By -
Date 11-20-2000 21:54
An annex in B2.1 Specification for Welding Procedure and Performance Qualification lists popular etches for several types of base metals.
What type of metal do you want to etch? Nital (Nitric) works well on a lot of materials. If you used it previously and it doesn't seem to work as well anymore, it may be time to mix a fresh batch.
Marty
If you are etchig S/S, we found a mixture of 75% hydrocloric and 25% Nitric works well. Double check that, though before mixing. That was a long time ago. If I'm wrong, someone please correct me. I don't want to be responsible for someone getting hurt.
I would like to know more about this mixture (75hydro & 25 nitric) if anyone can help. I'm looking for a quick etchant for macro evaluation of 409 ss. Would like to stir away from using picric solution or electo polishing if possible. Any chemists out there who might have an opinion on this mixture? Is it safe?
Thanks
KAM
That mixture is called "aqua regia" by the chemists (I'm a chemical engineer). It's the strongest acid solution that exists, being capable of dissolving even gold. It shouldn't be handled by someone who is a prophane in chemistry and isn't accostumed to handle strong chemical products.
Giovanni S. Crisi
Sao Paulo - Brazil
I have used it and yes it is strong and as with any acid solution, precautions must be taken to ensure safety. However, you must admit, it works well for etching S/S.
You need to provide additional information. Are you examining ferrous or non-ferrous alloys. Do you wish to make a macroscopic or microscopic examination? What are you trying to see in your examination? Certain solutions are used for different types of examinations.
The Procedure Handbook of Arc Welding from Lincoln Electric has a good section on etching solutions. And NDTIII is right, you need to be extremely careful with etching solutions.
Thank-you all for your responses. I am checking for proper penetration on tests given the welders, on mild steel, as required by my customer. I have been doing this for three years and I am very careful handling the Nitol. The reason I have asked this question is that I am having a difficult time locating more nitric acid. Thank-you again for your suggestions and I will do my home work.
Here's another good source for polishing and etching info:
http://www.buehlerltd.com/Technical%20Information/technicalfrm.html
I assume you are talking "macro" etching and not "micro" etching. Most of the info at this site deals with microetching, but you should find some info on macroetching also. Look under the link for "Iron".
Also try: http://www.metallography.com/
Marty
