ArcelorMittal’s S-in motion study focuses on solutions to lighten and strengthen today’s cars

November 2011- According to environmental case studies conducted by the World Steel Association, “for every 10 percent reduction in vehicle weight, fuel economy is improved between 1.9 percent and 8.2 percent. This range is based on driving cycle, vehicle size and powertrain selection.”

One material option for automakers who are striving to reduce weight is advanced high-strength steels, which, according to the Washington, D.C.-based American Iron and Steel Institute, can reduce structural weight by “as much as 25 percent and can cut total life-cycle CO2 emissions by up to 15 percent more than any other automotive material.”

To define the possibilities of automotive-grade steels, ArcelorMittal, which has U.S. and Americas headquarters in Chicago, embarked on a two-year research and development project called S-in motion, which focused on removing additional weight from a modern five-door, C-segment body-in-white using currently available steel grades and manufacturing processes.

“We have some very challenging new regulations coming for fuel economy and CAFE [Corporate Average Fuel Economy] requirements,” says Dr. Blake Zuidema, director, automotive product applications, Global Research and Development–East Chicago, ArcelorMittal. “The entire auto community, both the material suppliers as well as the designers, are scrambling to find the most cost-effective solutions to achieve these new standards.”

With S-in motion, ArcelorMittal wanted to “prove to ourselves as well as the automotive design community that there is still a lot of weight that can be taken out of the typical automobile body-in-white with just the advanced grades of steel that are commercially available to the carmakers today,” Zuidema says. “These are not future grades or what we call breakthrough or pie-in-the-sky or long-term-development products. All of the solutions we developed were with grades of steel that are available right now. Someone could start designing [these solutions] in a car tomorrow.”

Picking apart parts
S-in motion provides multiple solutions for 43 parts in a typical C-segment vehicle, and the study took into consideration the demanding North American rear-impact and side-impact requirements, demonstrating that weight savings between 12 to 19 percent could be achieved for body-side and rear modules.

According to the study, “manufacturers who implement the lightest solution for each part could save up to 19 percent of the typical vehicle weight based on a comparison with a baseline C-segment vehicle.”

Zuidema says the intensive study allowed the company to look at the limiting conditions of the parts. “Are they stiffness limited? Are they strength limited? If they’re strength limited, what do we need to make the parts as light as possible? S-in motion is the first step in the latest trend in materials development, which is reverse engineering where we use all the same tools that the OEM design community uses—design tools, structural models and crash models—in reverse. This enables us to see what properties are required to make that part perform as well as possible.”

S-in motion found B-pillars (the pillar between the rear and the front door on a vehicle) could combine laser-welded blanks with hot stamping to produce a part that features high-strength materials in the upper part but a lower level of strength in the lower part of the pillar.

The B-pillar design “allowed us to combine very high-strength [steel] in the upper part along with good energy absorption in the lower part with two different grades of steel that respond differently to the hot stamping,” Zuidema says. “That enables us to do multiple things with a single component. In this case, we were able to get a 20 to 25 percent weight reduction.

“One of the other things we found was in the passenger compartment. Many of the parts that form the safety cage that protects the occupants from intrusions during front, side or rear crashes and even for roof rollover, were strength limited and benefit from the application of some of the highest-strength steels we make,” he continues. “These insights are driving new directions in material applications.”

Joining multiple grades and gauges in hot stamping is “somewhat new,” according to Zuidema, and he expects laser welding to continue to branch into new applications, including exposed panels.

“There have been a couple of examples where laser welding methods have been used to join exposed panels,” he says. “The trick here is to put the laser weld in a fairly inconspicuous place where it is of minimal objection to the end consumer. There are some interesting ways you can hide the weld. I think it’s a very fruitful, potentially valuable application for laser welding, and I’m hoping that we’ll continue to break down some of the barriers to see even more of this in some of the exposed panels.”

A global effort
These and other solutions detailed in the S-in motion study focused on a full-vehicle perspective, allowing ArcelorMittal to evaluate an automobile on a much broader scale than it has done in the past, Zuidema says, calling the study “a global exercise on the part of ArcelorMittal.”

Automotive business accounts for 25 percent of ArcelorMittal’s total research and development budget. The company has several global laboratories that allow it to partner with carmakers on new products and processes: East Chicago, Ind.; Hamilton, Ontario; Maizéres, France; Montataire, France; and Gandrange, France.

“The resources of the global automotive R&D team were brought together for this project,” Zuidema says. “We actually had to develop two sets of solutions—one for Europe and one for North America—because the safety requirements and consumer expectations in Europe are quite a bit different than they are in the United States.

“ArcelorMittal also has a large number of subsidiaries that produce a wide range of steel products—stainless steels, long products, forging steels, as well as the the various flat steels for structural applications. We brought in experts to address the full range of products we can supply,” he continues. “We are also fortunate to have a number of part-manufacturing firms within the ArcelorMittal family. We brought them in as well to help with some of the manufacturing, costing and overall feasibility aspects. It was a true global effort.”

Thorough analysis is important to the automakers because it is imperative for them to make sure a new grade has been fully vetted before production begins.

“When a carmaker commits to putting a new grade of steel in a design, they’re making a huge commitment and taking a very big risk,” Zuidema says. “If they get through all the development cycles, which can last many months, and find themselves with an application they can’t really manufacture routinely or robustly, that can have huge ramifications on the timing of the program. Likewise, if they make it into production and later find issues, it can be extremely costly to them, both in terms of resolving the problem as well as reputation. They have to make sure that any new technologies are robust and ready to go. We’ve been working with them quite extensively to resolve the manufacturing challenges and to enable them to develop sufficient experience to convince them that these are things that can be implemented in robust, routine commercial production.”

New applications for steel in automobiles will help manufacturers come up with new designs that keep their products competitive while adhering to new regulations and consumer requirements.

“I can assure you somebody will find a way to make an affordable, low-cost, fuel-efficient vehicle that will appeal to consumers and meet all these challenges,” Zuidema says. “It is incumbent for us all to find the optimal solution.” MM

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