Narrow Weld Bead Research Articles

Effect of Continuous and Pulsed Current Gas Tungsten Arc Welding on Dissimilar Weldments Between Hastelloy C-276/AISI 321 Austenitic Stainless Steel

In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

The effect of the weld fusion zone shape on residual stress in submerged arc welding

A new multiple-electrode submerged arc welding technique has been developed that imparts improved fracture toughness properties in the heat affected zone, produces a narrower weld bead geometry, and can also be employed with lower heat inputs than conventional SAW. This study examines how the difference in the weld fusion zone profile affects residual stresses for weldments of API X70 steel made using the same consumable, heat input and restraint, varying only the shape of the weld fusion zone. The contour method and neutron diffraction have been employed to map and compare longitudinal and transverse residual stresses. Results show peak longitudinal stresses in the weld are within 50 MPa for both, and this is believed to be because they have the same heat input and hence similar heat affected zone size. By contrast, the peak stress in the transverse direction is 120 MPa lower for the new SAW technique. The reduction in transverse stress is attributed to a narrower fusion zone profile. The new SAW technique opens up the possibility of producing high quality narrower welds with lower heat input which could lead to significant reductions in residual stress.

Evaluation of Charpy impact toughness using side-grooved specimen for hybrid laser-arc welds of ultra-high-strength steel

This paper discusses the significance of a narrow hard weld bead, produced by hybrid laser-arc welding, on the Charpy absorbed energy. A parametric finite element analysis with various strength mismatching and bead widths has been conducted on the strain field of side-grooved and normal Charpy specimens. The narrow weld bead promotes the accumulation of plastic strain energy on the base metal side. This feature is more significant in the normal specimen than in the side-grooved specimen. The results show that the method based on the Weibull stress criterion for converting the absorbed energy of the side-grooved specimen to that of the normal specimen can be applied to hybrid laser-arc welds of ultra-high-strength steel. The converted energy is consistent with the absorbed energy measured in the normal specimen. This study indicated that the absorbed energy of side-grooved specimen corresponding to the absorbed energy of the normal V-notch specimen increases with increasing hard zone width. On the other hand, the influence of strength mismatch ratio on the difference of the absorbed energy is rather weak.

Coating Layer Characterization of Laser Deposited AlSi Coating over Laser Weld Bead

Corrosion protection of steel components is an important topic in automotive industry. Laser beam welding makes a narrow weld bead, thus minimizing the damage to the original coating on the steel material. However, the weld bead loses its original coating and is vulnerable to corrosive attack. It was demonstrated in this study that laser beam generated AlSi coating is an effective way to apply a protective coating on the weld bead. Coatings with different thickness and topography have been deposited under different laser power and processing speed. The microstructure of the as-deposited coating and its evolution after heat treatment has been studied. EDS was employed to analyze the distribution of chemical compositions of the laser generated coatings. Several metallic compounds of Al and iron have been identified. It was found that the type of metallic compounds can be influenced by the laser processing parameters.

The Effects of GMAW Parameters on Penetration, Hardness and Microstructure of AS3678-A350 High Strength Steel

Abstract This research aims to study the effects of various welding parameters in gas metal arc welding (GMAW) process on welding penetration, microstructure and hardness of AS3578-A350 high strength steel with the thickness of 10 mm. The welding process parameters were a welding current of 100-200A, an arc voltage of 20-30V, a welding speed of 20-60 cm/min and a gas shielding type of Ar and Ar+CO 2 . The summarized experimental results are as follows. An increase of the welding current and voltage affected to increase the penetration depth of the joint. However, when the welding speed was decreased, it increased the penetration depth of the joint. Using the Ar gas for shielding the weld area, produced the higher penetration depth and the less narrow weld bead than the joint that was shielded by the mix gas of Ar+CO 2 . The variation of the welding process parameters affected to produce the various microstructures of weld metal and heat affected zone and also showed the various kind of hardness along the weld joint.

Fluid and arc behavior with ultra high frequency pulsed GTAW

During ultra high frequency pulsed gas tungsten arc welding (UHFP-GTAW), the root radius of arc decreased with arc constriction that caused the narrower weld bead. The larger arc force created the more depression of surface, which had been important to increasing of weld penetration. Simultaneously, molten liquid metal is the key factor during welding process, and the mobility of molten pool was enhanced by weld behavior compared with conventional gas tungsten arc welding (C-GTAW). In the paper, the characteristics of arc behavior and fluid of molten pool was discussed with UHFP-GTAW. The results indicated the significant effect of the arc plasma on heat and force of molten pool with UHFP-GTAW. Further, the temperature diffusion of molten pool would reduce, which can limit the impact of arc heat on base metal effectively.

CTOD Toughness Correction for Laser Welded Joints with Narrow Hardened Zone

The influences of very narrow weld bead and highly strength overmatching on the fracture toughness of laser beam welded components are investigated. This study focuses on the difference of plastic constraint in fracture toughness specimen (3-point bend specimen, 3PB) and structural components with crack in the weld metal. The equivalent crack tip opening displacement (CTOD) ratio, β, for the correction of CTOD toughness for constraint loss in structural components is numerically analyzed. The narrowness of weld bead induces constraint loss by plastic deformation in the base metal, both the 3PB and structural components. Nevertheless, in the case of the wide plate with shallow crack, the highly strength overmatching elevates the opening stress. Therefore, it is found that the β increase with increasing strength mismatch ratio. The influence of highly strength overmatching on β is important for assessment of fracture performance of laser beam welded component. The applicability of β to correction of critical CTOD in laser beam welded components is discussed. The fracture toughness tests with the 3PB and tension panel (edge through-crack panel) of the laser beam welded joints were conducted at a low temperature in the brittle fracture range. It is indicated that β can be applied to the CTOD toughness correction in laser beam welded component.

Neutron Strain Scanning of Fibre and Diode Laser Welds in Stainless Steel and Ti6Al4V

Fibre lasers provide an unprecedented combination of high beam quality, brightness and low cost. Fibre laser beams can provide an exceptionally high power density beam with a relatively large depth of focus. Compared to more established laser welding technologies such as diode laser welding, fibre laser welding produces exceptionally narrow weld beads. As with all types of welding, fibre laser welding produces residual stresses in the material forming and adjacent to the weld. The SALSA instrument at the Institut Laue Langevin (ILL) has been used to make neutron diffraction measurements for both fibre and diode laser welded stainless steel 304 and Ti6Al4V. Clear diffraction peaks are obtained from stainless steel 304 and residual stress distributions are obtained. Little variation in residual stress distribution with welding parameters is seen. Ti6Al4V diffraction peaks are complicated by phase transformations on cooling. Transformed beta phase peaks in Ti6Al4V allow the extent of the heat affected zone to be determined.

The effect of arc behavior on weld geometry by high-frequency pulse GTAW process with 0Cr18Ni9Ti stainless steel

Based on 0Cr18Ni9Ti austenitic stainless steel plate (h = 6 mm), a study on arc behavior by ultrasonic frequency pulse gas tungsten arc welding (GTAW) process has been carried out. The results show that with the increasing pulse frequency, an obvious pinch effect of arc plasma has been detected and also the increment of arc voltage, stiffness, and force. Then, the method, combining weld appearance and numerical simulation, has been adapted for weld behavior on the basis of arc behavior by ultrasonic frequency pulse GTAW process. As a result of arc shrinkage, the root radius of arc decreased, which caused narrower weld bead. The larger arc force led to more depression of pool surface that made the downward heat source and external force point, which had been important to increasing weld penetration. Meanwhile, the mobility of molten pool was enhanced by weld behavior compared with conventional GTAW process.

Micro-Welding of Copper Plate by Frequency Doubled Diode Pumped Pulsed Nd:YAG Laser

Abstract A pulsed laser of 532 nm wavelength with ms range pulse duration was newly developed by second harmonic generation of diode pumped pulsed Nd:YAG laser. High electro-optical conversion efficiency more than 13% could be achieved, and 1.5 kW peak power green laser pulse was put in optical fiber of 100 μm in diameter. In micro- welding of 1.0 mm thickness copper plate, a keyhole welding was successfully performed by 1.0 kW peak power at spot diameter less than 200 μm. The frequency doubled pulsed laser improved the processing efficiency of copper welding, and narrow and deep weld bead was stably obtained.

Fracture Toughness Evaluation of Laser Beam-Welded Joints of 780 MPa-Strength Class Steel

For fracture assessment of steel structures with laser beam-welded joints, it is significantly important to evaluate the fracture toughness of the weld metal. However, the fracture toughness of weld metal is often impossible to measure by standard Charpy impact testing in the brittle-to-ductile transition or upper-shelf temperature region, because of fracture path deviation (FPD) from the weld metal due to narrow weld bead and a high degree of overmatching in strength. In this work, evaluated fracture toughness of laser beam-welded joints of 780 MPa-strength class (HT780) steel is examined by Charpy impact testing and CTOD fracture toughness testing. The improved Charpy impact tests, using the specimen with three parallel welds or the side-groove specimen, are conducted in order to prevent FPD. The applicability and significance of the improved impact test methods to the laser beam-welded joints of high-strength steel are investigated by means of Weibull stress analysis. The Weibull stress analysis indicates that the 3-weld method could not necessarily prevent FPD in laser beam-welded joints of HT780 steel, since side beads are not as hard as main weld beads, due to reheating at the main weld. On the other hand, a side-groove specimen is effective for avoiding FPD, but intrinsic VE of the weld metal could not necessarily be obtained by using this specimen.

Dissimilar Metal Welding of Austenite Stainless Steel and Carbon Steel Using Nd:YAG Laser a Continuous Wave

Dissimilar metal welding (DMW) are used widely in various industrial applications due to the practical importance from the technical and economic aspect. However, DMW have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMW have used the several of heat source to decrease such as faults. Laser welding process has, in recent years, attracted more attention due to its special features: a small heat-affected zone and narrow weld bead due to the low heat input; welding at high speed; welding can be carried out in areas of difficult access; contactless energy transfer; welding in an exact and reproducible manner; possibilities for automation and robotization, and welding performed in various atmospheres. In this paper, the weldability on dissimilar metal welding of austenite stainless steel and carbon steel using Nd:YAG laser with a continuous wave was experimentally investigated.

ステンレス鋼の高出力ファイバーレーザ溶接とその特徴的な溶接部の形成機構の解明

A high-power fiber laser can produce an ultra-high peak power density of MW/mm2 level corresponding to a focused electron beam, and is promising as one of the desirable heat sources for high-speed and deep-penetration welding. In this study, therefore, fiber laser welding and simultaneous observation with high-speed video cameras and X-ray transmission real-time imaging system were performed with the objective of obtaining a fundamental knowledge of welding phenomena and defect formation mechanisms in producing deep and narrow weld beads in Type 304 stainless steel. A 6 kW fiber laser beam through φ 100 μm feeding fiber or φ 300 μm process fiber could be focused at 1.1 MW/mm2 or 120 kW/mm2 peak power density, respectively. Consequently, deeply penetrated weld beads with narrow width were formed, and fully penetrated welds in 8 mm thick plate could be produced at less than 2 and 4.5 m/min for 120 kW/mm2 and 1.1 MW/mm2, respectively. In the case of the ultra-high power density, humping weld beads were formed at more than 6 m/min. This reason was attributed to the intermittent melt ejection from a small keyhole inlet and the subsequent melt flows on the narrow molten pool surface. On the other hand, in the case of the high power density, weld fusion zones with porosity, sound partial penetration welds and underfilled weld beads with large spatters were obtained at the welding speeds below 3 m/min, between 4.5 to 8 m/min and above 10 m/min, respectively. These formation mechanisms were interpreted by considering bubbles formation from a keyhole tip leading to pores captured by the solidifying front, the formation of a long molten pool suppressing and accommodating spattering, and the production of a narrow, short molten pool causing easy generation of spattering, respectively.

Effect of Plastic Constraint on Cryogenic Tensile Properties of Alloy A286 Electron-Beam-Welded Joints.

Electron-beam welding (EBW) is judged to be a suitable welding method of alloy A286, which is an iron-base superalloy with difficult weldability. The strength of the weld of this alloy changes to be reduced by the weld heat input. However, in case of the joints with narrow weld bead, increase of the strength may be expected by the effect of plastic constraint, such as those produced by EBW. In order to clarify the welded joint geometries which are affected by plastic constraint, tensile tests with varing relative thicknesses were conducted at 293K, 77K and 4K. As a result, it was clarified that tensile strength of the joints with relative thickness less than 0.8 increased with the effect of plastic constraint, and the order of degree depending on temperature was such that 4K<77K<293K.

Generation of an ultra‐high energy density electron beam and its application for deep penetration welding: Characteristics of a 500 kV electron beam heat source (1st report)

Summary This paper describes the development of an ultra‐high voltage electron beam heat source with an electron gun incorporating a stacked array of 11 electromagnetic acceleration units. The characteristics of the electron beam are studied, and a strongly focused electron beam with an ultra‐high average beam power density of 160 ∼ 170 kW/mm2 using a beam power of 140 ∼ 180 kW is successfully generated. Its applicability to flat‐position single‐pass welding of ultra‐thick stainless steel plates is investigated. This beam allows a penetration depth of max. 240 mm in flat‐position welding at a beam power of 180 kW and a welding speed of 6.7 mm/sec to be achieved while enabling a narrow weld bead to be produced with high efficiency.

５００ｋＶ電子ビーム熱源特性（第一報） 超高エネルギー密度電子ビームの発生と深溶込み溶接への適用

An urtra-high voltage electron beam heat source with an electron gun employing 11-stage electromagnetic accelerating units was developed. The characteristics of the electron beam were studied and a strongly focused electron beam with an ultra-high average beam power density of 160-170 kW/mm2 using a beam power of 140-180 kW was successfully generated. Applicability of 500 kV ultra-high voltage electron beam to welding was investigated and it was found that this beam enabled a penetration depth of max 240 mm in flat position welding with a beam power of 180 kW and a welding speed of 6.7 mm/s, allowing a narrow weld bead to be produced with high efficiency.

Weld metal/ferritic steel interface in laser welded austenitic/ferritic dissimilar steel joints

Austenitic/ferritic dissimilar steel joints are widely used in power generation systems. Such joints are normally produced using conventional welding processes such as tungsten inert gas welding and manual arc welding. Research and application experiences have proved that nickel based filler is preferable for producing an austenitic/ferritic joint when using conventional welding processes [1-5]. Laser beam welding has, in recent years, attracted more attention due to its special features: a small heat-affected zone (HAZ) and narrow weld bead due to the low heat input; welding at high speed; welding can be carried out in areas of difficult access; contactless energy transfer; welding in an exact and reproducible manner; possibilities for automation and robotization, and welding performed in various atmospheres [6]. Industrial application potentials of laser welding are being actively investigated worldwide. Laser welding of dissimilar metals has also been a topic of interest recently. The possibility of using a laser to weld austenitic/ferritic dissimilar metal joints and the effects of processing parameters have been reported [7, 8]. Weld metal/ferritic steel interfacial microstructure and properties have been a critical issue fo r austenitic/ferritic dissimilar steel joints. Since it is the weak point of the joints, considerable efforts have been devoted to characterize it and to understand its influence on the quality of the joints made by conventional welding processes [9-13]. Data for such interfaces of laser welding joints is, however, limited, but still very important. In the present study, a high power CO2 laser was used to join an austenitic stainless steel to a low alloy ferritic steel. The joints were produced in two modes: autogenous welding (without filler) and welding with nickel based filler wire. The interfacial microstructure between the weld metal and ferritic steel was examined in both the as-welded and post-weld heat treated conditions. The objective of this letter is to report some results concerning the interface made by laser welding in order to provide useful knowledge for assessing the process. Base materials were AISI 347 austenitic and 13CrMo44 low alloy steel tubes with 43.5 mm outside diameter, 4.5 mm wall thickness and length of 23 mm. The chemical compositions of the base materials are listed in Table I. The filler wire used in the present study was commercial nickel based ENiCrMo-3 of diameter 1.2 mm. Laser welding was performed using a continuous wave CO2 laser. Plasma control and shielding gases (helium) at flow rates of 20 and 32 lmin -1, respectively, were used. The welding nozzle, wire feed and workpiece arrangement is shown schematically in Fig. 1. Welding parameters are given in Table II. The tube/tube joints were cut after welding, and some of them were heat treated at 650 °C for 1 h. The metallographic samples were prepared using standard procedures including grinding, polishing and etching. Optical and electron microscopy were used, with energy dispersive X-ray spectroscopy (EDS) and electron probe microanalysis (EPMA) for analysing major alloying elements.

ステンレス鋼のプラズマ溶接の研究

Recently, plasma process has been applied to such industrial uses as cutting and spraying. Arc plasma is constricted by the gas flow and/or metallic wall of nozzle in a plasma process. The temperature and the thermal energy intensity of the constricted arc plasma are much higher than those of ordinary open arc. In the cutting and welding applications, it will be expected that the plasma stream has a property of line heat source similar to the one as observed in Electrlon Beam Welding.In this report the experimental results on the plasma welding of stainless steel plate are described briefly. The electric capacity of plasma welding torch used in these experiments is about 8 KW. The plasma welding is capable of producing a narrow and deep weld bead by the action of "Key Hole". And a sound weld is obtained by one pass of torch even for a 15 mm thick plate. With the above welding energy source, optimum welding conditions are established for various thickness of plate. Welding speed in plasma process is much higher than that in TIG welding and others at the same welding energy.Various tests on the microstructure, mechanical property and the deformation of weld specimen are carried out with satisfactory results.It was confirmed that the formation of key hole in crater of bead had much influence upon the welding results. When the key hole is not formed, porosity is contained in most weld beads. The formation of key hole is sensitive to the travelling speed.