300 Series Etch 1

[ndtkansas]

I would like to find a good etching solution to use in a production setting for 300 series stainless steel parts. We need to remove between 0.0002-0.0007" of material. Common grades are 304, 316....

 

[EdStainless]

Macro etch? why do you need to remove that much metal?
Sounds more like electroplidhing to me.
Look for info on commercial EP solutions. They are mixtures of sulfuric and phosphoric acids, and you will need a good DC power supply.
I don't know of any way to do it other than electrolytic.

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Plymouth Tube

 

[TVP]

ndtkansas,

Can you provide a little more background on the type of etching you want to perform? Is this etching to reveal the micro- or macrostructure? Or is this etching to remove material for some other purpose (aesthetic, dimensional control, etc.)? I agree with Ed that this sounds like a requirement that electropolishing will probably be necessary in order to meet.

 

[ndtkansas]

The reason for the etch is to remove smeared metal prior to Fluorescent penetrant inspection. It is a specification requirement.

 

[mcguire]

A very aggressive pickling solution is 2%HF/12%HNO3 (approx). Stainless producers use this for metal removal.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

Mac, We pickle in 24% Nitric/5% HF at 130-140F.
We can take a 0.001" off in 30 min.

Be aware that pickling will make the surface rougher. On 316 they get very rough.

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Plymouth Tube

 

[mcguire]

Wow, Ed. You go after it. Good information.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

for lower corrosion resistant grades (PH and 400) we lower the HF to 0.5%.
For high Ni high Cr (6%Mo and 625) we drop the Nitric to about 8%.

We are removing oxide and Cr deleted layer from annealed products.

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Plymouth Tube