spectrometer % carbon on hi chrome wear resistant iron untrustworthy ?

[Tmoose]

A supplier has said the % carbon in their spectrometer test results is not accurate enough "on these materials." So they test carbon another way, and hand write the passing results on the lovely computer generated report card that says the material flunked. Naturally this results in questions from everybody who receives the report.
[ul]Is it indeed common knowledge that spectrometers don't report carbon accurately ?[/ul]

thanks,

Dan T

 

[metengr]

What type of spectrometer was used for the analysis? LECO is probably one of the best for accurate determination of carbon, sulfur, nitrogen, oxygen and hydrogen.

 

[arunmrao]

I have been using OES for a very long time to analyse high chrome iron samples. Results are accurate, consistent and repeatable. If they are using a PMI well then C,Si, elements will not be displayed.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

And some OEs are not that great either.
But a Spectro unit should be able to be calibrated to handle this.
Sounds like they are being a bit lazy, or their machine needs some work.
Combustion (Leco) is considered an absolute method, I would take that as a good number.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

Carbon content in high chrome irons is usually 2.5-3.0%, and the carbon is in combined form.
Unlike in stainless steels where carbon content can be 0.03% max, I agree there is a question mark. It is best then to rely on a separate analysis for carbon content using a Leco.

Honestly, this is the first time I have heard of Carbon analysis using OES ( well calibrated) being termed suspect!!

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

arunmarao, I think that you hit it on the head, 'well calibrated'.
My hunch is that they simply have not bothered to optimize their method for this and are trying to brush it off.
It would be a lot cleaner to simply not report it and always give the Leco value.


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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Agree with Ed, the LECO value should be used and only reported.
With proper calibration and specific electrode used, OES could provide an accurate result. Because your lab has stated its Carbon results from its OES are inaccurate, take their word for it.

 

[MagBen]

Agreed to use combustion method in this case since question arose. However, I agree with arunmrao too OES is accurate and reliable. we test and certify carbon sometimes using OES even for alloys with as low as 0.01% carbon, and in these alloys carbon is a key element to control properties.

 

[bobjustbob]

I think it is unfair to call the supplier lazy using the LECO to perform the carbon test, they are a bit lazy in how they report the result to you. I would never send a CMTR with a hand written value on it. The Spectro OES can give you a carbon, if you are very careful with your gas, cleanliness, sample prep, and standardization, you can get a good consistent carbon. The shops I have worked in and been in prefer to use a LECO combustion style analyzer. It is a more robust test and easier to use in a production environment. Assuming the two machines are kept up and properly calibrated I would always trust the LECO combustion result over the OES.

 

[Tmoose]

Thank you. This has been very helpful.

Dan T