Bobby,
I use borax for flux, although I am soaking my billet (cold) in kerosene before I start. I view the weld as a separate step, so I treat it as such, before I start the actual drawing of the bar. It has to get hot and from what you describe, it aint hot enough. The flux needs to dance around, not just sweat. I see three stages of the flux besides it merely melting. Sweating, dancing, and foaming. I take mine out to weld when it just starts foaming. Not a minute more. The weld needs to be a dead blow, more of a press that's why I use my press to make the weld. Of course you can use a hammer, but you'll have to just bump it with a heavy hammer and not smack it with your regular forging hammer.