Hardfacing for steam turbine cylinder seal groove inner surface and welding method

Abstract

The application discloses a surfacing wear-resistant layer for the inner surface of a sealing groove of a steam turbine cylinder and a welding method. The surfacing wear-resistant layer comprises a transition layer and a hard alloy layer. The transition layer is welded on the whole bottom wall of a surfacing groove of the sealing groove of the steam turbine cylinder. The hard alloy layer is welded on the side wall of the surfacing groove. The transition layer is connected with the hard alloy layer and is used for separating the hard alloy layer from the base material of the sealing groove of the steam turbine cylinder. The hard alloy layer is used for contact matching with an assembly part which is inserted into the sealing groove of the steam turbine cylinder and is assembled with the steam turbine cylinder. The application can solve the wear problem of the sealing groove of the steam turbine cylinder and the assembly part under high temperature, effectively ensure the sealing property of the steam turbine cylinder under high temperature, and reduce the leakage of high temperature and high pressure steam in the steam turbine cylinder.

Description

Technical Field

[0001] This invention belongs to the field of steam turbine technology, specifically relating to a wear-resistant overlay layer for the inner surface of a steam turbine cylinder sealing groove and a welding method. Background Technology

[0002] Steam turbines are one of the three main pieces of equipment in thermal power plants. The turbine cylinder is the outer shell of the turbine. Both the rotor and the cylinder have high machining precision and operate in high-temperature and high-pressure environments. The main function of the turbine cylinder is to isolate the flow passage parts of the turbine, such as nozzles, diaphragms, and rotor, from the atmosphere, ensuring that steam completes the work process within the turbine. In addition, the turbine cylinder also supports certain stationary components of the turbine, such as diaphragms, nozzle chambers, and steam seals, and bears their weight. It also has to withstand the thermal stress caused by uneven temperature distribution along the axial and radial directions of the cylinder.

[0003] Patent CN1081724 discloses an I-shaped sealing structure with a sealing groove on the inner shell. Under high temperature and pressure, the I-shaped seal contacts and seals the inner surface of the sealing groove. Patent CN1139739 also discloses a similar I-shaped sealing structure with sealing grooves on the inner flanges at both ends and an I-shaped sealing ring installed in the middle. The sealing groove of the I-shaped sealing structure is prone to wear, so Stellite hard alloy is usually overlaid inside the groove to improve wear resistance and thus ensure sealing effect. Stellite is a cobalt-based alloy that is wear-resistant, corrosion-resistant, and oxidation-resistant, but it has poor weldability and is prone to cracking. In addition, with the continuous improvement of steam parameters in steam turbines, the materials of the cylinders are also constantly being upgraded. Currently, ultra-supercritical units mainly use 9-12% Cr advanced ferritic heat-resistant steel, and the alloy composition and microstructure of the material are becoming increasingly complex, increasing the difficulty of welding.

[0004] This invention proposes a technical solution of adding a solid solution-strengthened nickel-based alloy welding material as a transition layer, followed by Stellite alloy welding material. Utilizing the good weldability, ductility, toughness, and microstructure stability of nickel-based alloys, this approach can reduce residual stress and the risk of welding cracking. Furthermore, it can suppress element migration, balance the difference in linear expansion, and improve the microstructure stability during high-temperature and high-pressure service, thereby reducing the risk of cracking after service. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the present invention provides a wear-resistant overlay layer for the inner surface of the sealing groove of a steam turbine cylinder and a welding method, which can solve the wear problem of the sealing groove and sealing components of the steam turbine cylinder under high temperature conditions, effectively ensure the sealing performance of the steam turbine cylinder under high temperature conditions, and reduce the leakage of high temperature and high pressure steam in the steam turbine cylinder.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A wear-resistant weld overlay for the inner surface of a turbine cylinder sealing groove includes a transition layer and a hard alloy layer. The transition layer is welded to the entire bottom surface of the weld overlay bevel on the inner surface of the turbine cylinder sealing groove. The hard alloy layer is welded to the sidewall of the weld overlay bevel. The transition layer is welded to the hard alloy layer and serves to separate the hard alloy layer from the base material of the turbine cylinder sealing groove. The hard alloy layer is used to contact and engage with an assembly that is inserted into and assembled with the turbine cylinder sealing groove.

[0008] Furthermore, the transition layer is a solid solution reinforced nickel-based alloy welding material.

[0009] Furthermore, the welding material for the nickel-based transition layer is one of the following: welding electrode ENi6082, welding electrode ENi6182, welding electrode ENi6625, welding wire SNi6082, welding wire SNi6625, powder 82, and powder 625.

[0010] Furthermore, the welding material for the cemented carbide layer is one of STELLITE 6 cemented carbide, STELLITE 12 cemented carbide, and STELLITE 21 cemented carbide, and is not limited to welding rods, welding wires, and powders.

[0011] Furthermore, the width W1 of the transition layer is ≥2mm and the height H1 is 2-6mm, and the width W2 of the finished cemented carbide layer is ≥2mm and the height H2 is ≥12mm.

[0012] Furthermore, the inclination angle of the weld bevel sidewall is 0-20°.

[0013] A welding method for a wear-resistant overlay layer on the inner surface of a steam turbine cylinder sealing groove includes the following steps:

[0014] S1. The weld bevel is machined on the inner surface of the turbine cylinder sealing groove;

[0015] S2. Preheat the weld bevel;

[0016] S3. Weld a transition layer on the entire bottom wall of the weld bevel;

[0017] S4. Weld a hard alloy layer onto the sidewall of the weld bevel.

[0018] Furthermore,

[0019] In step S1: the weld bevel is machined using a machining method;

[0020] Between steps S1 and S2, the following steps are also included: grinding and cleaning the weld bevel, removing oil and rust from the weld bevel and the surrounding area, and measuring the dimensions and performing non-destructive testing on the surface of the weld bevel to be welded.

[0021] Step S3 specifically involves welding a transition layer onto the entire bottom wall of the weld bevel using one of the following welding methods: electric arc welding (such as tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding.

[0022] Between steps S3 and S4, the following steps are also included: dimensional measurement and non-destructive testing of the surface of the transition layer weld;

[0023] Step S4 specifically involves using one of the following welding methods: electric arc welding (such as tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding to weld on the sidewall of the weld bevel and fill the sidewall of the weld bevel to obtain the cemented carbide layer.

[0024] Furthermore,

[0025] In step S3: the width W1 of the welded transition layer is ≥2mm, and the height H1 is 2~6mm;

[0026] After step S4, the following steps are also included: visually inspecting and dimensionally inspecting the weld of the cemented carbide layer under hot conditions, then performing post-weld heat treatment, and machining the transition layer and cemented carbide layer according to the drawing requirements to ensure that the width W2 of the cemented carbide layer is ≥2mm and the height H2 is ≥12mm, removing the excess weld portion of the transition layer and the cemented carbide layer, and then visually inspecting, dimensionally inspecting and non-destructively testing the weld of the formed weld overlay wear-resistant layer to ensure that it meets the drawing requirements.

[0027] Furthermore,

[0028] In the steps between S1 and S2, in the steps between S3 and S4, and in the steps after S4: the non-destructive testing is penetrant testing;

[0029] In step S2: the weld bevel is preheated by local heating with flame or electric heating, or by overall furnace heating.

[0030] In step S3: During the welding of the transition layer, small-scale welding is adopted, and multi-layer and multi-pass welding is adopted. The surface quality of the weld is inspected between layers. Welding defects such as porosity, tungsten inclusion, slag inclusion, cracks, and lack of fusion are not allowed. If welding defects are found, they are ground off and then welding is continued. The interlayer temperature does not exceed 260°C.

[0031] In step S4: During the welding of the hard alloy layer, small-scale welding is adopted, and multi-layer and multi-pass welding is used. The surface quality of the weld is inspected between layers. Welding defects such as pores, tungsten inclusions, slag inclusions, cracks, and lack of fusion are not allowed. If welding defects are found, they are ground off and then welding is continued. The interlayer temperature does not exceed 350°C.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The wear-resistant weld overlay layer for the inner surface of a turbine cylinder sealing groove of the present invention includes a transition layer and a hard alloy layer. The transition layer is welded to the entire bottom wall of the weld overlay bevel on the inner surface of the turbine cylinder sealing groove, and the hard alloy layer is welded to the side wall of the weld overlay bevel. The transition layer and the hard alloy layer are welded together and serve to separate the hard alloy layer from the base material of the turbine cylinder sealing groove. The hard alloy layer is used to contact and fit with the assembly that is inserted into and assembled in the turbine cylinder sealing groove and assembles with the turbine cylinder. In the present invention, the transition layer connects the hard alloy layer and the base material of the turbine cylinder sealing groove. The welding material selected for the transition layer is required to have good weldability, better fusion with the base material of the turbine cylinder sealing groove, uniform transition of weld structure and properties, and good toughness. It can effectively alleviate the hardness difference between the base material of the turbine cylinder sealing groove and the hard alloy layer and balance the linear expansion difference between the base material and the hard alloy layer. The transition layer separates the cemented carbide layer from the base material at the bottom of the turbine cylinder sealing groove, reducing the dilution rate and surface stress of the base material. It also prevents cracking and peeling of the cemented carbide layer during welding and operation. Furthermore, the transition layer prevents the diffusion of Fe elements from the base material in the high-stress area at the bottom into the cemented carbide layer, thus extending its service life. In this invention, the cemented carbide layer is welded to the sidewall of the weld bevel on the inner surface of the turbine cylinder sealing groove. This cemented carbide layer contacts and engages with the fittings inserted into and assembled within the turbine cylinder sealing groove. This solves the wear problem between the turbine cylinder sealing groove and the fittings under high-temperature conditions, effectively ensuring the sealing performance of the turbine cylinder under high-temperature conditions and reducing the leakage of high-temperature, high-pressure steam within the turbine cylinder.

[0034] The welding method for the wear-resistant overlay layer on the inner surface of the turbine cylinder sealing groove of the present invention includes: processing an overlay bevel on the inner surface of the turbine cylinder sealing groove, preheating the overlay bevel, welding a transition layer on the entire bottom wall of the overlay bevel, and welding a hard alloy layer on the side wall of the overlay bevel. The process flow of this welding method is simple, and the welded wear-resistant overlay layer makes the turbine cylinder have a good sealing effect. Attached Figure Description

[0035] Picture 1 This is a schematic diagram of the weld overlay bevel machined on the inner surface of the turbine cylinder sealing groove in this invention.

[0036] Picture 2 This is a schematic diagram of the transition layer welded on the bottom wall of the weld bevel in this invention;

[0037] Picture 3 This is a schematic diagram of the structure of the hard alloy layer welded on the side wall of the weld bevel in this invention;

[0038] Picture 4 This is a schematic diagram of the structure of the inner surface of the turbine cylinder sealing groove after welding and precision machining in this invention.

[0039] The following are the labels in the attached figures: 1. Weld bevel, 2. Transition layer, 3. Hard alloy layer. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0041] like Picture 1-4 As shown, a wear-resistant weld overlay layer for the inner surface of a turbine cylinder sealing groove includes a transition layer 2 and a hard alloy layer 3. The transition layer 2 is welded to the entire bottom wall of the weld overlay bevel 1 on the inner surface of the turbine cylinder sealing groove, and the hard alloy layer 3 is welded to the side wall of the weld overlay bevel 1. The transition layer 2 and the hard alloy layer 3 are welded together and used to separate the hard alloy layer 3 from the bottom base material of the turbine cylinder sealing groove. The hard alloy layer 3 is used to contact and cooperate with the assembly that is inserted into and assembled in the turbine cylinder sealing groove and is assembled with the turbine cylinder.

[0042] In one embodiment, the transition layer 2 is a solid solution strengthened nickel-based alloy welding material; the solid solution strengthened nickel-based alloy welding material is one of the following: welding electrode ENi6082, welding electrode ENi6182, welding electrode ENi6625, welding wire SNi6082, welding wire SNi6625, powder 82, and powder 625. Table 1 shows the mass fraction of each major element in welding electrode ENi6082, Table 2 shows the mass fraction of each major element in welding electrode ENi6182, Table 3 shows the mass fraction of each major element in welding electrode ENi6625, Table 4 shows the mass fraction of each major element in welding wire SNi6082, Table 5 shows the mass fraction of each major element in welding wire SNi6625, Table 6 shows the mass fraction of each major element in powder 82, and Table 7 shows the mass fraction of each major element in powder 625.

[0043] Table 1. Mass fraction of major elements in welding electrode ENi6082 (%)

[0044] C Mn Fe Si Cu Ni Ti Cr Nb+Ta Mo 0.10 2.0-6.0 4.0 0.8 0.50 ≥63.0 0.5 18.0-22.0 1.0-3.0 2.0

[0045] Table 2. Mass fraction of major elements in welding electrode ENi6182 / %

[0046]

[0047]

[0048] Table 3. Mass fraction of major elements in welding electrode ENi6625 / %

[0049] C Mn Fe Si Cu Ni Cr Nb Mo 0.10 2.0 7.0 0.8 0.5 ≥55.0 20.0-23.0 3.0-4.2 8.0-10.0

[0050] Table 4. Mass fraction of major elements in welding wire SNi6082 / %

[0051] C Mn Fe Si Ni Ti Cr Cu Nb+Ta 0.10 2.5-3.5 3.0 0.50 ≥67.0 0.7 18.0-22.0 0.5 2.0-3.0

[0052] Table 5. Mass fraction of major elements in welding wire SNi6625 / %

[0053] C Mn Fe Si Cu Ni Al Ti Cr Nb Mo 0.1 0.5 5.0 0.5 0.5 ≥58.0 0.4 0.4 20.0-23.0 3.0-4.2 8.0-10.0

[0054] Table 6. Mass fraction of major elements in weld powder 82 (%)

[0055] C Mn Fe Si Ni Cr Nb+Ta 0.08-0.12 2.5-3.5 2.5-3.5 0.2-0.5 bal 14.0-17.0 2.0-3.0

[0056] Table 7. Mass fraction of major elements in weld powder 625 / %

[0057] C Mn Fe Si N Ni Al Ti Cr Nb Mo 0.03 0.2-0.5 1.50 0.3-0.5 0.14 bal 0.10 0.10 20.0-23.0 3.15-3.85 8.0-10.0

[0058] In one embodiment, the welding material for the cemented carbide layer 3 is one of STELLITE 6 cemented carbide, STELLITE 12 cemented carbide, and STELLITE 21 cemented carbide, and is not limited to welding rods, welding wires, and powders. Table 8 shows the mass fraction of each major element in STELLITE 6 cemented carbide, Table 9 shows the mass fraction of each major element in STELLITE 12 cemented carbide, and Table 10 shows the mass fraction of each major element in STELLITE 21 cemented carbide.

[0059] Table 8. Mass fraction of major elements in STELLITE 6 cemented carbide (%)

[0060] C Mn Si Cr Ni Mo Fe W Co 0.90-1.40 1.0 2.0 26.0-32.0 3.0 1.0 3.0 3.0-6.0 surplus

[0061] Table 9. Mass fraction of major elements in STELLITE 12 cemented carbide (%)

[0062] C Mn Si Cr Ni Mo Fe W Co 1.00-1.70 2.0 2.0 25.0-32.0 3.0 1.0 5.0 7.0-9.50 surplus

[0063] Table 10 Mass fraction of major elements in STELLITE 21 cemented carbide / %

[0064] C Mn Si Cr Ni Mo Fe W Co 0.15-0.40 1.5 2.0 24.0-29.0 2.0-4.0 4.5-6.5 5.0 0.50 surplus

[0065] A welding method for a wear-resistant overlay layer on the inner surface of a steam turbine cylinder sealing groove includes the following steps:

[0066] S1. A weld overlay bevel 1 is machined on the inner surface of the turbine cylinder sealing groove. The inclination angle of the sidewall of the weld overlay bevel 1 is 0-20°, the bottom dimension of the bevel is approximately 20-50mm, and the depth is approximately 14-80mm. See [link / description]. Picture 1 ;

[0067] S2. Grind and clean the weld bevel 1, and remove oil and rust from the weld bevel 1 and the surrounding area.

[0068] S3. Perform dimensional measurements and penetrant testing on the surface to be welded at weld bevel 1;

[0069] S4. Adjust the position of the turbine cylinder so that the surface to be welded of the weld bevel 1 is in the flat welding position.

[0070] S5. Preheat the weld bevel 1 by local heating with flame or electric heating, or preheat the weld bevel 1 by overall furnace heating.

[0071] S6. Using one of the following welding methods—electric arc welding (such as tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding—weld a transition layer 2 on the entire bottom wall of the weld bevel 1. During the welding process, use small-scale welding and multi-layer, multi-pass welding. Self-inspect the surface quality of the weld between layers, ensuring that there are no welding defects such as porosity, slag inclusions, tungsten inclusions, cracks, or lack of fusion. If welding defects are found, grind them off before continuing welding. The interpass temperature should not exceed 260℃. The height of the welded transition layer 2, H1, should be 2–6 mm. See [reference needed]. Picture 2 ;

[0072] S7. Perform dimensional measurements and penetrant testing on the surface of the weld seam in transition layer 2;

[0073] S8. Preheat the weld bevel 1 by local heating with flame or electric heating, or preheat the weld bevel 1 by overall furnace heating.

[0074] S9. Welding is performed on the sidewall of the weld bevel 1 using one of the following welding methods: electric arc welding (such as tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding. During the welding process, small-scale welding is used, and multiple layers and multiple passes are employed. The surface quality of the weld is self-inspected between layers, and welding defects such as porosity, slag inclusions, tungsten inclusions, cracks, and lack of fusion are not allowed. If welding defects are found, they are ground off, and welding continues. The interpass temperature does not exceed 350℃, and the weld bevel sidewall is filled to obtain a cemented carbide layer 3, wherein the width W3 of the cemented carbide layer 3 is ≥ 3mm. See [link to relevant documentation]. Picture 3 ;

[0075] S10. Perform visual and dimensional inspections on the weld of the cemented carbide layer 3 under hot conditions;

[0076] S11. Perform post-weld heat treatment;

[0077] S12. Perform precision machining on transition layer 2 and cemented carbide layer 3 according to the drawing requirements, ensuring that the width W2 of cemented carbide layer 3 is ≥ 2mm and the height H2 is ≥ 12mm. Remove any excess weld seams between transition layer 2 and cemented carbide layer 3. See [reference needed]. Picture 4 ;

[0078] S13. Perform visual inspection, dimensional inspection and penetrant testing on the welds of the formed wear-resistant overlay to ensure that they meet the requirements of the drawings and the flaw detection standards.

[0079] In this invention, the turbine cylinder is made of carbon steel, low alloy steel, or martensitic stainless steel (including ferritic heat-resistant steel), and the turbine cylinder sealing groove can be set on the inner surface, the split surface, or the end surface of the turbine cylinder.

[0080] In summary, by welding a hard alloy layer 3 to the side wall of the weld overlay bevel 1 on the inner surface of the turbine cylinder sealing groove, the present invention provides a contact fit between the hard alloy layer 3 and the assembly that is inserted into and assembled in the turbine cylinder sealing groove and is assembled with the turbine cylinder. This solves the wear problem between the turbine cylinder sealing groove and the assembly under high temperature conditions, effectively ensures the sealing performance of the turbine cylinder under high temperature conditions, and reduces the leakage of high temperature and high pressure steam in the turbine cylinder.

[0081] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A wear-resistant overlay layer for the inner surface of a turbine cylinder sealing groove, characterized in that: It includes a transition layer (2) and a hard alloy layer (3). The transition layer (2) is welded to the entire bottom surface of the weld overlay bevel (1) on the inner surface of the turbine cylinder sealing groove. The hard alloy layer (3) is welded to the side wall of the weld overlay bevel (1). The transition layer (2) is welded to the hard alloy layer (3) and is used to separate the hard alloy layer (3) from the base material of the turbine cylinder sealing groove. The hard alloy layer (3) is used to contact and cooperate with the sealing element that is inserted into and assembled in the turbine cylinder sealing groove and assembled with the turbine cylinder.

2. The wear-resistant overlay layer for the inner surface of the sealing groove of a steam turbine cylinder according to claim 1, characterized in that: The transition layer (2) is a solid solution reinforced nickel-based alloy welding material, and the hard alloy layer (3) is a Stellite alloy welding material.

3. The wear-resistant overlay layer for the inner surface of a turbine cylinder sealing groove according to claims 1 and 2, characterized in that: The welding material of the transition layer (2) is one of the following: welding electrode ENi6082, welding electrode ENi6182, welding electrode ENi6625, welding wire SNi6082, welding wire SNi6625, powder 82 and powder 625.

4. The wear-resistant overlay layer for the inner surface of a turbine cylinder sealing groove according to claims 1 and 2, characterized in that: The welding material for the cemented carbide layer (3) is one of STELLITE6 cemented carbide, STELLITE12 cemented carbide and STELLITE21 cemented carbide.

5. The wear-resistant overlay layer for the inner surface of a turbine cylinder sealing groove according to claim 1, characterized in that: The width W1 of the transition layer (2) is ≥2mm and the height H1 is 2-6mm. The width W2 of the hard alloy layer (3) is ≥2mm and the height H2 is ≥12mm.

6. The wear-resistant overlay layer for the inner surface of a turbine cylinder sealing groove according to claim 1, characterized in that: The inclination angle of the sidewall of the weld bevel (1) is 0 to 20°.

7. A welding method for an overlay wear-resistant layer on the inner surface of a turbine cylinder sealing groove, used for welding the overlay wear-resistant layer for the inner surface of a turbine cylinder sealing groove as described in any one of claims 1-6, characterized in that... Includes the following steps: S1. The weld bevel (1) is machined on the inner surface of the turbine cylinder sealing groove; S2. Preheat the weld bevel (1); S3. Weld a transition layer (2) on the bottom surface of the weld bevel (1); S4. Weld a hard alloy layer (3) onto the side wall of the weld bevel (1); S5. Machining the transition layer (2) and the hard alloy layer (3) to a depth exceeding the bottom surface of the weld bevel (1) by 1-5 mm.

8. The welding method for the wear-resistant overlay layer on the inner surface of the sealing groove of a steam turbine cylinder according to claim 7, characterized in that: In step S1: the weld bevel (1) is machined by means of machining; Between steps S1 and S2, the following steps are also included: grinding and cleaning the weld bevel (1), and degreasing and derusting the weld bevel (1) and the surrounding area, and measuring the dimensions and performing non-destructive testing on the surface to be welded of the weld bevel (1); Step S3 specifically involves welding a transition layer (2) on the entire bottom surface of the weld bevel (1) using one or more welding methods, such as electric arc welding (e.g., tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding. Between steps S3 and S4, the following steps are also included: dimensional measurement and non-destructive testing of the weld surface of the transition layer (2); Step S4 specifically involves using one or more welding methods, such as electric arc welding (e.g., tungsten inert gas welding, shielded metal arc welding, gas metal arc welding, plasma arc welding, etc.) and laser cladding, to weld the sidewall of the weld bevel (1) and fill the sidewall of the weld bevel to obtain the hard alloy layer (3).

9. The welding method for the wear-resistant overlay layer on the inner surface of the sealing groove of a steam turbine cylinder according to claim 7, characterized in that: Step S4 is followed by the following steps: visual inspection and dimensional inspection of the weld of the hard alloy layer (3) under hot conditions, and then post-weld heat treatment; Step S5 is followed by the following steps: dimensional inspection and non-destructive testing to ensure compliance with drawing requirements.

10. The welding method for the wear-resistant overlay layer on the inner surface of the sealing groove of a steam turbine cylinder according to claim 9, characterized in that: In the steps between S1 and S2, in the steps between S3 and S4, and in the steps after S4: the non-destructive testing is penetrant testing; In step S2: the weld bevel (1) is preheated by local heating with flame or electric heating, or the weld bevel (1) is preheated by overall furnace heating, and the preheating temperature is not lower than 200℃; In step S3: During the welding of the transition layer (2), the current of the shielded metal arc welding is 80-180A and the voltage is 20-25V, the current of the gas shielded welding is 150-230A and the voltage is 25-30V, and the interpass temperature does not exceed 260℃. In step S4: During the welding of the hard alloy layer (3), the current of the shielded metal arc welding is 90-160A and the voltage is 20-25V, the current of the gas shielded welding is 180-250A and the voltage is 26-30V, and the interpass temperature does not exceed 350℃.

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