ASTM B242-99 (2020) pdf free.Standard Guide for Preparation of High-Carbon Steel for Electroplating.
Electropolishing is used to remove highly stressedmetal and metal debris from the surface of cold-worked steel,thereby improving the bond strength and corrosion resistanceof electroplated coatings. It accomplishes this function withoutthe tendency to form smut，which may result from anodicetching. Because it does not etch the steel, it is preferred bysome electroplaters to anodic etching for preparing steelsurfaces for decorative electroplating. Proprietary mixtures ofphosphoric and sulfuric acids3for electropolishing are ofspecial interest in view of their ability to remove smut fromcast iron surfaces. The addition of chromic acid to sulfuric-phosphoric acid mixtures further provides a surface passivation that is beneficial in preventing rusting during transfer orduring temporary storage of steel prior to electroplating.An activating treatment after electropolishing can bebeneficial to subsequent electroplating. An example of asuitable activating treatment is anodic cleaning followed byacid dipping. Electropolishing can be used in addition to orinstead of anodic etching.
Electropolishing of finegrained steel provides auniform,smooth finish. Electropolishing of a coarse-grainedstructure (No. 6 or coarser) results in less smoothness. In eithercase, however, a word of caution must be interjected, namelythat any seams， voids, stringers， and other surface defects canbe damaging to the appearance of the electroplated coating.Yet, the removal of sharp edges or scratches and the removal ofnonmetallic inclusions in seams and stringers can reduce theharmful effect of these defects on the corrosion resistance ofthe electroplated steel.
The hydrogen may be largely removed andthe physical properties of the steel substantially restored byheating, for example, for 1 to 5 h at temperature in an ovenmaintained at a temperature of 150 to 260 °C, the temperatureand length of treatment depending on the severity ofembrittlement, the cross section of the article, the requirementsof the steel, and the kind and thickness of the electrodepositedcoatings.The baking should be done as soon as possible afterelectroplating,and before any supplementary chemical treat-ment of the electroplated surfaces. The best time and temperature in some cases must be established experimentally. Atemperature not exceeding 205 C is recommended for zinc-orcadmium-electroplated articles. A lower temperature may berequired if the coating is to be given a subsequent chemicaltreatment.ASTM B242 pdf download.