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How to tell Ferritic Stainless Steel from plain steel?

I am a metal recycler. Am having a hard time distinguishing Magnetic Stainless from highly polished plain steel. Usually found in things like rods inside copiers and printers. Is there any cheap, easy chemical test I can use?

Gary Williams
metals recycler - Mount Vernon, New York
August 12, 2008

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First of two simultaneous responses -- August 15, 2008

Scuff the surface with sandpaper
soak in saltwater overnight

if it rusts it's polished steel
if it doesn't or does very little it's stainless.

Marc Banks
Blacksmith - Melbourne, FL

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Second of two simultaneous responses -- August 17, 2008

Hi,
A simple and effective test would be to use copper sulphate ⇦ this on eBay or Amazon [affil links] solution. On low alloy steels a drop of solution will produce a copper deposit in a few seconds. Ferritic SS will not be stained. I have just spent a happy hour in my garage testing the procedure on various tools and domestic equipment (my wife was watching the Olympic Games). The copper sulphate was from my granddaughter's chemistry set.

The procedure is to dissolve copper sulphate into 50 ml water until no more can be dissolved. The solubility is quite low so only a small amount is used. Add 2-3 drops of dilute sulfuric acid - battery acid ⇦ this on eBay or Amazon [affil links] is fine. Place a drop of the sulphate solution on the item under test. A distinct copper layer will form on plain steel. Any oil or grease must be removed before applying the test solution.

Inevitably there a problem if you are dealing with nickel plated or lacquered parts because copper will not form on the surface. There is no easy to apply chemical method to overcome this. If in doubt, lightly grind away any surface coating before applying the copper sulphate.

Although this copper sulphate was obtained from a child's chemistry set safety procedures should be followed. Look to the safety data sheet for the chemical.

Harry Parkes
- Birmingham, UK