Yeah I'd been wandering if it might be worth while to coat the inside, or perhaps even the whole thing with some sort of refractory mud or some such. Sounds like it may be worth a shot.
@merlijny2k by "get a better flame" I presume you're meaning a larger burner? I do have the ability with my current setup to add a third torch in another hole. Just hadn't gotten around to trying it yet. I was thinking that even though my bricks get a lovely orange hot eventually (on the very inside that is, the outside stays relatively cool) I figured perhaps they weren't holding the calories adequately to allow the heat to build up to steel's yellow or white hot levels. (Not that I really want white hot for anything, but yellow would be lovely.)
Any input is certainly appreciated. I'd really like to be able to toy a little with forge welding. Eventually I'm planning on building a ribbon burner forge with a 20lb tank, some kaowool, and a proper refractory insulator, but for now anything I can get out of this little setup is a plus.
BTW, I went back to pure propane instead of MAP. I'd only been using that during the anvil hardening because one of my torch heads came with a MAP tank.