Repair welding method for gas turbine investment casting part

Abstract

The invention aims to provide a repair welding method for an investment casting part of a gas turbine, and belongs to the field of welding. Comprising the following steps: (1) eliminating surface defects; (2) the repair welding requirement is limited; (3) welding is carried out; (4) interlayer treatment; and (5) post-welding treatment. The invention encompasses repair welding processes for investment casting nozzle segments, bulkheads, turbine shrouds, and other investment casting stator parts made of cobalt-based alloys and cobalt-based alloys. Repair welding processing is carried out on local cracks, the production period can be greatly shortened, the production cost is saved on a large scale on the premise that the product quality is guaranteed, and the product requirements are met.

Description

Technical Field

[0001] The present invention relates to a welding method, in particular to a gas turbine welding method. Background Art

[0002] Investment casting is also called lost wax casting, which includes wax pressing, wax repairing, tree assembly, slurry dipping, wax melting, casting molten metal and post-processing the wax model of the parts. Then, the wax model is coated with mud. After the mud model is dried, it is put into hot water to melt the internal wax model. The mud model with the melted wax model is taken out and baked into a ceramic mold. Generally, a casting port is left when making the mud mold, and then the metal solution is poured from the casting port. After cooling, the desired product is obtained.

[0003] The investment casting parts of gas turbines are used for a long time at high temperature, so there is a high risk of cracks. During the production process, investment casting parts are generally more expensive and have a longer processing cycle, involving more processes and greater manufacturing difficulty. Summary of the invention

[0004] The purpose of the present invention is to provide a method for repairing welding of gas turbine investment casting parts which can greatly shorten the production cycle, save production costs on a large scale while ensuring product quality, and meet product requirements.

[0005] The object of the present invention is achieved in that:

[0006] The invention provides a method for repairing welding of gas turbine investment casting parts, which is characterized by comprising the following steps:

[0007] (1) Eliminate surface defects;

[0008] (2) Limit the requirements for repair welding;

[0009] (3) Carry out welding;

[0010] (4) Interlayer treatment;

[0011] (5) Post-weld treatment.

[0012] The present invention may also include:

[0013] 1. Step (1) Eliminating surface defects The specific steps are:

[0014] a. Locate defects by visual or penetrant testing of surface defects and radiography of sub-surface defects;

[0015] b. If the defects are eliminated before the pre-weld solution heat treatment, cutting or grinding may be used; otherwise, the defects are removed by cutting;

[0016] c. The amount of metal removed to repair the defect;

[0017] d. Remove enough excess metal to complete the cavity preparation.

[0018] 2. Step (2) The requirements for repair welding include:

[0019] Repair welding using gas tungsten arc welding process:

[0020] Clean the area to be welded: remove all inspection materials, heat treatment scale or other foreign matter, including grease, dirt, pencil marks, penetrants and developers; where oily contaminants are removed by degreasing, and non-oily contaminants are removed by liquid blasting, sandblasting or mechanical means;

[0021] The welding temperature of the casting shall not be lower than about 10°C;

[0022] Through-through defects use an argon backing or argon welding chamber; if copper is used in the backing fixture, it must be nickel or chrome plated and spaced away from the casting surface; argon is supplied to the back of the weld through perforations in a hollow copper backing plate or spoon; when welding on cored airfoils, use plugs to close the open ends of the cored holes after the welded supports are in place.

[0023] 3. Step (3) During welding:

[0024] For surface holes, weld in the center of the cavity and apply filler alloy in a spiral bead around the periphery of the cavity, allowing time to cool after each 360 degree rotation or when the weld pool reaches the melting point of the weld, with the temperature not exceeding 175°C; before the 360 ​​degree face of the spiral bead, remove all oxides and blend recessed and / or unfused areas smoothly; apply filler alloy continuously in the same manner until the cavity is filled;

[0025] For through holes, make an initial pass with filler alloy around the entire circumference of the cavity, ensuring that the bevel edges are fully fused and there is no unfused undercut on the back side of the weld; cool between passes, not exceeding 175°C, and apply filler alloy in successive passes around the remaining hole until the entire cavity is closed; then apply successive layers of filler alloy in the same pattern until the cavity is filled;

[0026] For edge welds of thin sections, where the cavity is in the form of a through notch, if the notch is close to the sidewall, apply the filler alloy first along the edge of the cavity closest to the sidewall and apply continuously, filling the cavity from the sidewall to the center of the airfoil; if the notch is not adjacent to the sidewall, apply the filler alloy along the portion of greatest thickness and continue to fill the cavity until the trailing edge is completed; allow cooling time between weld passes and grind and / or wire brush the weld deposit as needed after each weld pass.

[0027] 4. Step (4) interlayer treatment is specifically as follows: after each welding pass, check the weld surface, including the base material near the fusion zone and the weld for cracks and oxide inclusions; after each welding, use an electric grinding tool or a round brush with stainless steel bristles or sandblast and / or use a hand brush to grind burrs and clean each weld.

[0028] 5. The post-weld treatment of step (6) includes: after welding, grinding or machining the weld to the required contour of the inner and outer surfaces of the part, performing post-weld heat treatment on the casting. If straightening is required, it shall be performed before the final heat treatment, and the nozzle flow area correction shall be performed after the final heat treatment; the integrity of all materials shall be checked by visual inspection, fluorescent penetrant and radiography.

[0029] The advantages of the present invention are: the present invention covers the repair welding process of investment casting nozzle segments, partitions, turbine shrouds and other investment casting stator parts made of cobalt-based alloys and cobalt-based alloys. Repair welding of local cracks can greatly shorten the production cycle, save production costs on a large scale while ensuring product quality, and meet product needs. DETAILED DESCRIPTION

[0030] The present invention is described in more detail below with reference to examples:

[0031] A method for repair welding of gas turbine investment casting parts of the present invention comprises the following steps:

[0032] 1. Elimination of defects

[0033] The first step is to accurately locate defects through visual or penetrant inspection for surface defects and radiography for sub-surface defects.

[0034] The second step is to remove the defect by cutting (e.g., using a deburring tool) rather than grinding to minimize the depth of the area affected by machining in the repair area. Cutting or grinding may be used if the defect is removed before pre-weld solution heat treatment. However, care should be taken to avoid thermal inspection of the repair area.

[0035] The third step is to remove the amount of metal required to repair the defect. Before welding, the repair area is checked by fluorescent penetrant to see if the defect has been removed.

[0036] The fourth step completes the cavity preparation by removing only enough additional metal to obtain the correct configuration of the cavity.

[0037] 2. Repair welding requirements

[0038] Unless otherwise specified, repair welding shall be carried out by gas tungsten arc welding (GTAW).

[0039] The area to be welded must be clean. All grease, dirt, pencil marks, inspection materials such as penetrants and developers, heat treatment scale or other foreign matter must be removed. Oily contaminants should be removed by degreasing. Non-oily contaminants may be removed by liquid blasting, sandblasting or other suitable mechanical means.

[0040] The welding temperature of the casting must not fall below approximately 10°C. Preheating is not recommended.

[0041] All through-holes must use an argon backing or argon welding chamber. If copper is used in the backing fixture, it must be nickel or chrome plated and must be spaced far enough from the casting surface to prevent copper contamination of the casting. Argon is most effectively supplied to the back of the weld through perforations in a hollow copper backing plate or spoon. When welding on cored airfoils, the open ends of the cored holes should be closed with plugs after the welded backing is in place. This will ensure good argon coverage and prevent air from being drawn into the back of the weld.

[0042] 3. Welding

[0043] For surface holes, weld in the center of the cavity and apply filler alloy in a spiral bead around the periphery of the cavity. The entire spiral bead should not be completed in one pass. Time must be allowed to cool (temperature not exceeding 175°C) after each 360-degree rotation or when the weld pool reaches the welding melting point. All oxides should be removed and recessed and / or unfused areas blended smooth before proceeding to the next process (360 side of the spiral bead). Filler alloy is applied continuously in the same manner until the cavity is filled. The heat input must be kept to a minimum by using low currents using stringer beads and using higher travel speeds.

[0044] For through holes, make an initial pass with filler alloy around the entire circumference of the cavity, ensuring that the bevel edges are fully fused and there are no unfused undercuts on the back of the weld. Cool between passes (temperature not to exceed 175°C) and apply filler alloy in continuous passes around the remaining hole until the entire cavity is closed. Then apply successive layers of filler alloy in the same pattern until the cavity is filled. Interpass cleaning and low-heat welding techniques must be used.

[0045] For thin-section edge welds, such as the trailing edge of an airfoil, the cavity is usually in the form of a through notch. If the notch is adjacent to the sidewall, apply the filler alloy first along the edge of the cavity closest to the sidewall and continue to apply. Fill the cavity from the sidewall toward the center of the airfoil. If the notch is not adjacent to the sidewall, apply the filler alloy along the section of greatest thickness and continue to fill the cavity until the trailing edge is complete. Allow cooling time between weld passes and grind and / or wire brush the weld deposit as needed after each pass.

[0046] 4. Interlayer Processing

[0047] The welding temperature should be below 175°C after each welding pass. Visual inspection of the weld surface, including the base material near the fusion zone and weld for cracks, and for oxide inclusions, etc., after each welding pass should be done before welding, i.e. before any such defects are masked by smearing of the weld surface. All defects in the weld must be removed before fabrication.

[0048] After each weld, clean each weld properly by grinding away burrs using a power grinder or a round brush with stainless steel bristles or by sandblasting and / or grinding with a hand brush (stainless steel bristles), where applicable.

[0049] 5. Post-weld treatment

[0050] After welding, the weld should be ground or machined to the required profile on the inside and outside surfaces of the part. Castings should be post-weld heat treated in accordance with the regulations. If straightening is required, it should be performed before the final heat treatment, but nozzle flow area correction can be performed after the final heat treatment. Check the integrity of all materials using visual, fluorescent penetrant and radiographic methods.

[0051] 6. Main welding parameters

[0052] 1. Electrode: diameter 1.5-2.4mm, 2% tungsten plated, pointed.

[0053] 2. Average arc voltage: 12-14 volts, straight polarity, direct current.

[0054] 3. Welding current: Maximum 100 amps. The arc should be controlled to decay to 10 amps or less before interruption.

[0055] 4. Torch: A gas lens type cup must be used. Electrode stick out must be kept to a minimum to prevent electrode melting.

[0056] 5. Argon flow rate: The protective gas flow rate at temperature should be 15 to 20 CFH.

[0057] VII. Other requirements

[0058] Welding and heat treatment sequence

[0059]

[0060] (a) Repair is performed in the solution heated condition for optimum repairability of FSX414, but weld repairs can also be performed in the cast condition.

[0061] (b) For a size less than 10×10×10 mm (volume 1000 mm 3 )X40 and FSX414 repairs, solution heat treatment is optional, but if applicable, aging heat treatment is performed after welding.

[0062] (c) For FSX414 and N155 repair hemispherical weld preparation with diameter less than 10 mm (volume 260 mm 3 ), if the parts are in the aging heat treatment state, solution heat treatment and aging heat treatment are optional.

Claims

1. A method for repair welding of gas turbine investment casting parts, characterized in that: The following steps are included (1) Eliminate surface defects; (2) Limit the requirements for repair welding; (3) Carry out welding; (4) Interlayer treatment; (5) Post-weld treatment.

2. A method for repair welding of gas turbine investment casting parts according to claim 1, characterized in that: Step (1) Eliminating surface defects The specific steps are: a. Locate defects by visual or penetrant testing of surface defects and radiography of sub-surface defects; b. If the defects are eliminated before the pre-weld solution heat treatment, cutting or grinding may be used; otherwise, the defects are removed by cutting; c. The amount of metal removed to repair the defect; d. Remove enough excess metal to complete the cavity preparation.

3. A method for repair welding of gas turbine investment casting parts according to claim 1, characterized in that: The requirements for step (2) repair welding include: Repair welding using gas tungsten arc welding process: Clean the area to be welded: remove all inspection materials, heat treatment scale or other foreign matter, including grease, dirt, pencil marks, penetrants and developers; where oily contaminants are removed by degreasing, and non-oily contaminants are removed by liquid blasting, sandblasting or mechanical means; The welding temperature of the casting shall not be lower than about 10°C; Through-through defects use an argon backing or argon welding chamber; if copper is used in the backing fixture, it must be nickel or chrome plated and spaced away from the casting surface; argon is supplied to the back of the weld through perforations in a hollow copper backing plate or spoon; when welding on cored airfoils, use plugs to close the open ends of the cored holes after the welded supports are in place.

4. A method for repair welding of gas turbine investment casting parts according to claim 1, characterized in that: Step (3) During welding: For surface holes, weld in the center of the cavity and apply filler alloy in a spiral bead around the periphery of the cavity, allowing time to cool after each 360 degree rotation or when the weld pool reaches the melting point of the weld, with the temperature not exceeding 175°C; before the 360 ​​degree face of the spiral bead, remove all oxides and blend recessed and / or unfused areas smoothly; apply filler alloy continuously in the same manner until the cavity is filled; For through holes, make an initial pass with filler alloy around the entire circumference of the cavity, ensuring that the bevel edges are fully fused and there is no unfused undercut on the back side of the weld; cool between passes, not exceeding 175°C, and apply filler alloy in successive passes around the remaining hole until the entire cavity is closed; then apply successive layers of filler alloy in the same pattern until the cavity is filled; For edge welds of thin sections, where the cavity is in the form of a through notch, if the notch is close to the sidewall, apply the filler alloy first along the edge of the cavity closest to the sidewall and apply continuously, filling the cavity from the sidewall to the center of the airfoil; if the notch is not adjacent to the sidewall, apply the filler alloy along the portion of greatest thickness and continue to fill the cavity until the trailing edge is completed; allow cooling time between weld passes and grind and / or wire brush the weld deposit as needed after each weld pass.

5. A method for repair welding of gas turbine investment casting parts according to claim 1, characterized in that: Step (4) interlayer treatment is specifically as follows: after each welding pass, check the weld surface, including the base material near the fusion zone and the weld for cracks and oxide inclusions; after each welding, use an electric grinding tool or a round brush with stainless steel bristles or sandblast and / or use a hand brush to grind burrs and clean each weld.

6. A method for repair welding of gas turbine investment casting parts according to claim 1, characterized in that: The post-weld treatment of step (6) includes: after welding, grinding or machining the weld to the required contour of the inner and outer surfaces of the part, performing post-weld heat treatment on the casting. If straightening is required, it is performed before the final heat treatment, and the nozzle flow area correction is performed after the final heat treatment; the integrity of all materials is checked visually, by fluorescent penetrant and by radiography.

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