
With
TimeTemperatureTransformation
(TTT) diagrams or their cousins:
ContinousTemperatureTransformation
(CTT) diagrams, serious steel
science and serious steel making starts.
Everything we did so far, was only a prolonged foreplay, so to speak. Fun  but
not yet serious.
Like
phase
diagrams, TTT and CTT diagrams provide a kind of map that enables you to
get oriented in the wilderness of steel alloys, structures, processes, and
properties. Like phase diagrams once more, TTT or CCT diagrams are easy to read
after you learned a few rules  but not so easy to calculate.
I'm going to devote several modules to this topic.
 The Basic Idea or how to
get there without equations.
I will look at how fast some simple things happen at different temperatures.
Then I will put the pieces together to deduce how fast a phase transformation happens at different
temperatures. This produces a certain kind of diagram, and looking at that
diagram kind of "from the side" will produce a TTT diagram. Then I
look a bit at the differences between TTT and CCT diagrams.
 Theory or doing TTT
diagrams more quantitatively.
I will give the derivation of the JohnsonMehlAvramiKolmogorov equation that
is at the heart of TTT diagrams. Then I will reason why this
manysyllableequation is very useful but still a far cry from covering all
there is about those diagrams.
 Applications
I will demonstrate that you actually can get a lot of mileage out of using
questionable TTT diagrams in a fishy way. Then I will look at what it takes to
do it right.
 I will give you a basic idea of how to construct TTT,
CCT and
phase diagrams from experimental data.
