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 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 work, TiO2 nanoparticles with graphite are used to coat Duplex stainless steel (DSS) using the negative electrodeposition technique to protect it from corrosion. The anticorrosion performance of nanoparticle coatings that comprised a proper quantity of graphite particles was investigated using an open circuit potential and a potentiodynamic technique in a 1 M H2SO4 solution saturated with carbon dioxide. The corrosion rate of the DSS sample was lower when it was coated with TiO2/graphite than when it was uncoated, and the potential for corrosion increased from - 0.450 V for the uncoated DSS surface to - 0.410 V for the saturated calomel when it was coated with TiO2/graphite. Electrochemical studies discovered that TiO2/graphite coated DSS corrosion in sulfuric acid media had excellent protective qualities, with an effectiveness of 77.74 % when the current density was 0.957 milliamps per centimeter squared. It has been established by the findings of this study that Duplex stainless steel can be protected against corrosion in acidic conditions by the application of protective coating layers. The surface morphology of TiO2/graphite coating has demonstrated that it may withstand an acid attack due to its high adherence to the surface sample. X-ray diffraction was used to improve the accuracy of measurements for determining and researching the composition of the alloy surface's protective layer.

Microstructural and Electromagnetically Methods were performed for evaluation of aging phenomenon in 2304 Duplex stainless steel. The artificial aging process were carried out at temperatures of 700, 800 and 900 ° C and at 15, 60 and 120 minutes. For microscopic and hardness evaluations, optical microscopy equipped with image analysis software, scanning electron microscopy equipped with chemical analyzer, X-ray diffraction device and Vickers method were used. Then, for electromagnetic evaluation, the eddy current test at 100 kHz was performed, and the data were presented and evaluated as an impedance plan. The microscopic studies showed that with increasing aging intensity by increasing aging temperature and time, reduced the amount of ferrite phase. In contrast, the secondary phases of M23C6 carbide, Cr2N nitride, and secondary austenite form and grow in the microstructure. These secondary phases are formed within the ferrite phase and lead to a reduction in the volume fraction of the ferrite phase relative to the annealed sample. The most sever changes were observed at 900 ° C and 120 min. The results of electromagnetic evaluation have shown that with increasing the aging temperature and time, formation of more destructive phases and a sharp decreasing of ferrite content in the microstructure, the electromagnetic responses change appropriately by further reducing the inductive reactance and impedance index and further increasing the resistance index. Therefore, the severity of the aging phenomenon in the steel can be seen from its impedance plan.

Friction stir processing (FSP) was conducted on a SAF 2205 Duplex stainless steel at advancing speed of 50 mm/min and rotational speed of 400 rpm. Characterization of evolved material was studied using electron microscopy equipped with electron back scattered diffraction (EBSD) system. The results indicated that the severe plastic deformation and the heat generated during the FSP developed a very fine microstructure in the stir zone (SZ). It was found that the finest grains with average grain size less than 1 μ m were formed in the bottom of the SZ where the material was more likely to receive the lowest temperature in both constituent phases of ferrite and austenite. Therefore, it can be inferred that the material in the bottom of the SZ was less affected from the heat generated by the shoulder. The presence of such severe deformation along with the elevated temperature during the welding procedure inside the SZ activates the occurrence of continuous dynamic recrystallization mechanism throughout the material which seems to be responsible for grain refinement. Moreover, 111 and 110 pole figures of both constituent phases demonstrated that the rotating tool broke the initial microstructure, modified the pre-existence rolling texture of the starting material, and introduced simple shear texture components into the SZ.

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.

Nowadays Duplex stainless steels are widely used in natural corrosive environment such as sea water. Beside biological complexity of this environment, stainless steels alloy suffer from localized corrosion in sea water due to the presence of chloride and bromide aggressive ions. Pitting corrosion of a Duplex stainless steel at the presence of halide ions specially chloride and bromide has been investigated. Potentiodynamic polarization and potentiostaic polarization at applied anodic potentials (150, 300 and 450 mV) in 0.01, 0.1, 1 M NaCl and also constant concentrations of both Cl-+Br- ions at 25 and 45°C were studied. The results revealed that presence of bromide and chloride ions have a detrimental effects on pitting corrosion. These detrimental effects were appeared in increase on magnitude and lifetime of metastable pitting transients and also lowering pitting potential of the alloy. Morphological observation of metastable and stable pits by Scanning Electron Microscopy (SEM) in bromide containing solution proved the detrimental effect of these ions on pitting corrosion of Duplex stainless steels.

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.