Dear Saad Waqar!

What is the aim of the etching trials you've done? Did you want to check etching behavior of SS 316L in as-printed condition? I think no: you need to perform metallographic evaluation. I propose, first, to take one of the samples, re-polish it and then subject it in non-etched state to Scanning Electron Microscopy (SEM) examination. I hope, you will be able to see the grain structure, porosity (if it exists) and to perform EDS micro-analysis in the desired places. After that you will be able to decide what else do you want to see and how do you need do improve you SLM process.

I think, you need to compare the obtain grain size of the as-printed material with the initial powder particles size and to conclude about the degree of the grain growth occurred. Also, I recommend to check grain boundary composition to to know something about surface contamination through SLM as well as about solute drag effect (solute segregation near grain boundaries) through numerous re-heatings (during SLM). Check also if undesired carbides formed. It is important for SS of this class.

Try with 50% HCl (approx a10 ml) nd a few drops of concentrated Hydrogen peroxide for general grain boundary etch first. It looks like you are etching everything to various amounts here. Oxalic acid 10% electroetch also works well for good relief-grain boundary contrast. Good luck