Showing 15 results for Corrosion
M. Sabzi, S. Moeni Far, E. Najafi Birgani,
Volume 1, Issue 1 (1-2016)
Abstract
In this investigation, the effect of heat input of SMAW process on the corrosion behavior of Hadfield steel weld joints was investigated. For this purpose, 4 annealed sheets with thickness 25 mm prepared from Hadfield steel and then welding applied by SMAW process with 6.75 and 11.25 kJ/mm heat input values. For corrosion behavior evaluation of base metal and weld metal areas, potentiodynamic polarization and electrochemical impedance spectroscopy methods were used in the 3.5% NaCl solution. The result of corrosion tests indicated that by increasing the heat input in the SMAW process, the corrosion resistance in the weld metal were reduced. It was also found that in both heat input values, base metal had more corrosion resistance compared to weld metal.
M. Ansaripour, A. Soltanpoor, A. Ghasemi, M.r. Dehnavi,
Volume 2, Issue 1 (8-2016)
Abstract
The aim of this study was to evaluate the mechanical properties and corrosion behavior of friction stir welding (FSW) connection of A517 (B) steel plate. Mechanical properties and corrosion behavior of weld zone were evaluated after reaching to optimum FSW microstructure with the lowest martensite phase. Thus, after the identifying phase microstructure by SEM and XRD analysis, mechanical properties were analyzed by micro-hardness and tensile test. Micro hardness data shows slight increases in stir zone (SZ) compared with the base metal (BM); although a reduction of about 17% in hardness of heat-affected zone (HAZ) was sensible. Reduction of hardness in the HAZ was appeared as drop by about 12 percent of the yield strength and 19 percent of ultimate strength compared with BM. SEM images from fracture surface of the tensile sample showed bi-modal distribution of large and small Dimples being sings of softness of HAZ .Comparing corrosion behavior in solution consist of 3.5 wt% of NaCl showed that there was no passive layers to prevent dissolution of the metal in the SZ and BM. while BM and SZ had fairly similar corrosion rates, Difference of 50 mV between corrosion potential of SZ and BM showed that in galvanic condition, corrosion resistance of BM could be lower than SZ.
Mahdi Lashkari Ghoochani, Behrooz Beidokhti,
Volume 2, Issue 2 (11-2016)
Abstract
In this research 420 martensitic stainless steel welded with the ER308L, ER309L and ER420 fillers by GTAW method. The corrosion properties of the samples has been studied in 3.5% NaCl solution with and without CO2. Potentiodynamic polarization used to obtain the ER308L and ER309L have the best corrosion properties. In addition the welding process makes the 420 HAZ zone to be sensitized. The pitting potential of the samples has been decreased in presence of carbon dioxide. Furthermore, by adding CO2 to the solution the pH has been decreased and the corrosion potential reached near the -500 mV/SCE and the passivity current is also lowered.
, M. Ahl Sarmadi, M. Atapour, A. Behjat, H. Edriss, M. Vahman ,
Volume 4, Issue 1 (8-2018)
Abstract
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.
H. Mehrabi Sharifabad, M. Hajisafari,
Volume 4, Issue 1 (8-2018)
Abstract
In this research, two different filler metals, ERNiCrMo-3 and ER309L, were used for developing different microstructure, austenite (γ) and austenite and ferrite (γ+δ) in the weld metal and fatigue properties of welded samples were evaluated in the air and sea water environments. Microstructural studies indicated a good agreement between predicted microstructures via schiffler diagram and metallographic studies. Evaluation of fatigue properties in the air and sea water environments revealed the austenitic weld metal, like base metal microstructure, improved the fatigue strength of welded samples. Fractographic studies and FESEM-EDS analysis showed more ductile fracture of welded samples by using ERNiCrMo-3, formation of more uniform and deeper dimples in the final zone of fatigue fracture, than that of welded samples by using ER309L. Furthermore, unlike dimple formation centers in welded samples by using ER309L, Mo-Ti rich intermetallics caused formation of dimples in the welded sampled via ERNiCrMo-3.
A. Mahab, M. Farzam, R. Dehmolaei,
Volume 4, Issue 1 (8-2018)
Abstract
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..
M. Emadi, H. Mostaan, M. Rafiei,
Volume 5, Issue 2 (1-2020)
Abstract
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.
M. Chiani, M. Atapour,
Volume 5, Issue 2 (1-2020)
Abstract
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.
M.r. Samadi, H. Mostaan, M. Rafiei , M. Salehi,
Volume 6, Issue 1 (8-2020)
Abstract
Nowadays, aluminum and its alloys have extensive applications in marine and aerospace industrious owing to their excellent properties. Among these alloys, 5xxx series of aluminum alloys have also excellent corrosion resistance, high toughness and strength and also good weldability. Decrease in yield strength and also tensile strength due to the grain growth in the heat affected zone is of the main problems in the welding of these series of Al alloys. In this research work, gas tungsten arc weld joints in two modes i. e. direct current and pulsed current were compared in order to study the effect of this parameter on the microstructure, mechanical properties and corrosion resistance of weld joints. Also, the effect pulsed current parameters such as peak current and basic current were investigated. Microstructural evolutions and fracture surfaces of weld joints were examined by optical microscope and scanning electron microscope, respectively. It was found that the fracture behavior of all joints is in a ductile manner. Also, tensile test and electrochemical polarization were conducted in order to study the mechanical properties and corrosion behavior of weld joints.
Mojtaba Vakili-Azghandi, Ali Shirazi,
Volume 7, Issue 1 (8-2021)
Abstract
The results showed that the microhardness and tensile strength of the heat-affected zone as the weakest welding zone in some samples reduced up to 30% compared to the base metal. On the other hand, a decrease in rotational speed, an increase in tool movement speed, and the number of welding passes cause grain refinement and improve mechanical properties. However, the effect of decreasing the rotation speed and increasing the tool movement speed were shown to be more favorable due to less heat production. Accordingly, the hardness in the welded zone with a rotational speed of 600 rpm and a movement of 80 mm/min increased from 90 to 125 HV compared to the base metal, and the hardness reduction in the zones around the welded zone was only 5 Vickers. It was also found that reducing the grain size of the stir zone, while improving the mechanical properties leads to increasing the density of the surface pasive layer, preventing the attack of aggressive chlorine ions and thus reducing the corrosion intensity by 50 times in saline seawater.
Hossein Tahmasebi Manesh, Alireza Nasresfahani, Alireza Nasresfahani,
Volume 7, Issue 1 (8-2021)
Abstract
One of the applications of P460NH micro-alloy steel is its use in pressure vessel tanks. Electrode E8018-G can be used for welding this steel. In this study, to obtain the optimal welding parameters, the arc process based on ASME IX standard was used. Then, by sampling from the weld section, Vickers hardness test was performed and hardness profiles were drawn in different areas. Then the microstructure of each area was examined and compared with the hardness test results. The corrosion behavior of the heat affected zone, weld zone and base metal was investigated separately using the TOEFL polarization test in a 3.5% solution of NaCl. The results showed that the weld zone had the highest percentage of perlite (62%) and the base metal had the highest percentage of ferrite (73%). Also, the heat affected zone has the highest hardness number (298) and the base metal has the lowest value (210) in the Vickers scale. Evaluation of corrosion behavior of different areas also showed that the heat affected zone has the highest corrosion potential (-.651v) and the lowest corrosion current density (1.75×10-5 A/cm2). This is while the base metal has the lowest corrosion potential (-.691v) and the highest corrosion current density (1.2×10-6 A/cm2) compared to the weld metal and the heat affected zone.
Dr Behzad Binesh, Dr Sima Mirzaei, Mr Amin Taghi-Ahari,
Volume 7, Issue 2 (1-2022)
Abstract
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.
S. Varmaziar, M. Atapour, Y. Hedberg,
Volume 8, Issue 1 (8-2022)
Abstract
The influence of filler metals on the microstructure and corrosion behavior of AISI 316L welds was investigated. Gas Tungsten Arc welding (GTAW) process was applied to join the AISI 316L plates using ER 316L and ER 312 filler metals. The obtained microstructures were characterized by optical metallography and scanning electron microscope (SEM). Corrosion assessments were conducted in 3.5% NaCl using a three electrode cell. Open circuit potential and potentiodynamic polarization examinations were conducted on the welds and base metal. Microstructural evaluations indicated that a combination of austenite and ferrite phases was formed in the welds fabricated by both filler metals. Based on the micro hardness tests, the weld fabricated by ER 312 filler exhibited superior harness compared to the ER 316L weld. Corrosion evaluations also show that the weld metal obtained from two filler metals has a lower corrosion rate due to the higher amount of chromium and higher ferrite compared to the base metal. Also, the lower corrosion current of ER 312 weld metal compared to ER 316L weld metal is for this reason. In contrast to the base metal compared to the two welding metals, the result of the two filler metals has shown better pitting corrosion results according to the electrochemical tests and also the examination of the surfaces using an optical microscope after these tests, that these results are due to The presence of two phases of austenite and ferrite in the vicinity of each other in weld metals and the intensification of galvanic corrosion is due to the discharge of the austenite phase from chromium and molybdenum.
Ali Adelian, Khalil Ranjbar, Mohammadreza Tavakoli Shoushtari,
Volume 9, Issue 2 (8-2024)
Abstract
This research studied the effect of two-stage over aging treatmenton 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 two-stage over aging treatment can be increased by about 66 % compared to as-weld condition.
A. Etemadi, M. Kasiri-Asgarani, H. R. Bakhsheshi-Rad, M. Sadeghi Gogheri,
Volume 9, Issue 2 (1-2024)
Abstract
In this research, dissimilar joining of biodegradable AZ31 alloy to Ti-6Al-4V titanium alloy by rotary friction welding method was investigated with aim of preparation of pin or screw for orthopedic applications. optical and scanning electron microscope (sem) were used to investigate the microstructure, x-ray diffraction was conducted for phase analysis, torsion and micro-hardness tests were carried out to investigate mechanical properties, and polarization and electrochemical impedance spectroscopy were employed to evaluate corrosion resistance. in the welding procedure, rotational speed of 1100, 1200 and 1300 rpm and friction time of 2 and 4 seconds were considered as variable parameters, and two parameters of friction pressure and forge pressure were considered as constant parameters at 50 and 40 MPa, respectively. The microstructure of the joint zone showed that there is no deformation in the titanium alloy side. However, in the magnesium side, the greatest amount of deformation occurred with the distance from the joint line, where weld center zone (CZ), dynamic recrystallization zone (DRX), thermomechanical affected zone (TMAZ) and partial deformation zone (PDZ) are detected. The formation of intermetallic phases such as Mg2AlZn, Ti3Al and also the refining the grains size is the main reason for increasing the hardness of the magnesium side near the joint line up to 150 HV. The results of the torsion test showed that the welded sample has the highest shear strength of 81.51 MPa and also the highest corrosion resistance among other samples at a rotation speed of 1200 rpm and a friction time of 4 seconds.
