JOURNAL OF WELDING SCIENCE AND TECHNOLOGY OF IRAN
Year:2020 | Volume:5 | Issue:2 |Papers Count:12

In the present study, the effect of time and base metal microstructure on the Transient Liquid Phase (TLP) bonding of 304L stainless steel was studied. TLP was performed at 1050 0C for 5 and 60 minutes on the coarse grain austenitic and martensitic microstructure using BNi-2 interlayer. To prepare martensitic microstructure, as-received 304L was rolled at-15 0C up to 80% rolling reduction. TEM analysis was proved that the microstructure of 80% rolled samples consisted of two different morphologies of martensite namely as lath-type and dislocation cell type martensite. It was observed that the structure of bonded zone after 5 min has consisted of isothermally solidified zone (ISZ) containing γ solid solution and athermally solidified zone (ASZ) containing complex boride phases. Meanwhile, after 60 min of heating, the structure of bonded zone completely solidifies isothermally. The obtained results also showed that the martensitic microstructure considerably effect on the width of diffusion affected zone (DAZ) which was related to the reversion of martensite to ultrafine grain austenite during heating.

Increasingly, Welding is used in industry for assembled various products, such as ships, cars, trains and bridges. Welding distortion often results such as lack of accuracy during assembly and will have increases manufacturing costs. So, predict and reduce welding distortion is very important to improve the quality of welded structures. In this study, firstly, a prediction method of welding distortion, which merges thermo-elastic-plastic finite element method (FEM) and large deformation elastic FEM based on inherent strain theory, was developed. Secondly, the inherent deformations of weld joints in a large thin plate panel structure were calculated using the thermo-elastic-plastic FEM and their specifications were also examined. Then, using the obtained inherent deformations, the usefulness of the proposed elastic FEM was demonstrated through the prediction of welding distortion in the large thin plate panel structures. Finally, the influences of welding sequence on distortion were investigated. The results of elastic analysis shows distortion in edges and interior parts of the panels, that can be reduced by changing welding sequence to symmetrical welding sequence.

In this study, the effect of tool's forward velocity on the mechanical behavior of the Al-7075 alloy during friction stir welding was simulated. In this simulation, the Lagrangian method with rigid-Visco-plastic material was used. The results of the process temperature obtained by the simulation method were verified by the experimental friction stir welding test. Using the characteristic stress, strain and temperature relationships in the Al-7075 alloy were used. Also the changes material strength during the welding process by simulation was studied. The generated simulation defects was verified by experimental test.

In this study the effect of activating fluxes on the penetration depth, microstructure and mechanical properties of AISI316L austenitic stainless steel were evaluated by three TIG process variations (TIG, A-TIG and FB-TIG) and the results were compared together. . After selecting the optimal flux in the second stage, the effect of that on the penetration depth, microstructure and weld microhardness of welded 316L austenitic stainless steel by A– TIG and FBTIG methods, were evaluated and the results were compared by the sample which was welded by TIG process. At this stage, it was found that the depth and width to depth ratio in FB-TIG method is slightly greater than the other two methods. Also in FB-TIG method, eqiaxed dendritic zone in the center line of weld is slightly greater than in A-TIG method. Study of microhardness of weld in three methods shows that in A-TIG and FB-TIG methods hardness of center line is more than TIG method.

Friction stir welding (FSW) was conducted on AISI 304 austenitic stainless steel plate with 2 mm thickness. The FSW was performed at a welding and rotational speeds of 50 mm/min and 400 rpm, respectively. Microstructure observations by the optical microscopy showed that a severe grain refinement occurred in the stir zone (SZ). Electron backscattered diffraction analysis (EBSD) results indicated that high fraction of low angle grain boundaries (LAGBs) developed in the thermo-mechanically affected zone (TMAZ) through the occurrence of the dynamic recovery. Moreover, in the path from the TMAZ towards the SZ, the fraction of high angle grain boundaries (HAGBs) increased with decreasing the fraction of LAGBs through the occurrence of continuous dynamic recrystallization (CDRX). 100 Pole figure showed the formation of shear texture components of A*1 and A*2 in the SZ which implied the occurrence of CDRX mechanism.

Welded tubular joints are widely used in various industry structures for high efficiency subjected to pressure, bending and twisting. Welded structures are the main parts of structures, buildings, bridges, gas pipes, pressure vessels and power transmission equipment in the ship building, construction, oil, gas, petrochemical industries and power plants. A sample of pipe-welded joints is a X-tubular joint that has been investigated in this study. The main objective of the present work is to investigate the heat transfer and residual stress caused by the three-stage welding process in Xtubular joint made of St52 using Simufact Welding software. The welding process involves three welding steps using arc welding. The finite element model contains the thermal and mechanical properties of base metal and welding metal as a function of temperature. Also, advanced modeling tools such as mesh adaptation during the process and meshing compatible with the welding site, the birth and death technique of the element and the source of heat transfer have been used. Welding simulation showed that significant residual stresses were created in the joint after welding. Comparison of the results shows that the numerical results and empirical measurements are in good agreement with each other and the existing model can provide a good prediction of temperature distribution and stress control in this welding process.

This Research has been Conducted to Investigate the Effect of Preheating Temperature on the Weld Toughness of API 5L X65 Carbon Steel Material. Since the API 5L X65 PSL2 Micro Alloyed Material Is Widely Used in Oil and Gas Refinery Industries, In This Research, We Tried to Investigate the Effect of Preheated Temperature on the Welding Toughness of the Mentioned Steel. In This Research Two Steel Pipes with a Diameter of 46 Inches and a Thickness of 36. 5 mm Were Tested. The Pipes Were Welded With an Arc Welding of Tungsten Electrodes With Neutral Protective Gas (GTAW) and Shield Metal Arc Welding (SMAW) Combination Process Using a Filler Metal ER 80S-G and Electrode E8018-G. Before the Welding Operation, They Were Preheated at a Minimum Temperature of 100 Degree Celsius and a Maximum Temperature of 250 Degree Celsius and Controlled. Then, Charpy Impact Test Was Used to Investigate the Effect of Preheating Temperature on Toughness and Absorption of Welding Energy and a Metallographic Test Was Used to Investigate the Macroscopic and Microstructure of This Steel. Also in This Research, a Hardness Test Was Used to Determine the Hardness of Weld Metal. Based on the Obtained Result, the Controlled Preheated Temperature Due to Mild Cooling Rate Increased the Weld Toughness Properties and The Creation of Coaxial Fine Grains in the Crystalline Structure of the Steel Mentioned and Conversely, Inappropriate and Uncontrolled Preheating Temperature May Increase the Hardness and Strength and Reduce the Amount of Toughness and the Formation of Coarse Grained Columns in the Crystalline Structure Due to the High Cooling Rate. Base on this, it is Concluded That the Weld Metal with a Controlled Preheat Temperature has a Higher Toughness and Resistance to Impact, While Weld Metal with an Uncontrolled Preheat Temperature has Less Toughness and is More Sensitive to Cracking, Especially Hydrogen Cracks.

Magnesium alloys are very attractive materials owing to their properties of low density, high specific strength and stiffness, good castability, and weldability. AZ31 magnesium alloys show better situation in terms of weldability than the other, so it has more applications than other magnesium alloys. In this study, TIG and pulsed TIG welding method was used to welding the AZ31 alloy and finally microstructure and mechanical properties of welds with metallography, scanning electron microscopy, tensile test were examined. The results showed that the heat input affected the size of grains that are leading to changes in mechanical properties. Sample was welded with TIG welding with minimum current has maximum strength among the samples both pulsed TIG welding and TIG method. It is observed that with increasing frequency in TIG welding, strength is reduced. Despite the same IP and IB, higher frequency has created a stronger welding. Also increases the frequency leads to more fine-grained samples, resulting in increased strength.

Dissimilar weld joints between stainless steels and nickel based super alloys are extensively used in petrochemical, gas and oil applications. These joints jave great challenges from metallurgical transformations point of view. In this research, microstructural evolutions and corrosion behavior of laser weld joint between Inconel 625 and AISI 430 ferritic stainless steel were investigated. Ferritic stainless steels are less expensive and have magnetic properties in comparison with austenitic stainless steels. Scanning electron microscope and optical microscope were used in order to study the microstructures of weld metal and heat affected zone. It was found that fine dendritic microstructuresare formed in the weld metal which isgrown in a competition manner. An epitaxial growth was observed in the interface between AISI base metal and weld metal. No considerable grain growth was observed in the heat affected zone on Inconel 625. Corrosion resistance of weld joint was investigated in 3. 5 % wtNaCl solution using potantiodynamic polarization test. It was concluded that corrosion resistance is increased from AISI 430 base metal toward Inconel 625 base metal.

In this study, corrosion behavior of Ti-6Al-4V titanium alloy joint by friction stir welding with a rotational speed of 375 rpm and a travel speed of 100 mm/min was investigated. The welding procedure was carried out under β-transus temperature that was consisted of equiaxed grains in the stir zone. The corrosion behavior of the welded joint was investigated in 3. 5% NaCl solution at temperatures of 25, 37 and 80. Microstructure investigation of sample surfaces after electrochemical experiments was conducted using SEM. results revealed that the β phase was mainly corroded at all three testing temperatures, however the corrosion in the sample tested at 80 ° C was more considerable.

In this research, dissimilar welding of NiTi shape memory alloy to AISI 304 austenitic stainless steel Archwires was investigated. For this purpose, common straight orthodontic archwire with rectangular cross-section and dimensions of (0. 635 × 0. 432 mm) were selected and the laser welding technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD). Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and nonhomogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe2Ti, Cr2Ti, TiNi3, and Ti2Ni wereformed during laser welding in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe2Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of dissimilar laser welded archwires of these alloys.

In this article the effects of carburizing heat treatment on girth weld with containing titaniumoxide and titanium carbide nanoparticles (X-65 grade of gas pipeline) is evaluated. The charpy results show that in the carburized sample containing titanium oxide and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium carbide and titanium carbide nanoparticles), has been respectively increased by 6% and 42%. Also, the ultimate strength carburized sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium oxide and titanium carbide nanoparticles) has been respectively increased by 20% and 28%. The results show that the fatigue life in both carburized nano-alloy samples has been increased. The fatigue life in the carburized sample of titanium carbide nanoparticles has increased more than that of titaniumoxide nanoparticles. The fatigue test results show that in the carburized sample containing titanium carbide nanoparticles compared to the tempered sample containing titanium oxide nanoparticles, fatigue life (150-N force) has been increased by 20%. In this loading the fatigue life (tempered sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by 31%. The results show that the residual stress in both carburized nano-alloy samples has been decreased The hole drilling strain gage results show that in the tempered sample containing titanium oxide oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium oxide nanoparticles and titanium carbide nanoparticles), hoop residual stresses has been respectively decreased by 9% and 6%.