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  • 1.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical investigation of galling in a press hardening experiment with AlSi-coated workpieces2019In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 99, p. 85-96Article in journal (Refereed)
    Abstract [en]

    Press hardened steels are commonly used as a lightweight choice for manufacturing car components because of the high ratio of strength to weight. The use of ultra-high-strength steels for the design of lightweight vehicles contributes to the reduction of emissions of carbon dioxide while maintaining passenger safety. Stamping tools used in press hardening processes suffer harsh contact conditionsin terms of dramatic temperature changes, cyclic loadings, and complex interactions between coatings and oxidation. In mass production, tool wear is an inevitable problem that increases maintenance costs. Severe adhesive wear, also called galling, substantially occurs in the stamping tool used against Al—Si-coated workpieces. The galling that takes place during press hardening not only degrades the production quality but also shortens the service life of the tool. In order to properly arrange tool maintenance and minimize galling through adjusting process parameters, engineers need to know when and where galling occurs, based on modelling of the galling in press hardening simulations. In order to implement a galling simulation for press hardening, a modified Archard wear model is employed in the present study, which is a contact-mechanics-based model. The specific wear rate in the model is calibrated by the quantitative galling measurements of a high-temperature tribometer test. The tribological test is designed to mimic the press hardening conditions, where the correlations between galling and process parameters such as temperature, pressure, and sliding distance are outlined. The galling simulation is implemented in a full-scale press hardening experiment, and the predicted galling is validated in terms of severe galling positions and galling profiles. The galling profile evolution is correlated to variations in the contact conditions. Uncertainties in the numerical model, such as the choice of penalty scaling factor and friction coefficient, are analysed with a parameter study and discussed. This study demonstrates finite element (FE) simulations involving galling prediction in press hardening so as to improve product development and production efficiency.

  • 2.
    Decrozant-Triquenaux, Justine
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Courbon, Cedric
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    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.
    Tribological Behaviour of PVD Coated Tool Steels in Hot Forming of Aluminium Alloys2019In: CHS² 2019 - 7th International Conference on Hot Sheet Metal Forming of High Performance Steel, 2019Conference paper (Refereed)
    Abstract [en]

    Aluminium alloys are commonly used as light-weight materials in the automotive industry. Thisnon-ferrous family of metal alloys offers high versatility of properties and designs. In order to reduceweight and improve safety, grades with high strength-to-weight ratio, such as the 6XXX and 7XXXalloy series, are increasingly implemented in vehicles. These alloys, however, exhibit low formabilityand experience considerable springback when formed at low temperatures, and thus have to beformed at elevated temperatures. Severe adhesion and galling are known to be critical tribologicalchallenges in hot forming of aluminium. During the forming operation, adhesion and transfer ofaluminium onto the die surface take place. This phenomenon has a detrimental effect on the surfaceproperties, geometrical tolerances of the formed parts and maintenance of the dies. The influence ofsurface engineering as well as lubricant composition on adhesion and galling has not been sufficientlyinvestigated. Diamond-like-Carbon and Chromium Nitride PVD coatings applied on the toolsteel have shown promising results for reducing aluminium transfer at high-temperatures, especiallyin the presence of a lubricant. However, the interaction between lubricants and PVD coatings duringhot forming of aluminium alloys is not yet fully understood. The present study thus aims at characterisingthe high temperature tribological behaviour of selected PVD coatings and a lubricant duringsliding against an aluminium alloy. The objectives are to select promising lubricant-coating combinationsfor the given application and to study their tribological response in a high-temperature reciprocatingfriction and wear tester. The tests were carried out at 300°C, under dry and lubricatedconditions, in order to study the friction and wear performance. Uncoated tool steel reference testswere performed under dry and lubricated conditions and lubricated tests using DLC, CrN, CrTiNand CrAlN coated tool steel were performed and compared to the reference results. The initial andworn surfaces were analysed with white light 3D optical interferometry, scanning electron microscopy(SEM) and energy dispersive spectroscopy (EDS) with a view to understand the wear mechanisms.

  • 3.
    Decrozant-Triquenaux, Justine
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    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.
    Effect of Surface Engineered Tool Steels on Frition and Wear During Sliding Against Aluminium at High Temperatures2018In: The 18th Nordic Symposium on Tribology – NORDTRIB 2018, Uppsala, Sweden, 18-21 June 2018 / [ed] Uppsala University, 2018Conference paper (Other academic)
    Abstract [en]

    Usage of high-strength aluminium alloys is increasing for automotive applications due to high strength-to-weight ratios. Limited formability at room temperature requires hot forming for production of complex geometries. The occurrence of severe adhesion and material transfer negatively affects process economy and there is a need for effective solutions to overcome these issues. This work is focussed on the high-temperature tribological behaviour of Al6016 alloy and uncoated/PVD coated tool steels. Studies were conducted under dry and lubricated conditions using a high-temperature reciprocating tribometer. High friction in dry sliding for uncoated and coated tool steels was observed. Hexagonal boron nitride lubricant was not effective in reducing friction. DLC coating with a polymer lubricant resulted in the lowest friction and minimised material transfer.

  • 4.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental Evaluation of Galling Under Press Hardening Conditions2018In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 3, article id 93Article in journal (Refereed)
    Abstract [en]

    Severe adhesion, also referred to as galling, is a critical problem in press hardening, especially in stamping tools used for hot forming of Al–Si-coated ultra-high strength steel. Galling is known to develop rapidly on the tool surface and it negatively affects the quality of the formed products. Earlier research on this topic has focused on the galling initiation. However, studies on the galling development during extended sliding and the corresponding quantitative measurement still lack depth. In the present study, a tribological test is established to study the galling development under press hardening conditions. The tribological test set-up aims to simulate extended sliding between the Al–Si-coated boron steels and the tool die material. The contact conditions in the interface are studied by a numerical model of the tribological test. The friction coefficients and material transfer are discussed taking into account the variation of the different test conditions. Using the results from the tribological tests, the galling simulation is performed in the numerical model. A geometry-updated sample based on the galling (transferred material build-up) height is simulated and the consequent pressure fluctuation is obtained in the numerical model. This contributes to the explanation of the severe transferred material accumulation during the test.

  • 5.
    Deng, Liang
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A Tribological Test under Press Hardening Conditions for Galling Research2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 453-460Conference paper (Refereed)
  • 6.
    Pelcastre, Leonardo
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Heikkilä, Irma
    Swerea KIMAB, Stockholm.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High Temperature Tribological Behaviour of Thermal-Spray Coated Toll Steels Sliding Against Al-Si Coated Ultra-High Strength Steel2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 223-232Conference paper (Refereed)
  • 7.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of die Temperature on the Tribological Response During Interaction with Al-SI Coated Ultra-High Strength Steel2017In: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, p. 461-469Conference paper (Refereed)
  • 8.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of Zn coated UHSS sliding against hot-work tool steel at high temperatures2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, no Part-A, p. 423-432Article in journal (Refereed)
    Abstract [en]

    The increasing demands for light-weight components in vehicles contribute to the global expansion of hot sheet metal forming technologies. Structural components are typically produced using hot stamping of ultra-high strength steel (UHSS). This process allows forming of complex shapes whilst enabling control of the mechanical properties of the end product. Interest in zinc coated UHSS has increased in recent years in view of the corrosion protection it provides to the final components. There is a need for increased understanding of its tribological behaviour during the interaction with tool steel at elevated temperatures. In this work, tribological studies have been carried out in a novel hot strip tribometer. The aim was to study the effect of different operating conditions on the tribological behaviour of zinc coated UHSS sliding against a hot-work tool steel under un-lubricated conditions. The parameters studied in this work were; temperature, ranging from 400 °C to 700 °C; and contact pressure, from 5 to 30 MPa. The UHSS was initially heated up to austenitising temperature (840 °C) and then cooled down to the testing temperature. Upon stabilisation of temperature, the load was applied and sliding was carried out for a total of 1500 mm at 100 mm/s. The results showed a trend towards decreasing average coefficient of friction as temperature and contact pressure increased. Unstable friction behaviour was observed at low temperature (400 °C) and high contact pressure (30 MPa) whilst higher temperatures (600 °C) facilitated the development of a low and stable friction behaviour. It is proposed that the friction behaviour is controlled by the properties of the zinc phases in the coating developed during heating of the UHSS. The combination of high temperature and sliding conditions result in the removal of the uppermost oxide layer and the phases beneath control the friction behaviour.

  • 9.
    Furustig, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bates, Charles Anthony
    Danfoss Power Solutions ApS, Nordborg.
    Ennemark, Poul
    Danfoss Power Solutions ApS, Nordborg.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A strategy for wear analysis using numerical and experimental tools, applied to orbital type hydraulic motors2016In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 230, no 12, p. 2086-2097Article in journal (Refereed)
    Abstract [en]

    An accurate and reliable wear analysis requires detailed knowledge of the tribological conditions of the studied system. In this work, a numerical model which can quantify wear and is applicable to hydraulic motors is developed. Detailed tribological knowledge can be acquired through strategic experimental testing and numerical simulations. The model is constructed to include the effect on wear from varying lubricant film thickness. The development of the wear model includes consideration of wear observed in the Scanning Electron Microscopy (SEM) analysis of tested motors. The model is of the Archard type, in which the k-value is estimated from experiments, after considering the effect of lubrication. The contact pressure is the solution to a lubrication model that governs both the hydrodynamics of the lubricant film and the direct contact between the rough surfaces. To validate the model, a hydraulic motor is run at different operating conditions and the apparent wear depth is analysed after the tests. Numerical simulations mimicking the same configuration are performed and the predicted wear depths are compared to the experimental results. Similarities and differences are discussed and it is evident that a clear correlation exists between the wear predicted with the model and the measurement data of the apparent wear in the hydraulic motor. There are also discrepancies because of the model simplicity and the uncertainty in the specifications of the tested system. The results imply that wear analysis using numerical simulations aid the understanding of wear in machinery. The combined knowledge of physical conditions on different important scales enables in-depth analysis with numerical tools which cannot be achieved through experimental investigations alone. Furthermore, the numerical model can be refined leading to better wear predictions.

  • 10.
    Pelcastre, Leonardo
    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.
    Rolland, Anthony
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2016In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 228, p. 117-124Article in journal (Refereed)
    Abstract [en]

    The usage of the hot stamping process is of great importance due to the high demands for production of ultra-high strength steels (UHSS). An Al-Si coating is normally applied to the steel to prevent decarburisation and scaling during heating and to improve the corrosion resistance of the final component. During heating, the Al and the Si from the coating combine with the Fe from the steel substrate to form hard intermetallic phases. Little is known about the influence of the heating conditions on the tribological behaviour of the Al-Si coating during interaction with tool steels. The present work investigated different heat treatment parameters and the influence they had on the microstructure of the coating and the galling behaviour. With low alloying temperatures (700˚C), severe galling occurred and increasing the alloying temperature to 900˚C resulted in almost negligible material transfer. The reduction in galling was associated to the development of Fe2Al5 and FeAl2 at the surface.

  • 11.
    Yalamanchili, K.
    et al.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Jiménez-Piqué, E.
    Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, Center for Research in Nanoengineering, CRnE-UPC Avda. Diagonal 647, 08028 Barcelona.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bakoglidis, K.D.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Roa, J.J.
    Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, Center for Research in Nanoengineering, CRnE-UPC Avda. Diagonal 647, 08028 Barcelona.
    Jöesaar, M.P Johansson
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ghafoor, N.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Odén, M.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Influence of microstructure and mechanical properties on the tribological behavior of reactive arc deposited Zr-Si-N coatings at room and high temperature2016In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 304, p. 393-400Article in journal (Refereed)
    Abstract [en]

    Varying the Si-content in Zr-Si-N coatings from 0.2 to 6.3 at.% causes microstructural changes from columnar to nanocomposite structure and a hardness drop from 37 to 26 GPa. The softer nanocomposite also displays lower fracture resistance. The tribological response of these coatings is investigated under different contact conditions, both at room and elevated temperatures. At room temperature tribooxidation is found to be the dominant wear mechanism, where the nanocomposite coatings display the lowest wear rate of 0.64 × 10− 5 mm3/Nm, by forming an oxide diffusion barrier layer consisting of Zr, W, and Si. A transition in the dominant wear mechanism from tribooxidation to microploughing is observed upon increasing the test temperature and contact stress. Here, all coatings exhibit significantly higher coefficient of friction of 1.4 and the hardest coatings with columnar structure display the lowest wear rate of 10.5 × 10− 5 mm3/Nm. In a microscopic wear test under the influence of contact-induced dominant elastic stress field, the coatings display wedge formation and pileup due to accumulation of the dislocation-induced plastic deformation. In these tests, the nanocomposite coatings display the lowest wear rate of 0.56 × 10− 10 mm3/Nm, by constraining the dislocation motion.

  • 12.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of temperature on friction behaviour of tool steels sliding against Al-Si coated UHSS2016In: Proceedings of the 17th Nordic Symposium on Tribology : Nordtrib 2016, 2016Conference paper (Refereed)
    Abstract [en]

    In the automotive industry, a significant amount of components are formed using hot stamping. This process allows formation of complex shapes whilst controlling microstructure and mechanical properties of the end product. There are different tribological challenges encountered within the process due to the elevated temperature. The current studies focused on the tribological behaviour of different tool steels sliding against Al-Si coated steel (typically used in hot stamping) at different temperatures. It was observed that the tool steel temperature and the work-piece material temperature had a direct effect on friction level and stability and on the wear mechanisms; particularly in the occurrence of adhesive wear and material transfer onto the tool steels. In general, larger amount of material transfer and higher friction was observed with lower temperatures on the tool steel (~200˚C) and higher temperature of the work-piece material (~900˚C). The presence of oxides on the tool steel reduced the severity of material transfer and stabilised friction. However, the tool steel composition also affected the effectiveness in the stabilisation of the friction coefficient

  • 13.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of temperature on friction behaviour of tool steels sliding against Al-Si coated UHSS2016Conference paper (Refereed)
    Abstract [en]

    In the automotive industry, a significant amount of components are formed using hot stamping. This process allows formation of complex shapes whilst controlling microstructure and mechanical properties of the end product. There are different tribological challenges encountered within the process due to the elevated temperature. The current studies focused on the tribological behaviour of different tool steels sliding against Al-Si coated steel (typically used in hot stamping) at different temperatures. It was observed that the tool steel temperature and the work-piece material temperature had a direct effect on friction level and stability and on the wear mechanisms; particularly in the occurrence of adhesive wear and material transfer onto the tool steels. In general, larger amount of material transfer and higher friction was observed with lower temperatures on the tool steel (~200˚C) and higher temperature of the work-piece material (~900˚C). The presence of oxides on the tool steel reduced the severity of material transfer and stabilised friction. However, the tool steel composition also affected the effectiveness in the stabilisation of the friction coefficient.

  • 14.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hernandez, Sinuhe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mozgovoy, Sergej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Courbon, Cedric
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of oxide layers and near surface transformations on friction and wear during tool steel and boron steel interaction at high temperatures2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 330-331, p. 223-229Article in journal (Refereed)
    Abstract [en]

    Recent years have seen a continuously growing interest in high temperature tribological research. A significant part of this is driven by the need for improved understanding and knowledge pertaining to friction and wear and their control in the context of hot forming of high strength steels. Friction and wear characteristics of a sliding system are highly dependent on the properties of the two interacting surfaces. At high temperatures, the surface and material properties become extremely important since these systems often operate under unlubricated conditions. High temperature tribological processes are highly complex as these involve changes in mechanical properties due to microstructural changes; thermal softening; surface chemical and morphological changes due to oxidation and diffusion; deterioration of the surface and bulk material as a result of adhesive/abrasive wear and thermal fatigue. Many of these changes occur on the surfaces and/or in the near surface region. The formation of surface oxide layers and near surface layers with a highly refined microstructure (nano-structured) has been reported to have a significant influence on the tribological behaviour. An improved understanding of these effects is a prerequisite in an attempt towards controlling friction and wear at high temperatures. The main aim of this work is to investigate the formation of oxide layers and near surface transformed layers during tool steel and boron steel interaction at elevated temperatures and their relation to the friction and wear response. The results from sliding wear tests showed that under favourable conditions of temperature and load, a reduction of wear by three orders of magnitude and reduced friction by 50% was obtained. This was attributed to the formation of a composite layer structure involving a refined workhardened layer and a protective oxide layer on top. In the case of three body abrasive wear of boron steel, a reduction in wear rate when temperature increased (100–200 °C) has also been found. This reduction in three-body wear is due to the formation of a workhardened layer with a mechanically mixed layer of wear debris and fragmented silica particles on top. At higher temperatures (>500 °C), the softer matrix due to recrystallisation and phase transformations was unable to maintain a lower wear rate despite the presence of embedded fragmented silica particles.

  • 15.
    Pelcastre, Leonardo
    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.
    Courbon, Cedric
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of Al-Si-coated ultra-high-strength steel during interaction with tool steel at elevated temperatures: Influence of tool steel surface topography parameters on galling2015In: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture, ISSN 0954-4054, E-ISSN 2041-2975, Vol. 229, no 8, p. 1373-1384Article in journal (Refereed)
    Abstract [en]

    Galling is a severe form of adhesive wear encountered in metal forming operations. In hot stamping, an Al-Si coating is normally applied onto the ultra-high-strength steels to prevent decarburisation and to improve the corrosion resistance of the steel. Material transfer occurring from the coated ultra-high-strength steel to the tool surface has been identified as major issue in hot stamping. This transferred material impairs the quality of the produced parts and at the same time, it increases the costs of maintenance of the tools. This work focuses on the understanding of surface topography parameters and their effect on galling. Surface roughness level and orientation of the surface lay on tool surface have been studied. The results showed that a single parameter of the surface topography is not enough to describe the resistance to galling. Parameters such as Rv, Rp and Rsk are also important to consider in order to rank the galling resistance of the surface. The sliding direction with respect to the surface lay also had a significant influence on galling; sliding in the direction parallel to it resulted in substantially reduced material transfer.

  • 16.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yousfi, Amine
    Luleå University of Technology.
    Lund, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Abrasive wear behaviour of hardened high strength2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 90-97Article in journal (Refereed)
    Abstract [en]

    Abrasive wear in industrial applications such as mining, materials handling and agricultural machinery constitutes a large part of the total wear. Hardened high strength boron steels are known for their good wear resistance and mechanical properties, but available results in the open literature are scarce. This work aims at investigating how different quenching techniques affect the two-body abrasive wear resistance of hardened high strength boron steels. Furthermore, the wear as a function of depth in thicker hardened high strength boron steel plates has also been studied. The material characterisation has been carried out using microhardness, SEM/energy dispersive spectroscopy and three-dimensional optical surface profilometry. The results have shown that water quenched and tool quenched high strength boron steel had similar wear resistance. The main wear mechanisms appear to be microcutting combined with microfatigue. Workhardening during the abrasion process has been found to affect the abrasive wear.

  • 17.
    Prakash, Braham
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    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.
    Galling in hot sheet forming of high strength steels2014Conference paper (Refereed)
  • 18.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Rolland, Anthony
    Exchange Student LTU.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2014Conference paper (Other academic)
    Abstract [en]

    The usage of the hot stamping process is of great importance due tothe high demands for production of ultra-high strength steels (UHSS).An Al-Si coating is normally applied to the steel to preventdecarburisation and scaling during heating and to improve thecorrosion resistance of the final component. During heating, the Al andthe Si from the coating combine with the Fe from the steel substrate toform hard intermetallic phases. Little is known about the influence ofthe heating conditions on the tribological behaviour of the Al-Sicoating during interaction with tool steels. The present workinvestigated different heat treatment parameters and the influencethey had on the microstructure of the coating and the gallingbehaviour. With low alloying temperatures (700C), severe gallingoccurred and increasing the alloying temperature to 900C resulted inalmost negligible material transfer. The reduction in galling wasassociated to the development of Fe2Al5 and FeAl2 at the surface.

  • 19.
    Pelcastre, Leonardo
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Rolland, Anthony
    Division of Machine Elements, Luleå University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Division of Machine Elements, Luleå University of Technology.
    Influence of microstructural evolution of Al-Si coated UHSS on its tribological behaviour against tool steel at elevated temperatures2014In: Society of Tribologists and Lubrication Engineers Annual Meeting and Exhibition 2014, Society of Tribologists and Lubrication Engineers , 2014, Vol. 1, p. 463-465Conference paper (Refereed)
    Abstract [en]

    In recent years, the usage of the hot stamping process has increased due to the high demands for production of ultra-high strength steels (UHSS). In particular, more studies are being carried out pertaining to the Al-Si coated UHSS to understand its behaviour during the forming process as well as the performance of the produced parts. The Al-Si coating is applied to the UHSS with the aim of reducing decarburisation and to avoid the formation of thick oxide scales on the work-piece during the heating stage. Usage of the Al-Si coating has the added benefit of greatly improving the corrosion resistance and paintability of the produced components [1,2].

  • 20.
    Furustig, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On a strategy of wear analysis using numerical and experimental tools2014Conference paper (Refereed)
  • 21.
    Hardell, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Yousfi, Amine
    Luleå University of Technology.
    Lund, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Abrasive wear behaviour of hardened high strength boron steel2013Conference paper (Refereed)
  • 22.
    Das, Sanjeev
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of static and dynamic ageing on wear and friction behavior of aluminum 6082 alloy2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 60, p. 1-9Article in journal (Refereed)
    Abstract [en]

    In the present investigation the effect of static and dynamic ageing on the wear and friction behavior of aluminum alloy (AA 6082) sliding against tool steel (TS) surface has been studied. The AA 6082 alloy samples used in the present study were in as-cast, solutionized and peak aged conditions. Scanning electron microscope analysis of the debris and worn surfaces revealed the role of precipitates on the dry sliding wear behavior. Frictional behavior varies significantly for all the conditions at elevated temperature (180 °C) compared to room temperature (40 °C). Such response was attributed to the dynamic precipitations during elevated temperature test.

  • 23.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Galling mechanisms during interaction of tool steel and Al-Si coated ultra-high strength steel at elevated temperature2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 67, p. 263-271Article in journal (Refereed)
    Abstract [en]

    Occurrence of galling in hot forming is detrimental to the quality of produced parts and process economy. Material transfer from Al-Si coated work-piece to the tool material has been studied in this work. PVD coatings (AlCrN, TiAlN and DLC) on tool steel substrate have been considered as well as plasma nitriding and their tribological behaviour was compared to the case of an untreated tool steel. Galling initiates through accumulation and compaction of wear debris when untreated tools are used whereas the PVD coatings resulted in increased galling due to adhesion. Plasma nitrided tool steel showed negligible galling due to formation of glaze layers and the formation of such layers depends on the occurrence of wear of the nitrided tool steel.

  • 24.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature galling: influencing parameters and mechanisms2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Damage of forming tools at elevated temperatures is a major problem in metal forming processes such as hot stamping. Of special importance is the occurrence of adhesion and gross material transfer from the work-piece to the tool surface, a phenomenon known as galling. This type of damage adversely affects the quality of the produced parts and process economy due to frequent maintenance for refurbishing and/or replacing the tools. In view of its importance, several studies on galling have been conducted. However most of these studies pertain to conventional or cold forming processes.In this work, a systematic analysis of damage mechanisms of actual hot stamping tools and extensive high temperature tribological tests to investigate the tool-workpiece interaction have been carried out. The analysis of worn hot forming tools revealed that the main damage mechanisms encountered during hot forming of Al-Si coated ultra-high strength steel (UHSS) are fatigue, corrosion and material transfer. Amongst these mechanisms, material transfer (galling) is the most important from quality and productivity points of view. It was found that galling onto the tool steel is caused by accumulation and compaction of wear debris. Lumps of transferred material are formed through agglomeration of wear debris. The preferential sites for the accumulation of debris are defects on the tool surface or grinding marks generated during refurbishing. Hence, the surface topography of the tool is of great importance for controlling the material transfer. The most relevant parameters that influence galling during the interaction of Al-Si coated UHSS and tool steel were studied through laboratory tribological tests. It was found that controlling parameters such as Rvk, Rpk, Rsk and Sm can minimise galling on untreated tool steels. Furthermore, it was observed that sliding parallel to the surface lay of the tool results in reduced galling as the debris can escape the contact through the valleys of the tool surface.The usage of different PVD hard coatings, such as AlCrN, TiAlN and DLC, were considered as a possibility to alleviate galling. Additionally, the tribological response of plasma nitrided tool steel with and without a post oxidation treatment was also studied. The use of hard PVD coatings on the tool steel resulted in severe adhesion and material transfer during sliding against Al-Si coated UHSS at elevated temperature. This was due to the affinity between the constituents of the coating of the tool and the Al-Si coating. Plasma nitrided tool steel with post oxidation treatment showed negligible galling mainly due to the formation of protective oxide layers on the surface of the Al-Si coated steel. The formation of these layers reduced wear of the Al-Si coating and consequently the generation of Al-Si wear debris. The protective oxide layers are formed primarily by wear debris from the outermost layer of the post oxidised plasma nitrided tool steel. Heat treatments of the Al-Si coating revealed that the phases present in the coating are directly linked to the galling behaviour. Without sufficient temperature or time, stable and harder phases are not formed. This greatly increases the occurrence of galling by severe adhesion as the outermost layer of the coating (unalloyed Al) and the tool steel have high affinity. If the harder phases are formed, the mechanism for galling changes to accumulation and compaction of wear debris from the Al-Si coating and direct adhesion between the Al-Si coated UHSS and the tool steel is reduced.

  • 25.
    Pujante, J.
    et al.
    Fundació CTM Centre Tecnològic, Avda.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vilaseca, M.
    Fundació CTM Centre Tecnològic, Avda.
    Casellas, D.
    Fundació CTM Centre Tecnològic, Avda.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into wear and galling mechanism of aluminium alloy-tool steel tribopair at different temperatures2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 308, no 1-2, p. 193-198Article in journal (Refereed)
    Abstract [en]

    Aluminium alloys show poor formability at room temperature, and the production of complex components requires a series of high temperature forming processes, such as warm and hot forging, extrusion and hot sheet metal forming. Forming aluminium in these conditions subjects the tools to severe adhesive wear and galling, leading to increased energy needs, shorter tool life, lower part quality and increased cost. In this work, the wear mechanisms generated by aluminium alloys on forming tools have been studied by means of linear reciprocating sliding tests. Aluminium alloy AA2017 balls were slid against DIN 1.2344 (AISI H13) tool steel samples with various surface finishes at temperatures up to 450 °C. The main results show that the observed wear mechanisms are extremely dependent on the system temperature, ranging from pure abrasive wear to formation of layers of compacted aluminium debris and gross aluminium transfer in the form of lumps. On the other hand, tool surface finish has a limited effect on gross material transfer, but does affect the material transfer micromechanisms

  • 26.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Microstructural influence of the Al-Si coated UHSS on galling at elevated temperatures2013Conference paper (Refereed)
  • 27.
    Das, Sanjeev
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of static and dynamic ageing on friction and wear behaviour of aluminium 6082 alloy2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    In recent past, warm forming processes have been used successfully to increase the strength of age-hardenable alloys by dynamic precipitation. However, the influence of dynamic age hardening on the wear and friction behaviour of age-hardenable aluminium alloy is not clear. Therefore, in the present investigation the effect of static and dynamic ageing on the friction and wear behaviour of aluminium 6082 alloy (AA 6082) sliding against tool steel (TS) surface has been studied. The aluminium samples used in the present study were in as-cast, solitionised and peak aged conditions. Optical microscope revealed the presence of dendritic structure in both as-cast and solitionised samples. Scanning electron microscope analysis of the debris and worn surfaces revealed the wear mechanism and role of precipitates on the friction and wear results. At low temperature (40 C), the frictional behaviour of as-cast, solitionised and peak aged samples were similar. The wear rates at 40 C increased with increase in the amount of strain inside the specimens due to fine precipitations. At 180 C, a significant variation in the frictional behaviour of different specimens was observed. The wear rate of solitionised specimens at 180 C is higher compared to as-cast and aged specimens. The absence of hard phases at initial stage of the test and subsequent dynamic precipitates restricted to a thin layer were responsible for the increase in wear rate.

  • 28.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of tool steel surface topography on galling during hot forming of Al-Si coated ultra high-strength steels2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    Galling is a severe form of adhesive wear encountered in metal forming operations. In hot stamping, an Al-Si coating is normally applied onto the ultra high strength steels (UHSS) to prevent decarburisation and improve the corrosion resistance of the steel. Material transfer occurring from the coated UHSS to the tool surface has been identified as major issue in hot stamping. It is a known problem as this transferred material impairs the quality of the produced parts as well as increases the costs of maintenance of the tools. The present work focuses on the understanding of surface topography parameter and their effect on galling. Surface roughness level and orientation of the roughness marks (lay) on tool surface have been studied. The results showed that a single parameter of the surface topography is not enough to describe the resistance to galling. Parameters such as Rp, Rv and Rsk are also important to consider in order to rank the galling resistance of the surface. The sliding direction with respect to the surface lay also had a significant influence on galling; sliding in the direction parallel to it resulted in substantially reduced material transfer.

  • 29.
    Pelcastre, Leonardo
    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.
    Vargas, Natalia Herrera
    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.
    Investigations into the damage mechanisms of form fixture hardening tools2012In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 25, p. 219-226Article in journal (Refereed)
    Abstract [en]

    In metal forming operations such as form fixture hardening, the interaction between the tools and the work-piece is strongly influenced by the tribological properties at the interface. Damage or excessive wear of the tools can be detrimental to the quality of the final component and it also has an impact on the process economy due to increased maintenance or more frequent replacement of tools. The objective of this study was to investigate the damage mechanisms encountered in real form fixture hardening tools in order to understand the causes of tool failure and ultimately to come up with possible solutions for this problem.Advanced techniques such as Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) were used for obtaining an in-depth understanding of the different phenomena involved in the failure of form fixture hardening tools. Two different tools having different hardness values and microstructures that had been used in production were analysed.The damage mechanisms found included abrasive and adhesive wear, material transfer, corrosion and mechanical and thermal fatigue. The main damage mechanism was found to be cracking caused by mechanical stresses on the surface. Although both tools presented similar types of damage, the severity was different and it was strongly influenced by the microstructure.

  • 30.
    Pujante, Jaume
    et al.
    Fundació CTM Centre Tecnològic.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vilaseca, Montserrat
    Fundació CTM Centre Tecnològic.
    Casellas, Daniel
    Fundació CTM Centre Tecnològic / Universitat Politècnica de Catalunya.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into wear and galling mechanism of aluminium alloy-tool steel tribopair at different temperatures2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    Aluminium-based alloys present a number of interesting properties, such as lower density, corrosion resistance, thermal and electrical conductivity and good recyclability. For this reason, there is a strong trend in increasing the use of these alloys, particularly in the automotive industry [1, 2]. However, aluminium alloys show poor formability at room temperature, and the production of complex components requires a series of high temperature forming processes, such as warm and hot forging, extrusion and hot sheet metal forming [3]. Forming aluminium in these conditions subjects the tools to severe adhesive wear and galling, leading to increased energy needs, shorter tool life, lower part quality and increased cost.In this work, the wear mechanisms generated by aluminium alloys on forming tools have been studied by means of linear reciprocating sliding tests, performed in an Optimol SRV equipment. Balls of two different compositions (AA2017 and 99% pure aluminium) were slid against DIN 1.2344 (AISI H13) tool steel samples with various surface finishes at temperatures up to 450 ºC. The resulting wear tracks were studied by means of confocal microscopy and electron microscopy (SEM/BSE).The main results show that the observed wear mechanisms are extremely dependent on the system temperature, ranging from pure abrasive wear to formation of layers of compacted aluminium debris and gross aluminium transfer in the form of lumps. The choice of aluminium alloy can be very relevant on the wear behaviour of the system. On the other hand, tool surface finish has a limited effect on material transfer. [1] Miller W S, et al. Recent development of aluminium alloys for the automotive industry. Materials Science and Engineering A 280 (2000), pp 37-49 [2] Toros S, Ozturk F, Kacar I. Review of warm forming of aluminium-magnesium alloys. Journal of Materials Processing Technology 207 (2008), pp 1-12[3] Hanna M D. Tribological evaluation of aluminium and magnesium sheet forming at high temperatures. Wear 267 (2009), pp 1046-1050

  • 31.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Micro-mechanisms of galling at elevated temperatures2012In: International Colloquium Micro-Tribology 2012, Warsa, 2012, p. 29-30Conference paper (Refereed)
  • 32.
    Prakash, Braham
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    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.
    Hot forming tribology2011In: Proceedings of 3rd European Conference on Tribology (ECOTRIB 2011) / [ed] Friedrich Franek; Wilfried J. Bartz; Andreas Pauschitz; Joze Vizintin; Enrico Ciulli; Rowena Crockett, Wien: The Austrian Tribology Society , 2011, p. 9-10Conference paper (Refereed)
  • 33.
    Pelcastre, Leonardo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hot forming tribology: galling of tools and associated problems2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, the use of ultra high-strength steels (UHSS) as structural reinforcements and in energy-absorbing systems in automobiles has increased rapidly; mainly in view of their favourable strength to weight ratios. However, due to their high strength, the formability of UHSS is poor, thus complex-shaped UHSS components are invariably produced through hot-metal forming processes. The use of hot stamping or press hardening, which was developed during the 1970’s in northern Sweden, has become increasingly popular for the production of ultra high strength steels. In hot stamping, different tribological problems arise when the tool and work-piece interact during the forming process at elevated temperatures. Wear and surface damage of forming tools can be detrimental to the quality of the final product and these can also have an adverse impact on the process economy due to frequent maintenance or replacement of tools. In this work, a literature review pertaining to tribology of hot sheet metal forming has been carried out. This review has revealed that the awareness of tribology and its application in metal forming processes at high temperature has increased in the recent years. A considerable amount of work has been done to enhance the understanding of the response of different materials and parameters involved and also to improve the process itself. However, despite these developments, there exist major gaps in knowledge pertaining to the occurrence of friction and wear in hot sheet metal forming. Extensive experimental studies have thus been undertaken to bridge some of the knowledge gaps related to tool wear and failure mechanisms in the hot stamping process. These studies have involved both the systematic analysis of actual worn tools as well as parametric tribological investigations in the laboratory. The analysis of worn tools showed that friction is a crucial parameter in their operating life. It was observed that severe mechanical stresses are generated due to high friction during the work-piece/tool interaction. As a result of the cyclic thermal and mechanical loads imposed during the hot forming process, the stresses generated eventually lead to the occurrence of fatigue damage at the tool surface. Another important mechanism observed was material transfer from the work-piece to the tool surface. This is particularly common and detrimental in hot forming of coated work-piece material. The most common coating applied to the ultra high strength steel is a hot dip aluminium based coating, commonly referred to as Al-Si coating. The parametric studies carried out were aimed at understanding of the initiation mechanisms of material transfer from the Al-Si coated steel to the tool material. The results showed that severe galling occurs by accumulation and compaction of wear debris and becomes enhanced in tools having rough surfaces. The roughness defects on the surface promote accumulation of wear particles. Furthermore, high contact pressure also enhances the compaction of wear debris and consequently the severity of material transfer. It was observed that the severity of galling can be reduced by the use of smooth and hard surfaces. Additionally, the use of different PVD coatings on the tool steels showed an increased tendency on adhesion, causing a severe material transfer onto the tool surface.

  • 34.
    Pelcastre, Leonardo
    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.
    Herrera, Natlia
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the failure mechanisms of form fixture hardening tools2011In: Proceedings, 3rd International Conference Hot Sheet Metal Forming of High Performance Steel: June 13 - 17, 2011, Kassel, Germany / [ed] Mats Oldenburg; Kurt Steinhoff; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2011, p. 93-103Conference paper (Refereed)
  • 35.
    Pelcastre, Leonardo
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the occurrence of galling during hot forming of Al-Si-coated high-strength steel2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no 6, p. 487-498Article in journal (Refereed)
    Abstract [en]

    Galling is a severe form of adhesive wear associated with both cold and hot metal forming operations. In hot sheet metal forming of Al-Si-coated ultrahigh-strength steel (UHSS), transfer occurs from the coated UHSS to the tool surface. This leads to poor quality of produced parts, damage of expensive tooling, and increased downtime for maintenance of the tools. This study thus aims at identifying the salient mechanism(s), which give rise to initiation/occurrence of galling at elevated temperatures. This has been accomplished by analysing actual hot forming tools and through systematic parametric tribological investigations in the laboratory. The analysis of the actual tools has shown that the transferred layer consists of Al, Si, and Fe. The structure of the transferred materials is composed of sintered/compacted wear particles. The parametric study has shown that galling is dependent on the operating conditions. A strong relationship between the contact pressure and material transfer has been observed. The severity of galling is lower for smoother surfaces at low contact pressure. However, at high contact pressure, the influence of roughness under these conditions is insignificant. It has also been observed that hard-tool steel substrates reduce the severity of galling, particularly, at high contact pressure.

  • 36. Hardell, Jens
    et al.
    Pelcastre, Leonardo
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High-temperature friction and wear characteristics of hardened ultra-high-strength boron steel2010In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 10, p. 1139-1151Article in journal (Refereed)
    Abstract [en]

    The usage of ultra-high-strength boron steel (UHSS) in automotive industry has increased rapidly in the recent past. Forming of UHSS components is performed at elevated temperatures, which also offers the possibility of hardening through quenching directly after forming. However, the influence of hardening on friction and wear during relative sliding between the tool and the workpiece is unclear. Therefore, the friction and wear characteristics at elevated temperatures of hardened and unhardened UHSS and tool steel pairs are investigated in this study. The results show that both friction and wear at all the investigated temperatures are affected by hardening of the UHSS. For uncoated UHSS, the hardening resulted in lower friction and the tool wear increased at low temperatures, but was not affected at elevated temperatures. This was attributed to the higher hardness after hardening combined with the presence of an oxide scale on the UHSS after heating and quenching. For Al-Si-coated UHSS, the hardening reduced friction and tool steel wear at elevated temperatures, and also reduced the wear of the Al-Si-coated high-strength steel at low temperature mainly owing to the formation of an intermetallic layer on the Al-Si-coated UHSS surface after exposure to elevated temperatures.

  • 37. Pelcastre, Leonardo
    et al.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Investigations into the occurrence of galling during hot forming of Al-Si coated high strength steel2010Conference paper (Other academic)
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