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TESTING OF UNKNOWN ALLOYS


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What types of testing methods/procedures/machines are used to get an analysis from and unknown steel?

Who does these tests? Who has these types of machines? What industries or teaching institutions typically have them on hand?

 

I live near a major university and wondered if they might have this ability on campus. Could be a great exercise for a student to learn how to do the test as part of their class work. A real world test that is.

 

Ben

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Ben, what is usually done is called a spectral analysis. It burns a small bit of the metal then analyzes the spectrum of the light that comes off it as it does so, each alloy and element distorting the light a different way.

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I should require much material at all. Basically they are going to take a very thin foil of the sample and ionize it in a plasma arc or any number of ionizers. Mass spectrography is neat. You can build a simple one using a CD or DVD, a pair of razor blades, a box and some tape.

 

The ionizer is the tricky part. You have to ionize the sample in an inert gas, then somehow get those ions to the spectrometer's sensor.

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I should require much material at all. Basically they are going to take a very thin foil of the sample and ionize it in a plasma arc or any number of ionizers. Mass spectrography is neat. You can build a simple one using a CD or DVD, a pair of razor blades, a box and some tape.

 

The ionizer is the tricky part. You have to ionize the sample in an inert gas, then somehow get those ions to the spectrometer's sensor.

 

 

I gotta know more. Do you have link??

 

Ben

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  • 2 weeks later...

Carbon and Sulfur are typically measured using instrumentation developed by Leco - typical sample size for 1 run which will generate both C & S is 1 gram. Turnings, filings, drillings or a solid piece are acceptable. For nitrogen and oxygen, again a Leco instrument is used - sample size is normally about 1/2 gram and again may be turnings, filings, solid, or drillings. These are both combustion machines. For alloy content, a spectrometer is used, either an x-ray spectrometer or an optical emission spectrometer. For an x-ray spectrometer, you need a piece of metal big enough to cover the aperture in the sample holder. New spectrometers from Panalytical have an aperture diameter of 27mm. Older ones had one of 25 mm. The samples also need to be thick enough that they can be manipulated to be polished flat - some companies have sophisticated and expensive automatic polishing equipment. Others use belt grinders and hand polishing - a 120 grit finish works for analytical purposes. However, polishing media is important as it has the potential to affect your analytical results.

 

For an optical emission spectrometer, you also have to polish the sample, not necessarily as smooth as for an x-ray spectrometer, but 120 grit works there as well. You again have to cover an aperture, but they're typically smaller - about 1/2 inch in diameter or less. You have an arc generating a plasma that is then analyzed - you don't cover a much area as you do with an x-ray, so it's pretty common to take 2 burns per sample and average them if they're close to the same results. If not, you'll take more burns. I've found that optical emission will not work with products such as bloomery iron or true wrought iron - I've never been able to get a good burn and a good analysis. In general, OE is quicker, better for lighter elements (you can get readings for C & S). One drawback - to standardize them, you consume your standards doing burns, which you don't with an x-ray spectrometer. X-ray in my experience is better for more highly alloyed product - complex stainless and tool steels, cobalt alloys, nickel alloys, etc. and doesn't consume standards verifying the analytical curves. It doesn't work well with lighter elements such as carbon and sulfur. It can be used to measure alloy content of true wrought iron and modern bloomery iron. Most universities with a materials science or metallurgy program should have some of this instrumentation. Most steel mills do, many using customers have it, as well as foundries and forges.

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