High-strength Weld Research Articles

Failure Analysis of Weld Metal Cracking in Weld Joint of API 5L X 75 Pipelines Steel

The development of steel alloy which result thin walled, high strength API 5L X75 grade, a restricting parameter controlling widespread use of X75 is the susceptibility to weld metal tracks. The excellent weld ability of this grade of the pipe steel has enhanced the potential for the use of high strength cellulose consumable like E6010 in root pass welding, but the risk of hydrogen assisted cold cracking (HACC) is also increased because of the high strength weld metal. This investigation outlines , the use of grade (E6010) of commercial cellulose consumable to assess conditions leading to hydrogen assisted cold cracking in the diluted weld metal. The research contained clarification of the link among microstructure; preheat temperature and hardness amounts for the weld consumable and its effect on cracking susceptibility. The cracking morphology studies indicated that there are many ways in which the crack can propagate in the weld metal and HAZ region. The mode of cracking observed was microvoide coalescence.

Susceptibility for extrusion welding of AlMg alloys

The extrusion of hollow profiles from high strength aluminium alloys through porthole dies causes serious problem in practice. Mainly, this is due to low weldability of these alloys and high extrusion force. The present paper discusses the investigations undertaken to determine the weldability of hard AlMg alloys using the original method and device. Main advantage of the proposed method is that it allows for the reflection of real welding conditions occurring in a welding chamber of the porthole die. Weldability tests were performed for alloys: 5754 (3.5% Mg), 5083 (4.5% Mg), 5019 (5.6% Mg) and 5xxx (7.1% Mg) in a wide range of temperature, unit pressure (normal compressive stress) and duration of welding. Microstructure and strength properties of the welds were examined. Most favourable welding conditions for the tested alloys, allowing for obtaining high strength welds were defined. To validate the laboratory experiments the extrusion trials were performed in the industrial conditions, in which the round tubes from 5754 alloy were produced using the porthole dies. The tensile strength of the welds in the extruded tubes is comparable to that for the solid material. Strength of the welds as well as of the solid material strongly increases with magnesium content in the alloy.

Micromechanical evaluation of DP1000-GI dual-phase high-strength steel resistance spot weld

In situ micro-cantilever bending tests were carried out on resistance spot welded DP1000-GI dual-phase high-strength steel in order to derive the mechanical response of the welds. Notched micro-cantilevers were milled using focused ion beam milling at the base metal, inter-critical, fine-grained and coarse-grained heat affected zones, and fusion zone. It was shown that due to large plastic yielding, linear-elastic fracture mechanics are inapplicable. To evaluate the fracture toughness of different weld zones, cyclic loading was applied to track the crack size and the conditional fracture toughness of weld zones was measured using crack tip opening displacement and J-integral methods. It was found that micro-cantilever bending method provides insight to the fracture toughness and local mechanical response of different weld zones. The results obtained can be used to make an accurate correlation between resistance spot welding process, microstructure and mechanical response of DP1000-GI dual-phase high-strength steel welds.

Stress corrosion cracking behavior of SUS301L-MT stainless steel laser-arc hybrid welded joints

Laser-arc hybrid welding (LAHW) has potentially employed for the excellent welding of cold rolled SUS301L stainless steel, promising for the new generation subway vehicles underframe, due to its low heat input and high welding speed. However, the stress corrosion cracking (SCC) behavior of this type welded joints is still unclear, which may be a potential risk for its applications. Here, in combination with the fracture morphology, microstructure and potentiodynamic polarization of the weld metal (WM), heat affect zone (HAZ) and base metal (BM), the slow strain rate tensile (SSRT) method was applied to systematically investigate its SCC behavior of LAHW-based SUS301L-MT stainless steel in 3.5 wt.% NaCl solution. The result indicated that the SCC susceptibility index (ISSRT) of welded joints is 0.09, much lower than that of BM (0.23). The low ISSRT should be mainly attributed to the cathodic protection of austenite originated from the corroding δ-γ interfaces. We believe that this study will help to facilitate the wide applications of LAHW for new generation of subway vehicles underframe and others high strength welding structures.

Soldadura de aços estruturais de alta resistência

Soldadura de aços estruturais de alta resistência

Clear plastic transmission laser welding using a metal absorber

This paper presents a novel method for obtaining a clean and high-quality joint between clear plastics through transmission laser welding (TLW). In the proposed method, dye is replaced with metal as the absorber. The key factors that affect the welding quality of polyethylene terephthalate were investigated. These factors included laser input power, clamping pressure, and different absorbers (carbon black (CB), and Fe wire). Compared with the joint welded using the CB absorber, that welded using the Fe absorber was cleaner and impurity-free with more stable and higher welding strength. High welding strength was associated with the thermal conductivity of the utilized metal absorber. Results indicated that dye absorber could be feasibly substituted with metal in the TLW of clear plastic.

Influence of tool geometry on material flow and mechanical properties of friction stir welded Al-Cu bimetals

Al-Cu bimetallic sheets were friction stir welded by three different kinds of pin profiles (threaded cylindrical, threaded conical and pyramidal). Among the three pin geometries used, the threaded conical tool provided the best compromise between the different material flow regions and thereby the fewest defects and the highest weld strength were obtained with this tool. As the cylindrical tool has the lowest contact area, it resulted in insufficient material flow around the pin and tunnel defects appeared on the advancing side. A downward material flow is essential to avoid tunnel defects on the advancing side. It was not possible to obtain a weld efficiency of one hundred percent due to the existence of a micro-void analogous to kissing bond on the retreating side. This flaw is a result of a downward material flow, which is essential to obtain a defect-less weld on the advancing side. Torque values and temperatures during welding were directly related to the downward material flow. In samples without tunnel defects on the advancing side, higher values of torque and temperature were recorded.

Development of high-strength welding consumables using calculations and microstructural characterisation

The development of new welding consumables requires several samples and experiments that must be performed to achieve the required mechanical properties. In the development of a metal-cored wire with a target tensile strength of 1150 MPa and acceptable impact toughness, thermodynamic and kinetic calculations via MatCalc were used to reduce the experimental work and the resources required. Micro-alloying elements were employed to obtain high strength as an alternative approach to conventional solid solution hardening. Investigations of the microstructure were performed via atom probing to understand the effects of micro-alloying elements. In particular, the influences of different elements on the precipitation behaviour in the weld metal were evaluated. The calculated mechanical properties are in accordance with the results obtained from experiments and can be explained by microstructural investigations. The approach is exemplified through vanadium and clarifies an efficient development route.

Identification of Process Parameters in Electromagnetic Pulse Welding and Their Utilisation to Expand the Process Window

Impact welding, represented by the industrial processes explosion welding and electromagnetic pulse welding, offers unique advantages over conventional welding processes, especially fusion welding. The joint is produced during a high speed impact between two workpieces without additional heating or melting. Thus, even dissimilar metals can be joined. However, in contrast to fusion welding, the fundamentals are understood to a significantly lesser extent. In this publication, the effect of the density of the surrounding gaseous medium is investigated. The results show that a lower density results in a higher weld strength. At higher densities, a weld can even be inhibited completely. High speed images of the impact indicate that this is caused by the obstruction of the so-called jet due to the increased air resistance. In general, “jetting” describes the ejection of oxides, dirt and superficial material from the closing gap during the impact. It is presumed to be essential for the formation of the bond.

Study on Gas Tungsten Arc Welding Characteristics of Nickel based Aerospace Alloys

Welding of high strength and corrosion resistant materials is always been a challenging task for the researchers. This work investigates weld strength of Inconel 825 using gas tungsten arc welding (GTAW) process. A Box-Behnken design of 27 experimental runs was employed. Further full quadratic models were developed to predict different welding responses. The predictive performance of the model shows an average percentage error as 6.72% for UTS, 2.79% for YS and 17.75% for% E. Welding current (I) was found to be the most significant process parameter followed by welding speed (V) for each response. The process parameters were optimized using desirability graphical analysis with maximum desirability value of 0.7089.

Impact of friction stir welding (FSW) process parameters on tensile strength during dissimilar welds of AA2014 and AA6061

Friction Stir Welding (FSW) is a solid state joining technique which is universally used for joining of aluminium alloys in marine, aerospace, automotive and many other applications of commercial importance. In this present study, the effect of FSW parameters on the weldability of dissimilar aluminium alloys such as AA2014 and AA6061 were investigated. The two plates were aligned perpendicular to the rolling directions and the welding was carried out. The main objective of the experiment is to find out the maximum tensile strength. The experiments were conducted on a milling machine. Three factor three levels Central-Composite matrix in Response Surface Methodology (RSM) is employed to carry out the experimental investigation. The “Design Expert 8.0”, software was used for regression and graphical analysis of data collected. ANOVA was used to check the validity of the model. A designed FSW experiments were carried out to get a high strength welding by controlling the rotational, welding speed and tool pin diameter. The tensile tests were carried under tension at room temperature in order to analyze the mechanical response.

Effect of welding parameters on mechanical properties and microstructure of friction stir welded brass joints

Friction stir welding is a method developed for the welding of high-alloy aluminum materials which are difficult to combine with conventional welding methods. Friction stir welding of MS 63 (brass) plates used different tools (tapered cylindrical, tapered threaded cylindrical), tool rotational speeds (1040, 1500, 2080 rpm) and traverse speeds (30,45,75,113 mm.min−1). Tensile, bending, radiography and microstructure tests were carried out to determine the mechanical properties of brass plates joined by friction stir welding technique. Microstructure characterization studies were based on optical microscope and SEM analysis techniques. In addition, after joining operations, radiographs were taken to see the internal structure failure. Brass sheets were successfully joined to the forehead in the macrostructure study. In the evaluation of the microstructure, it was determined that there were four regions of base metal, thermomechanically affected zone (TMEB), heat-affected zone (HAZ) and stir zone. In both welding tools, the weld strength increased with increasing tool rotation speed. The particles in the stir zone are reduced by increasing of the tool rotation speed. Given the strength and % elongation values, the highest weld strength was achieved with tapered pin tool with a tool rotation speed of 1040 rpm and a tool feed speed of 113 min−1.

Friction stir welding of advanced high strength (bainitic) steels for automotive applications

Friction stir welding has been emerging to be the most prominent and sought after metal joining technology as it leaves the signatures of minimal phase transformation during welding and precise weld joint. On the other hand, Bainitic steel has been the candidate steel for automotive applications as it fuses and balances the characteristics mechanical strength and deformability. It can also be tuned playing with various strengthening mechanisms. Most importantly, in automotive sector, the ductility of cut-edges (stretch-formability), fatigue, and welding (about 300 spot welds in a car) are quite essential. In this connection, bainite can help in optimizing these key contents. Advanced bainitic steels (microalloyed bainitic steels, and carbon-free bainitic steels) are also being developed to improve the formability performance, sensitivity to damaging systems, and toughness compared to traditional bainitic steels. The present paper emphasizes the feasibility of friction stir welding on bainitic steel through depth of penetration at different stir speeds. The optimization of stir speed was done through profiling temperature changes (thermography) that occur during welding. The microstructural analysis was done to analyze the resulting phases during welding. To support the microstructural analysis, microhardness evaluation was also undertaken at all weld conditions.

Analysis of the effect of the thermomechanical processing on the laser weld joint of aluminum alloys of Al-Mg-Li and Al-Cu-Li

The paper presents the experimental investigation of the laser welding of high-strength aluminum-lithium alloys of Al-Cu-Li and Al-Mg-Li system followed by the thermal processing, aimed to the production of a high-strength weld joint. It is founded that the thermal processing (quenching, artificial ageing) of the welded joint increases its strength, however the variation of the microstructure and phase composition is different for the two systems of the alloys. The thermal processing permits getting the tensile strength of the welded sample of 0.9 of the basic alloy strength for Al-Cu-Li and 0.95 for Al-Mg-Li.

Effect of pre and post welding heat treatment in SiC-fortified dissimilar AA6061-AA2024 FSW butt joint

The present study focuses on the effect of pre and post welding heat treatments on microstructural and mechanical properties of SiC included Friction Stir Welded joints in AA6061 and AA2024 aluminium alloys. The annealing of base metals as a pre welding heat treatment leads to more uniform distribution of SiC particles in the weld nugget. The post welding artificial aging heat treatment results in joint strength near AA6061-T6 base metal strength. Besides, the pre annealing and post aging heat treatment result in tensile strength and toughness of 92 and 96% of AA6061-T6 tensile strength and toughness, respectively. The micro SiC reinforcement in the weld nugget results in at least 14% higher weld strength than joints post weld heat treatment and without SiC particles additive. The abnormal grain growth in the weld nugget after post welding heat treatment has negligible effect on joint strength.

In situ neutron diffraction measurement of strain relaxation in welds during heat treatment

ABSTRACTNeutron diffraction (ND) is commonly used to investigate the stress redistribution before and after post-weld heat treatment (PWHT) in welded structures. However, there is a lack of information on the evaluations of strains during PWHT. The present work employed in situ ND to measure the relaxation of residual strains during conventional PWHT in multi-pass high-strength low-alloy steel welds. It was found that strain relaxation occurs principally during the heating stage of the heat treatment. The findings have important economic bearings and can be used to characterise comparable material combinations and optimise the PWHT process for high-strength low-alloy weld joints. This unique information also provides a valuable benchmark for the finite element modelling of this complex process.

Influence of alloying elements on the mechanical properties of high-strength weld metal

ABSTRACTHigh-strength lightweight constructions are a crucial part of transportation systems and steel constructions optimised for low energy consumption. In this investigation, the aim is to understand the influence of different alloying elements on the mechanical properties of all-weld metal samples of high-strength filler metals. Metal-cored wires with adjusted chemistry were produced and the measured yield strength is compared with calculated values which were obtained by thermodynamic and kinetic simulations. By increasing the content of the matrix alloying elements, no increase in strength could be achieved, but compared to that, higher strength was obtained by the addition of Ti, Nb and Al in combination. Furthermore, the influence of different Ti, Al and N contents is presented and discussed.

Dynamic compressive behaviour of weld joints

Materials used in military applications have to withstand multiple threats like ballistics and explosions. Thus, high-strength low alloyed (HSLA) steels are used. The main joining technique for metals is welding. Therefore, analysing the dynamic impact behaviour of high-strength welds is very important to fulfil these demands. Investigation of welds at high strain rates has rarely been conducted in the past. To determine the dynamic impact behaviour of hybrid laser-arc welds, the Split Hopkinson Pressure Bar (SHPB) technique was used. The base material was a quenched and tempered fine-grained armour steel with yield strength of 1100MPa.First, a full hybrid laser-arc weld was investigated by extracting specimens consisting of weld metal and heat affected base material. The influence of two variables, the cooling time between 800°C and 500°C (t8/5) and strength of filler material, on the impact behaviour was studied. The cooling time t8/5 was varied by preheating to influence the microstructure in the HAZ and to analyse the effect on the hardness and dynamic compressive strength.Subsequent analysis to detail the original investigation was carried out by dilatometer heat treatment of specimens to create homogenous subzones of the weld. These specimens have a homogenous microstructure of HAZ and were tested by SHPB to determine the stress-strain characteristics for the different microstructures of HAZ.The results of the weld specimen showed the effect of preheating and filler material strength on the dynamic compressive behaviour. The analysis of the different microstructures of the HAZ indicated that especially the tempered microstructure caused a reduction in dynamic compressive strength.

Reduction of Defects in Al-6061 Friction Stir Welding and Verified by Radiography

Friction Stir Welding is a new innovating process of joining of two work pieces. It is an relatively a new joining process and highly useful in welding method, which can produce high strength weld without using any toxic materials like electrodes. In this method, weld is obtained by frictional produced between shoulder and work piece [1, 2]. Main parameters which are to be considered for FSW are spindle speed and feed rate. By providing suitable parameter during welding defects will not be occurring. Also, FSW is an eco-friendly process because there is no fumes production and no filler material. To get high quality of weld, then high heat should be generated. In this paper, Al-6061 material is welded by H-13 tool with different parameters and quality of weld is examined by using a non destructive testing method called Radiography.

Effects of evolution of nanoscale copper precipitation and copper content on mechanical properties of high-strength steel weld metal

Nanoscale copper precipitation in high-strength weld metal was characterised by using atom probe tomography (APT) and transmission electron microscopy. In as-deposited zone, there was no copper precipitation. During welding thermal cycling, nanoscale copper of 2–3 nm in radius precipitated with face-centred cubic (FCC) and body-centred cubic (BCC) structure. During post-weld heat treatment (PWHT), FCC copper precipitate became coarsen and BCC transformed into FCC. The highest hardness was in the reheated zone which subjected to the peak temperature below 500°C; while the lowest hardness was both in deposited zone and the reheated zone which subjected to the peak temperature greater than 810°C. After PWHT, the hardness became homogenous as well as decreased. With increasing copper content, the hardness was increased and the toughness was slightly decreased. After PWHT, the toughness decreased due to the change in the structure of copper precipitates.