Journal of Welding Science

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In this research, the effect of different welding parameters on residual stress and microstructure of the weld region, as well as the comparison of two methods of measuring residual stress using critical fracture longitudinal wave method and preformation method have been investigated. For this purpose, the taguchi DOE methodology is used as a statistical method to optimize four parameters of pulse current, base current, and pulse on time% and pulse frequency to minimize longitudinal residual stresses in austenite 304 AISI stainless steel. After welding, stress measurements were performed using two methods critical fracture longitudinal and perforation, and hardness, tensile and OM tests were performed on the specimens. The tests results show that at all levels of the pulse parameters arranged with the standard L9 Taguchi array, the incident heat input is irrefutable and the effect of this parameter is move then 50%. The optimum conditions obtained while the highest frequency level should be considered. The general trend is achieved from the residual stress measurement charts is consistent with the logic of stress distribution in both methods. Sample number 1 with stress equivalent to 232 MPa and sample number 9 with stress of MPa 126 in ultrasonic method with frequency 4 MHz have the highest and lowest stress among different samples, respectively. The size of the coaxial grains weld was directly related to the incoming heat, so that the least amount of coaxial grains in the welding center was related to specimens NO. 3 and 9 with grain size of 8 µm and 9 µm, which in these samples had the lowest amount of welding heat is measured. The samples 1 and 4 with HV 128 and HV 144 hardness and MPa 633 and MPa 639 have the least hardness and tensile strength and the highest strength and hardness of sampled 3 and 9 with 166 and 161 hardness and tensile strength MPa 703 and MPa 695.
 

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Dissimilar welding of AISI 304L austenitic stainless steel to AISI 409 ferritic stainless steel with GMAW process usingtwo Ar-O2 and Ar-CO2 shielding gas mixtures was studied. ER316LSi and ER309LMo filler metals were chosen by considering 5 and 15% delta ferrite according to the Schaeffler equations and diagram. Based on the observations, both filler metals accompanied by Ar-2%O₂ shielding gas resulted in acceptable weldments. Yield strength and UTS of tensile samples were 288 and 424 MPa, respectively. All tensile samples fractured in the ferritic base metal. Microhardness test results demonstrated that the maximum hardness of 190-200 HV was obtained from ER316LSi weld metal. The minimum hardness of 145 HV was found in the HAZ of 409 side mainly due to the grain coarsening. Microstructural examinations revealed needle-like precipitates formed perpendicular to each other in the HAZ of 409 stainless steel. It seemed that the pre-existing TiC precipitates evolved into the needle shape precipitates as a result of rapid heating and cooling rates during the welding process.
 

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The influence of heat-input and pre-heat treatment on the structure, mechanical and corrosion behaviors of 2205 duplex stainless steel joint by means of GMAW process was the goal of this study. In this regards, the welding process was done using different heat input in the range of 0.6 to 1.4 kJ/mm and different pre-heating treatments in the range of 25 to 100 ^oC. The microstructural properties of prepared samples were evaluated using x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Based on archived results, the microstructure of as-welded samples were combinations of Widmaneshtaten austenite which nucleated from boundaries and growth toward central part of ferrite grains. By increasing the heat-input, the percentages of ferrite and austenite phases decreased and increased, respectively. In this condition, the highest value of strength and ductility was achieved in as-weld samples with medium (1.0 kJ/mm) heat-input. The corrosion studies showed that the heat-input has negligible effects on corrosion behaviors of 2205 duplex stainless steel joint. It was also found that the pre-heating treatment has adverse effect on the mechanical properties of the junction.    

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Galvanic corrosion is an ever-present problem in all different environments, particularly in tanks. The goal of this project is to develop a finite element model that can be used with experimental data to characterize the corrosion of a galvanic weldments couple in an electrolyte. In this study sample are welded by gas tungsten arc welding and friction stir welding. According to ASTM G8, Evaluation of corrosion properties examined with cyclic polarization test in 0.5 molar H₂SO₄ andthe information required to validate the model was prepared. The finite element model is developed using COMSOL and Math Module through derivation of equations describing corrosion thermodynamics and electrochemical kinetics. The results showed that reducing in heat input to improve galvanic corrosion behavior in the weld sample.In addition to result of simulation reveal sample that welded by gas tungsten arc method had higher current density galvanic corrosion in comparison with friction stir sample.

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The effect of heat input of submerged arc welding process on the corrosion bahavior of weld metal of API X42 gas pipeline steel weld joint was investigated. For this purpose, 6 annealed sheets of 15mm thickness were prepared from the X42 microalloyed steel. Submerged arc welding process with varying heat input of 37.8, 18.9 and 12.6 kJ/mm was used for joint welding. Then potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to evaluate the corrosion behavior of the welded joints (in 3.5% NaCl solution). The evaluation of the microstructures of the welded metals in the weld joints were conducted using the scanning electron microscopy. X-ray diffraction was used for the analysis of the phases formed in the weld metal microstructure. Scanning electron microscopy observations and patterns obtained from the X-ray diffraction showed that the increase in heat input resulted in the increase in the amount of ferrite. The grain size also increased. Corrosion test results showed that by increasing the heat input of the weld process, the corrosion resistance increased..

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In this paper, numerical and empirical investigations of the effect of AISI 347 stainless steel interlayer on the microstructure, mechanical properties and fracture mode of AISI 321 stainless steel resistance spot welds have been conducted. For this purpose, two types of joints, the first free from inter layer and the second contains interlayer with 0.05 mm thickness as well as difference currents and times,were evaluated. In order to examine the mechanical properties including maximum force and tensile mode, tensile – shear test of the spot welds was done. The obtained results indicated that an increase in the welding time and current resulted in a change in fracture mode from interfacial to peripheral owing to an increase in fusion zone volume. The change in the chemical composition because of the presence of interlayer and an increase in cooling rate caused the formation of different phases as well as observation of the dispersed Martensite phase in fusion zone.
 

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In this study, first,diffusible hydrogen of cellulosic electrode E8010-P1 and low hydrogen electrode E8018-G was measured by mercury displacement method according to ISO3690. Then,the effect of preheating and post-heating on the sensitivity to hydrogen inducedcold cracking in welding of 18mm API5L X70 steel with these electrodes was investigated according to ISO17642-2. The results of visual inspection, penetrant test,metallographic examination, and hardness test showed that welding with cellulosic electrode leads to cracking unless both preheating and post-heating are applied.While in the case of low hydrogen electrode, cracking occurs only if no preheating or post-heating is applied.
 

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In this research, the dissimilar welding of St52 plain carbon steel to W400 wear resistant steel and its effect on the microstructure and wear properties of the wear resistant steel was investigated. The wear resistant steel was produced via direct quenching with nominal hardness of 400 HB. Gas tungsten arc welding was used for joining process. The results showed that welding led to hardness reduction, wear rate increase and also significant changes in microstructure of the heat affected zone of the wear resistant steel. According to the results, by increasing the heat input for about 9%, the hardness and wear rate of the heat affected zone was decreased 8% and increased 250%, respectively. According to the scanning electron microscopy observations the main wear mechanisms of the base metal were adhesion and abrasion. However, the wear mechanisms of the heat affected zone were mainly adhesion and delamination. By increasing the heat input, the delamination was increased significantly. 

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In this research, gas tungsten arc welding of dissimilar joint between 4130 low alloy steel and AISI 201 austenitic stainless steel was investigated. Four filler metals i. e. ERNiCr-3, ER 309L, ER 308L and ER 80SB2 were used. After welding, microstructural features of various areas and also fracture surfaces were examined using optical microscopy and scanning electron microscopy. Tensile test was conducted in order to study the mechanical properties of each joint. It was found that ERNiCr-3 is fractured from fusion zone and the others were fractured from 4130 base metal. Also, some second phase particles such as NbC were seen in the ERNiCr-3 weld joint. SEM observation showed that the fracture behavior of ERNiCr-3 weld joint is semi brittle and the others are ductile. The fusion zone of ERNiCr-3 weld joint was fully austenitic and consisted of equiaxed grains and no crack was seen in this area. The fusion zone of ER 308L and ER 309L were composed from cellular dendrite and finally ER 80S-B2 weld joint was consisted of lath martensite.

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In the TIG-MIG hybrid welding, higher weld efficiency and better weld quality are obtained with respect to each individual TIG and MIG welding methods. Moreover, in this method, the MIG arc is more stable in pure argon shielding gas. Therefore, in this study, the influence of TIG-MIG hybrid welding parameters on the welds appearance quality and welds depth to width ratio of a 316L austenitic stainless steel was investigated using optimum parameters of Taguchi design of experiments (DOE). Microstructure of the heat affected zone (HAZ) obtained from the hybrid welding was compared with those of each individual MIG and TIG welding techniques under equal heat-input condition. The results indicated that the most important parameter in the hybrid method to obtain the best appearance quality and the highest depth to width ratio is the distance between the two arcs. The MIG and TIG currents are the next influencing parameters. The width of HAZ and the size of constituent grains in hybrid welding with optimum parameter, were smaller than those of each individual TIG and MIG processes due to the higher associated cooling rate in the hybrid welding technique.

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High strength low alloy steels are widely used in gas industry, so shield metal arc welding in pipelines to transport natural gas from Iran is of great importance. For experimental investigation of seam weld and integrity of girth weld, destructive and non-destructive tests are required. In this article the effects of normal heat treatment on properties of multi pass welding in different situations (6-7:30 , 7:30-9 , 9-10:30 , 10:30-12) with 36 in outside diameter is evaluated by chemical,  metallography, tensile, toughness and hardness. The result shows that normalizing increases ferrite ratio in root pass and weld cap pass respectively 24 and 6 percent than base steel. Also the increase rate of ferrite in root, hot, filler, and the cap pass are respectively 32, 14, 12 and 7 percent before than normalizing. The elongation weld of was increased ratio than before the heat treatment in base metal respectively 65 and 5 percent. The impact energy alignment to weld (9-10:30) had a rate of 70 percent increase before the heat treatment. The increase rate of C, V and Ti in the weld zone according to base metal in situation of 6-7:30 are respectively 0.01, 0.003 and 0.005.

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In this research, microstructure and mechanical properties of AISI316 to AISI430 dissimilar joint were investigated. For this purpose, GTAW process using ER316L and ER2209 filler metals with diameter of 2.4 mm was used. The microstructure and fracture surface of the welded samples were characterized by optical microscopy and scanning electron microscopy. Also the mechanical properties of the welded samples were evaluated by tension, impact and microhardness tests. It was found that the microstructure of the welded sample with ER316L filler metal contained Widmanstatten austenite with inter-dendritic and lathy ferrites. Also, in the welded sample with ER2209 filler metal, Austenite phase in ferrite matrix was seen. In tension test, all samples were fractured from AISI430 side of the joint in a ductile manner. ER2209 weld metal indicated low impact energy of about 27 J, while ER316L weld metal indicated higher impact energy of about 43 J. The fracture surface in both welded samples indicated brittle fracture mode. The microhardness of the weld metal of the welded sample with ER316L filler metal was higher than the welded sample with ER2209 filler metal due to the presence of alloying elements, proper distribution of delta ferrite and finer microstructure.

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Shield metal arc welding on the high strength low alloy steels in pipelines to transport natural gas from Iran is of great importance. In this article the effects of annealing heat treatment on properties of multi pass welding in different situations (6-4:30 , 4:30-3 , 3-1:30 , 1:30-12) with 36 in outside diameter is evaluated by chemical,  metallography, tensile, toughness and hardness. Tensile test results showed the lowest yield strength (Vertical to weld and in position 6-4:30) equal to 348 MPa, and the lowest energy impact (Vertical to weld and in position 1:30-3) equal to 108J. The impact energy alignment to weld had a rate of 12 percent increase before the heat treatment. The amount of hardness variation in different areas and positions is negligible (less than 5 percent). Images of metallographic test made by light and electron microscopes demonstrated that the amount of perlite cap pass weld and heat affected zone near the weld metal were decreased compared to main metal to respectively 29 and 8 percent. The elongation weld of was increased ratio than before the heat treatment in base metal respectively 75 and 23 percent. The increase rate of C, V and Ti in the weld zone according to base metal in situation of 3-4:30 are respectively 0.02, 0.003 and 0.006.

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In the present study, effect of inclusions characteristics changing on the formation of acicular ferrite in submerged arc welding of API5l-X65 low alloy steel was investigated. Three different welding fluxes with different chemical composition and basicity index of 0.72, 0.82 and 0.99, and two different welding heat inputs of 1.6 kJ / mm and 2.4 kJ / mm were used to create inclusions with different characteristics such as chemical composition and size. The results indicate that inclusions acting as acicular ferrite nucleation sites and improvement of the microstructure and resulted mechanical properties, can be observed in welding conditions in which the welding flux with lowest basicity index and higher welding heat input. Under these conditions, the percentage of inclusions with a high titanium oxide value and size range of 0.5 to 1.5 micrometers is increased, which increases the amount of acicular ferrite in the microstructure. However, in other welding conditions, formation of grain boundary ferrite reduces amount of acicular ferrite and weakens mechanical properties of weld metal compared to the base metal.

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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.

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In this study the effect of activating fluxes on the penetration depth, microstructure and microhardness 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 FB-TIG 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.

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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.
 

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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.
 

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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 non-homogeneous 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.