etchant for 304 stainless

[sunthorn]

My company has decided to do weld sample analysis in house. We have all the needed Buehler equipment to prepare metallographic samples. I have sectioned off a sample of two peices of 304 that have been tig welded. I have already ground and polished the samples to a mirror finnish

I need to know what etchant to use to see grain structure of 304 stainless steel and the weld bead between them.

 

[cocobolorose]

There's a lot to choose from. I just etched a piece with 6H2O-6HCl-2HNO3, immerse for about a minute or so. Very good results.

 

[NickE]

That depends a lot on what you are looking at.... My leco metallography boodk says to use the following etchants for general structure:

10g Oxalic acid in 100ml H2O. Electrolytic at 6V for 1min.

10ml HNO3 & 10-50ml HCl & 30ml glycerine -- warning poison -- use fume hood. -- do not store.... (there are also modified versions of these, usin H2O instead of glycerine or adding acetic acid.

10gCrO3 in 100ml H2O. Electrolytic at 6V for 3-5min. attacks carbides.

5ml HCl, 1g picric acid, 100ml methanol or ethanol. immerse or swab for sec to 15min. Rx may be accelerated by adding a few drops of 3%H2O2

2g CuCl2 & 40ml HCl & 40-80ml ethanol or methanol. possibly add 40ml H2O. immmerse or swab for a few seconds to a few minutes.

There are definately other different etchants that can give you what you want.

DISCLAIMER: The above formulae are poisons. They can be hazardous. They can kill you. They will hurt you if you let them.



Nick
I love materials science!

 

[EdStainless]

First try the Oxalic acid electrolytic etch. Use a small lab type power supply. Attach one lead to metal tongs and hold the part (you will need to make contact with it). Attach the other lead to a strip of stainless and place it into the beaker of acid solution.
You can adjust the voltage and time to get the desired degree of etching.
If you are mounting parts and have difficulty making contact either mount them as short as possible and grind through the back of the mount or attach a papper clip to the part prior to mounting. Then you just have to grind down the back until the paper clip is exposed.

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