New Steel Brings Fuel Efficiency

Tuesday, June 30, 2015 @ 05:06 PM gHale

Auto manufacturers may soon get a big help in their quest to meet future fuel efficiency requirements with high-strength steel now in development.

The development of this new steel, known as a “third-generation advanced high-strength steel,” is under way at Missouri University of Science and Technology’s Kent D. Peaslee Steel Manufacturing Research Center.

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“We are currently refining the steel design to achieve ‘Gen 3’ mechanical property goals while also maintaining manufacturability,” said center director Dr. Ronald J. O’Malley, the F. Kenneth Iverson Endowed Chair of Steelmaking Technologies at Missouri S&T. “This is one of the most promising generation-three steels I’ve seen.”

Under the U.S. Department of Transportation’s Corporate Average Fuel Economy (CAFE) regulations, auto manufacturers must improve the fuel efficiency of their vehicles year-by-year through 2020. Regulators have set a tentative goal of increasing fuel efficiency to 54.5 miles per gallon for cars and light trucks by the 2025 model year.

Improvements in exhaust treatment systems, transmission efficiency and aerodynamics all contribute to better fuel efficiency. But reducing vehicle weight is also important in achieving the CAFE goals, O’Malley said.

“Automakers must make lightweight vehicles without sacrificing safety,” O’Malley said.

First-generation steel sees use in today’s cars and trucks. A second-generation product ended up developed, and it is stronger and more lightweight than the first-generation material, but O’Malley said it is too costly to produce and more difficult to manufacture. The third-generation steel under development by Missouri S&T metallurgical engineers should be lighter, easier to make and strong enough to address automakers’ safety concerns, he said.

The S&T researchers are employing a method known as TRIP – or transformation-induced plasticity – to obtain the performance required to meet safety and CAFE goals. It involves the transformation of an unstable crystal structure known as austenite, which normally exists at high temperatures, into martensite, a harder substance that develops as the steel deforms.

“The S&T alloy design employs a two-stage or ‘dual TRIP’ mechanism that leads to extreme work hardening and energy absorption, so it’s very good for automotive crash-worthiness,” O’Malley said.

Under the direction of Dr. David C. Van Aken, Curators’ Teaching Professor of metallurgical engineering, the Missouri S&T team has used an atomic modeling method known as density functional theory to identify alloying elements to create the dual TRIP character of these new steels.

The real challenge, however, lies with the large-scale production of these new steels. With the help of industrial partners, the researchers at Peaslee Steel Manufacturing Research Center are examining all aspects of the steel manufacturing “from melt practice to final formability by the automotive producer,” O’Malley said. A committee of representatives from four steel manufacturers – Nucor, U.S. Steel, AK Steel and ArcelorMittal – is overseeing the project.