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Date: 22 December 2014
New Steel-making process: Super-strong military armour could be easier and less expensive to manufacture  


Topic Name: New Steel-making process: Super-strong military armour could be easier and less expensive to manufacture
Category: Civil Engineering
    
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Research persons: Peter Brown

Location: Defence Science and Technology Laboratory, United Kingdom

Details

A team of scientists at the Defence Science
and Technology Laboratory
(DSTL), in collaboration with
Corus, have developed an advanced
armour steel called Super Bainite. The material is made through a process called
isothermal hardening. With this method, steel is heated to 1,000ºC, air-cooled
to 250ºC, then held there for eight hours before finally cooling it to room
temperature. The end result is an ultra-hard, crack-free steel.

'Other ultra-hard steels need to be quenched and tempered and tend to contain
costly elements to avoid cracking during processing,' said Peter Brown, head of
the DSTL research team. 'This conventional approach is effective, but also more
expensive, complicated and energy intensive than the Super Bainite manufacturing
route.'

Steel, a solution of carbon in iron, has been the industrial backbone of modern
society. Brown said scientists discovered in the early half of the last century
that heating and cooling steel in novel ways and adding other elements such as
silicon and manganese would change the configuration of iron atoms.

'In the bainite configuration the iron atoms are arranged fairly openly, whereas
in the austenite phase they are packed closely together,' added Brown. 'While
Super Bainite steel is mainly bainitic it also contains some austenite.'

He explained that Super Bainite's high carbon content and unusually low final
processing temperature makes its mixed microstructure incredibly fine. 'As a
consequence it's also extremely hard, which is one reason it's such a good
armour,' he added.

Brown said that Super Bainite is still experimental armour steel. 'Clearly, if
and when it becomes commercially available, it could be used to protect a
variety of defence platforms,' he added.

A number of civil applications, from armoured limousines to bulletproof
furniture for commercial and domestic premises, have also been proposed.

In addition to offering ballistic protection, a good armour needs to be
affordable. 'Armour that's prohibitively expensive or very difficult to process
is no use to anyone,' said Brown. 'Super Bainite's composition and processing
are inexpensive.'

He added that much of the process's cost and complexity has been removed using
Cambridge University software.

'Recent large-scale production trials with Corus have also demonstrated that the
Super Bainite manufacturing route can be conducted in the UK,' said Brown. 'From
a defence perspective, the availability of a secure onshore supply of
high-performance steel armour is strategically important.'

During a recent Horizon seminar at Cambridge University, Brown discussed adding
'holes' into the steel armour. These holes would actually provide a protective
advantage.

He said the trick is to think of them as circular 'edges' rather than holes.
When a bullet hits an edge, it gets deflected and turns from a sharp projectile
into a blunt fragment.

'The introduction of holes also reduces weight and stops cracks from spreading,'
he added. 'As a result, perforated Super Bainite steel armour is ballistically
very efficient.'

Brown and his research team are also studying manufacturing methods for other
kinds of high-performance materials. Kolsterising, in particular, is a new
process developed by the company Bodycote to increase surface hardness of
stainless steel.

'It's a new process for introducing carbon into the surface of austenitic
steels,' he said. 'The resulting surface region, although thinner than tissue
paper, is twice as hard as Super Bainite.'

Brown added that Kolsterising is still experimental and needs to be scaled up to
make thicker material.


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