Looks a bit like what they sold here as a Bolder with a solid front fork. I have a Trek 800 sport that is a bbit like that and is steel. However I replaced the solid front forks and went with suspension forks and a bew drive train. Still you are weilding at a wield so the old wield should be removed and redone. And find a Tig Wielder if we find that bit is indeed steel.