Summary for hydrogen embrittlement in galvanizing Discussion
hydrogen embrittlement in galvanizing is discussed as a risk tied more to prior processing than to the zinc bath itself. Nigel Green asked how to avoid it for heavy, tightly radiused, sometimes welded steel, and whether bright annealing, mechanical cleaning, or hot forming would help. Mike Stroia said steel should ideally be worked above 650 °C (1200 °F); if cold working is unavoidable, the parts should be stress relieved, and ASTM A143 covers safeguarding against embrittlement. Hadi Khosravi added that hydrogen can come from acid cleaning or electroplating, and suggested the problem may be uninhibited acid cleaning rather than workpiece stress alone. In a later question about En8, Daniel Montañés said several embrittlement mechanisms may be involved, including tempering embrittlement, mechanical stresses, and hydrogen embrittlement; he recommended normalizing formed parts where appropriate and avoiding acid etching when possible, using shot peening or more inhibitor instead.
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
Sudershan Walia
– 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,
Daniel Montañés
– Buenos Aires, Argentina
July 23, 2012
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