brick or steel flue?

why not use thick steel for a flue?

Thanks Nick

Now that I can post again, here is more about this. The fire brick that I see range from a max service temp of 2,200f to 2,800f. Steel has a max service temp of 2,300f to 2,700f. My set up is for a 150sf shed. It has been insulated and sealed well. My plans are to build a 4'' J stove out of 3/8ths A36 steel. I have a steel 8''od tank with 11 gauge wall. I will insulated it with a 10 to 1 vermiteulite mix. I have a 11'' drum to use around that.

I have seen posts about the steel flue burning out. How thick was the steel used in those? I have no problem if fire brick is the only way to go for long term service life. I just happen to have the steel at my shop already, no cost. Thanks for any help.

Thanks Nick