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Galvannealed vs. Hot Dip Galvanized

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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.

Sincerely,

Robert Bdeleted
industrial supply


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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 Sdeleted
- Billerica, Massachusetts


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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


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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


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A. 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 LeBlanc
galvanizing company - Windsor, Ontario, Canada


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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

Warm regards,

JOOMRATEE Yasseen
- Mauritius


+++++++

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 certainly did was to start by picking a nice answer they wanted to claim (50% won't be inspiring enough, but 90% wouldn't be believable enough; maybe 75%? Close, but too "round" ... so they shoot for 78%), and then design the "test" to deliver a number in that preferred range. A fly on the wall told me that the test probably went like this: "The difference you're seeing is too low ... move 2 feet further way from the model before you look at her ... no, now you're too high ... change the bulb from 60 Watts to 75 watts ... You see 78% difference now? Perfect! Cut. That's a wrap!")

So I guess my answer is that galvannealing improves paintability by 78 percent :-)

The zinc thickness of electrogalvanized (zinc electroplated) 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!

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, 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
- Chennai,India


sidebar
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!

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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?

Marc Masters
- 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?

Mehul Doshi
product developer - Maharashtra, Mumbai



A. Hi Mehul. I don't have a definitive answer for you, but I think galvanneal, due to the additional annealing, probably has more iron on the surface for more reliable adhesion.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

October 5, 2014

A. The difference between galvanizing and galvannealing is nothing except what we do do force iron to diffuse to zinc coating. This function is post annealing after zinc coating normally to 500 °C in a furnace about 30 meters long. In this treatment the iron will distribute to zinc coating and the brittle phase will become more homogenized; this will cause galvanized sheet to have more weld-ability especially for automotive applications.
Each way that it can diffuse iron to zinc coating will use like reducing Al in zinc bath and Si in steel substrate

jamal ashouri
msc - esfahan,Iran



Where to get metal in gunstock or dark slate, and how to form it?

March 14, 2014

Q. I HAVE GOT A REQUEST FOR CABINETS WRAPPED WITH METAL IN A GUNSTOCK COLOR OR DARK GRAY SLATE COLOR. WHERE CAN I GET THE MATERIAL AND HOW CAN I FORM IT?

DARRYL TERRY
renaissance - decatur, Alabama


March 2014

A. Hi Darryl. Please remember that people can have very different finishes in mind when they use words like "gunstock color" or "dark gray slate", so there is a fair probability that what you furnish may not be what the customer had in mind. But you could buy galvanized sheet (available in large quantity from a steel warehouse or small quantity from a hardware store). You could form it with a sheetmetal brake, and then you could try a patina for zinc. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

Novacan Black Patina for Zinc

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