Measurement of nodularity by NDT

I'm looking for non-destructive methods to verify graphite nodularity in a casting.
I'm aware of methods like UT, by measuring longitudinal velocity (vel.
increases with inc. in nodularity), or UT pulse attenuation (attenuation dec. with inc. in nodularity)
I was wondering if there's a direct correlation between HARDNESS and NODULARITY. my reasoning being increase in ductility with increase in nodularity.
Would the method be dependable?
Are there any other simple methods to measure or compare nodularity??
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I'm not a NDT person - but how about NMR or NMRT Nuclear Magnetic Resonance Testing. The sample is put in an RF field and specific frequencies are to the elements.
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Roon:
Look at http://www.ductile.org/member/researchactivity/proj37.pdf
Pittsburgh Pete
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Thank you very much for your replies.
I'll see what possibilities NMRT throws up.
thank you Pete for the link. That cleared up a lot of my doubts.
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Arun,
I believe I interviewed you several years ago. At the time you may have been working at Teledyne Casting Service in La Porte and you visited Cincinnati.
I doubt you would see a correlation in hardness vs nodularity. The ductility does not increase with nodularity; what should be considered is that for a given grade of ductile iron (considering the matrix, ferritic, pearlitic or mixed) that from a 100% Type I or II the decrease from 100% Type I and II will result in a corresponding decrease in elongation. However, the elongation decrease may not result in a measurable hardness decrease as the matrix will account for much of the hardness value obtained. In this case I am speaking of 3000Kg load on the 10 mm ball indenter - it would not be good practice to use Rockwell 'c' for castings.
The use of the ultrasonic methods have important ramifications for the control of ductile iron quality besides the nodularity. Yes it is true that with 100% (or close to it) nodularity, and depending upon nodule size, the velocity may approach 5800 m/s for ultrasonic testing. In a simple graded sort with the criteria of 75% to 80% range being 'passable' one can expect that the velocity will reduce to perhaps 5,000 m/s. Gray iron with Type A flakes will have a velocity of about 4500 for example.
More than this depending on the casting being inspected, UT testing can also prove that the casting has no or an allowable level of internal microporosity, existence of internal shrink, existence of chunky graphite, etc. through the measurement not only of the velocity but with the proper UT equipment the image scan will show attenuations and backwall losses.
http://www.ndt.net/article/dgzfp01/papers/p33/p33.htm
However, all the above being said it is possible also to obtain or make polishing equipment which would allow a field inspection of a casting (using suitable equipment) by light microscopy. In many cases this is not destructive to the part and since the nodularity is the desired thing to verify it will not depend on possible false correlations since it is a direct measurement.
Mark

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The best way is to do a replica refer www.metserve.co.za very dependable have used it many times to determine grade of cast iron. Regards Eric Vreugde
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