Dark etch effect on 410

[Shaw123]

I’ve experienced some dark etched areas on some 410SS billet during macro examination. The samples have also been micro examined. All etching was carried out using Kallings solution. The structure is tempered martensite but there is still the darker etched regions.

I know martensite appears dark under Kallings but these features appear burnt/over etch when compared to the other martensitic regions.
Does anyone know if there are any segregation or freckeling features that can occur in 410 material and cause this etch effect?

Thank you

 

[jsokal]

Might it be a case of "burning" during sample preparation,...i.e overly aggressive cutting?

John