P 281.2 - Industrial use of steel sheet composites with foamed aluminium Project 2 - Production and technical application of sandwich composites made of steel sheets with foamed aluminium

P 281.1: Industrial use of sheet steel composites with foamed aluminium Project 1: Sandwich constructions made of sheet steel with foamed aluminium The aim of this project is the development, production and characterisation of a new sandwich composite material based on sheet steel and foamed aluminium. aluminium foam-steel cover sheet. Such a sandwich composite represents an innovative construction method for lightweight construction based on a combination of purely metallic components. It combines the low density and functional properties of the foam core layer, such as energy absorption capacity and reduced thermal conductivity, with the good strength properties, surface quality and excellent elastic properties of steel. The rigid sandwich composite is primarily suitable for lightweight construction applications where a combination of functionally and structurally relevant properties is required, as the greatest benefit can be realised synergistically from the advantages of the individual components. In principle, a sandwich structure consisting of an aluminium foam core layer and steel cover sheets can be produced using various processes. The focus of this project is the roll cladding of a foamable aluminium semi-finished product produced by powder metallurgy with steel cover sheets to form a composite sheet, which can then be foamed to form a lightweight sandwich. As part of the project, activities were undertaken with regard to the development and optimisation of the cladding process and the foaming process in sandwich production. Investigations into alternative manufacturing processes and tests to characterise the pore structure in the aluminium foam and the boundary layer between the aluminium core and the steel cover sheets complement the process parameter studies. The properties of the new material aluminium foam sandwich with steel cover sheets can be characterised using standardised and newly developed methods. Basic characteristic values for the foam core layer are obtained from the compression test and the shear test. The bending test characterises the sandwich composite under a realistic load, while the peel test provides information on the adhesion of the components. Technological tests such as buckling tests and corrosion tests provide information on further application properties. Initial positive results regarding the formability of the unfoamed composite sheet and the weldability of the sandwich are also available, as are findings on the functional properties of the aluminium foam core layer. With regard to a possible application, considerations have been made for the calculation and design of sandwich components that take into account the special properties of the material. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 1997 Authors: Dipl.-Phys. J. Baumeister, Prof. Dr W. Bleck, Dipl.-Ing. H. von Hagen, Dipl.-Ing. D. Nicklas, Dipl.-Ing. M. Paschen, Prof. Dr G. Sedlacek, Dr M. Weber

P 283: Suitability of clinching and self-pierce riveting for joining high-strength steel sheets High-strength steels have attracted increasing attention from the sheet metal processing industry over the past 25 years. The automotive industry in particular is interested in the use of higher-strength steels in view of its endeavours to reduce weight. At present, micro-alloyed, phosphorus-alloyed and bake-hardening steels as well as multiphase steels with different strength and forming properties are available. Only by using optimised joining techniques is it possible to utilise the improved strength of the materials in joined structures in the form of increased strength or reduced sheet thickness. Resistance spot welded joints of higher-strength sheet steel only utilise the advantage of higher joint strength under quasi-static loading. Under oscillating loads, especially in the direction of head tension, the increased strength of higher-strength steels compared to soft, unalloyed deep-drawing sheets cannot be converted into increased strength of the spot-welded joints to the desired extent. The mechanical joining processes clinching and punch riveting with their different process variants represent interesting alternatives to resistance spot welding. The suitability of various single-stage non-cutting, single-stage cutting and multi-stage clinching processes as well as self-pierce riveting with semi-tubular and solid rivets for joining high-strength sheet steel was investigated in this research project. High-strength sheet steel materials in the thickness range from 0.6 mm to 2.5 mm were selected as test materials. These included micro-alloyed, phosphorus-alloyed and bake-hardening steels as well as dual-phase steels with yield strengths of 195 MPa to 544 MPa. Overall, the investigated processes are well suited to joining the higher-strength steel sheets. Limitations were observed in some cases due to limited joining forces and the selected tool dimensions. However, by selecting suitable parameters, all materials investigated can be joined appropriately. Under quasi-static loading, the strength of the mechanically joined joints of high-strength steel sheets was almost linearly related to the yield strength of the joining materials. Depending on the joining method and sheet thickness, there were different increases in joint strength with increased joint strength. Fatigue tests were carried out in stages on spot-welded and mechanically joined, component-like H specimens made from the materials ZStE 180 BH, ZStE 420 and DP 500. The self-pierce riveted joints of high-strength steels exhibited higher joint strengths under fatigue loading than comparable spot-welded joints. The Wöhler curves of the clinched joints were very flat and intersected with the Wöhler curves of the spot-welded joints, i.e. at low load amplitudes the clinched joints had a longer service life than the spot-welded joints. In contrast to the spot-welded joints, the potential of higher-strength steels can also be converted into increased joint strengths under fatigue loading with self-pierce rivet and clinch joints. Tests under impact loads were used to gain knowledge about the suitability of mechanically joined components in crash-prone areas. With increasing joint strength, a reduced deformation of the test specimens was observed. The deformation was independent of the joining method used. Tool life tests were carried out on clinching tools from three suppliers on soft deep-drawing sheets and micro-alloyed high-strength steel sheets. The tool life of the tools was greater than 200,000 joining points. Significant differences between tool wear on soft and high-strength grades could not be detected despite the increased joining forces when clinching the high-strength steels. The joint strengths remained largely constant over the service life of the tools. Clinching and self-pierce riveting are alternatives to spot welding of high-strength steel sheets, which contribute to adequately utilising the strength potential of these materials, particularly in the form of improved fatigue strength of joined assemblies. STUDIENGESELLSCHAFT STAHLANWENDUNG e .V. Publication: 2000 Authors: Prof. Dr O. Hahn, Dr.-lng. A. Schulte, Dipl.-Ing. H. Herter, Dr.-lng. S. Göklü, Dipl.-Ing. T. Stegemann

P 286: Prospective market study on the application of steel foams New materials have repeatedly celebrated spectacular successes in recent years. The novel combinations of properties of the new material "metal foam" also open up new application possibilities for metals. In the past, processes for the production of metal foams were described in patent literature and in a few specialised publications, although these were mostly non-ferrous metal foams. In recent years, considerable progress has been made in the field of aluminium foams with two fundamentally new processes. In particular, the powder metallurgical process developed at IFAM has already been transferred to various other metals (Zn, Pb, Sn, etc.). Initial, orientating tests have shown that a large number of pores can also be isolated and frozen in molten steel powder compacts. From this it can be assumed that iron-based materials can also be foamed. In order to be able to focus further development work on potential products with high market interest, it made sense to start with a kind of "forward-looking market study". The aim was to identify resilient steel foam products with interesting market potential in advance of the development work. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 1995 Authors: Dipl.-Ing. M. Weber

P 228: Investigations into the applicability of pressurised nitrogen-alloyed martensitic steels for surgical instruments and high-quality cutlery Corrosion of conventional metallic household cutlery made of martensitic steels is partly caused by the constantly increasing contamination of water with chlorine ions. Another cause of rapid corrosion is the use of aggressive cleaning agents, disinfectants and sterilising agents. If, for example, surgical instruments are exposed to solutions containing extremely reactive hypochlorides, such as those found in disinfectants, for a long period of time, significant signs of corrosion can be observed. The use of an extremely corrosion-resistant steel, both for high-quality consumer goods in the cutting and cutlery industry and for cutlery for medical, especially surgical use, is therefore obvious. Pressurised nitrogen-alloyed steels are a group of materials which, in addition to the required high corrosion resistance, can also exhibit excellent wear resistance, which, for example, essentially determines the cutting ability and edge retention of cutting edges. Two variants of pressurised nitrogen-alloyed steels were investigated as part of this research project. These are the grades X15CrNiMoN15-2-1 and X30CrMoN15-1, each with 0.30 to 0.50 %N. The tests on the two steel grades show that these pressurised nitrogen-alloyed steels, used for the production of high-quality cutting tools, have a significant potential for increasing wear resistance in the cutting performance test and corrosion resistance in the alternating immersion test. Both the hardness of the X15CrNiMoN15-2-1 steel and the cutting performance results are well above the required minimum values. The steel showed no signs of corrosion in the alternating immersion test. The difference to samples made of steel without a higher nitrogen content is considerable, so that the steel grade with nitrogen is also suitable for aggressive environmental conditions or for the manufacture of surgical instruments. The steel grade X30CrMoN15-1 with a higher carbon content even surpasses these results. Both the hardness values and the cutting performance results are higher or better than those of the other steel. The corrosion tests show the same outstanding resistance to the NaCI solution in the alternating immersion test. If pressurised nitrogen-alloyed steel grades become established on the market for high-quality cutlery and surgical instruments due to the advantages shown, the industry will achieve a leap in quality in the manufacture of highly stressed products. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 1999 Authors: Dr.-Ing. A. R. Rosenthal