Comeback in Car Construction: Return from Aluminium to Steel
After experimenting with aluminium in its luxury models, Audi returns to steel in the A8. The new model, which is due to be launched in 2018, also features steel solutions from Arcelor Mittal.
Next year, it is to be launched on the market: more than 40 % of the body of the new Audi A8 will be made of steel. This is in line with the trend among automobile manufacturers to use high-strength steels in new cars. It is a clear departure from the pure aluminium bodyshell, which Audi developed for the A8 in 1994.
Since then, steel has evolved enormously as a material. The tensile strength of steel has increased almost tenfold in the last 20 years, from 270 to 2,000 MPa. Arcelor Mittal is currently developing more than 80 new steel products. The steel range for the automotive industry comprises almost 200 special steel grades, half of which have been launched in the last ten years.
Almost One-Fifth of the Audi Body Made of Press Hardened Steel
Approximately 17 % of the body of the new A8 will be made of press hardened steel (PHS), some of which will be supplied by Arcelor Mittal. These steels have yield strengths of up to 1,500 MPa after press hardening. The weight-specific strength of these steels also exceeds that of the highly developed — and more expensive — aluminium grades.
Thanks to the development of new joining techniques, it is now easier than ever for automobile manufacturers to integrate high-strength steels into their vehicles. As these techniques are now fully developed and adopted by car manufacturers, a strong increase in the use of PHS in multi-material vehicles is expected. “Usibor is our main hot stamping product and has been a major commercial and technological success in the automotive industry worldwide," said Brian Aranha, Vice President of Arcelor Mittal Global Automotive. “The introduction of even more advanced products such as Usibor 2000, which is 10 to 15 % lighter than the previous hot-formed steels, will further increase the use of hot-formed products in vehicles in the future." Usibor is comparable to conventional press hardening techniques and processes. The combination of Usibor and Ductibor for laser-welded blanks offers several clear advantages, such as weight savings, more favorable crash behavior and cost savings through material and production optimization.
Steel Cars are "Green" Because They Have a Favorable Life Cycle
Dr. Bernd Mlekusch, Head of Audi's Lightweight Construction Centre, explains: "In the future there will be no cars that are made solely of aluminium. Press hardened steels (PHS) will play a special role in this development. PHS steels form the heart of a car's passenger compartment and protect the occupants in the event of a crash. PHS is superior to aluminium in terms of stiffness in relation to weight."
The turnaround from Audi back to steel is in line with an increasing trend that, according to the Steel Market Development Institute (SMDI), also exceeds the expectations of steel producers. Between 2006 and 2015, the use of high-strength multiphase steels in vehicles increased from an average of 36.7 kg per vehicle to 124 kg. That is a threefold increase in just ten years. Even more surprisingly, the use of high-strength steels has risen by around 10 % annually between 2012 and 2015, significantly more than forecast by steel producers.
Arcelor Mittal and the steel industry as a whole have jointly informed car manufacturers and other stakeholders about the importance of considering the Life Cycle Assessment. The Life Cycle Assessment takes into account the sum of emissions during the three phases of a vehicle's life cycle: production, use and disposal. To date, the regulations have only covered tailpipe emissions during the use phase," explains Brad Davey, Chief Marketing Officer of Arcelor Mittal NAFTA and Global Automotive. Studies show that aluminium produced in North America produces four to five times more greenhouse gas emissions than steel. In addition, aluminium production requires seven times as much energy as steel production. “If we want to determine how 'green' a vehicle really is, we need to measure emissions throughout its life cycle. Otherwise, the choice of a different material instead of high-quality steel will lead to a serious, irreversible environmental error," says Davey.
This article was first published by blechnet.
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