With Ford moving to aluminum body panels for the F-150 pickup and General Motors using carbon-fiber reinforced plastics in the Corvette, the automakers say they need to cut weight from vehicles to improve performance and fuel economy. Yet steel remains the leading material, by volume, in almost every car on the road.
Dr. Blake Zuidema, director of automotive product applications for global steelmaker ArcelorMittal, says the metal that has dominated the car business for more than a century isn’t going anywhere. Continued investments in new steel formulas and new production techniques let companies continue to use the relatively inexpensive metal, despite the need to shave weight wherever possible.
Zuidema recently talked about why steel will continue to be important for automakers.
TMV: With fuel economy targets getting more stringent, what can steel producers do to help?
BZ: In Europe, the target is 95g of CO2 per kilometer by 2021; and for NAFTA the target is 54.5mpg fuel efficiency by 2025, in two phases. The solution for both is essentially the same: deliver a 25% reduction in the weight of structural components and closures, or the body-in-white. The total weight of these parts typically ranges from 600kg to 800kg (1,300 lb to 1,750 lb). So that means we need to lighten them by 120kg to 160kg (264 lb to 350 lb).
The steel industry is constantly in a state of technological revolution. Our steels for the automotive sector are a perfect example. Steel’s strength has multiplied by almost 10 times during the past 20 years, from 270MPa to 1,700MPa tensile strength. These are phenomenal changes. And we don’t know where the limit is in terms of product development. Every day we open up new frontiers and do things which yesterday didn’t seem possible.
TMV: Will automakers have to turn to aluminum, magnesium, carbon fiber, and other materials to get the weight savings they need?
BZ: Steel can provide all the weight reduction that auto producers require to satisfy the new fuel efficiency standards, for all types of vehicle. That may come as a surprise to some. Other materials talk about being 30% or 40% lighter than steel, but that’s only accurate if you are using the steel of 2005 as a comparison. Today, we are working with completely different steels, which are the results of hundreds of millions of dollars of investment.
This includes our S-in-motion range of products. S-in-motion is a collection of more than 60 different advanced high-strength steels (AHSS) and ultra-high strength steels (UHSS) that can collectively take the weight out of a vehicle. These include both cold-stamped and press-hardened steels like our groundbreaking technology called Usibor UHSS.
When parts require the highest strength, Usibor provides the lightest solution of any materials. A great example is the award-winning, laser-welded, hot-stamped door ring co-developed with Honda for its 2014 Acura MDX. Not only did it achieve an 8 lb reduction in weight, but also the highest available collision safety rating from the Insurance Institute for Highway Safety.
Steel lightweighting in the Acura MDX
Working with American Honda and Manga International’s Cosma International operating unit, ArcelorMittal designed a custom door ring for Acura’s 2014 luxury crossover. The door ring replaced a multi-piece spot-welded assembly with a single, high-strength unit.
Ring production starts at ArcelorMittal Indiana Harbor in East Chicago, Ind., with Usibor 1500, an aluminum-silicon coated, advanced high-strength steel. The Usibor sheets are prepped at Delaco, an ArcelorMittal joint venture operation in Dearborn, Mich., to begin the blanking process. The blanks then go to ArcelorMittal Tailored Blanks in Pioneer, Ohio, where lasers remove the aluminum-silicon coating at points where it will laser-weld sheets of various thicknesses to create the blank. Without removing the coating, the weld point could become weak or subject to corrosion.
After the laser ablation, a quality control process is done both visually and via a high-tech process to ensure precision. Once the finished laser-welded blanks successfully pass inspection, they are shipped to Cosma where they are hot stamped into the finished door ring. Cosma then ships the parts to Honda’s Lincoln, Ala., plant where they become part of the MDX.
Honda expects to produce approximately 70,000 2014 Acura MDXs. With a weight savings of 8.6 lb per vehicle, this single application will reduce Honda’s fleet mass by about 602,000 lb, reducing carbon emissions during the vehicle’s useful life.
TMV: What sort of responses have you seen to the new alloys?
BZ: We sense that carmakers in North America see the value of light weighting with today’s commercial and emerging advanced steel grades, and their use of these grades continues to grow every year. In fact, use of our Usibor press-hardened steels is today growing faster than that of any automotive material.
TMV: What other advantages do you talk about with your customers?
BZ: We talk frequently about the total life cycle carbon emissions advantage of light-weight steel solutions. Making a ton of steel produces far less CO2 than producing a ton of aluminum, or magnesium, or carbon fiber. As a result, the as-manufactured carbon footprints of these alternative material vehicles are significantly higher than that of a lightweight AHSS vehicle. Despite the alternative vehicles’ slightly lower weight and lower use-phase CO2emissions, their manufacturing-phase disadvantage is never offset, and over the total vehicle life, the total life cycle carbon footprint of the AHSS vehicle will be smaller and friendlier to the environment.
TMV: If automakers reduce vehicle weights by using high-strength steel, volume shipments will fall. Do you expect the higher prices for more advanced materials to make up for the lower volumes?
BZ: This is always a difficult question to answer. On one hand, yes, lighter steels mean less steel per car. But we are also in a growing car market in North America, still coming out of the Great Recession. Building more cars each year will require more steel. Time will tell.
TMV: As you increase the strength of steel with the new alloys, will automakers have to invest to improve their blanking, cutting, stamping, and welding operations?
BZ: No. One of the huge advantages of lightweight steel is that it can be manufactured within the OEMs’ existing manufacturing infrastructure without any significant investment.
TMV: More multi-metal vehicles are entering production. What sort of R&D is ArcelorMittal doing to solve corrosion and other technical challenges for multi-metal construction?
BZ: ArcelorMittal is beginning to commercialize a new coating composition with a combination of zinc, aluminum, and magnesium. This new coating has proven to provide good protection where steel and aluminum come in contact. These coatings are already being used by car makers to make hybrid steel-aluminum doors – an aluminum outer panel joined to a steel inner door.