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Austenitic stainless steels reduce the weight of individual components by about 20 per cent
By Dean Jobb
Nickel Magazine, December 2008 -- “Any customer can have a car painted any
colour that he wants,” automotive pioneer Henry Ford once famously quipped. “-- so long as it is black.”
Likewise, today’s vehicle manufacturers could be soon producing cars and trucks with any frame the
customer wants, so long as it contains plenty of stainless steel.
A consortium of European carmakers and stainless steel manufacturers has spent three years testing
stainless steels for use in door pillars and other structural components of vehicle frame. The results show
that stainless – particularly nickel-containing-austenitic grades which gain strength as they are formed or
deformed – can replace carbon steel, saving weight without compromising the properties needed to protect
occupants in a crash.
With gasoline prices on a roller coaster ride and demand growing for hybrid and fuel-efficient vehicles
that cut greenhouse gas emissions, North American carmakers appear eager to change course.
“Weight costs money, it costs efficiency, and it costs fuel; it’s as simple as that,” says Roland
Gustafsson, manager of the consortium’s research project known as Next Generation Vehicle (NGV). “Every kilo
you can lose results in savings over the life of the car. When you have lower weight, you can redesign other
systems in the car. It’s a beneficial spiral: you can reduce the engine size, you can reduce the
gearbox.”
The NGV project was launched in 2005 by nine companies that provided research and test facilities and
brought together more than 150 engineers, scientists and software developers to explore ways to add stainless
components to cars. Audi, BMW, Fiat, DaimlerChrysler, Saab Automobiles and Volvo Car joined forces with
Outokumpu, ThyssenKrupp and ArcelorMittal Stainless Europe (Ugine & ALZ). The partners have so far
invested 5 million euros in the project, on top of donating research time and facilities, says
Gustafsson.
The results of the program were unveiled in late 2007 at the International Motor Show convention in
Frankfurt, Germany. Four grades of stainless were tested to determine their suitability in carmaking based on
mechanical properties, corrosion resistance, and their ability to be formed, machined and joined to other
materials. Three were austenitic steels: 1.4376 (S20100),
1.4318 (S30153)
and 1.4310 (S30100);
the fourth, 1.4162 (S32101),
was a duplex.
“The goal was to show the world it’s possible to use stainless steel for this type of application,” notes
Eric Sörqvist, manager of research and development for Outokumpu Automotive, a division of Finnish stainless
steel producer Outokumpu. Results for all four grades were excellent.
“The stainless steel lends itself well to making complicated components or components that require high
localized strength levels,” he says. “We know stainless steel can’t replace all materials, but in certain
spots and in certain applications, yes, there are advantages.”
One major advantage is weight. The NGV project confirmed that replacing sections of vehicle frames with
stainless can trim as much as 20 per cent off the weight of the component. Gustafsson, whose full-time
position is head of Volvo Technology Corporation in Gothenburg, Sweden, says it’s crucial that there be
compensation for all the additional weight coming in with the next generation of vehicles. As the industry
switches to building hybrid cars the weight savings achieved with stainless steel compensates for the added
weight of the electric motor and batteries that provide the second power source.
The austenitic grades, in particular, are well-suited to car manufacturing. They become stronger as they
are hydro-formed or cold-rolled into the shape of components, and this strength is necessary to meet
crash-safety standards. As well, the production processes create less scrap, saving material and reducing
costs.
The NGV project showed that stainless can be welded to the carbon steels now used in car frames; as a
result, carmakers can continue to use traditional metals while adding stainless where it works best. The
grades tested are readily joinable with basically all other types of steels, says Sörqvist, adding that
adhesives and waxes are used to prevent corrosion from developing at the joints.
Project engineers used nickel-containing stainless steel to build parts of a door post (known as a
B-pillar) for a Volvo S40, confirming that the material can be formed and joined with conventional steels and
is capable of withstanding crash testing. But Sörqvist says the project’s most remarkable breakthrough may be
the development of software programs that simulate all stages of production, taking metal through each step
of forming and welding. The programs enable engineers to see how substituting grades and fabrication
processes can improve the finished part.
“Without the software, it wasn’t really possible to simulate this in a proper way, taking into
consideration the deformation hardening and the way that happens,” he says. “It’s a big step forward,”
enabling carmakers and other manufacturers to determine the best materials and applications without having to
build and test parts that won’t make the grade. “It’s important for the use of austenitic materials in any
kind of application.”
As for automobiles, both Sörqvist and Gustafsson say the lighter weight of stainless steels and the fact
that austenitic grades can be made stronger during forming mean it is now possible to design vehicles from
the ground up, as it were.
The next stage is to produce a prototype of a complete vehicle frame using stainless steel components.
Toward that end, the NGV project is seeking North American carmakers as partners. Gustafsson says General
Motors, which is struggling to cope with the global economic crisis and increased demand for fuel-efficient
vehicles, has expressed interest.
“Our goal is to expand the Next Generation Vehicle project to North America,” he adds. “I would love to be
at the Detroit Motor Show in 2010 to show a complete vehicle structure made of these materials.”
Photos: Next Generation Vehicle Project and iStockphoto.com / Arno Massee
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