Showing papers on "Heat-affected zone published in 1990"

The effect of alloy composition and welding conditions on columnar-equiaxed transitions in ferritic stainless steel gas-tungsten arc welds

Abstract: The columnar-equiaxed transition (CET) was investigated in full penetration gas-tungsten arc (GTA) welds on ferritic stainless steel plates containing different amounts of minor elements, such as titanium and aluminum, for a range of welding conditions. In general, the fraction of equiaxed grains increased, and the size of the equiaxed grains decreased with increasing titanium contents above 0.18 wt pct. At a given level of titanium, the equiaxed fraction increased, and the size of the equiaxed grains decreased with increased aluminum content. The CET was ascribed to heterogeneous nucleation of ferrite on Ti-rich cuboidal inclusions, since these inclusions were observed at the origin of equiaxed dendrites in the grain refined welds. Titanium-rich cuboidal inclusions, in turn, were found to contain Al-Ca-Mg-rich inclusions at their centers, consistent with observations by previous investigators for other processes. The welding conditions, in particular, the welding speed, were observed to affect the occurrence of the CET. Increasing the welding speed from 3 to 8 mm/s increased the equiaxed fraction noticeably, but a further increase in speed to 14 mm/s had a smaller additional effect. A finite element model (FEM) of heat transfer was used to examine the role of the welding conditions on the local solidification conditions along the weld pool edge. The results are compared with existing models for the CET.

Reinforced solder, brazing and welding compositions and methods for preparation thereof

Abstract: A solder, brazing or welding composition having improved physical properties, comprising a continuous phase ranging from about 40% to about 99% by volume of a solder, brazing or welding metal or alloy, and a disperse phase ranging from about 60% to about 1% by volume and comprising a reinforcing material in particulate or fibrous form, the reinforcing material being graphite, silicon carbide, a metal oxide, an elemental metal, and/or a metal alloy A process for preparing the composite comprises providing a solder, brazing or welding metal or alloy, melting the metal or alloy, cooling the metal or alloy to a semi-solid state, subjecting the metal or alloy to vigorous shearing while in the semi-state, adding a reinforcing material as defined above to the metal or alloy during at least one of the cooling and shearing steps in an amount ranging from about 60% to about 1% by volume of the total volume, the reinforcing material being and remaining in particulate or fibrous form as a disperse phase, and solidifying the resulting composite The composite may have a non-dendritic microstructure or may be amorphous

Basic metal cored electrode

Abstract: A consumable welding element for arc welding comprising a steel sheath surrounding a compacted core containing metal alloying powders and an essentially 100% basic compound in an amount less than about 1.60% of the total weight of said element. The basic compound is calcium fluoride powder which is preferably in the range of about 0.1% to about 0.9% calcium fluoride powder by total weight of the element. As another feature the core of the element contains a specific agent for decreasing the amount of diffusible hydrogen in the weld metal. This new element may be a filler metal for TIG welding; however, it is preferably a consumable electrode for MIG welding.

Weldability of aluminium-lithium alloy 2090 using laser welding

Abstract: Lithium-containing aluminium alloys are of considerable current interest in the aerospace and aircraft industries because lithium additions to aluminium improve the modulus and decrease the density compared to conventional aluminium alloys. Many such alloys are under development for aircraft applications, which usually involves mechanical fastening. While aluminium-lithium alloys are fusion weldable with gas metal arc, gas tungsten arc and electron beam processes, they suffer from problems of weld porosity, heat-tearing cracking, poor penetration and low joint efficiency. In this paper, the weldability of aluminium-lithium alloys is briefly reviewed. The weldability of commercial aluminium-lithium alloy 2090 in the peak-aged condition was studied using laser welding. The quality of the welds was evaluated through mechanical tests (hardness and tensile tests) and microscopical observations. Mechanical property data and microscopical observations of the welds on prior surface-prepared (milled) material revealed a low degree of the weld surface degradation and an absence of porosity. This coupled with the attractive joint efficiencies suggest the superiority of the laser welding to conventional arc welding of this alloy. The performance of laser-welded butt joints is rationalized.

Low hydrogen basic metal cored electrode

Abstract: A consumable welding element for arc welding comprising a steel sheath surrounding a compacted core containing metal alloying powders and an essentially 100% basic compound in an amount less than about 1.60% of the total weight of said element. The basic compound is calcium fluoride powder which is preferably in the range of about 0.1% to about 0.9% calcium fluoride powder by total weight of the element. As another feature the core of the element contains a specific agent for decreasing the amount of diffusible hydrogen in the weld metal. This new element may be a filler metal for TIG welding; however, it is preferably a consumable electrode for MIG welding.

Dimensionless maps for heat flow analyses in fusion welding

Abstract: In the present investigation, attempts have been made to bridge the various analytical heat flow models (i.e. the thick plate, the medium thick plate, and the thin plate solutions) by establishing dimensionless maps for a general outline of the quasi-stationary temperature distribution pertaining to a moving heat source on plates of different thickness and thermal properties. The accuracy of the maps has been tested against extensive experimental data, as obtained from in situ thermocouple measurements and numerical analysis of a large number of stringer bead welds. It is shown that the thermal programme within the HAZ (heat affected zone) of such weldments can be adequately predicted from the medium thick plate solution for a wide range in operational conditions (including aluminium and steel welding).

The transition from shallow to deep penetration during electron beam welding

Abstract: Electron beam partial-penetration welds were made on 2024 aluminium and 304 stainless steel at travel speeds from 6.4 to 3200 mm/s (0.25 to 126 in./s). Different combinations of beam current and travel speed were selected to achieve a wide range of energy densities for three different power density beams, while the use of aluminium and stainless steel provided results for materials with widely different thermal properties. The cross-sectional shapes of the resulting welds were metallographically measured to determine relationships between the welding machine parameters (power beam diameter and travel speed) and the depth of penetration.

Cavity microstructure and kinetics during gas tungsten arc welding of helium-containing stainless steel

Abstract: Helium was implanted in type 316 stainless steel, through tritium decay, to levels of 0. 18, 2. 5, 27, 105, and 256 atomic parts per million (appm). Bead-on-sheet welds were then made using the gas tungsten arc (GTA) process. Intergranular cracking occurred in the heat-affected zones (HAZs) of specimens with helium concentrations equal to or greater than 2.5 appm. No such cracking was observed in helium-free control specimens or in specimens containing the lowest helium concentration. In addition to the HAZ cracking, brittle, centerline cracking occurred in the fusion zone of specimens containing 105 and 256 appm helium. Transmission and scanning electron microscopy results indicated that both the HAZ cracking and centerline cracking in the fusion zone resulted from the stress-induced growth and coalescence of cavities initiated at helium bubbles on interfaces. For the HAZ case, the cavity growth rate is modeled and shown to predict the experimentally measured 1-second time lag between peak weld temperature and the onset of cracking.

Effects of welding flux additions on 4340 steel weld metal composition

Abstract: The effects of CaF2, CaO and FeO additions on weld metal chemistry were evaluated for the manganese — silicate flux system. Comparisons were made between AISI 4340 steel and lowcarbon steel welds to understand the weld metal chemistry. The results show that the elemental transfer from the slag to the weld metal and vice versa cannot be consistently explained using thermodynamic data; e.g., the carbon/oxygen partition is apparently controlled by a CO reaction in the 1010 steel welds, but the AISI 1020 and 4340 steel welds show constant carbon contents despite increasing oxygen levels. In addition, data are reported as a resource for future analytical and comparative purposes. Introduction Submerged arc welding of high integrity can be achieved through proper selection of the wire and flux combination for the specific base metal and welding parameters. Small amounts of alloying elements such as nickel, chromium and molybdenum are added to steels to increase strength, hardness or toughness, as is the case with AISI 4340 steel. Generally, welding low-alloy steels requires more careful control of procedures and selection of consumables than welding the carbon steels. Moreover, the oxygen potential of the flux influences the loss or gain of alloying elements during welding, the weld-deposit oxygen content, and the type, size and distribution of oxide inclusions in the solidified weld metal. The effective application of the submerged arc welding process for joining high-strength, low-alloy steels depends heavily upon understanding the behavior of the flux. Understanding the elemental P. A. BURCK and D. L. OLSON are with the Center for Welding and joining Research, Colorado School of Mines, Golden, Colo. J £ INDACOCHEA is with the University of Illinois at Chicago, Chicago, III. transfer mechanisms between the flux and the weld metal can be attained by studying the influence of each chemical additive on the flux behavior. To determine the many slag/weld metal chemical reactions occurring simultaneously during welding, a state of thermodynamic equilibrium has been assumed to be attained. The basis for this assumption is that the high temperatures and high surface-to-volume ratio associated with the welding process counteract the short time available for a reaction to be completed (Ref. 1). Chai and Eagar (Ref. 2) reported that the very short times and the large thermal gradients involved in the process prevent overall slag-metal equilibrium from being reached. They also reported that an understanding of kinetics, in combination with the thermodynamic limits of the process, would be necessary to determine the final weld metal composition. Blander and Olson (Ref. 3) also discussed the influence of kinetics, the role of interfacial reaction, and the degree to which equilibrium is approached. This paper is a part of the systematic investigation undertaken by the Colorado School of Mines (Refs. 3-7) to better understand the behavior of different flux additions to the manganese-silicate and lime-silicate flux systems. The influence of FeO, CaO and CaF2 additions to a manganese-silicate flux on AISI 4340 steel weld metal chemistry is reported here. In addiKEY W O R D S Welding Flux Effects Flux Additions 4340 Steel Weld Metal Weld Composition Submerged Arc Fluxes 1020 Steel Weld Metal Ca2/CaO/FeO Addition Mn-Silicate Fluxes SAW Flux Systems tion, a comparison of the effects of CaF2 and FeO additions to a manganese-silicate flux on welds on AIS11020 and 4340 steels was made in an effort to understand the effect of alloying elements on weld metal chemistry. The results presented in this paper should be a useful database for future analytical modeling and comparisons. Materials and Procedure Single pass, bead-on-plate welds were made using the submerged arc welding process on AIS11010,1020 and 4340 steel base plates. The dimensions of the plates were 73 X 203 X 13 mm (2.9 X 8 X 0.5 in.). The welding wires used were AWS Type E70S-3 for welds produced on AISI 1010 and 1020 steels, and Type EM12K for AISI 4340 steel welds. Compositions of the base plates and welding wires are given in Table 1. The submerged arc welding process was performed using direct current, electrode positive. The welding parameters were maintained constant at 30 V, a travel speed of 8 mm/s (19 in./min), and the wire speed was varied to give 500 A. All welds were made with a heat input of 1.9 kj /mm (48 kj/in.). Three different flux systems were used in this investigation: Si02"MnO-FeO, Si02" MnO-CaO and Si02-MnO-CaF2. The fluxes were prepared using reagent grade chemical powders. The flux compositions were reported as wt-% MnO because M n 0 2 decomposes to form MnO during the melting operation used to produce the fused flux. The iron ion in the fused flux was determined to be in the Fe + state and is reported as wt-% FeO (Ref. 10). The reagent-grade powders were weighed and mixed prior to induction melting. The powders were then placed in a graphite crucible for the melting operation. All fluxes were brought to 1773 K. The crucible was then removed from the furnace and the flux poured onto a stainless steel plate to solidify. After cooling, the fused fluxes were crushed and sized. Fluxes sized 14 to 100 mesh were used for WELDING RESEARCH SUPPLEMENT 1115-s

Computerized radiographic sensing and control of an arc welding process

Abstract: This paper summarizes an effort in which real-time radiography was implemented for on-line arc welding process study and control. X-ray penetrating radiation was used for volume observation in the welding pool and the heat-affected zone during the weld process. The advantages of such a technique are online detection and monitoring of defect formation in the weld and capability to study metal fusion and filler metal/base metal interaction and metal transfer in the welding pool. This technique may also be used for postservice, real-time remote testing of weld quality.

Process and connection component using an electrical resistor for the welding of plastic elements

Abstract: The invention relates to the welding of components made of heat-fusing plastic, using an electrical heating resistor arranged in the thickness of a connection component. According to the invention, the resistor is a thin electrically conductive layer advantageously formed on a supporting film made of heat-fusing plastic and capable of causing the tearing of the layer at a specific temperature corresponding to the welding temperature of the components. The invention is used particularly for the thermal welding of polyethylene pipes used in the gas industry.

Method of automatically welding rails

Abstract: In a method of automatically welding rails, welding of bottom portions of the rails is carried out as root pass welding of a first layer according to CO2 gas shielded arc weld technique, and as continuous multilayer welding of layers above the first layer according to CO2 gas shielded arc weld technique without discontinuing the welding of a second layer and upper layers. In welding of ankle portions (R2) of the rails, a flux is rapidly added to promptly shift to electroslag weld. Then, welding is conducted to head surfaces (R5) of the rails by continuing electroslag weld technique. This automatic welding method enables high efficiency field welding of rails, obviating the need for any complicated switching operation of the electric power source and use of several kinds of welding materials.

Simultaneous In-Process Control of Heat-Affected Zone and Cooling Rate during Arc Welding A model is developed for independently regulating the time-temperature relationship of the HAZ and the centerline cooling rate

Abstract: The problem of process con­ trol in welding involves not only regulation of weld bead geometry, but also ther­ mally induced changes such as distortion, residual stresses and metallurgical trans­ formations near the weld. This paper ad­ dresses the last of these, and poses it as a feedback control problem. The objective is transformed to one of controlling the surface temperature field in-process, and using temperature feedback to implement such a scheme. A control model of the process is presented, and a parameter adaptive controller is designed to ensure consistent control system performance. A series of numerical simulations and exper­ iments using CMA welding is presented that confirms the model and illustrates the desired properties of the controller. With this system, the heat-affected zone and cooling rate (through their correlates in surface temperature-time relationships) can be regulated independent of each other, and gross disturbances to the tem­ perature field rejected totally in the steady- state. In addition, dynamic performance of the control system is illustrated, and the limits imposed by current hardware are discussed.

Hermetically sealed aluminum package for hybrid microcircuits

Abstract: A hybrid package in which Kovar feedthroughs are friction welded to an aluminum housing. Friction welding produces a very strong weld joint which resists the thermal stresses induced between the aluminum housing and Kovar feedthroughs by the large difference in their coefficients of thermal expansion. Friction welding also produces a very small heat affected zone, while brazing, soldering and other types of welding produce large heat affected zones which can cause annealing problems. The aluminum package is easy to machine, light in weight and provides good heat dissipation for the hybrid microcircuits in the package.

Resistance spot weldability of comparatively thick C-Mn-Cr-Mo dual phase steel sheet.

Abstract: Welding of comparatively thick (4 mm) C-Mn-Cr-Mo dual phase steel has been carried out by resistance spot welding process. Weldability of this steel has been studied by varying the electrode force and the primary welding parameters affecting the heat input such as the effective current and weld time. The influence of these welding parameters on the morphology, microhardness and the tensile shear strength of the weldment are investigated. Optimum welding parameters producing maximum joint strength are established as electrode force of 615 kg, effective current of 6 kA and weld time of 80 cycle. Weakening of weldment caused by excess tempering of martensite at the outer region of HAZ was not observed in the range of optimum welding conditions.

Connection component for together plastic elements by thermal welding

Abstract: The invention relates to a connection component equipped with an electrical resistor for the welding of elements made of heat-fusing plastic. According to the invention, the resistor takes the form of a single wire coated with an electrically insulating layer and having points of intersection, the coating layer fusing at a temperature between the fusion temperature of the components to be joined together and their temperature of thermal damage, so that short-circuits are generated on the wire and so that the stopping of the supply of current to the latter is commanded. The invention is used particularly for the thermal welding of polyethylene pipes used in the gas industry.

Direct TEM observation of microstructures of the austenitic/carbon steels welded joint

Abstract: The successive alteration of the microstructure from the weld metal zone through weld bonds to the heat-affected zone of a Cr18Ni13 austenitic-0.45% C steels welded joint has been observed using transmission electron microscopy. A new type of microstructure, called pearlite-like structure, has been found and the microstructural details of the weld interface (or fusion line) have been studied. Based on the definition of various zones of the dissimilar steels welded joints under the optical microscope, the transmission electron microscopic characteristics, including microstructures and compositions, of each zone are described and discussed.

Method for one-side root pass welding of a pipe joint

Abstract: A method for one-side root path welding of a pipe joint comprises the steps of forming a ring groove having a V-shaped bottom portion thereof at end faces of both pipes whose joint is circumferentially welded, attaching a backing material (16) to a butt portion of the pipes from an internal side of the pipes, running an automatic welding machine (1) along a guide rail (12) mounted on an outer surface of the pipes in the circumferential direction thereof, controlling a position of a welding torch (2) along a seam by means of an arc sensor, and welding root pass from the outer side of the pipes with a predetermined welding current and at a welding speed in a high-speed rotating arc welding of the pipes at a predetermined rotational speed and with a predetermined diameter of rotation The rotational speed of arc is from 10 to 150 Hz The rotation-diameter of the arc is from 1 to 4 mm The welding current is from 200 to 500 A The welding speed is from 75 to 300 cm/min

Effect of electrochemical reactions on submerged arc weld metal compositions

Abstract: The purpose of this work is to investigate the relative influence of electrochemical and thermochemical reactions on the weld metal chemistry in a direct current submerged arc welding process. Chemical analyses were carried out on the melted electrode tips, the detached droplets and the weld metal for both electrode-positive (reverse) polarity where the welding wire is anodic and electrode-negative (straight) polarity where the welding wire is cathodic

Gas metal arc welding of aluminum-based workpieces

Abstract: Method of welding aligned aluminum torque tube components, comprising (i) defining a stepped square-butt joint to be welded by preforming the ends of said torque tubes and assembling such ends together in the nested condition; (ii) establishing an electrical direct current arc between a positive consumable aluminum-based electrode and said joint as cathode, the arc being shrouded in a shielding gas consisting, by volume, of 2-5% oxygen and the remainder inert gas, the current to the arc being pulsed at a frequency of 40-60 cycles per second while maintaining an average current of at least 200 amps; and (iii) while holding the pulsed arc in a predetermined orientation (i.e., position angle 45-60°, lead angle 5-15°, transverse angle 12°) to the joint, moving the arc along the joint in a single pass at a relative speed of at least 60 inches per minute.

Simultaneous in-process control of heat-affected zone and cooling rate during arc welding

Abstract: The problem of process control welding involves not only regulation of weld bead geometry, but also thermally induced changes such as distortion, residual stresses and metallurgical transformations near the weld. This paper addresses the last of these, and poses it as a feedback control problem. The objective is transformed to one of controlling the surface temperature field in-process, and using temperature feedback to implement such a scheme. A control model of the process is presented, and a parameter adaptive controller is designed to ensure consistent control system performance. A series of numerical simulations and experiments using GMA welding is presented that confirms the model and illustrates the desired properties of the controller. With this system, the heat-affected zone and cooling rate (through their correlates in surface temperature-time relationships) can be regulated independent of each other, and gross disturbances to the temperature field rejected totally in the steady-state. In addition, dynamic performance of the control system is illustrated, and the limits imposed by current hardware are discussed.

Heat-affected zone toughness of SMA welded 12%Cr martensitic-ferritic steels

Abstract: The present work was done to examine the effects of varying welding procedures on HAZ toughness of 12 % Cr martensitic-ferritic steels. Two commercial base metals were selected of 12-mm (0.5-in.) thickness, varying in martensite-ferrite balance, and stabilized by Ti additions. Shielded metal arc (SMA) square-groove welds were made using 23 % Cr-12 % Ni electrodes, with Charpy impact tests on specimens notched through the thickness in the high-temperature HAZ. Further toughness testing was carried out on simulated HAZ samples produced using thermal cycles derived from actual weld runs

Quantitative investigation of heat affected zone cracking of aluminium alloy 6061

Abstract: (1990). Quantitative investigation of heat affected zone cracking of aluminium alloy 6061. Welding International: Vol. 4, No. 8, pp. 600-609.

Pulsed arc welding machine

Abstract: In a pulse arc welding machine which is adapted to feed at a constant speed a welding wire as a waste electrode to turn the molten lump of the wire tip end into a spray state with a pulse current so as to effect a welding operation, the risetime and falltime of the pulse current influence the bead outer appearance, the gas shielding property and welding function and are varied independently of the other parameters controlled by the machine in accordance with the material quality of the welding wire, the wire diameter, and the wire feeding speed.

The Energy Transfer Efficiency in Laser Welding Process

Abstract: The process efficiency of laser beam welding was measured as a function of travel speed Temperature measurements were carried out during the bead‐on‐plate laser welding of mild steel with a focused 2KW CO2 laser beam at various welding travel speeds The laser welding process efficiency (power delivered to work/power in the beam) was calculated from the ratio of the heat content of the welded the specimen to the available laser beam energy (power × time) In the deep penetration welding region at intermediate travel speeds, the laser beam welding process efficiency (equal to the beam absorptance) was about 65%; but it was only about 28% in the shallow penetration region at high travel speeds In deep penetration welding, multiple reflections within the penetration cavity enhance absorptance A calculation based on four reflections within the cavity can account for the observed process efficiency

Method and apparatus for electrically heat welding thermoplastic fittings

Abstract: An improved method and apparatus for electrically heat welding a thermoplastic fitting having an electric resistance heating element disposed therein. A controlled quantity of electric power is supplied to the heating element during the welding process to insure the making of a high quality weld. After the size of heating element and fitting are determined, a substantially constant voltage level electric power is supplied to the heating element of the fitting. When it is determined that the welding process is proceeding abnormally, the supply of electric power is terminated unless the abnormality is that the current level is too high. In that case, instead of terminating the welding process, the voltage of the electric power is reduced to that which results in current levels substantially equal to predetermined current levels for the size of heating element and fitting being welded which often results in a good weld being obtained even where the heating element is partially shorted out. Also, fires and other problems which have heretofore resulted due to such short circuits are prevented.

Metallographic investigations of the heat-affected zone II/parent metal interface cracking in 18Ni maraging steel welded structures

Abstract: During the fabrication of a large diameter pressure vessel out of 18 Ni maraging steel by manual TIG welding, microcracks were noticed at the heat-affected zone (HAZ)/parent metal interface. The location of these cracks was very different from those reported at the fusion zone/HAZ I interface due to “constitutional liquation”. Extensive optical metallography, scanning electron microscopy and energy dispersive X-ray analyses were carried out to identify the cause for the occurrence of these cracks. It is inferred from the experimental results that the microsegregation of titanium and nickel due to repeated thermal cycling during multipass welding led to the formation of TiC/Ti(CN) and stable austenite film on the grain boundaries. Under severe thermal stresses developed during welding, microvoids generated at the interface of TiC/Ti(CN) inclusions and austenite and further propagated intergranularly due to the premature failure of the austenite films.

Keyhole and weld shapes for plasma arc welding under normal and zero gravity

Abstract: A first order study of the interfacial (keyhole) shape between a penetrating argon plasma arc jet and a stationary liquid metal weld pool is presented The interface is determined using the Young-Laplace equation by assuming that the plasma jet behaves as a one-dimensional ideal gas flow and by neglecting flow within the weld pool The solution for the keyhole shape allows an approximate determination of the liquid-solid metal phase boundary location based on the assumption that the liquid melt is a stagnant thermal boundary layer Parametric studies examine the effect of plasma mass flow rate, initial plasma enthalpy, liquid metal surface tension, and jet shear on weldment shape under both normal and zero gravity Among the more important findings of this study is that keyhole and weld geometries are minimally affected by gravity, suggesting that data gathered under gravity can be used in planning in-space welding

Laser surface melting of AISI 4340 steel

Abstract: The microstructure and microhardness of AISI 4340 steel melted by a continuous wave ĈO2 laser are examined. The parameters investigated are overlap between adjacent passes, laser power, and scanning speed. After melting, three different zones were observed in the treated surface corresponding to the melted zone, the heat affected zone, and the overlapping zone. The melted zone displayed a fine cellular structure, while the other two zones displayed fine martensite or bainite structures. The fine structure and the high microhardness values, which were measured in the melted zone, are evidence of the high quenching rates which follow laser melting. An increase in the scanning speed and a decrease in laser power resulted in afiner microstructure and higher microhardness, and a reduction in the amount of overlap improved the overall microhardness.MST/1038