Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
  • B23K31/12—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to investigating the properties, e.g. the weldability, of materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K9/00—Arc welding or cutting
  • B23K9/23—Arc welding or cutting taking account of the properties of the materials to be welded
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
  • G09B19/00—Teaching not covered by other main groups of this subclass
  • G09B19/24—Use of tools
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/001—Turbines
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F30/00—Computer-aided design [CAD]
  • G06F30/20—Design optimisation, verification or simulation
  • G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]

Definitions

• the present invention relates to a method for a welding process control of Nickel based superalloy products.
• Nickel-based superalloys are widely used as materials for service at high temperatures, in particular, in the hot zones of gas turbines. Most important properties of superalloys are high-temperature creep resistance, fatigue life, oxidation and corrosion resistance, as well as their weldability and processability.
• Strain age cracking is observed in ⁇ '- ⁇ 3 ( ⁇ , ⁇ ) precipitate strengthened alloys during post weld heat treatment, or subsequent service at high temperatures. It is characterized by intergranular micro-cracking due to residual stresses developed during manufacture, or applied stresses arising from service exposure. The strain age cracking is promoted by high additions of Ti and Al, as well as C, S, B.
• Solidification cracking occurs in the newly formed weld bead when the mushy zone experiences tensile stresses. This defect is promoted by a wide solidification range for the alloy and low welding traverse speeds.
• Centerline grain boundary forms along the centerline of the weld bead at intermediate to high input heat levels and high welding speeds.
• the defect is promoted by higher alloying additions and impurity levels. It is characterized by a sharp teardrop-shaped weld pool, a coarse columnar grain structure across the weld bead and a high volume fraction of eutectic and brittle phases along the centerline.
• Grain boundary liquation cracking occurs within the HAZ adjacent to the weld bead as a consequence of local dissolution of grain boundary phases (mainly carbides and Laves phases). Susceptibility to grain boundary liquation cracking is dependent upon alloy composition, grain size (microsegregation is promoted by coarser microstructures), and welding speed.
• weldability of superalloys is also very sensitive to the process parameters, namely the effective power of a heat source and welding speed. Therefore one of the defect provoking factors consists in incorrect choice of operating parameters of welding process, the especially critical of which are power of the heat source (welding current, voltage) and the welding speed (electrode motion). Other parameters causing the defects are the composition of protective atmosphere or of a weld pool and the like as well as environmental conditions in the weld bead and heat-affected zone during welding.
• Ni-based superalloys are often used, e.g., in various hot components of gas turbines, comprising for example vanes, blades, discs, shafts and so on, thereby imposing additional requirements to the quality of a weld bead.
• EP225270A1 , GB2205109A, US6284392B1 , US20030170489A1), or weldability with a different material e.g. US20100059146A1, EP2172299A2.
• Other developments are devoted to modification of processing of superalloys, i.e. the casting operation (e.g. EP2151292A1), specific complex thermo-mechanical treatment (e.g. in WO 1999007902 A 1), the welding process itself (e.g. US20110089150A1 , W0201 1054864A1 , W0201 1058045 A 1 ), pre-, post-weld heat treatment (e.g.
• the aim of this invention is to provide a method for a welding process control for Nickel based superalloy that eliminates one or more of the above mentioned disadvantages singly or in any combination.
• a warning and information is provided about the possibility of a welding defect and its location, and recommendations are provided for changing at least one welding parameter to correct said defect.
• the method may further comprise displaying of a determined weldability property on a display device.
• determining of weldability properties of superalloys may include at least one of determining of localized weldability for each of the welding sections and determining of overall weldability for all welding sections.
• Such localized weldability could be used for determining local weldability, may be referred as spot weldability, of complicated shaped products, for example for transition portions between two portions of products having different shapes.
• the overall weldability could be determined as integrally weldability or as averaged weldability. It depends only on a method, which shall be implemented by producing the overall weldability from the local weldability basing on the properties and parameters of finish welded products of Ni based superalloys. Since such methods are well known in the art, further specification of such approach is omitted.
• Weldability properties of superalloys are determined basing on at least one criterion selected from the group consisting of a weld cracking criterion caused by tension stress and/or extending motion above the critical value aft the welding source, a faulty fusion criterion, a liquation cracking criterion and a grain boundary at centerline criterion.
• the invention provides a computer-readable medium carrying a computer program comprising instructions for implementing said method for a welding process control of Nickel based superalloy products.
• Fig. 1 illustrates an assessment of weldability for a range of nickel based superalloys according to US 20060042729;
• Fig. 2 schematically illustrates a mechanical-metallurgical approach used in the method
• Fig.3 illustrates flow diagram of the claimed method
• Fig.4 to 13 relate to an example of method of Fig. 3, wherein
• Fig. 4 illustrates a CAD model of welded parts including filler material in between
• Fig. 5 illustrates a finite element model based on CAD model
• Fig. 6 shows a temperature distribution at a certain time moment after onset of welding
• Fig. 7 shows Von Mises stress distribution at a certain time moment after onset of welding
• Fig. 8 illustrates a distribution of tensile stresses (o yy ) at a certain time moment after onset of welding
• Fig. 9 illustrates a distribution of plastic strains (von Mises) at a certain time moment after onset of welding
• Fig. 10, 1 1 illustrate an example showing places in which incomplete weld penetration occurred after welding with the heat input of 150 J/mm and welding speed of 5 mm/s: Fig.10 - location of defects; Fig.11 - temperature distribution showing melted area (in black);
• Fig. 12, 13 illustrate the example in which full weld penetration occurred after welding with the heat input of 240 J/mm and welding speed of 5 mm s: Fig.12 - location of defects (no defects); Fig.13 - temperature distribution showing melted area (in black).
• the present invention relating to a method for a welding process control of Nickel based superalloy products is proposed, the method providing increased quality of a welding joint and reduced amount of rejected welded products made of Ni-based superalloys.
• the authors of the present invention propose a new complex approach to the welding process control.
• Such a numerical simulation is a reliable tool for controlling the welding process and allows for assessing the feasibility of welding under the current welding conditions, including the parameters of welding equipment, composition of products to be welded and their geometry taken into account.
• the present invention differs from the conventional methods for a welding process control, based on adjustment of operating parameters within the predetermined limits, in that the method for a welding control provide, through the virtual welding, at any given time moment during the welding process a reliable response about feasibility of welding of Ni-based superalloys with a high quality welded products obtained and with the available operating parameters of welding equipment, material and geometry of welded products.
• the apparent advantage of the present invention is the ability to determine the quality of the resulted welding joint while making changes to the welding process parameters, such as changes introduced by the operator.
• the control provides an appropriate response to the changes introduced by the operator and indicates the feasibility of welding considering the entire combination of welding conditions, characterized by the operating parameters of the welding equipment, material and geometry of the welded products.
• the present invention also provides for a virtual welding, which is based on assessment of the actual weldability of Nickel-based superalloys.
• Weldability of superalloys can be regarded as a comprehensive and the most reliable criterion for determining a quality of the welding. Referring to Fig.1 one could see one approach for an assessment of weldability for a range of nickel based superalloys according to aluminum and titanium contents according to US 20060042729. Such approach does not allow assessing of weldability of superalloys to determine the quality of the resulted welding joint while making changes to the welding process parameters.
• the evaluation procedure for weldability of superalloys shall be based on using predetermined criteria, such as those proposed in the article of Dye D., Hunziker O. and Reed R.C, Numerical analysis of the weldability of superalloys, Acta materialia, 2001 , 49, 683-697, comprising mathematical descriptions of criteria for formation of certain defects, namely, for centerline grain boundary, constitutional liquation at second phases, and solidification cracking. In the claimed method can be used additional criteria.
• Fig. 2 The approach of Fig. 2 consists of two blocks.
• a “metallurgy” block is based on thermodynamic calculations (using software like ThermoCalc, FactSage etc) to evaluate phase transformations and transition temperatures for the alloy of given chemical composition, as well as temperature- dependant specific heat and density.
• a “thermo-mechanical” block is based on the coupled structural mechanics and heat transfer problem. Commercial software packages like ANSYS, LS-DYNA, SYSWELD, etc can be used.
• thermo- mechanics and metallurgy calculations providing the stress-strain state, temperature and phase distributions for the whole structure of welding joint at any time moment of the process. Based on this information, one could use different criteria to evaluate whether the welding will be successful for the given Ni base superalloy material, welding technology and geometry of finish welded product.
• Nickel-based superalloy products as shown in Fig. 3 will now explain with reference to Fig. 4 to 13.
• the method for a welding process control of Nickel-based superalloy products comprises first step of providing the data, relating to geometry of welded products, including geometrical parameters of products, welded bead and its position in the welded products.
• This data could be accumulated in a CAD model of welded products including welded bead.
• Such example CAD model is shown in Fig. 4, comprising two different parts to be welded.
• the method as shown in Fig. 3 comprises a step of selecting of a welding technology and welding equipment and subsequently providing of data, relating to parameters of the selected welding technology and welding equipment, including type and power of a welding source, power distribution, welding electrode feed rate.
• data could be obtained by respective scanning means and/or inputted by operator.
• the method comprises a step of generating, via a computing means, of a welding pattern basing on data relating to the geometry of welded products, the material of welded products and the parameters of the selected welding technology and welding equipment.
• FactSage is used to calculate phase distribution for the given alloy composition, including the equilibrium temperatures of liquidus, solidus and solvus, which are corrected using Guliver-Scheil model to take into account the kinetics of cooling process.
• SYSWELD is used to find the evolution of temperature and stress-strain fields. It also uses the calculation of FactSage through temperature-dependant thermo-mechanical properties. As output, one has the distributions of stresses, strains, and temperatures at each time moment of the welding process. This information is used in the proposed post-processing tool to make the recommendation whether the welding could be successful or not.
• the present invention provides for generation, via a calculation means, of a welding pattern basing on data relating to the 3D geometry of welded products, material of the welded products and the parameters of the selected welding technology and welding equipment, and performing a virtual welding in the form of a numerical simulation, e.g., by using a set of software modules, such as Thermocalc, FactSage, SYSWELD, ANSYS, LS-DYNA and the like.
• the welding pattern comprises: 1) a geometrical CAD model (see Fig.4), obtained by respective software means for example: SolidWorks, Pro/ENGI EER, CATIA, NX etc.; 2) a finite element model based on the CAD model (see Fig. 5); 3) a welding technology and welding equipment model, defining a size and a form of welding pool, for example as a Goldak's double ellipsoid, 4) whole set of additional welding pattern parameters, comprising at least power of welding equipment, electrode movement speed, sizing of the a Goldak's double ellipsoid, a pre-heating temperature, a composition of products to be welded, thermal properties of welded materials (e.g. temperature-dependent specific heat, density etc.), temperature-dependent thermo- mechanical properties (e.g. linear expansion coefficients, elastic moduli and constitutive behaviors thereto.
• a geometrical CAD model obtained by respective software means for example: SolidWorks, Pro/ENGI EER, CATIA, NX
• the method of Fig. 3 comprises performing, via a computing means, a process of virtual welding using said welding pattern to determine the parameters of the stress-strain state, temperature field and phase distribution for each section of a welding bead or a heat-affected zone at any time moment of the welding process.
• a virtual welding generally shall be considered as computer implemented numerical solving of a coupled thermo-mechanical problem including metallurgical/phase transformations.
• the virtual welding process is performed by a computing means basing on said computed welding pattern to determine predictive parameters of the stress-strain state, temperature field and phase distribution for one or more sections, preferable for each sections, of the welding joint and heat-affected zone at any time moment of the welding process.
• the example results of such virtual welding implementing are shown in Fig. 6 to 9, comprising a temperature distribution at a certain time moment after onset of welding, a von Mises stress distribution at a certain time moment after onset of welding, a distribution of tensile stresses (a yy ) at a certain time moment after onset of welding and a distribution of plastic strains (von Mises) at a certain time moment after onset of welding.
• the performing of the virtual welding will result in obtaining parameters of the stress-strain state, temperature and phase distribution for each section of a welding bead or a heat-affected zone at a given time moment (As shown in Fig. 6 to 9).
• Said virtual welding is coupled with a determining of weldability properties of superalloys under given conditions.
• a weld cracking criterion also referred as solidification cracking, which occurs at any time moment of the welding process, when there are a) tension stresses, and/or b) extending motions above the critical value in two-phase region aft the welding source;
• a liquation cracking criterion (caused e.g. carbide liquation) which occurs in the heat-affected zone by passing eutectic reaction: ⁇ + MeC ⁇ ⁇ + MeC + liquid, where ⁇ is the metal phase, MeC is a carbide phase stable at given conditions (e.g. NbC).
• ⁇ is the metal phase
• MeC is a carbide phase stable at given conditions (e.g. NbC).
• all criteria shall be included in a predetermined interval, however, it is possible to provide respective determining behavior for each criterion, for example a faulty fusion criterion, i.e. that the presence of metal areas in which temperature was never above the liquidus temperature during the whole welding process, shall be placed to zero.
• a notification is provided about possibility of obtaining high-quality welded products and welding of products is performed using the welding parameters determined during the process of virtual welding according to said welding pattern. Said welding will result in high quality product manufactured in optimal welding condition and free of defects (as shown in Fig. 11).
• Methods for welding of superalloy products are not limited specifically for the invention, and are known in the art. In particular, such method of welding is submerged arc welding, gas-shielded tungsten-arc welding, gas-shielded metal arc welding (MIG / MMA) etc.
• a warning and information is provided about the possibility of a welding defect and its location, and recommendations are provided for changing at least one welding parameter to correct said defect.
• the warning and information about the possibility of a welding defect and its location could be indicated using respective display means, as shown for example in Fig. 10 for an incomplete weld penetration occurred after welding)
• the method for a welding process control of Nickel-based superalloy products of claimed invention was applied for welding two superalloy sheets having length of 95 mm, width of 75 mm and thickness of 3 mm.
• the sheets ware made from Ni base alloy Inconel 718, having following composition:
• the CAD model as shown in Fig. 4 and the finite elements model as shown in Fig. 5 correspond to the welded product manufactured from said sheets.
• a welding process shall be performed along an X axis of Fig 4, starting from distal end.
• the TIG (tungsten inert gas) welding process with the following parameters was applied: energy per unit length 150 J/mm and welding speed of 5 mm/sec.
• the parameters of welding pool were: length 4 mm, width 3 mm, penetration 2 mm.
• Fig. 6 to 9 comprise a temperature distribution at a certain time moment after onset of welding, a von Mises stress distribution at a certain time moment after onset of welding, a distribution of tensile stresses (oyy) at a certain time moment after onset of welding and a distribution of plastic strains (von Mises) at a certain time moment after onset of welding.
• Said figures show the state at the moment of 5 sec after welding start.
• Fig. 10 shows that there is an incomplete weld penetration. This defect is caused by insufficient heating in said welding joint portions, as can be seen from Fig.
• the given example has demonstrated that the used welding pattern and computer implemented virtual welding process provide reliable results, allowing predicting the quality of welded products of Nickel-based superalloys.
• the selected welding parameters power of heat source and welding speed
• the selected welding parameters are appropriate for the given alloy composition, welding technology and geometry of the product to be welded and geometry of welding joint, and subsequent realize the welding process in optimal conditions.
• the invention will bring substantial economic benefit since the number of expensive trials and rejection of welded products will be significantly reduced or even eliminated.

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• 2012
  • 2012-04-12 RU RU2014145348A patent/RU2014145348A/ru unknown
  • 2012-04-12 EP EP12874269.9A patent/EP2836331A4/de not_active Withdrawn
  • 2012-04-12 WO PCT/RU2012/000281 patent/WO2013154451A1/en active Application Filing

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