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Jac@stafford.net
30-May-2016, 16:07
For the first time working with hardware store steel I am stumped, but not alarmed. Perhaps an expert can inform me. I am making a mount for a Linhof grip platform to a non-Linhof body.

It is going perfectly well ... to a point. After shaping it, grinding to dimensions, and sanding, RUST appears overnight. I do not live in an environment that produces rust so quickly. I will coat it in zinc and paint it but a question remains to show my ignorance.

What kind of steel rusts so quickly, and is it a good or bad thing?

Thank you!

Richard Wasserman
30-May-2016, 16:42
What kind of steel rusts so quickly, and is it a good or bad thing?

Crappy steel—which is a bad thing. Just a guess...

Jac@stafford.net
30-May-2016, 16:58
Crappy steel—which is a bad thing. Just a guess...

Thank you, Richard. It might be the case. However, I have a couple of knives that rust and they are easy to sharpen to a very good edge compared to so-called stainless. Lots to learn! Oh, of course my application has nothing to do with sharpening. :)
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Jim C.
30-May-2016, 17:43
hmmm, I'm assuming it's a splotchy light rust, hardware store steel is either galvanized sheets or low carbon cold rolled in rods and flats, neither should rust overnight after working,
unless there's some open oxidizing agent like an acid nearby where it's stored, or if you have sweaty hands it could be from that too, human sweat can be mildly acidic.

Rather than a zinc primer I'd recommend Rust Fix from Duplicolor, I've used it with Packard Shutter cases after cleaning out the rust.

jp
30-May-2016, 17:48
I've done bodywork on nicer cars that will rust overnight if not covered with primer the same day. Prime/paint immediately, or treat with something like por-15 which seems harder than paint.

cowanw
30-May-2016, 18:20
I have had good results with "Rust Converter" by Rust Check. It contains Phosphoric acid. It turns iron oxide into iron phosphate, which is very stable. Like bluing on guns. multiple applications as you let the item rust and you get an attractive 18%grey colour.

Sean Mac
30-May-2016, 19:06
The more refined steel is, the more quickly it rusts.

Wrought iron is good for hundreds of years. Modern "mild steel" needs a sacrificial layer of zinc to survive.

No free lunches with the iron molecule. Let it flash rust and phosphoric acid conversion is safe and easy.

EdWorkman
4-Jun-2016, 08:03
I've been to Winona MN a few times
Let's say it's not a dry heat.
If you are considering a hot dip zinc, unless you have access to a freebie, a brass or bronze or stainless steel might do better

HiHoSilver
4-Jun-2016, 16:54
I have had good results with "Rust Converter" by Rust Check. It contains Phosphoric acid. It turns iron oxide into iron phosphate, which is very stable. Like bluing on guns. multiple applications as you let the item rust and you get an attractive 18%grey colour.

Hardware store steel is usually a mild 1080 or similar. Any uncoated ferrous metal will start rusting immediately, depending on environment. If you're not finished working the piece, & will take a few more sessions, it really doesn't matter much as further sanding, etc will come off immediately. When done working, there are various primers or cold finishes (Brownell's Oxpho Blue?) that end the rust. Cowanw's recommendation sounds well worth trying.

Jac@stafford.net
4-Jun-2016, 18:04
I've been to Winona MN a few times
Let's say it's not a dry heat. [...]

So true! Living with the Mississippi River on one side with two lakes on the other side, all in a valley kinda makes a humid environment. :) Hope you enjoyed your visit, regardless.

I have been using a green zinc spray available here. I has worked very well. I have a collection of high-carbon fasteners which have only the zinc coating and they have been fine for years. The next time I get some I will post the product details.
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Harold_4074
4-Jun-2016, 21:24
The reason that your freshly sanded/ground steel developed "flash" rust overnight is because the work you did removed all traces of otherwise ubiquitous oil from the surface. Usually steel wool is all that is needed to clean it up, and the oil in the steel wool will keep it from recurring to some extent. It is perfectly normal to see flash rust develop at MIG or TIG welds, because the heat eliminates all oil (and any other organics, like paint) in the vicinity of the weld.

( If you want to see something really rust, try washing steel wool in fresh lacquer thinner...)