Q. What do you recommend for testing of blackened steel surfaces? We use a room-temperature chemical blackening process and wish to test for corrosion resistance prior to shipping the finished product. M. J.
A. Using the standard ASTM B 117 salt spray protocol, you will obtain somewhere around two hours of salt spray resistance from a hot blackening solution. The room-temperature black oxides have much less corrosion resistance.
I have always felt that the black oxide finish is primarily an appearance finish and is not of much help in terms of increasing corrosion resistance.
If you are applying the black finish to tools, I would recommend the hot process since you do obtain a little more abrasion resistance compared to the room temperature processes.
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