Desmutting Steel

Question:

I want to desmut my etched 1095 steel. What are the typical ranges of processing conditions for electrolytic cleaning using something like NaOH + citric acid, or ferric sulfate? C.H.

Answer:

Probably the most important thing to mention is the type of electrocleaning. In your application, you would be best off with anodic electrocleaning. In this case, the workpiece is the anode. Oxygen bubbles will be generated at the surfaces of your steel that will assist in smut removal. Cathodic electrocleaning would not be recommended for steel since you would generate hydrogen bubbles on the workpiece that could lead to hydrogen embrittlement of the material.

Other interrelated factors to consider would be time, temperature and current density. Generally electrocleaning baths are run at a fairly high temperature, in the range of 180–200°F. Current density for electrocleaning of mild steel would be in the range of 50–100 amps per square foot. Time would be on the order of two to five minutes. These are fairly broad ranges that will need to be experimented with in order to zero in on the optimal process.

One last consideration would be the cleaner. I am not sure if the ingredients you list above are all that are in it. If so, you may want to contact a supplier of electrocleaners since I believe you can get more performance from a better formulated cleaner. Silicate (at the correct ratio) will minimize base metal attack. Surfactants will lower the surface tension of the bath allowing smaller bubbles to release from the surface which will increase the efficiency of the process. However, it would have to be formulated with low foaming surfactants since there could be the tendency to generate foam because of the oxygen gas generation and associated bubbles.