Dear researchers,

I am studying the microstructure of the high strength steel cable using an optical microscope examination. My steel cable has the tensile strength of 1860 MPa and the chemical composition as (C 0.91, Si 0.07, Mn 0.45, S 0.003, Ni 0.01, Cr 0.28, Zn 0.31, and Fe balance). First, the sample surface was put into the epoxy modes with a diameter of 25 mm, and then they were polished using several diamond carbides. After that I have tried to use the acid solution with HNO3 3% in a period of 30 seconds to etch the sample surface, however, the surface is not good. I can not clearly observe the microstructural phases. Can you recommend a suitable acid solution to etch the surface of high strength steel?