Volume 56, Issue 10

Duplex stainless steel is widely used in the oil, chemical industry and to a lesser extent in the medical industry, because of the high mechanical properties, corrosion resistance and good weldability. In this study, AISI 2205 (22Cr5Ni3Mo) duplex stainless steel samples were joined using the CO 2 laser beam welding method. In order to determine the mechanical properties of the welded joints, tensile tests were applied and the hardness of the welded sample was measured on the cross-section. The microstructure characterization of welded samples was also carried out using optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Although, the mechanical properties of welded samples were found acceptable, the final microstructure of the welded metal and the heat affected zone (HAZ) were significantly affected by the ferrite phase due to the low heat input that caused high cooling rates, respectively.

Application fields for duplex stainless steels are drastically increasing. Industries producing and operating petrochemical process equipment, pipelines, bridges, pressure vessels, heat exchangers, rotors, and sea-water systems have a high demand for these steels. In this study, UNS S32205 duplex stainless steel plates of 3 × 40 × 145 mm were TIG welded with welding wires of W22 9 3 NL (2209). The main aim was to investigate the effects of various amounts of magnetic δ-ferrite and other important phases or intermetallic compounds that are formed during and after welding. The phase quantities differing by the welding conditions and argon shielding gas mixtures containing 0, 1, 3, 6, and 9 vol.-% N 2 are studied. The investigations included Charpy V-notch impact tests, weight loss corrosion tests, and microstructural analyses according to ASTM A 923 and magnetic δ-ferrite measurements according to EN ISO 17655, and EN ISO 8249 as well as image analyses according to ASTM E-562, ASTM E 1245 for a comparision of the effect of the amounts of all phases. The differences with respect to the welding parameters were also identified.

Duplex stainless steels are sensitive to high temperature exposure. The microstructure of the duplex stainless steels changes at high process temperatures. Such microstructural changes might affect the mechanical properties and corrosion resistance of duplex stainless steel. Therefore, the microstructural properties of 2205 duplex stainless steel welds were studied and respective microstructural changes during the welding process have been investigated by finite element analysis before fabrication process. 2205 duplex stainless steels were welded using the TIG process. The heat distribution along the cross section of weldments according to the TIG welding parameters was calculated by finite element analysis using ANSYS software. After metallographic preparation of the weldments, each sample was etched by electro-chemical method and the ferrite-austenite ratio was examined by light microscopy. The finite element analyses and microscopic results were compared and the mechanical properties of the weldments were investigated using hardness tests.

Contrary to other keyhole welding applications on duplex stainless steels, a proper cooling time and a dilution were achieved during hybrid plasma gas metal arc welding that provided sufficient reconstructive transformation of austenite without sacrificing its high efficiency and productivity. Simultaneous utilization of keyhole and metal deposition in the hybrid welding procedure enabled us to get an as-welded 11 mm-thick standard duplex stainless steel plate in a single pass. Metallographic examination on hybrid plasma-gas metal arc weldments revealed only primary austenite in ferrite matrix, whereas in addition to reconstructive transformation of primary austenite during solidification, secondary austenite was also transformed in a displacive manner due to successive thermal cycles during multi-pass gas metal arc welding. On the one hand, secondary austenite provided barriers and retarded the crack propagation during the tests in laboratory air. On the other hand, chromium and molybdenum depletion in the neighborhood of secondary austenite precipitates yielded relatively high crack propagation rates in multi-pass weldments under chloride attack.

Arc stud welding is used to weld predominantly pin-shaped metal parts to metal workpieces. This welding process plays an important role in the field of steel structures, bridge building, shipbuilding, vehicle manufacture, manufacture of household appliances and steam boiler construction. Due to its vital importance, it is very important to determine the influencing parameters on the mechanical and microstructural properties of the weldment. In this study, AISI 304 stainless steel studs were welded onto the same type of base plate. It was observed that welding current, welding time, plunge and lift are prominent stud welding parameters. Welding current and welding time must be selected properly to obtain a high quality performance weld joint.

Since MIL-A-46100D high hardness armor steel plates with excellent resistance to penetration exhibit high strength, selecting the proper electrode used in the gas metal arc welding process is particularly important to obtain a weld joint with high quality satisfying the adequate strength and toughness requirements at the same time. Selecting a consumable electrode with a lower strength than the armor material enhances the ductility and the toughness, reduces the risk of cracking in the weld zone, but it may lead to a considerable loss in strength of welded armor steel joints as well. Thus, an optimization of strength and toughness is required in welding high hardness armor steel plates. Within the scope of this study, two different austenitic stainless solid wires, one of which conforms to AWS 5.9 and the other one to AWS 5.28, and two different cored wires conforming to AWS 5.29 standards were analyzed and compared with respect to weld joint strength and toughness. Although weld joints fabricated with solid wires were superior in weld toughness, weld joints with austenitic cored wires exhibited considerably higher tensile strengths without a significant loss in toughness.

Friction stir spot welding is a newly developed joining technology which is expected to be used in the automotive industry for joining body parts made of aluminum sheets. The effect of the rotational speed and dwell time on the mechanical properties of dissimilar friction stir spot welded aluminum sheet alloys was investigated in this study. In the experimental studies, macro-structural characterization, micro-hardness tests and tensile shear tests were conducted. The experimental results showed that the tensile shear load and tensile deformation of the friction stir spot welded joints decreased roughly by 20 % and 25 %, respectively, when the rotational speed increased from 1000 rpm to 2000 rpm. On the other hand, when the dwell time increased from 3 s to 11 s, the tensile shear load increased roughly by 7 %, while the tensile deformation decreased roughly by 19 %, respectively.

High energy radiation is produced during arc welding applications. For this reason, it is important to investigate the process in detail with respect to the welding technique, electrical current and materials. In this study, the SMAW (shielded metal arc welding) technique was used to weld specimens made of stainless steel SS304 and of low carbon steel A36. Welding currents of 90, 105, 120 and 135 A were selected. The radiation types and luminosities were measured for each material as well as the respective magnitude of electrical current. During the welding applications, UV radiation was mostly observed. In addition, visible light and IR radiation in the range of 200 to 1000 nanometers on the optical scale were recorded. The effects of electric currents on the photon energy rates were clearly pronounced. A larger radiation energy was observed for the UV band for welding both materials at all parameters.

Residual stress distributions in multipass welded API 5L X70 steel plates were determined by numerical and experimental methods. SYSWELD finite element software was used for numerical simulations. Microstructure variations were also considered for calculation of residual stresses. The continuous cooling transformation diagram was obtained via JMatPro software. The results showed that residual stress distribution is sensitive to number of weld passes, and microstructure changes. The simulation results were compared with those obtained by Magnetic Barkhausen Noise measurements on the welded plates. Simulation and experimental results gave qualitatively similar tendencies for the variation of the residual stress state.

Al-Mg 5083 alloy was friction stir welded by varying welding variables, i. e., rotational speed, traversal speed and tool tilt angle. Welded specimens have been tested by the instrumented Charpy test to evaluate total absorbed energy, as well as the energy for crack initiation and the energy for crack growth. Subsequently, the fracture surface was examined by optical and scanning electron microscopy (SEM) to evaluate surface type of fracture, and to correlate the microstructure with the impact energy. Based on this, the optimum windows of FSW parameters for Al-Mg 5083 alloy welding have been defined.

Powder injection molding consisting of four stages – feedstock preparation, injection, debinding and sintering – is a unique technique to produce small and complex metal or ceramic components in high quantity. One of the limitations of this method is the production of thick components, which arises from difficulties in de-binding stage. In this study, a novel method is presented to produce thick components with large sections by powder injection molding using preformed inserts in the injection stage. By using a wrought insert on which the feedstock is injected, the thickness of an injected section that needs to be debound, is decreased, while the whole thickness of the component is still large. The key point in this method is the amount of diffusion welding of the wrought insert and the injected feedstock to form an integrated component. 316L stainless steel has been used as material for both insert and feedstock. The effects of insert/component diameter ratio and the sintering atmosphere on diffusion welding have been studied. Finally, a defect-free thick component with a diameter of 20 mm is fabricated with a bonded area at the interface of the insert and injected section having shear strength up to 427 MPa.

In this study, butt welding of commercial AZ31 magnesium alloy sheets has been investigated by using the tungsten inert gas welding process with alternating and pulsed current. Magnesium alloy welding, although well developed and understood, can present some problems, such as porosity, hot cracking, oxide formation, etc. Samples of the welded parts have been examined by optic microscopy and mechanic tests. Results showed that porosities and homogeneous micro size oxides were rarely found. Orientation of the weld microstructure in direction of the heat transfer were also rarely observed and equiaxed grain morphology was the dominant grain structure as in the base metals. In addition, fusion zone and HAZ of the welded samples have generally shown twins. This seems to be a very dominant grain type particularly in pulsed samples. Hot cracking was not observed in any samples. Results of mechanical tests showed that pulsed current seems to generate more favorable higher mechanical properties of weld joints than alternating current for magnesium alloys.

In this study, iron based sintered parts were welded by high frequency induction welding. The effects of surface roughness on the mechanical properties of induction welded samples were investigated. Polished and unpolished samples were welded and mechanically tested by three point bending test. The hardness of the samples increased from the base material towards the weld metal. The weld metal, heat affected zone and the base material of the samples were investigated by light microscopy. In contrast to the polished samples, corrosion attack was registered in the welded region of unpolished samples. According to the results, the welding duration affects the mechanical properties. However, the surface finishing process was the dominant factor for the bending strength of the welded samples.

In this study, dual phase (DP 600) steel plates with a thickness of 1 mm were joined by copper-based (CuAl8) wire using gas metal arc brazing technique. Specimens were prepared in butt joint form. Brazing operations were done at four different working angles: 50°, 60°, 70°, 80° and 90°, respectively. CuAl8 wire consisted largely of copper served as the filler metal. After completing the brazing operations, the tensile properties as well as the micro- and macro-structures of the joints were analyzed in order to investigate the joinability of DP 600 steel using gas metal arc brazing technique.

In this paper the primary objective was to establish a new and robust mathematic model that can be used to estimate the hardness in the heat affected zone of manual metal arc welds of low alloyed steels. The mathematical model was checked using a large database of experimental data, containing data for more than 1600 runs. Beside the conventional approaches using carbon equivalent formula, very sensitive coefficients have been included in the model that take into account the smallest chemical influence on the materials, like the oxygen content in ppm or other different elements such as Ti that can have a significant influence on the microstructure and mechanical properties of the welds. Also, the main welding parameters were considered in the mathematical model as primary variables and were combined with the chemical composition in a unitary formula.

The aim of this study is to investigate the effect of vanadium and tungsten on wear behavior of Fe-C-Cr based hardfacing alloys. The wear behavior of hardfacing layers was determined by dry sand/rubber wheel abrasion tests according to ASTM G-65. The results of the abrasion tests were interpreted by metallographic examinations, SEM and EDX analyses as well as hardness measurements. According to the results of the experimental studies, the effect of W and V addition was discussed.

This study aims to investigate the weldability of 1050 aluminum alloy (AA1050) and galvanized 1314 steel by the cold metal transfer (CMT) procedur, comparing it with respective welding of similar aluminum sheets. Mechanical properties of welded specimens were determined by tensile testing and hardness measurements. The study was completed by microstructural analysis. The results showed that CMT welding can be applied successfully to join aluminum and steel.

This publication presents an experimental study on the resistance spot welding of SPA-C steel sheets used in side wall and roof application of rail vehicles. SPA-C atmospheric corrosion resistant steel sheets with a thickness of 2.3 mm were joined by using resistance spot welding as lap joint. A timer and current controlled resistance spot welding machine with 120 kVA capacity and a pneumatic application mechanism with a single lever were used to join the specimens. Welding periods were chosen as 5, 10, 15, 20, 25 and 30 cycles (1 cycle = 0.02 s) and also welding currents were increased from 6 kA up to 14 kA by rising in steps of 0.5 kA. The electrode force was kept constant at 6 kN. The welding joints obtained were exposed to tensile peel and tensile shear tests and their nugget sizes were calculated by results of optical microscopy measurements. The effect of nugget sizes on tensile peel strength and tensile shear strength was researched by using related diagrams and the optimum welding currents and times were advised.

Aluminum alloys are used in various industries including marine, defense, automotive, transportation and aerospace. Common to all of these industries is the need to join aluminum parts using fusion based welding processes. However, there are some difficulties in welding aluminum alloys, such as, for instance, hot cracking. In this study, the aluminum alloys 5083 and 6061 were welded using the TIG process and two filler wires (AlSi12 and AlSi5). Six different alloy combinations were investigated, i. e., 5083-AlSi5-5083, 5083-AlSi12-5083, 6061-AlSi5-6061, 6061-AlSi12-6061, 5083-AlSi5-6061 and 5083-AlSi12-6061. The mechanical properties of the samples were evaluated by microhardness scans, tensile tests as well as Charpy and three point bend tests. In addition, microstructural investigations were performed by optical microscopy.

The solid-state friction welding method, which is widely used in the automotive, machinery, aviation and aerospace industry, was applied in this study. AISI 420 martensitic stainless steel, which is difficult to join by using fusion welding methods, and AISI 4340 tempered steel, which is commonly used in the automotive industry, were joined. During the welding process, three different rotations as 700, 1000 and 1300 rpm were used and parameters such as friction pressure, friction time, upset pressure as well as upsetting duration were kept constant. After the welding process, welded joints were examined macroscopically and microscopically, and their microhardness were measured. Then, torsion tests were performed on these samples. During the torsion tests, the samples fractured outside the welded joint regions. Thus, it was concluded that torsional strength of welded joint zones was high and AISI 420 and AISI 4340 steels were smoothly joined by friction welding.

Forged welded (damascus) steels are produced by traditional methods and mostly used in the design of decorative tools. These steels are well-known for their good mechanical properties. The process for making forged welded (damascus) steel consists of stacking alternating sheets of different kinds of steel on top of each other and then forge welding them together. In this study, the steels 1075 and 15N20 were used for the forging and folding procedure. The effect of fold numbers on the microstructure and mechanical behavior were investigated. The steel consisted of both materials, 54 and 250 layers, respectively, produced by forge welding. The pattern layers are homogeneous and regular, but after the process sections with up to 54 pattern layers were irregular. Steel 1075 has a pearlitic microstructure, while steel 15N20 has a ferritic microstructure. The impact toughness and tensile strength of the folded steels improved with increasing the number of folds.