Microstructure Of Fusion Zone Research Articles

Strengthen of Mechanism of 30CrMnSiNi2A Steel Welded Joint with Ultrasonic Impact Treatment

To analyze the strengthening mechanism of 30CrMnSiNi2A steel welded joint with ultrasonic impact treatment (UIT), the welded joint specimens were full coverage strengthened by the technology. The microstructure of the surface layer in fusion zone of the welded joint with and without UIT was investigated by optical microscopy (OM). The hardness and residual stress distributions along the thickness direction were also measured by micro-hardness tester and X-ray diffraction method respectively. The results show that the microstructure in fusion zone of the untreated 30CrMnSiNi2A steel welded joint were coarse dendrite, and there were many welding defects in this zone. UIT has the ability to achieve more compact microstructure with only small welding defects. The average hardness value of the treated specimens reached 571 HV, increased 14.4% as compared with that of the untreated specimen (499 HV). A residual compressive stress layer with thickness of 850 μm was also obtained from by UIT, and the maximum residual compressive stress was-347 MPa. The grain refinement, work hardening and residual compressive stress in fusion zone introduced by UIT increased its anti-fatigue performance.

Microstructural characterization of liquid nitrogen cooled Alloy 718 fusion zone

The interdendritic Laves phase and the microsegregation have been investigated in Alloy 718 fusion zone cooled with liquid nitrogen during welding. Conventional GTA welding process was employed with modified waveform and two types of shielding gas and filler metal (solid solution and age hardenable). The weld cooling rate was enhanced using liquid nitrogen cooling during Gas Tungsten Arc welding process. The resultant fusion zone microstructures were characterized using the metallurgical tools. Dendrite remelting phenomenon was observed from the optical micrographs. It was found that the enhanced cooling rate with liquid nitrogen reduced the interdendritic phases which were confirmed in both the electron microscopic and the X-ray diffraction analysis. The elemental mapping in scanning electron microscope-energy dispersive spectral analysis also confirmed the reduced microsegregation. The dendrite arm spacing was reduced from the range of 15–54μm (CCPHE–CCAR, conventional) to 3–17μm (CCPHE–CCAR, liquid nitrogen cooled) for the employed process variables. The computed weld cooling rate was found to be enhanced from seven to fifteen times than the conventional welding process.

The influence of various factors on the geometric profile of laser lap welded T-joints

The effect of processing parameters, assembly parameters, and plate thickness on the weld bead geometry was examined, and the microstructure and microhardness of the typical joints were investigated in this paper. There are two kinds of welds, these are the Y-type and V-type welds in different heat input. Heat input has a small effect on bead width at the interface when the thickness of face plate is more than 3 mm. The variation of bead geometry is little when gap and offset size is small, while porosity or depression forms with increasing gap and offset. Plate thickness exerts a remarkable effect on the bead width at interface, and a big bead width at interface can be achieved by adopting thin face plate. The centricity of the laser beam is a big problem in laser lap welding T-joints with thin core plate, while bead width at interface is small in laser lap welding T-joints with thick face plate. Microstructure of heat-affected zone and fusion zone is composed of lath martensite and bainitic ferrite. Microhardness of fusion zone is lowest due to the coarse lath martensite. The desired bead geometry of laser lap welded T-joints can be produced by adopting low welding speed, thin face plate, and small gap.

On the Use of Infrared Thermography for Analysis of Fatigue Damage in Ti6Al4V-Welded Joints

The present work is aimed at comparatively studying fatigue damage evolution of a pulsed Nd:YAG laser beam-welded (LBW) joint and the base metal (BM) of Ti6Al4V alloy subjected to cyclic loading. To reveal crack nucleation and propagation during the fatigue process, in situ fatigue was generated using infrared measurement methods. The results indicate that the rate of damage accumulated in the LBW joint was higher than in the BM specimens during a fatigue test, which decreased the fatigue life of the LBW joint. This observation is attributable to the LBW joint fusion zone microstructure, which has a higher void nucleation and growth rate compared with the BM microstructure.

Microstructure-properties correlation in fiber laser welding of dual-phase and HSLA steels

Similar and dissimilar welds of dual-phase (DP) and high strength low alloy (HSLA) steels were made by fiber laser welding (FLW). The welds were characterized with respect to microstructure, micro- and nano-hardness, and tensile properties. The fusion zone (FZ) in the DP welds consisted of fully martensitic structure; whereas HSLA and dissimilar weld FZ microstructure were mixture of martensite and bainite. Analytical transmission electron microscopy (TEM) confirmed bainite structures containing bainitic ferrite laths with intralath and interlath cementite. Precipitation of single variant carbides inside the bainitic ferrite laths were confirmed by measuring the interplanar spacing. The cooling rate in the FZ, estimated using Rosenthal equation, and continuous-cooling-transformation diagrams corroborated the microstructure formed. Nanoindentation was used to verify the hardness of these individual microconstituents, since a much lower nano-hardness for bainite (4.11GPa) was observed compared to martensite (6.57GPa) phase. Tensile failure occurred in the tempered area of the heat affected zone (HAZ) in the DP steel welded, which was confirmed by typical cup-like dimple fracture; likewise failure in the HSLA base metal, which occurred in dissimilar and HSLA welds, indicated distinctive dimple and shear dimple ductile morphology.

A novel rotating wire GMAW process to change fusion zone shape and microstructure of mild steel

In this paper, traditional gas metal arc welding process was modified to change the fluid flow in the molten pool by the rotary motion of filler metal (wire) accompanied by downward feeding process. The rotary motion of the wire transferred additional momentum into weld pool and bestowed the latter with rotating fluid flow characteristics. The rotating fluid flow of the weld pool decreased the penetration of the weld and refined the weld microstructure directly. The finer microstructure of the weld noticeably increased the tensile strength of the weld metal.

Effect of laser welding on mechanical properties of 70/30 Cu-Ni alloy welds

This article reveals the influence of laser welding process parameter, welding speed, on the mechanical and metallurgical properties of 3.5 kW CO2 laser machine welded joints of 70/30 Cu-Ni alloys. Laser welded joints were fabricated using different welding speeds of 1.0, 1.5, 2.0, and 2.5 m/min. The mechanical properties (hardness, tensile strength, and percentage elongation) of the welded joints were evaluated and correlated with the fusion zone microstructure. Optical microscopy and scanning electron microscopy were used to evaluate the metallurgical characteristics of the welded joints. The joints fabricated using a welding speed of 1.5 m/min exhibited fine, equiaxed, and uniformly distributed grains at fusion zone and resulted in superior mechanical properties than other joints.

Effect of Heat Input on Microstructure and Mechanical Properties of Inconel-718 EB Welds

In this paper effect of electron beam welding heat input on the microstructure and mechanical properties of Inconel 718 was studied. Sheet of 2mm thickness was used with an average grain size of 30μm. Five different heat inputs ranging from 36J/mm to 180J/mm were used to make full penetration welds. Welding current was varied from 18mA to 90mA and other welding parameters were kept constant. Change in heat input altered the geometry of the weld (width to depth ratio) and the microstructure of fusion zone (FZ) and heat affected zone (HAZ) also changed. As the heat input increased the interdentric spacing in FZ was increased from 3.5μm to 6μm. Grain boundary liquation was found in all the welds. Intensity of liquation increased with decrease in heat input and the microfissuring was observed only in the lowest heat input weld. Change in heat input did not significantly affect the tensile properties of the weld.

Evolution of M-A Constituents in HAZ and Its Effect on Toughness of MAG Joint of Granular Bainitic Steel Q690C

To study the evolution of M-A constituents and their effects on toughness of each HAZ(heat affected zone) sub-zone, a low carbon granular bainitic steel Q690 is welded using automatic metal active-gas welding(MAG) welding and Charpy V-notch impact test is carried out. The microstructures, fractograph and statistical results of M-A constituents is analysed. The results show that the microstructure of weld metal(WM) is acicular ferrite and the dimples on fracture surface of the WM are small and dense, showing ductile fracture feature. Although large amounts of M-A constituents existed in grain boundary in the WM, the toughness is not deteriorated owing to the blocky shape and small size. The microstructure of FZ(fusion zone) and CGHAZ(coarse grain heat affected zone) are upper bainite with string M-A constituents between them; the toughness of FZ is the worst because of the cleavage fracture of coarse grains; the toughness of other sub-zones, in which M-A constituents exist in grain boundary with small blocky shape, are close to base metal(BM). So, the evolution of distribution, size, and shape of M-A constituents is controlled by matrix microstructure; fine bainite and acicular ferrite could remedy the deterioration of toughness derived from M-A constituents; the microstructure control should focus on the matrix microstructure.

Microstructure and Softening of Laser-Welded 960 MPa Grade High Strength Steel Joints

The microstructural evolution of laser-welded 960 MPa grade high strength steel joints and its effect on softening behavior of heat affected zone (HAZ) were investigated in this paper. The results show that microstructure of HAZ and fusion zone (FZ) is composed of lath martensite and bainitic ferrite. The microstructure of mixed grained zone presents strip-like characteristics and small block martensite distributes along the grain boundary. The grain size near the fusion line is about 25 lm, and the grain size in the fine grain zone is less than 5 lm. Microhardness of HAZ and FZ is lower than base metal. The soft zone locates in transitional region between tempering zone and mixed grained zone due to the interaction of the martensite tempering and the recovery and recrystallization of the rolled microstructure. Microhardness of soft zone is 310 HV and drops 18% compared to base material. Welding heat input has a remarkable effect on the width of soft zone and microhardness. The tensile properties of weld joints are closely related to the softening behavior of HAZ.

Microstructure and corrosion behavior of multipass gas tungsten arc welded 304L stainless steel

The purpose of this study was to discuss the effect of single pass and multipass (double and triple pass) gas tungsten arc welding (GTAW) on microstructure, hardness and corrosion behavior of 304L stainless steel. In this investigation, 308 stainless steel filler metal was used. Microstructures and hardness of the weldments were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and Vickers microhardness (HV0.5). A ferritescope was also used in the non-destructive evaluation to observe the ferrite content on the weldments. Corrosion behavior of weldments in 1M H2SO4 solution at 25±1°C was investigated using potentiodynamic polarization and immersion tests. Results indicated that the microstructure of fusion zones exhibited dendritic structure contained lathy and skeletal δ-ferrite. The contents of δ-ferrite in the weld zone increased by increasing the number of passes. Therefore, as the number of passes increased, the hardness and corrosion resistance increased.

Simulation and experiment for crack arrest in remanufacturing

Remanufacturing is the only way for sustainable development of mechanical equipment manufacturing. For remanufacturing blanks containing cracks, the primary task is the prevention of crack propagation to ensure effectiveness of the manufacturing processes to follow. When pulsed current passes through a specimen, due to the existence of crack, the temperature around the crack tips rises sharply and may even climb above the fusion point of the material, which causes the crack tip to become blunt. In this work, with compressor rotor blade material FV520B as a specimen, the distributions of current density, temperature field, and stress field are calculated at the instant of discharge based on the thermo-electro-structure coupled theory. The crack arrest experiment is performed on high pulsed current discharge device of type HCPD-I. By making comparisons of morphology, microstructure, and size of fusion zone and heat-affected zone (HAZ) around the crack tip before and after energizing, the relationships between the sizes of fusion zone and the HAZ and the discharge energy and the current path are derived. The obvious partition and refined grains around the crack tip are prominent because of violent temperature change. The experimental and simulation results are found in fine agreement. The high current pulsed discharge can be used effectively to prevent a crack to further expand and show substantial potentials for application in remanufacturing domain.

Influence of post-weld hot rolling on the microstructure and mechanical properties of AZ31 magnesium alloy sheet

The as-rolled AZ31 Mg alloy sheet was welded by double-sided tungsten inert gas (TIG) welding, followed by annealing and hot rolling with different reduction. The influence of the rolling reduction on the microstructure, tensile properties and microhardness of the specimens was examined. Results showed that the microstructure of the weld fusion zone (FZ) and heat affected zone (HAZ) became more and more consistent with that of the base metal (BM) as the hot rolling reduction increased. The β-Mg17Al12 phases in the FZ dissolved gradually during hot rolling. Both the weld joint and BM were strengthened by hot rolling; the tensile strength of weld joint and BM were closest when the rolling reduction was 27%. The microhardness of the welded sheet increased with rolling reduction.

Influence of Welding Parameters on Weld Appearance and Mechanical Properties in Twin-Wire Tandem Submerged Arc Welding of HSLA Steel

Effects of welding parameters on the weld bead appearance and mechanical properties in twin-wire tandem submerged arc welding of a high-strength low-alloy steel were investigated. Steel plates were welded using different combinations of welding current, voltage, inter-wire spacing and welding speed. The weld joints were characterized in detail by metallography. Hardness and tensile properties of the specimens were measured. The experimental analysis reveals that good weld appearance can be obtained for a range of inter-wire spacing from 55mm to 80mm. Leading wire current, trailing wire voltage and welding speed are the major factors affecting weld bead profile and microstructures in weld metal and fusion zone. Greater welding speed tends to produce higher cooling rate and favors the formation of strengthening phases like acicular ferrite and bainitic structures resulting in better mechanical properties.

Investigation of Fusion Weldments of Semi-Solid Aluminium A356 Alloy: Pool Geometry and Microstructure

A fusion welding technique to join a semi-solid processed A356 cast plate is explored using Gas Tungsten Arc Welding (GTAW). Semi-solid metal (SSM) billets of non-dendritic microstructure produced by rheocasting in a mould placed inside a linear electromagnetic stirrer were used for this study. GTAW experiments were conducted to simulate different thermal gradients near the fusion zone. The geometries of the weld pool as well as the temperature gradient in the fusion boundary were measured to understand the microstructure evolution. Simulation of the welding process was performed to aid in the analysis. Quantitative metallography provided the shape factor as a measure of globularity of the primary a-Al phase. Based on the studies, a model has been proposed to explain the observation of globular microstructure in the fusion zone of the welds. Conclusions show a positive correlation of thermal gradient with globular microstructure formation in this class of alloys.

Austenitic and ferritic stainless steel dissimilar weld metal evaluation for the applications as-coating in the petroleum processing equipment

The current study presents some fundamental observations on the effects of the welding heat input in the chemical composition, microstructure, hardness and petroleum corrosion resistance of the fusion zone, formed by the AWS E309MoL austenitic stainless steel covered electrode and the AISI 410S ferritic stainless steel, being a dissimilar welding procedure. Such welding configurations are widely used as an overlay of equipment in the petroleum and gas industries. The welds were performed with the application of three different levels in heat inputs (6, 9 and 12kJ/cm). Samples of the weld metals were conventionally prepared for the microstructural characterization by light microscopy and scanning electron microscopy. A corrosion test with samples immersed in heavy oil heated at 300°C, was carried out for a period of 60h. The corrosion rate was determined by the weight loss given after the aforesaid test. The fusion zone microstructure has a typical δ-ferrite acicular morphology, from which the level of δ-ferrite was duly altered with the increases of the welding heat input, due to the variations in the composition of the weld metal caused by dilution. It was also concluded that the chemical composition and the weld metal microstructure had a slight influence in the material’s corrosion rate. As a matter of fact, the corrosion rate of the weld metals evaluated herein, was considered satisfactory with few variations between the welding heat inputs duly applied.

Microstructure and Mechanical Properties of Fiber Laser-Metal Active Gas Hybrid Weld of X80 Pipeline Steel

Fiber laser-metal active gas (MAG) hybrid welding process was explored to join X80 pipeline steel to improve the efficiency and performance of pipeline welding. During the hybrid welding process, five different positions are applied to simulate the practical pipe girth welding. The weldability is evaluated concerning the bead shape, hardness, tensile, impact properties, and microstructures of welded joints. The results reveal that the tensile strength is higher than that of the base metal and the weld has a good impact ductility and an excellent bend performance. At the same time, the difference in microstructure between the laser zone and arc zone of laser-MAG hybrid welding of X80 pipeline steel is observed. Compared with the arc zone, the laser zone has finer weld grains and a narrower heat affected zone (HAZ). The fusion zone microstructure of the arc zone mainly consists of columnar proeutectoid ferrite (PF) and fine acicular ferrite (AF), whereas that of laser zone comprises acicular ferrite, upper bainite (Bu), and granular bainite (BG), which verifies technical feasibility of hybrid welding in pipeline steel and lays a good foundation for practical application.

Computational Modeling of Microstructural-Evolution in AISI 1005 Steel During Gas Metal Arc Butt Welding

A fully coupled (two-way), transient, thermal-mechanical finite-element procedure is developed to model conventional gas metal arc welding (GMAW) butt-joining process. Two-way thermal-mechanical coupling is achieved by making the mechanical material model of the workpiece and the weld temperature-dependent and by allowing the potential work of plastic deformation resulting from large thermal gradients to be dissipated in the form of heat. To account for the heat losses from the weld into the surroundings, heat transfer effects associated with natural convection and radiation to the environment and thermal-heat conduction to the adjacent workpiece material are considered. The procedure is next combined with the basic physical-metallurgy concepts and principles and applied to a prototypical (plain) low-carbon steel (AISI 1005) to predict the distribution of various crystalline phases within the as-welded material microstructure in different fusion zone and heat-affected zone locations, under given GMAW-process parameters. The results obtained are compared with available open-literature experimental data to provide validation/verification for the proposed GMAW modeling effort.

High temperature tensile properties of laser butt-welded plate of Inconel 718 superalloy with ultra-fine grains

For successfully forming multi-sheet cylinder sandwich structure of Inconel 718 superalloy, high temperature tensile properties of laser butt-welded plate of Inconel 718 superalloy were studied. The experiment results show that tensile direction has great effect on elongation of the laser butt-welded plate. Under conditions of transverse direction tension, the maximum elongation reaches 458.56% at 950 °C with strain rate of 3.1×10−4 s−1, in which the strain rate sensitivity value m is 0.352 and the welding seam is not deformed. Under conditions of longitudinal direction tension, the maximum elongation is 178.96% at 965 °C with strain rate of 6.2×10−4 s−1, in which m-value is 0.261, and the welding seam contributes to the deformation with the matrix. The microstructure in as-welded fusion zone is constituted of austenite dendrites and Laves phase precipitated in interdendrites. After longitudinal direction tension, a mixed microstructure with dendrite and equiaxed crystal appears in the welding seam due to dynamic recrystallization. After high temperature deforming, many δ-phase grains are transformed from Laves phase grains but a small part of residual Laves phase grains still exist in the welding seam. The deformation result of multi-sheet cylinder sandwich structure verifies that high temperature plasticity of the laser butt-welded plate can meet the requirement of superplastic forming.

Microstructure, hardness and tensile properties of fusion zone in laser welding of advanced high strength steels

Fusion zone (FZ) of advanced high strength steel welds, with similar and dissimilar combinations, in diode laser welding was characterised in respect to microstructure, microhardness and tensile strength. Average FZ hardness and tensile properties were correlated to the respective microstructure and chemistry. A linear relationship of the FZ hardness with carbon content was observed for all welding combinations; however, carbon equivalent representing all the alloying elements in the FZ showed slightly better linear fit. The plot of calculated martensite hardness and experimental FZ hardness versus carbon content represented three regions: high carbon content, >0·15 wt-%, leads to fully martensitic microstructure with good hardness matching; reducing the carbon content to 0·1–0·15 wt-% resulted in mixed microstructure consisting dominantly martensite with few fraction of ferrite giving hardness value just below martensite hardness; and for low carbon content the microstructure was dominantly soft ferrite phase causing large deviation from martensite hardness. Fusion zone tensile strength was observed to follow linear relationship with hardness.On a caractérisé la zone de fusion (FZ) de soudage au laser à diodes de soudures avancées d’acier à forte résistance, avec combinaisons similaires et dissimilaires, par rapport à la microstructure, à la microdureté et à la résistance mécanique. On a corrélé les propriétés moyennes de dureté et de traction de la FZ à leur microstructure et à leur chimie respective. On a observé une relation linéaire de la dureté de la FZ avec la teneur en carbone pour toutes les combinaisons de soudage; cependant, l’équivalent en carbone représentant tous les éléments d’alliage de la FZ montrait un ajustement linéaire légérement meilleur. La courbe de la dureté calculée de la martensite et de la dureté expérimentale de la FZ par rapport à la teneur en carbone représentait trois régions: une teneur élevée en carbone, > 0·15 wt-% en poids, conduisait à une microstructure entiérement martensitique avec bonne corrélation de la dureté une réduction de la teneur en carbone à 0·1–0·15 wt-% en poids avait pour résultat une microstructure mixte consistant principalement de martensite avec quelques fractions de ferrite, donnant une valeur de dureté juste au-dessous de la dureté de la martensite; et pour une faible teneur en carbone, la microstructure était principalement une phase de ferrite molle produisant une grande déviation par rapport à la dureté de la martensite. On a observé que la résistance à la traction de la zone de fusion suivait une relation linéaire avec la dureté.