Papers by Keyword: Duplex Stainless Steel

Abstract: This study investigates the heat management in Duplex Stainless Steel (DSS) wall specimens produced by the Wire Arc Additive Manufacturing (WAAM), by optimizing the thermal cycles during their construction. A reduction in the inter-pass time was found to induce heat accumulation, which causes wall flaring, affects the ferrite/austenite balance, and leads to a reduction in the hardness of the mechanical part produced by DSS. In contrast, the introduction of an external cooling system enhances the geometry and helps control the temperature and microstructure of the produced parts, thereby achieving the required hardness. Therefore, the use of the external cooling system enables the production of parts with desirable mechanical properties in a shorter time.

Abstract: This study evaluates the influence of selected welding parameters on temperature distribution during the production of butt welds in DSS 2304 (EN 1.4362) using a dual IPG YLS 5000 fiber laser with a wavelength of 1.06 μm and a maximum output power of 5 kW. Numerical simulations were performed using ANSYS 2022 R2 software to analyze temperature fields in the weld area. The thermophysical properties of DSS were calculated using JMatPro v6.1 software based on its chemical composition. The geometric model was designed considering test samples with a thickness of 5 mm. A progressive finite element mesh was generated, employing 3D SOLID70 elements with a length of 0.1 mm in the welding zone along the weld trajectory. A conical volumetric heat source model was utilized. Third-kind boundary conditions were applied to define the cooling of welded sheets by convection and radiation through argon and ambient air. Numerical simulations were employed to analyze and optimize performance parameters, including laser power, and the power beam ratio of tandem dual beams for welding DSS 2304. The resulting temperature fields were verified using their comparison with the macrostructures of the produced welds. The mechanical properties of the welded joints were tested through tensile testing and microhardness measurements.

Abstract: This study investigates the influence of the thermal cycle induced by the multipass weld bead when double-pulsed Gas Metal Arc Welding (GMAW-DP) is used to join duplex stainless steel (DSS) with Lean Duplex Stainless Steel (LDSS) welds, with emphasis on microestructure evolution. The microstructures of the heated affected zone (HAZ) and weld metal (WM) were analysed by light optical micorscopy (LOM), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and high-energy synchrotron X-ray diffraction (HEXRD) in the different passes. They are formed by austenite and ferrite with different morphologies and fractions, associated to the dilution and thermal cycle experienced. The ferrite content was between 50 and 80%, considering the consumable used. Mechanical behaviour was evaluated by Vickers microhardness profiles. These results provide experimental data that contribute to the understanding of dissimilar welding of duplex stainless steels through GMAW-DP process.

Abstract: Runner blades of Kaplan turbines are elements subject to multiple mechanical and chemical stresses. For these reasons they suffer from pitting corrosion. Taking them out of production for repair involves relatively high costs, such actions can take up to 6 months. The identification of a technological or constructive solution for increasing pitting corrosion resistance is thus desirable. The paper proposes a combined technological and constructive solution for increasing corrosion resistance by pitting leading edges, the areas most affected by this type of corrosion. The experimental program highlighted the fact that the use of a similar material in terms of chemical composition and characteristics or a duplex stainless steel, deposited with linear energies lower than 1 kJ/mm, can lead to the generation of a layer that has good behaviour at pitting corrosion. The generated layer must have a thickness limited to 3 mm to avoid the appearance of additional vibrations at the blade level.

Abstract: The aim of this work is to examine and analyze, using response surface methodology, how the TIG welding process parameters of welding current (WC), welding speed (WS), and N₂ with argon as shielding gas affect the hardness and corrosion resistance of 2205 DSS weldments. Due to the equal amounts of ferrite and austenite phases and alloying elements, duplex stainless steel DSS offers good mechanical properties and corrosion resistance. The mechanical characteristics and resistance to corrosion of the weld zone, as well as the heat-affected zone of the DSS, are, however, disturbed as a result of the welding process since it changes the distribution of these two phases and also the alloy is thermally disturbed. Therefore, in this work, an in-depth investigation of the effects of the above-mentioned parameters on the DSS quality has been performed. Results showed that increasing welding current while decreasing welding speed, which corresponds to the highest heat input, led to lower critical pitting potential and weld zone hardness but higher heat-affected zone hardness. The same results were obtained for decreasing welding current while increasing welding speed, which correspond to the lowest heat input. However, the addition of a small percent (%) of N₂ to argon shielding gas resulted in increasing the critical pitting potential and decreasing the hardness in welds and heat-affected zones. Numerically, the RSM planned experimental results showed that an optimum welding current of 175A, welding speed of 170 mm/min, and 10% N₂ with argon as shielding gas maximized the critical pitting potential up to 318 mV and optimized the hardness of the weld and heat-affected zone to about base metal hardness of 288 and 286 HV, respectively.

Abstract: The change in hardness due to 475°C embrittlement was investigated in the melt-run GTA welds of type 329J4L duplex stainless steel. A ferritic phase was hardened with ageing at 673-773K due to the phase decomposition into Fe-rich and Cr-rich phases, while an austenitic phase was barely hardened with ageing. Hardness in a ferritic phase was rapidly increased with ageing in the base metal (BM) region, and the hardening rate was reduced in the order of BM, weld metal (WM) and heat affected zone (HAZ). The ferrite/austenite fractions in HAZ and WM were higher than that in BM, furthermore, Cr content in a ferritic phase was lowered and Ni content in it was contrarily heightened in the same order of BM, WM and HAZ. A computed phase diagram suggested that the chemical composition of a ferritic phase in each region was located in the nucleation/growth region not spinodal decomposition region, which was situated between the spinodal and binodal lines. Computer simulation of phase decomposition phenomena in a ferritic phase using phase field model revealed that phase decomposition was accelerated with an increase in Cr content and a decrease in Ni content. It followed that Cr would enhance the 475°C embrittlement and Ni would inhibit it, because of the increased/decreased driving force of the phase decomposition. The difference in 475°C embrittlement behaviour at each region could be attributed to the difference in the chemical composition of a ferritic phase caused by the ferrite/austenite phase transformation during welding.

Abstract: Duplex stainless steels (DSSs) are being increasingly employed in the oil and gas and chemical industries, which, despite their high alloying degree and high resistance to general corrosion, are subject to pitting and crevice corrosion. According to their resistance to pitting and crevice corrosion, steels are ranked according to the PREN. However, nowadays there are many grades of DSSs, in which the content of Cr, Mo and N varies in different quantities, therefore the selection of the grade must be carried out with great care, considering not only PREN, but also the production technology, operating conditions, and the geometry of products. The crevice corrosion behaviors of three grades of duplex stainless steels quenched from 1050, 1100 and 1200 °C were studied in FeCl₃ solution at 50°C. It is shown that PREN allows to rank only different grades in terms of corrosion resistance. With a constant PREN value, but with different contents of ferrite and austenite in steel, completely different values of the corrosion rate can be obtained, therefore, PREN must be used with great care. It was found that in the studied steels, the optimal ferrite content, at which the lowest crevice corrosion rate is achieved, is at 65 vol.%.

Abstract: The three cutting edge drills are not the most common drills, nevertheless, are characterized by superior stability, excellent precision and finishing, due to the intersection of three cutting edges at one point. In general, stainless steels are considered as difficult to machine materials due to their tendency to work harden, their toughness and relatively low conductivity, leading to poor surface finish, poor chip breaking and built-up-edge formation. In the case of duplex stainless grades, the high strength, and the very good corrosion resistance, only compared with austenitic steels, make these materials as an alternative to the austenitic stainless steels, with superior mechanical properties. In this study, the performance of the drills with two and three cutting edges were evaluated in the drilling of duplex stainless steels, when low-pressure external cooling or high-pressure internal cooling were applied. Whether used drills of two or three cutting edges, the most important factor to increase the number of holes made, is the use of high-pressure internal cooling, in detriment of external low-pressure external cooling. The drills of three cutting edges have better results in roughness and dimensional tolerance of the holes. However, these drills proved to be more fragile and more sensitive to the cutting parameters. The use of three cutting edges drills is recommended for situations where hole quality is more important, while two cutting edges drills is recommended for situations where productivity is the main objective.

Abstract: Duplex stainless steel has become one of the fastest-growing materials in the stainless steel family due to pitting resistance, stress-corrosion cracking, the combination of excellent mechanical properties, production features, and the area of applications such as oil and gas, nuclear and thermal power plants, chemical processing industries, saltwater processing industries, and pipeline systems. However, it is more difficult to machine due to its high toughness, low thermal conductivity, and ductility. The experiment has conducted using 2205- Duplex Stainless steel round bar material considering carbide cutting tools using Computer Numerical Control lathe to estimate machining time to address and meet the industrial need. Using Central Composite Designed by using Response Surface Methodology technique develops a second-order mathematical model based on the machining parameters. The Analysis of Variance technique was used to investigate the material's performance characteristics, and the impact of cutting parameters on the work piece was analyzed using the Design Expert-V12 software. Cutting speed is the most crucial determining factor compared to other factors. The Genetic Algorithm is trained and tested in MATLAB to evaluate the best possible solutions. The genetic Algorithm recommends the most outstanding lowest predicted value of 1.2204 mm. The confirmatory analysis shows the experimental values, and their error percentage is within ±2%; these shows indicated predicted values are very close to the Genetic Algorithm results. The conclusions were in good agreement with the experimental machining time values.

Abstract: In the present work, the possibility of using solution treatment to improve the cavitation erosion resistance of the duplex stainless steel surfacing layers was discussed. The effect of solution treatment on cavitation erosion resistance of duplex stainless steels was investigated. The results showed that the solution treatment can adjust the ratio of ferrite to austenite, reduce the precipitation content, and make the incubation period longer, leading to an increase in the cavitation erosion resistance of the duplex stainless steel surfacing layers. The sample treated at 900°C and water quenching was shown to have the best resistance to the absorption of the energy produced by cavitation erosion, and hence the best cavitation erosion resistance.