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1.
H. T. Lin M. L. Grossbeck B. A. Chin 《Metallurgical and Materials Transactions A》1990,21(9):2585-2596
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. 相似文献
2.
Evolution of microstructure and texture in Mg-Al-Zn alloys during electron-beam and gas tungsten arc welding 总被引:3,自引:0,他引:3
The evolution of microstructure and texture in the AZ-series Mg alloys subjected to electron-beam welding and gas tungsten
arc welding are examined. Electron-beam welding is demonstrated to be a promising means of welding delicate Mg plates, bars,
or tubes with a thickness of up to 50 mm; gas tungsten arc welding is limited to lower-end thin Mg sheets. The grains in the
fusion zone (FZ) are nearly equiaxed in shape and ∼8 μm or less in size, due to the rapid cooling rate. The as-welded FZ microhardness and tensile strength are higher than the
base metals due to the smaller grain size. The weld efficiency, defined as the postweld microhardness or tensile strength
at the mid-FZ region divided by that of the unwelded base metal, is around 110 to 125 pct for electron-beam welding and 97
to 110 pct for gas tungsten arc welding. There are three main texture components present in the electron-beam-welded (EBW)
FZ, i.e.,
(with TD//
),
(with ND∧
∼15 deg), and
(with WD∧
∼30 deg), where TD, ND, and WD are the transverse, normal, and welding directions, respectively. The crystal growth tends
to align toward the most closed-packed direction,
. The texture in gas tungsten arc welded (GTAW) specimens is more diverse and complicated than the EBW counterparts, due to
the limited and shallow FZ and the lower cooling rate. The cooling rates calculated by the three-dimensional (3-D) and two-dimensional
(2-D) heat-transfer models are considered to be the lower and upper bounds. The cooling rate increases with decreasing Al
content, increasing weld speed, and increasing distance from the weld top surface. The influences of the FZ location, welding
speed, and alloy content on the resulting texture components are rationalized and discussed. 相似文献
3.
M. Vasudevan M. V. Kuppuswamy A. K. Bhaduri 《Transactions of the Indian Institute of Metals》2010,63(1):1-10
Automated Gas Tungsten Arc Welding (GTAW) with filler wire addition using a wire feeder is a candidate process for welding
of 316LN austenitic stainless steel, which is the major structural material for the Indian 500 MWe Fast Breeder Reactors.
In GTAW, the quality of the weld is characterized by the weld-bead geometry as it influences the mechanical properties and
its performance during service. This paper discusses the development of computational model using genetic algorithm for determining
the optimum/near-optimum GTAW process parameters for obtaining the target weld-bead profile during automatic welding of 316LN
stainless steel. Using the experimental data generated on the influence of process variables on weld-bead geometry, regression
models correlating the weld-bead shape parameters with the process parameters were developed for determining the objective
function in genetic algorithm. Close agreement was achieved between the target weld-bead profile and the model-computed weld-bead
profile. This study has shown that use of genetic algorithm is an appropriate methodology for optimising process parameters
to obtain target weld-bead profile in GTAW with wire feeder of 316LN stainless steel. 相似文献
4.
This article presents a mathematical model simulating the effects of surface tension (Maragoni effect) on weld pool fluid
flow and weld penetration in spot gas metal arc welding (GMAW). Filler droplets driven by gravity, electromagnetic force,
and plasma arc drag force, carrying mass, thermal energy, and momentum, periodically impinge onto the weld pool. Complicated
fluid flow in the weld pool is influenced by the droplet impinging momentum, electromagnetic force, and natural convection
due to temperature and concentration gradients, and by surface tension, which is a function of both temperature and concentration
of a surface active element (sulfur in the present study). Although the droplet impinging momentum creates a complex fluid
flow near the weld pool surface, the momentum is damped out by an “up-and-down” fluid motion. A numerical study has shown
that, depending upon the droplet’s sulfur content, which is different from that in the base metal, an inward or outward surface
flow of the weld pool may be created, leading to deep or shallow weld penetration. In other words, it is primarily the Marangoni
effect that contributes to weld penetration in spot GMAW. 相似文献
5.
Distribution of the heat and current fluxes in gas tungsten arcs 总被引:2,自引:0,他引:2
The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined
experimentally following an experimental technique developed previously. The results indicate that arc length is the primary
variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width
of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed
as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6
mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer
efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of
a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most
useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported.
Formerly Research Assistant, is with the Department of Materials Science and Engineering, Massachusetts Institute of Technology,
Cambridge, MA 相似文献
6.
A mathematical model of gas tungsten arc welding considering the cathode and the free surface of the weld pool 总被引:4,自引:0,他引:4
A two-dimensional axisymmetric numerical model, including the influence of the cathode and the free surface of the weld pool,
is developed to describe the heat transfer and fluid flow in gas tungsten arc (GTA) welding. In the model, a boundary-fitted
coordinate system is adopted to precisely describe the cathode shape and deformed weld-pool surface. The current continuity
equation has been solved with the combined arc plasma-cathode system, independent of the assumption of current density distribution
on the cathode surface, which was essential in the previous studies of arc plasma. It has been shown that the temperature
profile, the current, and the heat flux to the anode show good agreement with the experimental data. Moreover, the current
and the heat-flux distributions may be affected by the shape of the cathode and the free surface of the weld pool. 相似文献
7.
Q345D high-quality low-carbon steel has been extensively employed in structures with stringent weld-ing quality requirements.A multi-objective optimization of welding stress and deformation was presented to design reasonable values of gas metal arc welding parameters and sequences of Q345D T-joints.The optimized factors included continuous variables (welding current (I), welding voltage (U) and welding speed (v)) and discrete variables (welding sequence (S) and welding direc-tion (D)).The concepts of the pointer and stack in Visual Basic (VB) and the interpolation method were introduced to optimize the variables.The optimization obj ectives included the different combina-tions of the angular distortion and transverse welding stress along the transverse and longitudinal dis-tributions.Based on the design of experiments (DOE) and the polynomial regression (PR) model, the finite element (FE) results of the T-joint were used to establish the mathematical models.The Pareto front and the compromise solutions were obtained by using a multi-objective particle swarm optimization (MOPSO) algorithm.The optimal results were validated by the corresponding results of the FE method, and the error between the FE results and the two-objective results as well as that be-tween the FE results and the three-objective optimization results were less than 17.2% and 21.5%, respectively.The influence and setting regularity of different factors were discussed according to the compromise solutions. 相似文献
8.
Numerical analysis of metal transfer in gas metal arc welding 总被引:1,自引:0,他引:1
The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport
processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model
include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing
free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to
the welding current is estimated by assuming several different types of current density distribution on the free surface of
the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular
to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition
zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between
calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption
agree well with those observed in experiments. 相似文献
9.
10.
Weld-metal nitrogen concentrations far in excess of Sieverts-law calculations during gas tungsten arc (GTA) welding of iron
are investigated both experimentally and theoretically. A transient, threedimensional mathematical model has been developed
to calculate the residual nitrogen concentrations during GTA welding. This model combines calculations for the plasma phase
with those for nitrogen absorption and for the transport of nitrogen by convection and diffusion in the weld metal and diffusion
throughout the weldment. In addition, the model takes into account the roles of turbulence and the nitrogen desorption reaction
in affecting the residual nitrogen concentration in the weldment. Autogeneous GTA welding experiments in pure iron have been
performed and the resulting nitrogen concentrations compared with the modeling results. Both experimental and modeled nitrogen
concentrations fall in a range between 2.7 and 4.7 times higher than Sieverts-law calculations at a temperature of 2000 K.
Modeled nitrogen concentrations correlate well with the experimental results, both in magnitude and in the general trends,
with changes in the travel speed and nitrogen addition to the shielding gas. 相似文献
11.
This article describes a theoretical investigation on the arc parameters and metal transfer in gas metal arc welding (GMAW)
of mild steel using argon and helium shielding gases. Major differences in the predicted arc parameters were determined to
be due to large differences in thermophysical properties. Various findings from the study include that an arc cannot be struck
in a pure helium atmosphere without the assistance of metal vapor, that a strong electromagnetic cathode force affects the
fluid flow and heat transfer in the helium arc, providing a possible explanation for the experimentally observed globular
transfer mode and that the tapering of the electrode in an argon arc is caused by electron condensation on the side of the
electrode.
Formerly Graduate Student, Massachusetts Institute of Technology 相似文献
12.
M. Labudovic R. Kovacevic I. Kmecko T. I. Khan D. Blecic Z. Blecic 《Metallurgical and Materials Transactions A》1999,30(6):1597-1603
The surface modification of a Ti-6Al-4V alloy using a gas tungsten arc, as a heat source, was studied. The experimental results
show that the titanium alloy surface can be melted and nitrided using pure nitrogen or a nitrogen/argon mixture shielding
atmosphere. The resolidified surfaces are 0.9 to 1.2-mm thick and contain titanium nitride dendrites, α-titanium, and α″-titanium
(martensite). The average dendrite arm spacing is influenced by the electrode speed. Small titanium nitride dendrites are
homogeneously distributed in the resolidified surfaces. The microstructure and phase constitution in the resolidified surfaces
were determined and analyzed, and the mechanism of the formation of titanium nitrides is discussed. The results show that
the nitriding kinetics obey parabolic laws and are, therefore, controlled by nitrogen diffusion. The nitrogen-concentration
depth profiles, calculated using Fick’s second law of diffusion, are compared to experimental nitrogen depth profiles, showing
satisfactory agreement. 相似文献
13.
Sung H. Ko Choong D. Yoo Dave F. Farson Sang K. Choi 《Metallurgical and Materials Transactions B》2000,31(6):1465-1473
The dynamic behavior of stationary fully penetrated gas tungsten arc weld pools was investigated through numerical simulation.
The effects of arc pressure, electromagnetic force, and surface tension gradients on surface depression, convection, and temperature
distribution were calculated. The top surfaces of fully penetrated pools were easily depressed since they were only supported
by surface tension. Circulatory convection patterns were generated by electromagnetic forces and surface tension gradients
and were significantly affected by the vertical velocity component produced by pool oscillation. The temperature distribution
in and around the pool was influenced by pool convection. During pool formation and growth, the fully penetrated molten pool
sagged dramatically when the bottom pool diameter approached the top diameter. The sagged pool oscillated with higher magnitude
and lower frequency than partially penetrated or fully penetrated pools before sagging occurred. The dynamic behavior and
the amount of material lost during melt-through were affected by the pool size and the magnitude of arc pressure. 相似文献
14.
以WNQ690钢为研究对象,采用气保护焊接工艺,焊接线能量控制在15kJ/cm,WER70NH匹配WNQ690钢进行焊接,研究WNQ690钢焊接性能及焊接组织结构。接头抗拉强度为750MPa,冷弯性能优良,焊缝-40℃平均冲击功为137J,熔合线及热影响区冲击功均达到较高水平,焊接接头的HV10硬度在234-300之间,说明WNQ690钢淬硬倾向较小。WNQ690钢材的组织为回火贝氏体,焊接接头过热区组织为贝氏体,焊缝中含有较多的针状铁素体和少量的先共析铁素体,焊接热影响区的细小贝氏体组织使焊接热影响区具有较高的冲击韧性。 相似文献
15.
In the modeling of the gas metal-arc (GMA) welding process, heat inputs to the workpiece by the arc and the metal transfers
have been considered separately. The heat energy delivered due to the metal transfer has been approximated in the form of
a cylindrical volumetric heat source, whose dimensions of the radius and the height are dependent on the molten metal droplet
characteristics. The pinch instability theory (PIT) and the static force balance theory (SFBT) of drop detachment have independently
been used to obtain the expressions for various characteristics of the drop,i.e., the drop radius, the drop velocity, and the drop frequency at various welding parameters. The occurrence or the nonoccurrence
of finger penetration, routinely found in the GMA welding at high welding currents, has been satisfactorily explained by the
cylindrical heat source model. The effect of various welding parameters,e.g., the welding current, the wire radiusetc., on the weld bead penetration characteristics has been investigated. In this modeling effort, the heat conduction equation
has been solved in three dimensions. 相似文献
16.
HUANG Zhijun 《Baosteel Technical Research》2023,(4):22-27
Gas metal arc welding experiments were conducted on two types of steels with 0.41% carbon equivalent(Ceq) and 0.31% Ceq using WER70T wire and 20% CO2 and 80% Ar as shielding gas.The two types of steels show satisfactory weldability.The transition temperatures of 50% upper shelf energy(Tk0.5) for Charpy-V impact test of both the welded joints are below-40 ℃.However, the toughness of the fusion line zone and heat-affected zone(HAZ) of the two steel joint... 相似文献
17.
A transmission electron microscopy (TEM) investigation of the electron beam (EB) and gas tungsten arc (GTA) fusion zones of
2090 indicates that in both the as-welded and aged conditions, the EB and GTA fusion zones lack the volume fraction and the
homogeneity of strengthening precipitates found in the base metal. In the underaged and peak-aged conditions, the δ′ phase
is the primary strengthener, the volume fraction ofT
1 present being too low to be effective. TheT
1, precipitates are found either in the vicinity of other inclusions or at the dendrite boundaries. As the strength increases
with postweld aging, the elongation decreases to 1 pct. The presence of the boundary phases and Cu- and Cl-containing inclusions
at the boundaries leads to poor elongation. The joint efficiencies of the peak-aged EB and GTA weldments (EBWs and GTAWs,
respectively) are 75 and 55 pct at 293 K and 75 and 50 pct at 77 K, respectively. Both EBWs and GTAWs have relatively low
elongations. 相似文献
18.
《Canadian Metallurgical Quarterly》1998,37(3-4):293-303
A comprehensive thermofluids numerical model of stationary gas tungsten arc (GTA) welding has been developed and used to examine the effects of thermofluids phenomena on the temperatures and flow velocities in the weld pool and their impact on the resultant weld dimensions for welds produced in high vs low thermal conductivity metals. A dynamic grid re-mapping technique was used to map a block of finite elements into the liquid weld pool to permit use of a k–ε turbulence model in the liquid. Simulations for low conductivity AISI 304 stainless steel show that good correlation with experimental data was only possible if the effects of fluid flow and turbulent mixing in the weld pool were modeled accurately. Conversely, simulations in higher conductivity metals, 6061 and 1100 aluminum, showed that while the average flow velocities and level of turbulence were higher, their effect on the final temperatures and weld pool dimensions were less significant. 相似文献
19.
Numerical analysis of metal transfer in gas metal arc welding under modified pulsed current conditions 总被引:2,自引:0,他引:2
A method has been proposed to pulsate current in gas metal arc welding (GMAW) to achieve a specific type of desirable and
repeatable metal transfer mode, i.e., one drop per pulse (ODPP) mode. This method uses a peak current lower than the transition current to prevent accidental
detachment and takes advantage of the downward momentum of the droplet oscillation to enhance the detachment. A numerical
model with advanced computational fluid dynamics (CFD) techniques, such as a two-step projection method, volume of fluid (VOF)
method, and continuum surface force (CSF) model, was used to carry out the simulation for the metal transfer process. The
Gauss-type current density distribution was assumed as the boundary condition for the calculation of the electromagnetic force.
The calculations were conducted to demonstrate the effectiveness of the proposed method in achieving the desired metal transfer
process in comparison with conventional pulsed current GMAW. Also, the critical conditions for effective use of this proposed
method were identified by the numerical simulation. Comparison showed good agreement between calculation and experimental
results. 相似文献
20.
L. N. Belyanchikov 《Russian Metallurgy (Metally)》2012,2012(6):478-483
The I?CV and voltage-baric characteristics of the dc arc glowing in argon between a tungsten cathode and a molten anode made of titanium, chromium, or manganese are studied at various gas pressures, arc currents, and arc lengths. The arc is probed to establish the relation between the voltage drop across the arc and its regions on the anode material and the melting conditions. 相似文献