| 1. |
- Hardell, Jens, et al.
(författare)
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Effect of oxide layers and near surface transformations on friction and wear during tool steel and boron steel interaction at high temperatures
- 2015
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 330-331, s. 223-229
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Hernandez, Sinuhe
(författare)
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Friction and Wear Phenomena in Steels at Elevated Temperatures
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different grades of steels are often exposed to high temperatures whether during their shaping/forming or during their use in several applications. This exposure to high temperature has a great bearing on the resulting friction and wear phenomena in steels due to changes in their surface and near-surface properties. This means that the wear and frictional behaviour will be no longer controlled nor determined by the original properties of steels but rather by the changes in steels surfaces brought about by high temperatures. A thorough understanding of friction and wear phenomena in steels under these conditions is crucial in terms of control as well as prediction of friction and wear. This thesis has focussed on friction and wear phenomena in some selected steels suitable for working at high temperatures.The initial part of this work concentrated on investigating the effect of load and temperature on the friction and wear behaviour of tool steel sliding against boron steel in a pin-on-disc (POD) test configuration. This investigation revealed the formation of oxidised protective layers and their role in reducing wear and friction at elevated temperatures.Experimental studies in a specially designed high temperature tribometer for simulating tool-workpiece interaction in hot sheet metal forming were also carried out using similar conditions to those used in the POD tests. These studies corroborated the presence and importance of oxidised layers at elevated temperatures. However, the thickness of oxidised layers was lower compared to those on the POD specimens. The results showed a good correlation between mechanisms of wear and friction especially at 400 °C. As in the case of the POD studies, the main wear mechanisms were adhesion and three body abrasion.Further, three-body abrasive wear behaviour of different tool steels, heat treated high-Si steels and boron steel at different temperatures was also investigated. The two main wear mechanisms identified were microploughing and microcutting. The results revealed near surface modifications in steel surfaces such as work hardened layers, mechanically mixed layers and recrystallization of ferrite grains. The wear behaviour of different steels was strongly influenced by the occurrence of these transformations as well as changes in mechanical properties like hardness and toughness.Nanoindentation and multiple-pass nanoscratch tests were carried out using a high temperature nanoindenter with a view to investigate the relationship between mechanical properties measured (hardness, fracture toughness, plasticity index) and the tribological behaviour of different tool steels. Higher volume losses were obtained for tool steels with low hardness and high plasticity index values.
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| 3. |
- Hernandez, Sinuhe, et al.
(författare)
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High temperature friction and wear mechanism map for tool steel and boron steel tribopair
- 2014
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Ingår i: Tribology - Materials, Surfaces & Interfaces. - 1751-5831 .- 1751-584X. ; 8:2, s. 74-84
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Tidskriftsartikel (refereegranskat)abstract
- Tribological systems working under severe conditions like high pressures, sliding velocities and temperatures are subjected to different phenomena such as wear, oxidation and changes in mechanical properties. In many cases, there are several mechanisms occurring simultaneously.The predominating type(s) of wear mechanism(s) presented will depend on the materials in contact, operating parameters and surrounding environment. In this work, high temperature tribological studies of boron steel sliding against tool steel were conducted using a pin-on-disc machine under unlubricated conditions at five different temperatures ranging from 25 to 400C, three different loads: 25, 50 and 75 N (contact pressures of 2, 4 and 6 MPa respectively) and a sliding speed of 0.2 ms-1. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were used for analysing the resulting damage and tribolayers of the worn surfaces. Additionally, hardness measurements were carried out in a special hot hardness rig in the same temperature range as that used in pin-on-disc tests. The results have shown that for a given load, the wear rate of boron steel decreased as the temperature increased, reaching itslowest value at 400C at 50 N. In the case of the tool steel, it could be observed that at 200C and above, the wear rate decreased as the load increased. This behaviour is consistent with the formation of a protective oxidised layer initiated at 100C. At higher temperatures, such layers become more pronounced. The obtained data were finally used to construct a friction and wear mechanism map for this material pair that takes temperature and pressure into account.
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| 4. |
- Hernandez, Sinuhe, et al.
(författare)
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High-Temperature Friction and Wear of Boron Steel and Tool Steel in Open and Closed Tribosystems
- 2018
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Ingår i: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 61:3, s. 448-458
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Tidskriftsartikel (refereegranskat)abstract
- More and more components in automotive, material processing and mining industries are operating under harsh conditions involving high temperatures and high contact pressures. Tribotesting for such applications is done using both open (one surface meeting a fresh counter-surface) and closed (one surface follows the same track on the counter-surface) test configurations. In order to enable development of new materials and processes intended for such conditions, there is a need for better understanding pertaining to tribological phenomena occurring under these different test configurations.In this work, friction and wear characteristics of quenched and tempered tool steel sliding against boron steel (22MnB5) have been studied. The experiments were conducted using a specially designed hot strip tribometer (HST) under dry conditions at R.T. and 400°C in open as well as closed configurations. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were carried out to analyse the worn surfaces. Additionally, the results from the closed test configuration were compared to previous tests carried out with the same materials and parameters using a pin-on-disk (POD) test rig. The results have shown that wear was reduced at higher temperatures as well as with repeated sliding on the same contacting surfaces (i.e. closed configuration) compared to those with open configuration. A good correlation of wear mechanisms and coefficient of friction between closed configuration tests and those carried out with the POD test rig was observed especially at 400°C.
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| 5. |
- Hernandez, Sinuhe, et al.
(författare)
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High temperature three-body abrasive wear of 0.25C 1.42Si steel with carbide free bainitic (CFB) and martensitic microstructures
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 360-361, s. 21-28
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 6. |
- Hernandez, Sinuhe, et al.
(författare)
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High temperature wear mechanism map for tool steel and high strength boron steel
- 2012
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Ingår i: 15th Nordic Symposium on Tribology - NordTrib 2012. - Trondheim : Department of Geography, Norwegian University of Science and Technology.
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Konferensbidrag (refereegranskat)abstract
- Machine components moving relative to each other at elevated temperatures can be found in applications such as power generation, aerospace, metal working, etc. The identification and understanding of the wear mechanisms are extremely important for solving problems related to systems operating at high temperatures. Presentation of the results in the form of wear maps enables e.g. design engineers to select appropriate materials for these applications [1, 2].In this study, unidirectional sliding wear tests of ultra-high strength boron steel against tool steel were conducted under unlubricated conditions using a pin-on-disc machine.Studies ranging from room temperature to 300 °C with a sliding speed of 0.2 ms-1 and a contact pressure of 2 MPa were carried out. Wear rates of both materials were obtained by weight loss measurements. Surface damage and chemical composition of tribolayers have been obtained by means of scanning electron microscope/energy dispersive spectroscopy to identify the dominant wear mechanism(s).The preliminary results have shown that the wear rate of boron steel decreased almost one order of magnitude as the temperature increased from room temperature to 300 °C. This behavior is consistent with the formation of a protective glaze layer initiated at 100°C. At higher temperatures, such layers become more extensive. The collected data was finally used to construct a wear map for this material pair that takes temperature into account.
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| 7. |
- Hernandez, Sinuhe
(författare)
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High Temperature Wear Processes
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Moving machine assemblies are increasingly exposed to extreme operating conditions involving high temperatures owing to demands on higher power densities, high performance/efficiency and extreme environments. The changes in surface and near surface properties of contacting surfaces caused by exposure to high temperature and deformation govern the occurrence of friction, wear and material transfer of the tribological system. However, these changes have not been thoroughly investigated. In order to enable development of new products and processes, there is a need for new knowledge pertaining to tribological phenomena occurring at elevated temperatures.One of the most commonly used engineering materials is steel as it offers a good compromise between performance and cost even at high temperatures. For example, prehardened (quenched and tempered) tool steels are commonly used in hot forming dies can also be employed in other technological applications involving elevated temperatures. Although the research pertaining to hot stamping, and high temperature tribology in general, has significantly grown during the last years there are still knowledge gaps that need to be bridged. Adhesion and abrasion have been identified as the most dominant wear mechanisms in high temperature tribological systems but the detailed understanding of the mechanisms is still inadequate.The objective of this work is therefore to obtain a deeper understanding of the tribological phenomena associated with adhesion and abrasion that takes place at high temperatures. Unidirectional sliding wear tests have been conducted in order to investigate the influence of contact pressure and temperature on the wear and friction characteristics of tool steel and boron steel pair. Tribological studies involving boron steel, tool steels and heat-treated high-Si steels in a three body abrasive environment were also carried out with a view to explore the effect of temperature on the wear rate, wear mechanisms and to correlate this with material properties like hot hardness and toughness.The results from the unidirectional sliding tests showed that the frictional behaviour of tool steel and boron steel is load and temperature dependent. In general the friction coefficient decreases as both temperature and load are increased as a result of the formation of oxide layers. At temperatures above 200 °C, the compaction and sintering of these layers led to the formation of a wear protective glaze layer. Consequently, the wear rate for both materials decreased at elevated temperatures. Additionally, a friction and wear mechanisms map was developed for the investigated materials.In the case of abrasive wear tests, the results showed that the main wear mechanism presented for each material varied with temperature. In general, a transition from micro-ploughing to a combination of micro-cutting and micro-ploughing was present. The tool steels and boron steel showed a decrease in wear rate in the range of 100 to 400 °C compared to that at room temperature. This was attributed to the toughness in case of the tool steel and the formation of a protective tribolayers for the boron steel. Above 400 °C the wear rate increased for these three materials mainly due to the recovery and recrystallization processes. The wear rate of the high-Si steels increased with testing temperature. At 500 °C, these steels had the same hardness and the differences in wear were attributed to the changes in the material toughness.
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| 8. |
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| 9. |
- Hernandez, Sinuhe, et al.
(författare)
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Influence of temperature on abrasive wear of boron steel and hot forming tool steels
- 2015
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 338-339, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- In many industrial applications the occurrence of abrasive wear results in failure and replacement of components. Examples of these applications are found in mining, mineral handling, agriculture, forestry, process and metalworking industry. Some of these applications also involve operation of relatively moving surfaces at elevated temperatures which increases the severity of wear. A typical example of high temperature wear phenomena is that of tool steels during interaction with boron steel in hot forming. Some studies have been carried out regarding the high temperature tribological behaviour of these materials but results pertaining to their high temperature three body abrasive behaviour have not been published in the open literature. In this work, the high-temperature three body abrasive wear behaviour of boron steel and two different prehardened tool steels (Toolox33 and Toolox44) was investigated using a high temperature continuous abrasion machine (HT-CAT) at different temperatures ranging from 20 °C to 800 °C using a load of 45 N and a sliding speed of 1 ms-1. The wear results were correlated to the hot hardness of the different materials measured by means of a hot hardness tester (HHT) at a load of 10 kgf. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) techniques were used to characterise the worn surfaces. The hot hardness measurements of the three different materials showed a slight but continuous decrease of hardness from room temperature to 600 °C. At temperatures above 600 °C the hardness showed a sharp decrease. The wear rate of Toolox 44 was constant from 20 °C to 400 °C. On the other hand, Toolox33 and boron steel, showed a reduced wear rate from 20 °C to 400 °C attributed to an increased toughness and the formation of wear-protective tribolayers respectively. At higher temperatures (from 400 °C to 800 °C), the wear rate for these materials increased mainly due to a decrease in hardness and the occurrence of recrystallization processes.
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| 10. |
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| 11. |
- Mallipeddi, Dinesh, 1987, et al.
(författare)
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Surface integrity of machined electron beam melted Ti6Al4V alloy manufactured with different contour settings and heat treatment
- 2020
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Ingår i: Procedia CIRP. - : Elsevier BV. - 2212-8271. ; 87:20, s. 327-332
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Konferensbidrag (refereegranskat)abstract
- The powder-bed-fusion-based Electron Beam Melting (EBM) is rapidly gaining interest as a feasible process in the manufacturing industry for producing intricate Ti6Al4V components. However, there is still a challenge of reducing production time and optimizing surface roughness. One way to improve surface roughness is to optimize the melting strategy, i.e. contour setting. This not only influences the obtained surface topographical features, but also the production time. Most industrial applications require subtractive post processing (machining) to obtain a desired functional surface. This paper is concerned with analysing surface and subsurface in turning of Ti6Al4V alloy, manufactured by EBM using different contour settings. Also, the effect of subsequent heat treatment, i.e. Hot Isostatic Pressing (HIP) is studied. The results indicate that avoiding of contours require a machining allowance of 1 mm to obtain surface roughness of about 0.5 µm (Sa). In case of three and five contours the machining allowance can be reduced to 0.25 mm. Microstructural differences originating from the subsequent HIP operation show no effect on machinability. Tensile residual stresses are generated when reaching down to the heat effected zone of contour settings.
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| 12. |
- Tomala, A., et al.
(författare)
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Tribological performance of some solid lubricants for hot forming through laboratory simulative tests
- 2014
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 74, s. 164-173
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Tidskriftsartikel (refereegranskat)abstract
- Tribological research concerning sliding contacts at temperatures of 500–1000 °C has received limited attention. Industrial systems operating under high temperatures can be readily found in sheet metal forming processes. The control of friction during the tool-workpiece interaction and minimization of tool wear are both crucial in maintaining the products quality. The application of solid lubricants can be a possible approach in accomplishing these goals.The objective of this work is to investigate the reliability of combined model and component tests under solid lubricating conditions. The laboratory tests showed that both methodologies provide consistent results in exploring potential of the solid lubricants
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