Welding and heat treatment method for GH4070T and GH984G small-caliber dissimilar material pipes for 650 DEG C ultra-supercritical boiler

Abstract

The invention discloses a welding and heat treatment method for GH4070T and GH984G small-caliber dissimilar material pipes for a 650 DEG C ultra-supercritical boiler, and relates to a welding and heat treatment method for GH4070T and GH984G small-caliber dissimilar material pipes for a 650 DEG C ultra-supercritical boiler. Before welding, the groove is machined into a V shape and cleaned, and spot welding fixing is conducted; an ERNiCrCoMo-1 welding wire is selected for manual argon tungsten-arc welding, various welding parameters are controlled, and preheating is carried out according to the room temperature, and the interlayer temperature, the welding seam thickness and the like are controlled. And aging strengthening heat treatment is carried out after welding. And finally, 100% RT inspection is carried out according to the NB / T 47013 standard. The method solves the problems of easy generation of defects in welding, narrow process window, difficult compatibility of heat treatment systems and the like in the prior art, and ensures the quality of welding joints.

Description

Technical Field

[0001] The invention relates to a welding and heat treatment method of GH4070T and GH984G small-caliber dissimilar material pipes for a 650°C ultra-supercritical boiler. Background Art

[0002] In the current field of thermal power units, 650℃ ultra-supercritical boilers have become the core direction of development and upgrading of thermal power units at home and abroad due to their outstanding performance advantages. The thermal efficiency of this boiler has successfully exceeded 50%, and the coal consumption for power supply is only about 254g / kWh, showing extremely high energy utilization efficiency. However, with the substantial improvement of boiler parameters, the requirements for high-temperature component materials have become increasingly stringent, and the material grade of high-temperature components must be correspondingly increased to high-temperature alloys with high nickel content.

[0003] Among many high-temperature alloy materials, GH4070T and GH984G high-temperature nickel-iron-based alloys stand out and become candidate high-temperature nickel-based alloys for 650℃ advanced ultra-supercritical boilers. Both alloys have excellent high-temperature mechanical properties, can stably withstand various stresses in high-temperature environments, and ensure the normal operation of boiler components; they also have excellent corrosion resistance, which can effectively resist the erosion of various corrosive substances during boiler operation and extend the service life of components; and they are also easy to process, which is convenient for making various complex shapes of components to meet the design requirements of boilers. The main chemical composition of GH4070T is Ni-25Fe-20Cr-Ti-Al. The unique strengthening mechanism is mainly based on the precipitation strengthening of γ′ phase (Ni(Al,Ti)), and supplemented by solid solution strengthening through Cr, Mo, and Co elements. This strengthening method makes GH4070T have good strength and stability at high temperatures. However, at present, there is no mature welding process for GH4070T and other dissimilar materials at home and abroad.

[0004] GH984G is a high-temperature nickel-iron alloy developed by the Institute of Metal Research, Chinese Academy of Sciences. Its main chemical composition is 42Ni-22Cr-20Fe-2Mo-Al-Ti-Nb. Its strengthening mechanism is solid solution strengthening with elements such as Cr, Mo, and Nb, supplemented by precipitation strengthening with a small amount of Al and Ti. This strengthening mode gives GH984G excellent comprehensive performance.

[0005] However, nickel-iron-based alloys face many challenges during the welding process due to their complex elemental composition. If the welding heat input, interlayer temperature and welding parameters are not properly controlled, defects such as thermal cracks and poor fusion are very likely to occur, which will seriously affect the quality and reliability of the welded joint. If the post-weld heat treatment is not performed properly, strain aging cracks will also occur, and if the number and size of the precipitation strengthening phase γ′ and grain boundary carbides are not appropriate, it will greatly affect the service life of the alloy. In addition, the poor fluidity of the welding molten pool, coupled with the differences in physical properties such as melting point, thermal conductivity, and thermal expansion coefficient between dissimilar materials, results in a very narrow welding process window, making it extremely difficult to obtain welded joints with qualified performance.

[0006] In addition, the use state of GH4070T is aging state, requiring 800±15℃ / 4h aging strengthening heat treatment; the use state of GH984G requires 730-800℃ / 4h aging strengthening heat treatment. This makes it difficult to make the post-weld heat treatment system of these two dissimilar nickel-iron alloy joints compatible.

[0007] In summary, for the welding of GH4070T and GH984G dissimilar nickel-iron based alloy materials, the selection of welding materials, the determination of welding process and the formulation of heat treatment process are extremely critical, which are directly related to the quality of welded joints and the safe and stable operation of 650℃ ultra-supercritical boilers. Summary of the invention

[0008] The present invention aims to solve the problems of welding defects, narrow process window, and poor compatibility of heat treatment systems in the prior art, and provides a welding and heat treatment method for GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boilers.

[0009] The present invention provides a welding and heat treatment method for GH4070T and GH984G small-diameter dissimilar material pipes for a 650°C ultra-supercritical boiler, comprising:

[0010] 1. Preparation before welding: Process the groove to be welded into a V shape, grind the inner and outer surfaces of the parent material at least 10mm from the edge of the groove until the metallic luster is exposed, clean the groove and both sides of the inner and outer walls with acetone or alcohol, then assemble the GH4070T pipe to be welded and the GH984G pipe to be welded, and fix them with manual argon arc spot welding;

[0011] 2. Preparation of welding materials: ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire is used as welding wire for manual tungsten inert gas welding; the process parameters of manual tungsten inert gas welding are: the current is direct current, the current range is 80-130A, the voltage range is 9-13V, the welding speed is 50-80mm / min, the maximum heat input is 2kJ / mm, the welding gun protection argon gas flow rate is 8-15L / min, and the back protection argon gas flow rate is 8-10L / min;

[0012] 3. Post-weld heat treatment: After welding, local or overall aging heat treatment is carried out to complete the pipe welding; the aging heat treatment temperature is 785-815°C, the heating rate is 110-180°C / h, and the time is 4h.

[0013] Beneficial effects of the present invention:

[0014] When welding the two pipes GH4070T and GH984G, the present invention selects a suitable nickel-based alloy as a filling material to ensure the high-temperature performance of the entire welded joint. Before welding, a suitable welding groove is formulated to avoid defects such as incomplete penetration and poor fusion caused by too small a groove angle and poor fluidity of the molten pool; by doing a good job of pre-welding cleaning and inter-layer cleaning, external pollutants are removed, the content of impurity elements in the weld is reduced, and the probability of low-melting-point eutectics is reduced; during the welding process, the inter-layer temperature, welding parameters, and weld thickness are strictly controlled to limit heat input to avoid thermal cracks and excessive oxidation of the weld; by standardizing the inter-layer cleaning requirements, the purity of the entire welded joint is ensured to avoid defects such as poor inter-layer fusion; the post-weld heat treatment system is determined according to the performance of the material itself to avoid the negative impact of improper heating speed and obtain a welded joint that meets the product use requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the groove to be welded. DETAILED DESCRIPTION

[0016] Specific implementation method 1: A welding and heat treatment method of GH4070T and GH984G small-diameter dissimilar material pipes for a 650°C ultra-supercritical boiler in this implementation method includes:

[0017] 1. Preparation before welding: Process the groove to be welded into a V shape, grind the inner and outer surfaces of the parent material at least 10mm from the edge of the groove until the metallic luster is exposed, clean the groove and both sides of the inner and outer walls with acetone or alcohol, then assemble the GH4070T pipe to be welded and the GH984G pipe to be welded, and fix them with manual argon arc spot welding;

[0018] 2. Preparation of welding materials: ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire is used as welding wire for manual tungsten inert gas welding; the process parameters of manual tungsten inert gas welding are: the current is direct current, the current range is 80-130A, the voltage range is 9-13V, the welding speed is 50-80mm / min, the maximum heat input is 2kJ / mm, the welding gun protection argon gas flow rate is 8-15L / min, and the back protection argon gas flow rate is 8-10L / min;

[0019] 3. Post-weld heat treatment: After welding, local or overall aging heat treatment is carried out to complete the pipe welding; the aging heat treatment temperature is 785-815°C, the heating rate is 110-180°C / h, and the time is 4h.

[0020] In this embodiment, the groove is processed into a V-shape of 60-70°, with a suitable blunt edge and a gap between the grooves, which is convenient for the formation and filling of the molten pool during welding and reduces the possibility of poor fusion. Grinding the groove edge and cleaning it to remove water, oil and other impurities can prevent these impurities from generating gas during the welding process, thereby avoiding the formation of defects such as thermal cracks.

[0021] This embodiment uses manual argon arc spot welding to fix and ensures that the misalignment is less than 0.5mm, which helps to maintain the relative position of the weldments during formal welding, ensures uniform heat distribution during welding, reduces stress concentration caused by misalignment, and thus reduces the probability of defects such as thermal cracks.

[0022] This embodiment uses ERNiCrCoMo-1 high-temperature nickel-based alloy strip welding wire, whose specific chemical composition can be well matched with the two parent materials GH4070T and GH984G during the welding process. While filling the weld, it ensures the strength and toughness of the weld, improves crack resistance, and reduces the occurrence of defects such as thermal cracks.

[0023] This implementation method accurately controls parameters such as current, voltage, welding speed, and heat input to ensure reasonable heat input during welding. For example, if the maximum heat input is 2kJ / mm, it can avoid problems such as coarse grains and excessive thermal stress caused by excessive heat input, and prevent thermal cracks from occurring; the appropriate current, voltage, and welding speed range is conducive to controlling the shape and size of the molten pool, ensuring the forming and fusion quality of the weld, and reducing poor fusion defects.

[0024] This embodiment uses a suitable argon gas flow rate for torch protection and back protection, which can effectively prevent the weld metal from oxidizing when in contact with air at high temperature, avoid impurities produced by oxidation affecting the quality of the weld, and reduce defects such as inclusions. Using straight or a small amount of oscillation welding, controlling the arc length, avoiding tungsten inclusions, and controlling the thickness of each layer of weld, etc., all help to ensure the stability of the welding process and the quality of the weld, and reduce the occurrence of defects.

[0025] This embodiment selects an aging strengthening heat treatment temperature of 785-815°C, a heating rate of 110-180°C / h and a holding time of 4h, which, on the one hand, avoids the premature precipitation of the precipitation strengthening phase due to the slow heating rate and causes strain aging cracks, and on the other hand, prevents excessive thermal stress from being generated by the heating rate being too fast. Holding at 800±15°C for 4h can release residual stress through stress relaxation, making the parent material structure stable and free of abnormal phases, thereby accurately controlling the precipitation of the precipitation strengthening phase γ′ and the number and size of grain boundary carbides, ensuring the service life of the alloy.

[0026] This embodiment comprehensively considers the characteristics of the two materials, and the aging strengthening heat treatment temperature range of 785-815°C is a comprehensive consideration of the 800±15°C / 4h / air-cooling aging strengthening heat treatment required by GH4070T and the 730-800°C / 4h / air-cooling aging strengthening heat treatment required by GH984G, taking a relatively compromise temperature range, which can take into account the performance requirements of the two materials to a certain extent, so that after the weld joint is heat treated, both materials can obtain better performance, solving the compatibility problem of the heat treatment systems of the two.

[0027] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that: the V-shaped angle in step 1 is 60-70°, and the blunt edge is 0-0.5 mm. The other steps and parameters are the same as those in specific implementation method 1.

[0028] Specific implementation method three: This implementation method is different from specific implementation method one in that: the joint assembly in step one ensures that the misalignment is less than 0.5 mm, and the joint clearance is 2.5 to 3.5 mm. Other steps and parameters are the same as those in specific implementation method one.

[0029] Specific implementation method 4: This implementation method is different from specific implementation method 1 in that: in step 1, the incoming state of the GH4070T pipe to be welded is in solid solution state, and the use state is in aging state; the incoming state of the GH984G pipe to be welded is in solid solution state, and the use state is in aging state. Other steps and parameters are the same as those in specific implementation method 1.

[0030] Specific embodiment 5: This embodiment is different from specific embodiment 1 in that the main components of the ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire described in step 2 are 0.05-0.15% C, 20-24% Cr, 10-15% Co, ≤1% Si, ≤1% Mn, ≤0.6% Ti, 0.8-1.5% Al, 8-10% Mo, ≤3% Fe and the balance Ni. The other steps and parameters are the same as those in specific embodiment 1.

[0031] Specific implementation method 6: This implementation method is different from specific implementation method 1 in that: in step 2, when the room temperature is lower than 10° C., the area of ​​the parent material on both sides of the welding joint of the GH4070T pipe to be welded and the GH984G pipe to be welded is preheated before welding, and the preheating temperature is 15-20° C. The other steps and parameters are the same as those in specific implementation method 1.

[0032] In this embodiment, preheating is performed when the room temperature is lower than 10° C. to remove moisture and avoid the formation of pore defects.

[0033] Specific implementation method 7: This implementation method is different from specific implementation method 1 in that: in step 2, the back side protective argon gas is continuously applied at least until the third layer of welding is completed. The other steps and parameters are the same as those in specific implementation method 1.

[0034] Specific implementation eight: This implementation differs from specific implementation one in that: after each welding in step two is completed, the interlayer temperature is controlled to ≤150°C by air cooling, spraying or wiping cooling water, and the chloride ion content in the cooling water is required to be ≤25mg / L. Other steps and parameters are the same as those in specific implementation one.

[0035] The interlayer temperature control in this embodiment is as follows: after each welding is completed, the interlayer temperature is controlled to be ≤150°C by air cooling, spraying or wiping cooling water, and the chloride ion content in the cooling water is limited. This can prevent problems such as grain growth, structural deterioration, crystallization cracks, liquefaction cracks, etc. caused by excessive interlayer temperature, thereby ensuring the stability of the welding process and broadening the welding process window.

[0036] Specific implementation method 9: This implementation method is different from specific implementation method 1 in that: after each welding in step 2 is completed, when there is oxidation on the weld surface, a special iron-free aluminum oxide grinding wheel is used to grind or other mechanical methods are used to remove the oxide film; at the same time, before the next welding, the weld surface and the groove are cleaned with alcohol or acetone before subsequent welding. Other steps and parameters are the same as those in specific implementation method 1.

[0037] Specific embodiment 10: This embodiment differs from specific embodiment 1 in that: the manual tungsten inert gas arc welding described in step 2 adopts a straight or slightly oscillating welding method, the molten pool is observed during welding, the arc length is controlled to be 2 to 3 mm, and the thickness of each layer of weld is controlled to be no greater than 2.5 mm. The other steps and parameters are the same as those of specific embodiment 1.

[0038] The beneficial effects of the present invention are verified by the following examples:

[0039] Embodiment 1: A method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for a 650°C ultra-supercritical boiler comprises:

[0040] 1. Preparation before welding: Process the groove to be welded into a V shape, grind the inner and outer surfaces of the parent material within a range of at least 10mm from the edge of the groove until the metallic luster is exposed, clean the groove and both sides of the inner and outer walls with acetone or alcohol to remove water, oil and other dirt, and then assemble the GH4070T pipe to be welded and the GH984G pipe to be welded, ensuring that the misalignment is less than 0.5mm, the gap between the two ends is 2.5-3.5mm, and they are fixed by manual argon arc spot welding; the V shape is 60-70°, and the blunt edge is 0-0.5mm; the incoming state of the GH4070T pipe to be welded is a solid solution state, and the use state is an aging state; the incoming state of the GH984G pipe to be welded is a solid solution state, and the use state is an aging state;

[0041] 2. Preparation of welding materials: ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire is selected as the welding wire for manual tungsten inert gas arc welding; the process parameters of manual tungsten inert gas arc welding are: the current is direct current positive connection, the current range is 80-130A, the voltage range is 9-13V, the welding speed is 50-80mm / min, the maximum heat input is 2kJ / mm, the welding gun protection argon gas flow rate is 8-15L / min, and the back protection argon gas flow rate is 8-10L / min; the main components of the ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire are 0.05-0.15% C, 20-24% Cr, 10-15% Co, ≤1% Si, ≤1% Mn, ≤0.6% Ti, 0.8-1.5% A in percentage by mass l. 8-10% Mo, ≤3% Fe and the balance Ni; when the room temperature is lower than 10℃, the area of ​​not less than 200mm of the parent material on both sides of the welding joint of the GH4070T pipe to be welded and the GH984G pipe to be welded shall be preheated before welding, and the preheating temperature shall be 15-20℃; during welding, the back protection argon gas shall be maintained at least until the end of the third layer of welding; after each welding is completed, the interlayer temperature shall be controlled to ≤150℃ by air cooling, spraying or wiping cooling water, and the chloride ion content in the cooling water shall be ≤25mg / L; after each welding is completed, when there is oxidation on the weld surface, a special iron-free alumina grinding wheel shall be used for grinding or other mechanical methods to remove the oxide film; at the same time, before the next welding, the weld surface and the groove shall be cleaned with alcohol or acetone before subsequent welding. The manual tungsten inert gas arc welding adopts a straight or slightly oscillating welding method. During welding, the molten pool is observed and the arc length is controlled to be 2 to 3 mm to avoid tungsten inclusion. The thickness of each layer of weld is controlled to be no more than 2.5 mm. The shielding gas is welding-grade argon gas with a purity of more than 99.99%.

[0042] 3. Post-weld heat treatment: After welding, local or overall aging heat treatment is performed to complete the pipe welding; the temperature of aging heat treatment is 785-815℃, the heating rate is 110-180℃ / h, and the time is 4h; on the one hand, it can avoid the precipitation of precipitation strengthening phases due to too slow heating rate, which causes strain aging cracks, and on the other hand, it can prevent the heating rate from being too fast and effectively reduce the thermal stress generated during the heating process. The purpose of keeping warm at 800±15℃ for 4h is to release residual stress through stress relaxation. After heat treatment, the parent material has good microstructure stability and no abnormal phases.

[0043] 4. Post-weld inspection: After welding is completed, the welded joints shall be subjected to 100% RT inspection according to NB / T 47013 standard. The inspection level shall not be lower than AB level, and the qualified level shall be I level.

[0044] Through strict inspection means, the present invention can timely discover possible internal defects in the welding joint, ensure that the welding quality meets the requirements, avoid safety hazards caused by welding quality problems, and ensure the reliability of the entire welding and heat treatment process from the perspective of quality control.

[0045] When welding the two pipes GH4070T and GH984G, the present invention selects a suitable nickel-based alloy as a filling material to ensure the high-temperature performance of the entire welded joint. Before welding, a suitable welding groove is formulated to avoid defects such as incomplete penetration and poor fusion caused by too small a groove angle and poor fluidity of the molten pool; by doing a good job of pre-welding cleaning and inter-layer cleaning, external pollutants are removed, the content of impurity elements in the weld is reduced, and the probability of low-melting-point eutectics is reduced; during the welding process, the inter-layer temperature, welding parameters, and weld thickness are strictly controlled to limit heat input to avoid thermal cracks and excessive oxidation of the weld; by standardizing the inter-layer cleaning requirements, the purity of the entire welded joint is ensured to avoid defects such as poor inter-layer fusion; the post-weld heat treatment system is determined according to the performance of the material itself to avoid the negative impact of improper heating speed and obtain a welded joint that meets the product use requirements.

[0046] This embodiment solves the welding and post-weld heat treatment problems of GH4070T+GH984G dissimilar nickel-iron-based alloys, which are candidate materials for 650°C ultra-supercritical boilers, and has reference significance for the selection of welding materials, welding process control and formulation of heat treatment systems when welding similar aging-hardened and solid solution-hardened nickel-based alloys and nickel-iron-based alloys.

Claims

1. A welding and heat treatment method for GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boilers, characterized in that The method includes:

1. Preparation before welding: Process the groove to be welded into a V shape, grind the inner and outer surfaces of the parent material at least 10mm from the edge of the groove until the metallic luster is exposed, clean the groove and both sides of the inner and outer walls with acetone or alcohol, then assemble the GH4070T pipe to be welded and the GH984G pipe to be welded, and fix them with manual argon arc spot welding; 2. Preparation of welding materials: ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire is used as welding wire for manual tungsten inert gas welding; the process parameters of manual tungsten inert gas welding are: the current is direct current, the current range is 80-130A, the voltage range is 9-13V, the welding speed is 50-80mm / min, the maximum heat input is 2kJ / mm, the welding gun protection argon gas flow rate is 8-15L / min, and the back protection argon gas flow rate is 8-10L / min; 3. Post-weld heat treatment: After welding, local or overall aging heat treatment is carried out to complete the pipe welding; the aging heat treatment temperature is 785-815°C, the heating rate is 110-180°C / h, and the time is 4h.

2. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1 is characterized in that The V-shape described in step 1 is 60-70° and the blunt edge is 0-0.5 mm.

3. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1 is characterized in that The mating assembly described in step 1 ensures that the misalignment is less than 0.5 mm and the mating clearance is 2.5 to 3.5 mm.

4. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1 is characterized in that In step 1, the incoming state of the GH4070T pipe to be welded is a solid solution state, and the use state is an aging state; the incoming state of the GH984G pipe to be welded is a solid solution state, and the use state is an aging state.

5. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1 is characterized in that The main components of the ERNiCrCoMo-1 high temperature nickel-based alloy strip welding wire described in step 2 are 0.05-0.15% C, 20-24% Cr, 10-15% Co, ≤1% Si, ≤1% Mn, ≤0.6% Ti, 0.8-1.5% Al, 8-10% Mo, ≤3% Fe and the balance Ni.

6. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1, characterized in that In step 2, when the room temperature is lower than 10°C, the area of ​​the parent material of not less than 200 mm on both sides of the welding joint of the GH4070T pipe to be welded and the GH984G pipe to be welded is preheated before welding, and the preheating temperature is 15-20°C.

7. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1, characterized in that During welding in step 2, the back side protective argon gas is continuously applied at least until the third layer of welding is completed.

8. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1, characterized in that After each welding pass in step 2 is completed, the interlayer temperature is controlled to ≤150°C by air cooling, spraying or wiping cooling water, and the chloride ion content in the cooling water is required to be ≤25mg / L.

9. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1, characterized in that After each welding pass in step 2 is completed, if there is oxidation on the weld surface, use a special iron-free aluminum oxide grinding wheel or other mechanical methods to remove the oxide film; at the same time, before the next welding, use alcohol or acetone to clean the weld surface and the groove before subsequent welding.

10. The method for welding and heat treating GH4070T and GH984G small-diameter dissimilar material pipes for 650°C ultra-supercritical boiler according to claim 1, characterized in that The manual tungsten inert gas arc welding described in step 2 adopts a straight or slightly oscillating welding method. During welding, the molten pool is observed and the arc length is controlled to be 2 to 3 mm; the thickness of each layer of weld is controlled to be no greater than 2.5 mm.

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