Iron and Steel Near Zero K
Date: October 2005
If you freeze iron to extremely low temperatures (approaching
absolute zero?), does it become brittle and breakable, or stronger?
Is this the same for steel?
In general, as the temperature is reduced metals becomes stronger, but
more brittle, at the same time. The temperature does not have to be very
near absolute zero. Assuming that the iron is not quenched to form a glass,
but is "regular old iron", the structure becomes more rigid (i.e.
stronger). However, because the atoms cannot move past one another so
readily at low temperatures, the metal becomes less ductile (i.e. more
brittle). So when a crack is started it propagates rapidly through the
metal causing it to fail.
All metals will become brittle once they drop below what is known as the
metal's transition temperature. Determining the transition temperature is
not that easy, but at temperatures near absolute zero, they are both
definitely brittle. For different metals with different compositions, the
transition temperature can have a wide range. Since the transition
temperature is not a sharp point in the testing, a range is given. That is
to say, you cannot say that steel has a transition temperature of "x"
degrees, but has a range where the failure is more likely to be brittle, say
between "x" and "y" degrees. Anything below this range is definitely
brittle failure. One of the classic examples of this transition temperature
problem was the Liberty Ships during World War II. Ask your local librarian
to get you some books or articles on the Liberty Ships. What happened with
the Liberty ships is that the iron used for the ship had a transition
temperature that was above the temperature of the North Atlantic where some
of these ships were helping take supplies to Russia. They would hit a big
wave and literally snap in two because the water temperature caused the
metal to become brittle instead of forgiving of large, unexpected loads.
Thanks for using NEWTON.
Chris Murphy, P.E.
Air Force Research Laboratory
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Update: June 2012