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A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U N E 2 0 1 6
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GUEST DITORIAL
parameters can be varied suddenly, gently, or in complex
combinations to affect the structure and properties of met-
als. For example, the Flash Bainite of Gary Cola relies on
short time scales where the steel is not able to homogenize
its carbon concentration even on amicroscopic scale so that
different regions transform to unexpected microstructures
during rapid cooling. In contrast, the same phases require
many days to evolve when very large chunks of steel are
induced into a uniformnanocrystalline state.
Using fluids to cool metals during heat treatment is
another fascinating technology. Red-hot forgings that are
300 tonnes in weight can now be quenched into violently
flowing water without generating steam or bubbles of any
sort! Likewise, minute regions of metal surfaces can be
altered using pulsed lasers.
I hope that in these few words I have been able to con-
vey the excitement of the subject. I recommend the proceed-
ings of IFHTSE 2016, which includes articles that cover the
plunging of red-hot swords into slaves and using ionic liq-
uids as quenchants.
Sir Harry Bhadeshia
Tata Steel Professor of Metallurgy
Department of Materials Science & Metallurgy
University of Cambridge
The same material can achieve
a huge range of properties by
exploiting heat treatment.
hus, steel can be made weaker
than aluminum or stronger than
millimeter-sized graphene or carbon
nanotube samples. The properties of
metals rely on size, shape, chemical
composition, mechanical process-
ing, and thermal treatment. The technologies available for
thermal treatments are now astounding in their versatility.
It is important therefore for engineers to appreciate some
basic principles of heat treatment.
Heat treatment involves the motion of atoms. Because
the extent to which atoms can move in the solid state
depends exponentially on the inverse of temperature, and
linearly with time, it follows that temperature has a much
bigger effect than time. So an 80-ms heat treatment of steel
at 600°C is about seven orders of magnitude more potent
than holding a steel at 200°C for 10 days. On the other hand,
very large components cannot be heat treated uniformly in
short pulses of time. Thus, designing steel that transforms at
low temperatures where the time scales required are long
can be a positive advantage.
Concealed within this simple description of time and
temperature is variety, because these two independent