If it were me I would go with the 316 SS and split it in to 2 grates 30"X24" if possible makes it easier to clean them!
Just my 2 cents worth!

 

304 is the typical alloy used in commercial kitchens. Be sure it is 304L. The "L" is a critical distinction here. The low carbon is necessary
308 is a welding alloy. Not appropriate.
316 is overkill. Again, 316L is ok, 316 is not.

If it were me, I'd contact the guy selling this stuff:
http://www.ebay.com/itm/140547351845

Most likely you can buy a complete grill for less than you'll be paying for the metal alone.

 

Check this and answer your question yourself:

Graph shows time to sensitisation for corrosion. I mean corrosion caused by aglomeration of chrome carbides inside the alloy, and therefore reduction of chromium volume in some regions.
Tell me please how is this type of corrosion called in English.

I'm sure that the temperature ot the grates will not exceed 400*C.
Both 304 and 304L will work

 

I'm sure that the temperature ot the grates will not exceed 400*C.
Both 304 and 304L will work

I've seen the stainless grates on my Weber glow when the wife leaves the grill on high to burn off grease and forgets about it.
You're right that cooking temperatures would never get that high, but a grill can in the right (wrong) conditions. Anyway, the difference in price between 304 and 304L is negligible (if you can even find plain 304). Same cannot be said for the difference in price between 304 and 316. 316 is WAY overkill.

 

Buy a sheet of 304L expanded metal. All the benefits of stainless steel, none of the fabrication time and cost.

 

BOOM! What DAB said.

Plus, replacing expanded metal when it's worn out is so much easier and cheaper than the stainless material.

 

To me if you are not going to use Inconel which I do not even know if it is allowed against food because of all the nickel in it. I would just use 1/2" or 5/8" iron square bar. With a 3/4" or 1" square bar for support. Inconel is a super high temp dead alloy that barely distorts when you heat it. But iron bar will hold up for a while. And it will keep costs down. I used to make them for guys that did barbeque here in New York. I am sure it will distort with time. But what metal will not?

Sincerely,

William McCormick

 

No need to spend the extra on stainless. Go to your local metal supply and ask for expanded sheet: 3/4-9 flattened. Its inexpensive and heavily used as BBQ grill grate. Very common. If you want stainless it comes in stainless also.

 

Did these about 10 years ago from 304. Never heard any complaints.