Hello,
I'm a first year student, we have a steel alloy that consists of 0.6 wt.% carbon, but when we measured the carbon content in austenite using XRD, we got 1.30 wt.% carbon.
How can austenite phase contains more carbon than the total amount of carbon in the alloy itself?
I was wondering how you measured the carbon content using XRD. Could you elaborate on that? Mainly because the carbon in austenite is not crystalline, so you should not be able to detect it using XRD. If you have conducted some sort of lattice parameter analysis, most probably there is an error in that. Also, the measurement of retained carbon in austenite is a little more complex and cannot be done using just XRD.
Have a look at this publication-
Article On measurement of carbon content in retained austenite in a ...
Lattice parameters are influenced not only by C but by other things, like crystal defects (dislocations). Plus line widening occurs also because of a grains size and has an instrumental component. Was everything accounted for?
As Vladimir Dusevich says, the line widening and the lattice parameters depend on a number of variables. Have you carried out a thorough Rietveld analysis on your XRD data in order to calculate lattice parameters. Even this is not foolproof, but it gives more reliable results if done correctly.
I'm guessing you used an empirical relationship between Carbon wt.% and lattice parameter to arrive at your result?
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