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Passivating blacksmith forged stainless steel

We are planning to blacksmith forge 303 and 304 Stainless steel. This process happens on a steel anvil using steel hammers, heated in a gas style and sometimes coal burning forge. Will we need to passivate the forged parts after forging?

Tai Williams
Owner-Metalworking business - Danville, California, USA
2003

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First of two simultaneous responses --

Only if you want it to remain stainless, i.e. no red rust.

Toby Padfield
Automotive module supplier - Michigan
2003

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Second of two simultaneous responses --

I doubt if passivation is going to do you much good. You are beating iron (steel) into your stainless surface to a point that conventional passivation will not remove all of it enough to pass a salt spray or a CASS test. There is a possibility that you may not need to passivate anyway. Try it and see. If it fails, consider electropolish.

James Watts
- Navarre, Florida
2003

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Tai Williams,

In response to your question about passifying your forged s/steel. It will be imperative to passify after forging due to corrosion that will occur. The carbon that is raised to the surface due to heating the stainless,as well as the contamination from the tools will rust the stainless quite rapidly,depending on the environment;i.e., marine,salty etc.Our stainless products are generally in a marine environment we passify after the fabrication,grinding,welding etc and then again just before the last step in the polishing process,usually for mirror finishing if theres a lot of heat involved. hope this is helpful.

Paul Grant
Stainless Fabrication/Polishing - Port Stephens, Australia
2003

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If you want to reduce corrosion and rusting, you should consider electropolishing the stainless steel after forging it. The "blacksmith" treatment of the metal will certainly change the surface chemistry of the stainless steel, as well as increasing the amount of surface carbon. It will also induce localised work hardening into the stainless steel. Electropolishing will equipotenialise the steel's surface and protect it from corrosion. If you use a bath that contains phosphoric acid (and dare I even suggest some hexavalent chromium?) you will certainly improve its corrosion resistance.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003

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You definitely need to passivate the surface, but with the 303 you have added problems with the sulfur. You must pretreat the stainless with high pH alkaline cleaner to remove the sulfur and then electropolish and/or passivate. We have good procedures for doing this with citric acid based systems if you still need help.

The best system is to electropolish and passivate afterwards.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2003