Use flux or not? The real question is do you understand what flux is for?
Flux is used to reduce the temperature at which the surface elements (scale, impurities, etc.) become fluid on the surface of the metal. It protects the surface from erosion due to air or gas blasting against the metal. Therefore if you do not use flux you must raise the temperature enough to make the elements on the surface fluid.
In order to take the mystery out of forge welding you must realize that flux may not be required, but it does, in most cases, make it easier. What is important to understand is all the different things that enter into the equation of when to use flux. Such as:
Does it have the capability to get to forge welding temperature or just almost? Many gas forges, especially those that are not aspirated (induced air,) are designed only to achieve forging temp not forge welding temperature. For welding in gas forges heat needs to be able to circulate all the way around or whatever it is resting on will be sucking the heat.
There can be many things here that can cause issues with forge welding, but more often than not it is the coal. Lots of info on coal in the previous blog, but many are using coal that cannot get to the temperature we need for a good solid forge weld. The only way to know for sure is to test it .
Were you at welding temperature all the way through or only at the surface?
- Hydrous or Anhydrous Flux
We use water to cool our metal. So if your flux is hydrous (contains water) it probably is cooling your metal. Flux also tends to clump when wet which keeps it from seeping into the crevices we are trying to weld.
There are many types of flux and everyone has a trick as to how they apply it. Find one you like, but try new ones too so you can make sure you are still using the one that works best for you.
Have you tried any of these:
Silica sand, mud daubers nest, roach proof or boric acid, Depot Flux or anhydrous borax, ezweld, forge borax, iron mountain flux, crescent weld and many, many more.