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Thread: Tiny rust spots coming through annealed (stained) Stainless Steel?

  1. #1

    Tiny rust spots coming through annealed (stained) Stainless Steel?

    I know the myth about SS not rusting, but I'm having an issues where after washing, a piece I was practicing on is now showing small spots of rust through the annealed (stained) section, ruining the anneal (stain). This was a piece that I slowly stained and there were no visible sparks. Any ideas on how to prevent it? Is it even possible? If this had been a customer item, I would be very unhappy with this result.
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  2. #2
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  3. #3
    Thanks Josh, this looks promising.

  4. #4
    There are also many different varieties of Stainless Steel, the 300 series SS are the most impervious to rust/staining, but a lot of things are made from 400 series, 13-8, 15-5, 17-4 and any number of other grades I can't think of at the moment and they will rust. Passivation is what we had to do on all the aircraft parts, they get dipped in Nitric acid, this would get rid of any surface impurities in the castings and also when machining you would transfer particles of HSS (high speed steel) from drill bits and other tools as you cut the parts
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  5. #5
    Quote Originally Posted by Brian Lamb View Post
    There are also many different varieties of Stainless Steel, the 300 series SS are the most impervious to rust/staining, but a lot of things are made from 400 series, 13-8, 15-5, 17-4 and any number of other grades I can't think of at the moment and they will rust. Passivation is what we had to do on all the aircraft parts, they get dipped in Nitric acid, this would get rid of any surface impurities in the castings and also when machining you would transfer particles of HSS (high speed steel) from drill bits and other tools as you cut the parts
    The piece that I ran was 18/10 and a few 18/0 pieces though I'm not sure the exact type of SS they were. What's strange is that similar pieces, but different brands, are doing fine with no issues at all. Is there a DIY version of Citrisurf? Looks like a citric acid/water mix.
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  6. #6
    speaking of transfer- I've had some 304 rust up pretty good, but I'm pretty sure the reason was the SS went thru the same Timesaver that sanded plain steel not long before.



  7. #7
    I'm kind of wondering if I should test my pieces by running them through my dish washer after to see what rusts and what doesn't. I hate to have to add another step to this process, but I can't have pieces rusting after a few days and the customer washed it. How difficult or time consuming is passivation at home? I think I should stick with citric acid if I try it, but I really wish I could avoid having to use it at all. But these are consumer pieces, not industrial, and I guarantee people will be really angry if their stuff rusts.
    Trotec Speedy 300 - 80 watt
    Tykma Minilase - 20 watt fiber (MOPA)
    CorelDraw X7

  8. #8
    The 18/10 and 18/0 series are used in a lot of silverware, pretty impervious, but eventually you get stains. They used to sell Nitric acid for swimming pools, it's mostly Muriatic now. I used to have a gallon around for stripping cadmium or zinc plating off of hinges before I welded them onto a gate.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  9. #9
    Quote Originally Posted by Brian Lamb View Post
    The 18/10 and 18/0 series are used in a lot of silverware, pretty impervious, but eventually you get stains. They used to sell Nitric acid for swimming pools, it's mostly Muriatic now. I used to have a gallon around for stripping cadmium or zinc plating off of hinges before I welded them onto a gate.

    Thanks Brian, I appreciate the responses. When you say eventually, you mean weeks, months, or years? I guess what I'm asking is if I DIY a citric acid mix and treat it, is it worth it? What's crazy is that I'm only scuffing it, so it's not quite annealed (stained), but I'm definitely not engraving so I'm not even sure why it's rusting to begin with. Seems odd that it's revealing enough to make it rust.
    Trotec Speedy 300 - 80 watt
    Tykma Minilase - 20 watt fiber (MOPA)
    CorelDraw X7

  10. As mentioned earlier 300 series is probably the most rust resistant. 400 is a very different alloy, I have not worked much with 18/10 or other variations. I suspect you have some contamination from a mild steel used to cut the stainless. You can use a copper sulfate test on the alloy and if any carbon steel is present it will flash a rose copper bluish color. It’s pretty cheap stuff and can be found at most lab or science stores.
    The only other thing I can think of is maybe when you heat up the steel with the laser some grain migration is occurring causing the rust protective elements to be void between the grains or vaporized and leaving the steel more susceptible to rust.

  11. #11
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    When I was doing stainless projects, I had a stainless steel wire brush and polishing wheels that never touched carbon steel, only stainless. Never any steel wool, it must all be stainless steel.
    Last edited by Bill George; 12-31-2017 at 9:45 AM.
    Retired Guy- Central Iowa. , Ray Fine 20w Galvo Fiber laser , LightObject 40w CO2. MakerGear M2 3D Printer. Qe60+ Vinyl cutter. Automation Tech Chinese 6040 Router running on Mach3 and UC400ETH

  12. #12
    Well, it's been my experience that once passivated you might be talking years in time before the parts would take on a stained appearance. We would get airplane parts back for re-work that had seen years of flying through who knows what kind of weather and they would show some slight staining. I think for the cost of some acid it might be worth a try. It's also hard to say how good of stainless you are starting with... given a lot of stuff is made in China, and it's not aircraft stuff where certifications on the material are required... what you really have is anybody's guess.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  13. I agree Bill, absolutely anything made of carbon steel coming in contact with the stainless will cause rusting. Including as you said wire brushes or wheels, grinding disk, I wouldn’t even use a polishing wheel. That being said I have a “stainless” Weber grill that I don’t believe on the top surface of the grill has been in contact with any carbon steel, I could be wrong. Anywho it has rust all over the top. It’s easily removed with a wire brush but my point is I believe it’s a low grade of stainless that will rust like carbon steel over a long period of time.

  14. #14
    So what do engravers that engrave firearms, jewelry, etc do passivation? Outside of industrial applications, who else here is worrying about this after engraving on SS?
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  15. #15
    We've engraved about a zillion things on stainless over the last 10 years. Never seen it, not worried about it. I suspect it was cup/brand specific. What was the brand of cup you used? Any chance it was a China knock off? If so, I wouldn't put too much thought into it and I'd blame it on the cheap cups. If it is a Yeti, I'd not be too worried, since Yeti engraves cups in house as well.

    Before I'd start trying to have cups passivated, I'd stop doing cups.
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