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shouldco t1_isgah1l wrote

Reply to comment by BigBobby2016 in How come some Galvanized steel panel have patterns? by LameTrouT

Yes and no.

The prominence of the patten varies to the point of not being discernible. In theory you could have a single crystal but let's just say that is practically impossible for anything commercially produced.

Basically each section of the pattern is a single crystal of zinc. Which means there was basically one nucleation point every 1/2 a square inch or so. In order to get that few you need a pretty smooth piece of steel so it is more prominent on things like cold rolled steel and sheet metal. Stuff like cast steel has a very rough texture and can have thousands of nucleation points per sqin and as such you will basically just see a flat gray color with the naked eye.

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Br4veSirRobin t1_isghn1y wrote

It's called galvanneal and it is used in painted car panels. After dipping in zinc the steel goes through a furnace to slow nucleation-crystallization. It is a matte gray finish and paint sticks to it very well.

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LameTrouT OP t1_isgicpz wrote

I believe they must do this for hand rails ls that get a color after getting gavinized?

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Br4veSirRobin t1_isgj7kg wrote

The patterns on the surface of galvanized steel are called 'spangle'. People who use galv steel order spangle size. Antimony is used in the molten zinc bath for spangle size control among other process controls. Metallurgist here.

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cr0n1c t1_ish88jy wrote

So far down to find someone finally saying Spangle. Thank you.

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Br4veSirRobin t1_isgirrk wrote

True. Any painted galvanize is is usually galvanneal. I was a metallurgical engineer in both carbon steel and titanium.

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shouldco t1_isgmwn7 wrote

Thank you, I was unfamiliar with that industrial application.

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