How to etch heat treated spring steel for observing prior austenite grain size (AGS) 1

[Best99]

Dear all,

After quenching and tempering. I did the tempering at 500℃x24hr for grain boundary embrittlement.Then etched by this solution

1. Saturated picric solution 50 ml (4g picric acid mix with water)
2. Surface-active-agent, Sodium dodecylbenzensulfonate 5ml
3. HCL 1.0ml

As a result, I cannot get clearly AGS as well.

Could you please guide me the how to get clearly AGS step by step

Thank you for your comment

 

[metengr]

http://www.georgevandervoort.com/me...oundaries-in-heat-treated-steels-article.html