Abstract
KEYWORDS
Lightweight construction; aluminium; multiphase steels; mild steel; TRIP steel; dual phase steel; duplex steel
ABSTRACT
The design criteria of a modern automobile with a reduction in weight and high safety requires new lightweight construction methods and/or new materials, with an increased formability and with a high strength level at a wide strain rate spectrum. In recent years a lot of new developments have been done in this field. One development was the use of aluminium in designing the whole car body with this light material. Another development, which leads to an extremely good relationship between lightweight construction, safety, easy to repair and easy to recycle, was the development of new steels, the so called multiphase steels with new hardening mechanism. These materials are now available. Tensile strengths reaching from 500MPa to more than 1400MPa can be achieved by a specific combination of the microstructure components in combination with individual process parameters. For example it has now been shown how the properties of these steels can be influenced by utilising the microelements niobium and titanium. These elements, which act in solid solution and also in the precipitated condition with the elements carbon and nitrogen, are added to the steel for getting a better microstructure with an extraordinary combination of the materials properties. The differences in the properties of these materials like mild steel, dual phase steel, duplex steel and TRIP (transformation induced plasticity) steel are presented. Comparisons of the ductility-strength relation and also the specific energy absorption, between these different steel grades and aluminium and magnesium based materials, give the data basis for engineers for modern car body design. Especially the extraordinary strength-ductility relationship of the TRIP steels offers new possibilities for significant weight savings and good body stiffness.