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Deep Etch in High Temperature Steels

I have a need to be able to etch a pattern into a high temperature steel. (Sorry, I don't know which alloy we will be using yet. However, you can bet it has plenty of nickel, chrome, and cobalt in it as these typically do.)

What I am thinking of doing is to use a photoresist and then a chemical / acid etch. The etch needs to be .007" deep and have a smooth finish in the etched area when complete.

I am a bit dubious as to how smooth a finish I can get with a chemical / acid etch. (Being new to doing this.) Should this be followed up by a electropolish? If the photoresist areas are still coated, will that help protect those areas from being electropolished? How smooth a finish could I expect an etch by itself to achieve at this depth?

Any pointers or suggestions as to acids / resists, and techniques would be greatly appreciated. I'm a bit new to this area and so I would welcome all advice and/or pointers. Oh, while I have posted this in the non-professional area (since I am not a professional finisher), I have a fair amount of experience in chemistry, machine work and am reasonably technically adept and this is for a commercial project.

Thanks,

(Oh, this project is still in the prototype phase and so right now, we are exploring what directions are available.)

Art Pollard
- Provo, Utah

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Etching through a photo resist is a common procedure but a straight forward chemical etch with something such as ferric chloride ⇦this on eBay or Amazon [affil links] will tend to undercut the photoresist. By contrast electro-polishing will not tend to undercut.

Electro-polishing etched surfaces is not very effective in producing a smoothed surface. Why not electro-polish the entire pattern into the surface? In this way you will minimize undercut as well as get a smooth surface and you will eliminate the need to perform two operations on your parts.

We routinely polish 50 caliber machine gun barrels and remove as much as .003 inches as well as putting a programmed taper into the bore. By comparison etching .007 inches using a photo resist seems relatively straightforward.

The photoresists that I have worked with all resist the electropolishing electrolyte with no problems, so your concept seems sound to me.

Good luck with your project.

John Holroyd
- Elkhorn, Wisconsin