For a Plain Low C, you could use Nital for grain boundaries observations, but also is possible use Marshall´s reagent, Picral or klemm´s +Polarized+sensitive tint, depending of the aim of you analysis and steel frequently is easy to use Nital for reveal grain boundaries in low C steels.

But if you want obtain information about of crystallographic orientation, is necessary to use another technique like EBSD.

I'd go for an acidic solution, it really depends on the steel you want to analyze.

For 304L I used proficiently oxalic acid solution..but again depends on what you want. For grain rotation or orientation changes you could consider the use of EBSD but that's another story..

First, you must determine initial each grain orientation of your material before "machining", again after this. For low carbon steel, for instance, HSLA steel, you can use : "nital solution at 3% and combined saturated picric acid aqueous solution-200ml + xylen–ethanol solvent system-50ml" to reveal grain boundaries....

For a Plain Low C, you could use Nital for grain boundaries observations, but also is possible use Marshall´s reagent, Picral or klemm´s +Polarized+sensitive tint, depending of the aim of you analysis and steel frequently is easy to use Nital for reveal grain boundaries in low C steels.

But if you want obtain information about of crystallographic orientation, is necessary to use another technique like EBSD.

You can try different grades of Nital, I suggest you to go and check the related ASTM standard or ASTM Metal Handbook... The concentration and duration will change in relation with the grade of your steel.

Thank you so much for all helpful responses!

Nital, Picral,Villela's reagent

Dr. Pulla Sammaiah, SR Engineering College, Warangal.

Different grades of Nital solution needed for etching

Nital (100 ml ethanol and 1-10 ml Nitric Acid) or Picral (100 ml Ethanol and 2-4 grams) are recommended etchants for low carbon steel. Some recommend to use Vilella's Reagent (45 ml Glycerol, 15 ml Nitric Acid and 30 ml HCl) too.

For low alloy steel you may use Marshall's reagent: 25g Oxalic acid, 10 ml H2O2, one drop H2SO4, and 1000 ml water. The sample should be immersed for 5 minutes at 20C.

Nital, Picral are standard I would say.