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from the traditional to something diferent, from steel to aluminum? Hall answers that overall, the required changes to handle advanced high- strength steels (AHSS) from mild steels are "more incremental" than going from mild steel to aluminum. "You can use the existing structure, but maybe make some modifcations." For example, there might be increased tooling costs for handling AHSS, but the front-of-the- line systems—like the magnetic loading devices for the stamping presses—don't have to be replaced. If cost is the key consideration, then that's something that needs to be considered. But there are some instances where the AHSS materials require a signifcant change in the way parts for body-in- white applications are performed. For example, there are the frst-generation AHSS materials, martensitic grades, that have to be hot stamped or roll formed in order for them to achieve their properties. The materials may have the high strength that OEMs are looking for (>800 MPa) for applications like B-pillars and roof rails (the material is very good at repelling intrusion into the passenger compartment), but the processing is costly. "Automakers," Hall says, "would like to replace that techno- logy with something they can stamp in their current plants at room temperature." Which leads to the development of third-generation advanced high strength steels (3GAHSS). ("Wait a minute," you might be thinking. "This has gone from frst-generation to third-generation. What about the second?" According to Hall, there are second-generation materials that ofer "really good elongation and pretty good strength." These materials are austenitic stainless and TWIP (twinning-induced plasticity) steels. Because of their stain- less chemistries, which means alloying elements like chromium and nickel, they tend to be more expensive. What's more, they weld diferently than other steels. So, Hall says, these materials don't have a great deal of application in auto.) And 3GAHSS leads to another acronym, ICME. That stands for "Integrated Computational Materials Engineering." Which is essentially a method by which there is the use of computer-aided design of multiphase steel microstructures with the goal of developing materials that have high strength and good ductility.* A four-year ICME project with funding from the U.S. Department of Energy ($6-milion with 30% in-kind matching) and the participation of FCA, Ford and General Motors, SMDI, universities, engineering companies, and a national lab was initiated in 2013. The objective is to develop two steels that are highly ductile but strong: • 12,000 MPa tensile strength with 30% elongation • 15,000 MPa tensile strength with 25% elongation So far, two years in, they've developed limited quantities of the frst material, a duplex TRIP (transformation-induced plasticity) steel. They are getting closer to the second, Hall says, but the elongation metric hasn't been met. These steels, she explains, would allow vehicles to be built that are both light and strong (light because the materials are strong, thereby resulting in the opportunity to use thinner gauges), and without huge changes to the stamping or body shops. The elephant in the ofce is the 2015 Ford F-150. The Ford Dearborn Truck Plant is approximately 15 miles to the southeast of Hall's ofce. If anyone talks about the F-150, the words aluminum truck are certainly part of the conversation. "But with a steel frame," Hall interjects. Clearly, the auto industry is undergoing a transition from what has, with few exceptions, been a steel-centric process and product to one that is more of a multi-material mix, with the primary alternative material being aluminum. (Hall cites an article from 1953 in an automotive magazine that claimed that by 1960, steel would be replaced in cars by aluminum, magnesium and plastics. It's not that some things never change; it's that some things don't change a whole lot.) But what is happening is that there is the replacement of steel for things like closure panels, while the bodies-in- white—or, in the case of pickups, frames—tend to remain primarily steel because of its capability to absorb crash energy or to provide occupant protection. So it seems that what's happening is that the "skin" of some vehicles is being replaced by aluminum. What's seemingly lost in the discussion of things like the "aluminum F-150" is that closure and hang-on panels account for about 8% of the mass of a vehicle, while the body-in- white (or frame) accounts for as much as 28%, according to a report from World Steel Dynamics (October 2014). So it is almost as though when it comes to materials used in cars, rhetoric is trumping reality. One more comment from Hall in this regard: "Advanced high-strength steel is the fastest growing material on a vehicle." Who knew? *It should be pointed out that ICME is not a steel-only methodology. According to "Integrated Computational Materials Engineering: A Transformational Discipline for Improved Competitiveness and National Security" by the National Research Council [National Academies Press]: "ICME promises to eliminate the growing mismatch between the materials development cycle and the product development cycle by integrating materials computational tools and information with the sophisticated computational and analytical tools already in use in engineering felds other than materials. ICME will be transformative for the materials discipline, promising to shorten the materials development cycle from its current 10-20 years to 2 or 3 years in the best scenarios. ICME will permit materials to be "design solutions" rather than selections from a static menu." AD&P; > May 2015 > FEATURE > Steel: Where It Is & Where It Is Going > Gary S. Vasilash > gsv@autofeldguide.com 34