test example 11 of the present application.

[0049] Figure 24 The hardness curve distribution diagram after repair welding of the P91 steel plate in the test example 11 of the present application.

[0050] Figure 25 The hardness curve distribution diagram after repair welding of the P91 steel plate in the test example 11 of the present application.

[0051] Figure 26 The Charpy impact result diagram of each position after repair welding of the P91 steel plate in the test example 12 of the present application.

[0052] Figure 27 The Charpy impact result diagram of each position after repair welding of the P91 steel plate in the test example 12 of the present application.

[0053] Figure 28 The Charpy impact result diagram of each position after repair welding of the P91 steel plate in the test example 12 of the present application. DETAILED DESCRIPTION

[0054] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0055] The test materials and reagents used in the following embodiments, unless otherwise specified, can be obtained from commercial channels.

[0056] The specific technologies or conditions not specified in the embodiments can be carried out according to the technologies or conditions described in the literature in the art or according to the product instructions.

[0057] Embodiment 1

[0058] The embodiment provides a P91 steel welded joint repair method, including the following steps:

[0059] S1, the test steel plate is a P911 steel plate, the size of the P911 steel plate is 350mm(length)×150mm(width)×26mm(thickness), and the supply unit is Shanxi Taigang Stainless Steel Co., Ltd. As shown in FIG. a, the P911 steel plate has a V-shaped groove with an angle of 55°, and the groove gap and the blunt edge are both 2mm. Figure 1

[0060] ​The groove of the P911 steel plate is butt welded by manual arc welding (SMAW), and the welding machine is WSME-500P. The welding material is E9015 B91, the diameter of the E9015 B91 electrode is 3.2 mm, and the mass fraction of the chemical components of the deposited metal is as follows: C 0.111%, Mn 0.590%, Si 0.217%, Cr 8.293%, Ni 0.307%, Mo 1.028%, S 0.006%, P 0.01%, V 0.185%, Nb 0.00315%, and the rest is Fe. The tensile strength of the E9015 B91 is 730 MPa, the yield strength is 610 MPa, the elongation is 20%, and the impact energy at 20 ℃ is 85 J. The first welding process is as follows: preheating at 150-200 ℃ before welding, welding heat input is 15 kJ / cm, the interpass temperature is controlled at 150-200 ℃, and post-welding heat treatment is performed at 250 ℃ for 2 h. After the first welding of the groove of the P911 steel plate, the welding joint is as shown in FIG. 1b. Figure 1

[0061] After the first welding of the test piece and sufficient cooling, a repair welding groove is chiseled on the basis of the original welding seam by mechanical processing, the repair welding groove is a 60° V-shaped groove, and the groove depth is 13 mm; and the inside of the repair welding groove is treated so that there is no step or four corners, oxide skin, oil stain, rust, etc. in the inside of the repair welding groove, so as to ensure that the repair welding groove is smooth and clean.

[0062] S2, the repair welding is performed in a multi-layer and multi-pass repair welding manner, the welding material is ENiCrFe-3, the ENiCrFe-3 is purchased from Lincoln Welding Material in the United States, and the diameter of the ENiCrFe-3 is 3.2 mm; the ENiCrFe-3 comprises the following components in mass fraction: C 0.048%, Mn 7.32%, Si 0.69%, Cr 17%, Ni 65.2%, S 0.002%, P 0.011%, Cu 0.03%, Nb 2.04%, Ti 0.06%, Fe 7.5%, and the rest is Co. The repair welding part and the periphery are preheated to 100-150 ℃ before repair welding, the interpass temperature of the repair welding is 100 ℃, and the welding line energy is 15 kJ / cm.

[0063] S3, the repair welding part and the periphery of the steel plate after the repair welding are knocked by a pneumatic pick, and the knocking frequency is 5000 times / min.

[0064] Example 2

[0065] The embodiment provides a P91 steel welded joint repair method, which is different from the embodiment 1 in that the groove depth of the repair welding groove in the step S1 is 6.5 mm, and the other operations are the same as those in the embodiment 1.

[0066] Example 3 ​

[0067] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 1 in that the slotting depth of the repair welding slot in the step S1 is 19.5 mm, and other operations are the same as those in the embodiment 1.

[0068] Embodiment 4

[0069] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 1 in that the interpass temperature of the repair welding in the step S2 is 150 DEG C, and other operations are the same as those in the embodiment 1.

[0070] Embodiment 5

[0071] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 4 in that the welding line energy of the repair welding in the step S2 is 10 kJ / cm, and other operations are the same as those in the embodiment 4.

[0072] Embodiment 6

[0073] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 4 in that the welding line energy of the repair welding in the step S2 is 20 kJ / cm, and other operations are the same as those in the embodiment 4.

[0074] Comparative Example 1

[0075] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 1 in that the welding material in the step S2 is E9015 B9, the repair welding part and the periphery are preheated to 180 DEG C before the repair welding, the interpass temperature of the repair welding is 200 DEG C, and other operations are the same as those in the embodiment 1.

[0076] Comparative Example 2

[0077] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 1 in that the step S3 is omitted, that is, the P91 steel plate after the repair welding is not subjected to the knocking treatment, and other operations are the same as those in the embodiment 1.

[0078] Comparative Example 3

[0079] The embodiment provides a P91 steel welded joint repairing method which is different from the embodiment 7 in that the repair welding part is knocked after each layer of welding in the process of the repair welding in the step S2; after the repair welding is completed, the repair welding part is directly heated to 100-150 DEG C in the step S3, the repair welding part is tightly wrapped with the heat preservation cotton, and the slow cooling is performed to the room temperature. Other operations are the same as those in the embodiment 7.

[0080] Test Example 1

[0081] The welding joint and the bevel appearance of the repair welding in the embodiments 1, 2 and 3 are respectively as shown in Figure 2 ,3 As shown in FIG. 4, it can be seen that the welds after the three slot depth repair welding are all regularly shaped, uniform and beautiful, and have good formability.

[0082] The weld cross sections of the welded joints after the repair welding of Examples 1, 2 and 3 were intercepted, and the samples were etched by using 10% nitric acid alcohol etchant to detect the macroscopic morphology of the joints, and the metallographic macroscopic photographs were obtained as shown in FIG. 2. Figure 5 As shown in FIG. 2, it can be seen that the repair welded zone (RWZ) and the original welded zone (OWZ) of the repair welded joints of the three slot depths are reasonably arranged, the weld layer thickness is controlled to be moderate, no cracks are generated in the repair welded zone, the original weld and the welding heat affected zone; the fusion line between the base material and the repair welded zone and the repair welded zone and the original welded zone is clear, no incomplete fusion and incomplete penetration occurs between the weld layers, and no welding defects such as pores and slag are generated on the weld metal cross section, which meets the requirements of GB / T226-2015, indicating that the P91 steel welded joint repair method has good repair effect on larger and smaller cracks.

[0083] Test Example 2

[0084] The weld cross sections of the welded joints after the repair welding of Examples 1, 4 and Comparative Example 1 were intercepted, and the samples were etched by using 10% nitric acid alcohol etchant to detect the macroscopic morphology of the joints, and the metallographic macroscopic photographs of the samples were obtained as shown in FIG. 5. Figure 6 As shown in FIG. 5, it can be seen that when the interpass temperature of the repair welding is 100°C (a), 150°C (b) and 200°C (c), that is, in the cold repair welding and hot repair welding two welding processes, the repair welded zone (RWZ) and the original welded zone (OWZ) of the repair welded joints are reasonably arranged, the weld layer thickness is controlled to be moderate, no cracks are generated in the repair welded zone, the original weld and the welding heat affected zone; the fusion line between the base material and the repair welded zone and the repair welded zone and the original welded zone is clear, no incomplete fusion and incomplete penetration occurs between the weld layers, and no welding defects such as pores and slag are generated on the weld metal cross section, which meets the requirements of GB / T226-2015. Figure 6 Figure 6 Figure 6

[0085] Test Example 3

[0086] According to the Metallographic Microstructure Test Method (GB / T 13298-91), the metallographic microstructure of the welded joints after the repair welding of Examples 1, 4 and Comparative Example 1 was tested after polishing and etching, and the metallographic microstructure photographs of the repair welded zone were obtained as shown in FIG. 6. Figure 7 As shown in FIG. 6, it can be seen that when the interpass temperature of the repair welding is 100°C (a), 150°C (b) and 200°C (c), that is, in the cold repair welding and hot repair welding two welding processes, the repair welded zone (RWZ) and the original welded zone (OWZ) of the repair welded joints are reasonably arranged, the weld layer thickness is controlled to be moderate, no cracks are generated in the repair welded zone, the original weld and the welding heat affected zone; the fusion line between the base material and the repair welded zone and the repair welded zone and the original welded zone is clear, no incomplete fusion and incomplete penetration occurs between the weld layers, and no welding defects such as pores and slag are generated on the weld metal cross section, which meets the requirements of GB / T226-2015. Figure 7 Figure 7 ​​​​c、7d) when, the weld structure is in the form of cellular dendrites, the solidification mode is A solidification mode, the weld metallographic structure is A solid solution, showing segregation characteristics, there are precipitates in the grain and at the grain boundary, the intragranular precipitates are in the form of granules (or small blocks), the grain boundary precipitates are mainly in the form of intermittent cotton, no micro cracks and other micro defects are found. When the interpass temperature of the repair welding is 200℃ Figure 7 e、7f) when, the weld structure is mainly lath martensite structure, no micro cracks and other micro defects are found.

[0087] According to the above method, the metallographic microstructure of the welded joints after repair welding of example 4, example 5 and example 6 was tested, and the weld metallographic structure photos of the repair welding zone are shown in Figure 8 Figure 8 a、8b, the welding line energy is 10 kJ / cm, Figure 8 c、8d, the welding line energy is 15 kJ / cm, Figure 8 e、8f, the welding line energy is 20 kJ / cm. As can be seen from the figure, the weld structure of the repair welding zone under the three heat inputs is all austenite structure, the solidification mode is full austenite mode (A), and the weld is composed of cellular crystals, cellular dendrites and equiaxed crystals. When the heat input is 10 kJ / cm, the dendrites in the weld zone are parallel due to the fast cooling speed; when the welding heat input increases to 15 kJ / cm, the weld structure of the repair welding zone presents a cross-interlocking dovetail lap shape; when the heat input further increases to 20 kJ / cm, the cooling speed of the weld metal slows down, the high-temperature residence time is longer, the dendrite shape of the weld metal is mainly in the form of parallel distribution, and a small amount of cross-interlocking dovetail lap shape. In addition, when the heat input is 10 kJ / cm, the intragranular precipitates in the weld are in the form of granules; when the heat input is 15 kJ / cm, the intragranular precipitates are in the form of granules (or small blocks), and the grain boundary precipitates are in the form of intermittent cotton; when the heat input further increases to 20 kJ / cm, there are granular (or small block) precipitates in the grain and at the grain boundary, and the size and amount of the precipitates increase with the increase of the heat input. No micro cracks and other micro defects are found in the repair welding zone under the three different welding heat inputs.

[0088] According to the above method, the metallographic microstructure of the welded joints after repair welding of example 4 and comparative example 2 was tested, and the weld metallographic structure photos of the repair welding zone are shown in Figure 9 . As can be seen from the figure, the weld structure of the repair welding zone after welding is A structure, and there is no knocking treatment after welding Figure 9 a、9b, the intragranular precipitates of the repair welding zone are small block-shaped, and the grain boundary precipitates are in the form of intermittent cotton; while the repair welding zone after the wind pick hammering treatment Figure 9 c、9d, the intragranular precipitates of the repair welding zone change to granules.

[0089] Test example 4​

[0090] The SEM morphology and EDS analysis of the weld joint of the repair welding area of Example 1, Example 4 and Comparative Example 1 after repair welding were carried out by using a scanning electron microscope, and the SEM morphology and EDS characterization results of the weld metal of the repair welding area are shown in Figure 10 , Figure 11 .

[0091] Figure 10 a, 10b corresponds to the temperature of 100℃, 150℃, respectively, from the SEM morphology diagram, the microstructure of the weld is austenite dendrite + precipitated phase, the gray black area in the figure is the internal area of austenite dendrite, and the white area exists in the interdendritic area and the internal area of dendrite; EDS spectrum analysis of the precipitated phase and globular in the white area shows that the white precipitated phase is mainly NbC and Cr 23 C6; the gray globular is a composite oxide inclusion of MnO-SiO2-TiO2-Cr2O3.

[0092] Figure 11 Corresponding to the temperature of 200℃, from the SEM morphology diagram, a small amount of inclusions exist in the weld metal; EDS spectrum analysis shows that the inclusions in the weld metal contain Ca, Al, Si, Mn, S, O and other elements, it is speculated that the inclusions are a composite structure with SiO, CaO, Al2O3 alloy oxide as the center and MnS wrapped outside.

[0093] The SEM morphology and EDS analysis of the weld joint of the repair welding area of Example 1, Example 5 and Example 6 after repair welding were carried out by using a scanning electron microscope, and the SEM morphology and EDS characterization results of the weld metal of the repair welding area are shown in Figure 11 , Figure 12 , Figure 12 a, 12b, 12c correspond to the welding line energy of 10kJ / cm, 15kJ / cm, 20kJ / cm, respectively.

[0094] The SEM morphology and EDS analysis of the weld joint of the repair welding area of Example 1 and Comparative Example 2 after repair welding were carried out by using a scanning electron microscope, and the SEM morphology and EDS characterization results of the weld metal of the repair welding area are shown in Figure 13 , Figure 13 a, 13b corresponds to the pneumatic pick hammering and no pneumatic pick hammering, respectively.

[0095] Test Example 5

[0096] According to the "Metallographic Microstructure Test Method" (GB / T 13298-91), the metallographic microstructure test of the weld joint after repair welding of Example 1 and Example 4 was carried out, and the metallographic microstructure photos at the fusion line between the repair welding area and the original weld area are shown in Figure 14 .Figure 14 a, 14b corresponds to the interpass temperature of 100°C, Figure 14 c, 14d corresponds to the interpass temperature of 150°C.

[0097] Test Example 6

[0098] Line scanning energy spectrum analysis was performed on the vicinity of the RWZ fusion zone of the welded joints after repair welding of Example 1, Example 4, Example 5, and Example 6, and the results are shown in Figs. 15b, 15c, and 15d, respectively. Figure 15 、 Figure 16 Figure 15 a, 15b is a line scanning energy spectrum graph of the vicinity of the RWZ fusion zone when the interpass temperature of repair welding is 100°C and 150°C, respectively.

[0099] Figure 16 a, 16b and 16c are line scanning energy spectrum graphs of the vicinity of the RWZ fusion zone when the welding line energy of repair welding is 10 kJ / cm, 15 kJ / cm, and 20 kJ / cm, respectively. From OWZ to RWZ, the content of Fe element decreases sharply on both sides of the fusion zone interface, and a transition layer is found beside the fusion boundary. The element transition in this area is also relatively steep. This area is the so-called dilution layer. It can also be found from the figure that a large amount of austenitizing elements such as Ni, Cr, and Mn enter the fusion zone, which can help to increase the austenitizing stability and increase the hardening tendency of the area.

[0100] Test Example 7

[0101] The residual stress of the weld metal at the repair welding position of Example 1, Example 4, and Comparative Example 1 was detected by the drilling method, and the measurement results are shown in Table 1.

[0102] Table 1 Measurement results of residual stress of weld metal at repair welding position under different interpass temperature repair welding processes

[0103]

[0104] The residual stress of the weld metal at the repair welding position of Example 1, Example 5, and Example 6 was detected, and the measurement results are shown in Table 2.

[0105] Table 2 Measurement results of residual stress of weld metal at repair welding position under different welding line energy repair welding processes

[0106]

[0107] The residual stress of the weld metal at the repair welding position of Example 1, Comparative Example 2, and Comparative Example 3 was detected, and the measurement results are shown in Table 3.

[0108] Table 3 Measurement results of residual stress of weld metal at repair welding position under different post-weld heat treatment repair welding processes

[0109] ​

[0110] As can be seen from Tables 1 to 3, the P91 steel welded joint is repaired by adopting the multi-layer and multi-pass repair welding mode under the conditions that the inter-pass temperature is 100-150°C and the welding line energy is 10-20 kJ / cm, so that the residual stress of the welded joint is effectively reduced; after the repair welding is completed, the post-weld internal stress is further reduced by knocking the repair welding part and the periphery; the "synergistic effect" caused by the dendritic morphology and precipitate morphology of the repair welding seam metal makes the energy threshold required for the nucleation, development and expansion of micro-cracks different, so that the repaired joint can maintain high strength and toughness, thereby realizing the optimization of the residual stress of the repair welding seam of the welded joint, the microstructure and mechanical properties of the repair welding seam and the fusion zone, and further improving the reliability and service life in the subsequent service process.

[0111] Example 7

[0112] The embodiment provides a P91 steel welded joint repair method, which is different from the embodiment 1 in that a P91 steel special-shaped member for a high-parameter thermal power plant is used as a sample, and other operations are the same as those in the embodiment 1.

[0113] Example 8

[0114] The embodiment provides a P91 steel welded joint repair method, which is different from the embodiment 7 in that the inter-pass temperature of the repair welding in the step S2 is 150°C, and other operations are the same as those in the embodiment 7.

[0115] Example 9

[0116] The embodiment provides a P91 steel welded joint repair method, which is different from the embodiment 7 in that the welding line energy of the repair welding in the step S2 is 10 kJ / cm, and other operations are the same as those in the embodiment 7.

[0117] Example 10

[0118] The embodiment provides a P91 steel welded joint repair method, which is different from the embodiment 7 in that the welding line energy of the repair welding in the step S2 is 20 kJ / cm, and other operations are the same as those in the embodiment 7.

[0119] Comparative Example 4

[0120] The embodiment provides a P91 steel welded joint repair method, which is repaired by adopting the hot repair welding mode, and is different from the embodiment 7 in that the welding material used in the step S2 is E9015 B9, the repair welding part and the periphery are preheated to 180°C before the repair welding, the inter-pass temperature of the repair welding is 200°C, and other operations are the same as those in the embodiment 7.

[0121] Comparative Example 5

[0122] The embodiment provides a P91 steel welded joint repairing method, which is different from that of the embodiment 7 in that the step S3 is omitted, that is, the shaped member after the repair welding is not knocked, and other operations are the same as those in the embodiment 7.

[0123] Test example 8

[0124] According to the first part: room temperature test method in the metal material tensile test (GB / T 228.1-2010), the shaped members in the embodiment 7, the embodiment 8 and the comparative example 4 are subjected to the tensile test at room temperature (25 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 17 Figure 17 a, 17b corresponds to the track-to-track temperature of 100 DEG C and 150 DEG C respectively.

[0125] According to the above method, the shaped members in the embodiment 7, the embodiment 9 and the embodiment 10 are subjected to the tensile test at room temperature (25 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 18 Figure 18 a, 18b and 18c correspond to the welding line energy of 10 kJ / cm, 15 kJ / cm and 20 kJ / cm respectively.

[0126] According to the above method, the shaped members in the embodiment 7 and the comparative example 5 are subjected to the tensile test at room temperature (25 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 19 Figure 19 a, 19b corresponds to no wind pick knocking and wind pick knocking respectively.

[0127] Test example 9

[0128] According to the second part: high temperature test method in the metal material tensile test (GB / T 228.2-2015), the shaped members in the embodiment 7, the embodiment 8 and the comparative example 4 are subjected to the tensile test at high temperature (550 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 20 Figure 20 a, 20b corresponds to the track-to-track temperature of 100 DEG C and 150 DEG C respectively.

[0129] According to the above method, the shaped members in the embodiment 7, the embodiment 9 and the embodiment 10 are subjected to the tensile test at high temperature (550 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 21 Figure 21 a, 21b and 21c correspond to the welding line energy of 10 kJ / cm, 15 kJ / cm and 20 kJ / cm respectively.

[0130] According to the above method, the shaped members in the embodiment 7 and the comparative example 5 are subjected to the tensile test at high temperature (550 DEG C), and the shaped member appearance after the tensile test is as shown in the following table. Figure 22 Figure 22 ​​​​​​a, 22b respectively corresponding to no pneumatic pick hammering, pneumatic pick hammering.

[0131] Test Example 10

[0132] The mechanical parameters of the weld metal in the repair welding zone of the special-shaped member in Test Example 8 and Test Example 9 during the tensile test at room temperature (25℃) and high temperature (550℃) are shown in Table 4.

[0133] Table 4 Tensile test results of the weld metal in the repair welding zone at room temperature and high temperature

[0134]

[0135] The tensile test mechanical property test results of Example 7, Example 9 and Example 10 are shown in Table 5.

[0136] Table 5 Tensile test results of the weld metal in the repair welding zone at room temperature and high temperature

[0137]

[0138] The tensile test mechanical property test results of Example 7 and Comparative Example 5 are shown in Table 6.

[0139] Table 6 Tensile test results of the weld metal in the repair welding zone at room temperature and high temperature

[0140]

[0141] As can be seen from Tables 4-6, the special-shaped member of P91 steel is repaired by the multi-layer and multi-pass repair welding method under the conditions of inter-pass temperature of 100-150℃ and welding line energy of 10-20kJ / cm, which effectively reduces the residual stress of the welded joint. After the repair welding is completed, the post-weld internal stress is further reduced by knocking the repair welding part and the surrounding area. The "synergistic effect" caused by the dendritic morphology and precipitate morphology of the weld metal in the repair welding zone makes the energy threshold required for the nucleation, development and expansion of micro-cracks different, and thus the repaired joint can maintain high strength and toughness, thereby realizing the optimization of the residual stress of the weld metal in the repair welding zone, the microstructure and mechanical properties of the repair welding seam and the fusion zone, and further improving the reliability and service life in the subsequent high-parameter power plant service process.

[0142] Test Example 11

[0143] According to the "Hardness Test Method for Welded Joints" (GB / T 2654-2008), the special-shaped member in Example 7, Example 8 and Comparative Example 4 was subjected to micro Vickers hardness test by using a HVS-10 type Vickers hardness tester, and the hardness curve distribution is shown in Figure 23 Figure 23 ​a, 23b, 23c correspond to the interpass temperature of 100℃, 150℃, 200℃ respectively.

[0144] According to the above method, the micro Vickers hardness test was carried out on the profiled members in Example 7, Example 9 and Example 10, and the hardness curve distribution is shown in Figure 24 , Figure 24 a, 24b, 24c correspond to the welding line energy of 10kJ / cm, 15kJ / cm, 20kJ / cm respectively.

[0145] According to the above method, the micro Vickers hardness test was carried out on the profiled members in Example 7 and Comparative Example 5, and the hardness curve distribution is shown in Figure 25 , Figure 25 a, 25b correspond to no wind pick hammering after welding and wind pick hammering respectively.

[0146] Test Example 12

[0147] According to the Charpy impact test method of metal materials (GB / T 229-2007), the Charpy impact test was carried out on the profiled members in Example 7, Example 8 and Comparative Example 4, and the Charpy impact results of the repair welding joints at each position are shown in Figure 26 , Figure 26 a, 26b, 26c correspond to the interpass temperature of 100℃, 150℃, 200℃ respectively. In the figure, WM represents the welded metal, FL represents the position at the fusion line, and FL+2 represents the position at +2mm outside the fusion line.

[0148] From Figure 26 a, 26b, it can be seen that the impact toughness of the repair welding seam center at the interpass temperature of 150℃ is better than that at the interpass temperature of 100℃, which is mainly due to the fact that the increase of the interpass temperature is beneficial to reduce the residual stress at the welding seam, thereby having a certain improvement effect on the impact toughness; and by comparing 26a, 26b and 26c, it can be seen that the impact toughness of the repair welding seam center at the interpass temperature of 100℃ and 150℃ is better than that at the interpass temperature of 200℃, that is, the impact toughness of the repair welding seam center after cold repair welding of the welding seam of the profiled member by using the repair method of the present application is better than that after hot repair welding; this is because the hot repair welding seam mainly has lath martensite structure, and there are large phase change stress and restraint stress in the welding seam, while the cold repair welding has no phase change, and there is no phase change stress in the welding seam only the restraint stress.

[0149] According to the above method, the Charpy impact test was carried out on the profiled members in Example 7, Example 9 and Example 10, and the Charpy impact results of the repair welding joints at each position are shown in Figure 27 . Figure 27a, 27b, and 27c correspond to welding heat inputs of 10 kJ / cm, 15 kJ / cm, and 20 kJ / cm, respectively. As can be seen from the figure, under all three heat inputs, the center of the weld repair maintains relatively high impact toughness, while the fracture toughness is lowest at the fusion line and +2 mm outside the fusion line due to localized high strength, low plasticity, and the material's restraining effect.

[0150] Charpy impact tests were conducted on the irregularly shaped components in Example 7 and Comparative Example 5 according to the above method, and the Charpy impact results at various locations of the welded joints were obtained as follows: Figure 28 As shown. Figure 28 a and 28b correspond to no pneumatic hammering after welding and pneumatic hammering, respectively. As can be seen from the figure, the average impact absorption energy at +2mm outside the fusion line after pneumatic hammering is 58.3J, which is about 50J higher than the average impact absorption energy of the repair weld joint without treatment. This is mainly because the residual stress in the heat-affected zone of the weld is released by the hammering and extrusion, so the impact toughness of this area is significantly improved.

[0151] The implementation principle of this application is as follows: This application adopts a multi-layer, multi-pass welding method to repair the welded joints of P91 steel irregular components under the conditions of interpass temperature of 100-150℃ and welding line energy of 10-20kJ / cm, effectively reducing the residual stress of the welded joints; after the repair welding is completed, the post-weld internal stress is further reduced by tapping the repair welding area and its surroundings. The "synergistic effect" caused by the dendritic morphology and precipitate morphology of the weld metal in the repair welding area makes the energy threshold required for the nucleation, development and propagation of microcracks different, thereby enabling the repaired joint to maintain high strength and toughness. This achieves the optimization of the residual stress of the weld in the repair welding area, the microstructure and mechanical properties of the repair weld and the fusion zone, thereby improving the reliability and service life of high-parameter thermal power plants during subsequent operation.

[0152] The repair method described in this application has the advantages of simple process, easy operation, low cost and high repair efficiency. It does not require post-weld heat treatment and can reduce post-weld stress by hammering. It is especially suitable for repairing large workpieces and has the advantages of convenient operation, energy saving and environmental protection. It also has good repair effect on both large and small cracks.

[0153] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of repairing a P91 steel welded joint, characterized in that: It comprises the following steps: S1, chiseling a repair welding groove on the weld of the workpiece, the repair welding groove is a V-shaped groove with an angle of 55-60°, and the depth of the repair welding groove is not greater than 75% of the wall thickness; S2, performing repair welding in a multi-layer and multi-pass manner, the welding material is ENiCrFe-3, the inter-pass temperature of the repair welding is 100-150℃, the welding line energy is 10-15 kJ / cm, and the repair welding position and the periphery are preheated to 100-150℃ before the repair welding; ENiCrFe-3 comprises the following components in mass fraction: C 0.048%, Mn 7.32%, Si 0.69%, Cr 17%, Ni 65.2%, S 0.002%, P 0.011%, Cu 0.03%, Nb 2.04%, Ti 0.06%, Fe 7.5%, and the rest is Co, the diameter of ENiCrFe-3 is 3.2 mm; S3, knocking the repair welding position and the periphery of the workpiece after the repair welding, and the number of knocking is 4800-5200 times / min.

2. The method for repairing a P91 steel welded joint according to claim 1, characterized in that: In the S1, the inside of the repair welding groove is treated to make the inside of the welding groove flat and clean.

3. The method for repairing a P91 steel welded joint according to claim 1, characterized in that: In the S2, the inter-pass temperature of the repair welding is 100℃, and the welding line energy is 15 kJ / cm.

4. The method for repairing a P91 steel welded joint according to claim 1, characterized in that: In the S3, the number of knocking is 5000 times / min.

5. Application of the P91 steel welded joint repair method according to any one of claims 1-4 in the repair welding of special-shaped components in high-parameter thermal power plants.

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