Corrosion Resistance of Black Oxide Coatings on Mild and Corrosion Resistant Steels

摘要

The various processes were reviewed and evaluated for their effectiveness in blackening mild steel, 300 and 400 corrosion resistant steels. The corrosion resistance of these coatings were also investigated. A low temperature Class 4 proprietary alkaline-oxidizing process was proposed for blackening only the 300 series stainless steels in lieu of the fuzed salt oxidizing process which operates at 760F. The Class 2 alkaline-chromate process did not blacken the 300 series stainless steels. Class 3 and Class 4 processes did. The mild steel control panels, coated and uncoated, failed the salt spray test in one hour. The electrodeposited coating failed in three to four hours. Freshly abraded control stainless steel panels 302, 310 and 321 were without rust after 500 hours. Proprietary coatings A-1 and B applied to freshly abraded 302 and 310 series stainless steel panels were without rust after 500 hours. On the 321 series stainless steel panels, initial rust was noted on Coating A-1 after 165 hours and on Coating B after 141 hours. The 300 series stainless steels specimens coated with the type 3 (molten dichromate process) failed in the salt spray test in one hour. (Author)