I just found this. It is about carbide but the basics are the same.
Brazing Tungsten Carbide for the First Time
The surface condition of tungsten carbide can make the difference between parts that are joined with a strength of 100,000 psi. and parts that fall off by themselves. You need to make sure the surface is clean and ready for brazing. The best way to determine this is to use a tungsten carbide supplier that can tell you about the surface condition of your parts. Often good tungsten carbide comes ready to braze from the manufacturer. If the parts do not adhere well see the chapter on cleanliness and surface treatment.
Do not get the tungsten carbide oily or greasy. Make sure the steel is clean also. Do not heat either part without a protective flux coating.
Flux Braze alloy joins to metal. Metal oxidizes faster if it is hot. If you heat metal without flux you will form an oxide layer that is similar to rust. Brazing over oxide is like painting over rust. Rarely doe anyone get in trouble using too much flux.
Braze alloy There are many choices. The safest to use is a pretinned tip or trimetal also called plymetal or sandwich. It comes as ribbon. It is flat and has unique properties that relieve stress caused by overheating. It is a tremendous aid when heating large parts or working with a torch. It is more expensive than wire. If you are starting and doing just a few parts this is safer and probably easier.
0.15" (15 thousandths) is about as thick a ribbon as you will need.
Prepare a clean piece of steel. Make sure there are no oils or greases. Alcohol and detergent or soap may both be necessary. Easy Off Oven Cleaner works very well but is dangerous. Remember steel comes oiled to keep it from rusting. An oil layer you cannot see or feel can ruin a braze joint.
Coat the steel with a layer of Black Flux. (Black flux has more Boron than White Flux and works longer at higher temperatures.)
Put down your piece of braze alloy cut to shape and coat with a light layer of flux.
Put the clean tungsten carbide on top of the flux layer and coat the outside with a thick layer of flux.
Hold the part in place with a ceramic rod while brazing.
Heat the whole part as evenly as possible until the whole joint is at the proper temperature. This is usually at least a dark cherry red. Remember that the part has to be hot enough all the way through. This can be a problem even on the parts as small as saw tips.
Once the parts are hot enough you will see the alloy flow out of the joint. You may also feel the part move just a bit as the alloy turns liquid. Once the part is the right color (dark cherry red to cherry red) and the alloy is coming out just a bit (and it may feel mushy), then wiggle the part just a little bit to allow any flux or fumes to escape. If you work the part too hard you can force all the braze alloy out of the joint and ruin it.
The flux cleans off with warm water. You can use mild brushing if you wish to speed the process.