TECHNICAL FIELD
[0001] The present disclosure, in general, relates to welding technology. In particular the present invention relates to a method for optimizing parameters to obtaining defect-free dissimilar metal welds of Alloy 617 (ASME Code Case: 2439) and Alloy 740H (ASME code case 2701-2) plates using ASME ER NiCrCo-1 (AWS A5.14) filler material.
BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In Advanced Ultra Super Critical (AUSC) power plants, steam temperatures are of the order of 700/720°C in Superheater and Reheater sections of Boiler, High Pressure (HP) and Intermediate Pressure (IP) turbines. This requires boiler sections and valves to be made up of Ni-base superalloys for withstanding such high temperatures.
[0004] Technical Problem: The entire components cannot be made up with single Ni-base superalloy, which increases the investment would be extremely high. Hence, high temperatures of boiler sections where temperatures are of the order of 600/650°C are proposed to be made up of alloy 617 and above this temperature Alloy 740H is made. Therefore, dissimilar welding joint between alloy 617 and alloy 740H becomes inevitable. Further, post weld heat treatment temperature of alloy 617 and alloy 740H has a huge difference, which makes the dissimilar jointing process highly difficult.
[0005] Prior state of art
[0006] In US6753504B2 patent, a procedure for welding a Ni-base superalloy with a steel was explained. This joining was carried out by having an intermediate layer (IN 617) on the Ni-base superalloy (IN 625 containing Nb which leads to weld solidification cracking) and then joining this to the steel using Metal Active Gas process or Tungsten Inert Gas welding process. This is employed for obtaining crack-free welded rotors for turbo-machinery applications.
[0007] In US20130301309A1 patent, a procedure for obtaining dissimilar metal welds using buttering technique is discussed in detail for applications related to welding large components such as turbine rotor. In the method disclosed by this patent, dilution ratio of buttering layer to metal is less than 50%. This can be employed for welding large components such as turbine rotor.
[0008] In US8308051B2 patent, welding method for welding dissimilar metals (i.e., one high melting point material with one lower melting point material) were discussed using friction stir welding process. The method involves presence of rotary tool which makes the interface softer and later joins them to obtain a sound weld joint. Joints between steel and aluminium were successfully obtained using this technique.
[0009] In US200880067214A1 patent, a novel method of having a transition for superheater or reheater tubes by mechanical forming and hot isostatic pressing (HIP) is discussed. This method eliminates the need for arc welding or other fusion welding processes. The transition is from ferritic T11 or T22 steel (ASME A213 type) to TP347 or TP 304 type austenitic steels (which resist higher temperatures).
[0010] WO2001083151A1 patent discusses joining dissimilar metals such as steels and aluminium using new technique. In this invention, Aluminium is retrogressively heat treated locally at the joint prior to electromagnetic forming (EMF) or magnetic pulse welding (MPW). This technique led to development of stronger welds.
[0011] EP2617512A1 patent discusses the procedure for producing weld joints between Ni-base superalloy impeller and steel shaft. The welds are obtained by fusing the metals (mixing ratio by weight) in the ratios of 0.5 to 0.8. The welds obtained are sound and crack-free.
[0012] Technical problem: With reference to the above patents, all of them are successful in development of dissimilar metal welds which are defect free. But they require sophisticated techniques such as HIP or EMF or MPW. None of them can employ techniques as such buttering with ER NiCrCo-1 filler using Tungsten Inert Gas welding or Gas Tungsten Arc Welding directly and sequential post buttering heat treatment to avoid filler weldment heat treatment to obtain a dissimilar weld joint.
[0013] Technical solution: Accordingly, there is a need to develop thick section welds between Alloy 740H and Alloy 617 for component applications in AUSC power plants where steam temperatures of weldment is around 700/720°C.
OBJECTS OF THE DISCLOSURE
[0014] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed hereinbelow.
[0015] It is a general object of the present disclosure to develop a method for employing Gas Tungsten Arc Welding (GTAW) with commercially available ER NiCrCo-1 filler with heat treatment cycle for obtaining final weld on-site without any separate heat treatment processing, i.e., between Alloy 740H and Alloy 617 materials.
[0016] It is another object of the present disclosure, the method can be relied on for reproducibility.
[0017] It is another object of the present disclosure to provide a method where the welding procedure produces qualified side bend tests without showing up any cracks.
[0018] It is another object of the present disclosure to utilize the method not only for plates but also for tubes, pipe, forged sections, etc. where weldments of Alloy 740H and Alloy 617 are envisaged.
[0019] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY
[0020] This summary is provided to introduce concepts related to joining of dissimilar Alloy 617 with Alloy 740H for advanced fossil boiler applications. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0021] In an embodiment, the present disclosure relates to a method for obtaining dissimilar welds of Alloy 617 and Alloy 740H with ER NiCrCo-1 filler material using conventional, Gas Tungsten Arc Welding process is provided. The edge prepared groves of alloy 617 plate and is buttered with ErNiCrCo-1 using Semi-Automatic Gas Tungsten Arc Welding process up to the thickness of 25 mm. Alloy 617 buttered base plates are subjected to post buttering heat treatment at the temperature of 980°C for 2 hours and allowed cool inside the furnace for stress reliving purpose. Further welded using ErNiCrCo-1 filler material (0.8 mm diameter) with back purging of Argon gas to produce welded alloy based plate. After that the welded alloy based plate is subjected to post heat treatment and allowed cool inside the furnace for aging of Alloy 740H.
[0022] In an aspect, the chemical compositions of the alloy base plates and the filler material are measured by Optical Emission Spectrometry.
[0023] In an aspect, the buttered layer of both alloy base plate is machined up to 7 mm to meet the edge preparation design for given weld joint.
[0024] In an aspect, the edge prepared groves of alloy 617 base plates are is buttered with ErNiCrCo-1 using GTAW process up to the thickness of 25 mm.
[0025] In an aspect, the setup for welding is prepared with 2° revered pre-bending to reduce the distortion.
[0026] In an aspect, each stage to test the residual stress is measured using hole drilling method to ensure the post heat treatment stress levels of alloy 617 side.
[0027] In an aspect, the tensile testing is carried out at various temperatures for the welded plates.
[0028] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[0029] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0030] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:
[0032] FIG. 1 illustrates a block diagram for optimizing parameters for joining of dissimilar metal alloy base plates.
[0033] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter.
DETAILED DESCRIPTION
[0034] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[0035] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a",” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0037] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0038] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0039] According to the present invention, a method for obtaining dissimilar welds of Alloy 617 and Alloy 740H with ER NiCrCo-1 filler material using conventional, Gas Tungsten Arc Welding process is provided. The base materials considered for the method are Alloy 617 and Alloy 740H (ASME Code Case 2439). The filler material used for welding is ER NiCrCo-1 grade.
[0040] Referring to fig.1, after preparing the groove edge on Alloy 617 plate, buttering (overlay) of ErNiCrCo-1 filler wire using Semi-Automatic Gas Tungsten Arc Welding process done to build-up 25 mm on groove surface. Alloy 617 buttered base plate is on Alloy base plate 617, buttering (overlay) of ErNiCrCo-1 filler wire using Semi-Automatic Gas Tungsten Arc Welding process to build up 25 mm on groove surface.
[0041] Alloy 617 buttered base plate is subjected to post buttering heat treatment at the temperature of 980°C for 2 hours and is then allowed to cool inside the furnace for stress reliving purpose. Further, the buttered layer of both base metal is machined up to 7 mm to meet the edge preparation design for given weld joint. The setup for welding is prepared with 2° revered pre-bending to reduce the distortion. The Run-on and run-off plates made of stainless steel are used during welding process.
[0042] The Argon gas back-purging provision is given during root pass welding. During root pass welding and subsequent hot pass welding, the base metal plates are not clamped during the remaining passes. The plates are clamped using a fixture to avoid distortion. Welding is carried out using semi-automatic Gas Tungsten Arc Welding (GTAW) system. Between the passes, the material is cleaned using acetone followed by wire-brush to remove any inter-pass oxides.
[0043] During various welding trials conducted, defects such as porosity, lack of fusion, weld depression, etc. are detected by radiographic testing. These are later eliminated by optimizing the welding parameters. The optimized parameters employed during welding are indicated in Table 1. It took a total of 42 passes to successfully complete the welding. Welded plate is subjected to post heat treatment temperature of 800°C for 4 hours and allowed to cool inside the furnace for aging of Alloy base plate 740H.
[0044] Table 1: Optimized welding parameters employed during welding using GTAW process
Welding parameter Details
Filler diameter 0.8 mm
Preset 5 mm on each side
Welding process GTAW
Shielding flow rate 12 LPM
Back Purging 4 LPM
Interpass temperature <150oC
Preheat temperature Nil
Current 115A
Voltage 13 - 14V
welding speed 100 mm/min
wire feed 800 mm/min

[0045] Each stage residual stress is measured using hole drilling method to ensure the post heat treatment stress levels of alloy base plate 617. It is noted in table 2 for reference. All the weld plates which are passed through radiographic testing only are considered for further characterization and sample preparation after discarding 15 mm from each end.
[0046] Table 2: Average results residual stress measure on alloy 617 side using hole drilling method at heat affect zone of weldment in different stages.
Condition HAZ Max Stress (MPa)
as buttered Alloy 617 468
Heat treatment@980?C Alloy 617 66

[0047] The Transverse tensile testing is carried out at various temperatures (ambient and 750oC) from the welded plates and the results are reported in Table 3. The bend samples cut from the radiographically qualified portions transverse to the weld direction as per AWS B 2.0. These are subjected to 180o side bend testing. The weld regions did not develop any cracks during bend testing. This indicates the successful development of welding procedure for these welds.
[0048] Table 3: Average results after tensile testing at various temperatures
T (oC) 0.2% YS (MPa) UTS (MPa)
24 487 892
750 374 585
[0049] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

Claims:We claim:
1. A method for optimizing parameters for joining of dissimilar metal alloy base plates. It comprises of steps:
buttering the edge of alloy base plate 617 and alloy base plate 740H with ERNiCrCo-1 as a filler material using Gas Tungsten Arc Welding (GTAW);
treating the buttered alloy base plate 617 with a post buttering heat treatment and cooling the alloy base plate 617 after the treatment inside a furnace to relieve stress;
welding the alloy base plate 617 and alloy base plate 740H further with ErNiCrCo-1 using back purging of Argon gas to produce welded alloy based plate; and
subjecting the welded alloy based plate for post heat treatment to cool inside the furnace for aging treatment to further age alloy base plate 740H.

2. The method as claimed in claim 1, wherein the buttered layer of both alloy base plate is machined up to 7 mm to meet the edge preparation design for given weld joint.

3. The method as claimed in claim 1, wherein the edge prepared groves of alloy base plates are buttered with ErNiCrCo-1 using GTAW process up to the thickness of 25 mm.

4. The method as claimed in claim 1, wherein the setup for welding is prepared with 2° revered pre-bending to reduce the distortion.
5. The method as claimed in claim 1, wherein each stage to test the residual stress is measured using hole drilling method to ensure the post heat treatment stress levels of alloy base plate 617.

6. The method as claimed in claim 1, wherein tensile testing is carried out at various temperatures for the welded plates.