How to identify stainless steel?

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I know that stainless steel does not attract magnet, I know that stainless steel has appearance that looks like stainless steel, but sometimes it is quite difficult to tell. In addition to magnet test, any further test I can do in my home?
 

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  • #2
phinds
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I know that stainless steel does not attract magnet,
Then you "know" incorrectly. Some stainless steel IS magnetic. Google it.
 
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  • #3
HAYAO
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Like phinds said, stainless steel like martensitic steel are magnetic.

Stainless steel contains fair amount of Cr. Cr is the main reason why stainless steels are "stainless".

I never tried this, but I think this is relatively safe (make sure you wear gloves, goggles, and lab coat; do not get the chemicals on your skin) so I'll try my best to answer the OP's question.
You could try partially dissolving stainless steel in acid (for example HCl 1 - 2M), take the water solution, and use some sort of chelating agent. Then you could try using NaOH (1 - 2 M?) to change the pH so that Fe(chelate) precipitates, leaving Cr in the water solution. Check the color and see if it is the supposed to be color of Cr(chelate). I believe this method can be quantitative as well.

I don't know what chelates should be used, so you need to look that up. HCl and NaOH can be bought by general consumers in my country.
 
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Stainless steel contains fair amount of Cr. Cr is the main reason why stainless steels are "stainless".

I never tried this, but I think this is relatively safe (make sure you wear gloves, goggles, and lab coat; do not get the chemicals on your skin) so I'll try my best to answer the OP's question.
You could try partially dissolving stainless steel in acid (for example HCl 1 - 2M), take the water solution, and use some sort of chelating agent. Then you could try using NaOH (1 - 2 M?) to change the pH so that Fe(chelate) precipitates, leaving Cr in the water solution. Check the color and see if it is the supposed to be color of Cr(chelate). I believe this method can be quantitative as well.

I don't know what chelates should be used, so you need to look that up. HCl and NaOH can be bought by general consumers in my country.
Do you need chelates?
Qualitative separation of Cr and Fe has other possibilities.
Like ´hydrogen peroxide in basic solution. Fe is oxidized to brown Fe(OH)3 precipitate (you need stronger oxidants for ferrate), while Cr is oxidized to yellow chromate solution.
 
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  • #5
HAYAO
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Do you need chelates?
Qualitative separation of Cr and Fe has other possibilities.
Like ´hydrogen peroxide in basic solution. Fe is oxidized to brown Fe(OH)3 precipitate (you need stronger oxidants for ferrate), while Cr is oxidized to yellow chromate solution.
Oh yeah, didn't think about that. Haha. Thanks. :-p
 
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Even without any chelation, adding alkali to Fe solution precipitates either Fe(OH)2, which is at first white but then rapidly turns green and then brown of Fe(OH)3 due to air oxygen, or directly the brown Fe(OH)3. Neither Fe(OH)2 nor Fe(OH)3 will dissolve in excess alkali, unless you apply a strong oxidant like hypochlorite, and then the solution is purple.
Cr(OH)3 precipitate is grayish green and unlike Fe(OH)3 it dissolves in alkali without adding oxidant, giving a solution that is green. Oxidizing Cr(OH)3 in alkali can be done not only by hypochlorite but also by hydrogen peroxide, and the colour turns to yellow.
Solutions and precipitates of iron:
https://woelen.homescience.net/science/chem/solutions/fe.html
Solutions and precipitates of chromium:
https://woelen.homescience.net/science/chem/solutions/cr.html
 
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