TECHNOLOGUE Frank Markus

Frank Markus

TECHNOLOGUE

Illustration Samuel A. Minick Ultra-High-Smallness Steel

Cheap gas makes vehicle buyers eager to pay for space, comfort, and capability and utterly unwilling to spend a dime on fuel economy. But although our embarrassingly ineffective government feels bad about the oil use and carbon dioxide production this free-market reality results in, it doesn’t have the cojones to fix the problem efficiently with a gas tax. Instead, it passes the buck to automotive engineers who must figure out ways to sneak fuel efficiency into vehicles without buyers noticing on the window sticker. A potential success story on that front: affordable steel that’s about as light and strong as aluminum.

It’s called NanoSteel. It’s designed to be producible in existing steel mills and stamped using conventional tooling typically used for today’s more advanced steels, and it delivers ultra-high strength. As the name implies, the magic happens at the nanometer grain-structure scale, thanks to the discovery of new thermochemical-enabling mechanisms that create nanostructures exhibiting unique combinations of strength and ductility.

Conventional wisdom says changing the ratio of some elements of the company’s recipe to increase strength would result in steel that is too brittle. But the alloy and resulting nanostructures that Providence, Rhode Island-based NanoSteel have developed prevent “coarsening” of the steel grains during processing. Instead, NanoSteel’s tiny grain structures undergo nanophase refinement at high temperatures to produce grains and structures that are smaller by an order of magnitude than in typical advanced high-strength steels. The resulting sheet steel is capable of being stamped in a conventional forming process, and the steel does some of its hardening during the forming process.

How light is it? German engineering consultancy EDAG designed a car body

NanoSteel could achieve the weight savings of aluminum while costing substantially less.

structure identical to the one designed for a NHTSA lightweight vehicle study, patterned after a 2011 Accord using three grades of thinner-gauge NanoSteel in exactly the same stampings. The result was 10 percent weight savings relative to the NHTSA car, or a 30 percent improvement over the Accord baseline with equivalent crashworthiness and noise, vibration, and harshness levels. That result saw just 4.6 percent less weight savings than an aluminum lightweight vehicle produced by EDAG in a parallel study, but NanoSteel points out that closing that gap could be easily accomplished by optimizing all the stamped parts’ section shapes to fully exploit the formability of NanoSteel.

That’s the real secret sauce here. Every structural element in a vehicle must meet targets for strength and stiffness. Both the strength and stiffness of the part are dependent on its gauge thickness and the design of the part’s shape and section.

Today’s highest-strength steels severely limit an engineer’s freedom to tune a part’s shape, which forces an increase in gauge thickness and weight to generate the required stiffness or strength. The strongest parts in today’s car bodies—things such as B-pillars—must be stamped while they’re red hot (requiring pricier equipment) to get the right combination of strength and formability. Without heating, other highstrength steels are limited to simple “hat” sections to form the part. Adding more refined features such as corrugations would very likely permit a reduction in gauge thickness.

NanoSteel’s improved formability permits this fine-tuning of shapes without heating up the part during stamping. Because that EDAG study used carryover part shapes, NanoSteel is confident that a further optimized body structure could achieve the weight savings of aluminum while costing substantially less to produce. NanoSteel does not own steel mills; it is licensing its recipe to existing steel suppliers and is close to providing commercial material samples to various automakers that are expected to begin incorporating the material into their next generation of vehicles. Who’d say no to a big, comfy, cheap, higher-mpg car that magnets stick to? Q