Showing papers on "Heat-affected zone published in 1994"

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—I. Haz temperature and strain rate distribution

Abstract: The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part I the different components of the model are outlined and analytical solutions presented which provide quantitative information about the HAZ temperature distribution for a wide range of operational conditions. Moreover, a general procedure for modelling the HAZ strain rate distribution has been developed by introducing a series of kinematically admissible velocity equations which describe the material flow fields in the radial, the rotational, and the axial direction, respectively. Calculations performed for both types of materials show that the effective strain rate may exceed 1000 s −1 in positions close to the contact section due to the high rotational velocities involved. Application of the model for evaluation of the response of AlMgSi alloys and AlSiC metal matrix composites to the imposed heating and plastic deformation is described in an accompanying paper (Part II).

Interactive laser welding at elevated temperatures of superalloy articles

Abstract: A process is provided for laser welding a superalloy article (20) by pre-heating the entire weld area and region adjacent to the weld area of the article to a ductile temperature within the range of 1400-2100 degrees F with an induction heat coil (14) and maintaining such tem-perature during welding and solidification of the weld; and welding the preheated ar-ticle using a laser (11) with a powder al-loy feed (12), with a control system which controls the laser powder feed (12) and a motion system on which the article is fix-tured, wherein the control system includes a vision system which digitizes the weld area of the article (20) providing a path for the laser to follow.

Control of Microstructures and Properties in Steel Arc Welds

Abstract: Control of Microstructures and Properties in Steel Arc Welds provides an overview of the most recent developments in welding metallurgy. Topics discussed include common welding processes, the thermal cycle during welding, defects that may occur during the welding process, the metallurgy of the material, metallurgical processes in the heat-affected zone and the fused metal, and the relationship between microstructures and mechanical properties. The book's final chapter presents examples of welded joints, illustrating how modern theories are capable of predicting the microstructure and properties of these joints. This book is an excellent resource for welding engineers, metallurgists, materials scientists, and others interested in the subject.

Porous coated implant and method of making same

Abstract: The method forms a thin layer of metal mesh (14) on the surface (12) of the implant (10) for the bonding with a porous surface layer (16) to prevent the formation of notches within the body of the implant (10) The layer of metal mesh (14) can be formed by a number of known methods including conventional welding processes such as arc welding, resistance welding, electron beam welding, laser beam welding, friction welding, ultrasonic welding, cladding The porous metal surface layer (16) is preferably formed from titanium wire or titanium beads in a known process The porous surface layer (16) is bonded by a known process such as diffusion bonding, sintering, welding, or cladding By bonding the porous surface layer (16) to the thin layer of metal mesh (14), notches normally formed in the body of the implant (10) are substantially eliminated Therefore, the designer of the implant (10) is not limited as to the location and amount of porous surface layer (16) to be placed on the implants (10)

Vision-based weld pool width control

Abstract: Methods for controlling weld penetration for arc welding processes from top-side measurements have long been sought. One indirect variable that has been reported to correlate with penetration is weld pool geometry. A system which uses weld pool geometry sensing for controlling weld penetration is described in this paper. The system uses a miniature camera mounted in a modified coaxial viewing torch to view the weld pool. A robust machine vision algorithm has been developed for this system to measure weld pool width. The algorithm was designed to locate the edges of the weld pool despite the presence of other edges caused by the heat affected zone, scratches, marks, and weld pool impurities. The algorithm uses a matched edge filter and a majority voting scheme to measure the width of the pool. A control system was developed to regulate weld pool width in the presence of disturbances caused by such items as incorrect parameter settings, small variations in material composition, and material thickness changes. Experiments were conducted to test the control system by simulating some of these disturbances. The experiments demonstrated that for certain classes of materials, this technique works quite well. However, for other materials such as stainless steel 304,more » surface impurities in the weld pool visually obscure the weld pool and its edges to such a degree that the system fails to lock onto the edges of the pool.« less

A Study on the Three-Dimensional Analysis of Heat and Fluid Flow in Gas Metal Arc Welding Using Boundary-Fitted Coordinates

Abstract: Computer simulation of three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding has been studied by considering the three driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, and the surface tension force at the weld pool surface. Molten surface deformation, particularly in the case of GMA welding, plays a significant part in the actual weld size and should be considered in order to accurately evaluate the weld pool convection. The size and profile of the weld pool are strongly influenced by the volume of molten electrode wire, impinging force of the arc plasma, and surface tension of molten metal. In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary. The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously.

Plasma arc welding apparatus and welding method using the same

Abstract: A plasma arc welding apparatus which includes a plasma torch, and a space retaining member fixed to the plasma torch and positioned at a free end portion thereof between a free end of the plasma torch and a material to be welded, and which is used to carry out a welding operation by pressing the free end portion of the space retaining member against the material to be welded. A plasma arc welding method used to carry out a welding operation by pressing a free end portion of a space retaining member against a material to be welded, by using a plasma arc welding apparatus including a plasma torch, and a space retaining member fixed to a base portion of the plasma torch and positioned at a free end portion thereof between a free end portion of the plasma torch and a material to be welded.

Infrared sensor for top face monitoring of weld pools

Abstract: The development of a novel sensor for the measurement of bead size in tungsten inert gas (TIG) welds is described. A passive vision-based sensor combines infrared imaging of the weld pool and selective optical filtering, both to reduce excessive arc glare and improve contrast between weld pool and heat affected zone (HAZ). The arc interruption and external illumination techniques, used by others, are not required. Image quality is shown to be comparable to that obtained with external illumination and superior to that of arc interruption methods. The technique has been successfully applied to both pulsed and continuous TIG welding of stainless steel in order to maintain the bead size during a welding run.

The influence of electron-beam welding parameters on heat-affected-zone microfissuring in INCOLOY 903

Abstract: The microfissuring in the heat-affected zone (HAZ) of electron-beam-(EB-) welded thermomechanically processed INCOLOY 903 has been studied with a view to reducing the incidence of microfissuring and to obtaining a better understanding of the influence of EB welding parameters on it. For a given heat of material, microfissuring susceptibility has been quantitatively related to EB welding parameters and the shape of the weld pool. Fractional factorial experimental study of welding parameters showed that a reduction in welding speed and an increase in EB current for a given heat input would minimize HAZ microfissuring in the alloy. It was observed that with lower travel speeds, bccause of the shallower temperature gradients in the HAZ, the amount of liquated grain boundary area is less, thus leading to decreased microfissuring. Considerable HAZ microfissuring was observed on the coarse grain boundaries of warm-worked grains. The microfissures appeared to initiate in regions slightly removed from the fusion line. Minimal microfissuring was observed on the grain boundaries of fine recrystallized grains. These boundaries, however, had a thickened appearance bccause of the formation of Nb-enrichedy phase by the process of grain boundary liquid film migration (LFM). The origin of the liquid on the grain boundaries is suggested to be due to the constitutional liquation of preexisting primary carbides (partial), fine MC carbides, and MNP-type phosphides. It is suggested that substantial occurrence of LFM in the HAZ minimizes microfissuring by decreasing the total temperature range of solidification and also by enabling the grain boundary liquid to solidify without the occurrence of low-melting terminal eutectic reaction.

Welding gas purging apparatus and method

Abstract: An apparatus and method for purging reactive gases from the vicinity of a molten weld during the welding process, having particular application to the welding of industrial process piping systems and pipelines, especially stainless steel and other alloy pipelines. A system is disclosed for boosting purging speed and efficiency by providing a multidirectional flow of purging gas adjacent to the interior walls of the pipe sections being joined. The rate of purge gas flow is automatically adjusted in response to changing gas pressures in the vicinity of the progressing weld.

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—II. Haz microstructure and strength evolution

Abstract: The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part II the heat and material flow models presented in the first paper (Part I) are utilized for prediction of the HAZ subgrain structure and strength evolution following welding and subsequent natural ageing. The modelling is done on the basis of well established principles from thermodynamics, kinetic theory and simple dislocation mechanics. The models are validated by comparison with experimental data, and are illustrated by means of novel mechanism maps. These show the competition between the different process variables that contribute to microstructural changes and strength losses during friction welding of AlMgSi alloys and AlSiC metal matrix composites.

Method and device for ultrasonic welding

Abstract: A method and a device for modifying the energy-applying surface of an ultrasonic welding horn to join two complex thermoplastic parts by applying a thin film to the surface of the horn is disclosed. The thin film is applied to insure that a proper weld occurs along a complex and intricate pattern of energy directors located between the parts.

Process and apparatus for welding sheet metal edges

Abstract: Sheet metal edges to be welded are preheated prior to welding. At a given welding speed, this results in a smaller temperature gradient in the material to be welded. Consequently the welding speed can be increased, or material which would otherwise provide poor weld quality can be welded at a high temperature gradient. The preheating is carried out for example by high-frequency excitation of the material to be welded.

CO2 shielding gas effects in laser welding mild steel

Abstract: The most widely used shielding gases for laser welding of steels are helium and argon. Helium produces significantly more penetration than argon in penetration‐mode laser beam welding. Another gas that has been proposed as an alternative to these inert gases is carbon dioxide. The benefits of using carbon dioxide as a shielding gas for laser welding are that it costs less than helium and argon and that it provides nearly the same penetration as helium. The major drawback to its use as a shielding gas for mild steel is that it can cause porosity and other weld discontinuities. In this investigation helium and carbon dioxide were investigated as shielding gases in the laser welding of a fully killed 1018 steel, a semikilled 1018 steel, and an unkilled 1018 steel. Helium was generally found to produce discontinuity‐free welds, although small quantities of very fine centerline porosity were observed in the fully killed and semikilled steels. Carbon dioxide was found to provide an average of 70% of the penetration obtained with helium. The surface appearance and formation of porosity in welds made using carbon dioxide shielding was found to be dependent on the amount of deoxidizing element in the weld pool. While porosity‐free welds were formed in the semikilled steel (0.22% Si), low silicon or other deoxidizer content resulted in poor surface appearance and entrapped porosity in both the fully killed and unkilled steels in this investigation, presumably due to the formation of carbon monoxide in the weld pool. The addition of ferrosilicon powder to the weld pool effectively controlled the formation of carbon monoxide in these welds and resulted in porosity‐free welds with carbon dioxide shielding. The results of this investigation indicate that carbon dioxide can be used as a cost‐effective shielding gas for penetration‐mode welding of carbon steels. It was found that sufficient levels of deoxidizing elements must, however, be available in the molten pool to control porosity.

The use of supercomputer modelling of high-temperature failure in pipe weldments to optimize weld and heat affected zone materials property selection

Abstract: The creep deformation and damage evolution in a pipe weldment has been modelled by using the finite-element continuum damage mechanics (CDM) method. The finite-element CDM computer program Damage xx has been adapted to run with increased speed on a Cray XMP/416 supercomputer. Run times are sufficiently short (20 min) to permit many parametric studies to be carried out on vessel lifetimes for different weld and heat affected zone (HAZ) materials. Finite-element mesh sensitivity was studied first in order to select a mesh capable of correctly predicting experimentally observed results using the least possible computer time. A study was then made of the effect on the lifetime of a butt welded vessel of each of the commonly measured material parameters for the weld and HAZ materials. Forty different ferritic steel welded vessels were analysed for a constant internal pressure of 45.5 MPa at a temperature of 565 degrees C; each vessel having the same parent pipe material but different weld and HAZ materials. From these studies it has been concluded that good creep rupture ductility and strength of the weld material are necessary to achieve long vessel lifetimes. Vessel lifetimes are not strongly influenced by the HAZ material properties provided that the rupture strength is maintained above that of the parent pipe material, and that the ductility is greater than one half of that for the parent pipe material. Also it is found that the optimum design can be achieved with both the weld and the HAZ materials having properties of high primary creep strain, mean secondary creep strain, mean rupture strain, and long rupture lifetime, relative to the base or parent pipe material. A lifetime improvement has been demonstrated of 30% over that obtained for the initial materials property data. A methodology for weldment design has been established which uses supercomputer-based CDM analysis techniques; it is quick to use, provides accurate results, and is a viable design tool.

Welding method for rotatable shafts

Abstract: An improved welding method is provided for repairing broken rotors. The welding method preferably employs a 2.25Cr-1.0Mo-0.3V-type filler metal, preferably deposited using a narrow groove welding technique. The broken pieces are aligned end to end. A narrow groove is formed to substantially remove the end surfaces. The groove is preheated, filled with the welding filler metal, and postheated, resulting in a strong, high temperature resistant, long lasting weld.

Arc instability phenomena in GMA welding

Abstract: This paper analyzes arc and metal transfer instability phenomena in GMA welding that depend on arc length, the oxidizing potential of the shielding gas and the power supply V/I characteristic. The instability process was associated with abrupt changes in arc current and voltage levels and could seriously affect operation by causing repulsive globular transfer in short circuiting conditions. As instability effects were observed for oxygen levels up to approximately 2%, it can be significant in applications that demand a how oxidizing gas media, as in the welding of alloy steels and nonferrous alloys. The experimental program consisted of two sets of trials using either constant voltage or constant current operation

Heat input and dilution effects in microalloyed steel weld metals

Abstract: The sensitivity of weld metal microstructure and mechanical properties to variations in both heat input (i.e., cooling rate) and weld dilution in submerged arc (SA) welding of microalloyed steel was examined. Weldments were prepared with weld metal dilutions of approximately 40% and 70% at heat inputs of 2.0, 3.3, 4.6, and 5.3 kJ/mm, using two commercial welding wires and a basic commercial flux. The high dilution welds, which were ordinary bead-on-plate welds, resulted in microstructures that ranged from ferrite with aligned second phase at low heat inputs to acicular ferrite at high heat inputs. Special over-welding techniques were used to make the low dilution welds, allowing use of the same welding parameters as those for the high dilution welds. The technique involved remelting of weld metal to simulate the effect of multipass welding. The microstructure of these welds was predominantly acicular ferrite, independent of heat input. As a consequence, the low dilution welds had superior toughness compared to the high dilution welds.

Simultaneous temperature measurements on laser welded seams with at least two pyrometers in relation to monitoring process parameters and weld quality

Abstract: In laser butt welding of metal sheets, in particular sheets of unequal thicknesses, the temperature is measured at two points behind the liquid-solid interface. From combination of the two readings obtained a series of process data can be derived whereby the welding process can be monitored.

Pipe making welding method of clad stainless steel pipe

Abstract: PURPOSE: To provide a welding method of a seam weld zone in the case of production of a clad stainless steel pipe by a method, such as UOE, from a clad steel consisting of an austenitic stainless steel having excellent corrosion resistance as a base metal on an inside surface side and a low alloy steel having excellent strength as a base metal on an outside surface side. CONSTITUTION: The seam part 3 of the clad steel is subjected to edge prepn. of a double Vee shape of which the depth of the groove 4 on the inside surface side is 80 to 130% of the thickness of a cladding metal 2, the angle is 60 to 80°, the route thickness is 3 to 5mm and the angle on the outside surface side is 60 to 80°. The groove part 5 on the outside surface side is subjected to tack welding with a welding wire for the low alloy steel; thereafter, the inside and outside surfaces are subjected to submerged arc welding with one pass. As a result, the inside surface weld zone free from the defects occurring in component dilution is obtd. COPYRIGHT: (C)1995,JPO

Plasma arc augmented laser welding

Abstract: The authors describe a technique of arc augmentation to increase the capability of the laser during laser welding. The novel process, Plasma Arc augmented Laser Welding, is still under development.

Heat transport in melt flowing past the keyhole in deep penetration welding

Abstract: A theoretical analysis is carried out on the transfer of heat into the workpiece in deep penetration welding. Special attention is given to the effect of melt flow on the transfer efficiency. It is found that the widely used model by Noller, which disregards the melt flow past the keyhole, overestimates the heat transfer. The difference is most significant at high welding speeds. The temperature distribution obtained in this work is more confined, leading to a shorter weld pool.

Microstructures in hot wire laser beam welding of HY 80 steel

Abstract: Laser beam welding of 13 mm plates of HY 80 steel resulted in different microstructures in the fusion zone depending on the welding process. Autogenous welds resulted in an untempered martensitic structure, whereas, with the introduction of a hot wire filler metal, the microstructures depended on the wire feed. A slow feed resulted in a mixed martensite–bainite microstructure and a fast wire feed resulted in a microstructure that is primarily acicular ferrite. The chemistry of the as deposited weld metals was different in each case. The thermal profiles for the autogenous weldment were calculated based on a two parameter model of laser welding that utilises the fusion zone boundary as a measure of ‘best fit’. Based on the cooling rate of the autogenous fusion zone, cooling rates for the two welds with hot wire filler metal were rationalised. Using these cooling rates, the chemistry of the weld metal and a model of microstructural development of the weld metal, a computer calculation was made which...