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Baghdadchi, A. (2024). Directed Energy Deposition Additive Manufacturing and Welding of Duplex Stainless Steel using Laser Beam. (Doctoral dissertation). Trollhättan: University West
Open this publication in new window or tab >>Directed Energy Deposition Additive Manufacturing and Welding of Duplex Stainless Steel using Laser Beam
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

Duplexa rostfria stål (DSS) med en ferritisk-austenitisk mikrostruktur används inom ett brett spektrum av tillämpningar tack vare hög korrosionsbeständighet och goda mekaniska egenskaper. Effektiv och framgångsrik produktion och sammanfogning av DSS kräver noggrann kontroll av processer och en djupgående förståelse av sambanden mellan kemisk sammansättning, termiska cykler, resulterande mikrostrukturer och egenskaper. I detta arbete studerades svetsning och metalldeponering (direct energy deposition) av DSS med hjälp av laseroch resulterande mikrostrukturer samt egenskaper utvärderades.

I den första delen svetsades ett lägre legerat FDX 27 duplex rostfritt stål, som har en TRIP-effekt (transformation-induced plasticity), med laser och laseruppvärmdes med ren argon eller ren kvävgas som skyddsgas. Svetsgodsets austenitandel var 22% för argonskydd och 39% för kvävgasskydd under svetsningen. Färre nitrider observerades med kvävgasskydd jämfört med argonskydd. Laseruppvärmning påverkade inte signifikant nitrid- eller austenitandelen för argonskydd. Dock resulterade laseruppvärmningen av svetsen med kvävgasskydd i minskad nitridandel samtidigt som austenitandelen ökade till 57%, vilket visar effektiviteten av detta tillvägagångssätt.

Analys av fasfraktion är viktig för DSS eftersom balansen mellan ferrit och austenit påverkar egenskaperna. För TRIP-stål måste risken för martensitomvandling av austenit under provberedningen också beaktas. Ferrit, austenit och martensit identifierades och kvantifierades med hjälp av ljusoptisk mikroskopi (LOM) och analys med hjälp av diffraktion av bakåtspridda elektroner (EBSD electron backscatter diffraction). Det visade sig att mekanisk polering gav upp till 26% deformationsinducerad martensit, medan ingen martensit observerades efter elektrolytisk polering.

I den andra delen användes en systematisk metodik i fyra steg för att utveckla procedurer för additiv tillverkning av standardkomponenter i 22% krom DSS med metalldeponering och laser med svetstråd som tillsatsmaterial (DED-LB/w), kombinerad med varmtrådteknologi. I de fyra stegen tillverkades enkelsträngar, enkelväggar, ett block och slutligen en cylinder med en inre diameter på 160 mm, tjocklek på 30 mm och höjd på 140 mm. Genom att implementera denna metodik med en stegvis ökning av den deponerade volymen och geometrisk komplexitet kan additiva tillverkningsprocedurer framgångsrikt användas för utveckling av metallkomponenter med betydande storlekar. Den deponerade mikrostrukturen var ojämn och innehöll upprepade områden med hög ferrithalt och nitrider samt områden med hög andel av austenit. Värmebehandling i 1 timme vid 1100°C homogeniserade mikrostrukturen, löste upp nitriderna och jämnade nästan ut ferrit- och austenitandelarna. Hållfasthet, duktilitet och seghet var goda för cylindern, jämförbara med de av smidda typer av 2205 DSS, både som deponerad och efter värmebehandling. Gropfrätning och korrosionsmotstånd visade att mikrostrukturella skillnader, inklusive förhållande ferrit till austenit, fördelning av legeringselement i ferrit och austenit och närvaro av nitrider, påverkade korrosionsmotståndet för DED-LB/w DSS. Det visades också att, tillsammans med sönderfallet av ferrit till Fe-rika (α) och Cr-rika (αʹ) faser, bidrar kluster av Ni, Mn och Si-atomer till sprödhet vid 475°C hos DSS tillverkade av DED-LB/w.

Detta arbete har visat att en laser framgångsrikt kan användas som värmekälla vid tillverkning av DSS både för svetsning och additiv tillverkning. Utmaningar som kväveutarmning, låga austenitandelar och bildning av nitrider måste dock hanteras genom noggrann processtyrning och/eller värmebehandling.

Place, publisher, year, edition, pages
Trollhättan: University West, 2024. p. 90
Series
PhD Thesis: University West ; 63
Keywords
Duplex stainless steel; Laser welding; Additive manufacturing; Direct Energy Deposition using a Laser Beam; Microstructure characterization, Duplexa rostfria stål; Lasersvetsning; Additiv tillverkning; Metalldeponering med laser; Mikrostruktur
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-21251 (URN)978-91-89325-71-5 (ISBN)978-91-89325-70-8 (ISBN)
Public defence
2024-04-22, C118, Gustava Melins gata, Trollhättan, 10:00 (English)
Opponent
Supervisors
Note

All papers are CC BY 4.0

Paper F is  submitted.

Available from: 2024-03-11 Created: 2024-02-20
Baghdadchi, A. & Movahedi, M. (2023). Consumable pin-friction stir spot welding of Al-Mg-Si alloy via pre-created hole and refilling: Microstructure evolution, defects, and shear/tensile failure load. Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, 237(17)
Open this publication in new window or tab >>Consumable pin-friction stir spot welding of Al-Mg-Si alloy via pre-created hole and refilling: Microstructure evolution, defects, and shear/tensile failure load
2023 (English)In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 237, no 17Article in journal (Refereed) Published
Abstract [en]

Since Al-Mg-Si alloys are widely used in the transportation industry, it is important to produce a sound and robust weld between the sheets of these alloys. The focus of this work is on the tensile-shear and cross-tension strengths of the consumable pin-friction stir spot welds (CP-FSSWs) without an exit-hole between the Al-6061 aluminum sheets. Before welding, a hole was created at the joint region in the base sheets and then, it was filled using a rotating consumable pin. The tensile-shear, cross-tension, and microhardness tests were employed to evaluate the mechanical properties of the spot welds. The results showed that the pre-created hole was entirely filled during the welding process. While a complete bond was formed between the consumable pin and the lateral surface of the hole, there were three distinct regions at the interface of the pin and the bottom of the hole: complete bond, kissing bond, and defects. Enhancement of the tool rotational speed decreased the area of the complete bond in the weld compared to the other regions. A linear relationship existed between the bonding area and weld failure load in the cross-tension test. The proposed relationship approved the impact of the swirly region at the interface of the base sheets on the weld strength. While in the cross-tension test, the weld failure load decreased from ∼2800 to ∼1950 N, it improved from ∼10,500 to ∼12,000 N in the tensile-shear test with enhancement of the tool rotational speed from 700 to 2000 rpm. The hardness measurements demonstrated that there was no common heat affected zone softening after CP-FSSW.  

Place, publisher, year, edition, pages
Sage Publications, 2023
Keywords
Aluminum alloys; Friction; Friction stir welding; Heat affected zone; Magnesium alloys; Silicon alloys; Spot welding; Tensile strength; Tensile testing; Al 6061; Base sheet; Consumables; Cross-tension; Failure load; Fracture surfaces; Friction stir spot weld; Friction stir spot welding; Tensile shears; Tension tests; Microstructure
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-19818 (URN)10.1177/09544062231151566 (DOI)000922866700001 ()2-s2.0-85147590348 (Scopus ID)
Available from: 2023-09-13 Created: 2023-09-13 Last updated: 2024-01-04Bibliographically approved
Baghdadchi, A., Cary, C., Sridhar, N., Valiente Bermejo, M. A., Fink, C. & Andersson, J. (2023). Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wire. Journal of Materials Research and Technology, 26, 6741-6756
Open this publication in new window or tab >>Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wire
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2023 (English)In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 26, p. 6741-6756Article in journal (Refereed) Published
Abstract [en]

Microstructure characteristics and pitting corrosion of a duplex stainless steel (DSS) manufactured by laser metal deposition with wire (LMDw) were studied. The layer-by-layer LMDw process resulted in a mixed microstructure of predominantly ferrite with 2% austenite and chromium-rich nitrides, and reheated regions with ~33% austenite. The high cooling rate of LMDw restricted the distribution of Cr, Mo, and Ni, in ferrite and austenite, while N diffuses from ferrite to austenite. Subsequent heat treatment at 1100 C for 1 h resulted in homogenized microstructure, dissolution of nitrides, and balanced ferrite/austenite ratio. It also led to the redistribution of Cr and Mo to ferrite, and Ni and N to austenite. At room temperature, cyclic potentiodynamic polarization measurements in 1.0 M NaCl solution showed no significant differences in corrosion resistance between the as-deposited and heat-treated samples, despite the differences in terms of ferrite to austenite ratio and elemental distribution. Critical pitting temperature (CPT) was the lowest (60 C) for the predominantly ferritic microstructure with finely dispersed chromium-rich nitrides; while reheated area with ~33% austenite in as-deposited condition achieved higher critical temperature comparable to what was obtained after heat treatment (73 and 68 C, respectively). At temperatures above the CPT, selective dissolution of the ferrite after deposition was observed due to depletion of N, while after heat treatment, austenite preferentially dissolved due to Cr and Mo concentrating in ferrite. In summary, results demonstrate how microstructural differences in terms of ferrite-to-austenite ratio, distribution of corrosion-resistant elements, and presence of nitrides affect corrosion resistance of LMDw DSS.

Keywords
Additive manufacturing, Duplex stainless steel, Laser metal deposition, Localized corrosion, Microstructure-property relation
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-20883 (URN)10.1016/j.jmrt.2023.09.037 (DOI)001139454200001 ()2-s2.0-85171616425 (Scopus ID)
Note

CC BY 4.0

Available from: 2023-12-28 Created: 2023-12-28 Last updated: 2024-04-12
Baghdadchi, A., Patel, V., Li, W., Yang, X. & Andersson, J. (2023). Ductilization and grain refinement of AA7075-T651 alloy via stationary shoulder friction stir processing. Journal of Materials Research and Technology, 27, 5360-5367
Open this publication in new window or tab >>Ductilization and grain refinement of AA7075-T651 alloy via stationary shoulder friction stir processing
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2023 (English)In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 27, p. 5360-5367Article in journal (Refereed) Published
Abstract [en]

This study investigates the microstructural evolution, mechanical properties, and fracture behavior of AA7075-T651 aluminium alloy subjected to stationary shoulder friction stir processing (SSFSP). SSFSP samples were produced at three different rotational speeds in a range of 600–1000 rpm. The results reveal that SSFSP leads to a uniform grain refinement within the Stir Zone (SZ), reducing the grain size to approximately 2–3 μm from the initial 15 μm in the base material (BM) irrespective of the probe rotational speeds. After SSFSP, the elongation increased by over 50 % at the cost of 10 % reduction in the ultimate tensile strength for all samples. It was worth to note that variations in tool rotational speed exhibited minimal influence on the microstructure and mechanical properties, offering wide range of probe rotational speeds. This could be attributed to the use of non-rotating shoulder with prob dominated microstructure in the SZ. Fractographic analysis confirmed the ductile nature of fractures, revealing development of fine dimples due to grain refinement. This work underscores the effectiveness of SSFSP in achieving significant grain refinement followed by drastic increase in ductility, which offers valuable insights for using stationary shoulder at wider range of rotational speed.

Keywords
Aluminium alloy, Friction stir processing, Stationary shoulder, Mechanical properties, Grain size
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-21002 (URN)10.1016/j.jmrt.2023.11.041 (DOI)001115512600001 ()2-s2.0-85178958390 (Scopus ID)
Note

CC-BY 4.0

The authors would like to thank for the financial support from the funded project by Postdoctoral Science Foundation China [2019M663815].

Available from: 2023-11-24 Created: 2023-11-24 Last updated: 2024-01-05Bibliographically approved
Patel, V., Wouters, H., Baghdadchi, A., De Backer, J., Igestrand, M., Azimi, S. & Andersson, J. (2023). Robotic friction stir welding in lightweight battery assembly of extrusion-cast aluminium alloys. Journal of Advanced Joining Processes, 8, Article ID 100156.
Open this publication in new window or tab >>Robotic friction stir welding in lightweight battery assembly of extrusion-cast aluminium alloys
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2023 (English)In: Journal of Advanced Joining Processes, ISSN 2666-3309, Vol. 8, article id 100156Article in journal (Refereed) Published
Abstract [en]

The present study focuses on developing lightweight assembly of two different aluminium alloys extruded and high pressure die cast (HPDC) for battery frame assembly in BEV. The goal is to produce defect-free welds in lap configuration with smooth surface finish. Stationary shoulder friction stir welding (SSFSW) was employed with welding speeds of 3–15 mm/s. EBSD analysis revealed two groups of grains in the stir zone (SZ) due to dynamic recrystallization. Moreover, the grain size of the SZ significantly decreased compared to both alloys. The cast alloy contains large iron particles, and that were broken by the rotating probe, and the stirred material consisted of fine dispersed precipitates. Tensile-shear test found the fracture location at the hook area near to cast, and a model representing fracture behavior is also discussed. With increasing welding speed from 3 to 5 mm/s, the tensile strength found ∼95 and ∼100 MPa, respectively without any significance difference in the fracture behavior and location. Overall, this study provides valuable insights such as materials mixing, grain refinement, and joint strength in dissimilar joining using SSFSW. The findings could be useful in developing optimized welding parameters and improving the overall quality and productivity of the SSFSW process for battery pack assembly in BEV.

Keywords
Stationary shoulder friction stir weldingAluminium alloysHPDCExtrusionLightweightBEV
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-21003 (URN)10.1016/j.jajp.2023.100156 (DOI)001085211200001 ()2-s2.0-85172304340 (Scopus ID)
Note

The funding support from the VINNOVA project of EVASTIR (2019-03114) with industry partners Volvo Cars Corporations, Hydro Extruded Solutions, ESAB, and i-Weld project H2020-MSCA-RISE-2018 (Project number: 823786) are highly acknowledged.

CC-BY 4.0

Available from: 2023-11-24 Created: 2023-11-24 Last updated: 2024-04-03Bibliographically approved
Jadidi, A., Azhiri, R. B., Baghdadchi, A. & Salmanibideskan, A. (2022). Lap joining of aluminum 5052 to copper by optimum friction stir spot welding process. The International Journal of Advanced Manufacturing Technology
Open this publication in new window or tab >>Lap joining of aluminum 5052 to copper by optimum friction stir spot welding process
2022 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015Article in journal (Refereed) Published
Abstract [en]

In the present study, lap joints of dissimilar 5052 aluminum alloy and pure copper were fabricated by friction stir spot welding process. The work was aimed to find simultaneous effect of parameters such as tool rotary speed (1000, 1500, and 2000 rpm) and dwell time (5, 10, and 15 s) on lap shear force (LSF), hardness, and microstructure evolution. Also, statistical models of the quality characteristics were developed to understand which parameter has dominant effect on quality characteristics. Research findings showed that to obtain sound joints with high lap shear strength, tool rotary speed of 1500 rpm and dwell time of 15 s should be selected. It provides sufficient heat input for mechanical interlocking and prevents the formation of coarse and thick intermetallic compounds (IMCs) in the stir zone. On the other hand, to achieve maximum hardness, 2000 rpm tool rotary speed should be chosen to provide enough heat for formation of intermetallic compound and 10Â s dwell time should be used to prevent enough time for microstructure refining. Moreover, from the statistical analyses, it was found that dwell time and tool speed are the significant factors for lap shear strength and hardness, respectively. In order to attain simultaneous maximum strength and hardness, tool speed of 1630 rpm and dwell time of 14 s should be used. In such condition, lap shear strength of 1980 N and hardness of 78 V are achieved with desirability of 86%. 

Place, publisher, year, edition, pages
Springer Science and Business Media Deutschland GmbH, 2022
Keywords
Aluminum alloys; Copper; Friction; Friction stir welding; Hardness; Microstructure; Shear flow; Speed; Spot welding, Dissimilar joints; Dwell time; Friction stir spot welding; Intermetallics compounds; Joint configuration; Lap joint; Lap joint configuration; Lap shear strength; Rotary speed; Spot-welding process, Intermetallics
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-18171 (URN)10.1007/s00170-021-08541-x (DOI)000745822400001 ()2-s2.0-85123478779 (Scopus ID)
Available from: 2022-03-24 Created: 2022-03-24 Last updated: 2022-03-24
Baghdadchi, A. (2022). Laser Welding and Additive Manufacturing of Duplex Stainless Steels: Properties and Microstructure Characterization. (Licentiate dissertation). Trollhättan: Högskolan Väst
Open this publication in new window or tab >>Laser Welding and Additive Manufacturing of Duplex Stainless Steels: Properties and Microstructure Characterization
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

Duplexa rostfria stål (DSS) är viktiga konstruktionsmaterial tack vare derasutmärkta mekaniska egenskaper och goda korrosionsbeständighet. Vid svetsningoch additiv tillverkning krävs noggrann styrning av parametrar och kunskap om processernas inverkan på mikrostrukturen för att uppnå önskade egenskaper.Lasersvetsning, värmebehandling med laser och additiv tillverkning i form av lasermetalldeponering med tråd (LMDw) har därför studerats för DSS.

Det duplexa stålet FDX 27 lasersvetsades utan tillsatsmaterial och med argon ellerkväve som skyddsgas. Kvävgasskydd gav mer austenit och färre nitrider änargonskydd. En efterföljande laservärmebehandling löste upp nitriderna då kväve användes som skyddsgas och austenithalten ökade till 57%. Austeniten i FDX 27kan vid deformation omvandlas till martensit. Två metoder för identifiering av martensit utvecklades därför: en färgetsmetod för ljusoptisk mikroskopi samt en metod som utnyttjar bakåtspridda elektroner (EBSD) vid elektronmikroskopi.Som mest bildades 26% martensit vid mekanisk provpreparering medan elektropolerade prover endast innehöll austenit och ferrit.

Procedurer togs fram för additiv tillverkning av komponenter, i 22% krom duplexa rostfria stål, med LMDw kombinerat med varmtrådsteknik. Slutprodukten var en 140 mm hög cylinder med 160 mm inre diameter och tjocklek av 30 mm. Mikrostrukturen var inhomogen med periodiskt omväxlande ferritiska områden med nitrider, och områden med stor andel austenit.Värmebehandling under 1 timme vid 1100oC eliminerade nitriderna och gav en homogen struktur med ca. 50% austenit. De mekaniska egenskaperna var, både före och efter värmebehandling, jämförbara med de typiska för motsvarande stål. Högst hållfasthet uppmättes före värmebehandling med sträckgränsen 765 MPa och brottgränsen 865 MPa, medan den största förlängningen var 35% efter värmebehandling. Slagsegheten var upp till 300 J vid -10oC men varierade med hur provstavens brottanvisning var orienterad relativt byggriktningen.Laser är en lämplig energikälla vid svetsning och additiv tillverkning av duplexa rostfria stål. Utmaningar som kväveförlust, låga austenithalter och nitridbildning kan hanteras med noggrann processkontroll och/eller värmebehandling.

Place, publisher, year, edition, pages
Trollhättan: Högskolan Väst, 2022. p. 174
Series
Licentiate Thesis: University West ; 38
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-18126 (URN)978-91-89325-19-7 (ISBN)978-91-89325-18-0 (ISBN)
Presentation
2022-03-08, J111, Gustava Melins Gata 2, Trollhättan, 10:00 (English)
Supervisors
Available from: 2022-03-08 Created: 2022-02-07 Last updated: 2022-03-02Bibliographically approved
Baghdadchi, A., Hosseini, V., Valiente Bermejo, M. A., Axelsson, B., Harati, E., Högström, M. & Karlsson, L. (2022). Wire laser metal deposition of 22% Cr duplex stainless steel: as-deposited and heat-treated microstructure and mechanical properties. Journal of Materials Science, 57(21), 9556-9575
Open this publication in new window or tab >>Wire laser metal deposition of 22% Cr duplex stainless steel: as-deposited and heat-treated microstructure and mechanical properties
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2022 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 57, no 21, p. 9556-9575Article in journal (Refereed) Published
Abstract [en]

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

Keywords
A-stable; Build direction; Defect-free; Heat treated condition; High quality; Hot wires; Laser metal deposition; Microstructures and mechanical properties; Programmable logic control system; Secondary austenite
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-18106 (URN)10.1007/s10853-022-06878-6 (DOI)000744401200004 ()2-s2.0-85123120534 (Scopus ID)
Available from: 2022-02-07 Created: 2022-02-07 Last updated: 2024-04-12Bibliographically approved
Baghdadchi, A., Hosseini, V. & Karlsson, L. (2021). Identification and quantification of martensite in ferritic-austenitic stainless steels and welds. Journal of Materials Research and Technology, 15, 3610-3621
Open this publication in new window or tab >>Identification and quantification of martensite in ferritic-austenitic stainless steels and welds
2021 (English)In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 15, p. 3610-3621Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier Editora Ltda, 2021
Keywords
Duplex stainless steel, Mechanical polishing, Electrolytic polishing, Phase analysis, Martensite, Electron backscatter diffraction
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17790 (URN)10.1016/j.jmrt.2021.09.153 (DOI)000712162500008 ()2-s2.0-85117073816 (Scopus ID)
Note

 This study received support from the EU-project H2020-MSCA-RISE-2018 Number 823786, i-Weld, and the Swedish Agency for Economic and Regional Growth through the European Union–European Development Fund

Available from: 2021-12-22 Created: 2021-12-22 Last updated: 2024-02-20
Baghdadchi, A., Hosseini, V., Hurtig, K. & Karlsson, L. (2021). Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating. Welding in the World, 65, 499-511
Open this publication in new window or tab >>Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating
2021 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 65, p. 499-511Article in journal (Refereed) Published
Abstract [en]

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).

Keywords
Austenite; Duplex stainless steel; Heat affected zone; Heat treatment; Industrial heating; Microstructural evolution; Nitrides; Nitrogen; Shielding; Welding, Austenite formation; Autogenous laser welding; Chemical compositions; Duplex stainless steel (DSS); Equilibrium phase diagrams; Nitride formation; Nitrogen content; Thermodynamic calculations, Argon lasers
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-16028 (URN)10.1007/s40194-020-01026-7 (DOI)000587932200001 ()2-s2.0-85095716448 (Scopus ID)
Funder
EU, European Research Council, H2020-MSCA-RISE-2018 Number 823786
Note

Open access funding provided by University West. James Oliver and Ravi Vishnu from the Outokumpu Stainless AB (Avesta, Sweden) are appreciatively acknowledged for their help and support. This study received great support from the EU-project H2020-MSCA-RISE-2018 Number 823786, i-Weld, and the Swedish Agency for Economic and Regional Growth through the European Union – European Development Fund.

Creative CommonsAttribution 4.0 International License

Available from: 2020-11-16 Created: 2020-11-16 Last updated: 2024-02-20Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6820-4312

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