Journal of Welding Science

Transient liquid phase (TLP) bonding of AISI 304L stainless steel was carried out using BNi-2 amorphous interlayer. The microstructure of the joint area was studied by using optical and scanning electron microscopes and energy dispersive spectroscopy. The effect of bonding temperature (1030-1110 °C) was studied on the microstructure and corrosion behavior of the TLP bonded samples. Electrochemical corrosion resistance of the bonded samples was evaluated in 3.5% NaCl solution at room temperature. The mechanism of the microstructure formation and the solidification sequence at the joint area were discussed. Ni- and Cr-rich borides, Ni-Si-B compound and fine Ni3Si particles were identified in the γ-Ni matrix at the joint centerline. The microstructural investigations revealed that the solidification sequence of these phases is: L→ γ + L → γ + Ni boride + Cr boride + L → γ + Ni boride + Cr boride + Ni-Si-B Compound. The highest corrosion resistance was observed in the sample bonded at 1070 °C for 30 min, which is comparable to that of the as-received AISI 304L stainless steel. It was attributed to the bond region microstructure with a negligible amount of eutectic constituents formed in the athermally solidified zone.

The welding joints were investigated due to the significance of similar welding of Corten A weathering steel and its dissimilar welding with St12 plain carbon steel in industrial applications. The gas metal arc welding (GMAW) technique with carbon dioxide shielding gas was utilized in the present work. The welding process comprised current and voltage control, welding wire injection rate, shielding gas rate, welding speed, connection configuration, and microstructure evolution. Mechanical properties and microstructure evolution in similar and dissimilar joints and weld defects were evaluated by tensile, bending, hardness, metallographic, and radiographic tests. The weld microstructure in similar and dissimilar joints included grain boundary ferrite, acicular ferrite, and WidmanStatten ferrite. The tensile strengths of the similar and dissimilar joints were respectively 497 and 303 MPa. The weld zone hardness was 210 and 180 Vickers for similar and dissimilar joints, respectively. In conclusion, similar welding outperformed dissimilar welding considering weld joint defects, mechanical properties, and microstructure.
 

The aim of the present study is to investigate the mechanical and microstructural properties of 1.7225 steel in laser welding process using Nd:YAG pulsed laser device and then to determine the optimal focal length relative to the part in the welding area. After welding, microstructural characterization, microhardness and tensile tests were performed. Evaluations showed that the optimal focal length for welding of steel sheet 1.7225 with a thickness of 1 mm, it was about 9 mm and the focus was 1 mm below the surface of the part. Due to the high thermal concentration and cooling rate in laser welding, a completely martensitic microstructure has been observed in the molten and heat-affected regions of all specimens. In this alloy, the hardness of the base metal is 310±10 HV. After welding, the hardness of the sample with the optimal focal length   has reached 625±10 HV in the heat affected zone and 730±10 HV in the melting zone. Also, the results of tensile test showed that the tensile properties of the sample with the optimal focal length were almost similar to the base steel and fracture was observed in the base steel region.
 

In this investigation the effect of oxides powders of SiO₂, MoO₃ and CuO on the depth of penetration, microstructure and hardness profile of GTAWeld precipitation hardening martensitic 17-4PH was assessed. Samples were taken from 17-4PH steel sheet with the dimensions of 150*50 mm and with the thickness of 5 mm, and were welded by oxide powder of SiO₂, MoO₃ and CuO. Results showed that using oxide powder increased the penetration depth of the welded joints by about 150 percent compared to the normal condition. Also, it was shown that although using SiO₂ powder increased the penetration depth to about 7.49 mm, it provides inferior weld bead appearance. The use of MoO₃ and CuO powder increased the penetration depth of the weld to about 5.3 mm. Although inclusions were found throughout the side of the weld bead when MoO₃ powder was employed for welding. The microstructure of the weld in different samples did not vary and included dendritic structure with delta ferrite located between the dendrites. The hardness profile of the welded joints showed the closeness of the hardness of the welded joints using different oxide powder with the base metal.
 

Stainless steel cladding is the formation of an alloy by creating a thin layer of stainless steel on another metal. In this research, a layer of SA240-TP316 austenitic stainless steel was coated on SA516-GR60 steel. Experiments were conducted to compare the mechanical properties of SA240-TP316 and claded SA516-GR60 steel welds in order to investigate the possibility of replacing the SA240-TP316 steel alloy. Examining the results of the chemical analysis of SA240-TP316 alloy shows that the coating has a similar chemical composition to SA240 alloy and with increasing depth, the hardness of the weld metal and the percentage of chromium is higher and the percentage of molybdenum in the weld alloy is lower. Comparing the ultimate strength of SA516 alloy after cladding and welding with SA240 stainless base alloy shows the improvement of tensile strength. In the first case, the strength changes in the range of 470 to 503 MPa and in the second case in the range of 477 to 570 MPa. The highest hardness was obtained in the heat affected area. Bending test showed that bending without cracking up to 180 degree angle is a sign of weld metal remaining ductile. The results of the impact test also show the ability to absorb energy, especially around the voltage of 150 volts.

 

In multi-pass welding, the heat-affected zone formed in each pass is subjected to another thermal cycle by the next pass. This problem locally changes the microstructure of the heat-affected zone depending on the position of each area relative to the melting line of the next pass, and the overlapping of the heat-affected areas will lead to complex microstructures. In this research, based on the practical conditions of pipe production in the factory, including submerged arc welding with four electrodes in two passes from the inside and outside of the pipe, the thermal cycles of the heat-affected zone were first analyzed. Simulation of thermal cycles of heating and cooling up to the peak temperatures of 950, 1150 and 1350 °C was performed in a dilatometer and the transformation behavior and microscopic structure were studied. Simultaneous modeling of precipitation dissolution and austenite grain growth was done. It was observed that the grain growth reaches a limit in 300 seconds. The main cause of grain growth at temperatures below and above 1150 °C, is the dissolution of fine and coarse deposits of niobium carbonitride, respectively. Also, the modeling of austenite formation and decomposition was done using the classic JMAK equation. It was observed that the parameter n does not depend much on temperature; while parameter k strongly depends on temperature, transformation amount and austenite grain size.
 

This study aimed to investigate the effect of electron beam welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between 17-4PH stainless steel and Ti6Al4V alloy. For this purpose, the welding of these two alloys was performed with an copper interlayer with a thickness of 1 mm. Two different welding speeds of 0.7 and 0.9 m/min with four levels of beam offset  (0, 0.2, 0.4 and 0.6 mm) from the center of the interlayer towards the steel were used to accomplish the experiments. The results show that by using the copper interlayer with thickness of 1 mm, the cracks caused by the formation of intermetallic compounds are removed from the weld pool. At the interface between the titanium and the weld pool, at the beam offset  of 0 and 0.2 mm, a solid solution of copper and TiCu2 intermetallic compounds is formed, while at the beam offset  of 0.4 and 0.6 mm, a solid solution of copper and TiCu intermetallic compounds is formed. The weld pool, at the beam offset  of 0 and 0.2 mm, consists of TiCr2+TiFe2 intermetallic compounds while at the beam offset  of 0.4 and 0.6 mm, solid solution of iron (α-Fe), solid solution of copper and TiCu intermetallic compounds are formed. The highest value of hardness is observed at the interface between the weld pool and the titanium alloy, as well as at the interface between the weld pool and the steel, which is due to the presence of intermetallic compounds with high hardness in these regions. By increasing the welding speed and the beam offset, the hardness value decreases, which is due to the reduction of brittle intermetallic compounds in the joint structure. By increasing the beam offset from 0.4 mm to 0.6 mm at the speed of 0.7 m/min, the shear strength increases from 180 MPa to 210 MPa and at the speed of 0.9 m/min, the shear strength raises from 230 MPa to 250 MPa. The welded sample with the welding speed of 0.9 m/min and the beam offset of 0.6 mm has the highest shear strength equal to 250 MPa. The failure in all samples happened at the interface between the weld pool and the titanium alloy, which shows that the weakest region in the joint is this interface.

In this study, we employed the active TIG method with ultrasonic vibration (UV) for welding 316L steel. Throughout the active tungsten inert gas (A-TIG) welding process, a high-frequency ultrasonic generator produced high-intensity acoustic waves at an optimal frequency of 20.3 kHz and a vibration amplitude of 8 micrometers. These waves were directed into the molten weld pool, covered by SiO2 nanoparticles serving as an activating flux. The effect of UV and nanoparticles on weld geometry and weld microstructure was analyzed and compared with conventional TIG welding proces. The results indicated that the use of nanopowder not only increased weld penetration by approximately 17.5% but also reduced the Weld Bead Width (WBW) by 28% compared to Conventional TIG. These values increased by 25% and decreased by 35%, respectively, in the presence of ultrasonic waves. Additionally, the introduction of nanomaterials into the molten pool led to finer grains. The ultrasonic waves played a crucial role in ensuring the uniform distribution of these nanomaterials in the melt, ultimately resulting in an enhanced microstructure of the weld.

In this research, the effect of temperature and time parameters are investigated on the microstructure and mechanical properties of  dissimilar brazing of 17-4 PH stainless steel and Ti-6Al-4V alloy with BNi-2 filler metal. The microstructure of the joint is evaluated with optical and scanning electron microscopes and the mechanical properties of the joint are also evaluated with tensile-shear and microhardness tests. It can be seen that at a constant temperature of 1050°C, increasing the time from 15 to 30 minutes decreases the shear strength from 34.66 to 29.39 MPa. Formation of brittle intermetallic compounds like NiTi2 and FeTi2 increase strength and promote brittle fracture.At a fixed time of 15 minutes, increasing the temperature from 1050 to 1100 °C causes the strength to increase from 34.66 to 38.46 MPa. Also, the increase in temperature and time increases the ISZ thickness formed in the joints on the side of the filler metal - Ti-6Al-4V from 41.40 to 81.48 microns. The increase in temperature and time also causes more diffusion of boron into the SS-filler joint, which forms various boron compounds and widens this region.

316 steel is used in transportation, space, and chemical equipment. This steel is in demand in these industries due to its durability. It is used to increase the lifespan and renovate equipment. The research explores the impact of laser energy density on st6 cladding. It specifically focuses on the microstructure and geometric characteristics of the cladding. The cladding is applied on 316 steel. The experiment was designed with energy density changes from 40 to 116 J/mm and powder rate changes between 12 and 20 g/min. Optical and electron microscopic images were used to evaluate the samples. The results indicated that the dendritic arms grew larger with increased energy density. The dimensions increased from 1.5 to approximately 3. In other words, the speed of cooling is doubled. Increasing energy density from 40 to 75 J/mm reduced cobalt to chromium ratio from 2 to 0.7. It also decreased cobalt to iron ratio from 35 to 3. The changes emphasize how energy density affects microstructure and phase transformations.

In this study, the effects of friction stir welding (FSW) parameters on the properties of dissimilar joints formed between 5083 aluminum alloys and 316L austenitic stainless steel, with a thickness of 4 mm, are investigated. The tool speed is varied in the range of 16 to 25 mm/min, while the tool rotation speed is maintained at a constant value of 250 rpm. To examine the microstructure of different weld regions, both optical and scanning electron microscopes are employed. To assess the mechanical properties, hardness and tensile tests are conducted. The results shows the formation of a composite region characterized by steel reinforcement particles dispersed within an aluminum matrix. At the steel-aluminum interface, a single layer of discontinuous intermetallic composition with a thickness of approximately 2 micrometers is observed. Notably, when the rotation speed is set to 250 rpm and the tool speed is 16 mm/min, a tensile strength of 298 MPa and ductility of 26% (93% of the tensile strength and 50% of the ductility of the 5083 aluminum alloy) are achieved.

In this study, the microstructure and mechanical properties of dissimilar resistance spot welding of AISI 430 steel and S500 MC steel were investigated. To carry out this research, Taguchi's L9 array was used to determine the number of samples and determine the range of variables of each sample, and after welding the samples and performing the shear tensile test, the sample with the highest tensile shear strength (13740 N) and the highest amount of fracture energy (102160 Joules), was considered as the best example; Also, the variables of this sample, i.e., welding current of 12 kW, welding time of 12 cycles, and electrode force of 3 kN, had the highest signal-to-noise values, and these values were chosen among the best range of variables among the proposed variables. Then, a microhardness test was performed on the welded sample with the above variables, and microstructural studies were performed by optical microscope and scanning electron microscope. The hardness of the weld zone was observed to be about 400 Vickers, and the microstructure of the weld metal consisted of ferrite, martensite, and Widmannstatten ferrite.

This research studied the effect of two-stage over aging treatment on the pitting corrosion behavior and microstructure of the weld metals in the 17-4 precipitation hardening stainless steel. For this purpose, this steel was subjected to solution annealing heat treatment at 1035°C for one hour before welding. Then gas tungsten arc welding (GTAW) was performed using ER630 similar filler metal. Subsequently, a section of the weldment was subjected to two-stage over aging treatment. The microstructure and corrosion resistance of the weld zone after the two-stage over aging treatment were investigated and compared with the weld zone behavior in the as-weld condition. Microstructural studies showed that the two-stage over aging treatment of the weld zone led to the tempering of the martensitic, the formation of more reversed austenite, and the formation of α-ferrite. The volume fraction of austenite in the as-weld condition was approximately %7 and increased to about %30 after two-stage over aging treatment, a four-fold increase. The pitting potential (EPit) of weld metal was -18.15 mv in the as-weld condition and reached 122.54 mv after two-stage over aging treatment, which also signifies an improvement in pitting resistance. The two-stage over aging treatment also reduced the potential differences between the different parts of welding zones reducing the galvanic corrosion occurrence. The assessment of mechanical properties through impact test revealed that impact resistance after

This study aimed to investigate the effect of diffusion welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between AISI 418 stainless steel and Inconel 738 superalloy using Ni interlayer with a thickness of 50 µm. The experiments were performed in a vacuum furnace at three temperatures of 1000, 1050 and 1150 °C for 45, 60, 75 and 90 min under the pressure of 5 MPa.The results show that voids and non-bonded areas are seen in the samples that were bonded at a lower temperature (1000 °C). By increasing the joining temperature from 1000 °C to 1050 °C, all micro discontinuities have disappeared, which shows that the microplastic deformation of roughness has improved. Then, by increasing the temperature to 1150 °C,non-bonded areas are observed in the joint due to the reduction of pressure on the contact surfaces. When pure nickel is used as an interlayer, intermetallic compounds of
γ' [Ni3(Al, Ti)] are formed in the γ matrix phase on the side of Inconel 738 superalloy while compounds of FeNi3 and γ (γFe, Ni) are formed on the side of AISI 418 stainless steel. According to the results of line scan analysis, the slope and penetration of elements in Inconel 738 superalloy is lower than AISI 418 stainless steel , which indicates less penetration in Inconel 738 superalloy. In the sample welded at the temperature of 1050 °C and the time of  90 Min, the penetration value of the nickel interlayer in AISI 418 stainless steel  and Inconel 738 superalloy was 40 µm and 35 µm, respectively. By comparing the maximum hardness, it can be concluded that the joint at the temperature of 1050 °C and the time of 90 Min has a lower maximum hardness than other samples. Therefore, it has better joint characteristics than other samples in terms of intermetallic compounds. The highest value of shear strength was obtained at the temperature of 1050 °C and the time of 90 Min, which is equal to 270 MPa.