Selection of high heat coloring alloy

[fastline12]

We have some artsy people requesting parts be machined, then heat colored with a flame. These parts do not have any structural concerns. We ran some tests with some PH stainless materials for customer consideration and they were looking for more "pop". I am now considering a Ti alloy unless we can find a stainless alloy that will color nice?

If we select a Ti alloy, cost and machinability will likely be the ONLY considerations. I have never compared all the alloys to determine which is cheaper, easier, etc. I am hoping a metallurgist can offer advice? Due to the cost of Ti, I was hoping there was a Ni alloy that contained just enough Ti to get the colors we need without the price tag and obvious structural benefits.


Any other materials may be considered as well. The only consideration is flame treatments only, no clear coats, paint, etc. They are looking for a raw display of material.

 

[mrfailure]

Don't know what you mean by "pop". You can get a vivid spectrum of colors using carbon and alloy steels from heat tinting. Leaded steels are particularly easy to machine.

Aaron Tanzer

 

[fastline12]

The arts product will be displayed outdoors and subject to the elements so SS and Ti are being requested. "Pop" just refers to the bright color appearance of the material. It seems that though SS colors up, it does not seem to product the bright blues the customer desires. There is a HUGE difference in price for Ti though. We are trying to find a solution that will be corrosion resistance, reasonable to machine, reasonable price, and will heat color similar to Ti (if that is possible)?

 

[EdStainless]

The problem with doing this to a stainless is that the color is from chome oxide, and forming these very thick layers will reduce the corrosion resistance.
Their are people that us an electrolytic process to color stainless that leaves very thin films, good color, and does not reduce the corrosion resistance.

http://www.millenniumtiles.com/#application-color.php

Doing this by heating you want a stainless with as much Cr as possible.
What are machining, bar?

Are they passivating after this? They might need to with SS to prevent rusting.

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Plymouth Tube

 

[fastline12]

Most of it will be machined from plate or flat bar. Our test coupons showed a rather thin color layer that could be 50% removed with a quick polish. Obviously with something like this, structural no-no's are observed. This will actually have partial cover from the elements and certainly not submersed. I have no doubt there might be some corrosion of SS. There have been no plans to post treat as of yet. Material selection is primary right now.

So will a higher Cr SS compare at all the vibrant coloration of Ti? If Ti is selected, is there a grade that is more reasonably priced? I am only really familiar with structural grades for aerospace.

 

[EdStainless]

Well not as bright as Ti, but a stainless like 430 or 439 develops a lot of color, nice blues.
You have to keep the heat tint very thin to get bright colors.
And the more polished the starting surface the brighter the color will be.

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Plymouth Tube

 

[redpicker]

Just to add, I don't think Ti will give you any color other than white/gray. I don't have a lot of experience with Ti, but I did some heat treating of Ti in an open atmosphere in school and, as I recall, the surface remained white, but it did form a grayish scale; not the black scale you get with iron. I guess if you polish the Ti, you might get some color to develop, but I would expect it to be rather faint, not the brilliant blues you can get with polished 400 stainless steels, as Ed mentions.

rp

 

[mrfailure]

Remember, the color of the heat tint is really dependent on the thickness of the surface oxide film, as coloration is created by the interaction of light with this film. 400-series stainless as Ed suggests should do the trick, but I would try resulfurized Type 416 or 420F for this purpose as they have the machinability you want.

Aaron Tanzer

 

[TVP]

Here are some options for electrochemical coloring of stainless steel:

http://www.gagecorp.net/gmsite/coloredstain.htm

http://test.henkel-epol.com/en/serv...procedures/colouring-of-stainless-steel-.html

http://www.theinoxincolor.com/en.html

 

[EdStainless]

The whole trick to tint coloring any metal is the thickness of the oxide.
It needs to be an interference layer, that is the thickness needs to be on the order of the wavelength of light.
Then it will act like the oil sheen on water causing refraction.
Ti will give great colors, but you have to heat very gently.
As the layer gets thicker they get dull and shift toward the natural color of the oxide itself.
In Ti this white/grey, in stainless it is black/brown.

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Plymouth Tube

 

[ornerynorsk]

If your people are open to other methods, there are some old-school metal colouring techniques (non-thermal) in machinery's handbook. Also, there is a company called Steel F/X which supplies many metal treatments.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[fastline12]

It might be something to bring up. What non-thermal options are you referring to? Just curious.

 

[EdStainless]

There are some old school chemical staining methods.
But some of the chemicals are interesting.
The new stuff is electrochemical.

Do they really want it all one color of do they want variations and shading?


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Plymouth Tube

 

[fastline12]

They are looking for variation in color used to accept key features of the work. We are not artists here and will do what we can..which I believe will be acceptable for them. A sample was brought over exhibiting the typical heat rainbow they are looking for. However, Damascus type designs would certainly impress them. They are not looking for a single shade.

The goal is to have a "raw" appearance, not plated or otherwise coated.