Electropolishing produces the most spectacular results on 300 series stainless steels. The resulting finish often appears bright, shiny, and comparable to the mirror finishes of “bright chrome” automotive parts. On 400 series stainless steels, the cosmetic appearance of the parts is less spectacular, but deburring, cleaning, and passivation are comparable.
Solutions are available to electropolish most common metals. Notable exceptions include cast alloys of zinc, aluminum, brass, bronze, and carbon steel. Investment cast stainless steels may also be difficult to electropolish to a satisfactory finish unless parts are solution annealed after heat treating. In general, only the 200 and 300 series stainless steels, certain tool steels, copper, and some single-phase brass alloys can be electropolished to mirror finishes. The principal effects on other types of metal are deburring, smoothing, improvement of surface finish, and increased adhesion of plated coatings.
Electropolishing produces a combination of properties which can be achieved by no other method of surface finishing. Mechanical grinding, belting, and buffing can produce beautiful mirror-like results on stainless steel, but the processes are labor-intensive and leave the surface layer distorted, highly stressed, and contaminated with grinding media. The passivation methods commonly employed produce clean, corrosion resistant surfaces, but do not achieve the bright, lustrous appearance obtained by electropolishing. The corrosion resistance of electropolished stainless steel exceeds that of standard passivation processes.
Electroplating can produce extremely bright finishes, but the finish is a coating which can chip or wear off. Electroplated surfaces may also exhibit hydrogen embrittlement which must be stress-relieved in a separate step. Neither passivation nor electroplating can accomplish burr removal.
Processes are available for chemical deburring and brightening of steel and stainless steel, but these methods cannot match the surface improvement produced by electropolishing. The corrosion resistance produced by such processes is decidedly inferior to that produced by electropolishing.