Hello R. Saxena ,

I recently worked with 17-4 PH, and though I am definitely not an expert, I can share my experience with you.

I have used Kaling I reagent on 17-4 PH sintered parts (initial powder size with a D50 = 10-12 µm).

My protocol is a 200 ml solution containing 1/3 H20, 1/3 EtOH, 1/3 HCl (which concentration is vaguely given : 25-37%). My samples were always mounted in epoxy resin, and therefore I etched only 1 polished face. I dipped completely the sample in the solution with "manual stirring" meaning I gently moved the sample in the solution during etching.

Below 30s I usually do not see grain boundaries very well, and above 1 minute it looked always too etched like your pictures seems to be. So the time was about the same than yours, about 45s. However from one day to the other that time could change by 10s... (may be the temperature ?). In my opinion, I think your samples were maybe etched for too long.

Once etched I rinsed the sample under water for at least two minutes. This gave me the microstructure I attached in the file which I think is ok (optical microscope observation and only sintered on the left side). I also put a sample after solution treatment (on the right side) which does not look great with the same etching procedure. I also performed ageing (H900) but optically it looked very similar to the one after solutionizing.

I hope this helps.

Best regards,

Alexis B.

You could maybe try some of these:

http://www.metallography.com/bboard/messages/2002/11492.html

Hello, R. Saxena

In this study, we used Villela's reagent (80 mL of ethanol, 5 mL of

hydrochloric acid and 1 g of picric acid), but it was after heat treatment.

Article Damage associated with the interaction between hydrogen and ...

Thankyou Alexis Burr Iara Gripp Oliveira Jesper V. Carstensen for you replies. It seems very helpful and I will definitely try it.

Etching with Fry’s reagent with the required composition of CuCl2, HCl and ethanol for 10−15 sec

Thankyou Atef S. Hamada Sir for your valuable suggestion.