Steel Gets Strong. Economical. And Environmentally Correct.
Companies working to achieve 2025 fuel economy goals through mass reduction may be looking at non-ferrous alternatives for body-in-white applications. But they just might look again at steel.
Although it might seem as though materials including aluminum and composites of various compositions are where the action is when it comes to new developments for auto applications, steel is not taking the proverbial back seat to any material in this regard, says Dr. Blake Zuidema, director, Automotive Product Applications, ArcelorMittal (arcelormittal.com). Sure, he works for a steel company and he’d be likely to say that.
Zuidema makes a compelling case for the ferrous material, checking off all of the key categories of concern for those charged with creating new cars and trucks.
As in cost. Safety. Environmental correctitude.
Did I mention cost?
Could there be a more to-the-point rationalization for the use of advanced steels than this: “By going to advanced steel grades, the OEM community can save billions of dollars in stamping and assembly infrastructure than if they went to an alternative lightweight material.”
Yes: Billions. Of. Dollars.
“In assembly plants,” he notes, “the numbers get very large, very quickly.”
Now while costs are an abiding concern, there is also the challenge of lightweighting vehicles, especially as vehicle manufacturers work their way toward the 54.5-mpg mandate of 2025.
“Based on public domain information we’ve been able to gather from the EPA and NHTSA, accounting for all of the powertrain improvements that are expected between now and 2025, accounting for the improvements from electrification and the degree to which these electrified powertrains are likely to penetrate the new vehicle fleet by 2025, and accounting for all of the non-body-in-white weight reductions that are reasonably achievable, there is still a gap,” Zuidema says.
So what’s an OEM to do?
“The only way to close that gap and get to the 2025 mandate is through additional body-in-white weight reductions, and we calculated that it is going to take, on average, about 20 to 25 percent body-in-white weight reductions, based on the 2009 baseline on which all of the EPA and NHTSA rules were based, to achieve the fuel economy.”
Zuidema explains that ArcelorMittal has been working its way toward vehicular mass reduction for a number of years. In 2010, for example, the company, through a program it calls “S-in motion,” set about to lightweight a C-segment compact car. They selected a baseline of vehicles that were introduced in the 2006 timeframe. The result of applying an array of materials, some 36 percent of which are advanced high-strength steels, they essentially replaced 43 parts and ended up with a weight reduction on the order of 16 to 20 percent. While there were processes used that weren’t necessarily mainstream back then—like hot stamping—Zuidema stresses that it was just an initial step.
In 2014, he continues, they developed a solution for full-size pickup trucks. Here, they addressed the cab, front and rear doors, box, tailgate and frame. The baseline were pickups launched in 2010. Here, they were able to achieve weight reduction on the order of 23 to 26 percent.
“Today, we’re rolling out our latest set of S-in motion solutions for a platform of midsize cars and sport utility vehicles. In this we’re achieving a 20 to 26 percent weight reduction against a baseline of vehicles entering production in roughly the 2013 timeframe.”
While the company has been hard at work developing new materials (e.g., “Our new Fortiform series of third-generation advanced high strength steels is relying on a process called ‘quenching and partitioning,’ which allows us to do with process that which would normally require heavy alloying and thereby it allows us not only to keep the cost down by keeping the alloys fairly lean, but it also allows us to maintain good manufacturability: By keeping the alloys down, we make it easier to paint, coat and maintain good surface quality.”), they’ve gone well beyond the simple part replacement to performing structural optimization.
“We are applying the same body structure design tools that are employed by the automotive body design community,” he says. And not only are they using those tools to design parts, but to actually develop steels.
That is, he explains that ArcelorMittal designers, without consulting the grade book that’s full of information about the existing steels, design parts such that they are light, low cost and safe. That information is then used to determine the hypothetical grades that would be necessary to fulfill those requirements. That is taken to the product development team, which is charged with creating the processes and the structures needed to meet the requirements.
“Rather than doing something in the laboratory and coming up with a grade and then finding an application for it, we are looking at each application in a car structure and then determining, from a body structure design and performance standpoint, what the optimum grades are.”
But know that there is a need not only for the materials, but from doing load-path optimization. Looking at the weight reductions that they now calculate can be achieved, Zuidema reckons that about two thirds come from the material and the remainder from doing structural optimization.
“But it isn’t just about weight reduction,” he says. “We’re also working to improve safety.”
Nowadays, it seems as though there isn’t a new car, crossover or SUV introduced that doesn’t have a considerable amount of hot-stamped steel making up the passenger compartment. These materials can absorb loads without buckling. But there are other instances—like front rail end tips—where deformation is sought so that crash energy is absorbed. Zuidema says that in their development of the midsize car/sport utility case the baseline vehicles didn’t perform well on the shallow offset crash tests but their model made the grade.
At what cost is all of this achieved? Zuidema admits that compared to steels from back in the day, “The cost of a coil of steel on a per ton basis is certainly going to be a little bit higher as the sophistication of the grades goes up—but we’re finding that in many cases that while we’re increasing in terms of the cost per ton, we are using fewer tons so it is almost a dead wash.”
And for the end customers of vehicles who may be environmentally inclined? “Using the most credible, scientifically defensible input assumptions for life-cycle analysis, we’re showing that steel still provides the lowest carbon footprint.”
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