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Black smut produced on the surface of a nitride high carbon steel after acid dip

2003

Q. Dear friends,

Having to electroless nickel plate a mold made of Uddeholm's IMPAX high carbon steel, that has been nitride and polished, I encountered the following problem:
After alkaline cathodic cleaning and acid dipping (HCl 50% diluted with water),and before proceeding to nickel strike, the surface became black (carbon smut probably?).

Searching in bibliography I found several suggestions like cyanide dip, cyanide or alkali anodic treatment, anodic acid etch, anodic or periodic reverse treatment in a solution containing NaCN, NaOH and tetrasodium salt,etc.

Since the piece is a polished mold, I would prefer to avoid anodic treatment. Any suggestions?
Any other procedure that will not cause the production of this smut on the surface?

Thanks in advance,

CHRISTOS SIGALAS
plating shop- ATHENS, ATTICA, GREECE

A. Only attempt the suggested anodic treatments or acid dips if you can do it in a conspicuous area or better another part with equal treatment. Have ready an EN striper as you probably will need it. What we have found to provide the necessary micro-roughness and avoid smut is a blast with superfine AlO2 (mesh 600) after a thorough manual clean, blow off the sand, rinse and directly to the Woods; let stay for few seconds (only to soak it in), strike for 1-2 min, rinse, EN plate at least 0.002" to allow for final polish. Carefully inspect the surface right after the strike. Complicated geometries are prone to incomplete coverage in areas of low current density, thus you may have smut or adhesion problems in those areas. If everything seems OK, bake the mold right after the plate. Re-polish.

Guillermo Marrufo
Monterrey, NL, Mexico
2003

Mr. Marrufo,

Thank you for your suggestion. Any particular EN stripper without toxic fumes?

CHRISTOS SIGALAS [returning]
- Athens, Greece
2003

adv.

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