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  • 1.
    Blomqvist, H
    et al.
    Department of Structural Chemistry, Stockholm University.
    Noreus, D
    Department of Structural Chemistry, Stockholm University.
    Babushkin, O
    Nion, F
    Luleå tekniska universitet.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structure and resistivity correlations in Mg₂NiH₄ studied with in situ X-ray diffraction2003In: Journal of materials science letters, ISSN 0261-8028, E-ISSN 1573-4811, Vol. 22, no 21, p. 1487-1489Article in journal (Refereed)
    Abstract [en]

    Structure and resistivity correlations in Mg2NiH4 was studied using in situ X-ray diffraction. Microtwinning was found to be sensitive to the applied mechanical pressure or grinding and by compressing the heated hydride sample in a tablet press. The resistivity increased before the low-temperature->high temperature phase transition.

  • 2.
    Caballero, Francisca G.
    et al.
    Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Madrid, Spain.
    Pujante, Jaume
    Eurecat Centre Tecnològic de Catalunya, Spain.
    Sourmail, Thomas
    Asco Industries Research (CREAS), Hagondange, France.
    Rementeria, Rosalia
    Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Madrid, Spain.ArcelorMittal Global R&D, SLab—Steel Labs, Avilés, Spain.
    De-Castro, David
    Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Madrid, Spain.
    Dierickx, Pierre
    Asco Industries Research (CREAS), Hagondange, France.
    Ramírez, Giselle
    Eurecat Centre Tecnològic de Catalunya, Spain.
    Sidoroff-Coicaud, Christine
    NTN-SNR Rulements SA, Annecy, France.
    Moghaddam, Pouria Valizadeh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Advanced Heat Treatments and Complex Ferritic Structures for Bearing Steels2019In: Metals, E-ISSN 2075-4701, Vol. 9, no 11, article id 1137Article in journal (Refereed)
    Abstract [en]

    Nanostructured bainitic steels exhibit an optimum strength/toughness combination as a consequence of their extremely fine structure. They have also demonstrated potential for wear-resistance applications. The aim of this work was to develop bearing steels by the multi-scale control of complex ferritic structures, designed using atomic transformation theory and processed by novel heat treatments. Based on the results, the new ball bearings outperformed conventional grades, approaching more expensive material options. 

  • 3. Chen, Xiang
    et al.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    In-situ high temperature X-ray studies of austempering transformation in high silicon cast steel2009In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 49, no 8, p. 1220-1224Article in journal (Refereed)
    Abstract [en]

    The in-situ X-ray diffraction observations of the bainitic transformation of high silicon cast steel were performed using the high temperature X-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The experimental result has shown that the volume fraction of austenite ceases to a constant value which indicate that the transformation is almost finished after holding for about 1000 s. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (gamma(LC)) and the high-carbon austenite (gamma(HC)). The volume fraction of bulk austenite with low carbon decreases greatly at the early stage of transformation and then tends towards zero. The lattice parameter of both low-carbon and high-carbon austenite increases with the holding time due to the carbon partition from the supersaturated ferrite to the austenite. The experimental results supports that the bainite growth is by a diffusionless mechanism when austempering temperature is in the lower bainite transformation temperature range.

  • 4. Chen, Xiang
    et al.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Grahn, Johnny
    In-situ SEM observation on fracture behavior of austempered silicon alloyed steel2009In: China Foundry, ISSN 1672-6421, Vol. 6, no 3, p. 185-190Article in journal (Refereed)
    Abstract [en]

    Crack initiation, propagation and microfracture processes of austempered high silicon cast steel have been investigated by using an in-situ tensile stage installed inside a scanning electron microscope chamber. It is revealed that micro cracks always nucleate at the yielding near imperfections and the boundary of matrix-inclusions due to the stress concentration. There are four types of crack propagations in the matrix: crack propagates along the boundary of two clusters of bainitic ferrite; crack propagates along the boundary of ferrite-austenite in bainitic ferrite laths; crack propagates into bainitic ferrite laths; crack nucleates and propagates in the high carbon brittle plate shape martensite which is transformed from some blocky retained austenite due to plastic deformation. Based on the observation and analysis of microfracture processes, a schematic diagram of the crack nucleation and propagation process of high silicon cast steel is proposed.

  • 5.
    Erlandsson, Ove
    et al.
    Luleå tekniska universitet.
    Lagerkrans, Stefan
    Näslund, Reinhold
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Maskinhandboken2000Book (Other academic)
  • 6.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Borasi, Luciano
    Luleå University of Technology.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, F.
    Department for Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
    Optimization of Quenching Temperature to Minimize the Micro Segregation Induced Banding Phenomena in Quenching and Partitioning (Q&P) Steels2019In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 90, no 1, article id 1800281Article in journal (Refereed)
    Abstract [en]

    Mn, Cr, and Si are favorable elements for designing the quenching and partitioning (Q&P) steels while the microsegregation of them is a common phenomenon in the steels. This segregation makes the bands of enriched and depleted Mn–Cr regions, which affects the Ms temperature of the bands and consequently influence the volume fraction of initial martensite, retained austenite, and secondary fresh martensite in different bands. This issue leads to non-homogeneity in the microstructure and mechanical properties. In this study, the optimization method to minimize the inhomogeneity by selection of the quenching temperature is demonstrated.

  • 7.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Borasi, Luciano
    Luleå University of Technology.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    University of Saarland .
    Process Control Maps to Design an Ultra-High Strength-Ductile Steel2019In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 35, no 10, p. 1173-1184Article in journal (Refereed)
  • 8.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
    Guitar, M. Agustina
    Department of Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    Department of Materials Science, Functional Materials, Saarland University, Saarbrücken, Germany.
    Effect of Carbon Partitioning, Carbide Precipitation, and Grain Size on Brittle Fracture of Ultra-High-Strength, Low-Carbon Steel after Welding by a Quenching and Partitioning Process2018In: Metals, ISSN 2075-4701, Vol. 8, no 10, article id 747Article in journal (Refereed)
    Abstract [en]

    To improve the weld zone properties of Advanced High Strength Steel (AHSS), quenching and partitioning (Q&P) has been used immediately after laser welding of a low-carbon steel. However, the mechanical properties can be affected for several reasons: (i) The carbon content and amount of retained austenite, bainite, and fresh martensite; (ii) Precipitate size and distribution; (iii) Grain size. In this work, carbon movements during the partitioning stage and prediction of Ti (C, N), and MoC precipitation at different partitioning temperatures have been simulated by using Thermocalc, Dictra, and TC-PRISMA. Verification and comparison of the experimental results were performed by optical microscopy, X-ray diffraction (XRD), Scanning Electron Microscop (SEM), and Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Scanning Diffraction (EBSD) analysis were used to investigate the effect of martensitic/bainitic packet size. Results show that the increase in the number density of small precipitates in the sample partitioned at 640 °C compensates for the increase in crystallographic packets size. The strength and ductility values are kept at a high level, but the impact toughness will decrease considerably.

  • 9.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gunasekaran, Suresh
    Department for Materials Science, Functional Materials, Saarland University.
    Hedayati, Ali
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    Department for Materials Science, Functional Materials, Saarland University.
    Microstructure analysis and mechanical properties of Low alloy High strength Quenched and Partitioned Steel2016In: MSMF 2016: Materials Structure & Micromechanics of Fracture, 2016Conference paper (Refereed)
  • 10.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gunasekaran, Suresh
    Hedayati, Ali
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    Department for Materials Science, Functional Materials, Saarland University, D-66041 Saarbrücken, Germany.
    Microstructure analysis and mechanical properties of Low alloy High strength Quenched and Partitioned Steel2017In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 258, p. 574-578Article in journal (Refereed)
    Abstract [en]

    Gleeble study of the quenching and partitioning (Q&P) process has been performed onDomex 960 steel (Fe, 0.08 %C, 1.79 %Mn, 0.23 %Si, 0.184 %Ti, and 0.038 %Al). The effect ofdifferent Q&P conditions on microstructure and mechanical properties were investigated. The aimof the process is to produce a fine grained microstructure for better ductility and controlled amountsof different micro-constituents to increase the strength and toughness simultaneously. Threedifferent quenching temperatures, three partitioning temperatures and three partitioning times havebeen selected to process the 27 specimens by Gleeble® 1500. The specimens were characterized bymeans of OM, SEM, XRD, hardness and impact tests. It was found that, fine lath martensite withretained austenite is achievable without high amount of Si or Al in the composition although lack ofthese elements may cause the formation of carbides and decrease the available amount of carbon forpartitioning into the austenite. The hardness increases as the quenching temperature is decreased,however, at highest partitioning temperature (640◦C) the hardness increases sharply due to extensiveprecipitate formation.

  • 11.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Strandqvist, Nanny
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Navara, Erik
    Mücklich, Frank
    Department for Materials Science, Functional Materials, Saarland University.
    Effect of tempering on microstructure and mechanical properties of laser welded and post-weld treated AHSS specimens2017In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 891, p. 18-24Article in journal (Refereed)
    Abstract [en]

    An advanced high strength steel (0.08 wt.%C, 1.79 wt%Mn, 0.23 wt%Si) was subjected to different post-weld heat treatments by quenching & tempering treatments (Q&T) after laser welding to reduce the risk of martensite formation in a few seconds based on an idea of quench and partitioning (Q&P), mechanism. The thermal stability of retained austenite, microstructure development and mechanical properties have been studied at 2 tempering temperatures of 440°C (Ms) and 636°C (Bs), both for 15 minutes, by means of electron microscopy, dilatometry, hardness profile and tensile tests. Dilatometer study unveiled that redistribution of carbon atoms and precipitation of transition carbides occur around 150°C and austenite decomposition occur at 600°C. Tempering at 636°C resulted in notable effect on the mechanical properties, while no significant difference was detected at 440°C, except a slight hardness drop. The strength increased up to 12% for the different specimens without significant loss in ductility for all specimens tempered at 636°C, which may be caused by precipitation hardening and recrystallization of martensite lath boundaries during tempering around 600°C.

  • 12.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    Department for Materials Science, Functional Materials, Saarland University.
    Post weld-treatment of laser welded AHSS by application of quenching and partitioning technique2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 698, p. 174-182Article in journal (Refereed)
    Abstract [en]

    Two-step quenching and partitioning (Q&P) treatment was applied on specimens of an advanced high strength steel (AHSS) after laser welding, for post welding treatment. In order to avoid formation of brittle martensite phase, which usually form due to very high cooling rate of laser welding. To simulate the effect of different Q&P parameters after welding in the most critical part of HAZ, several cycles were performed in Gleeble simulator and analyzed in advance. Subsequently some of the cycles were repeated after laser welding by using an induction heater close to the weld. Different techniques including SEM, EBSD and XRD were used to analyze the microconstituents of the structure and mechanical properties were investigated by micro-hardness measurements across the weld, tensile and impact toughness tests. The final structure consists of controlled amount of tempered martensite with precipitates, bainite laths and small amount of fresh martensite depending on the thermal cycles. In addition, samples heated at a temperature between Ms and Bs (in this case 540C) showed the best mechanical properties. Therefore, this technique not only improves the microstructure and mechanical properties of the fusion zone (FZ) and heat affected zone (HAZ) but gives also a quick industrial processing method for post welding treatments.

  • 13.
    Forouzan, Farnoosh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zhang, Hanzhu
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mücklich, Frank
    University of Saarland .
    Study of The Kinetics of Precipitation in an AHSS steel after Laser Welding and Quenching and Partitioning2017Conference paper (Other academic)
  • 14.
    Garcia-Mateo, Carlos
    et al.
    National Centre for Metallurgical Research (CENIM-CSIC), Department of Physical Metallurgy, Madrid, Spain.
    Sourmail, Thomas
    Ascometal-CREAS (Research Centre) Metallurgy, Hagondange cedex, France.
    Caballero, Francisca García
    Department of Physical Metallurgy, National Centre for Metallurgical Research (CENIM-CSIC), Madrid, Spain.
    Smanio, Véronique
    Ascometal-CREAS (Research Centre) Metallurgy, Hagondange cedex, France.
    Kuntz, Matthias
    Robert Bosch GmbH, Materials and Process Engineering, Stuttgart, Germany.
    Ziegler, C.
    ALD Vacuum Technology GmbH, Hanau, Germany.
    Leiro, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Elvira, Roberto
    Gerdau IzD, S. A. Barrio Ugarte, Basauri, Spain.
    Teeri, T.
    Metso Minerals Oy, Tampere, Finland.
    Nanostructured steel industrialisation: Plausible reality2014In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 30, no 9, p. 1071-1078Article in journal (Refereed)
    Abstract [en]

    It is not the first time that a consortium of steel makers, end users and scientists end up with unique approaches and developments in the physical metallurgy of steels. The present paper reveals the scientific and technological developments of a consortium sharing a common intrigue and interest for a unique microstructure, nanostructured bainite. Also known as low temperature bainite, its unique properties rely solely on the scale of the miscrostructure obtained by heat treatment at low temperature (150-350°C). Careful design based on phase transformation theory, some well known metallurgy facts and the necessary industrial experience were the ingredients for a further step towards the industrialisation of these microstructures.

  • 15.
    Hedayati, Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Asghari, Saeed
    Institute of Materials and Energy, Iranian Space Research Cente.
    Alinoori, Amir Hosein
    Institute of Materials and Energy, Iranian Space Research Cente.
    Koosha, Morteza
    Institute of Materials and Energy, Iranian Space Research Cente.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effects of coating thickness on corrosion and contact resistance behavior of TiN coated AISI 316L as bipolar plates for PEMFC2016In: Iranian Journal of Hydrogen & Fuel Cell, ISSN 2383-1618, Vol. 3, no 2, p. 137-149Article in journal (Refereed)
    Abstract [en]

    In the polymer electrolyte membrane fuel cells (PEMFCs), low corrosion resistance and high interfacial contact resistance (ICR) are two controversial issues in usage of AISI 316L stainless steel as a metallic bipolar plate. For solving these problems, investigation and development of different coatings and/or surface treatments are inevitable. Corrosion behavior and ICR of AISI 316L specimens coated with 1, 2, and 3 µm thick TiN were investigated. Potentiodynamic (PD), potentiostatic (PS) and electrochemical impedance spectroscopy (EIS) tests were conducted at 80 °C in pH3 H2SO4+2 ppm HF solution purged with either O2 or H2 under both simulated cathodic and anodic conditions. The PS corrosion test results revealed that the current densities of the specimens were below 1 µA cm−2. In the simulated cathodic condition, an increase of coating thickness from 1 to 3 µm led to a relatively large decrease of the current density from 0.76 to 0.43 µA cm−2. Furthermore, the ICR values of the coated specimens after the PS test were lower than that of the uncoated specimen before the PS. In general, the TiN coating decreases the ICR, and has enough corrosion resistance in simulated PEMFC conditions. However, none of the coatings achieved the DOE ICR targets.

  • 16.
    Hernandez, Sinuhe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Leiro, Alejandro
    Ripoli, Manel Rodriguez
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sundin, Karl-Gustaf
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature three-body abrasive wear of 0.25C 1.42Si steel with carbide free bainitic (CFB) and martensitic microstructures2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 360-361, p. 21-28Article in journal (Refereed)
    Abstract [en]

    In the present work, the wear behaviour of different steels has been investigated under a three body abrasive environment at room and elevated temperatures. High-silicon steel (0.25C-1.42Si) was austempered at 300 and 320 ˚C in order to obtain two carbide-free bainitic steels with different mechanical properties. The same steel subjected to two different quench and temper heat treatments was used as a reference material for mechanical and wear testing. The steels were subjected to three-body abrasive wear by means of a high temperature continuous abrasion tester (HT-CAT). The tests were done at 25, 300 and 500 °C respectively. All samples showed similar wear rates at room temperature. At 500 °C, the material austempered at 320 ˚C showed the highest toughness and the lowest wear rate. High temperature hardness and impact toughness tests showed that abrasive wear is not only influenced by hardness but also by the toughness of the material. Owing to their good strength/toughness combination CFB steels could prove to be an important material for abrasive wear applications

  • 17.
    Kankanala, Anusha
    et al.
    Luleå tekniska universitet.
    Leiro, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    The tribological behaviour under rolling/sliding conditions of carbide-free bainitic steel austempered at different temperatures2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. Three different batches of samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1h. Rolling with 5% sliding wear tests were performed with each batch of samples for different test cycles, namely 6000, 18000 and 30000 cycles respectively, in order to study the wear performance of these specific steels. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by the scanning electron microscopy and X-ray diffraction techniques. Micro-hardness profiles were also obtained to analyze strainhardening effects beneath the contact surfaces. The results indicate that the harder material exhibited overall lower wear rates for all test cycles studied i.e., the one austempered at 250°C showed superior rolling/sliding wear resistance than the rest. It is also interesting to note that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles.Furthermore the results appear to indicate that the initial roughness of the samples has no major effect on the outcome of the results. The higher wear performance of the sample austempered at 250°C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples suffer the TRIP phenomenon since, after wear, no retained austenite could be detected by XRD.

  • 18.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kankanala, Anusha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of carbide-free bainitic steel under dry rolling/sliding conditions2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 2-8Article in journal (Refereed)
    Abstract [en]

    The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1 h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18000 and 30000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstructure containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by scanning electron microscopy and X-ray diffraction. Micro-hardness profiles were also obtained in order to analyze strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250 °C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial roughness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250 °C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD.

  • 19.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Roshan, Arash
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fatigue of 0.55C-1.72Si Steel with Tempered Martensitic and Carbide-Free Bainitic Microstructures2014In: Acta Metallurgica Sinica (English Letters), ISSN 1006-7191, E-ISSN 2194-1289, Vol. 27, no 1, p. 55-62Article in journal (Refereed)
    Abstract [en]

    High-Si spring steel was heat treated in three different ways: Quenching and tempering at 460 °C to obtain a tempered martensite microstructure, and austempering at 300 and 350 °C, respectively, to obtain two different carbide-free bainitic microstructures. In the steel austempered at 350 °C, both the bainite lath thickness and retained austenite content were higher than those of the steel austempered at 300 °C. Rotating-bending fatigue tests were done in order to evaluate the effect of each heat treatment on the high-cycle fatigue behavior of the steel. When the austempering temperature was 300 °C, the endurance limit was increased by 25% despite a 5% reduction in tensile strength when compared with that of the quenched and tempered steel. The relationship between endurance limit [Rfat (50%)] and ultimate tensile strength (Rm) was higher for the austempered samples in comparison with that of the quenched and tempered material. Therefore, it is believed that the presence of retained austenite affects the relationship between endurance limit and tensile strength.

  • 20.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sourmail, T.
    ASCOMETAL-CREAS.
    Samanio, V.
    ASCOMETAL-CREAS.
    Caballero, F.C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Garcia-Mateo, C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Elvira, Roberto
    Gerdau Sidenor I+D.
    Wear of nano-structured carbide-free bainitic steels under dry rolling-sliding conditions2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 298-299, no 1, p. 42-47Article in journal (Refereed)
    Abstract [en]

    Specially designed steels with carbon contents from 0.6 to 1.0 wt.% were isothermally transformed at very low temperatures, between 220 and 270 °C, in order to obtain a nano-structured bainitic microstructure. It is shown that the wear resistance in dry rolling-sliding of these nano-structured steels is significantly superior to that ofbainitic steels transformed at higher temperatures with similar hardness values.In addition to the highly refined microstructure, the transformation under strain to martensite (TRIP effect), contributes to the plasticity of the nano-scaled steels, increasing surface hardness during testing, thus reducing the wear rate.

  • 21.
    Li, Wen-Bin
    et al.
    Luleå tekniska universitet.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Besök vid järnvägstekniska forskningsinstitutioner i Kina 5-16 mars 1998: reserapport1999Report (Other academic)
  • 22. Magnusson, Claes
    et al.
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Engström, E.
    Pedersen, T.F.
    FORCES Institute.
    Creating tailor-made surfaces with high power CO2-lasers1991In: Proceedings of the first ASM Heat Treatment and Surface Engineering Conference in Europe: held May 22nd-24th, 1991, in Amsterdam, the Netherlands, Trans Tech Publications Inc., 1991, p. 443-458Conference paper (Refereed)
  • 23.
    Makarova, Irina
    et al.
    Chemical Technology and Engineering Faculty, Department of Chemistry, Technology of Electrochemical Production and Electronic Engineering Materials, Belarusian State Technological University, Minsk, Belarus. Department of Separation and Purification, School of Engineering Science, LUT University, Finland.
    Dobryden, Illia
    KTH Royal Institute of Technology, Surface and Corrosion Science Division, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Stockholm, Sweden.
    Kharitonov, Dmitry
    Chemical Technology and Engineering Faculty, Department of Chemistry, Technology of Electrochemical Production and Electronic Engineering Materials, Belarusian State Technological University, Sverdlova str. 13a, 220006, Minsk, Belarus. Jerzy Haber Institute of Catalysis and Surface Chemistry of Polish Academy of Sciences, Krakow, Poland.
    Kasach, Aliaksandr
    Chemical Technology and Engineering Faculty, Department of Chemistry, Technology of Electrochemical Production and Electronic Engineering Materials, Belarusian State Technological University, Minsk, Belarus.
    Ryl, Jacek
    Gdansk University of Technology, Department of Electrochemistry, Corrosion and Materials Engineering, Gdansk, Poland.
    Repo, Eveliina
    Department of Separation and Purification, School of Engineering Science, LUT University, Finland.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nickel-nanodiamond coatings electrodeposited from tartrate electrolyte at ambient temperature2019In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 380, article id 125063Article in journal (Refereed)
    Abstract [en]

    In this study, nanocrystalline Ni and Ni-diamond coatings were obtained by electrodeposition from tartrate electrolyte at ambient temperature aiming at improving corrosion and wear properties of the material. The created surfaces were investigated with regard to microhardness, adhesion, wear- and corrosion-resistance. The various methods such as atomic force microscopy, scanning electron microscopy, electrochemical impedance spectroscopy and linear polarization technique were applied to study the coating surface properties. The introduction of nanodiamond particles into the coating led to a rougher surface structure and a bigger grain size in comparison to bare nickel coating. Our study shows that the addition of 5·10−2 (g dm−3) of nanodiamonds to the plating bath is enough to obtain composite coatings with a clear increase in microhardness and wear resistance. The slightly improved corrosion resistance of the coating, decrease in corrosion current density from 0.41 to 0.14 μA cm−2 in neutral chloride-containing medium, and nobler values of the corrosion potential were also observed.

  • 24.
    Moghaddam, Pouria Valizadeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Caballero, Francisca G.
    National Center for Metallurgical Research (CENIM-CSIC).
    Sourmail, Thomas
    ASCOMETAL, HAGONDANGE.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Corrigendum to: The role of retained austenite in dry rolling/sliding wear of nanostructured carbide-free bainitic steels, Wear 428–429 (2019) 193 - 2042020In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 446-447, article id 203072Article in journal (Refereed)
  • 25.
    Moghaddam, Pouria Valizadeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The role of retained austenite in dry rolling/sliding wear of nanostructured carbide-free bainitic steels2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 428-429, p. 193-204Article in journal (Refereed)
    Abstract [en]

    The dry rolling/sliding wear of nanostructured bainite has been investigated and compared with that of a conventional quenched and tempered bearing steel. In order to elucidate the role of retained austenite on the wear performance, high silicon hypereutectoid bearing steel with an identical alloy composition was heat treated to obtain different microstructures with similar hardness and different amounts of retained austenite. The results indicate that the nanostructured bainite can meet the minimum hardness requirements for bearing applications. Moreover, the nanostructured bainite outperformed the tempered martensitic steel in terms of wear resistance. The work hardening capacity and thus wear resistance increases due to the transformation of retained austenite into martensite. The results of XRD analyses show that the higher stability of retained austenite and strength of bainitic ferrite leads to better wear performance. It is demonstrated that the stability of retained austenite outweigh the influence of retained austenite content on wear resistance. Adhesion and oxidation were identified as the main wear mechanisms. In addition to microstructure, surface oxidation also plays a prominent role in determining the wear resistance. 

  • 26.
    Pineda Huitron, Rosa Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lopez, Pavel E. Ramirez
    Casting and Flow Simulation Group, Process Metallurgy Department, SWERIM AB, Luleå, Sweden. Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jentner, Robin
    Luleå University of Technology.
    Kärkkäinen, Maija E.
    SSAB Europe Oy Raahe works, Raahe, Finland.
    Converging criteria to characterize crack susceptibility in a micro-alloyed steel during continuous casting2020In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 772, article id 138691Article in journal (Refereed)
    Abstract [en]

    The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thermo-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000°C while strain rates covered a range from 0.001 to 0.1s−1. Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900°C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.

  • 27.
    Pineda Huitron, Rosa Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hot cracking of Structural Steel during Laser Welding2017In: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 258, article id 012005Article in journal (Refereed)
    Abstract [en]

    Laser welding is an important technique in many industries due to its high precision in operation, its local and fast processing, narrow welds and its good weld surface quality. However, the process can involve some complications due to the rapid heating and cooling of the material processed, resulting in physical and metallurgical effects as thermal contraction during solidification, giving as a result the presence of residual stresses in the narrow weld. Formation of defects during the process is an important topic to be evaluated in order to achieve better performance of the steels in use. In the present work, defects formed during laser welding of a structural steel have been investigated. The defects formed have been identified and the causes of the defects are discussed. Possible strategies for improvement of the welding procedure and final weld result are proposed. The defects were analysed by optical and scanning electron microscopy and hardness measurement. Cracks were located in the middle of the fusion zone and followed both inter-granular and trans-granular paths. Impurities as manganese sulphides were found along the welding direction, and could act as sites for crack formation. The cracks formed during solidification of the weld are identified as solidification cracks. This kind of cracks is usually caused by solidification shrinkage and thermal contractions during the process, which appear in the fusion zone and sometimes in the heat affected zone.

  • 28.
    Sourmail, Thomas
    et al.
    Ascometal-CREAS (Research Centre) Metallurgy, BP 70045, Hagondange cedex 57301.
    Caballero, Francisca García
    Department of Physical Metallurgy, National Centre for Metallurgical Research (CENIM-CSIC), Madrid.
    García-Mateo, Carlos
    Department of Physical Metallurgy, National Centre for Metallurgical Research (CENIM-CSIC), Madrid.
    Smanio, Véronique
    Ascometal-CREAS (Research Centre) Metallurgy, BP 70045, Hagondange cedex 57301.
    Ziegler, C.
    ALD Vacuum Technology GmbH, Wilhelm Rohn Str. 35, Hanau.
    Kuntz, Matthias
    Robert Bosch GmbH, Materials and Process Engineering, PO Box 300240, Stuttgart.
    Elvira, Roberto
    Gerdau IzD, S. A. Barrio Ugarte, Basauri.
    Leiro, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Teeri, T.
    Metso Minerals Oy, PO Box 237, Tampere.
    Evaluation of potential of high Si high C steel nanostructured bainite for wear and fatigue applications2013In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 29, no 10, p. 1166-1173Article in journal (Refereed)
    Abstract [en]

    The present study is concerned with the potential of high carbon, high silicon steel grades isothermally transformed to bainite at low temperature (

  • 29.
    Steimberger, Cerafino
    et al.
    Luleå tekniska universitet.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Johansson, Pernilla
    Höganäs AB.
    Wear Analysis of PM Compacts with Bainitic Microstructures, Under Unlubricated Sliding Conditions2015In: Procedia Materials Science, ISSN 2211-8128, Vol. 9, p. 578-589Article in journal (Refereed)
    Abstract [en]

    Ferrous and non-ferrous alloys can be processed by PM. Complex shapes and good surface finishes can be achieved, leading to promising applications, if mechanical properties are demonstrated to be high enough. At the same time, both bainitic and carbide free bainitic microstructures have proved to be excellent candidates for wear applications. Therefore, the aims of this project were steered towards analysing wear behaviour of PM compacts, in relation to their bainitic microstructures.Three materials were employed and two conditions were taken into account: materials before and after austempering. A reference material was considered, corresponding to Distaloy DC with Mo and Ni. Microstructure was analysed in all the cases by means of optical and scanning electron microscope and it was related to the behaviour observed. Pin on plate reciprocating sliding test without lubricant was utilised in order to measure friction coefficient and specific wear rate in the pins. Effects of alloying elements were also examined.It was found that austempering decreased impact resistance, but enhanced hardness in Distaloy DC. In contrast, the other two materials presented the opposite behaviour. However, the presence of additional alloying elements in the initial composition fulfilled to increase wear resistance, compared to the reference material. A possible interaction between pores and oxides that may influence wear behaviour was observed. Si allowed carbide free bainitic microstructure to form but heterogeneity could not be prevented. Therefore, the advantage of this microstructure could not be fully used. Results obtained in the present work can lead to new wear applications for PM products, containing bainitic microstructures.

  • 30.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bainitic Steel: Microstructures and Tribological Properties2016In: Encyclopedia of Iron, Steel, and Their Alloys, Boca Raton, FL: CRC Press, Taylor & Francis Group , 2016, p. 265-270Chapter in book (Refereed)
    Abstract [en]

    The microstructure in bainite with nano-sized grains or plates shows in addition to high strength and toughness also excellent wear resistance especially in sliding and sliding–rolling wear. In addition to very fine-grained structure, the austempering treatment of alloys with increased Si and/or Al content results in ferritic–austenitic microstructure. Mechanical energy transferred by wear to the material surface results in a phase transformation of the austenite to martensite. This transformation gives an increase in the wear resistance of the materials in addition to other strengthening effects as grain size and deformation strengthening.

  • 31.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Controlling infiltration when brazing P/M parts and during manufacture of aluminium metal matrix composites2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Infiltration is used in the production of several different material groups as electric contact materials, copper infiltrated sintered steels and metal matrix composites. The mechanism of infiltration causes also unwanted difficulties in processing as brazing of porous sintered compacts. The common question, in this work has been, how is it possible to control infiltration in different materials processing techniques? In joining of powder metallurgically (P/M) produced porous compacts, by brazing, the inherent porosity of the compacts causes the melt filler metal to infiltrate the interconnected pore channels of the P/M parts, by capillary forces. This will result in high penetration depths and filler metal consumption and a limited amount of filler metal will be available for the joint. In the production of metal matrix composites (MMC:s), the difference in surface energies between the metallic and ceramic components prohibits a spontaneous infiltration of the metallic phase into the ceramic porous body. This work includes a general analyse of the different physical and mechanical methods to control infiltration in brazing of porous compacts and processing of MMC:s respectively. The experimental part of the work concentrates on the study of physical methods for the infiltration control. Brazing of porous sintered compacts has been studied experimentally through different thermal treatments. A special (Cu-Ni-Mn-Si) filler-metal, developed by others in order to facilitate alloying between iron in P/M- compacts and the elements in the filler-metal, has been used and the results has been studied by optical and scanning electron microscopy and the mechanical strength and hardness has been measured. In the work on MMC:s a method for processing of aluminium matrix-alumina reinforced composites by spontaneous infiltration has been studied by wetting and in- situ high temperature X-ray experiments. The investigation of brazing shows that the filler metal starts to melt already at 930 oC and a two phase alloy is developed in the joint. The diffusion of elements from the filler metal and the sintered compact causes a development of an alloy with high melting temperature in the surface area of the sintered compact that blocks the surface pores from continued infiltration. The wetting experiments show that the spontaneous infiltration in production of MMC:s is enabled by chemical reactions in the system concerned. The in-situ X-ray experiments show that the formation of magnesium-nitride appears below 600 oC. The formation of AlN as a second reaction product in the spontaneous infiltration has been detected for compact tested after a processing cycle with increased pressure of nitrogen- gas in the processing furnace. The in-situ X-ray study of the spontaneous infiltration has shown that the formation of magnesium nitride could be detected. The results show also that it is possible to study chemical reactions at and above the melting temperature of the metallic constituent of the system. The results show also that it would be possible to create alumina-aluminium MMC with different hardness levels.

  • 32.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structure and properties of advanced fine grained steels produced using novel thermal treatments2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fine grained advanced steels exhibit favourable mechanical properties for applications requiring high strength, ductility and impact toughness. These properties result from a microstructure containing a fine distribution of several phases including ferrite, austenite, martensite and bainite. The bainite phase is in the form of fine lamellas of ferrite and carbon-enriched austenite which due to proper control of the chemical composition is lacking the nanometre scaled carbides associated with traditional bainite. The mechanisms of bainite phase transformations in steels have been debated since the naming of bainite in 1934, and range from diffusion-controlled (reconstructive) to diffusionless (displacive). Interest in the manufacture and application of fine grained advanced multiphase steels can be dated back to the 1970s, and it has been intensified after the turn of the century with the industrial production and application of such steels. The structure and mechanical properties of fine grained advanced steels produced using novel thermal treatments are described. The results of in-situ x-ray diffraction studies of the austenite to bainite transformation process provide information about the effect of carbon redistribution on the formation of transformation products. Transformation microstructures created by various thermal treatments are characterised using optical and scanning electron microscopy, which reveal the presence of martensite, bainite (in various forms), ferrite and retained austenite. Microstructural control is found to be possible by quenching the steels from the austenite phase to temperatures below the start temperature of martensite formation (determined by steel composition). The quenching is followed by isothermal treatment for varying times at temperatures related to the formation of transformation products (bainite in particular). This combined heat treatment also increases the rate of phase transformation in comparison with isothermal treatments. Thus multiphase microstructures are produced, which are found to possess favourable mechanical properties, in particular tensile strength, toughness and wear resistance. In press hardening of 0.26wt-carbon steels, by using the combined heat treatment described, the yield strength was found to be comparable to existing materials and the ductility was found to be higher. Welding tests of medium carbon steel with control of the post weld time temperature cycle in accordance with the combined heat treatment process minimized the risk of brittle phase formation in the weld as well as the heat affected zone. In addition the wear resistance in sliding as well as in rolling-sliding was shown to be better for austempered medium carbon high-silicon steels with fine grained ferritic austenitic microstructure in comparison with conventional steels. The presented work can be regarded as a contribution to the current world-wide effort to develop the 3rd generation advanced high-strength steels, which are expected to be a substantial part of the structural steel market before the end of the present decade. The switch to such steels in a large number of applications in manufacturing of transport vehicles and other products, will be comparable with the switch from plain carbon steels to HSLA steels in the seventies and eighties.

  • 33.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Time diffusivity estimations in press hardening and welding processes with quenching and partitioning heat treatments2013In: Book of Abstracts, 7th EEIGM International Conference on Advanced Materials Research: March 21 - 22, 2013, LTU, Luleå - SWEDEN, 2013, p. 1-Conference paper (Refereed)
    Abstract [en]

    The quenching and partitioning heat treatment process has been used in press hardening and welding processes of advanced high strength steels with the purpose to increase the phase transformation rate. Different quenching and partitioning temperatures and times were used in order to optimize microstructure and mechanical properties. Hardness measurements, tensile testing, light microscopy, scanning electron microscopy and XRD-measurements have been used in order to characterize the materials. The results show that calculations of the time diffusivity during the partitioning period can be used as a tool in predicting the final hardness of the steels. In combination with knowledge of the microstructure can these calculations be used in optimization of the heat treatment process in welding and press hardening.

  • 34.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Arén, Björn
    Luleå tekniska universitet.
    Fogning av sintergods: en litteraturöversikt1983Report (Other academic)
  • 35.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bax, Benjamin
    Department of Materials Science, Saarland University, Saarbrücken.
    Navara, Erik
    Jihlava.
    Weldability of hardenable silicon alloyed spring steel.2010Conference paper (Refereed)
    Abstract [en]

    One serious concern, related to high strength steels, is their weldability. An interesting high strength steel group contains a carbide free bainitic microstructure. This special microstructure, consisting of ferrite plates and stabilized austenite, is achieved by austempering a steel containing suitable amounts of Si and / or Al. These elements will suppress the formation of carbides resulting in an ausferritic structure. In this work, different pre- and post-weld treatments have been tested in order to avoid the formation of martensite in the weld and the heat affected zone of a medium carbon silicon- alloyed spring steel, 55Si7, in austempered condition. High power fibre-laser equipment has been used for the welding operation and furnace- and induction- heat treatments have been utilized to produce the pre- and post weld heating cycles. The resulting microstructures were investigated by optical- and scanning electron microscopy and the microhardness values and profiles for the different microstructures were measured. The most promising results were achieved by a combination of a pre- and post-weld heat treatment at 300oC and a heat treatment method based on the quenching and partitioning concept, resulting in hardness values as low as 500 and 430 HV, respectively. In comparison to this, welding without heat treatment resulted in a martensitic microstructure with hardness values of 800 HV.

  • 36.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chen, Xiang
    Tsinghua University.
    In situ x-ray observation of bainitic transformation of austempered silicon alloyed steel2009In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 24, no 4, p. 1559-1566Article in journal (Refereed)
    Abstract [en]

    The in situ x-ray diffraction observations of the bainitic transformation were conducted by using the high-temperature x-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The d{110} value of bainitic ferrite decreases with increasing austempering temperature, which is related to the decrease of carbon concentration in bainitic ferrite. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation at any austempering temperatures. This asymmetry diffraction peak after the formation of bainitic ferrite could be attributed to a heterogeneous distribution of carbon in different regions of austenite and show that two types of austenite with different carbon contents, low-carbon austenite (?LC) and the high-carbon austenite (?HC), exist during the transformation. The microstructure after cooling down to room temperature is presented to show the effectiveness of the x-ray diffraction analysis.

  • 37.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Chen, Xiang
    In-situ high temperature X-ray studies on bainitic transformation of austempered silicon alloyed steels2010In: THERMEC 2009: 6th International Conference on Processing & Manufacturing of Advanced Materials, August 25 - 29, 2009, Berlin, Germany / [ed] T. Chandra, Stafa-Zuerich: Trans Tech Publications Inc., 2010, p. 3086-3092Conference paper (Refereed)
    Abstract [en]

    The in-situ X-ray diffraction observations of the bainitic transformation of silicon alloyed steels were performed using the high temperature X-ray diffraction technique. The experimental results have shown that the volume fraction and carbon content of austenite remains a constant value which indicate that the transformation is almost finished after the early stages of austempering transformation. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (γLC) and the high-carbon austenite (γHC). The experimental results supports that the bainite growth is by a non-diffusive mechanism when austempering temperature is in the lower bainite transformation temperature

  • 38.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gülfem Özügürler, Almila
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ion, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Eriksson, Katarina
    Gestamp HardTech AB, Luleå, Sweden.
    Chandra Somani, Mahesh
    Centre for Advanced Steels Research, University of Oulu, Oulu, Finland.
    Pentti Karjalainen, Leo
    Centre for Advanced Steels Research, University of Oulu, Oulu, Finland.
    Allain, Sébastien
    Institut Jean Lamour, Université de Lorraine, Nancy, France.
    Garcia Caballero, Francisca
    National Center for Metallurgical Research (CENIM-CSIC), Madrid, Spain.
    Hot Forming of Ultra-Fine-Grained Multiphase Steel Products Using Press Hardening Combined with Quenching and Partitioning Process2019In: Metals, ISSN 2075-4701, Vol. 9, no 3, article id 357Article in journal (Refereed)
    Abstract [en]

    Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination of strength and ductility in the final parts. Microstructures were characterized using optical and scanning electron microscopy and X-ray diffraction. Tensile strengths (Rm) of 1190 and 1350 MPa and elongations to fracture (A50mm) of 8.5 and 7.4%, were achieved for the two high-silicon steels having 0.15 and 0.26 wt % C, respectively. Preliminary results show that press hardening together with a QP heat treatment is an effective method of producing components with high strength and reasonable tensile ductility from low carbon containing steels that have the potential for carbide free bainite formation. The QP treatment resulted in faster austenite decomposition during partitioning in the steels in comparison with an austempering treatment.

  • 39.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Heino, V.
    Tampere University of Technology, Department of Materials Science.
    Ojala, N.
    Tampere University of Technology, Department of Materials Science.
    Haiko, O.
    University of Oulu, Faculty of Technology, Materials Engineering.
    Hedayati, Ali
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Erosive-abrasive wear behavior of carbide-free bainitic and boron steels compared in simulated field conditions2018In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, no 1, p. 3-13Article in journal (Refereed)
    Abstract [en]

    The wear resistance of carbide-free bainitic microstructures have recently shown to be excellent in sliding, sliding-rolling, and erosive-abrasive wear. Boron steels are often an economically favorable alternative for similar applications. In this study, the erosive-abrasive wear performance of the carbide-free bainitic and boron steels with different heat treatments was studied in mining-related conditions. The aim was to compare these steels and to study the microstructural features affecting wear rates. The mining-related condition was simulated with an application oriented wear test method utilizing dry abrasive bed of 8–10 mm granite particles. Different wear mechanisms were found; in boron steels, micro-cutting and micro-ploughing were dominating mechanisms, while in the carbide-free bainitic steels, also impact craters with thin platelets were observed. Moreover, the carbide-free bainitic steels had better wear performance, which can be explained by the different microstructure. The carbide-free bainitic steels had fine ferritic-austenitic microstructure, whereas in boron steels microstructure was martensitic. The level of retained austenite was quite high in the carbide-free bainitic steels and that was one of the factors improving the wear performance of these steels. The hardness gradients with orientation of the deformation zone on the wear surfaces were one of the main affecting factors as well. Smoother work hardened hardness profiles were considered beneficial in these erosive-abrasive wear conditions.

  • 40.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Heino, V.
    Tampere University of Technology, Department of Materials Science.
    Ojala, N.
    Tampere University of Technology, Department of Materials Science.
    Haiko, O.
    University of Oulu, Faculty of Technology, Materials Engineering.
    Hedayati, Ali
    The effects of microstructure on erosive-abrasive wear behavior of carbide free bainitic and boron steels2016In: Nordic Symposium on Tribology - NORDTRIB 2016, 2016Conference paper (Refereed)
  • 41.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hosseini, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedayati, Ali
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Kornacker, Eva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fernandez, Maria Teresa
    CIDAUT Foundation, Boecillo, Spain.
    Sanz, Javier
    CIDAUT Foundation, Boecillo, Spain.
    Gonzalez, Manuel I.
    CIDAUT Foundation, Boecillo, Spain.
    Cañibano, Esteban
    CIDAUT Foundation, Boecillo, Spain.
    Mechanical and microstructural evaluation of high performance steel (S700MC) for road restraint systems2020In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 108, article id 104251Article in journal (Refereed)
    Abstract [en]

    The suitability of using high performance steel (S700MC) for road restraint systems (RRS) under very high containment level was evaluated in this study. To investigate the influence of the crash on the mechanical behaviour of the steel, different test pieces were tested by tensile and hardness testing, and examined by scanning electron microscopy (SEM). The tensile test results of S700MC showed a noticeable increase in yield strength at 0.2% elongation (Rp0.2) from 744 to 935 MPa, and ultimate tensile strength (UTS) from 810 to 1017 MPa, before and after crash tests (BC and AC, respectively). S700MC showed ~9% lower elongation at fracture value in comparison with S275JR and S355JR steels. Besides, fracture toughness, was significantly higher for S700MC (133 and 148 MJ/m3 for BC and AC, respectively) compared to conventional mild steels (108–118 MJ/m3). Microstructural observations of head-part of all S700MC samples revealed equi-axed grains. The fracture surface of tensile tested samples before crash, showed elongated grains accompanied by pore formation. Among after crash samples, one test piece showed intergranular cracks while no intergranular cracks were observed for the other crashed pieces which resulted in the lower Rp0.2 (813 MPa) and UTS strength (847 MPa) and fracture toughness (125 MJ/m3). The results showed that although RRS manufactured with S700MC undergoes severe mechanical deformation, the risk of brittle fracture is very low and this is beneficial from industrial as well as social point of view.

  • 42.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kumar, Ranga Naveen
    Infotech Enterprises Limited, Engineering Company, Hyderabad.
    Linz, Mathias
    Department of Materials Science and Engineering, Saarland University, Saarbrücken.
    Kankanala, Anusha
    Open University, Milton Keynes.
    Bäck, Fredrik
    Bosch Rexroth Mellansel AB.
    Standing contact fatigue analyse of steels with different microstructures2014In: Materials Structure & Micromechanics of Fracture VII: 7th International Conference on Materials Structure and Micromechanics of Fracture, MSMF 2013; Brno; Czech Republic; 1 July - 3 July 2013 / [ed] Pavel Šandera, Stafa-Zurich: Trans Tech Publications Inc., 2014, p. 622-626Conference paper (Refereed)
    Abstract [en]

    A Standing Contact Fatigue (SCF) test set up has been developed in order to facilitate quick testing of contact fatigue resistance of material surfaces. In this method the sample is pressed against a hard ball rapidly and the resulting crack formation is studied in order to evaluate the SCF resistance. Induction hardened surfaces of cam-ring steel and steels with pearlitic, martensitic, bainitic, ausferritic and quench and tempered microstructures have been studied. Characterization was performed by optical microscopy, scanning electron microscopy and hardness measurements. Ring-cone cracks were found at the edge of the indentations but inside the indent in the surface hardened cam-ring steel samples. Sectional views revealed that these cracks also grow underneath the indentation. Radial cracks were found in non-surface hardened samples. The test of the SCF resistance of steels with different microstructures showed that the ausferritic microstructures tested shoved better SCF resistance than the quench and tempered samples with similar hardness. A comparison between different tempering temperatures of surface hardened steels showed that samples tempered at the higher temperature 240 °C resulted in better SCF resistance

  • 43.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindström, A.
    Rubin, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Navara, E.
    Odén, Magnus
    Materials selection for saw mill dust cutter blades2006In: Pellets 2006: proceedings of the Second World Conference on Pellets ; in Jönköping, Sweden, 30 May - 1 June 2006, Stockholm: Swedish Bioenergy Association (SVEBIO) , 2006, p. 151-155Conference paper (Refereed)
  • 44.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ojala, N.
    Tampere University of Technology, Department of Materials Science, Tampere Wear Center.
    Heino, V.
    Tampere University of Technology, Department of Materials Science, Tampere Wear Center.
    Rau, Christoph
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gahm, Christian
    LKAB, Produktion Teknik, SE-98381 Malmberget.
    Erosive and abrasive wear performance of carbide free bainitic steels: comparison of field and laboratory experiments2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 98, p. 108-115Article in journal (Refereed)
    Abstract [en]

    Carbide free bainitic (CFB) steels have been tested in two heat treated conditions and compared with currently used quenched and tempered (QT) steel in an industrial mining application subjected to erosive-abrasive wear. A conventional sliding abrasion and a new application oriented high-stress erosion wear tests were performed in laboratory. The results of the erosion and the field tests were compared. The microstructural changes were investigated by optical and scanning electron microscopy. The hardness and hardness profiles of the steels were measured. The results showed that in the laboratory tests, the abrasion and erosion wear rates of the CFB steels were 35 and 45% lower respectively in comparison to the QT steel. In the field test, the mass losses of the CFB steels were about 80% lower in comparison with the QT steel. The improved wear resistance of the CFB steel can be explained by its higher hardness and higher work hardening. The erosion wear test was able to simulate the work hardening effect and the wear mechanisms observed in the field test samples.

  • 45.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pino, David
    Surface hardening of ausferritic Si-steels2007In: European School of Materials Science and Engineering, fourth research conference: preceedings of the fourth meeting of the European School of Materials Sciencie and Engineering / [ed] Marc Anglada, Barcelona: CPDA-ETSEIB , 2007, p. 173-176Conference paper (Refereed)
  • 46.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pino, David
    Luleå tekniska universitet.
    Lundmark, Jonas
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wear characteristics of surface hardened ausferritic Si-steel2007In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 14, no 1, supp 1, p. 245-248Article in journal (Refereed)
    Abstract [en]

    High strength steels can be produced by austempering of Si-containing steels. It is possible to achieve high toughness and good wear resistance in these steels. Surface hardening of this group of steels can further increase the surface hardness and wear resistance and in combination with high strength in the bulk, also the fatigue strength. Surface hardening by laser-hardening has been performed on steel 55Si7 after austempering of the steel in order to create a ferritic-austenitic carbide free microstructure. Tempering effects and hardness values have been studied. Optical as well as scanning electron microscopy has been used together with x-ray diffractometry in the characterization of the micro-structural changes. Wear resistance testing of austempered and laser hardened samples respectively of the Si-alloyed steel have been reported and also compared with that of the conventional Cr-alloyed steel. The results of the specific phase transformation from austenite to martensite during wear process will be reported

  • 47.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pino, G
    Wiklund, Greger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Laser surface hardening of steel with ausferritic structure2008In: SMT22: 22nd international Conference on Surface Modification Technologies, Sept. 22-24, 2008, Trollhättan, Sweden, 2008Conference paper (Refereed)
    Abstract [en]

    High strength steels can be produced by austempering of Si-containing steels. High toughness and good wear resistance are properties possible to achieve. Surface hardening of this group of steels can give an additional increase of the surface hardness and wear resistance. Laser surface hardening has been used in order to increase the surface hardness of the steel 55Si7. The effect of surface hardening on the ferritic-austenitic carbide- free microstructure created for this steel has been studied. Optical as well as scanning electron microscopy has been used in the characterization of the micro-structural changes.

  • 48.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rau, Christoph
    Luleå tekniska universitet.
    Gahm, Christian
    LKAB, Produktion Teknik, SE-98381 Malmberget.
    Erosive and abrasive wear resistance of carbide free bainitic steels2014Conference paper (Refereed)
    Abstract [en]

    34125Erosive and abrasive wear resistance of carbide free bainitic steelsEsa Vuorinen1*, Christoph Rau1, Christian Gahm21Dept. of Engineering Sciences and Mathematics, Luleå University of Technology, Sweden2LKAB, Produktion Teknik, SE-98381 Malmberget, Sweden* E-mail: Esa.Vuorinen@ltu.se , Phone: +46 920 493449, Fax: +46 920-491084Steels with fine ferritic-austenitic lath microstructure with high strength and toughness have also shown to have good sliding and sliding-rolling wear resistance. In this work has one of these so called carbide free bainitic (CFB) steels been tested in two heat treated conditions and compared with currently used quench and temper (QT) steel in an industrial application subjected to a complex mixture of erosion- and abrasion-wear in combination with impact resistance. In addition have these steels been subjected to abrasive laboratory test.The wear resistance has been determined by the specific wear rate for the laboratory tested samples and by measuring the volume and weight losses in the field tests. The microstructural changes in the steels have been investigated by optical- and scanning electron-microscopy. The hardness and hardness changes of the different steels have been investigated.The results show that the abrasive wear rate of the CFB steel is up to 50 % lower in comparison to the QT steel in the laboratory tests. The field tests show that the volume and weight loss of the CFB steel in the 2 tested conditions is less than 10 % in comparison with that of the currently used QT steel. The improved wear resistance of the CFB steel can be explained by the higher hardness and higher increase of the hardness in the surface layer of the CFB steel.

  • 49.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vang, Jesper
    Luleå tekniska universitet.
    Malo, Carradot
    Luleå tekniska universitet.
    Johansson, Pernilla
    Höganäs AB.
    Navara, Erik
    Jihlava.
    Powder metallurgically produced carbide free bainite2014In: Metallography XV / [ed] Margita Longauerová ; Pavol Zubko, Trans Tech Publications Inc., 2014, p. 480-486Conference paper (Refereed)
    Abstract [en]

    Steels with carbide free bainitic (CFB) microstructures show excellent strength, toughness and wear resistance. Cast or wrought products produced by conventional metallurgy have become introduced in manufacturing of machine components. The required silicon addition of more than 1.5wt% in CFB-steels limits the possibilities to produce components by P/M methods. The aim of this work has been to investigate the possibilites to produce CFB-steels by pressing and sintering. Four different powder mixtures based on Distaloy DC powder have been pressed to a relative density of 90 % and sintered in a N2-H2 atmosphere at 1150 °C. The sintered components were austenitized followed by austempering above the martensite start temperature. Tensile and impact testing together with microhardness measurements have been performed. The microstructures were studied by optical microscopy as well as SEM and XRD-methods. The tensile strength values achieved varied from 313 to 737 MPa, the elongation after fracture were between 0.1 and 0.2%. The impact toughness values varied between 4 and 11 J. The hardness of the bainite after short sintering time varied between 630 and 710 HV and the hardness of the CFB was 350 HV after short sintering time but reached 573 after prolonged sintering. The microstructure consisted mainly of bainite, small amount of CFB mixed with austenite but also of ferrite and retained austenite after short sintering time. A longer sintering time created a structure consisting of mainly CFB with bainite and a small amount of ferrite. The most interesting applications for P/M produced CFB-containing steels should be components subjected to sliding or rolling-sliding wear loads, as gears. The hardness and strength values achieved in the present work indicate that P/M produced CFB-steels can prove superior to conventional P/M steels in many applications

  • 50.
    Vuorinen, Esa
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Wang, Lin
    Luleå tekniska universitet.
    Stanojevic, Sanja
    Luleå tekniska universitet.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of retained austenite on rolling-sliding wear resistance of austempered silicon alloyed steel2009In: Hot sheet metal forming of high-performance steel, CHS2: 2nd international conference, June 15-17 2009, Luleå, Sweden. Proceedings / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Parkash, Auerbach: Verlag Wissenschaftliche Scripten , 2009, p. 339-347Conference paper (Refereed)
1 - 50 of 50
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