In this study, the mechanical properties of dissimilar welding of Super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L by gas tungsten arc welding process with direct current electrode negative polarity was investigated. For this purpose, two filler metals including ER25104L and ER309LMo were used. In order to achieve suitable structure and excellent mechanical properties in the mentioned joints, controlling of the heat input and pre heating were among the effective and controllable parameters. Microstructures of the weld metals, were evaluated using optical microscopy and scanning electron microscopy was used to analyze fracture surface. In addition, the mechanical properties including the bend test, ultimate strength, impact resistance and hardness were investigated. All the specimen underwent ductile fracture in HAZ in the tension test. The maximum fracture energy related to the ER 25104L the welded specimen. The maximum and minimum hardness corresponded to the ER 25104L and ER 309LMo, respectively. Finally, it was seen that for the joints, between the super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L, the ER 251 04L filler provided the optimum qualities.

In this paper, using the Taguchi method, the parameters affecting the toughness of super duplex stainless steels in friction stir welding were optimized. In order to achieve optimal conditions, maximum toughness, the quality characteristic was used as the higher the better. Analysis of Taguchi results showed that in order to achieve optimal conditions in super duplex stainless steel weldments must have a tool rotational speed of 500 rpm, a welding speed of 60 mm / min, an initial pressure of 70 MPa and a tool tilt angle with the workpiece is equal to 3 degrees. Under optimal conditions, the toughness obtained from the confirmation test was 61 J, which was very close to the predicted toughness (58 J). Analysis of variance was also performed on the results of signal to noise (S/N) ratio. According to the results of analysis of variance, the tool rotational speed parameter with an influence percentage of 64% was the most effective parameter on toughness in friction stir welding of super duplex stainless steels. On the other hand, the parameters of welding speed (with an influence percentage of 17 %), initial 2 pressure (with an influence percentage of 16%) and tool tilt angle to the workpiece (with an influence percentage of 3%) were in the next ranks. Also, SEM micrographs from fracture surface of the samples in the impact test proved that the sample that had the least toughness in the impact test had a cleavage morphology and as a result, brittle fracture. This was while the morphology of the fracture surface of the tested sample under optimal conditions (with the highest toughness in this study = 61 J) had a large amount of fine and deep dimples. The presence of these dimples in large quantities indicated ductile fracture and eventually reaching the highest toughness.

In this study, the microstructure and mechanical properties of dissimilar welding of Super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L by gas tungsten arc welding process with direct current electrode negative polarity was investigated. For this purpose, two filler metals including ER25104L and ER309LMo were used. The microstructure of the different zone in each joint, including weld metals, heat affected zone, interface were evaluated using optical microscopy and the relationship between mechanical properties and microstructure of welded joints is evaluated. Results indicate that austenitic and ferritic structures such as dendrite in the weld metal 25104L, 309LMo weld metal was observed as the primary ferrite with austenitic matrix. In addition microstructure was seen as skeleton ferrite morphology. In addition, the mechanical properties including the bend test, ultimate strength, impact resistance and hardness were investigated. All the specimen underwent ductile fracture in HAZ in the tension test. The maximum fracture energy related to ER25104L. The welded specimen with ER25104L filler metal showed the maximum elongation. The maximum and minimum hardness corresponded to the ER25104L and ER309LMo, respectively. Mechanical properties of joints welded by the two kinds of filler metals are satisfactory, althought the mechanical properties of 25104L filler metal is superior to that by 309LMo filler metal. Based on the present work, it is concluded that 25104L provides the optimum qualities for joining dissimilar metals between 32750 super duplex stainless steel and 304L austenitic stainless steel.

In this paper the studies of the two-phase super Plasticity stainless steels is studied. The aim of this study obtained the suitable criteria to thermo-mechanical treatment condition for decrease the microstructure (grain size) and super plasticity property in two-phase stainless steels. Also here we want to show the appropriate ranges of temperature and strain rate used in the process super plasticity to obtain maximum elongation for this kind of steel. The results showed that by using thermo-mechanical treatment that consists of dissolving, rolling and annealing, the grain size can be achieved to 0.5-4 mm.The maximum elongation is achieved 1000% in the temperature range 800-1000oC and strain rate is achieved 0.01-0.1 s-1. Under these conditions, the sensitivity coefficient of strain rate is around 0.6.

In this study, the microstructure of dissimilar welding of super duplex stainless steel UNS 32750 to austenitic stainless steel AISI 304L was investigated. For this purpose, gas tungsten arc welding process (DCEN) and two filler metals including ER25104L and ER309LMo were used. The microstructure of the different zone in each joint, including weld metals, heat affected zone, interface were evaluated using optical microscopy was investigated. The investigations showed that austenitic and ferritic structure such as dendrite, weld metal 25104L, with secondary Austenite, 309LMo weld metal was observed as the primary ferrite with austenitic matrix. In addition microstructure was seen as skeleton ferrite morphology. The interface of 304L austenitic stainless steel by two filler metals with epitaxial growth and interface of super duplex UNS 32750 Was seen high ferrite content.

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.

Super duplex stainless steel is a kind of duplex stainless steel that has pitting resistant equivalent number over than 40. Unified Numbering System (UNS) S32750 is a common super duplex stainless stee, that is mostly applied in oil and gas refinery industries, because of its proper corrosion-resistant properties. Therefore, joining of these steels by welding is very important, but the greatest problem in this regard is the corrosion and decrease in mechanical properties after welding.. In this research, UNS S32750 has been joined by friction stir welding method. The tool being used in this research was a WC with 16mm shoulder diameter, 5 mm pin diameter, and 1.9 mm height. X-ray diffraction showed that harmful phases, such as sigma or chi have not been formed. Microstructure study indicated that grain size in the stir zone has decreased. Vickers Hardness Test Method has been applied on welded samples. Moderate micro hardness of base metal was 285 Vickers but, the microhardness increased in the stir zone to 360 Vickers, because of decreasing the grain size. The cyclic polarization determined that potential and corrosion current of joint metal by friction stir welding method was similar to base metal. Also, it was revealed that ferrite percentage in the stir zone doesn’t decrease very much because the friction stir welding heat input is very low and the colding rate is very high.

Steel 2205 is one of the most famous duplex stainless steels. The microstructure of this steel composed of ferrite and austenite in similar amount. Therefore, in order to improve mechanical properties through microstructure, thermo mechanical processes such as controlled hot rolling and forging should be applied. It is not possible to employ the usual heat treatment. It shows the importance of our knowledge about the steel behavior during hot deformation and the effective mechanisms on the structural change. In the present study, hot compression in two pass process was performed on the 2205 specimens at the constant strain rate of 0.01 S-1 and the temperature of 950oC, 1050oC and 1150oC.The interval time between two pass were selected as 5, 10, 50 and 100 seconds and  ec »0.7ep was chosen. The results reveal that increasing interval time causes to increase the amount of work softening before the recrystallization leads to decrease in grain size and hardness.

In this study, the corrosion behavior of super duplex stainless steel UNS S32750 and tungsten arc welding with filler metals AWS ER2594 duplex stainless steel in acidic solution containing chloride ions have been investigated. Microstructure of weld joints evaluateby light and electron microscope and corrosion behavior examine by open circuit potential and cyclic polarization tests. The results showed that increas in heat input leads to a change in the distribution of alloying elements, formation of intermetallic phases around grain boundaries and the shifting balance between austenite and ferritein phases in weld region. Based on the cyclic polarization tests, cross-weld and base metal active behavior and have good corrosion resistance due to the presence of high alloying elements. As well as increase in heat input leads to an increase in current density and decrease in the pitting potential.