| 1. |
- Heikkilä, Irma, 1965-, et al.
(författare)
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Clean forming of stainless steel and titanium products by lubricious oxides
- 2012
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Ingår i: Proceedings of NORDTRIB. - Trondheim : NTNU. - 9788214052701
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Konferensbidrag (refereegranskat)abstract
- Big social benefits can be attained through increased use of stainless steel or titanium in new sheet metal applications. Unfortunately, forming of these materials is often a challenging and costly operation, that can lead to environmental and health problems when solving the technical limitations. One possible method to overcome these problems is to use an oxide layer with optimised properties to reduce friction during forming, either as a substitute to lubricants, or acting as a conversion layer for environmental friendly lubricants. The most beneficial group of oxides for low friction is called lubricious oxides with a rutile crystal structure. Oxides of Ti, Mo, V, and Zn can build rutiles under certain contact temperatures during rolling and forming. The aim of this investigation is to evaluate if oxides designed on metal sheets display a lubricious effect under conditions similar to industrial forming processes. Preliminary evaluations show a beneficial influence of two oxides types, on stainless steel and on titanium. More work is needed to test the lubricating effect in other forming operations and to analyse the sustainability aspects for products manufactured with this alternative surface.
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| 2. |
- Hutchinson, Bevek, et al.
(författare)
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Vanadium microalloying for ultra-high strength steel sheet treated by hot-dip metallising
- 2017
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 33:4, s. 497-506
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-high strength steel sheets have been subjected to heat treatments that simulate the thermal cycles in hot-dip galvanising and galvannealing processes and evaluated with respect to their resulting mechanical properties and microstructures. The steels contained suitable contents of carbon (∼0.2%), manganese (1.2%) and chromium (0.4%) to ensure that they could be fully transformed to martensite after austenitisation followed by rapid cooling in a continuous annealing line, prior to galvanising. Different contents of vanadium (0–0.1%) and nitrogen (0.002–0.012%) were used to investigate the possible role of these microalloying elements on the strength of the tempered martensite. Vanadium, especially when in combination with a raised nitrogen content, helps to resist the effect of tempering so that a larger proportion of the initial strengthening is preserved after the galvanising cycle, giving tensile strength levels exceeding 1000 MPa. Different deoxidation practices using aluminium or silicon have also been included. These showed similar strength levels at corresponding carbon contents but the bendability of the Si-killed steel sheet was considerably superior. Microstructural examinations have been made on the annealed steels but the reason for the beneficial effect of vanadium is still not fully explained. It is concluded that microalloying with vanadium is a very promising approach in the development of corrosion-resistant ultra-high strength steel sheet products.
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| 3. |
- Martin, David, et al.
(författare)
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Analysis for robust sheet forming processes at high temperatures - Hotform : Analyser för robusta plåtformningsprocesser vid höga temperaturer - Hotform
- 2015
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Rapport (refereegranskat)abstract
- Project vision Building accurate and robust models of the hot forming process requires a detailed understanding of a number of key technical questions pertaining to what is a technologically very complex process, including: The physical metallurgy, microstructure and properties of modern hot formable steels during and after the hot stamping process The thermophysical properties (thermal diffusivity, thermal expansion) of modern sheet steels and modern tool materials used in the hot stamping process The constitutive behavior (strength, work hardenability, anisotropy) of the sheet material during forming Real temperature-time histories of the formed sheet during hot forming, and heat transfer between sheet and tool The behavior of the Al-Si coating applied to modern hot formable steels during heating and forming The role of tool material and surface finish and the influence of different classes of surface coatings on the tribology of the hot forming The answers to these questions can be distilled down into a series of technical parameters and material data which are required for use in finite element simulation. The project aimed to develop methods and conduct experiments which would provide these technical parameters as a way of improving the quality and usefulness of finite element simulation tools for the hot stamping process. The overall goals of the project were Increase understanding of technical features of the hot forming process Develop new experimental methods for the analysis of hot forming Enhance forming simulation accuracy Shorten lead time for tool production To maximize the efficiency of the forming tools relative to the cost Increased productivity of the hot forming process
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| 4. |
- Melander, Arne, 1948-, et al.
(författare)
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Spring back evaluation for high and ultra high strength sheet steels with the bending under tension machine
- 2015
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Ingår i: International Journal of Material Forming. - : Springer. - 1960-6206 .- 1960-6214. ; 8:1, s. 137-144
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Tidskriftsartikel (refereegranskat)abstract
- The Bending Under Tension (BUT) machine is used for evaluation of spring back in sheet metal forming. A strip is drawn over a rotating cylindrical die with different restraining forces. The strip is allowed to spring back after drawing and the curvature of the strip is measured. The loading sequence is typical to wall sections of pressed components, side wall curl, where the material has been bent, unbent and finally unloaded. The test was performed on four high and ultra high strength steels with tensile strengths in the range from 800 MPa to 1300 MPa. A clear separation of the data for the four steels was demonstrated. It was analysed to what extent the differences in spring back between the different steels was related to the differences in tensile strengths. A finite element simulation model was used to simulate the strip curvature after BUT testing. The material parameters of the model were fitted to monotonic uniaxial and equibiaxial tests and uniaxial cyclic tests. The model could describe the experimental data in a satisfactory way.
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