Best Stainless Steel for Mirror like Surface.

[zj4041]

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.

 

[btrueblood]

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...

 

[zj4041]

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

 

[Metalguy]

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

 

[Compositepro]

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

 

[mcguire]

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/

 

[btrueblood]

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.

 

[zj4041]

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.

 

[zj4041]

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.

 

[mcguire]

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/

 

[unclesyd]

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.

 

[zj4041]

ive been using the data sheet from omega-

http://www.omega.com/temperature/z/pdf/z088-089.pdf

no worries, im going to calculate the emissivity based on wall temperature.

 

[EdStainless]

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

 

[mcguire]

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/

 

[unclesyd]

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.

 

[mcguire]

Now, who could that be?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[IRstuff]

So, how about chrome plating?

TTFN

FAQ731-376

 

[mcguire]

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/

 

[IRstuff]

OK, how about electroless nickel, then?

TTFN

FAQ731-376

 

[mcguire]

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/