Audi’s A8 switches back to steel after experimenting with aluminium in its luxury models. Scheduled for release in 2018, the body structure of the new A8 will be made up of over 40 percent steel, following the trend to use more advanced steels. That’s a marked turnaround on the all-aluminium body-in-white which Audi developed for the A8 in 1994.
Steel has moved on dramatically since the 1990s. Around 17 percent of the new A8 body structure will be comprised of press hardenable steel (PHS), some of which will be supplied by ArcelorMittal. These steels have yield strengths up to 1500 MPa after press hardening. The strength-to-weight ratio of these grades outperforms even the most advanced (and costly) aluminium.
Dr. Bernd Mlekusch, head of the Audi’s Leichtbauzentrum
|Old A8 D4 (2009)||New A8 D5||Change|
|Steel||8%||40.5% (17% PHS)||+32.5%|
One area that benefits is safety. Dr. Bernd Mlekusch, head of the Audi’s ‘Leichtbauzentrum’ (Lightweight Construction Center) was recently quoted as saying that the use of more steel in the new Audi A8 should help to improve the way cars are made lighter: “There will be no cars made of aluminium alone in the future. Press hardened steels (PHS) will play a special role in this development. PHS grades are at the core of a car’s occupant cell, which protects the driver and passengers in case of a collision. If you compare the stiffness-weight ratio, PHS is currently ahead of aluminium.”
(source: Frankfurter Allgemeine Zeitung, ‘Audi: more steel in cars in the future’, published 11 April 2017)
Audi’s switch back to steel is part of a growing trend which is even surpassing the expectations of steelmakers according to data released by the Steel Market Development Institute (SMDI). Between 2006 and 2015, the use of advanced high strength steels in vehicles has grown from an average of 81 pounds per vehicle (36.7 kg) to 275 pounds (124 kg) in 2015. That’s a threefold increase in just ten years. What’s more surprising is that over the period 2012 to 2015, the use of AHSS has increased by around 10 percent each year, well above steel industry forecasts.
Incerease of AHSS
With the advent of new joining technologies, it has never been easier for automakers to incorporate advanced high strength steels into their vehicles. As these technologies mature and are adopted by carmakers, the use of PHS in the multi-material vehicles of the future is set to grow strongly.
ArcelorMittal and the steel industry as a whole have been working collaboratively to educate automakers and stakeholders on the importance of life cycle analysis, or LCA. LCA looks at total emissions generated during the three stages of a vehicle’s life – production, drive phase and disposal.
“Right now, regulations only consider tailpipe emissions generated during the drive phase,” said Brad Davey, chief marketing officer, NAFTA and global automotive for ArcelorMittal. “However, each material used in vehicle production contributes to lightweighting and improves fuel economy, but each does so at a different cost to the manufacturer – and to the environment.”
Studies show that aluminum emits four to five times more GHGs than steel. “If we want to know how “green” a vehicle really is, we have to measure emissions over its entire life cycle. Otherwise, choosing an alternative material over advanced steel will result in a huge and irreversible environmental mistake,” said Davey.