Stainless Steel Electrochemical Etching

Electrolyte Solution, Electrical Etching Voltage and Current.

Better metallographic etching techniques for delineating grain boundaries for grain-size determinations in annealed austenitic stainless steels, and for delineating the microstructural constituents in carbon-steel-stainless-steel bimetal components such as weldments, weld overlays, or cladding have been long-standing needs. Accordingly, two improved electrolytic-etching techniques were developed and are described herein.

The first technique involves electrolytic etching of annealed austenitic stainless steel with a solution of 60 percent nitric acid-40 percent water and with low voltages and current densities ( 1 volt and 6–14 mA/cm2) to delineate the grain boundaries.

The second technique involves the use of conventional nital or picral etchants and electrolytic etching with a 50 percent nitric acid-50 percent water solution at specific voltages and current densities (1.2 volts and 20 mA/cm2) to reveal the structure of a carbon-steel-stainless-steel weldment. The nital or picral etchant is used to etch the carbon steel, and the electrolytic etchant is then used to etch the stainless steel without heavily overetching the carbon steel.