I don't know about steel, but brass and copper will melt before you reach cone 5.
You need a high temperature wire, which is called Nichrome wire. Do you see the blackness of the metal in the picture you have attached? that is how the Nichrome wire burns at cone 5, I have just yesterday used this wire for a different purpose (see "Nichrome wire" in "In the Studio" Forum).
Another option for you if you want to use copper or brass is to make the holes on your pieces, allowing for shrinkage, and then epoxy the metal after the clay has been fired. That is what I do when I make my Mexican Style Tree of Life, see attached picture, look close to the white dove, it is hanging with a thin wire and on the clay structure in the green part you can see the loop that I epoxy after the firing, I did the same on the back of the dove.
Thanks for your reply and the picture. I am new to working with clay and didn't know about the Nichrome wire. Also I never thought of the option of putting in holes to glue the wire in after firing. Thats a good alternative though I'd rather include it from the start.
From looking at the chart that AtomicAxe sent, it looks like I could use carbon steel, which I'm pretty sure is what the oxidized wire is that I get from the hardware store.
But ts not my kiln that I will be using, so I want to be positive that any wire I use won't melt. I wanted to get more educated about it before getting the kiln owners permission.
If they don't like the idea, then I have the other option.
Do you have a favorite source where you buy the Nichrome wire?