Welding method for turbine valve chamber

Abstract

The embodiment of the present application provides a welding method of a steam turbine valve chamber, the steam turbine valve chamber is connected to an air inlet end of a steam turbine, the steam turbine valve chamber comprises a valve seat body, a first cylindrical part and a second cylindrical part, one end of the second cylindrical part is integrally connected with the valve seat body, the welding method of the steam turbine valve chamber is used for welding one end of the first cylindrical part to an end of the second cylindrical part which is away from the valve seat body, and the welding method of the steam turbine valve chamber comprises the following steps: a first preheating step, first and second cylindrical parts are first preheated; a first welding step, a first welding material is used to fillet weld between the first and second cylindrical parts; a second preheating step, the first and second cylindrical parts are second preheated; a second welding step, a second welding material is used to weld to fill the groove, and the second welding material is different from the first welding material; and a post-welding heat treatment step, the steam turbine valve chamber is tempered and heat treated. The welding method of the steam turbine valve chamber can effectively control the risk of post-welding cracks.

Description

Technical Field

[0001] This invention relates to the field of welding processes, and more particularly to a welding method for a steam turbine valve chamber. Background Technology

[0002] The inlet temperature of a steam turbine valve chamber is typically high. Furthermore, with the increase in unit capacity, the inlet temperature of ultra-supercritical steam turbines further increases. Therefore, the steam turbine valve chamber uses GX12CrMoWVNbN10-1-1, a material with superior high-temperature resistance. Its high alloy content significantly increases the difficulty of welding. Moreover, the main microstructure of the fusion zone and overheated zone in the welded joint is martensite, which leads to increased hardness and decreased plasticity and toughness in the weld and heat-affected zone, thereby increasing the risk of welding cracks. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned and / or other technical problems and provide a welding method for a steam turbine valve chamber that can effectively control the risk of post-weld cracks.

[0004] This application provides a welding method for a steam turbine valve chamber. The steam turbine valve chamber is connected to the inlet end of a steam turbine. The steam turbine valve chamber includes a valve seat body, a first cylindrical portion, and a second cylindrical portion. One end of the second cylindrical portion is integrally formed and connected to the valve seat body. The welding method for the steam turbine valve chamber involves welding one end of the first cylindrical portion to the end of the second cylindrical portion opposite to the valve seat body. The welding method for the steam turbine valve chamber includes: The first preheating step involves preheating the first cylindrical portion and the second cylindrical portion. In the first welding step, the bevel between the first cylindrical part and the second cylindrical part is welded using the first welding material as the root pass; The second preheating step involves preheating the first cylindrical portion and the second cylindrical portion. The second welding step involves using a second welding material, different from the first welding material, to fill the bevel; and... The post-weld heat treatment step involves tempering the turbine valve chamber.

[0005] In one possible implementation, the turbine valve chamber is made of GX12CrMoWVNbN10-1-1 material; the first preheating step has a preheating temperature ≥150℃; the first welding step uses W ZCrMoWVNb9 1 1 welding wire and argon arc welding of the first welding material to perform root pass welding on the bevel; the second preheating step has a preheating temperature ≥220℃; the second welding step uses E ZCrMoWVNb9 1 1 B 4 2 H5 welding electrode.

[0006] In one possible implementation, the interpass temperature is ≤300℃ in both the first and second welding steps.

[0007] In one possible implementation, the second welding step includes, when welding is interrupted, wrapping the bevel and a 150mm radius on both sides of the bevel with a heating element to maintain the temperature of the bevel and the 150mm radius on both sides of the bevel above 220°C.

[0008] In one possible implementation, the post-weld heat treatment includes a tempering temperature of 720℃~740℃ and a holding time of ≥4h.

[0009] In one possible implementation, during the post-weld heat treatment, after the holding period of the tempering heat treatment is completed, the cooling rate is ≤70℃ / h.

[0010] In one possible implementation, after the second welding step, the weld formed in the second welding step is cooled to 90°C to 120°C and kept at that temperature for at least 1 hour.

[0011] In one possible implementation, during the process of cooling the weld to 90℃~120℃, the cooling rate is ≤70℃ / h.

[0012] In one possible implementation, the ends of the first cylindrical portion and the second cylindrical portion facing each other are provided with single-sided bevels, and the opposing single-sided bevels form the bevels. The width of the bevels gradually increases radially outward from the first cylindrical portion. In the first welding step, argon gas is filled into the interior of the turbine valve chamber, and the inner circumferential surfaces of the ends of the first cylindrical portion and the second cylindrical portion facing each other are covered by the argon gas.

[0013] In one possible implementation, the ends of the first cylindrical portion and the second cylindrical portion facing each other are provided with single-sided bevels, and the opposing single-sided bevels form the bevels. The width of the bevels gradually increases radially outward from the first cylindrical portion. Before the first welding step, pads are fixedly provided on the inner surfaces of the ends of the first cylindrical portion and the second cylindrical portion facing each other, corresponding to the weld seam, to fix the first cylindrical portion and the second cylindrical portion together.

[0014] In one possible implementation, the welding portion of the turbine valve chamber is located between the coaxially arranged, adjacent first and second cylindrical portions, and in the first and second welding steps, the real-time welding position is symmetrical about the axis of the first and second cylindrical portions.

[0015] This application provides a welding method for a turbine valve chamber, comprising: a first preheating step, preheating a first cylindrical portion and a second cylindrical portion; a first welding step, performing a root pass weld on the bevel between the first cylindrical portion and the second cylindrical portion; a second preheating step, preheating the first cylindrical portion and the second cylindrical portion; a second welding step, filling the bevel; and a post-weld heat treatment step, tempering the turbine valve chamber. In this embodiment, preheating within the above temperature range according to the different welding materials can reduce the actual cooling rate of the weld and heat-affected zone formed in the second welding step, allowing austenite more time to decompose at higher temperatures, thereby obtaining tempered martensite with higher toughness, rather than quenched martensite. Furthermore, preheating can make the temperature distribution of the entire turbine valve chamber more uniform, reducing the temperature gradient, thereby significantly reducing the thermal stress and final residual stress during welding. It also allows the weld metal to remain at higher temperatures for a longer time, which is beneficial for the escape of gases and impurities from the weld metal, reducing the residual hydrogen content of the weld metal, and reducing defects such as porosity and slag inclusions. Tempering the turbine valve chamber helps eliminate residual welding stress, improves the microstructure continuity of the fusion zone and superheated zone, and promotes further hydrogen escape. This effectively controls the risk of post-weld cracking. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a welding method for a steam turbine valve chamber provided in an optional embodiment of this application; Figure 2 This is a cross-sectional schematic diagram of a turbine valve chamber welded using a welding method provided in an optional embodiment of this application. Figure 3 This is a cross-sectional view of the turbine valve chamber after the pad is fixedly installed, according to a welding method for a turbine valve chamber provided in an optional embodiment of this application.

[0017] Figure label: Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0019] In the description of this application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. "First," "second," etc., are only used to distinguish each other, and do not indicate their degree of importance or order, etc. "Parallel," "perpendicular," etc., are not strict mathematical and / or geometric limitations, and also include errors that can be understood by those skilled in the art and are permissible in manufacturing or use.

[0020] As mentioned earlier, the inlet temperature of the turbine valve chamber is typically high. Furthermore, with the increase in unit capacity, the inlet temperature of ultra-supercritical turbines further increases. Therefore, the turbine valve chamber uses GX12CrMoWVNbN10-1-1, a material with superior high-temperature resistance. Specifically, the elemental content of this material, by weight percentage, is as follows: C: 0.11%~0.14%, Si: 0.20%~0.50%, Mn: 0.80%~1.20%, P: ≤0.02%, S: ≤0.01%, Cr: 9.2%~10.2%, Ni: 0.6%~0.8%, Mo: 0.90%~1.05%, V: 0.18%~0.25%, W: 0.95%~1.05%, Al: ≤0.02%, Nb: 0.05%~0.08%, N: 0.04%~0.06%, with the remainder being Fe. For the above materials, there is no GB or GB / T standard in China that is completely corresponding to them. The closest standard in the industry is JB / T ZG12Cr10Mo1W1NiVNbN.

[0021] The material has a high content of alloying elements, which significantly increases the difficulty of welding it. Moreover, the main microstructure of the fusion zone and overheated zone in the welded joint is martensite, which will lead to increased hardness and decreased plasticity and toughness in the weld and heat-affected zone, thereby increasing the risk of welding cracks.

[0022] This application provides a welding method for a turbine valve chamber, comprising: a first preheating step, preheating a first cylindrical portion and a second cylindrical portion; a first welding step, performing a root pass weld on the bevel between the first cylindrical portion and the second cylindrical portion; a second preheating step, preheating the first cylindrical portion and the second cylindrical portion; a second welding step, filling the bevel; and a post-weld heat treatment step, tempering the turbine valve chamber. In this embodiment of the invention, preheating within the above temperature range according to the different welding materials can reduce the actual cooling rate of the bevel and heat-affected zone, allowing austenite more time to decompose at higher temperatures, thereby obtaining tempered martensite with higher toughness, rather than quenched martensite. Furthermore, preheating can make the temperature distribution of the entire turbine valve chamber more uniform, reducing the temperature gradient, thereby significantly reducing the thermal stress and final residual stress during welding. It also allows the weld metal to remain at a higher temperature for a longer time, which is beneficial for the escape of gases and impurities in the weld metal, reducing the residual hydrogen content of the weld metal, and reducing defects such as porosity and slag inclusions. Tempering the turbine valve chamber helps eliminate residual welding stress, improves the microstructure continuity of the fusion zone and superheated zone, and promotes further hydrogen escape. This effectively controls the risk of post-weld cracking.

[0023] It should be noted that the accompanying drawings in this application are only for the purpose of illustrative purposes and understanding of this embodiment, and are not intended to limit this application in any way. They are not necessarily drawn to scale.

[0024] The following is in conjunction with the appendix Figure 1-3 The welding method of the turbine valve chamber 10 provided in the embodiments of this application will be described in detail.

[0025] like Figure 1 and Figure 2 As shown, the welding method for the turbine valve chamber 10 includes: In the first preheating step S120, the first cylindrical portion 220 and the second cylindrical portion 230 are preheated. In the first welding step S130, the first welding material is used to perform a root pass weld on the bevel between the first cylindrical portion 220 and the second cylindrical portion 230. In the second preheating step S140, the first cylindrical portion 220 and the second cylindrical portion 230 are preheated. In the second welding step S150, a second welding material is used to fill the bevel, the second welding material being different from the first welding material; and... Post-weld heat treatment step S170 involves tempering heat treatment of the turbine valve chamber 10.

[0026] In this embodiment of the invention, preheating within the above temperature range according to the different welding materials can reduce the actual cooling rate of the weld 240 and the heat-affected zone formed in the second welding step, allowing austenite more time to decompose at higher temperatures, thereby obtaining tempered martensite with higher toughness instead of quenched martensite. Furthermore, preheating makes the temperature distribution of the entire turbine valve chamber 10 more uniform, reducing the temperature gradient, thus significantly reducing thermal stress and final residual stress during welding. It also allows the weld metal to remain at higher temperatures for a longer period, facilitating the escape of gases and impurities from the weld metal, reducing the residual hydrogen content of the weld metal, and reducing defects such as porosity and inclusions. Tempering the turbine valve chamber 10 helps eliminate welding residual stress, improves the microstructure continuity of the fusion zone and overheated zone, and promotes further hydrogen escape. Therefore, the risk of post-weld cracking is effectively controlled.

[0027] The turbine valve chamber 10 is connected to the inlet end of the turbine (not shown in the figure). The turbine valve chamber includes a valve seat body 210, a first cylindrical part 220 and a second cylindrical part 230. One end of the second cylindrical part 230 is integrally formed and connected to the valve seat body 210. The welding method of the turbine valve chamber 10 is used to weld one end of the first cylindrical part 220 to the end of the second cylindrical part 230 that is away from the valve seat body 210.

[0028] In some optional embodiments, the turbine valve chamber is made of GX12CrMoWVNbN10-1-1 material; the first preheating step has a preheating temperature ≥150℃; in the first welding step, the first welding material is WZCrMoWVNb9 1 1 welding wire, and the bevel is welded by argon arc welding using the first welding material; the second preheating step has a preheating temperature ≥220℃; in the second welding step, the second welding material is EZCrMoWVNb9 1 1 B 4 2 H5 welding electrode.

[0029] By using the above welding materials, the composition of the welding material and the base material is consistent in some key elements, avoiding premature nucleation and growth of creep cavities caused by compositional differences. Moreover, V and Nb in the welding material can inhibit grain growth, while W also helps to achieve a balance between strength and toughness.

[0030] Among them, W ZCrMoWVNb9 1 1 is the grade of European standard EN ISO 21952-A. If welding materials from the Voestalpine Welding Group are used, their grade is BÖHLER C 9 MVW-IG. According to American standards, this welding material belongs to AWSA5.28 / ASME SFA-5.28: ER90S-B9 (mod). This solid tungsten inert gas (TIG) welding wire belongs to the Chinese standard GB / T8110 "Steel Wire for Fusion Welding", but there is no directly corresponding grade. Specifically, welding and test blocks were prepared according to Chinese standard GB / T 25774.1-2023 "Inspection of Welding Materials - Part 1: Preparation of Test Specimens for Mechanical Properties of Deposited Metals of Steel, Nickel and Nickel Alloys". The content of each element in the deposited metal obtained by welding with the above welding wire is as follows: C: 0.11%, Si: 0.35%, Mn: 0.45%, Cr: 9.0%, Ni: 0.75%, Mo: 0.98%, V: 0.2%, Nb: 0.06%, W: 1.05%, N: 0.04%, with the remainder being Fe.

[0031] E ZCrMoWVNb 9 1 1 B 4 2 H5 is the grade of the European standard EN ISO 3580-A. If welding materials from the Voestalpine Welding Group are used, their grade is BÖHLER FOX C 9 MVW. According to American standards, this welding material belongs to AWS A5.5 / ASME SFA-5.5: E9015-B92 H4. This basic low-hydrogen coated electrode belongs to the Chinese standard GB / T 5118 "Low Alloy Heat-Resistant Steel Welding Electrodes," but there is no directly corresponding grade. Specifically, welding and test blocks were prepared according to the Chinese standard GB / T 25774.1-2023 "Inspection of Welding Materials - Part 1: Preparation of Test Specimens for Mechanical Properties of Deposited Metals of Steel, Nickel and Nickel Alloys". The content of each element in the deposited metal obtained by welding with the above-mentioned welding rods, by weight percentage, is as follows: C: 0.1%, Si: 0.2%, Mn: 0.6%, Ni: 0.6%, Cr: 8.5%, Mo: 1%, Nb: 0.05%, W: 1%, V: 0.2%, N: 0.04%, Al: 0.001%, and the remainder is Fe.

[0032] The welding material and the base metal have the same composition in key trace elements such as C, W, V, Nb, and N, which ensures the formation of carbides—MC and M—in the weld metal at high temperatures. 23The types, quantities, and stability of C6 and nitrides are basically the same as those of the base metal, avoiding premature nucleation and growth of creep cavities caused by compositional differences. Therefore, the high-temperature creep strength of the welded joint during long-term service at the intake temperature of the ultra-supercritical steam turbine is comparable to that of the base metal. Moreover, the appropriate amount of V and Nb in the welding material forms fine carbonitrides—VN and Nb(C, N)—during the welding cooling process, inhibiting grain growth; at the same time, the solid solution strengthening effect of W combined with the tempered martensite structure formed after tempering treatment achieves a balance between strength and toughness. This ensures that the impact energy of the weld metal meets the design requirements and does not become embrittled due to the hardened structure. Because the composition of the welding material is very similar to that of the base metal, the chemical potential difference on both sides of the fusion zone is extremely small, reducing the low-melting-point eutectic phases and coarse carbides generated due to compositional supercooling. This makes the fusion zone no longer a weak point of the joint, and creep cracks or cold cracks are less likely to initiate there. Furthermore, the matched nitrogen content in the welding material, working in conjunction with Al, forms dispersed particles such as AlN and VN in the heat-affected zone, hindering excessive austenite grain growth. Simultaneously, the matched W and Mo content ensures uniform precipitation of secondary hardening phases during tempering, preventing abnormal increases in localized hardness. The coarse martensite in the overheated zone is effectively softened during post-weld tempering, resulting in decreased hardness and restored toughness.

[0033] In some optional embodiments, the interpass temperature is ≤300°C in the first welding step and the second welding step.

[0034] Controlling the interpass temperature within the aforementioned range can suppress further austenite grain growth and ensure that the previous weld pass has partially completed martensitic transformation before welding the next pass. Slight self-tempering is achieved during interpass preheating, but the transformed martensite is not marginalized by austenite due to excessively high interpass temperatures. Furthermore, interpass temperatures within this range allow hydrogen in the weld metal to escape during multi-pass welding, which also helps control excessive migration of alloying elements. Moreover, interpass temperatures below 300°C promote a finer weld metal microstructure, making it easier to obtain uniform tempered martensite after final tempering, thus achieving both the required hardness and impact strength.

[0035] In some optional embodiments, the second welding step includes, when welding is interrupted, wrapping the bevel and a 150mm radius on both sides of the bevel with a heating element to maintain the temperature of the bevel and the 150mm radius on both sides of the bevel above 220°C.

[0036] During welding interruptions, the diffuse hydrogen in the bevel and heat-affected zone can remain in an open escape channel, preventing it from becoming trapped and forming crack initiation points due to excessively low temperatures. Furthermore, no new phase transformation stress peaks are generated during the interruption, restoring the microstructure to the state before the interruption. Moreover, arc initiation can be performed directly after the interruption without reheating, reducing the cumulative damage to the heat-affected zone caused by repeated heating. Additionally, the bevel and surrounding temperature remain above the lower limit of the preheating range during the interruption, without disrupting the process window.

[0037] Because the turbine valve chamber 10 is large in volume and requires thick materials (e.g., over 30mm), many welding passes are needed, resulting in a lengthy second welding step, potentially lasting several hours. Heating elements are installed to maintain the temperature of the bevel and the metal on both sides of the bevel. Even if the second welding step coincides with shift changes or workers' lunch breaks, the heating elements maintain the temperature of the bevel and the metal on both sides of the bevel, preventing a significant drop in temperature even with prolonged welding interruptions. Specifically, tracked heating plates can be used to wrap around the bevel and the metal on both sides of the bevel.

[0038] Since 220℃ falls within the effective temperature window for hydrogen diffusion in this material, which is typically 150℃ to 300℃, the hydrogen diffusion coefficient remains sufficiently high at this temperature, allowing it to continue diffusing into the weld 240 surface and deep into the base metal. If the temperature drops below 150℃, the hydrogen diffusion rate decreases sharply, and supersaturated hydrogen remaining in the hardened structure accumulates at stress concentration points, inducing delayed cracking. Maintaining a temperature above 220℃ preserves the hydrogen diffusion capacity in the weld metal, reducing the hydrogen content in weld 240 and preventing crack initiation due to excessively low temperatures. The martensitic transformation termination temperature of GX12CrMoWVNbN10-1-1 is approximately 80℃ to 120℃. The 220℃ maintained during welding interruption is significantly higher than this temperature, meaning that during the interruption, weld 240 and the heat-affected zone remain in a state where austenite has partially transformed but not completely transformed (or has completely transformed into martensite but is in the early stages of tempering). If the temperature drops below the martensitic transformation termination temperature, the martensitic transformation will complete abruptly without stress control, generating additional phase transformation stress. When welding resumes, the new weld will apply a thermal cycle to the already transformed martensitic layer, easily leading to interlayer cracking. Maintaining a temperature above 220°C avoids the impact of alternating hot and cold temperatures on the microstructure stability. Furthermore, without insulation, weld 240, after cooling to room temperature, needs to be reheated to the preheating temperature of the first or second preheating step before welding can continue. Each reheating is equivalent to applying an additional thermal cycle to the heat-affected zone, exacerbating grain coarsening and carbide precipitation in the overheated zone. During the interruption, weld 240 and the metal within a 150mm radius on both sides are maintained above 220°C. When welding resumes, it is only necessary to ensure the temperature is below the upper limit of the interlayer temperature; if this is met, arc initiation can proceed directly, eliminating the need for reheating. Normal welding can then proceed directly without additional heating or cooling time, and the damage to toughness caused by repeated thermal cycles is avoided.

[0039] In some optional embodiments, the tempering temperature of the post-weld heat treatment is 720°C to 740°C, and the holding time is ≥4h.

[0040] In this embodiment of the invention, tempering within the above temperature range and time range can fully soften the hardened microstructure, reduce the hardness of the weld 240 and the heat-affected zone, precipitate stable secondary carbides, promote further escape of residual hydrogen, and ensure high-temperature creep strength. Simultaneously, it eliminates welding residual stress, reduces the risk of reheat cracking, and improves the microstructure uniformity of the fusion zone and overheated zone.

[0041] The non-equilibrium hardened martensite formed after welding undergoes complete decomposition at 720℃~740℃. The dislocation density within the martensite laths decreases significantly, supersaturated carbon precipitates as carbides, and the matrix transforms into tempered martensite. Holding at this temperature for ≥4 hours ensures a uniform softening effect throughout the entire thick-walled section, especially in the fusion zone and overheated zone, preventing the formation of a high-hardness area in the center due to insufficient holding.

[0042] The temperature range of 720℃ to 740℃ falls near the secondary hardening peak of this material. At this temperature, strong carbide-forming elements such as V, Nb, and W combine with C to precipitate highly dispersed MC-type (V / Nb-rich) carbides and M. 23 C6-type (Cr / W rich) carbides. These carbides are extremely stable at service temperatures, hindering dislocation movement and thus providing high-temperature creep strength matching that of the base material. Holding for ≥4 hours allows these nanoscale carbides to fully nucleate and grow moderately. During long-term service in the turbine valve chamber 10, the joint did not experience significant creep-accelerated failure. The long holding time promoted short-range diffusion of alloying elements. In the fusion zone, elements such as C, Cr, and W diffuse from high-concentration areas to low-concentration areas, reducing microsegregation caused by differences in composition between the base material and the weld material. In the overheated zone, the dislocation network within the coarse martensitic laths is reorganized, and carbides precipitate uniformly along the original austenite grain boundaries and lath boundaries, eliminating local stress concentration points and restoring the toughness of the entire heat-affected zone. The high temperature of 720℃~740℃ greatly increases the diffusion coefficient of hydrogen, while the heat preservation for ≥4h provides sufficient kinetic conditions for hydrogen diffusion, enabling it to diffuse from the center of the thick-walled weld 240 to the surface and escape into the atmosphere, thus completely eliminating the hidden danger of delayed cracking after welding.

[0043] At temperatures between 720℃ and 740℃, metal atoms possess sufficient thermal activation energy for creep and stress relaxation. Through dislocation climb, grain boundary sliding, and micro-plastic deformation, the macroscopic residual tensile stress generated during welding is effectively released. This ultimately leads to a more uniform stress distribution at the weld joint.

[0044] In some optional embodiments, during post-weld heat treatment, after the holding period of the tempering heat treatment is completed, the cooling rate is ≤70℃ / h.

[0045] In this embodiment of the application, controlling the cooling rate within the above range can suppress additional thermal stress and prevent cold cracking during the tempering process.

[0046] At the end of the 720℃~740℃ holding period, a slight temperature gradient may still exist in weld 240, the heat-affected zone, and the interior of the base material. If the cooling rate is too fast, the surface cools much faster than the core, generating new thermal shrinkage stress. This, combined with residual stress that has not yet fully relaxed, may induce tempering cold cracks at the fusion line or in the overheated zone, especially in the case of a large valve chamber wall thickness in the embodiments of this application. A cooling rate of ≤70℃ / h keeps the cross-sectional temperature difference very small, compressing the additional thermal stress below the material yield. In addition, MC and M precipitated during the 720℃~740℃ holding period... 23 C6 will continue to grow and spheroidize during the initial cooling period above 500℃. Controlling the cooling rate to ≤70℃ / h allows sufficient time for carbide coarsening and short-range diffusion of alloying elements in the turbine valve chamber 10 within this temperature range. This avoids excessively rapid cooling leading to freezing of non-equilibrium carbides, which would result in continued aging precipitation, hardness rebound, and easy formation of creep cavities during subsequent service at temperatures above 600℃.

[0047] In some optional embodiments, after the cooling and heat preservation step S160 and the second welding step, the weld 240 formed in the second welding step is cooled to 90°C~120°C and kept at 90°C~120°C for at least 1 hour.

[0048] In this embodiment of the invention, after the second welding step, the weld 240 is cooled to the above temperature and held for at least 1 hour. This allows for sufficient isothermal transformation time near the martensitic transformation endpoint temperature, causing the retained austenite to essentially disappear and the phase transformation stress to be initially released. This provides a uniform microstructure and the lowest risk of cracking for subsequent high-temperature tempering.

[0049] The martensitic transformation termination temperature in the base metal is approximately 80℃~120℃. If the weld is cooled directly to room temperature, some austenite will freeze within the microstructure due to excessively rapid cooling or carbon enrichment, forming retained austenite. This retained austenite decomposes during subsequent tempering or service, leading to volume changes and stress concentration, reducing dimensional stability and creep strength. Holding the weld at 90℃~120℃ for at least 1 hour provides sufficient time for the isothermal transformation of austenite to martensite, ensuring the transformation is as complete as possible. Therefore, it can significantly reduce the retained austenite content in the weld 240 and the heat-affected zone, resulting in a near-complete transformation of the microstructure into martensite.

[0050] Martensitic transformation is a volumetric expansion process that generates significant phase transformation stress. If the weld is rapidly cooled to room temperature immediately after welding, the phase transformation stress combined with residual welding stress can easily lead to microcracks at the fusion line or in the overheated zone. Holding the weld at 90℃~120℃ for at least 1 hour allows for low-temperature tempering of the newly formed martensite, initially releasing some dislocations and stresses within it, thus reducing the crack driving force. This reduces the risk of delayed cracking in the weld seam 240 and the heat-affected zone during cooling.

[0051] If the weld is cooled immediately after welding and then immediately reheated for tempering, the different cooling rates at different thicknesses will lead to inconsistent martensitic transformation. For example, the surface layer may have completely transformed, while the core may still have residual austenite. This uneven microstructure will cause varying degrees of carbide precipitation at different locations during tempering, resulting in uneven hardness distribution after tempering. Holding at 90℃~120℃ for 1 hour allows the entire cross-section to undergo a near-complete martensitic transformation, resulting in a uniform microstructure. This ensures consistent response throughout the subsequent tempering process, ultimately achieving uniform hardness and microstructure, providing a unified starting point for further tempering.

[0052] Furthermore, after holding at the aforementioned temperature range for one hour, weld 240 can be directly heated to 720℃~740℃ for tempering, without needing to cool to room temperature first and then reheat. This not only saves energy and time, but more importantly, it reduces the additional stress cycle caused by thermal expansion and contraction during the cooling-then-heating process, which is particularly beneficial for thick-walled valve chambers.

[0053] In some optional embodiments, during the process of cooling the weld 240 to 90°C~120°C, the cooling rate is ≤70°C / h.

[0054] By cooling down at the aforementioned rate, the rate and temperature range of martensitic transformation are controlled to avoid cracks caused by the concentrated release of phase transformation stress. At the same time, sufficient time is provided for hydrogen escape and self-tempering, and the temperature field is uniform as the martensitic transformation enters the holding stage after complete transformation, laying a foundation for a uniform microstructure and low stress in the initial state for subsequent tempering.

[0055] Specifically, the martensitic transformation initiation temperature of the aforementioned base material is approximately 380℃~400℃, and the transformation termination temperature is approximately 80℃~120℃. The temperature range of 90℃~120℃, from the welding temperature, precisely covers the majority of the martensitic transformation temperature range. If the cooling rate is too rapid, the martensitic transformation will occur explosively within a narrow temperature range. This is because the martensitic transformation causes approximately 4% volume expansion, leading to stress concentration and release. This stress, combined with residual welding stress, easily generates microcracks at the fusion line or in the overheated zone. A slower cooling rate of ≤70℃ / h allows martensite to form gradually over a wider temperature range, dispersing and releasing the phase transformation stress, thus preventing the stress peak from exceeding the material's strength limit and causing phase transformation cracks.

[0056] Hydrogen has a much higher solubility in austenite than in ferrite or martensite. After welding, weld 240 remains in the austenitic state, where hydrogen solubility is high. As the temperature decreases, austenite transforms into martensite, and hydrogen solubility drops sharply, requiring the supersaturated hydrogen to diffuse outwards. A slower cooling rate of ≤70℃ / h prolongs the residence time of weld 240 and the metal near weld 240 in the high-temperature zone of 400℃~200℃, providing a sufficient time window for hydrogen escape, promoting full hydrogen escape, and reducing the risk of delayed cracking.

[0057] Because the walls of the turbine valve chamber 10 are typically thick, the outer wall cools down quickly during natural cooling, while the inner wall cools down slowly, resulting in a significant temperature difference between the inside and outside. This leads to a transient stress field where the outer wall is under tension and the inner wall is under compression. If the cooling rate is too fast, this thermal stress may exceed the tensile strength of the material, causing cracks at existing casting defects in the cast steel. The aforementioned cooling rate, however, makes the cooling rate of the entire turbine valve chamber 10 more uniform, and the thermal stress level is much lower than that under natural cooling conditions. Therefore, it can reduce the temperature difference between the inner and outer walls of the turbine valve chamber 10, preventing the thick-walled turbine valve chamber 10 from cracking due to thermal stress.

[0058] During a slower cooling process, the martensite formed earlier undergoes some degree of self-tempering during the subsequent slow cooling, resulting in a slight decrease in hardness and a slight increase in toughness. If the cooling rate is too fast, self-tempering does not have time to occur, and all martensite enters room temperature in a fully quenched state, resulting in high hardness and poor toughness. Slow cooling allows martensite formed at different temperatures to undergo varying degrees of self-tempering, leading to a more homogeneous final microstructure.

[0059] If the cooling rate is too rapid, the internal temperature will still be significantly higher than the external surface temperature while the outer surface temperature reaches 90℃~120℃, resulting in uneven actual temperature during the holding period and poor consistency in the completion of martensitic transformation at different locations. A slow cooling rate of ≤70℃ / h ensures that the temperature difference across the entire cross-section is minimal when reaching the target temperature, and the effect of holding for at least 1 hour can be consistently achieved across the entire cross-section, ensuring complete martensitic transformation.

[0060] In some optional embodiments, the ends of the first cylindrical portion 220 and the second cylindrical portion 230 facing each other are provided with single-sided bevels, and the opposing single-sided bevels form bevels. The width of the bevels gradually increases radially outward from the first cylindrical portion 220. In the first welding step, argon gas is filled into the interior of the turbine valve chamber 10, and the inner circumferential surfaces of the ends of the first cylindrical portion 220 and the second cylindrical portion 230 facing each other are covered with argon gas.

[0061] In the first welding step, the turbine valve chamber 10 is filled with argon gas, which can isolate the air behind the weld 240, prevent the root weld 240 and the heat-affected zone from high-temperature oxidation, improve the purity of the deposited metal and the integrity of interlayer fusion, and lay the foundation for the high-temperature creep performance and toughness of the entire welded joint.

[0062] Specifically, elements such as Cr, W, and V in the welding material and base metal have a strong affinity for oxygen. If the back side is exposed to air, the high-temperature molten pool will rapidly react with oxygen in the air to generate oxides such as Cr2O3, WO3, and V2O5. These oxides have high melting points and high densities, and will remain in the root weld 240 as solid inclusions, severely reducing the purity and creep strength of the deposited metal. After argon gas is introduced, the inner circumferential surfaces of the ends of the first cylindrical part 220 and the second cylindrical part 230 facing each other, i.e., the back side of the weld, are completely isolated by the inert gas, preventing oxidation reactions from occurring.

[0063] During welding, the molten pool absorbs surrounding gases. If there is air on the back side of the molten pool, nitrogen and oxygen in the air will dissolve into the molten pool. As the deposited metal cools, the solubility of nitrogen decreases sharply, causing it to precipitate as bubbles, forming nitrogen pores; oxygen reacts with alloying elements to form oxide inclusions. After argon purging, the atmosphere on the back side is free of nitrogen and oxygen, fundamentally reducing the sources of nitrogen pores and oxide inclusions, thus ultimately reducing porosity and slag inclusion defects in the root weld 240. After oxygen dissolves in the molten pool metal, oxide scale not only exists on the back surface but may also form an oxide film on the front side of the root pass. During the subsequent filler pass fusion of the root pass, these oxide films become slag inclusions at the fusion interface, reducing interlayer bonding strength. After argon purging, the root pass is free of oxide inclusions, and the fusion interface with the subsequent filler pass is clean, ensuring the continuity of the entire weld 240.

[0064] During the root pass soldering, the heat-affected zone on the back side is also heated to near its melting point. If there is air on the back side, oxygen will diffuse inward along the austenite grain boundaries, forming grain boundary oxidation, which weakens the grain boundaries and reduces impact toughness. After argon gas is introduced for protection, grain boundary oxidation is completely suppressed, and the toughness of the heat-affected zone on the back side is preserved.

[0065] like Figure 3 As shown, in some optional embodiments, the ends of the first cylindrical portion 220 and the second cylindrical portion 230 facing each other are provided with a single-sided bevel, and the opposing single-sided bevels form a bevel. The width of the bevel gradually increases along the radial outward of the first cylindrical portion 220. The welding method of the turbine valve chamber includes: setting a pad block step S110. Before the first welding step, a pad block 260 is fixedly set on the inner side of the ends of the first cylindrical portion 220 and the second cylindrical portion 230 facing each other to fix the first cylindrical portion 220 and the second cylindrical portion 230.

[0066] A pad 260 is provided on the inner side of the turbine valve chamber 10 corresponding to the bevel to fix the inner circumferential surfaces of the first cylindrical part 220 and the second cylindrical part 230. This can support the metal on the inner circumferential surfaces of the first cylindrical part 220 and the second cylindrical part 230 on both sides of the bevel, thereby significantly reducing the deformation of the metal on both sides of the weld 240 in the axial and circumferential directions, and thus improving the dimensional and positional accuracy of the turbine valve chamber 10.

[0067] Specifically, due to the large size of the turbine valve chamber 10, the welding time for each pass is relatively long. During the welding process, the welding heat input is concentrated on the bevel side. During the cooling process after welding, the weld 240 will shrink circumferentially and axially along the turbine valve chamber 10. Moreover, the parts welded first are not affected by the heat of adjacent areas in the weld 240 before welding, so the shrinkage of the parts welded first is greater. This results in different shrinkage in different parts of the turbine valve chamber 10 in the circumferential direction, which will cause the weld 240 of the turbine valve chamber 10 to tend to deform into an ellipse. The pad 260 can limit the axial deformation of the area around the weld 240 and also inhibit the radial deformation of the weld 240, thereby reducing the deformation impact of welding on the turbine valve chamber 10. The spacer 260 can be spot welded to the inner side of the first cylindrical part 220 and the second cylindrical part 230 at the position corresponding to the weld 240, so that the spacer 260 can be removed from the inner side of the first cylindrical part 220 and the second cylindrical part 230 after tempering.

[0068] In some optional embodiments, the welding portion of the turbine valve chamber 10 is located between coaxially arranged adjacent first cylindrical portion 220 and second cylindrical portion 230. In the first welding step and the second welding step, the real-time position of the welding is symmetrical about the axis 250 of the first cylindrical portion 220 and the second cylindrical portion 230.

[0069] In this embodiment of the invention, by making the real-time welding position symmetrical about the first cylindrical part 220 and the second cylindrical part 230, the heating point can be symmetrical about the axis 250 during the welding heating process of the first welding step and the second welding step. Then the shrinkage generated after welding at this position is also symmetrical. Therefore, the bending effect of the axis 250 of the first cylindrical part 220 and the second cylindrical part 230 caused by thermal expansion and contraction after welding can be reduced as much as possible, thereby improving the straightness of the first cylindrical part 220 and the second cylindrical part 230 and reducing the difficulty of connecting the turbine valve chamber 10 with the subsequent pipeline.

[0070] In some optional embodiments of the present invention, the first cylindrical portion 220 needs to be welded to the second cylindrical portion 230. The second cylindrical portion 230 is closer to the center of the valve chamber than the first cylindrical portion 220. The first cylindrical portion 220 can be a portion in the turbine valve chamber 10 used to connect adjacent pipes. Specifically, in the turbine valve chamber 10, two first cylindrical portions 220 can be respectively provided corresponding to the second cylindrical portion 230. More specifically, the axes 250 of the two second cylindrical portions 230 can be perpendicular to each other.

[0071] In the first and second welding steps, if the welding process is completed manually, two workers can weld on both sides of the first cylindrical portion 220 and the second cylindrical portion 230 respectively, with the real-time welding position symmetrical about the axis 250 of the first cylindrical portion 220. If a welding robot is used, welding can be performed simultaneously at two positions, with the real-time welding position being the same as that of a human. Alternatively, welding can be performed simultaneously at four positions, in which case the central angle between adjacent real-time welding positions relative to the axis 250 of the first cylindrical portion 220 is always maintained at 90°.

[0072] In this embodiment of the application, the welding method for the turbine valve chamber 10 is as follows: Step S110: Set a pad block 260 on the inner side of the turbine valve chamber 10 corresponding to the bevel.

[0073] In the first preheating step S120, the turbine valve chamber 10 is preheated to a temperature ≥150℃.

[0074] In the first welding step S130, argon gas is introduced into the turbine valve chamber 10, and the turbine valve chamber 10 is subjected to argon arc welding using WZCrMoWVNb9 1 1 welding wire. In the first welding step, the interpass temperature is ≤300℃. The real-time position of the weld is symmetrical about the axis 250 of the first cylindrical part 220 and the second cylindrical part 230.

[0075] The second preheating step S140 involves preheating the turbine valve chamber 10 to a temperature ≥220℃.

[0076] In the second welding step S150, E ZCrMoWVNb 9 1 1 B 4 2 H5 welding rods are used to fill the bevel. In the second welding step, the interpass temperature is ≤300℃. The real-time welding position is symmetrical about the axis 250 of the first cylindrical part 220 and the second cylindrical part 230. If the welding process is interrupted, the bevel and the area within 150mm on both sides of the bevel are wrapped with heating elements to maintain the temperature of the bevel and the area within 150mm on both sides of the bevel above 220℃.

[0077] In step S160, the weld 240 is cooled to 90℃~120℃ and kept at that temperature for at least 1 hour. During the cooling process, the cooling rate is ≤70℃ / h.

[0078] In post-weld heat treatment step S170, the turbine valve chamber 10 is subjected to post-weld heat treatment. The tempering temperature of the tempering heat treatment is 720℃~740℃, and the holding time is ≥4h. After the holding time of the tempering heat treatment is completed, the cooling rate is ≤70℃ / h.

[0079] It should be noted that, in this patent application, nouns and pronouns relating to persons are not limited to specific genders. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0080] Finally, it should be noted that the above are merely preferred embodiments of this application, used only to illustrate the technical solution of this application, and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A welding method for a steam turbine valve chamber (10), the steam turbine valve chamber (10) being connected to the inlet end of a steam turbine, the steam turbine valve chamber comprising a valve seat body (210), a first cylindrical portion (220), and a second cylindrical portion (230), one end of the second cylindrical portion (230) being integrally formed and connected to the valve seat body (210), the welding method for the steam turbine valve chamber (10) being used to weld one end of the first cylindrical portion (220) to the end of the second cylindrical portion (230) facing away from the valve seat body (210), characterized in that, The welding method for the turbine valve chamber (10) includes: The first preheating step involves preheating the first cylindrical portion (220) and the second cylindrical portion (230). In the first welding step, the bevel between the first cylindrical portion (220) and the second cylindrical portion (230) is welded using the first welding material as the root pass; The second preheating step involves preheating the first cylindrical portion (220) and the second cylindrical portion (230). The second welding step involves using a second welding material to fill the bevel, the second welding material being different from the first welding material; The post-weld heat treatment step involves tempering the turbine valve chamber (10).

2. The welding method for the turbine valve chamber (10) according to claim 1, characterized in that, The turbine valve chamber is made of GX12CrMoWVNbN10-1-1 material; the first preheating step has a preheating temperature ≥150℃; in the first welding step, the first welding material is W ZCrMoWVNb9 1 1 welding wire, and the bevel is welded by argon arc welding using the first welding material; the second preheating step has a preheating temperature ≥220℃; in the second welding step, the second welding material is E ZCrMoWVNb9 1 1 B 4 2H5 welding electrode.

3. The welding method for the turbine valve chamber (10) according to claim 2, characterized in that, In the first welding step and the second welding step, the interpass temperature is ≤300℃.

4. The welding method for the turbine valve chamber (10) according to claim 3, characterized in that, The second welding step includes, when welding is interrupted, wrapping the bevel and a 150mm area on both sides of the bevel with a heating element to maintain the temperature of the bevel and the 150mm area on both sides of the bevel above 220°C.

5. The welding method for the turbine valve chamber (10) according to claim 1, characterized in that, In the post-weld heat treatment, the tempering temperature of the tempering heat treatment is 720℃~740℃, and the holding time is ≥4h.

6. The welding method for the turbine valve chamber (10) according to claim 5, characterized in that, In the post-weld heat treatment, after the holding period of the tempering heat treatment is completed, the cooling rate is ≤70℃ / h.

7. The welding method for the turbine valve chamber (10) according to claim 1, characterized in that, After the second welding step, the weld (240) formed in the second welding step is cooled to 90℃~120℃ and kept at 90℃~120℃ for at least 1 hour.

8. The welding method for the turbine valve chamber (10) according to claim 7, characterized in that, During the process of cooling the weld (240) to 90℃~120℃, the cooling rate is ≤70℃ / h.

9. The welding method for the turbine valve chamber (10) according to any one of claims 1-8, characterized in that, The first cylindrical portion (220) and the second cylindrical portion (230) have a single-sided bevel at their ends facing each other, and the opposite single-sided bevel forms the bevel. The width of the bevel gradually increases along the radial direction outward of the first cylindrical portion (220). In the first welding step, argon gas is filled into the interior of the turbine valve chamber (10), and the inner circumferential surfaces of the ends of the first cylindrical portion (220) and the second cylindrical portion (230) facing each other are covered by the argon gas.

10. The welding method for the turbine valve chamber (10) according to any one of claims 1-8, characterized in that, The first cylindrical portion (220) and the second cylindrical portion (230) have a single-sided bevel at their ends facing each other, and the opposite single-sided bevel forms the bevel. The width of the bevel gradually increases along the radial outward direction of the first cylindrical portion (220). Before the first welding step, a pad (260) is fixedly provided on the inner side of the ends of the first cylindrical portion (220) and the second cylindrical portion (230) facing each other to fix the first cylindrical portion (220) and the second cylindrical portion (230) together.

11. The welding method for the turbine valve chamber (10) according to any one of claims 1-8, characterized in that, The welding part of the turbine valve chamber (10) is located between the coaxially arranged adjacent first cylindrical part (220) and second cylindrical part (230). In the first welding step and the second welding step, the real-time position of the welding is symmetrical about the axis (250) of the first cylindrical part (220) and the second cylindrical part (230).

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