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How to tell Ferritic Stainless Steel from plain steel? [New York] 

August 12, 2008

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, NY, USA

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

Hi,
A simple and effective test would be to use copper sulfate 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 epuipment (my wife was watching the Olympic Games). The copper sulfate was from my grandaughter's chemistry set.

The procedure is to dissolve copper sulfate 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 sulphuric acid - battery acid is fine. Place a drop of the sulfate 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 sulfate.

Although this copper sulfate 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, West Midlands, United Kingdom