In new research published in Nature, Professors Nack J. Kim and Hansoo Kim and doctoral student Sang-Heon Kim at the Graduate Institute of Ferrous Technology (GIFT) at Pohang University of Science and Technology (POSTECH) have developed a new type of steel with improved tensile strength and lightness.
There is a growing demand for lightweight structural materials as an alternative to conventional steels which are heavy and impractical in developing future energy efficient vehicles. Studies on lightweight steels have shed light on the effectiveness of aluminum alloying in increasing the strength-to-weight ratio and reducing density. However, increasing aluminum content in lightweight steels results in poor ductility.The research team at GIFT has found a solution to this problem by taking an unconventional alloy design approach.
The secret, the team explains, lies in causing new structure shapes to be formed during the heating process
and by using the right mix of ingredients. They used the traditional mix of iron, carbon, aluminum and manganese and then added some nickel. The nickel, they found reacted with the aluminum, creating nanometer sized B2 crystals
that formed within and between the steel grains during the annealing process. To make sure the crystals were spread evenly among the metal, the team studied samples under an electron microscope. Chemists know that B2 crystals are resistant to shearing, thus steel with such crystals should be extremely strong, and that is what the researchers found when they tested their new alloy. Besides being lightweight, this new steel possesses an excellent combination of strength and ductility, which are far superior to those of traditional steels.
With this innovative approach, stronger and more ductile lightweight steels have been created, solving the long standing problem of poor ductility caused by the formation of brittle intermetallic compound particles. The team plans to work with POSCO to produce its new product later this year, ushering in a new era of high-specific-strength steels that will be lightweight and strong enough to produce fuel efficient vehicles and other transportation systems.