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Scientists invent a new Steel as strong as Titanium, but 10 times cheaper

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Scientists in South Korea have invented a new steel alloy that boasts
the same strength-to-weight ratio as titanium – the super-strong metal
we use to construct jet engines, missiles, spacecraft, and medical
implants – but it can be produced for one-tenth of the cost. 

Image: It’ll be like this steel, except more super. Credit / Shutterstock.com
In
order to develop this new kind of metal, the team from Pohang University
of Science and Technology had to overcome a problem that had stumped
materials scientists for decades, says William Herkewitz at Popular Mechanics.
“In the 1970’s, Soviet researchers discovered that adding aluminium to
the mix when creating steel can make an incredibly strong and
lightweight metal, but this new steel was unavoidably brittle,” he says.
“You’d have to exert lots of force to reach the limit of its strength,
but once you did, the steel would break rather than bend.”
The
issue is that steel on its own is very strong and cheap, but it’s
super-heavy. So it’s not that useful in constructing aircraft, and while
it’s enjoyed a good run in the car manufacturing industry, the
fuel-efficiency people have come to expect is just not possible when
you’re trying to support all that hefty steel. According to The Economist,
between 1995 and 2011, the weight of steel in an average light vehicle
fell from 68.1 percent to 60.1 percent, and it’s only going to get
lower.
So you need to mix steel with something to make it lighter, and
aluminium is the obvious candidate, because it’s so lightweight and
cheap. The problem here is that when you try to mix aluminium and steel –
an alloy of iron, aluminium and carbon – sometimes the aluminium and
iron atoms would fuse together in weird ways, forming dense, crystalline
structures referred to as B2. 

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And while these structures were certainly
strong, they were brittle, which means you really didn’t have to do
much to them before they’d crumble and break. Scientists tried adding
manganese to the mix, which helped reduce the brittleness, but not
enough.
And then, lead researcher and materials scientist, Hansoo
Kim, had an idea – manipulate the structure of the aluminium-steel alloy
on the nanoscale.
“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,” he told Herkewitz at Popular Mechanics.
So his team figured out that if they moved the B2 crystals around and
separated them from each other, the rest of the alloy structure could
fill in the gaps and protect them from breaking apart. 
The key to working this out was adding a tiny bit of nickel, The Economist reports:
“The
nickel reacts with some of the aluminium to create B2 crystals a few
nanometres across. These crystals form both between and within the
steel’s grains when it is annealed (a form of heat treatment). B2
crystals are resistant to shearing, so when a force is applied to the
new material, they do not break. This stops tiny cracks propagating
through the stuff, which gives it strength. That strength, allied with
the lightness brought by the aluminium, is what Kim was after.”
The team has published the results in Nature,
and they hope that other materials scientists around the world will use
their method to come up with more weird and wonderful new alloys for
the market. 
They’re currently in discussion with POSCO, one of the world’s largest steel manufacturers, to see if they can get their ‘super-steel’ out into the production line. 

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