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Products and solutions, 2003-09-09, 02:00 AM

ThyssenKrupp Stahl supplies high-performance steels for the VW Touareg and Porsche Cayenne

At the IAA 2003 Frankfurt Motor Show, ThyssenKrupp Stahl AG is presenting the body-in-white of Volkswagen`s new sport utility vehicle (SUV), the Touareg. Along with the Porsche Cayenne, an SUV built on the same platform, the Touareg features more modern multi-phase steels in its body than any other production car. It achieves top ratings in terms of crash behavior and body stiffness, even with its relatively low BIW weight of 392 kilograms. 64 percent of the BIW is made of high-strength or ultrahigh strength steels. This includes many complex-shaped components, showing that the boundaries for using high-strength steels in car manufacture have been pushed back significantly. 28 percent of the BIW of the Touareg consists of modern multi-phase steels supplied along with other high-strength materials by ThyssenKrupp Stahl AG.

In recent years, the Duisburg-based company has introduced improvements to more than half of its steel grades and in the process resolved the conflict between high strength and good forming properties, among other things with a broad range of new multi-phase steels. These materials offer outstanding strain hardening properties, based on a tailored combination of hard and soft microstructure phases. In the case of the dual-phase steels, for example, the microstructure consists of soft ferrite with embedded hard martensite islands. The multi-phase steels also include the so-called TRIP steels which have a mainly bainitic-ferritic structure and embedded islands of retained austenite which transform into hard martensite during stamping operations. TRIP stands for Transformation Induced Plasticity.

The Touareg has a unibody structure with integrated frame. The load-bearing structure of the body-in-white with side beams, A and B pillars and side roof frame is made almost entirely of multi-phase steels. With tensile strengths of 600 and 700 megapascals (MPa) after forming and correspondingly high energy absorption capacity, these materials ensure safety both in the body`s crumple zones and in the passenger cell. Additional passenger protection in the event of side impact is provided by a B cross rail made of the complex-phase steel CPW 800 from ThyssenKrupp Stahl with a tensile strength of 800 MPa in delivered condition. It connects two seamless drawn reinforcing tubes with strengths from 1,400 to 1,800 MPa. The tubes extend along each side of the vehicle between the wheels.

Depending on load requirements, the components in the Touareg`s body are joined by resistance spot welding and laser beam welding, laser brazing, MIG brazing and MAG welding. It has been shown that multi-phase steels can be processed reliably and effectively with modern joining techniques. One highlight is the roof joint, produced by laser brazing. This high-speed process produces reliable and reproducible joints requiring practically no reworking. As shown in the development of the SUV, multi-phase steels have the same fatigue strength in shear as mild deep drawing steels.

Lightweight steel construction with supreme safety and stability levels: the Touareg shows how the potential of modern high-strength and ultrahigh-strength steels can be exploited consistently through innovative design solutions and efficient joining techniques. The stiffness of the body is shown in a typical load situation for SUVs, maximum torsional loading in an off-road situation: even when one of the wheels is no longer in contact with the ground, all doors and the tailgate can be opened and closed without difficulty. The static torsional stiffness of the Touareg body is 36,900 Newton-meters per degree - a top value in the sport utility vehicle segment.

ThyssenKrupp Steel AG
Dietmar Stamm
Tel.: +49 203 / 52 - 2 62 67
Fax: +49 203 / 52 - 2 57 07

Bernd Overmaat
Tel.: +49 203 / 52 - 4 51 85
Fax: +49 203 / 52 - 2 57 07

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