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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Does magnetizing stainless steel decrease its corrosion resistance?

Q. If I magnetize the AISI 420, there is a possibility to decrease its corrosion resistance?

Edson Rodrigues
Industrial Mechanical Engineer - Camacari, Bahia, Brazil
March 29, 2016

A. Hi Edson. I doubt it, and I've never heard of the magnetizing or degaussing of steel or stainless steel affecting its corrosion resistance, but I don't actually know. So I hope your posting draws some responses :-)

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 2016

March 29, 2016

A. I think I'll just quote this article directly:
http://www.bssa.org.uk/topics.php?article=76

"Unlike martensitic steels, the austenitic stainless steels are not hardenable by heat treatment as no phase changes occur on heating or cooling.
Softening is done by heating in the 1050-1120 °C range, ideally followed by rapid cooling.
This is of course the complete opposite to martensitic steels, where this sort of treatment would harden the steel.

Cold worked austenitic stainless steels will contain some 'strain induced' martensite, which, as well as making the steel partially 'ferro-magnetic', can also reduce the corrosion resistance.
A highly stressed cold worked structure may also have lower general corrosion resistance than a fully softened austenitic structure."

With a austenitic (300 series) stainless steel, if it has become magnetic then it is generally heat treated (called annealing in this case) to undo the effects of the cold working that caused it. 420, being a martensitic grade, I believe is always magnetic.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

Q. I would like to thank for the responses from everybody.

In order to clarify my question, I am referring to putting an AISI 420 stainless steel together with a magnet. After separating the steel from the magnet, there remains a residual amount of magnetization in the steel. In this situation, can the AISI 420 decrease its corrosion resistance?

Edson Rodrigues
EF Engenharia - Camacari, Bahia, Brazil
March 29, 2016

A. Hi again. As before, I suspect no effect, but don't know for sure. But degaussing is a very simple standard procedure employed on even very cheap steel articles like hardware.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 2016

March 31, 2016

A. Hi Edson
Your magnetic stainless may attract any stray iron particles onto the surface and could create potential corrosion sites

Geoff Smith
Hampshire, England

March 31, 2016

Hi everybody,

Thank you for your responses.

About the coments from Geoff, I agree, but I'm referring to the corrosion of the stainless steel itself, not the agregate iron corrosion.

Edson Rodrigues
EF Engenharia - Camacari, Bahia, Brazil

April 7, 2016

A. I was going to jump in here and say "No, being magnetically charged doesn't affect the corrosion resistance at all". And then Geoff noted something I'd completely missed! Good point!

So I'd change my answer, noting that no, having your 420 magnetic doesn't affect corrosion resistance just because it's been magnetically charged. But as Geoff points out, if the magnetism attracts particles that may activate the surface, then yes, the overall corrosion resistance of the system may be reduced.

Lee Gearhart
metallurgist - E. Aurora, New York

Hi Lee,

Very good response. Now, I think that my inquiry was totaly respnded.
Thank to Lee and to everybody.

Edson Rodrigues [returning]
EF Engenharia - Camacari, Bahia, Brazil
April 9, 2016

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