Galvannealed vs. Hot Dip Galvanized
Q. Dear Sirs; I am the owner of a small midwest supplier of industrial cleaning compounds and iron phosphates. One of my top accounts is going to start producing their products (currently cold rolled steel) using galvannealed steel. My question is what is the best way to prep this metal prior to painting? The products mentioned are rather large and bulky, and would not fit on a conveyor or monorail system.
Q. 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
- Billerica, Massachusetts
First of two simultaneous responses-- .
A. 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-- .
A. 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], ASTM A924 [link is to spec at TechStreet] , and ASTM 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
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 LeBlanc
galvanizing company - Windsor, Ontario, Canada
Q. 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
A. Hello, Joomratee. Galvanneal is designed to be painted; galvanized is designed to be left unpainted (although it is certainly possible to successfully paint it). So galvanneal is more paintable, and I think that's pretty much the whole answer. To try to answer "by what percentage" would force you to tell us what spec you will use to measure adhesion and under what circumstances (aging time, edges vs. flats, and how you intend to assign percentages, and what formula you want used to correlate this data into a single index.
I often see a television commercial which promises that a particular cosmetic "reduces the appearance of fine lines by 78 percent" and I have to chuckle about how they've quantified such an obviously qualitative parameter. What they obviously did was pick a nice answer they wanted to claim (90 percent won't be believable; 50% won't be inspiring enough), and then design the "test" to deliver a number in that preferred range. A fly on the wall told me that the test went like this: "Too low, too low, move 8" further way before you look at her ... no no, too high, change the bulb from 60 Watts to 75...")
So I guess my answer is 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!
Ted Mooney, P.E. RET
Brick, New Jersey
November 13, 2009
Q. 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
November 13, 2009
Hi, Fanish. Do you mean thick vs. thin sheets, old vs. new sheets, pickled & oiled vs. cold finished, high carbon vs. low carbon, large sheets vs. small ones, flat vs. formed, sharp edged vs. rounded edge?
Sorry, I don't know the answer to your question, but this forum usually offers more enthusiasm towards questions which describe an actual situation rather than cast in the abstract. Sometimes a potential responder doesn't feel like replying if it will take several pages to cover every possible if, and, & but. Thanks!
September 22, 2010
A. To answer your question I need to ask a few.
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
Q. Hi I own 3 processing houses (Slitting & Cut To Length) in India.
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