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Sökning: WFRF:(Karlsson Leif 1956 )

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1.
  • Johansson, Birgitta, et al. (författare)
  • Atrial function after left atrial epicardial cryoablation for atrial fibrillation in patients undergoing mitral valve surgery
  • 2012
  • Ingår i: Journal of Interventional Cardiac Electrophysiology. - : Springer Science+Business Media B.V.. - 1383-875X .- 1572-8595. ; 33:1, s. 85-91
  • Tidskriftsartikel (refereegranskat)abstract
    • PURPOSE: To explore the effects on atrial and ventricular function of restoring sinus rhythm (SR) after epicardial cryoablation and closure of the left atrial appendage (LAA) in patients with mitral valve disease and atrial fibrillation (AF) undergoing surgery.METHODS: Sixty-five patients with permanent AF were randomized to mitral valve surgery combined with left atrial epicardial cryoablation and LAA closure (ABL group, n = 30) or to mitral valve surgery alone (control group, n = 35). Two-dimensional and Doppler echocardiography were performed before and 6 months after surgery.RESULTS: At 6 months, 73% of the patients in the ABL group and 46% of the controls were in SR. Patients in SR at 6 months had a reduction in their left ventricular diastolic diameter while the left ventricular ejection fraction was unchanged. In patients remaining in AF, the left ventricular ejection fraction was lower than at baseline. The left atrial diastolic volume was reduced after surgery, more in patients with SR than AF. In patients in SR, the peak velocity during the atrial contraction and the reservoir function were lower in the ABL group than in the control group.CONCLUSIONS: In patients in SR, signs of atrial dysfunction were observed in the ABL but not the control group. Atrial dysfunction may have existed before surgery, but the difference between the groups implies that the cryoablation procedure and/or closure of the LAA might have contributed.
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2.
  • Rohlin, Anna, et al. (författare)
  • A mutation in POLE predisposing to a multi-tumour phenotype
  • 2014
  • Ingår i: International Journal of Oncology. - : Spandidos Publications. - 1019-6439 .- 1791-2423. ; 45:1, s. 77-81
  • Tidskriftsartikel (refereegranskat)abstract
    • Somatic mutations in the POLE gene encoding the catalytic subunit of DNA polymerase epsilon have been found in sporadic colorectal cancers (CRCs) and are most likely of importance in tumour development and/or progression. Recently, families with dominantly inherited colorectal adenomas and colorectal cancer were shown to have a causative heterozygous germline mutation in the proofreading exonuclease domain of POLE. The highly penetrant mutation was associated with predisposition to CRC only and no extra-colonic tumours were observed. We have identified a mutation in a large family in which the carriers not only developed CRC, they also demonstrate a highly penetrant predisposition to extra-intestinal tumours such as ovarian, endometrial and brain tumours. The mutation, NM_006231.2:c.1089C>A, p.Asn363Lys, also located in the proofreading exonuclease domain is directly involved in DNA binding. Theoretical prediction of the amino acid substitution suggests a profound effect of the substrate binding capability and a more severe impairment of the catalytic activity compared to the previously reported germline mutation. A possible genotype to phenotype correlation for deleterious mutations in POLE might exist that needs to be considered in the follow-up of mutation carriers.
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3.
  • Wennergren, Mattias, 1993, et al. (författare)
  • Swedish Child Health Services Register: a quality register for child health services and children's well-being.
  • 2023
  • Ingår i: BMJ paediatrics open. - : BMJ. - 2399-9772. ; 7:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Swedish child health services (CHS) is a free-of-charge healthcare system that reaches almost all children under the age of 6. The aim for the CHS is to improve children's physical, psychological and social health by promoting health and development, preventing illness and detecting emerging problems early in the child's life. The services are defined in a national programme divided into three parts: universal interventions, targeted interventions and indicated interventions.The Swedish Child Health Services Register (BHVQ) is a national Quality Register developed in 2013. The register extracts data from the child's health record and automatically presents current data in real time. At present, the register includes 21 variables.We aim to describe data available in the BHVQ and the completeness of data in BHVQ across variables.Child-specific data were exported from the register, and data for children born in the regions were retrieved from Statistics Sweden to calculate coverage.The register includes over 110000 children born between 2011 and 2022 from 221 child healthcare centres in eight of Sweden's 21 regions. In seven of the eight regions, 100% of centres report data.The completeness of data differs between participating regions and birth cohorts. The average coverage for children born in 2021 is 71%.The BHVQ is a valuable resource for evaluating Child Health Services nationally, with high coverage for the youngest children. As a result of continuous improvement of the services, the possibility to follow the development of children's health in Sweden is possible through the register. When fully expanded, the register will be a natural and essential part of developing preventive services, improving healthcare for children below 6years of age and a tool for developing evidence-based child health interventions.
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4.
  • Baghdadchi, Amir, 1994- (författare)
  • Directed Energy Deposition Additive Manufacturing and Welding of Duplex Stainless Steel using Laser Beam
  • 2024
  • 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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5.
  • Baghdadchi, Amir, 1994-, et al. (författare)
  • Identification and quantification of martensite in ferritic-austenitic stainless steels and welds
  • 2021
  • Ingår i: Journal of Materials Research and Technology. - : Elsevier Editora Ltda. - 2238-7854. ; 15, s. 3610-3621
  • 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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6.
  • Baghdadchi, Amir, 1994- (författare)
  • Laser Welding and Additive Manufacturing of Duplex Stainless Steels : Properties and Microstructure Characterization
  • 2022
  • 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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7.
  • Baghdadchi, Amir, 1994-, et al. (författare)
  • Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating
  • 2021
  • Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 65, s. 499-511
  • 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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8.
  • Baghdadchi, Amir, 1994-, et al. (författare)
  • Wire laser metal deposition additive manufacturing of duplex stainless steel components -Development of a systematic methodology
  • 2021
  • Ingår i: Materials. - : MDPI. - 1996-1944. ; 14:23
  • 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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9.
  • Baghdadchi, Amir, 1994-, et al. (författare)
  • Wire laser metal deposition of 22% Cr duplex stainless steel : as-deposited and heat-treated microstructure and mechanical properties
  • 2022
  • Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 57:21, s. 9556-9575
  • 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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10.
  • Cederberg, Emil, et al. (författare)
  • Physical simulation of additively manufactured super duplex stainless steels : microstructure and properties
  • 2020
  • Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
  • 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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11.
  • Eriksson, Siw, 1962, et al. (författare)
  • ‘Co-Creation’ is On Everyone’s Lips – Designers’ Perception of Opportunities For and Barriers To Co-Creation in Product Development Organizations
  • 2022
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Co-creation, aimed at encouraging users to become active partners throughout the development process, has been widely discussed in academia for the last 10-15 years as a strategy for sustainable design of products that fulfil users’ needs and enhance users’ experience of future products. However, despite the fact that universities have undertaken to educate future designers on methods and tools for co-creation with users, we emphasize that there is still a noticeable gap between theory and practice, as designers’ opportunities for incorporating co-creation activities in product development organizations remain limited. The aim of this study, consisting of twelve semi-structured, in-depth interviews with design practitioners from Swedish industry, was to create a deeper understanding of the extent to which designers can and do actively involve users in the design process in industrial organizations. While we found that designers were interested and willing to work in a more user-centered way, there was no evidence of co-creation with users. The companies’ marketing departments were mainly responsible for customer/user contact, identifying and communicating user/customer requirements by means of traditional marketing methods. Hence direct communication between designers and users was rarely supported. Moreover, the informants often experienced a strong reluctance from the marketing department to provide them with necessary contacts, as this might interfere with their relationship with the customer. The barriers to accessing users were even more pronounced for designers in consultancy firms, where the customer functioned as the link to the market and frequently declined to allocate resources to user studies, arguing that they already possessed the necessary knowledge or that such studies were too costly. Consequently, irrespective of intra- or inter-organizational settings, designers’ ability to access users often depended on individual motivation and initiatives rather than organizational factors.
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12.
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13.
  • Eriksson, Siw, 1962, et al. (författare)
  • Genuine co-design : an activity theory analysis involving emergency nurses in an interdisciplinary new product development project of a novel medical device
  • 2021
  • Ingår i: International Journal of Human Factors and Ergonomics. - 2045-7804 .- 2045-7812. ; 8:4, s. 331-369
  • Tidskriftsartikel (refereegranskat)abstract
    • This study analysed a series of workshops and explored prerequisites for interdisciplinary co-design among industrial designers, design engineers and users in the development of a novel medical device. Presented as a case study, this paper focus on what affects participants’ transformative processes towards genuine participation in co-design processes. Based on activity theory, we suggest that co-design activities have to support not only users, but all participants, shifting their perspectives beyond their own domain’s rules, motives, objects and division of labour, i.e., beyond their own activity system, to support users’ participation as equal members in design teams. We propose that genuine co-design requires a holistic approach where a neutral arena, an impartial facilitator, clear rules of play, along with representational artefacts as mediating tools in the formation of a new collective activity system to foster equality, mutual value and long-term knowledge generation. Such approach requires a process over time. 
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14.
  • Eriksson, Siw, et al. (författare)
  • Product Representations as Mediating Tools in the Development of New Medical Technology
  • 2018
  • Ingår i: Design4Health - Fifth International Conference on Design4Health.. - 9781843874218
  • Konferensbidrag (refereegranskat)abstract
    • Involving users in the design process of new products and services is generally disputed as a prerequisite for fulfilling users' needs and requirements. The importance of user involvement has been argued also regarding the development of new medical technology. Collaboration between users and developers/designers is however not without problems due to differences in, e.g. background, training, perspective, and vocabulary. In order to address these differences, the need for different 'mediating tools' has been emphasized. One type of mediating tools is product representations (PRs). Earlier studies have most often focused on the type of PR that should be used in different phases of the development process in order to get input on different designs. This paper describes instead how and in what situations different PRs mediated communication and collaboration between professional users (medical experts) and designers in an innovation project targeting a solution for long-term monitoring of brain activity based on electroencephalographic (EEG) signals.
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15.
  • Fahlström, Karl, 1986-, et al. (författare)
  • Correlation between laser welding sequence and distortions for thin sheet structures
  • 2017
  • Ingår i: Science and technology of welding and joining. - : Informa UK Limited. - 1362-1718 .- 1743-2936. ; 22:2, s. 150-156
  • Tidskriftsartikel (refereegranskat)abstract
    • Thin ultra-high strength steel shaped as 700 mm long U-beams have been laser welded in overlap configuration to study the influence of welding sequence on distortions. Three different welding directions, three different energy inputs as well as stitch welding have been evaluated, using resistance spot welding (RSW) as a reference. Transverse widening at the ends and narrowing at the centre of the beam were measured. A clear correlation was found between the weld metal volume and distortion. For continuous welds there was also a nearly linear relationship between the energy input and distortion. However, the amount of distortion was not affected by a change in welding direction. Stitching and RSW reduced distortion significantly compared to continuous laser welding.
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16.
  • Fahlström, Karl, 1986-, et al. (författare)
  • Effect of Laser Welding Parameters on Porosity of Weldsin Cast Magnesium Alloy AM50
  • 2018
  • Ingår i: Modern Approaches on Material Science. - 2641-6921. ; 1:2, s. 25-32
  • Tidskriftsartikel (refereegranskat)abstract
    • Pores in the weld metal lower the mechanical properties of the weld. It is therefore important to understand the pore formation mechanisms and find procedures that could reduce porosity. This study focused on laser welding of 3 mm thick magnesium alloy AM50, investigating how different parameters affect porosity formation. Low levels of porosity content were achieved by either increasing the welding speed or using a two-pass welding approach. It was found that higher welding speeds did not allow pores,which were pre-existing from the die-casting process, to have sufficient time to coalesce and expand. In the two-pass welding technique, pores were removed as a result of a degassing process which occurred through the second pass.
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17.
  • Fahlström, Karl, 1986- (författare)
  • Laser welding of ultra-high strength steel and a cast magnesium alloy for light-weight design
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • There is a strong industrial need for developing robust and flexible manufacturing methods for future light-weight design. Better performing, environmental friendly vehicles will gain competitive strength from using light weight structures. In this study, focus has been on laser welding induced distortions for ultra-high strength steel (UHSS) where trials were performed on single hat and double hat beams simulating A-pillar and B-pillar structures. Furthermore, also laser welding induced porosity in cast magnesium alloy AM50 for interior parts were studied. For UHSS, conventional laser welding was done in a fixture designed for research. For cast magnesium, single-spot and twin-spot welding were done. Measurements of final distortions and metallographic investigations have been performed. The results show that the total weld metal volume or the total energy input were good measures for predicting the distortions within one steel grade. For comparing different steel grades, the width of the hard zone should be used. The relation between the width of the hard zone, corresponding to the martensitic area of the weld, and the distortions is almost linear. Additionally, compared with continuous welds, stitching reduced the distortions. For cast magnesium, two-pass (repeated parameters) welding with single-spot gave the lowest porosity of approximately 3%. However, two-pass welding is not considered production friendly. Twin-spot welding was done, where the first beam provided time for nucleation and some growth of pores while reheating by the second beam should provide time for pores to grow and escape. This gave a porosity of around 5%. Distortions and porosity are the main quality problems that occur while laser welding UHSS and cast magnesium, respectively. Low energy input seems to generally minimize quality issues. Laser welding shows high potential regarding weld quality and other general aspects such as productivity in light-weight design for both high strength steel and cast magnesium.
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18.
  • Fahlström, Karl, 1986-, et al. (författare)
  • Low Porosity in Cast Magnesium Welds by Advanced Laser Twin-Spot Welding
  • 2019
  • Ingår i: Materials Sciences and Applications. - : Scientific Research Publishing, Inc.. - 2153-117X .- 2153-1188. ; 10:1, s. 53-64
  • Tidskriftsartikel (refereegranskat)abstract
    • Porosity is reported to be a major issue when welding cast magnesium. Therefore, it is important to understand the pore formation mechanisms and find procedures that could be used to reduce porosity. This study investigated the possibility of using twin-spot optics for reducing the porosity in laser welded cast magnesium. Two twin-spot welding setups were compared using either a beam splitter or twin-spot welding with primary and secondary (placed in front of the primary optic) optics. The results showed that welding with a dual optic setup with a defocused secondary beam reduced the volumetric porosity in the weld to 5%. The highest levels of volumetric porosity were 30%, and were a result of using the dual optic setup, but with a defocused primary beam. No clear relation between the level of porosity and power or welding speed was found. It was found that the amount of porosity depended on the balance of the energy input (controlled by defocusing) between the two beams. Porosity formation can be reduced if the energy from the first beam results in the nucleation and initial growth of pores. Reheating by the second beam then allows the pores to grow and escape from the molten material without melting additional base material. Furthermore, twin-spot welding is shown to be a promising combination of a production friendly solution and high quality welding.
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19.
  • Fahlström, Karl, 1986-, et al. (författare)
  • Metallurgical effects and distortions in laser welding of thin sheet steels with variations in strength
  • 2017
  • Ingår i: Science and technology of welding and joining. - : Informa UK Limited. - 1362-1718 .- 1743-2936. ; 22:7, s. 573-579
  • Tidskriftsartikel (refereegranskat)abstract
    • Geometrical distortions occur while welding, but the understanding of how and why they occur and how to control them is limited. The relation between the weld width, weld metal volume, total energy input, width of hard zone and distortions when laser welding three different thin sheet steels with varying strength has therefore been studied. Weld metal volume and total energy input show a good correlation with distortion for one steel at a time. The best correlation with the when including all three steel grades was the width of the hard zone composed of weld metal and the martensitic area in the heat affected zone. © 2017 Institute of Materials, Minerals and Mining.
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20.
  • Harati, Ebrahim, 1986-, et al. (författare)
  • Applicability of Low Transformation Temperature welding consumables to increase fatigue strength of welded high strength steels
  • 2017
  • Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 97, s. 39-47
  • Tidskriftsartikel (refereegranskat)abstract
    • Application of Low Transformation Temperature (LTT) consumables in welding is a recent approach to increase the fatigue strength of welds. In this paper high strength steels with yield strengths ranging from 650-1021 MPa were fillet and butt welded using different LTT and conventional consumables. The effects of weld metal chemical composition on phase transformation temperatures, residual stresses and fatigue strength were investigated. Lower transformation start temperatures and hence lower tensile or even compressive residual stresses were obtained close to the weld toe for LTT welds. Fatigue testing showed very good results for all combinations of LTT consumables and high strength steels with varying strength levels. For butt welds, the characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to 46% higher when compared to corresponding welds made with conventional filler materials. In fillet welds, a minimum FAT improvement of 34% and a maximum improvement of 132% was achieved when using LTT wires. It is concluded that different LTT consumables can successfully be employed to increase fatigue strength of welds in high strength steels with yield strength up to 1021 MPa. Weld metals with martensite transformation start temperatures close to 200°C result in the highest fatigue strengths.
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21.
  • Harati, Ebrahim, 1986-, et al. (författare)
  • Comparison of effect of shot-peening with HFMI treatment or use of LTT consumables on fatigue strength of 1300 MPa yield strength steel weldments
  • 2020
  • Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 64:7, s. 1237-1244
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, T-joint samples in a 1300 MPa yield strength steel were produced using conventional or low transformation temperature (LTT) type consumables. The welded samples were either subjected to high-frequency mechanical impact (HFMI) treatment or to shot-peening. Fatigue testing was performed under fully reversed, constant amplitude bending load. Shot-peening gave a significant increase in fatigue strength for more than around 50,000 cycles. Shot-peened LTT welds had the highest fatigue strength, with conventional welds being shot-peened having slightly lower fatigue strength. HFMI treatment of conventional and LTT welds improved the fatigue strength also, but to a lesser extent, keeping the slope in the SN diagram close to three, while shot-peened samples had a slope of 5–7. Significant differences in compressive residual stress were seen between the different welds, with the most compressive stress found in the shot-peened samples. This was probably one of the main reasons for the improved fatigue life of shot-peened samples. © 2020, The Author(s).
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22.
  • Harati, Ebrahim, 1986- (författare)
  • Improving fatigue properties of welded high strength steels
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In recent years a strong interest has been expressed to produce lighter structures.One possible solution to reduce the weight is to utilize high strength steels and use welding as the joining method. Many components experience fatigue loadingduring all or part of their life time and welded connections are often the prime location of fatigue failure. This becomes more critical in welded high strength steels as fatigue strength of welds does not increase by increasing the steel strength. A possible solution to overcome this issue is to use fatigue improvement methods.The main objectives of this project are, therefore, to increase understanding of the factors that control fatigue life and to investigate how the fatigue strength improvement methods; high frequency mechanical impact (HFMI) treatment and use of Low Transformation Temperature (LTT) consumables will affect fatigue properties of welds in high strength steels. In this regard, Gas Metal Arc Welding(GMAW) was used to produce butt and fillet welds using LTT or conventional fillers in steels with yield strengths ranging from 650-1021 MPa and T-joint weldsin a steel with 1300 MPa yield strength. The effect of HFMI on fatigue strength of the welds in 1300 MPa yield strength steels was also investigated. Butt and fillet welds in 650-1021 MPa steels were fatigue tested under constant amplitude tensile loading with a stress ratio of 0.1 while T-joints were fatigue tested under constant amplitude fully reversed bending load with a stress ratio of -1. The nominal stress approach was used for fatigue strength evaluation of butt and fillet welds whereas the effective notch stress approach was used in case of T-joints. Relative effectsof the main parameters such as residual stress and weld toe geometry influencing fatigue strength of welds were evaluated. Residual stresses were measured using X-ray diffraction for as-welded and HFMI treated welds. Neutron diffraction was additionally used to investigate the near surface residual stress distribution in 1300 MPa LTT welds.Results showed that use of LTT consumables increased fatigue strength of welds in steels with yield strengths ranging from 650-1021 MPa. For butt welds, the vii characteristic fatigue strength (FAT) of LTT welds at 2 million cycles was up to46% higher when compared to corresponding welds made with conventional fillermaterials. In fillet welds, a maximum improvement of 132% was achieved when using LTT wires. The increase in fatigue strength was attributed to the lower tensile residual stresses or even compressive stresses produced close to the weldtoe in LTT welds. Weld metals with martensite transformation start temperatures around 200 °C produced the highest fatigue strength. In 1300 MPa yield strength steel, similar FAT of 287 MPa was observed for LTT welds and 306 MPa for conventional welds, both much higher than the IIW FATvalue of 225 MPa. The relative transformation temperatures of the base and weldmetals, specimen geometry and loading type are possible reasons why the fatigue strength was not improved by use of LTT wires. Neutron diffraction showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It was additionally found that there arevery steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe. Due to difficulties to accurately measure residual stresses locally at the weld toe most often in the literature and recommendations residual stresses a few millimetre away from the weld toe are related to fatigue properties. However, this research shows that caution must be used when relating these to fatigue strength, in particular for LTT welds, as stress in the base materiala few millimetre from the weld toe can be very different from the stress locally at the weld toe.HFMI increased the mean fatigue strength of conventional welds in 1300 MPa steels about 26% and of LTT welds by 13%. It increased the weld toe radius slightly but produced a more uniform geometry along the treated weld toes. Large compressive residual stresses, especially in the longitudinal direction, were introduced adjacent to the weld toe for both LTT and conventional treated welds. It was concluded that the increase in fatigue strength by HFMI treatment is due to the combined effect of weld toe geometry modification, increase in surface hardness and introduction of compressive residual stresses in the treated region.It was concluded that the residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welds. This is based on the observation that a moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm, in fillet welds. Also, a higher fatigue strength was observed for HFMI treated conventional welds compared to as welded samples having similar weld toe radii but with different residual stresses.
  •  
23.
  • Harati, Ebrahim, 1986-, et al. (författare)
  • Improving fatigue strength of welded 1300 MPa yield strength steel using HFMI treatment or LTT fillers
  • 2017
  • Ingår i: Engineering Failure Analysis. - : Elsevier BV. - 1350-6307 .- 1873-1961. ; 79:September, s. 64-74
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatigue improvement techniques are widely used to increase fatigue strength of welded high strength steels. In this paper high frequency mechanical impact (HFMI) and a Low Transformation Temperature (LTT) filler material were employed to investigate the effect on fatigue strength of welded 1300 MPa yield strength steel. Fatigue testing was done under fully reversed, constant amplitude bending load on T-joint samples. Fatigue strength of LTT welds was the same as for welds produced using a conventional filler material. However, HFMI treatment increased the mean fatigue strength of conventional welds about 26% and of LTT welds about 13%. Similar distributions of residual stresses and almost the same weld toe radii were observed for welds produced using LTT and conventional consumables. HFMI increased the weld toe radius slightly and produced a more uniform geometry along the treated weld toes. Relatively large compressive residual stresses, adjacent to the weld toe were produced and the surface hardness was increased in the treated region for conventional welds after HFMI. For this specific combination of weld geometry, steel strength and loading conditions HFMI treatment gave higher fatigue strength than LTT consumables.
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24.
  • Harati, Ebrahim, 1986-, et al. (författare)
  • Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel
  • 2017
  • Ingår i: Materials. - : MDPI. - 1996-1944. ; 10:6, s. 1-14
  • Tidskriftsartikel (refereegranskat)abstract
    • Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.
  •  
25.
  •  
26.
  • Harati, Ebrahim, et al. (författare)
  • The relative effects of residual stresses and weld toe geometry on fatigue life of weldments
  • 2015
  • Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 77, s. 160-165
  • Tidskriftsartikel (refereegranskat)abstract
    • The weld toe is one of the most probable fatigue crack initiation sites in welded components. In this paper, the relative influences of residual stresses and weld toe geometry on the fatigue life of cruciform welds was studied. Fatigue strength of cruciform welds produced using Low Transformation Temperature (LTT) filler material has been compared to that of welds produced with a conventional filler material. LTT welds had higher fatigue strength than conventional welds. A moderate decrease in residual stress of about 15% at the 300 MPa stress level had the same effect on fatigue strength as increasing the weld toe radius by approximately 85% from 1.4 mm to 2.6 mm. It was concluded that residual stress had a relatively larger influence than the weld toe geometry on fatigue strength.
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27.
  • Hasselqvist-Ax, Ingela, et al. (författare)
  • Early cardiopulmonary resuscitation in out-of-hospital cardiac arrest.
  • 2015
  • Ingår i: The New England journal of medicine. - 1533-4406 .- 0028-4793. ; 372:24, s. 2307-15
  • Tidskriftsartikel (refereegranskat)abstract
    • Three million people in Sweden are trained in cardiopulmonary resuscitation (CPR). Whether this training increases the frequency of bystander CPR or the survival rate among persons who have out-of-hospital cardiac arrests has been questioned.
  •  
28.
  • Hellstrand, Stefan, 1955, et al. (författare)
  • Measuring sustainability in healthcare: an analysis of two systems providing insoles to patients with diabetes
  • 2021
  • Ingår i: Environment, Development and Sustainability. - : Springer Science and Business Media LLC. - 1573-2975 .- 1387-585X. ; 23, s. 6987-7001
  • Tidskriftsartikel (refereegranskat)abstract
    • There is an increasing demand to quantify the footprints, ecological, economic and social, in terms of the effect of different interventions in healthcare. The aim of this study was to compare two systems providing patients with diabetes with insoles in terms of their eco-logical, economic and social footprints. Prefabricated insoles (PRI) were compared with custom-made insoles (CMI). Using a welfare-economic monetary approach, costs were estimated for (1) treatment, (2) travelling to and from the hospital in terms of both fuel and time consumed by the patients and (3) society through emissions contributing to climate change. The proportion of patients/year that could be supplied within the same budget, for each individual treatment, was calculated. The cost of the insoles was 825 SEK (PRI) and 1450 SEK (CMI), respectively. The cost, mean value/patient due to the consumption of patients’ time at the department, was 754 SEK (PRI) and 1508 SEK (CMI), respectively. Emissions, in terms of CO2 equivalent, were 13.7 (PRI) and 27.4 (CMI), respectively. Using PRI, a total of 928 patients could be provided/year compared with 500 patients if CMI are used. By using PRI, the cost/treatment was reduced by 46%. The cost of treatment dominated and the cost of time consumed by patients were also substantial. The societal cost of contributing to climate change was of low importance. By using PRI, the needs of 86% more patients could be met within the same budget. Using these methods, the contri-bution of healthcare systems to the 17 Sustainable Development Goals approved by the UN can be quantified.
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29.
  • Holmgren, Christina M, et al. (författare)
  • Changes in Medication Preceding Out-of-hospital Cardiac Arrest Where Resuscitation Was Attempted
  • 2014
  • Ingår i: Journal of Cardiovascular Pharmacology. - : Lippincott Williams & Wilkins. - 0160-2446 .- 1533-4023. ; 63:6, s. 497-503
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective: To describe recent changes in medication preceding out-of-hospital cardiac arrest (OHCA) where resuscitation was attempted. Methods: OHCA victims were identified by the Swedish Cardiac Arrest Register and linked by means of their unique 10-digit personal identification numbers to the Prescribed Drug Register. We identified new claimed prescriptions during a 6-month period before the OHCA compared with those claimed in the period 12 to 18 months before. The 7-digit Anatomical Therapeutical Chemical codes of individual drugs were used. The study period was November 2007-January 2011. Results: OHCA victims with drugs were (1) older than those who did not claim any drugs in any period (70 +/- 16 years vs. 54 +/- 22 years, P < 0.001), (2) more often women (34% vs. 20%, P < 0.001), and (3) had more often a presumed cardiac etiology (67% vs. 54%, P < 0.001). The OHCA victims were less likely to have ventricular tachycardia/ventricular fibrillation as the first recorded ;rhythm (26% vs. 33%, P < 0.001) or to survive 1 month (9% vs. 17%, P < 0.0001). New prescriptions were claimed by 5122 (71%) of 7243 OHCA victims. The most frequently claimed new drugs were paracetamol (acetaminophen) 10.3%, furosemide 7.8%, and omeprazole 7.6%. Of drugs known or supposed to cause QT prolongation, ciprofloxacin was the most frequent (3.4%) altogether; 16% had a new claimed prescription of a drug included in the "qtdrugs.org" lists. Conclusions: Most OHCA victims had new drugs prescribed within 6 months before the event but most often intended for diseases other than cardiac. No claims can be made as to the causality.
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30.
  • Hosseini, Vahid A., 1987-, et al. (författare)
  • Influence of multiple thermal cycles on microstructure of heat-affected zone in TIG-welded super duplex stainless steel
  • 2016
  • Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 60:2, s. 233-245
  • 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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31.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • A novel arc heat treatment technique for producing graded microstructures through controlled temperature gradients
  • 2017
  • Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 121:May, s. 11-23
  • 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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32.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • A physical simulation technique for cleaner and more sustainable research in additive manufacturing
  • 2021
  • Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526 .- 1879-1786. ; 285
  • 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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33.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Bead by bead study of a multipass shielded metal arc-welded super-duplex stainless steel
  • 2020
  • Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 64:2, s. 283-299
  • 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.
  •  
34.
  •  
35.
  • Hosseini, Vahid, et al. (författare)
  • Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel
  • 2017
  • Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 68:4, s. 405-415
  • Tidskriftsartikel (refereegranskat)abstract
    • This is a study of the effect of repetitive TIG (tungsten inert gas) welding passes, melting and remelting the same material volume on microstructure and corrosion resistance of 2507 (EN 1.4410) super duplex stainless steel. One to four weld passes were autogenously (no filler added) applied on a plate using two different arc energies and with pure argon shielding gas. Sensitization testing showed that multipass remelting resulted in significant loss of corrosion resistance of the weld metal, in base material next to the fusion boundary, and in a zone 1 to 4 mm from the fusion boundary. Metallography revealed the main reasons for sensitization to be a ferrite-rich weld metal and precipitation of nitrides in the weld metal, and adjacent heat affected zone together with sigma phase formation at some distance from the fusion boundary. Corrosion properties cannot be significantly restored by a post weld heat treatment. Using filler metals with higher nickel contents and nitrogen containing shielding gases, are therefore, recommended. Welding with a higher heat input and fewer passes, in some cases, can also decrease the risk of formation of secondary phases and possible corrosion attack.
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36.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Effect of sigma phase morphology on the degradation of properties in a super duplex stainless steel
  • 2018
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 11:6
  • 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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37.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Fe and Cr phase separation in super and hyper duplex stainless steel plates and welds after very short aging times
  • 2021
  • Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 210
  • 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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38.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Ferrite content measurement in super duplex stainless steel welds
  • 2019
  • Ingår i: Welding in the World. - : Springer Verlag. - 0043-2288 .- 1878-6669. ; 63:2, s. 551-563
  • 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.
  •  
39.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Influence of Fabrication Route and Copper Content on Nature and Kinetics of 475 °C- Embrittlement in Cu-Containing Super Duplex Stainless Steels
  • 2023
  • Ingår i: Steel Research International. - 1611-3683 .- 1869-344X. ; 4, s. 1-12
  • 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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40.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
  • 2018
  • Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 139, s. 390-400
  • 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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41.
  • Hosseini, Vahid, et al. (författare)
  • Multipass Autogenous TIG Welding of Super Duplex Stainless
  • 2015
  • Ingår i: 16th national conference of welding and inspection, Yazd, Iran. - Yazd. - 9786001363009
  • Konferensbidrag (refereegranskat)abstract
    • Multipass welding of super duplex stainless steels (SDSS) needs further characterization due to their growing applications inpetrochemical and offshore industries. This study, as a result, is aimed at investigating the effects of the number of passesand the arc energy on the microstructure and properties of 2507-type SDSS (UNS S32750). From one to four TIG weldpasses were autogenously applied on a plate using two different arc energies and with pure argon gas as the shielding gas.Chemical analysis showed increasing nitrogen loss with an increasing number of passes and increasing arc energy.Microstructural analyses revealed formation of nitrides in the weld metal and heat affected zone, and sigma phase at somedistance from the fusion boundary. Thermal cycle analysis in combination with Thermo-Calc calculations indicated thatexcessive reheating cause degradation of corrosion properties of multipass weldments, by reducing the pitting resistanceequivalent number of austenite to less than 40. Multipass welding resulted in a more ferritic weld metal microstructure and anincreased hardness.Recommendations, based on the present study, are as follows: 1) Corrosion attack can occur not only in the weld zone andnext to the fusion boundary, but also in a location at some distance from the fusion zone due to reheating in the sigma phaseformation temperature range. This should be considered in inspection procedures 2) Nitrogen loss degrades the mechanicaland corrosion properties of weldments even when welding with a low heat input. Using filler metals with higher nickelcontents and nitrogen containing shielding gases are therefore recommended. 3) It is often recommended to use a heat inputin the lower end of the recommended 0.3-1.5 kJ/mm range in multipass welding of super duplex stainless steels. However,welding with a higher heat input and fewer passes, in some cases, can decrease the risk of formation of secondary phases.
  •  
42.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Nanoscale phase separations in as-fabricated thick super duplex stainless steels
  • 2021
  • Ingår i: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 56:21, s. 12475-12485
  • 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.
  •  
43.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Physical and kinetic simulation of nitrogen loss in high temperature heat affected zone of duplex stainless steels
  • 2019
  • Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 6
  • 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.
  •  
44.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Precipitation kinetics of Cu-rich particles in super duplex stainless steels
  • 2021
  • Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 15, s. 3951-3964
  • 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.
  •  
45.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • Predicting ferrite fractions in single pass super duplex stainless steel welds : thermal cycle analysis and phase transformation modeling
  • 2019
  • Ingår i: ESSC and DUPLEX 2019. - Wien : Austrian Society for Metallurgy and Materials (ASMET). ; , s. 180-197
  • 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.
  •  
46.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • 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
  • 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.
  •  
47.
  • 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.
  •  
48.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • 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
  • 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.
  •  
49.
  • Hosseini, Vahid, 1987-, et al. (författare)
  • 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
  • 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).
  •  
50.
  • Johansson, Mikael, 1982-, et al. (författare)
  • Evaluation of test results and ranking criteria for Varestraint testing of an austenitic high-temperature alloy
  • 2020
  • Ingår i: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 64, s. 903-912
  • Tidskriftsartikel (refereegranskat)abstract
    • Varestraint testing is commonly used to evaluate hot cracking susceptibility of materials. In this paper, the dependence of operators and evaluation technique on test results is studied for a high-temperature austenitic stainless steel (UNS S31035). Samples were tested at six different strain levels ranging from 0.7 to 3.8%. Four different operators evaluated the same samples following the same instructions on how to measure the cracks manually in an optical microscope at x 25 magnification. The largest variation among operators evaluation was found for low strain levels where small and few cracks were found. In addition, one of the four operators used image analysis to evaluate the samples at x 50 magnification. The average total crack length and total number of cracks in fusion zone and heat-affected zone were approximately 1.5 times higher when using image analysis compared with manual evaluation. Image analysis at x 50 made it possible to detect smaller cracks compared with manual evaluation at x 25 magnification, contributing to an increased number of cracks detected. The maximum crack length using image analysis at x 50 was similar to manual evaluation made at x 25 magnification and was the criterion that showed the least variation in this study. However, further comparisons using other magnifications are needed to verify the agreement between manual evaluation and image analysis found in this study. An advantage with evaluation using image analysis is that it provides traceable results. A harmonized standard for Varestraint testing, and especially for evaluation, would decrease the variation among operators and laboratories.
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