Showing papers on "Weldability published in 2018"

Weldability of thermoplastic materials for friction stir welding- A state of art review and future applications

Abstract: Polymer composites have certain advantages over metals in terms of mechanical as well as metallurgical properties. These can be joined with similar as well as dissimilar polymer composites (subject to certain conditions like glass transition temperature, rheological properties etc.). In last 20-25 years number of techniques and concepts has been developed to offer the possibility of joining of polymeric materials which have similar or dissimilar characteristics. In present scenario mechanical fastening and adhesive bonding is replaced by applying welding concepts like: laser transmission welding, friction stir welding (FSW), ultrasonic welding, hot fusion resistance welding etc. The FSW is one of the most acceptable welding techniques for production of structural/industrial components. In this present work, requirements of FSW and its process capability has been highlighted for joining of similar/dissimilar polymeric materials for future prospective.

Effect of heat treatment variations on the mechanical properties of Inconel 718 selective laser melted specimens

Abstract: The wide usage of Inconel 718 alloy is based on its fusion weldability and its availability in many different forms including cast, wrought and powder. Thus with the emergence of additive manufacturing (AM) techniques for metals, Inconel 718 is a prime candidate for materials to be considered. Powders that have been developed for powder metallurgy are readily available for use in various AM processes such as selected laser melting (SLM) powder bed. While much research has focused on optimizing the deposition parameters to achieve fully densified specimens, subsequent heat treatments and their effect on the microstructure also need to be understood. This study evaluated the microstructure of SLM specimens of Inconel 718 after various heat treatments and compared the resulting effect on the quasi-static mechanical properties.

Microstructures and mechanical properties of a welded CoCrFeMnNi high-entropy alloy

Abstract: The response of the CoCrFeMnNi high-entropy alloy to weld thermal cycles was investigated to determine its applicability as an engineering structural material. Two processes were used: high-energy-...

Homogenization of P91 weldments using varying normalizing and tempering treatment

Abstract: Creep strength enhanced ferritic/martensitic P91 steel is considered as a candidate material for the reactor pressure vessels and reactor internals of Very High Temperature Reactor (VHTR). Heterogeneous microstructure formation across the P91 weldments lead to premature Type IV cracking and makes the weldability of P91 steel a serious issue. The present research work describes the effect of normalizing and tempering (N&T) treatment on microstructure evolution in various zones of gas tungsten arc welded (GTAW) P91 pipe weldments. For N&T treatment, P91 pipe weldments were subjected to various normalizing (950–1150 °C) and tempering (730–800 °C) temperature. The effect of varying heat treatment on tensile properties and hardness of P91 pipe weldments were studied for V-groove and narrow-groove weld designs. The effect of increase in normalizing temperature (fixed tempering temperature) resulted in increase in strength and hardness, while increase in tempering temperature (fixed normalizing temperature) resulted in the decrease in strength and hardness of P91 steel weldments. The better combination of strength, ductility and microstructure were obtained for the maximum normalizing temperature of 1050 °C and tempering temperature of 760 °C.

Effect of post weld heat treatment on weldability of high entropy alloy welds

Abstract: The effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.

Mechanical properties of friction stir welded St 37 and St 44 steel joints

Abstract: In this study, the weldability of lower strength St 37 grade steel plate with a higher strength steel plate (i. e., St 44) using the friction stir welding technique has been studied. St 37...

Weldability of marine grade AA 5052 aluminum alloy by underwater friction stir welding

Abstract: Friction stir welding (FSW) is a solid-state joining process producing high-quality welds with lower residual stresses and improved mechanical properties. Underwater FSW is a variant of FSW process which controls heat conduction and dissipation along the weld line improving the joint properties. The feasibility of underwater friction stir welding of AA 5052 H32 aluminum alloy to improve the joint performance than normal friction stir welding is addressed in this paper. The effects of tool rotational speed and welding speed on ultimate tensile strength by underwater and normal friction stir welding were analyzed and compared. It was observed that the tensile strength of underwater welded joints was higher than normal FSW joints except at 500 rpm. Maximum tensile strength of 208.9 MPa was obtained by underwater friction stir welding at 700 rpm tool rotational speed and welding speed of 65 mm/min. The optimum process parameters for achieving maximum tensile strength by normal FSW were compared with underwater FSW. The result showed that the ultimate tensile strength obtained by underwater FSW was about 2% greater than that of the normal FSW process. The joints with maximum tensile strength during underwater and normal welding fractured at the retreating side of the welded joint. Microstructural examination revealed that heat-affected region was not found in underwater welding. Microhardness was decreased slightly towards the stir zone. Fractography observation revealed that the welded joints exhibiting higher joint efficiency failed under ductile mode.

Effect of Cu, Cr and Ni alloying elements on mechanical properties and atmospheric corrosion resistance of weathering steels in marine atmospheres of different aggressivities

Abstract: This paper studies the individual and combined effect of adding Cu (0.26–1.06 wt%), Cr (0.54 wt%) and Ni (0.92–2.92 wt%) alloying elements to carbon steel with regard to mechanical behaviour and atmospheric corrosion resistance in two marine atmospheres with different chloride deposition rates (20 and 71 mg Cl−/m2 · d). Mechanical properties are assessed in terms of yield strength, ultimate strength, elongation, hardness and weldability, while atmospheric corrosion resistance is evaluated by determination of corrosion losses, rust layer structure, and nature of the corrosion products formed. The best atmospheric corrosion resistance is obtained with weathering steel (3 wt% Ni), which would be suitable for use unpainted in marine atmospheres of moderate salinity (≤20 mg Cl−/m2 · d), though a longer cooling time would be required during its manufacture in order to assure adequate weldability.

Laser welding of NiTi shape memory sheets using a diode laser

Abstract: NiTi shape memory alloy (SMA) are widely applied in many industrial domains, such as biomedical, aerospace, automotive and power plants, due to its outstanding functionality including superelasticity (SE) and shape memory effect (SME) The machining process of this material is challenging with a lot of barriers Accordingly, joining techniques can be an alternative approach to design the shape memory components with more flexibility Among all methods, laser welding process is a reliable and economical technique for joining of NiTi alloys However, thermal process influences strongly on the strength and functionality of the NiTi welded joints in the Heat Affected Zone (HAZ) and the Fusion Zone (FZ) Indeed, the transformation temperature of NiTi alloy can be altered due to varying in the material composition Therefore, controlling of the operational parameters, including laser power, scan speed or focal distance lead to an effective improvement in the mechanical and the functional behavior of NiTi joints It consequently enhances the weldability of this material This current study investigates the laser welding of NiTi thin sheets with a High-Power Diode Laser (HPDL) and reports microstructural, functionality, and mechanical effects of the process in following

A Review on Nano-Scale Precipitation in Steels

Abstract: Nano-scale precipitation strengthened steels have drawn increasing attention from the materials community recently due to their excellent mechanical behaviors at room temperature, high specific strength to weight ratio, superior radiation resistivity, good weldability, and many more to mention. With the advent of technology, such as synchrotron X-ray, atom probe tomography (APT), and high resolution transmission electron microscopy (HR-TEM), probing precipitates down to the atomic level has been made possible. In this paper, various nano-scale precipitate strengthened steels are compiled with the aim to identify the effects of size and number density of precipitates on the mechanical properties. Besides, the strengthening mechanisms, slip systems, and dislocation-precipitate interactions are reviewed. Moreover, the nucleation and stability of precipitates are also discussed. Finally, the challenges and future directions of the nano-scale precipitate strengthened steels are explored.

Studies on the weldability, mechanical properties and microstructural characterization of activated flux TIG welding of AISI 321 austenitic stainless steel

Abstract: The presence of titanium in AISI 321 austenitic stainless steel, mitigates the corrosion when deployed in specific applications such as boiler shells, aircraft exhaust manifolds and process equipment. Using Commercial flux purchased from Edison Welding Institute (EWI), studies were conducted to note the effect of Activated Tungsten Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds and compared with conventional TIG welding. A thin flux layer was applied to the surface of the 6 mm thick plate, followed by a conventional TIG welding process. The bead on trial results shows that compared with the TIG welding process, the flux causes the weld depth to increase, weld bead width to decrease and weld area to increase. This incredible depth of penetration (DOP) has been accomplished by the mechanisms of reversal of Marangoni flow and Arc constriction. From various experimental trials, arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm min−1 were found to be optimal and subsequently used as input parameters to produce a good quality A-TIG welded butt joint. The welded joint is subjected to transverse and longitudinal tensile and bend tests, charpy impact toughness tests, microhardness, optical microscope, x-ray diffraction analysis, ferrite number measurement and Scanned electron fractography. The welded joint exhibited improved tensile strength, bend and charpy impact toughness and hardness. The weld metal microstructure was observed to be austenite, delta-ferrite and TiC intermetallic compounds (Titanium carbides). The XRD pattern indicates that austenite and ferrite phases are present in both base and weld metal. The results of Fischer Feritscope FMP30 (ferrite measurement) show that the content of delta-ferrite in the weld metal (5.9 FN) is much higher than the parent metal (1.2 FN) and shows excellent mechanical properties in the A-TIG welded joint. Scanned electron fractography indicates that the failure of weld metal and base metal occurs in the ductile mode of fracture.

Microstructure and Tensile-Shear Properties of Resistance Spot-Welded Medium Mn Steel

Abstract: The medium Mn steels are gaining increasing attention due to their excellent combination of mechanical properties and material cost. A cold-rolled 0.1C5Mn medium Mn steel with a ferrite matrix plus metastable austenite duplex microstructure was resistance spot-welded with various welding currents and times. The nugget size rose with the increase of heat input, but when the welding current exceeded the critical value, the tensile-shear load increased slowly and became unstable due to metal expulsion. The fusion zone exhibited a lath martensite microstructure, and the heat-affected zone was composed of a ferrite/martensite matrix with retained austenite. The volume fraction of retained austenite decreased gradually from the base metal to the fusion zone, while the microhardness presented a reverse varying trend. Interfacial failure occurred along the interface of the steel sheets with lower loading capacity. Sufficient heat input along with serious expulsion brought about high stress concentration around the weld nugget, and the joint failed in partial interfacial mode. Pull-out failure was absent in this study.

Welding of S960MC with undermatching filler material

Abstract: High strength structural steels are in high demand thanks to their favorable mechanical properties. They offer high strength with sufficient toughness and good forming capabilities. Applications range from shipbuilding, to offshore constructions, cranes, and pipelines. A lot of current research focuses on weldability of high strength low alloy (HSLA) steels, especially improving the toughness in the weld zone, i.e., weld metal (WM) and heat affected zone (HAZ). In the present work, four different fusion welding processes using undermatching filler metal are compared on 8-mm thick sheets of S960MC structural steel. The welding processes include electron beam, laser hybrid, plasma, and gas metal arc welding. The welded joints are characterized by means of mechanical testing, tensile, impact, and hardness testing, and microstructural investigaton, light optical, and scanning electron microscopy. Furthermore, microprobe analysis of the weld metal was used to investigate the chemical composition of the weld metal.

Investigation on laser welding of selective laser melted Ti-6Al-4V parts: Weldability, microstructure and mechanical properties

Abstract: In this study, laser welding was successfully used to join selective laser melted (SLMed) to SLMed and SLMed to wrought Ti-6Al-4V specimens. The microstructures, microhardnesses, tensile performances, fatigue lives and fatigue crack growth rates (FCGRs) of the welded specimens as well as SLMed specimens were investigated. It is found that the stress-relieved SLMed Ti-6Al-4V has a good laser weldability. The SLMed to SLMed and SLMed to wrought joints have similar microstructures (columnar prior β grain boundaries with inside acicular α′), microhardnesses (410 HV–450 HV), ultimate tensile strengths (UTSs) (~ 1200 MPa), yield strengths (YSs) (~ 1080 MPa) and FCGRs in the welding zones, which are also similar to those of SLMed specimens. But the fatigue lives of SLMed to SLMed and SLMed to wrought joints are lower than those of SLMed Ti-6Al-4V, and much lower than those of traditionally wrought annealed Ti-6Al-4V. Heat treatment on SLMed to SLMed joints decreases the microhardnesses (390 HV–410 HV), UTSs (1106 MPa), YSs (1008 MPa) and FCGRs in the welding zones, but shows no improvements on the fatigue lives. It can be concluded that microstructures significantly influence the microhardnesses, UTSs, YSs and FCGRs of the welded and SLMed specimens, but have very limited influences on the fatigue lives due to the existences of pores. Pores play a more decisive role in the fatigue lives, but have very limited influences on the UTSs, YSs and FCGRs.

Gas tungsten arc welding of 7075 aluminum alloy: microstructure properties, impact strength, and weld defects

Abstract: Precipitation-hardened 7075 (Al-Zn-Mg-Cu) aluminum alloys have low specific density and high strength. Because of these advantages, they are commonly used as construction materials in the aerospace industries. Even though they have such important and common areas of usage, their weldability is quite difficult. It is important to weld this alloy used in these industrial areas. In this study, 3 mm-thick 7075-T651 aluminum alloy materials were joined using different welding currents via gas tungsten arc welding (GTAW) method. The metallographic examinations were carried out to determine macrostructural and microstructural properties of the weld zones. Also, notch impact and hardness tests were performed to determine the mechanical properties of the welded samples. The results obtained as a result of the tests were evaluated and interpreted. The grain size of the weld center increased due to heat input occurring with increase of the welding current. Micro cracks (hot cracking) occurred in the roots of welding seams. The increase in the welding current affected the hardness distribution of the weld zone. The impact strength of the welded sample was negatively affected by the grain coarsening and micro cracks in the welding seam.

Review of current waveform control effects on weld geometry in gas metal arc welding process

Abstract: Control of welding parameters is an important factor in gas metal arc welding (GMAW) because these parameters determine the heat input, cooling conditions, and time during which the microstructure and the geometry of the weld are formed. It is therefore essential that sufficient heat is transferred to highly conductive metals like aluminum and appropriate heat input used with very sensitive metals such as stainless steel and high-strength steels or when welding dissimilar metals. The objective of this study is to identify parameters of current, voltage waveforms, and electrode feeding motion that directly contribute to improvement in metal and heat transfer conditions from the electrode to the base metals. The effects of these parameters on welded joint geometry are determined. The work critically reviews research on the effect on welded joints of control of current waveform, voltage, and the alternating electrode and analyzes the different parameters that promote forces acting during metal transfer. Experiments and case studies based on controlled waveforms are discussed. The analysis shows that in controlled short-circuit gas metal arc welding (CS-GMAW), all identified parameters contribute to control of heat input and reduction in the amount of spatter and fumes generated. Variable polarity gas metal arc welding (VP-GMAW) is found to be particularly effective for aluminum welding because of its good control of mass metal transfer and weld penetration. Mixed waveform approaches (i.e., 20 pulses/controlled short circuit) improve weldability in difficult welding positions.

Effects of thread interruptions on tool pins in friction stir welding of AA6061

Abstract: In this work, effects of pin thread and thread interruptions (flats) on weld quality and process response parameters during friction stir welding (FSW) of 6061 aluminium alloy were quantified. Otherwise, identical smooth and threaded pins with zero to four flats were adopted for FSW. Weldability and process response variables were examined. Results showed that threads with flats significantly improved weld quality and reduced in-plane forces. A three-flat threaded pin led to production of defect-free welds under all examined welding conditions. Spectral analyses of in-plane forces and weld cross-sectional analysis were performed to establish correlation among pin flats, force dynamics and defect formation. The lowest in-plane force spectra amplitudes were consistently observed for defect-free welds.

Assessment of Steel Subjected to the Thermomechanical Control Process with Respect to Weldability

Abstract: The study is concerned with the assessment of the weldability of steel S700MC subjected to the thermomechanical control process (TMCP) and precipitation hardening and characterised by a high yield point. Appropriate mechanical and plastic properties of steel S700MC were obtained using the thermomechanical control process through precipitation, solution, and strain hardening as well as by using grain-refinement-related processes. Constituents responsible for the hardening of steel S700MC include Ti, Nb, N, and C. The hardening is primarily affected by (Ti,Nb)(C,N)-type dispersive precipitates sized from several nanometres to between ten and twenty nanometres. The welding process considerably differs from TMCP conditions, leading to the reduction of plastic properties both in the heat-affected zone (HAZ) and in the weld area. This study demonstrates that in cases of TMCP steels, where the effect of precipitation hardening is obtained through titanium and niobium hardening phases, the carbon equivalent and phase transformation γ–α cannot constitute the basis of weldability assessment. The properties of welded joints made from the above-named group of steels are primarily affected by the stability of hardening phases, changes in their dispersion, and ageing processes. The most inferior properties were identified in the high-temperature and coarse-grained HAZ area, where the nucleation of hardening phases in the matrix and their uncontrolled reprecipitation in the fine-dispersive form lead to a sharp decrease in toughness.

Microstructural and Corrosion Properties of Cold Rolled Laser Welded UNS S32750 Duplex Stainless Steel

Abstract: The main goal of this work was to study the effect of plastic deformation on weldability of duplex stainless steel (DSS). It is well known that plastic deformation prior to thermal cycles can enhance secondary phase precipitation in DSS which can lead to significant change of the ferrite-austenite phase ratio. From this point of view one of the most important phase transformation in DSS is the eutectoid decomposition of ferrite. Duplex stainless steels (DSSs) are a category of stainless steels which are employed in all kinds of applications where high strength and excellent corrosion resistance are both required. This favorable combination of properties is provided by their biphasic microstructure, consisting of ferrite and austenite in approximately equal volume fractions. Nevertheless, these materials may suffer from several microstructural transformations if they undergo heat treatments, welding processes or thermal cycles. These transformations modify the balanced phase ratio, compromising the corrosion and mechanical properties of the material. In this paper, the microstructural stability as a consequence of heat history due to welding processes has been investigated for a super duplex stainless steel (SDSS) UNS S32750. During this work, the effects of laser beam welding on cold rolled UNS S32750 SDSS have been investigated. Samples have been cold rolled at different thickness reduction (e = 9.6%, 21.1%, 29.6%, 39.4%, 49.5%, and 60.3%) and then welded using Nd:YAG laser. Optical and electronical microscopy, eddy’s current tests, microhardness tests, and critical pitting temperature tests have been performed on the welded samples to analyze the microstructure, ferrite content, hardness, and corrosion resistance. Results show that laser welded joints had a strongly unbalanced microstructure, mostly consisting of ferritic phase (~60%). Ferrite content decreases with increasing distance from the middle of the joint. The heat-affected zone (HAZ) was almost undetectable and no defects or secondary phases have been observed. Both hardness and corrosion susceptibility of the joints increase. Plastic deformation had no effects on microstructure, hardness or corrosion resistance of the joints, but resulted in higher hardness of the base material. Cold rolling process instead, influences the corrosion resistance of the base material.

Cold Cracking of S460N Steel Welded in Water Environment

Abstract: This paper shows results of weldability testing of fine-grained high -strength low- alloy S460N steel welded in water environment by covered electrodes. The tests were carried out by using the CTS test specimens with fillet welds. Four specimens were welded under water and one specimen in air. Welded joints were subjected to non-destructive visual and penetration tests. The accepted joints were then subjected to macroscopic and microscopic inspection and Vickers hardness measurements as well. The experiments showed that S460N steel welded in water environment is characterized by a high susceptibility to cold cracking.