Metal finishing Q&As since 1989

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Hydrogen Embrittlement after Chromium Plating

Dear Sir,

My name is Cristiano, I live in Brasil and I would appreciate if you could provide me with info to clear out some doubts:

Regarding Baking Process after Chromium Plating on Metal Alloys to release Hydrogen I have some questions:

What is the effect of time variation between the end of the plating process and the beginning of the bake cycle, as regards the hydrogen release ? An increase in this time would compromisse the hydrogen removal and would make the metal or part prone to Hydrogen Embrittlement failure ?

How would that affect a Cr-Mo-V (Chromium Molibidenium Vanadium Steel Alloy) ?

Best Regards.

Jose Pereira
Student - Rio de Janeiro, Brasil
2004

Hydrogen gets in the crevices of the grain boundaries of the metal in the etching process and some in inefficient plating processes like chrome. After the chrome layer is established, virtually no more hydrogen gets into the metal. The hydrogen permeates the metal in these grain boundaries over time weakening the metal. Baking expands the gas and forces it out in the very tiny pores in the plate. The thicker the plate, the harder it is to get the hydrogen out. The higher the temp, the faster it is removed. Limits are many metals further soften or anneal or temper above 400F. The longer the part is baked, the more hydrogen is removed. The longer you wait to bake the part after plate, the deaper the hydrogen has gone and the harder it is to get it out as well as it has allready damaged the part some.

The harder the part metal is, the more effect hydrogen embrittlement is. It has virtually no effec on cold rolled steel, but is a killer on fully hardened 4140 steel.

Small amounts of alloy metals have virtually no effect on hydrogen embrittlement.

James Watts
- Navarre, Florida
2004