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Avoiding Hydrogen Embrittlement in Galvanizing - How?
Q. Heavy support steel - Formed with tight radius and welded in some cases.
How is Hydrogen embrittlement avoided when hot dip galvanizing.
It has been suggested that bright annealing before dipping will prevent embrittlement or mechanical cleaning not chemical cleaning before dipping.
If forming is performed hot not cold it is also suggested that this prevents embrittlement.
Any information would be appreciated.
Nigel Green- Oxon, England
2002
A. I have read that the steel should be worked above 650 °C (1200 F). If cold working cannot be avoided, the pieces should be stress relieved. Depending on the severity of the bend Strain age embrittlement may be the problem. ASTM A143 highlights some of this (Standard practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement). You should be able to find it through the European Galvanizers Association (www.egga.com).
Good luck,
Mike Stroia- Canton, Ohio
2002
A. Hydrogen to be absorbed comes from 2 sources. 1-acid cleaning 2- electroplating of metal with hydrogen reduced at cathode. Please see if you are using inhibitor in acid cleaning. It seems that the problem comes from your uninhibited acid used for cleaning more than stresses in the workpieces which in turn is weak point after hydrogen absorbing to it.
Hadi Khosravi- Tehran, Iran
2002
Q. I am an Industrialist and want to know does En8 material break after hot dip galvanize due to stresses? If yes, then please advise at what temperature should we normalize.
Thanks
- India
July 21, 2012
A. Mr Walia,
The parts you are galvanizing, are tempered? There could be tempering embrittlement, embrittlement because of mechanizing stresses or Hydrogen embrittlement...
The first one, you could avoid with normalizing your formed parts at a normalizing temperature (this could depend on the oven, I'm not an expert on this area but you could make some tests to see the microstructure of the material to adequate the process) and heating below normalizing temperature AFTER tempering to achieve final hardness (specified by client) and stress relieving.
The second one, normalizing can do the same thing for this...
The third one, clean or etch before galvanizing with shot peening instead of hydrochloric acid, or add more inhibitor in the acid. The acid etching always make the risk of Hydrogen embrittlement some higher, so if you can clean without etching in acid, the better.
I hope this help you getting better! Best regards,
- Buenos Aires, Argentina
July 23, 2012
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