I have just started a PhD lately; the project is about characterisation
of microstructure of steels with bainitic and acicular ferritic
structure; I need to create CCT diagrams from dilatometric curves of
the aforementioned materials. Now, setting those critical points
indicating the start /beginning of the transformation seems somewhat
fuzzy to me; could anyone give me some hints/references/articles about
the way it's done?
Thanks in advance,
Look at the article by George Eldis titled "A critical review of data
sources for isothermal transformation and continuous cooling diagrams"
in the symposium book "Hardenability Concepts with Applications to
Steel", (edited by D. V. Doane and J. S. Kirkaldy TMS-AIME 1978, pages
Thank your for the replies.
Now, more specifically, having the dilatometric curve and its derived
one, I normally put the tangents on the curve to get the critical
points. However, from time to time the derived curve is amazingly rough
and oscillating, thus it's pretty hard to place a line on the curve. Do
you have any trick to overcome this?
The tangent method should work pretty well. I've used this method
before and its fairly accurate. If you have a quench dilatometer,
quench at different points of the curve to try to capture the phase
forming by metallography. Although this may be hard for acicular and
bainitic structures and work intensive. The other thing to look at is
the gain setting on the LVDT, I don't quite know why your curve is
choppy. It should be smooth linear thermal contraction or expansion
followed by the phase changed. Otherwise there may be controler issues.
Oh yeah, I know of two research groups to look up.
1) Prof. Van der Zwaag has published some neat papers on dilatometry.
2) Prof. Boyd has done some excellent work on the characterization of
bainitic and acicular microstructures using dilatometry.