×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Best Stainless Steel for Mirror like Surface.

Best Stainless Steel for Mirror like Surface.

Best Stainless Steel for Mirror like Surface.

(OP)
What stainless steel is best for mirror like finish/polish?
I am considering 321 316 or 321. Are they all about the same.. is does one polish better than the other?

FYI: this is to reduce the emissivity/radiation HT of the surface.

Thanks.

RE: Best Stainless Steel for Mirror like Surface.

The hardest alloys will polish best.  Hard-drawn 301 or 302 sheet, or 440...

Alloys with more chrome will hold that polish longer (not oxidize as rapidly).  309, 310...

RE: Best Stainless Steel for Mirror like Surface.

(OP)
so in comparison between 321 and 304... 321 is harder so it will polish better? and both have about the same amount of chrome so they will both hold the polish the same way.. correct ?  ... is it correct to say 321 will polish better then 304  

RE: Best Stainless Steel for Mirror like Surface.

No, 321 is not harder than 304.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein  

RE: Best Stainless Steel for Mirror like Surface.

Polishing will have more effect on the type of reflection (specular versus scattering) that on the absorbtivity of the surface.  

RE: Best Stainless Steel for Mirror like Surface.

I just measured a group of stainless steels for reflectivity and emittance for this purpose. Austenitics are distinctly better than ferritics. Just choose one based on the environment it will face. 304 is good except near sea spray. In that case use 316.
 Don't spend too much on a pretty finish. That only affects the specularity of the reflection, not the percentage of light reflected.
304 bright anneal will be very hard to improve upon. This can be purchased from service center stock. Anything more will be diminishing returns.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: Best Stainless Steel for Mirror like Surface.

Hard-drawn or hard-rolled products are harder (have higher y.s.) than others.  They will deform less, and tend to embed less abrasives during the act of polishing.  302 and 301 are more typically supplied in sheet with 1/4-hard or higher ratings.

CPro, there are published values for s.s. in most heat transfer textbooks that are much lower for "polished" than "mill" finish.  Yes, specularity plays a role in lowering emissivity, but I think the ability to clean, and keep clean (i.e. free of heavy oxidation) is also part of it.  It's easier to see the dullness of oxidation build-up on a previously polished surface.

RE: Best Stainless Steel for Mirror like Surface.

(OP)
I am begining an experiment to see if nickel plated chromolly has lower emissivity than polished ss 321. Based on my application; I hope to find out that they are the same or nickel plated chromolly is better.  

RE: Best Stainless Steel for Mirror like Surface.

(OP)
I am begining an experiment to see if nickel plated chromolly has lower emissivity than polished ss 321. Based on my application; I hope to find out that they are the same or nickel plated chromolly has lower emmissivity.  

RE: Best Stainless Steel for Mirror like Surface.

Be careful of data generated with reflectometers which use only selected wavelengths. Stainless has poor reflectivity for blue light which is specified in ASTM 1549. This procedure gives falsely low values for stainless.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: Best Stainless Steel for Mirror like Surface.

mcquire,
In your vat repertoire of SS information do you have any information on the emissivity and reflectance of from a preoxidized surfaace on SS?

the reason for asking is that I was asked to do this on some 316 SS panels by using steam air + an organic for essentially the same purpose as the OP.  I oxidized about 20 2'x 2' panels and shipped the off and never heard anything back.  

RE: Best Stainless Steel for Mirror like Surface.

321 will contain many TiC inclusions by design.  If you can't stand many tiny surface flaws then stick with 316.
A cold rolled sheet to high hardness will help.
The final surface will need to be electropolished to remove any smeared material.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Best Stainless Steel for Mirror like Surface.

In answer to unclesyd, the emissivity will jump to that of the oxide, or about 0.85. The reflectance will be 1 minus 0.85, or 0.15.
Mirror-like stainless have emissivity of 0.05 to 0.10 with reflectivity of 0.90 to 0.95.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: Best Stainless Steel for Mirror like Surface.

mcquire
Thanks, they weren't doing what I thinking they were doing.  Your information has got my curosity up.  inquiring minds have got to know and the problem is that this group always worked behind closed doors and probably didn't leave any record.

RE: Best Stainless Steel for Mirror like Surface.

Chromium is odd for a metal. It has high emissivity, 0.64, and therefore absorbs much of the solar energy instead of reflecting it.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: Best Stainless Steel for Mirror like Surface.

I retract my statement on chromium, having found tables listing its emissivity at less than 0.10 in the polished condition. The same for nickel. The key is that polished, un-oxidized metals, in general, are highly reflective and have very low emissivity. The issue is how low they stay un-oxidized.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: Best Stainless Steel for Mirror like Surface.

Thought I said that? ;)

We used to gold plate a lot of heat shielding for s/c use, the issue was not oxidation build up in the vacuum environment of space, but the oxidation of the surface during the months leading up to launch.  Radiant heating being the only heat transfer method available, surface finishes become critical to maintaining temperature environments for spacecraft.  Gold being very noble, the oxide issue is avoided.  Similarly, at higher temperatures (where gold may diffuse into substrates) rhodium or other platinum group "noble" metals were sometimes used.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources