| 1. |
- Andersson, Joel, 1981-, et al.
(författare)
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Welding of special alloys
- 2023
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Ingår i: Welding of Metallic Materials. - : Elsevier. - 9780323906708 - 9780323905527 ; , s. 279-316
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Specialty alloys are a broad group of materials providing superior properties to common materials and are therefore used for more demanding applications. Specialty alloys require sophisticated manufacturing routes, e.g., vacuum metallurgy, to account for all the alloying elements needed to finalize the specific alloy for its intended purpose. The alloys of Duplex stainless steels, superalloys, and Titanium alloys are examples of so-called specialty alloys where aerospace, chemical, and petrochemical industries are just a few areas mentioned where these specialty alloys are frequently used. Duplex stainless steel, had superior mechanical properties and corrosion resistance, making them a sustainable choice for a wide variety of applications i.e., petrochemical industries. The superalloys, and especially the precipitation hardening ones belong to a unique plethora of alloys commonly used in aerospace as well as land-based gas turbines which possess superb mechanical performance at elevated temperatures. However, the superalloys are unfortunately very challenging to process, not at least regarding weld cracking. With their high specific strength and corrosion resistance, titanium alloys are favorable for numerous applications. However, they react readily with oxygen at elevated temperatures and therefore inert atmosphere must be used during welding.
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| 2. |
- Baghdadchi, Amir, 1994-
(författare)
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Directed Energy Deposition Additive Manufacturing and Welding of Duplex Stainless Steel using Laser Beam
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Duplex stainless steels (DSSs), with a ferritic-austenitic microstructure, are used in a wide range of applications thanks to their high corrosion resistance and good mechanical properties. However, efficient and successful production and joining of DSS require precise control of processes and an in-depth understanding of the relations between composition, processing thermal cycles, resulting microstructures and properties. In this study welding and direct energy deposition of DSS using a laser beam, resulting weld and component microstructures, and properties are explored.In the first part a lean FDX 27 DSS, showing the transformation-induced plasticity (TRIP) effect, was autogenously laser welded and laser reheated using pure argon or pure nitrogen as shielding gas. The weld metal austenite fraction was 22% for argon-shielding and 39% for nitrogen-shielding in the as-welded conditions. Less nitrides were found with nitrogen-shielding compared to argon-shielding. Laser reheating did not significantly affect nitride content or austenite fraction for argon-shielding. However, laser reheating of the nitrogen shielded weld removed nitrides and increased the austenite fraction to 57% illustrating the effectiveness of this approach.Phase fraction analysis is important for DSS since the balance between ferrite and austenite affects the properties. For TRIP steels the risk of austenite-to-martensite transformation during sample preparation also has to be considered. Ferrite, austenite and martensite were identified and quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis. It was found that mechanical polishing produced up to 26% strain-induced martensite, while no martensite was observed after electrolytic polishing.In the second part a systematic four-stage methodology was applied to develop procedures for additive manufacturing of standard 22% Cr DSS components employing direct energy deposition using a laser beam and wire feedstock (DED-LB/w) combined with the hot wire technology. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder with an inner diameter of 160 mm, thickness of 30 mm, and height of 140 mm were produced. Implementing this methodology with a stepwise increase in the deposited volume and geometrical complexity can successfully be used when developing additive manufacturing procedures for significantly sized metallic components. The as-deposited microstructure was inhomogeneous and repetitive including highly ferritic regions with nitrides and regions with high fractions of austenite. Heat treatment for 1 hour at 1100°C homogenized the microstructure, dissolved the nitrides, and almost balanced the ferrite and austenite phase fractions. Strength, ductility, and toughness were at a high level for the cylinder, comparable to those of wrought type 2205 steel, both as-deposited and after heat treatment. The pitting corrosion resistance revealed that microstructural differences, including ferrite-to-austenite ratio, alloying element distribution in ferrite and austenite , and the presence of nitrides, affected the corrosion resistance of DED-LB/w DSS. It was also shown that alongside the decomposition of ferrite into Fe-rich (α) and Cr-rich (αʹ) phases, clustering of Ni, Mn, and Si atoms are contributing to the 475°C -embrittlement of DSS manufactured by DED-LB/w.This study has illustrated that a laser beam can successfully be used as heat source in processing of DSS both for welding and additive manufacturing. However, challenges like nitrogen loss, low austenite fractions and nitride formation have to be handled by precise process control and/or heat treatment.
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| 3. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Identification and quantification of martensite in ferritic-austenitic stainless steels and welds
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier Editora Ltda. - 2238-7854. ; 15, s. 3610-3621
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims at the phase identification and quantification in transformation induced plasticity duplex stainless steel (TDSS) base and weld metal containing ferrite, austenite, and martensite. Light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis were employed to analyze phases. Samples were either mechanically or electrolytically polished to study the effect of the preparation technique. Mechanical polishing produced up to 26% strain-induced martensite. Electrolytic polishing with 150 g citric acid, 300 g distilled water, 600 mL H3PO4, and 450 mL H2SO4 resulted in martensite free surfaces, providing high-quality samples for EBSD analysis. Martensite identification was challenging both with LOM, due to the similar etching response of ferrite and martensite, and with EBSD, due to the similar lattice structures of ferrite and martensite. An optimized Beraha color etching procedure was developed that etched martensite distinctively. A novel step-by-step EBSD methodology was also introduced considering grain size and orientation, which successfully identified and quantified martensite as well as ferrite and austenite in the studied TDSS. Although here applied to a TDSS, the presented EBSD methodology is general and can, in combination with knowledge of the metallurgy of the specific material and with suitable adaption, be applied to a multitude of multiphase materials. It is also general in the sense that it can be used for base material and weld metals as well as additive manufactured materials.
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| 4. |
- Baghdadchi, Amir, 1994-
(författare)
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Laser Welding and Additive Manufacturing of Duplex Stainless Steels : Properties and Microstructure Characterization
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Duplex stainless steels (DSS), with a ferritic-austenitic microstructure, are used ina wide range of applications thanks to their high corrosion resistance and excellent mechanical properties. However, efficient and successful production and joining of DSS require precise control of processes and an in-depth understanding o frelations between composition, processing thermal cycles, resulting microstructures and properties. In this study laser welding, laser reheating, and laser additive manufacturing using Laser Metal Deposition with Wire (LMDw) ofDSS and resulting weld and component microstructures and properties are explored.In the first part a lean FDX 27 duplex stainless steel, showing the transformation induced plasticity (TRIP) effect, was autogenously laser welded and laser reheated using pure argon or pure nitrogen as shielding gas. The weld metal austenite fraction was 22% for argon-shielding and 39% for nitrogen-shielding in as-welded conditions. Less nitrides were found with nitrogen-shielding compared to argonshielding. Laser reheating did not significantly affect nitride content or austenite fraction for argon-shielding. However, laser reheating of the nitrogen shieldedweld removed nitrides and increased the austenite fraction to 57% illustrating the effectiveness of this approach.Phase fraction analysis is important for DSS since the balance between ferrite and austenite affects properties. For TRIP steels the possibility of austenite tomartensite transformation during sample preparation also has to be considered. Phases in the laser welded and reheated FDX 27 DSS were identified and quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis. An optimized Beraha color etching procedure was developed for identification of martensite by LOM. A novel step-by-step EBSD methodology was also introduced, which successfully identified and quantified martensite as well as ferrite and austenite. It was found that mechanical polishing produced up to 26% strain-induced martensite, while no martensite was observed after electrolytic polishing.In the second part a systematic four-stage methodology was applied to develop procedures for additive manufacturing of standard 22% Cr duplex stainless steel components using LMDw combined with the hot wire technology. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder with an inner diameter of 160 mm, thickness of 30 mm, and height of 140 mm were produced. The as-deposited microstructure was inhomogeneous and repetitive including highly ferritic regions with nitrides and regions with high fractions ofaustenite. Heat treatment for 1 hour at 1100 ̊C homogenized the microstructure, removed nitrides, and produced an austenite fraction of about 50%. Strength, ductility, and toughness were at a high level for the cylinder, comparable to those of wrought type 2205 steel, both as-deposited and after heat treatment. The highest strength was achieved for the as-deposited condition with a yield strength of 765 MPa and a tensile strength of 865 MPa, while the highest elongation of 35% was found after heat treatment. Epitaxial growth of ferrite during solidification, giving elongated grains along the build direction, resulted in anisotropy of toughness properties. The highest impact toughness energies were measured for specimens with the notch perpendicular to the build direction after heat treatment with close to 300 J at -10oC. It was concluded that implementing a systematic methodology with a stepwise increase in the deposited volume and geometrical complexity can successfully be used when developing additive manufacturing procedures for significantly sized metallic components.This study has illustrated that a laser beam can successfully be used as heat source in processing of duplex stainless steel both for welding and additive manufacturing. However, challenges like nitrogen loss, low austenite fractions and nitride formation have to be handled by precise process control and/or heat treatment.
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| 5. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating
- 2021
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Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 65, s. 499-511
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Tidskriftsartikel (refereegranskat)abstract
- Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N2-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N2-shielded welding followed by N2-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N2-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N2-shielding. The amount of nitrides was lower in N2-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N2-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds. © 2020, The Author(s).
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| 6. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Wire laser metal deposition additive manufacturing of duplex stainless steel components -Development of a systematic methodology
- 2021
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 14:23
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Tidskriftsartikel (refereegranskat)abstract
- A systematic four-stage methodology was developed and applied to the Laser Metal Deposition with Wire (LMDw) of a duplex stainless steel (DSS) cylinder > 20 kg. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder were produced. This stepwise approach allowed the development of LMDw process parameters and control systems while the volume of deposited material and the geometrical complexity of components increased. The as-deposited microstructure was inhomogeneous and repetitive, consisting of highly ferritic regions with nitrides and regions with high fractions of austenite. However, there were no cracks or lack of fusion defects; there were only some small pores, and strength and toughness were comparable to those of the corresponding steel grade. A heat treatment for 1 h at 1100 degrees (C) was performed to homogenize the microstructure, remove nitrides, and balance the ferrite and austenite fractions compensating for nitrogen loss occurring during LMDw. The heat treatment increased toughness and ductility and decreased strength, but these still matched steel properties. It was concluded that implementing a systematic methodology with a stepwise increase in the deposited volume and geometrical complexity is a cost-effective way of developing additive manufacturing procedures for the production of significantly sized metallic components.
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| 7. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Wire laser metal deposition of 22% Cr duplex stainless steel : as-deposited and heat-treated microstructure and mechanical properties
- 2022
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 57:21, s. 9556-9575
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Tidskriftsartikel (refereegranskat)abstract
- Duplex stainless steel (DSS) blocks with dimensions of 150 × 70x30 mm3 were fabricated by Laser Metal Deposition with Wire (LMDw). Implementation of a programmable logic control system and the hot-wire technology provided a stable and consistent process producing high-quality and virtually defect-free deposits. Microstructure and mechanical properties were studied for as-deposited (AD) material and when heat-treated (HT) for 1 h at 1100 °C. The AD microstructure was inhomogeneous with highly ferritic areas with nitrides and austenitic regions with fine secondary austenite occurring in a periodic manner. Heat treatment produced a homogenized microstructure, free from nitrides and fine secondary austenite, with balanced ferrite and austenite fractions. Although some nitrogen was lost during LMDw, heat treatment or reheating by subsequent passes in AD allowed the formation of about 50% austenite. Mechanical properties fulfilled common requirements on strength and toughness in both as-deposited and heat-treated conditions achieving the highest strength in AD condition and best toughness and ductility in HT condition. Epitaxial ferrite growth, giving elongated grains along the build direction, resulted in somewhat higher toughness in both AD and HT conditions when cracks propagated perpendicular to the build direction. It was concluded that high-quality components can be produced by LMDw and that deposits can be used in either AD or HT conditions. The findings of this research provide valuable input for the fabrication of high-performance DSS AM components
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| 8. |
- Cederberg, Emil, et al.
(författare)
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Physical simulation of additively manufactured super duplex stainless steels : microstructure and properties
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of high performance super duplex stainless steel (SDSS) during additive manufacturing (AM) has been investigated using a novel arc heat treatment technique. Tungsten inert gas (TIG) arc pulses were applied on a disc shaped sample mounted on a water-cooled chamber to physically simulate AM thermal cycles. SDSS base metal and a duplicated additively manufactured structure (DAMS) were used as initial microstructures. Samples were melted one, five, or 15 times by arc heat treatment. Samples were also produced with a controlled slope down of the current to create slower cooling compared to pulsing. Microstructure characterization and modelling were performed to study the evolution of microstructure and properties with successive AM cycles. Microstructural changes were dependent on the number of reheating cycles, cooling rate, and peak temperature. In particular, the DAMS austenite morphology and fraction changed after reheating to peak temperatures above 700 °C. Nitrides and sigma were observed in the high and low temperature heat affected zones, respectively. Sensitization to corrosion was more pronounced in reheated DAMS than in the base metal. Hardness was increased more by multiple remelting/reheating than by slow cooling. It was found that AM thermal cycles significantly affect SDSS properties especially for an initial microstructure similar to that produced by AM. © 2020 Elsevier B.V.
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| 9. |
- Hosseini, Vahid A., 1987-, et al.
(författare)
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Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel
- 2016
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Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 60:2, s. 233-245
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Tidskriftsartikel (refereegranskat)abstract
- The influence of heat input and multiple welding cycles on the microstructure of the heat-affected zone in autogenously TIG-welded 6 mm 2507 type super duplex stainless steel plates was investigated. In order to produce multiple thermal cycles, one to four pass bead-on-plate welds were made with arc energies of 0.47 and 1.08 kJ/mm, corresponding to heat inputs of 0.37 and 0.87 kJ/mm. Several thermocouples were attached to record thermal cycles on the front and back sides of the plates. Finite element modelling was successfully done to map and correlate measured and calculated peak temperatures. Only minor changes were seen in the ferrite content at 1 and 2 mm from the fusion boundary. Nitrides formed in all passes of the low heat input samples in a region next to the fusion boundary, but only after the third and fourth passes of the high heat input samples. Sigma phase precipitated only in a zone heated to a peak temperature in the range of approximately 828 to 1028 °C. Multiple reheating was found to promote precipitation of sigma phase relatively more than slower cooling. A precipitation free zone was observed between the nitride and sigma phase bands. The precipitation behaviour could be understood from equilibrium phase diagrams, evaluation of local thermal cycles and by correlating results from the modelling and measurements of peak temperatures. It is suggested that the peak temperature, the accumulated time in the critical temperature range between approximately 828 and 1028 °C, and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase formation.
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| 10. |
- Hosseini, Vahid A., 1987-, et al.
(författare)
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Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel
- 2016
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Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 98, s. 88-97
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28 wt% in the base metal to 0.17 wt% and 0.10 wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and arc energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.
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| 11. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
- 2017
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 121:May, s. 11-23
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel arc heat treatment technique to produce samples with graded microstructures through the application of controlled temperature gradients. Steady state temperature distributions within the sample can be achieved and maintained, for times ranging from a few seconds to several hours. The technique reduces the number of samples needed to characterize the response of a material to thermal treatments, and can consequently be used as a physical simulator for materials processing. The technique is suitable for conventional heat treatment analogues, welding simulations, multi-step heat treatments, and heat treatments with controlled heating and cooling rates. To demonstrate this technique, a super duplex stainless steel was treated with a stationary TIG arc, to confirm the relationship between generated steady-state temperature fields, microstructure development, hardness, and sensitization to corrosion. Metallographic imaging and hardness mapping provided information about graded microstructures, confirming the formation of secondary phases and microstructure sensitization in the temperature range 850–950 °C. Modelling of temperature distributions and thermodynamic calculations of phase stabilities were used to simulate microstructure development and associated welding cycles.
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| 12. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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A physical simulation technique for cleaner and more sustainable research in additive manufacturing
- 2021
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526 .- 1879-1786. ; 285
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) introduces a new domain for zero waste and cleaner production. Research for verification of materials in AM and effects of the process on the material behavior, however, demands a significant amount of materials, energy, and man-hours. The design of suitable physical simulation techniques that can duplicate complex AM thermal cycles without performing AM is therefore crucial for cleaner and more sustainable AM research. This paper aims at introducing a novel technique to reproduce AM thermal cycles in a controlled way on a small sample, thereby supporting sustainable alloy verification and cleaner research. In this technique, a stationary arc is applied to a disc-shaped sample mounted on a water-cooled chamber, where the arc and water provide rapid heating and cooling, respectively. In the present study, a super duplex stainless steel (SDSS) was used as the experimental alloy to simulate the evolution of microstructure and properties during wire-arc additive manufacturing. The experiment was performed using the stationary arc with the holding time of 5 s, applied 1, 5, or 15 times. The total processing time was only 450 s (7.5 min) for the 15 a.m. thermal cycles experiment. The SDSS showed a progressive increase in the austenite fraction at 600–1200 °C and the formation of detrimental sigma phase at 700–1000 °C, but a reduction of austenite fraction above 1300 °C. The results were in good agreement with the literature, verifying the applicability of the physical simulation technique for AM research. Calculations showed that using arc heat treatment as the initial step is 6–20 times more efficient in different respects (materials, energy, and man-hours) compared to wire arc additive manufacturing. Therefore, this methodology can be implemented to gain an understanding of materials in AM applications thereby eliminating the need for investments in additive manufacturing of a specific component. © 2020
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| 13. |
- Hosseini, Vahid A., 1987-, et al.
(författare)
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Study of the effect of tool geometry on semisolid stir welding of a AZ91 magnesium alloy
- 2015
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Ingår i: Proceedings of the 18th International Conference on Joining Materials. - : JOM-Institute. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Semisolid stir welding is a newly developed method suitable for joining of the magnesium alloy AZ91. In this study, the effect of tool geometries on the joint properties such as bending strength and the occurrence of porosity are studied. A 2 mm-thick Mg-25%Zn interlayer was placed between two AZ91 plates and the plate was heated up to 530°C before joining. At this temperature, when both the interlayer and the base metal were in the semisolid state, a stirrer was introduced into the joint. Drill-tip and round shape stirrer tools were employed at three different stirring rates. Welds produced with the two methods showed similar properties in the shear punch test. However, using the round tool geometry resulted in welds with excellent bending strength closely matching that of the base metal especially at the highest stirring rate. The improved properties when using the round tool was a result of the formation of a very fine and uniform microstructure with a low content of porosity.
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| 14. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Bead by bead study of a multipass shielded metal arc-welded super-duplex stainless steel
- 2020
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Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 64:2, s. 283-299
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Tidskriftsartikel (refereegranskat)abstract
- The present study aims at investigating bead geometry and the evolution of microstructure with thermal cycles in multipass shielded metal arc welding of a V-groove 13-mm type-2507 super-duplex stainless steel (SDSS) plate. The weld consisted of 4 beads produced with arc energies of 0.81-1.06 kJ/mm. The upper beads showed lower base metal (BM) dilution than the first bead. Thermal cycles were recorded with thermocouples, indicating that the cooling rate decreased in the as-deposited weld zone when adding a new bead. Ferrite fraction in the as-welded condition was lower for the upper beads. The austenite grain morphology in reheated passes varied depending on the local peak temperatures and the number of reheating passes. Sigma phase precipitated in a location reheated by the third and fourth passes that was subjected to a critical peak temperature for sigma precipitation. Ferrite content, measured using image analysis and Fisher FERITSCOPE technique, showed that the ferrite fraction moved toward 50/50% in the weld metal with an increasing number of reheating cycles. Finally, a schematic map showing an overview of the microstructure in the multipass SDSS weld was introduced.
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| 15. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Correction to : Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals (Welding in the World, (2018), 62, 3, (517-533), 10.1007/s40194-018-0548-z)
- 2018
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Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 62:4, s. 893-
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Tidskriftsartikel (refereegranskat)abstract
- Unfortunately due to typesetting mistakes, Tables 4-€“6 have been displayed erroneously in the article. © 2018, International Institute of Welding.
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| 16. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel
- 2018
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Sigma phase is commonly considered to be the most deleterious secondary phase precipitating in duplex stainless steels, as it results in an extreme reduction of corrosion resistance and toughness. Previous studies have mainly focused on the kinetics of sigma phase precipitation and influences on properties and only a few works have studied the morphology of sigma phase and its influences on material properties. Therefore, the influence of sigma phase morphology on the degradation of corrosion resistance and mechanical properties of 2507 super duplex stainless steel (SDSS) was studied after 10 h of arc heat treatment using optical and scanning electron microscopy, electron backscattered diffraction analysis, corrosion testing, and thermodynamic calculations. A stationary arc was applied on the 2507 SDSS disc mounted on a water-cooled chamber, producing a steady-state temperature gradient covering the entire temperature range from room temperature to the melting point. Sigma phase was the major intermetallic precipitating between 630 °C and 1010 °C and its morphology changed from blocky to fine coral-shaped with decreasing aging temperature. At the same time, the average thickness of the precipitates decreased from 2.9 μm to 0.5 μm. The chemical composition of sigma was similar to that predicted by thermodynamic calculations when formed at 800-900 °C, but deviated at higher and lower temperatures. The formation of blocky sigma phase introduced local strain in the bulk of the primary austenite grains. However, the local strain was most pronounced in the secondary austenite grains next to the coral-shaped sigma phase precipitating at lower temperatures. Microstructures with blocky and coral-shaped sigma phase particles were prone to develop microscale cracks and local corrosion, respectively. Local corrosion occurred primarily in ferrite and in secondary austenite, which was predicted by thermodynamic calculations to have a low pitting resistance equivalent. To conclude, the influence of sigma phase morphology on the degradation of properties was summarized in two diagrams as functions of the level of static load and the severity of the corrosive environment.
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| 17. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Effect of welding parameters on semisolid stir welding of Mg-9Al-1Zn magnesium alloy
- 2016
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Ingår i: Transactions of Nonferrous Metals Society of China. - 1003-6326 .- 2210-3384. ; 26:10, s. 2586-2594
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Tidskriftsartikel (refereegranskat)abstract
- Semisolid stir welding of AZ91 was investigated with focus on the joining temperature and rotational speed. An Mg-25% Zn interlayer was located between two AZ91 pieces and the system was heated up to the semisolid state of base metal and interlayer. The weld seam was stirred using a drill-tip at different joining temperatures and rotational speeds. Optical and scanning electron microscopes were employed to study microstructure, cavity formation, and segregation. Hardness profile and shear punch test were also employed to rank the welds based on their quality and homogeneity. Results showed that the lowest cavity content (2.1%) with the maximum ultimate shear strength (about 188 MPa) was obtained in weld with the joining temperature of 530 degrees C and the rotational speed of 1600 r/min. Low quality welds and a reduction of ultimate shear strength were observed at very high or low rotational speeds and joining temperatures. The process, in conclusion, produced close mechanical properties to those of the base metal and homogenous quality throughout the joint, when the intermediate temperature and rotational speeds were employed.
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| 18. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Fe and Cr phase separation in super and hyper duplex stainless steel plates and welds after very short aging times
- 2021
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Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- Fe and Cr phase separation in ferrite, causing 475°C-embrittlement, was studied after very short aging times in super duplex stainless steel (SDSS) and hyper duplex stainless steel (HDSS) plates and welds. Atom probe tomography showed that hot-rolled SDSS, experiencing significant metal working, had faster kinetics of phase separations compared to the SDSS and HDSS welds after 5 min aging at 475 °C. The surface of the 33-mm SDSS plate had faster Fe and Cr phase separation and larger toughness drop. A higher density of dislocations next to the austenite phase boundary in ferrite, detected by electron channeling contrast, can promote the phase separation at the surface of the plate with lower austenite spacing. The toughness dropped in HDSS welds after aging, but SDSS welds maintained their toughness. An inverse simulation method considering an initial sinusoidal nanometric Cr and Fe fluctuation showed that Ni increases the interdiffusion of Cr in the system, resulting a higher degree of phase separation in SDSS welds than the HDSS weld. Within the composition range of the studied SDSS and HDSS materials, the processing influences the Fe and Cr phase separation more than the variation in composition during short aging or typical fabrication times.
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| 19. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Ferrite content measurement in super duplex stainless steel welds
- 2019
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Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 63:2, s. 551-563
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Tidskriftsartikel (refereegranskat)abstract
- Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.
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| 20. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Influence of Fabrication Route and Copper Content on Nature and Kinetics of 475 °C- Embrittlement in Cu-Containing Super Duplex Stainless Steels
- 2023
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Ingår i: Steel Research International. - 1611-3683 .- 1869-344X. ; 4, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hot-rolling, hot isostatic pressing (HIP), welding, as well as copper content on 475 °C-embrittlement is studied in super duplex stainless steels. The as-received samples are solution annealed and quenched. Then, to study the kinetics and nature of phase transformations during fabrication, the samples are aged for a very short duration of 5 min at 475 °C. Atom probe tomography results reveal that the processes involving more plastic deformation such as hot rolling and HIP accelerate chromium and iron phase separation and cause precipitation of copper-rich particles (CRPs) in ferrite, resulting in significant toughness loss. In contrast, the weld does not show a high level of chromium and iron phase separation or CRPs precipitation, preserving its toughness after the short aging. The experiment and the inverse interdiffusion calculations reveal that raising the copper content slow down chromium and iron phase separation but significantly increase the CRP number density and decrease the toughness of the HIPed material. Precipitation simulation of CPRs show that the model must be modified based on each processing condition. It is concluded that hot rolling and HIP accelerate 475 °C-embrittlement, which cannot be prevented by raising the copper content.
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| 21. |
- Hosseini, Vahid, 1987-
(författare)
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Influence of multiple welding cycles on microstructure and corrosion resistance of a super duplex stainless steel
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Super duplex stainless steel (SDSS) has found a wide use in demanding applications such as offshore, chemical and petrochemical industries thanks to its excellent combination of mechanical properties and corrosion resistance. Welding of SDSS, however, is associated with the risk of precipitation of secondary phases and formation of excessive amounts of ferrite in the weld metal and heat affected zone. The present study was therefore aimed at gaining knowledge about the effect of multiple welding thermal cycles on the microstructure and possible sensitization to corrosion of welds in SDSS.Controlled and repeatable thermal cycles were produced by robotic welding. Oneto four autogenous TIG-remelting passes were applied on 2507 type SDSS plates using low or high heat inputs with pure argon as shielding gas. Thermal cycles were recorded using several thermocouples attached to the plates. Thermodynamic calculations and temperature field modelling were performed in order to understand the microstructural development and to predict the pitting corrosion resistance. Etching revealed the formation of different zones with characteristic microstructures: the fused weld zone (WZ) and the heat affected zone composed of the fusion boundary zone (FBZ), next to the fusion boundary, and further out Zone 1 (Z1) and Zone 2 (Z2). The WZ had a high content of ferrite and often nitrides which increased with increasing number of passes and decreasing heati nput. Nitrogen content of the WZ decreased from 0.28 wt.% to 0.17 wt.% after four passes of low heat input and to 0.10 wt.% after four passes of high heatinput. The FBZ was reheated to high peak temperatures (near melting point) and contained equiaxed ferrite grains with austenite and nitrides. Zone 1 was free from precipitates and the ferrite content was similar to that of the unaffected base material. Sigma phase precipitated only in zone 2, which was heated to peak temperatures in the range of approximately 828°C to 1028°C. The content of sigma phase increased with the number of passes and increasing heat input. All locations, except Z1, were susceptible to local corrosion after multiplere heating. Thermodynamic calculations predicted that a post weld heat treatment could restore the corrosion resistance of the FBZ and Z2. However, the pitting resistance of the WZ cannot be improved significantly due to the nitrogen loss. Steady state and linear fitting approaches were therefore employed to predict nitrogen loss in autogenous TIG welding with argon as shielding gas. Two practical formulas were derived giving nitrogen loss as functions of initial nitrogen content and arc energy both predicting a larger loss for higher heat input and higher base material nitrogen content. A practical recommendation based on the present study is that it is beneficial to perform welding with a minimum number of passes even if this results in a higherheat input as multiple reheating strongly promotes formation of deleterious phases.
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| 22. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
- 2018
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 139, s. 390-400
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Tidskriftsartikel (refereegranskat)abstract
- A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures.
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| 23. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Nanoscale phase separations in as-fabricated thick super duplex stainless steels
- 2021
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Ingår i: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 56:21, s. 12475-12485
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Tidskriftsartikel (refereegranskat)abstract
- Nanoscale phase separations, and effects of these, were studied for thick super duplex stainless steel products by atom probe tomography and mechanical testing. Although nanoscale phase separations typically occur during long-time service at intermediate temperatures (300-500 degrees C, our results show that slowly cooled products start to develop Fe and Cr separation and/or precipitation of Cu-rich particles already during fabrication. Copper significantly slowed down the kinetics at the expense of Cu-rich particle precipitation, where the high-copper material subjected to hot isostatic pressing (HIP), with Delta t(500-400) of 160 s and the low-copper hot-rolled plate with Delta t(500-400) of 2 s had the same level of Fe and Cr separation. The phase separations resulted in lower toughness and higher hardness of the HIP material than for hot-rolled plate. Therefore, both local cooling rate dependent and alloy composition governed variations of phase separations can be expected in as-fabricated condition.
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| 24. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Physical and kinetic simulation of nitrogen loss in high temperature heat affected zone of duplex stainless steels
- 2019
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Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- High temperature heat affected zone (HTHAZ) of duplex stainless steels is prone to local corrosion attack due to a high ferrite fraction and nitride formation. Literature commonly attributes formation of this undesirable microstructure to rapid cooling from high peak temperatures. However, this study investigated the possible role of nitrogen loss in HTHAZ using a combination of physical and kinetics simulation. Applying a stationary gas-tungsten arc (GTA) on a water-cooled plate, a technique known as arc heat treatment, showed that considerable nitrogen loss occurred already after 0.5 min up to 150 µm from the fusion boundary. This zone was extended to 1300 µm after 600 min arc heat treatment. The results of bead-on-plate GTA welding and Gleeble testing replicating the thermal cycle in HTHAZ showed that the ferrite fraction of the real HTHAZ was 7% higher than that for Gleeble samples. This agrees with results from arc heat treatment, where ferrite fraction was found to increase due to nitrogen loss. Numerical and Dictra approaches were developed to simulate the kinetics of nitrogen loss in HTHAZ considering ferrite as the nitrogen rapid diffusion path towards the weld pool. Simulation showed good agreement with both welding and physical simulation. A combination of thermodynamic and kinetics simulations properly predicted the ferrite fraction at 1100 °C for different arc heat treatment times. In conclusion, the experiments (physical simulations and GTA welding) and kinetics simulation showed that nitrogen was lost from HTHAZ to the weld pool. © 2019 Acta Materialia Inc.
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| 25. |
- Hosseini, Vahid, 1987-, et al.
(författare)
-
Precipitation kinetics of Cu-rich particles in super duplex stainless steels
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 15, s. 3951-3964
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Tidskriftsartikel (refereegranskat)abstract
- Complex precipitation behavior of Cu-rich particles (CRPs) was investigated and simulated in continuously cooled and quench-aged super duplex stainless steel. Atom probe tomography (APT) and scanning electron microscopy showed that slow cooling resulted in nonuniform multimodal CRP precipitation and spinodal decomposition, while in the fast cooled and quench-aged conditions, more uniform precipitation of CRPs with no visible spinodal decomposition was found. Depletion of Cu, Ni, and Mn was observed in the ferrite next to the CRPs during growth, but not during dissolution. Some evidence of Ostwald ripening was seen after slow cooling, but in the quench-aged condition, particle coalescence was observed. Large CRPs disappeared next to a ferrite–austenite phase boundary after slow cooling when Cu was depleted due to the diffusion to austenite as also predicted by moving boundary Dictra simulation. Comparing Cu depleted areas next to CRPs analyzed by APT and moving boundary Dictra simulation of CRP–ferrite showed that the effective Cu diffusion coefficient during the early-stage precipitation was about 300 times higher than the Cu diffusion coefficient in ferrite at 475 °C. Using the effective diffusion coefficient and a size-dependent interfacial energy equation, CRP size distribution was successfully predicted by the Langer–Schwartz model implemented in Thermo-Calc Prisma. Applying a short aging time and continuous cooling increased the hardness and decreased the toughness values compared to the solution annealed condition. A nonuniform distribution of Cu in ferrite, the duplex structure, and partitioning of alloying elements among different phases are factors making CRP precipitation in duplex stainless steels complex.
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| 26. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Predicting ferrite fractions in single pass super duplex stainless steel welds : thermal cycle analysis and phase transformation modeling
- 2019
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Ingår i: ESSC and DUPLEX 2019. - Wien : Austrian Society for Metallurgy and Materials (ASMET). ; , s. 180-197
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Konferensbidrag (refereegranskat)abstract
- The relationship between welding process parameters, welding thermal cycle, and the final microstructure is of great importance for reliable fabrication of welded super duplex stainless steels (SDSS) structures. The present study was primarily aimed at investigating the relationship for root/single pass welding of type 2507 SDSS. Fourteen welds were produced using GMAW, GTAW, SAW, and SMAW with different joints geometries, plate thicknesses, and welding parameters. Thermal cycles were recorded using several thermocouples attached to the plates and thermocouples were also harpooned into the weld pool. Weld pool geometries and base metal dilution in the weld metal were determined for all welds. The general trend was that the ferrite fraction of the weld zone increased with increasing cooling rate and base metal dilution in the weld metal. The ferrite fraction was in the range 49-64% for all welds. Kinetics of austenite formation was modeled using computational thermodynamics (Thermo-Calc & DICTRA) to predict the ferrite fractions in the weld zone and calculated fractions were in good agreement with experimental results. Some conflicting results showed that in addition to dilution and cooling rate, the possible nitrogen loss must be taken into account when evaluating and predicting ferrite fraction. It was concluded that the above approach can be used for prediction of the ferrite fraction of super duplex stainless steel single pass welds. Â 2019 ESSC and DUPLEX 2019 - 10th European Stainless Steel Conference - Science and Market, 6th European Duplex Stainless Steel Conference and Exhibition. All rights reserved.
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| 27. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Spinodal Decomposition in Functionally Graded Super Duplex Stainless Steel and Weld Metal
- 2018
-
Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 49A:7, s. 2803-2816
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature phase separations (T < 500 °C), resulting in changes in mechanical and corrosion properties, of super duplex stainless steel (SDSS) base and weld metals were investigated for short heat treatment times (0.5 to 600 minutes). A novel heat treatment technique, where a stationary arc produces a steady state temperature gradient for selected times, was employed to fabricate functionally graded materials. Three different initial material conditions including 2507 SDSS, remelted 2507 SDSS, and 2509 SDSS weld metal were investigated. Selective etching of ferrite significantly decreased in regions heat treated at 435 °C to 480 °C already after 3 minutes due to rapid phase separations. Atom probe tomography results revealed spinodal decomposition of ferrite and precipitation of Cu particles. Microhardness mapping showed that as-welded microstructure and/or higher Ni content accelerated decomposition. The arc heat treatment technique combined with microhardness mapping and electrolytical etching was found to be a successful approach to evaluate kinetics of low-temperature phase separations in SDSS, particularly at its earlier stages. A time-temperature transformation diagram was proposed showing the kinetics of 475 °C-embrittlement in 2507 SDSS.
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| 28. |
- Hosseini, Vahid, 1987-
(författare)
-
Super duplex stainless steels : Microstructure and propertiesof physically simulated base and weld metal
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-temperature processing and application of super duplex stainless steel(SDSS) are associated with the risk of changes in the ferrite/austenite balance and precipitation of secondary phases. This study was therefore aimed at improving knowledge about effects of thermal cycles on the microstructure and properties of SDSS base and weld metal. Controlled and repeatable thermal cycles were physically simulated using the innovative multiple TIG reheating/remelting and the arc heat treatment techniques. In the first technique, one to four autogenous TIG-remelting passes were applied. During arc heat treatment, a stationary arc was applied on a disc mounted on a water-cooled chamber thereby subjecting the material to a steady state temperature gradient from 0.5 minute to 600 minutes. Microstructures and properties were assessed and linked to thermal history through thermal cycle analysis, thermodynamic calculations and temperature field modelling, Remelting studies showed that nitrogen loss from the melt pool was a function of arc energy and initial nitrogen content and could cause highly ferritic microstructures. Heat affected zones were sensitized by nitride formation next to the fusion boundary and sigma phase precipitation in regions subjected to peak temperatures of 828-1028°C. Accumulated time in the critical temperature range, peak temperature and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase precipitation. Arc heat treatment produced graded microstructures in SDSS base and weld metal with the formation of a ferritic region at high temperature due to solid-state nitrogen loss, precipitation of sigma, chi, nitrides, and R-phase with different morphologies at 550-1010°C and spinodal decomposition below 500°C. This caused sensitization and/or increased hardness and embrittlement. Results were summarized as time-temperature-precipitation and properties diagrams for base and weld metal together with guidelines for processing and welding of SDSS.
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| 29. |
- Hosseini, Vahid, 1987-
(författare)
-
Super duplex stainless steels Microstructure and propertiesof physically simulated base and weld metal
- 2019
-
Ingår i: Stainless Steel World. - 1383-7184. - 9789187531972 ; :December, s. 8-9
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- High-temperature processing and application of super duplex stainless steel(SDSS) are associated with the risk of changes in the ferrite/austenite balance and precipitation of secondary phases. This study was therefore aimed at improving knowledge about effects of thermal cycles on the microstructure and properties of SDSS base and weld metal. Controlled and repeatable thermal cycles were physically simulated using the innovative multiple TIG reheating/remelting and the arc heat treatment techniques. In the first technique, one to four autogenous TIG-remelting passes were applied. During arc heat treatment, a stationary arc was applied on a disc mounted on a water-cooled chamber thereby subjecting the material to a steady state temperature gradient from 0.5 minute to 600 minutes. Microstructures and properties were assessed and linked to thermal history through thermal cycle analysis, thermodynamic calculations and temperature field modelling, Remelting studies showed that nitrogen loss from the melt pool was a function of arc energy and initial nitrogen content and could cause highly ferritic microstructures. Heat affected zones were sensitized by nitride formation next to the fusion boundary and sigma phase precipitation in regions subjected to peak temperatures of 828-1028°C. Accumulated time in the critical temperature range, peak temperature and the number of thermal cycles are the most relevant criteria when evaluating the risk of sigma phase precipitation. Arc heat treatment produced graded microstructures in SDSS base and weld metal with the formation of a ferritic region at high temperature due to solid-state nitrogen loss, precipitation of sigma, chi, nitrides, and R-phase with different morphologies at 550-1010°C and spinodal decomposition below 500°C. This caused sensitization and/or increased hardness and embrittlement. Results were summarized as time-temperature-precipitation and properties diagrams for base and weld metal together with guidelines for processing and welding of SDSS.
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| 30. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Time-temperature-precipitation and property diagrams for super duplex stainless steel weld metals
- 2018
-
Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 62:3, s. 517-533
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Tidskriftsartikel (refereegranskat)abstract
- Super duplex stainless steel (SDSS) weld metal microstructures, covering the complete temperature range from ambient to liquidus, were produced by arc heat treatment for 1 and 10 min. Temperature modeling and thermodynamic calculations complemented microstructural studies, hardness mapping and sensitization testing. After 1 min, intermetallics such as sigma and chi phase had precipitated, resulting in moderate sensitization at 720–840 °C. After 10 min, larger amounts of intermetallics resulted in hardness up to 400 HV0.5 and more severe sensitization at 580–920 °C. Coarse and fine secondary austenite precipitated at high and low temperatures, respectively: The finer secondary austenite was more detrimental to corrosion resistance due to its lower content of Cr, Mo, and N as predicted by thermodynamic calculations. Increased hardness and etching response suggest that 475 °C embrittlement had occurred after 10 min. Results are summarized as time-temperature-precipitation and property diagrams for hardness and sensitization.
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| 31. |
- Hosseini, Vahid, 1987-, et al.
(författare)
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Wire-arc additive manufacturing of a duplex stainless steel : thermal cycle analysis and microstructure characterization
- 2019
-
Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 63:4, s. 975-987
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of microstructures with thermal cycles was studied for wire-arc additive manufacturing of duplex stainless steel blocks. To produce samples, arc energy of 0.5kJ/mm and interlayer temperature of 150 degrees C were used as low heat input-low interlayer temperature (LHLT) and arc energy of 0.8kJ/mm and interlayer temperature of 250 degrees C as high heat input-high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers4 beads in each layerfor LHLT and 15 layers3 beads in each layerfor HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 degrees C, compared with HHHT. A higher austenite fraction (+8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 degrees C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-arc additively manufactured duplex stainless steel samples (35-60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800-1200 degrees C).
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| 32. |
- Valiente Bermejo, María Asunción, 1972-, et al.
(författare)
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Monitoring Thermal Cycles in Multi-pass Welding
- 2016
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Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - : Swedish Production Academy. ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Differently from any previous investigation in welding, this research work presents a novel development that allows temperature to be measured and recorded simultaneously with up to 32 thermocouples indifferent locations of a welding joint. Four experiments were designed to optimise the measurement technique by comparing the performance of three types of thermocouples (K, N, C) insulated with different materials and varying the insertion technique of the thermocouples in the joint. Results showed that type-K thermocouple had the best performance and proved that glass fibre insulation provided better protection than Inconel. The optimised measurement procedure developed in this work enables to monitor the thermal cycles in multi-pass welds. That information is essential in multi-pass welding of materials such as super duplex stainless steels, carbon steels or nickel alloys, as heating them repeatedly makes them susceptible to the formation of brittle phases and in turn it influences their mechanical and corrosion properties. This technique could be really important for future applications such as temperature modellingor prediction of mechanical properties and microstructure in relation to the thermal cycle experienced by alloys susceptible to the formation of undesirable phases.
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| 33. |
- Vattappara, Kevin, et al.
(författare)
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Physical and thermodynamic simulations of gamma-prime precipitation in Haynes (R) 282 (R) using arc heat treatment
- 2021
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 870
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Tidskriftsartikel (refereegranskat)abstract
- Haynes 282 is a Ni-based gamma prime (gamma') strengthening alloy with a balanced combination of high temperature properties and fabricability. This paper aims to study the evolution of the microstructure and hardness using a novel physical simulation method called arc heat treatment, followed by thermodynamic modeling of gamma' precipitation. For the arc heat treatment, a steady state temperature gradient was generated using a stationary tungsten inert gas arc on a sample mounted onto a water-cooled chamber. The steady state condition ranged from room temperature to the liquidus and was achieved within the first few sec-onds. Aged and solutionized samples were arc heat treated for 1.5 min, 30 min, and 4 h. The experiments were complemented with temperature modeling, equilibrium calculations, and gamma' precipitation simulations. A unique graded microstructure formed in the arc heat-treated samples. It consisted of a fusion zone with a dendritic microstructure; a region with the dissolution of all secondary phases (MC carbides, grain boundary carbides, and gamma'); a region with MC and grain boundary carbides; a gamma' precipitation zone; and the base metal. The temperature range of the dissolution area extended to lower temperatures with increasing arc heat treatment dwell time. The gamma' precipitation zone showed a distinct etching response coupled with high hardness. The hardness and the temperature range of the gamma' precipitation zone increased with increasing arc heat treatment time. The gamma' radii increased with increasing time and temperature. The gamma' precipitation model, simulated with TC Prisma, showed very good agreement with the experimental results. Finally, the results were used to develop time-temperature precipitation and hardness diagrams.
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