Showing papers on "Heat-affected zone published in 1989"

Formation of acicular ferrite at oxide particles in steels

Abstract: Experimental steels similar in composition to structural grades were prepared from weld metal deposits to study the formation of acicular ferrite under conditions experienced in the heat affected zone for a range of welding processes. The formation of acicular ferrite under these conditions is found to be dependent on the presence of a suitable distribution of oxide inclusions > 0·4 μm in size. The characteristics and proportion of acicular ferrite in the microstructure also depend on the prior austenite grain size and cooling rate. The relationship between these factors is presented in a simplified quantitative model, which is supported by data from limited welding trials. Metallographic observations suggest that acicular ferrite forms in two stages. The first involves the formation of relatively large primary acicular ferrite plates by multiple nucleation at intragranular inclusion sites, and the second involves the formation of many smaller acicular ferrite grains that grow sympathetically from...

Ultrasonic welding of PEEK graphite APC-2 composites

Abstract: The ultrasonic welding process is modeled using a five part model that includes mechanics and vibration of the parts, viscoelastic heating, heat transfer, flow and wetting, and intermolecular diffusion. The model predicts that melting and flow occur in steps, which has been confirmed by experiments. The model also indicates the possibility of monitoring joint quality by measuring the dynamic mechanical impedance of the parts during welding, which has also been verified experimentally by indirectly monitoring the magnitude of the impedance. via measurements of both the power and the acceleration of the base. When the melt fronts of the energy directors meet, at the end of welding, the dynamic impedance of the composites' interface is shown to rise rapidly. This raises the possibility of developing closed loop control procedures for the ultrasonic welding of thermoplastic composites. Ultrasonic welding of polyetheretherketone (PEEK) graphite APC-2 composites produced joints with excellent strengths.

Apparatus and method of short circuiting arc welding

Abstract: Apparatus and method to reduce spatter and allow better semi-automatic welding in short circuiting arc welding of the type using a single D.C. power supply for causing a welding current to pass through a welding wire extending variable distances from a holder and between the welding wire and a workpiece at a molten metal pool on the workpiece. The welding current flows in response to an arc voltage while the welding wire is fed from the holder toward the workpiece whereby the welding wire is subjected to a succession of welding cycles each of which include an arcing condition during which the wire is spaced from the pool and a short circuit condition during which a molten metal ball formed on the end of the wire contacts the metal pool and then transfers from the wire to the workpiece by a necking action. In this type of welding operation, the invention involves the application of a preselected amount of energy into the wire during the arcing condition for each welding cycle, which preselected amount of energy slightly exceeds the known value of energy necessary to melt a given volume of metal to form a consistent molten metal ball onto the end of the wire. This constant energy is divided between the resistance heating of the wire extending from the wire holder and the anode heating caused by the arc during each arcing condition of a cycle. Consequently, constant energy is inputted to the end of the wire irrespective of changes in the amount of wire extension or stick-out.

Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels

Abstract: Theoretical and experimental investigations were carried out to determine the effect of process parameters on weld metal microstructures of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions. The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions investigated, the observed fusion zone structure ranged from duplex austenite (γ)+ferrite (δ) to fully austenitic or fully ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur. There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on the basis of the thermal cycles. The present investigation clearly demonstrated the potential of the computational model to provide detailed information regarding the heat transfer conditions experienced during welding.

Ultrasonic welding of thermoplastics in the far‐field

Abstract: Ultrasonic welding is one of the most popular techniques for joining thermoplastics because it is fast, economical, and easily automated. In near-field ultrasonic welding, the distance between the horn and the joint interface is 6 mm or less. This study investigated the near-field ultrasonic welding of amorphous (acrylonitrile-butadiene-styrene and polystyrene) and semicrystalline (polyethylene and polypropylene) polymers. High frequency ultrasonic wave propagation and attenuation measurements were made in order to estimate the dynamic mechanical moduli of the polymers. The estimated moduli were entered into a lumped parameter model in order to predict heating rates and energy dissipation. Experimental results showed that variations in the welding pressure had little effect on energy dissipation or joint strength; Increasing the amplitude of vibration increased the energy dissipation and the weld strength. For the semicrystalline polymers, increasing the weld time improved strength up to weld times greater than 1.5 s, where strength leveled off. For the amorphous polymers, the weld strength increased with Increasing weld time up to times of 0.8 s; for longer weld times, the power required was too high, causing overloading of the welder. Monitoring of the energy dissipation and static displacement or collapse provided valuable information on weld quality.

Turbine system having more failure resistant rotors and repair welding of low alloy ferrous turbine components by controlled weld build-up

Abstract: System for repairing worn surfaces of steam turbine components and especially high pressure turbine rotors, are disclosed. These systems include depositing a first layer of weld metal on a worn surface of the component, whereby a heat-affected zone is created. A second layer of weld metal is then deposited over the first layer using a greater amount of heat to temper at least a portion of the heat-affected zone produced by the first layer. The preferred embodiments include the use of gas tungsten arc welding for providing fine-grain size and more creep resistance, especially in the weld and heat-affected zone. The resulting build-up can be machined, for example into a blade fastening to produce a component having properties equal to or better than the base-metal alloy. The invention also provides a longer lasting turbine system, including rotors which have serrated steeples that are more resistant to failure.

More creep resistant turbine rotor, and procedures for repair welding of low alloy ferrous turbine components

Abstract: A more creep resistant turbine rotor and novel methods for repairing worn surfaces of Cr-Mo-V steam turbine components are disclosed. These methods include specified alloy compositions and welding procedures that minimize weld stresses and cracking. These alloys exhibit improved creep and fatigue properties and are preferably deposited using a gas tungsten arc welding procedure. Bead sequencing, cooling side plates and the use of run-off tabs are also disclosed for minimizing welding defects in turbine rotors and discs.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part I - theoretical analysis

Abstract: A computational and experimental study was carried out to quantitatively understand the influence of the heat flow and the fluid flow in the transient development of the weld pool during gas tungsten arc (GTA) and laser beam welding of Type 304 stainless steel. Stationary gas tungsten arc and laser beam welds were made on two heats of Type 304 austenitic stainless steels containing 90 ppm sulfur and 240 ppm sulfur. A transient heat transfer model was utilized to simulate the heat flow and fluid flow in the weld pool. In this paper, the results of the heat flow and fluid flow analysis are presented.

Application of continuous cooling transformation diagrams for welding of steels

Abstract: In the search for better and more consistent properties in steel welds, the study of microstructure versus mechanical properties has indicated a clear need for a more systematic and detailed presentation of the γ→α phase transformation reaction. The usual method of presenting such data is the continuous cooling transformation (CCT) diagram which relates the composition, cooling rate, and austenite grain size of the material to its γ→α. transformation temperature and resultant microstructure. Many hundreds of such diagrams have been produced throughout the world to describe the transformation behaviour of most grades of commercial steel when subjected to various heat treatment procedures. The majority of these diagrams are designed for typical industrial heat treatment processes, which usually involve re-austenitisation in the low temperature region of the austenite phase field (850–900°C), followed by continuous cooling by quenching, air cooling, or furnace annealing. Unfortunately, such diagrams ...

Method of making hemmed joints utilizing laser welding

Abstract: Methods of laser welding zinc coated galvalized steel are disclosed. In a method that relates to forming hem joints for motor vehicle body components a sheet of steel is provided with a plurality of V-shaped tabs. When a hem joint is formed the V-shaped tabs together with a surface of another sheet of steel form gas venting channels that provide an escape passage for gas vapors that are developed when the zinc coating is vaporized by laser welding. In another method of laser welding, one of the steel sheets has an axially extending wall that is V-shaped to provide a V-shaped groove and the wall has spaced gas vent holes.

Apparatus for short circuiting arc welding

Abstract: An improvement in a short circuiting arc welding apparatus comprising a single D.C. power supply causing a welding current to pass through a welding wire extending from a holder and between said wire and workpiece at a molten metal pool on the workpiece, wherein the current flows in response to an arc voltage and the welding wire is subjected to a succession of welding cycles. Each of the welding cycles includes an arcing condition during which said wire is spaced from the pool and the energy applied to said wire exceeds a given value raising the temperature at the end of the wire to a molten temperature to form a molten metal ball on the end of the wire and a short circuit condition during which the molten metal ball on the end of the wire first contacts said molten metal pool and then transfers from the wire to the workpiece by a necking action breaking the molten metal ball from the wire to initiate an arc in a subsequent welding cycle. The welding cycles have a generally fixed frequency of repetition. The improvement comprises providing the power supply with a chopper circuit for applying a succession of input current pulses across the wire and workpiece at a pulse frequency substantially greater than the generally fixed frequency of repetition of the welding cycles and a pulse width changing circuit for adjusting current flow between the wire and the workpiece many times during each of the welding cycles.

Metal Transfer in Gas Metal Arc Welding: Droplet Rate A study of droplet rates for various transfer modes verifies optimum operating parameters

Abstract: This study reports the changes in droplet-trans fer mode and rate during gas metal arc welding as the voltage is varied at a series of current levels. The droplet-transfer rate was found to be maximum (approximately 100 s_1) for the voltage/current combi­ nations that are normally suggested by the electrode manufacturers and are con­ sidered optimum in the judgment of experienced welders. At voltages above or below the TV-wide optimum range, the transfer rate decreased by about 10 s_1 per V in the vicinity of the optimum condition. Furthermore, statistical analysis of the arc current and voltage data showed that during operation outside the optimum range, the welding arc was unstable and the current output was very irregular with varying cycle time between each droplet transfer. At the maximum droplet-transfer rate, the droplet-transfer cycle time was very consistent and revealed a narrow rate range, which correlated with the high stability and lower spatter at these optimum operating conditions. The possibility of using the concept of maximum droplet-transfer rate range with minimum rate fluctuation and corresponding arc current-voltage signals as a means of short-circuiting welding process control and automation is being considered. At voltages below the optimum range, high-speed video recording confirmed that the short- circuiting transfer was very unstable and the arc reignited explosively. Above the optimum voltage, the arc became longer and the droplets became visibly larger, with mixed globular and short-circuiting transfer. The droplets, however, were no longer directed uniformly to the weld pool, resulting in increased spatter. arc (FCA), submerged arc (SA) and gas tungsten arc (GTA) welding. With the exception of GTA welding, all these pro­ cesses require a consumable electrode, which has the dual function of carrying the current that heats the weld pool and providing filler metal to complete the weld joint. This dual function has long been a topic of research. Spraragen and Lengyel (Ref. 1) reviewed the basic princi­ ples of an electric arc and summarized the development of the field of welding arc physics. In particular, they concluded that in the area of liquid metal transfer from the electrode to the weld pool, the electromagnetic pinch force, gravity, shielding gas drag force and surface ten­ sion are the major forces that act on the electrode tip. Using high-speed cinemat­ ographic techniques, Muller, Greene, and Rothschild (Ref. 2) found that large spher­ ical liquid-metal droplets in a GMA arc decreased in size with increasing current. As the electrode feed rate was continu­ ously increased, however, a sudden decrease in droplet size occurred at what was termed the transition current. In addition, they determined that with inert gas shielding, the droplet composition remained constant during the metal trans­ fer. Lesnewich (Refs. 3-5) investigated the physics of arc welding using SMA and CMA welding. Particularly, he studied the effects of welding process parameters such as current, voltage, electrode polar-

Finite-element modeling of heat flow in deep-penetration laser welds in aluminum alloys

Abstract: A two-dimensional finite-element nonlinear transient heat conduction model was developed and used to simulate deep-penetration keyhole laser welds in aluminum alloys. The weld thermal profiles were calculated in an arbitrary reference plane as the laser beam approached and passed the plane. From the calculated thermal profiles, three-dimensional quasi-steady-state shapes of the weld pools were determined. The predicted weld bead shape and dimensions were in good agreement with the experimental results. The experimental laser welds in aluminum alloys contained large amounts of porosity. The model predicted large mushy zones for aluminum laser welds during solidification, which in turn increase the probability of porosity formation by increased bubble entrapment.

Welding of parts separated by a gap using a laser welding beam

Abstract: A method for welding two portions of a cover for a torque converter at an overlap joint using a welding beam includes directing the welding beam at the radially outer cover in the vicinity of the overlap at an acute angle with the plane of the cover portions in the vicinity of the overlap. The angle is chosen so that the focal point of the welding beam is located on the radially outermost cover portion near the inner surface and distant from the outer surface. In this way, before fusion occurs, temperature gradients are induced through the thicknesses of the cover portions tending to reduce radial expansion of the outer cover and increase radial expansion of the inner cover. The effect of these thermal bending moments and the effect of the increase in mean temperature of the covers due to the welding beam combine to reduce or eliminate the thickness of the gap that exists before welding begins. The covers are held in position and moved relative to the welding beam at a rate that permits a hydraulically tight weld of high strength to be made between the covers.

Thickness effects in the vibration welding of polycarbonate

Abstract: In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. Past work on welding characterized the effects of weld parameters such as the weld frequency, the weld pressure, and the weld time, on the welding process and weld strength, and showed that the most important parameter affecting weld strength Is the weld penetration—the decrease in the distance between the parts being welded that is caused by lateral outflow of material in the molten film. However, those weld studies were based on specimens of constant nominal thickness (6.35 mm, 0.25 in). This paper is concerned with the effects of specimen thickness on the weld process and weld strength.

Pulse MIG welder for welding thin-walled copper-nickel pipe

Abstract: A welding station for welding thin-walled copper-nickel pipe. An electronic welding station (10) has an output circuit (13) which provides arc welding power having the arc characteristics specified by a weld parameter selection circuit (12). A welding torch and feeder assembly (11) has a controller (20) which is responsive to a predetermined event, such as the passage of time since the start of the arc, or the average temperature of the pipe (25) as indicated by two temperature-measuring devices (30, 32). The controller (20) adjusts the wire feed speed, the pulse frequency, the pulse width, the welding voltage, the welding current and/or other parameters so as to cause the arc to have the parameters most desired for welding copper-nickel pipe. The present invention provides for a hotter arc for starting the welding operation, thereby obtaining good penetration and bonding, and a cooler arc for continuing the welding operation, thereby preventing burn-through of the pipe (25).

Austenite grain growth, microstructure and hardness in the heat-affected zone of a 2.25 Cr-1Mo steel

Abstract: Submerged arc weldings were made on thick plates of a 2.25 Cr-1Mo steel (where the composition is in approximate weight per cent), using different heat inputs in the range 1.1–5.8 MJ m−1. The microstructures in the heat-affected zone (HAZ) were identified, and the austenite grain size and hardness were measured. The microstructure is predominantly bainitic, but some martensite was observed at low heat inputs. The observations in real weldings were compared with those made in welding simulations, using dilatometric tests. In these, the relevant transformation temperatures were determined. The austenite grain size was correlated to the thermal cycle, which was experimentally obtained at one point of the HAZ in each welding experiment. The grain size D, obtained by the linear intercept method, is well described by the kinetic equation Dn−D0n = kI where I is the “kinetic strength” of the thermal cycle which depends on the activation energy Q for grain growth. A method based on the dilatometry results was developed which allows the determination of the grain growth exponent n, independently of Q. With this method, we obtained n = 3.17. This is consistent with the welding data. The best value of Q was found to be 180 kJ mol−1. The grain size in welds was found to be comparable with that measured in the dilatometric specimens, for the same “kinetic strength” of the cycles.

Welding apparatus coated with spatter-resistant and electrically conductive film

Abstract: A welding contact tip or a weld nozzle is provided with a coating comprising a film of tungsten disulfide or other low friction material. The film provides resistance to weld spatter without interrupting electrical contact between the contact tip and electrode wire.

Welding of coated metals

Abstract: The invention provides a method and apparatus for welding together two metal workpieces, at least one of which has thereon a coating material which enters a fluid or visco-elastic phase at a temperature below the melting temperature of the workpieces, the method comprising the steps of subjecting the workpieces to a preliminary preparative treatment at a zone to be welded and thereafter applying (preferably be means of a high-energy beam such as a laser beam) sufficient heat to the workpieces at the weld zone to effect there the welding together thereof, wherein the preliminary preparative treatment comprises preheating the workpieces to the said lower temperature and pressing them together, at the zone to be welded, with a force sufficiently great to expel coating material from between the workpieces at the weld zone, thereby to improve the quality of the subsequent weld.

System for control of weld arc development

Abstract: A method of welding metals wherein the size and shape of a weld pool as w as the traversing of the arc from one metal to the other is commanded magnetically by predetermined data, which data is updated by observing and characterizing isotherms in the weld pool, comparing the observed isotherms with a predetermined set of desired isotherms and then updating the command data for optimum performance.

Method of submerged arc welding a thick steel plate with large heat input and submerged arc welding flux

Abstract: A method of submerged arc welding of thick steel plates with a large heat input and flux for submerged arc welding which comprises: forming a groove having a multi-angle shape which has at least two different angular inclination when a single side submerged arc welding for perfect penetration is conducted under a condition of an welding heat input of 100 to 1000 kJ/cm; using submerged arc welding flux SiO2 : 5 to 28% by weight, MgO: 15 to 35% by weight, CaO: 5 to 15% by weight, CaF2 : 2 to 20% by weight, Al2 O3 : 5 to 15% by weight, and TiO2 : 2 to 10% by weight as the main components, and containing iron powder by 30% by weight or less and either or both of Si and Mn in the metallic form by 10% by weight, the submerged arc welding flux having a particle size distribution arranged such that the proportion of the particle size distribution arranged such that the proportion of the particle which have a size finer than 36 mesh is 20% by weight or less and the proportion of the particles which have a size 14 mesh or finer but 36 mesh or rougher is 60% by weight or more; and conducting the welding.

Spray mode gas metal arc welding process

Abstract: A spray mode gas metal arc welding process employing a shielding gas mixture consisting essentially of (A) 3 to 8 volume percent carbon dioxide, (B) 30 to 40 volume percent argon and (C) the balance helium

Friction welding apparatus

Abstract: A friction welding apparatus for preparing weldments by fictional contact of the weld members which includes sensors for measuring torque, axial forces, and other variables important to the control of the welding process, and for facilitating the obtainment of process information useful in correlating process conditions with weld quality. The apparatus includes means for the substantially frictionless coupling of the component providing the axial normal force on the aligned shafts upon which the weld pieces are mounted. The coupling, which contributes to accurate torque measurements, comprises a substantially frictionless, single-contact-point coupling provided by the point of contact between two adjacent spherical surfaces. The welding apparatus is also provided with a vacuum-braked air drive assembly for substantially instantaneously stopping relative rotation between the weld members after fusion of the members has occurred, thereby preventing undesirable over-run and resulting stress formation in the weld zone.

Hot-rolled Steel Sheet with Excellent Flash Weldability for Automotive Wheel Rim Use

Abstract: As for the steels for wheel rim, CC killed steel will be more prevalent instead of rimmed steel in accordance with the increase of CC ratio in steel production. In addition, from the point of weight reduction of cars, high strength steels are tried to put into practice. As far as wheel rim is concerned, flash weldability is very important as well as formability of steels.In this report, flash weldability of CC killed steel, HSLA (High Strength Low Alloy) and DP (Dual Phase) steels are investigated. In flash welding of CC killed steel, control of Al content, in addition to Si and Mn contents, is found to be required in order to avoid the detect formation due to Si-Mn-Al oxide. On the other hand, coiling temperature is important in high strength steels, especially DP steels, in order to prevent softening of weld heat affected zone.

A Newly Developed Ti-Oxide Bearing Steel Having High HAZ Toughness

Abstract: A study was carried out on the transformation characteristic of a newly developed Ti-O steel in comparison with that of ordinary steels. The microstructure of the weld heat affected zone (HAZ) in the Ti-O steel is characterized by the formation of intragranular ferrite plate (IFP), or so-called acicular ferrite, which was found to start from titanium sesquioxide (Ti 2 O 3 ) particles dispersed in the matrix of the steel. The welding thermal cycle simulation test on the Ti-O steel showed that IFP development takes place over a wide range of conditions such as heating temperature and chemical composition. The high stability of Ti 2 O 3 particles at high temperature explains the effect of the former condition. The effect of the latter can be well understood from the distribution of Ti 2 O 3 particles, which is irrelevant to the microsegregation of alloying elements such as manganese and niobium. IFP formation restricts development of ferrite side plate, refines the effective grain size, and improves HAZ toughness. Various experimental results suggested that the Ti 2 O 3 particle has an IFP formation function through the manganese sulfide (MnS) attached on it.

New results on the spin welding of plastics

Abstract: Short welding times make spin welding particularly suitable for mass production. This paper presents an analysis of the friction phase, which makes it possible to estimate the influence of the welding parameters and the material being welded on the temperature in the welded zone, the melt rate, and the torque in the spin welding of semicrystalline thermoplastics. A comparison of experimental and calculated results shows an acceptable correlation. In addition, the influence of speed, axial pressure, and braking on the weld seam quality of different amorphous and semicrystalline thermoplastics is discussed.

A Study on Heat and Mass flow in Stationary Gas Tungsten arc Welding using the Numerical Mapping Method

Abstract: The phase changing problem at the liquid-solid interface that occurs during stationary gas tungsten arc (GTA) welding has been studied by considering the four driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, the aerodynamic drag force and the surface tension force at the weld pool surface. In the numerical simulation, difficulties associated with the irregular shape of the moving interface have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the liquid-solid boundary. This method also has the capacity to handle the time-dependent changing solution domain of the moving boundary problem and could be applied effectively to this transient weld pool development problem with the moving boundary and phase change condition.