XRD - X-ray diffraction
XRD - X-ray diffraction
(OP)
we have sent 440C to a lab to find the % of the retaining austenite. the lab asked us the % of carbides. they said it is used in calculation of the retained austenite.
1) is there a book value in some military spec, or else to specify the carbides % for 440C material?
2) or, the % of carbides varies from lot to lot, so, it needs to be determined by some "test".
anyone can help me?
thanks a lot.
1) is there a book value in some military spec, or else to specify the carbides % for 440C material?
2) or, the % of carbides varies from lot to lot, so, it needs to be determined by some "test".
anyone can help me?
thanks a lot.





RE: XRD - X-ray diffraction
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RE: XRD - X-ray diffraction
RE: XRD - X-ray diffraction
RE: XRD - X-ray diffraction
Provided they are using proper calibration techniques, why would they need to know the weight percent (or volume percent) of carbides to make this determination? I suggest that you contact them and pose this question. Let us know what they say.
Maui
www.EngineeringMetallurgy.com
RE: XRD - X-ray diffraction
A year ago, the test lab cert said "Note, 15% carbides assumed in calculation".
This time, the lab asked us what percent carbides should be used. I asked why ask us, it should be either a book value or result of a test.
The test lab says "This is based on a NADCAP requirement and had to be applied since May 2011"
I asked last time your report said 1.1% retained austenite and assumed 15% carbides. what the retained austenite would be if carbides at 0 and 30%"
The lab says "0% would be 1.3%; 30% would be 0.9 (which we would report as <1.0%)"
The lab then said a micro analysis to determine the carbides %, $140.14 per sample.
RE: XRD - X-ray diffraction
Maui
www.EngineeringMetallurgy.com
RE: XRD - X-ray diffraction
Polish and etch samples and then look at enough fields to get a statistically meaningful value.
Of course for this application you don't need super good statistics since the austenite value isn't that sensitive to the carbide content.
But that begs the question, if you polish and etch samples for micros why not just do the retained austenite that way instead of XRD?
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Plymouth Tube
RE: XRD - X-ray diffraction
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Maui
www.EngineeringMetallurgy.com
RE: XRD - X-ray diffraction
Now I see the issues.
My experience has been with lower C, higher alloy grades where the austenite is distinct enough to measure optically.
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Plymouth Tube
RE: XRD - X-ray diffraction
metalhead
RE: XRD - X-ray diffraction
Here is a reference specific to retained austenite determination in Type 440C that mentions the effect of carbide concentration:
http://camet-lab.com/retained_austenite.html