Journal of Welding Science

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High-strength low alloy steels are a class of steels used in applications that require high strength and good weldability, including ship hulls, gas pipelines and oil industry. One way to build parts is fusion welding that create areas with a large grain size in the heat-affected zone and increased susceptibility to hydrogen cracking. One way to solve this problem is to use solid state friction stir welding process. In this study, microstructural evaluation and mechanical properties of friction stir welding X-60 cross sections examined by optical microscope and by tensile and micro-hardness tests. The results indicate that changing welding parameters and thereby, change the heat input during friction stir welding have a great impact on maximum temperature and cooling rate that cause creating ferrite and bainitic ferrite in the weld zone. This change in microstructure of weld zone cause to improve mechanical properties that increase yield strength from 380 MPa to 420 MPa .Also, the friction stir process cause increasing hardness of 220 Vickers to an average of 280 Vickers and uniform distribution of hardness in the cross-section of friction stir joints.

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A517 is a low alloy high-strength steels that due to its high strength, toughness and weldability is used in ship building and submarine hulks. The welded areas of this steel often require repairs. In this study, the effect of number of welding repair on microstructure and mechanical properties of A517 steel is studied. Four samples (samples without repair, once repaired, twice repaired, and three times repaired) were welded by SMAW welding. Microstructural studies were carried out by using optical and scanning electron (SEM) microscopes. The effect of the number of repairs on mechanical properties of samples were investigated by using tensile, bending, impact and hardness The profile of hardness illustrated that the hardness in the heat affected zone near the base metal increased by repeated repairs while the hardness of this zone reduced in the third repaired sample. By repeating the welding repair, tensile and yield strengths of the welding areas were reduced and fracture impact toughness of heat affected zone at -51^○C was increased. Generally, the results of tensile tests of second and third repaired indicated that the strength of these samples were not meet the ASME IX standard requirements, so welding steel A517 in the second and third repairs is not acceptable.
 

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Cold roll bonding (CRB) is a solid state welding process, where the bonding is established by compressive plastic deformation of the metals. This process is applicable for a large number of materials. In addition, materials that cannot be bonded by traditional fusion-based processesmight be bonded by CRB process. In this research, cold roll welding of brass and IF steel was studied .The effects of process parameters such as reduction of thickness, pre-rolling annealingconditions and surface roughness on the mechanical propertiesof welded strips were investigated. The peeling and shear punch testswere used to investigate the mechanical properties of welded samples .It was observed that the bond andshear strengthswere enhanced by increasing the reduction and surface roughness. Also, annealing treatment before the CRB process increased the bond strength anddecreasedthe shear strength. Finally, optical and scanning electron microscopes were used to evaluate the fracture surfaces of the tensile and peelingtest specimens.

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Friction stir spot welding (FSSW) is a type of solid state welding that is used in the connection of small pieces and light metals such as aluminum alloy especially. The technical problem during melting of aluminum alloys is one of the most important reasons for developing application of friction stir welding for aluminum alloys. In this research, the effects of important processing parameters such as tool rotation speed, dwell time, plunge depth of tool and sheets thickness on the mechanical properties such as failure force and energy of FSS welded AA-3105 alloy have been experimentally studied using micro hardness and tensile tests. Tensile-shear tests show four different fracture modes of weld failure which consist of shear fracture, circumferential fracture, nugget pull out fracture and fracture in base material modes. The results show that the weld strength drops with increasing the tool rotation speed. Strength and hardness of weld and weld zone increase and then decrease with increasing dwell time of rotational tool which it can be obtained an optimum value of dwell time. Strength and fracture energy and load of welds increases with increasing the sheet thickness

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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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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 Ni alloying element on the characteristics of deposited weld metal of E7018-G electrode was evaluated. Therefore, electrodes contained different amounts of Ni (0-1.7wt.%) were designed, manufactured and welded via SMAW process. Microstructural studies revealed dichotomy effect of Ni on the deposited weld metal microstructure, i.e. increasing the Ni content up to 1.2wt.% improved the formation of acicular ferrite in the weld metal microstructure and caused significant grain refinement at the reheated zone of weld metal. While, higher Ni content (>1.2wt.%) resulted in some raising in the widmannstatten ferrite content in the weld metal. Strength multiplied by impact energy parameter (UTS×CVN) was used for mechanical properties assessment. Mechanical properties evaluation revealed the highest UTS×CVN parameter achieved in the weld metal contained 1.2wt.% Ni. Hardness of the weld metal increased with increasing Ni content which is related to the formation of micro constituents in the microstructure of weld metal and increasing their content with increasing Ni content.

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In this paper experimentally, the friction-stir welding of the polypropylene sheets with 40% glass fiber has been investigated. Comparison to other welding methods, the strength of the joint is the most important feature in this process. Many parameters such as tool geometry, rotational speed, linear velocity, and tilt angle are very important as input parameters in this type of welding. Therefore, in the present study, the effect of these parameters on the friction-stir welding of the polypropylene composite sheets have been extracted. Experiments are based on the Taguchi method and the orthogonal L9 array that are suitable for three-level designs. Statistical analysis have been performed as variance (ANOVA) and signal-to-noise ratio. Based on the results, the tool with a screw cone-cylindrical pin has a better apparent quality and higher tensile-shear strength. Results analyze show the rotational speed has the most significant effect on the tensile-shear strength and appearance of the weld. The joint with maximum tensile strength is obtained at rotational speed of 1000 rev/min, welding speed of 20 mm/min and tilt angle of 1 degree.

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In this research, the effect of vibration at the resonant range (75 Hz) on the hardness and tensile strength of AA-5083-H321 aluminum alloy, were welded by gas metal arc welding (GMAW) investigated. Vibration forces were ranged from 850 N to 2200 N, under identical welding parameters. Tensile strength and hardness testing of welded samples were performed. After mechanical tests, the fracture surfaces of welds were examined using scanning electron microscope (SEM) and discussed. The results showed that with increasing vibration force, the tensile strength and fracture strength of the specimens were welded during vibration, were increased by about 3 and 9 percent, respectively, compared to the non-vibrated weld sample. However, no significant change was observed in the hardness of the welded specimens. Mean grains size and heat affected zone of the sample was welded was welded with conventional GMAW, were about 200 μm and 1800 μm, but due to inducing vibration, as vibration force increased from 850 N to N 2200 N, Mean grains size was reduced to about 75 μm and HAZ was reduced from about 1000 μm to 700 μm, that is, about 44 to 61%.

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In this study, the effect of tool's advance 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 welding test. Using the characteristic stress, strain and temperature relationships in the Al-7075 alloy, the changes and the relationship between the material strength during the welding process by simulation was studied. The generated simulation defects was verified by experimental test.

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In this article the effects of carburizing heat treatment on girth weld with containing titanium oxide 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 titanium oxide 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%.
 

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The structural and hardness developed in advanced high-strength steel DP590 have been investigated with the help of optical microscopy and scanning electron microscopy on resistance spot welded specimens. The hardness diagram of the weld sections was prepared by microhardness test and the temperature peak and heat distribution were simulated by menas of the Abaqus software. The results show that according to the temperature generated in each region of the weld nugget, the HAZ and base metals have different microstructures, and these difference affects the hardness of the regions. The presence of tempered martensite islands with a fraction of 44% in ferrite matrix in base metal, mainly martensitic structure in the nugget, and martensitic structure along with scattered areas of ferrite in the HAZ was observed. The results of the microhardness tests showed difference in hardness values of the regions, and also it was observed that the hardness values increased in the HAZ and weld zone. The hardness values measured in the nugget, base metal, and HAZ were around 400, 200, and 450 HV which were in accordance with the observed structures

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Resistance Spot Welding (RSW) is one of the effective manufacturing processes used widely for joining sheet metals. Prediction of weld strength of welded samples has great importance in manufacturing and different methods are used by researchers to find the fracture force. In this article, the Adaptive Neuro-Fuzzy Inference System (ANFIS) is utilized for prediction of joint strength in welded samples by RSW. A design of experiments (DOE) is prepared according to effective process parameters includes welding current, welding cycle, cooling cycle and electrode force. The sheet metal samples prepared from AISI 1075 carbon steel. Tensile test specimens are prepared and the tensile-shear strength of welded samples are measured. A model is developed according to ANFIS and trained according to teaching-learning based optimization algorithm. 70 % of test data used for network train and the remained 30 % used for access the accuracy of trained network. The accuracy of the trained network was assessed and the results show that the trained network can predict the joint strength with high accuracy. The determination factor (R²) and mean absolute percentage error (MAPE) are 0.99 and 0.48 % for trained data and 0.95 and 6.2% for test data.

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In this study, in order to modify the weld structure obtained from repair welding of AZ91C magnesium alloy and improvement of tensile strength, input parameters such as current intensity and preheating temperature were optimized for this alloy. T6 heat treatment was separately done befor and after the welding to homogenize the microstructure and improvement of the mentioned properties. Using variance analysis, the accuracy of the models was checked and analyzed. Optical microscopy, scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and tensile tests were used to characterize the microstructure and mechanical properties of the repaired parts. The results of microstructural studies showed that the samples 2 (samples that were subjected to T6 heat treatment before and after welding) had continuous precipitates which these precipitates affected the strength due to the interruption of more slip planes and creating stronger barriers in the path of dislocations, resulting the better mechanical properties as compared with samples 1 (samples that were subjected to heat treatment only after welding). Also, by plotting response surface graphs and level diagrams, the highest tensile strength for samples 1 was observed at preheating temperatures of 493 to 513 K and current intensities of 80 to 90 A, and for samples 2 at temperatures of 513 to 553 K and current intensities of 100 to 110 A.

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