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Galvannealed vs. Hot dip galvanized
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Hello ,
Can anyone tell me the difference between a hot dip galvanize steel from a galvannealed steel? Thanks.
Most likely, which is cheaper? Can they both be powder coated?
Sharon S [last name deleted for privacy by Editor]- Billerica, Massachusetts
First of two simultaneous responses-- .
Hot dipped galvanized steel is produced by immersing steel into a bath of molten zinc, resulting in the formation of a pure zinc coating on the steel surface. "Galvanneal" refers to steel with a zinc-iron alloy coating. This is produced by heating a hot dipped galvanized surface so that the zinc coating and the top layer of the steel surface essentially meld together to form a zinc-iron alloy. Galvanneal would most likely be more expensive because of the additional processing. Either surface can be powder coated but you should consult the powder coating manufacturer to determine what type of pretreatment is required.
Patrick Patton- Westlake, Ohio
Second of two simultaneous responses-- .
1. Both processes involve coating the object with molten Zinc in a batch or continuous process. The main difference is that with the Galvannealed steel, the object is then post-processed by heating in an oven to induce diffusion alloying, creating the characteristic Zinc-Iron (6-15%) coating. See ASTM A653 [link is to spec at TechStreet], A924 [link is to spec at TechStreet], and A902 [link is to spec at TechStreet].
2. Expect the Galvannealed steel price to reflect the cost of the extra processing (heat treatment).
3. Both can be effectively powder coated. Check with the steel and powder coating vendors and reference ASTM D2092 [link is to spec at TechStreet] for the most effective surface preparation techniques.
Ted Bellinger- Merrifield, Virginia
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Sharon,
I'm a metallurgical engineer working in a galvanizing plant and I have to admit that Patrick and Ted answered your question very well. Just to add a few details of my own, a galvanneal steel has better paintability and weldability than galvanized steel. However it is less resistant to corrosion since the coating is lighter and not as adhesive to steel (because of the diffusion of iron in the zinc coating).
Luc LeBlancgalvanizing company - Windsor, Ontario, Canada
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Dear Sir,
Kindly clarify as to what percentage extent is paintability and weldability increased with galvannealed process compared to galvanised sheet, and point out the technical differences of galvannealed to this time electro-galvanised metal sheet.
Thank you for your assistance
Warm regards,
- Mauritius
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Hello, Joomratee. Galvanneal is designed to be painted; galvanized is designed to be left unpainted (although it is certainly possible to successfully paint it) -- and I think that's pretty much the whole answer. To try to answer "by what percentage" galvanneal is more paintable forces us to ask you whether you mean primary adhesion, secondary adhesion, freedom from undercutting, or resistance to filiform corrosion, and what spec you will use to measure adhesion and assign percentages to the differences, and what formula you want us to use to correlate this disparate data into a single index.
I've seen television commercials promising that some cosmetic or other will "reduce the appearance of fine lines by 78 percent" and I chuckle that they've "quantified" such an obviously qualitative parameter via crazy gymnastics. So I guess my answer would be that galvannealing improves paintability by 78 percent :-)
The zinc thickness of electrogalvanized sheet is far more controllable than the thickness of hot dip galvanized, but it is usual for the thickness to be far less -- perhaps 1/4 the thickness of hot dipping. Patient application of the search engine will reveal dozens of threads about that subject on this site. Good luck!
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
November 13, 2009
I want to know what kind of steel sheets can be galvannealed. Is there any constraint in galvannealing all kinds of steel sheets. If so why?
Fanish Tiwari- Chennai,India
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S |
November 13, 2009
Hi, Fanish. Sorry, I don't know the answer to your question, but this forum tends to offer better answers to questions which are cast in terms of actual situations. If you don't get an enthusiastic response, please tell the readers the details of your situation so the potential responder doesn't feel he has to cover a dozen ifs/ands/buts. Thanks! Regards,
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September 22, 2010
To answer your question I have a few myself.
Typically galvanizing is done in a line with coil which can then be sheeted. There are certainly other galvanizing processes with an actual dipping that could be done to coat sheets of steel.
I have yet to hear of anyone willing to put a galvanneal product on a sheet; this would involve laying the sheets down to run them thru an annealing cycle. Typically the annealing is done within seconds of the galv coating being applied. What type of application are you looking at?
- fishers, Indiana, USA
March 21, 2011
Hi I own 3 processing houses (Slitting & Cut To Length) in India. We stock Cold Rolled, Hot Dip Galvanize, Galvannealed, Aluminized Steel & Stainless Steel material.
My Question is
Why manufacture Galvannealed steel whereas a zero spangle or skinpass Hot Dip Galvanize steel can give almost similar type of powder coating finish?
Product Developer - Maharashtra, Mumbai
^- Privately contact this inquirer -^