In an Axeman Anderson, coal feeds in the top, gets burned as it settles and the ashes are pushed out from the bottom. I wanted to see how long it took to go through one stove full of coal. I took a cube block of steel, 1" by 1" by 3/4" and set it on the very top of the pile of fuel. I kept checking the ashes with a magnet. 40 hours later it completed it's trip and here's a picture of it. It still weighs about the same!
I've used my hotblast furnace to heat up some 3/8" steel rod when I made some tools for poking the fire and getting clinkers out of the grates.I bent a 45* angle on one end and a handle on the other end.It only took 1 or 2 minutes to get it really red.Bent like butta. DON
I knew it would go through without jambing. Plenty of room. No lead! This was a piece of steel bar that I had kicking around. 100% cold rolled steel. I poked into the fire once with a copper tube... the end melted. I didn't expect the steel to melt like that though, I figured it would just turn red, then come out in the same shape as when it went in. It sure does get hot in there!
Cast iron has a melting point about 4-600* higher than steels depending on the grades. It will also hold it's shape better as it approaches it's melting point. As a material for shaker grates, it has about a 600* advantage over steel IIRC.