Stainless corrosion and maintenance - Page 8 - SailNet Community
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post #71 of 71 Old 11-11-2019
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Re: Stainless corrosion and maintenance

Originally Posted by overbored View Post
Yes you can. The key is to not use any tools to cut or grind that have been used on any other metal like steel. Do not touch the SS with any thing steel like steel files, steel saw blades or carbon steel drill bits. clean the weld area to remove all oxides and weld with as much shielding gas as possible or in a vacuum chamber. Use 316L material and filler rod if possible. weld at the lowest heat that will still produce the weld size that is required. clean the surface after welding with clean scotchbrite pads or wheels and then passivate properly. any time the SS is touched with a mechanical polishing device, scratched or even wiped clean you are removing the chromium oxide from the surface and could be exposing the iron in the surface of the SS to the elements and it could cause rust. so frequent passivation is always recommended.
I have been in the fabricating business for 45 years and I use Spotless stainless because it works the best on boat hardware of any I have tried.
There really are two issues: 1) sensitization as a result of chromium carbide formation during welding, and 2) contamination of the surface with iron. As overbored points out, sensitizaton can be avoided by using low carbon stainless (e.g. 316L) and by using the mininimum amount of heat that still results in a good weld. If the stainless has been stabilized through addition of Nb or Ta then sensitization is unlikely to occur. Rusting through contamination can be avoided by not touching the stainless with steel or by cleaning afterward.

Once sensitized, the only way to restore the stainless is by a heat treatment that dissolves the chromium carbides. According to the TTT diagram of 316 stainless, one would have to heat to at least 1000C to accomplish that. If you'd try to passivate sensitized stainless steel without redissolving the carbides, you would corrode the stainless pretty badly.

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