Black Iron Coating?

Angle "iron" is really steel, right? Wire brush it, heat it up again till it glows cherry red, then let it cool and wire brush again.
Then cook.
Milo, the real metals expert, would know for sure..

I would go with stainless....

I believe that SS takes a lot more heating up than MS. Someone else will know the numbers if it's important. I was once going to make an SS BBQ plate, but was advised of the heating up issue by a colleague more knowledgeable in this area than me. I guess a grill is different to a plate in the way it cooks, so I could be OK.

Why don't you buy replacement grates directly from the manufacturer or from one of the Big Box stores.......they are usually ceramic coated steel.

Just a thought.

Cheap bastard!! Want to do it myself!!

Heat it up a few times in the fire pit and then wire brush and if you want sand the metal back. The stuff on the surface sounds like its just mill scale from the hot rolling process used to make the angle. After cleaning it up, grill away. The oil from the meat will soak into the surface of the metal and protect it from rusting as well as providing extra "flavour" to your meat:)

That could be lead oxide from lead paint.

Check it with a lead test kit before you grill anything on it.

Or before you wire brush it.

If you are going to put food straight on the grate, and it is stainless steel, remember that stainless contains both nickel and Chromium. Don't.

If you are saying not to use stainless as a cooking surface because of nickel and Chromium then I supose every person that eats food cooked in take away food stores & restaurants in Australia will be in trouble as it is a required health standard to have all cooking equipment stainless steel, like Grillers, deep fryers, hot plates etc We also use stainless steel fry pans & sauspans at home SO Maybe we're all gonna die from chromium poisoning

You said you replaced grates. Sounds like the original one oxidized or "burned up". This is not uncommon if you use it, especially with lump charcoal. If it is the ones that the food sits on just brush them off before use.

You could sun them past a sand blaster to remove anything that is there. I also rebuilt my grates for the same reason, but I did mine out of 3/8" SS and SS 1x1 angle. I just let the dog lick them to get them clean the first time. They have developed a nice deep brownish color now, and are as good as when I welded them 4 years ago.