Old-fashioned steel has been one of the most reliable and ubiquitous building materials for centuries, so it might seem a bit outmoded to talk of a steel breakthrough. But researchers at Pohang University of Science and Technology in South Korea may have made steel cool again, not to mention stronger and lighter, reports Popular Mechanics.

The researchers have devised a method for creating an aluminum-steel alloy that is more flexible, lightweight and stronger than any kind of steel ever made.

This isn't the first time anyone has thought to add aluminum to the steel mix. Back in the 1970s, Soviet scientists recognized that by blending steel and aluminum, they could forge an ultra-strong, lightweight metal, but these advantages were always superseded by one major drawback: it was incredibly brittle. When significant force was applied, it always broke rather than bent.

The problem is that when you fuse aluminum and iron atoms together, that tends to create tough, crystalline structures called B2, which are what make the aluminum-steel alloys so brittle. No one has ever found a way around this problem, until now. Hansoo Kim and his team at Pohang discovered that if the B2 crystals could be dispersed properly throughout the steel, the surrounding alloy could insulate them from splintering.

"My original idea was that if I could somehow induce the formation of these B2 crystals, I might be able to disperse them in the steel," explained Kim.

It's not as simple as it sounds. Kim and his team spent years painstakingly heat-treating and thinly rolling their steel in repeated attempts to control when and where B2 crystals were formed. They experimented by adding bits to the mix. Nickel, for example, offered the particularly important advantage of making the crystals form at a much higher temperature. Finally, they mastered the technique.

The result of all this work is a viable aluminum-steel alloy that is 13 percent less dense compared to normal steel, and with a comparable strength-to-weight ratio compared to titanium alloys. That's significant, and it could make aluminum-steel alloy the building material of the future.

"Because of its lightness, our steel may find many applications in automotive and aircraft manufacturing," said Kim.