Today I would like to discuss the technique of brazing 304 stainless steel with ordinary bare bronze brazing alloy. Although there are special nickel bronze brazing alloys for this task, they are more expensive and more difficult to locate. Furthermore, it is of my belief that this task being a little more difficult will greatly enhance the skills of the persistently practicing brazer.
First and foremost, you MUST use oxyacetylene with a quality tip. The reason for this is other gas torches normally sufficient for brazing regular steel do not allow for correct heat management. Often times, torches that run off MAPP or propane produce a flame that is too broad and bushy enlarging the area affected by heat. This presents two problems, one is there is not enough heat focused on the actual joint, and two because you need to hold the flame to the stainless longer, you almost always oxidize to the point where the brazing alloy will not adhere.
With the proper torch and equipment, brazing 304 stainless is a simple task to learn. I stress bare bronze alloy for brazing because you want to be able to apply copious amounts of flux to the joint. Applying the flux at the right temperature is crucial. The flux I used was a white paste general purpose flux which is designed for most metals. If applied too hot then it will burn and the surface of the stainless will be a sticky dark brown color that will never let brazing to occur. You need to apply the torch flame to heat it just before the metal discolors and apply the flux allowing to flow and protect the stainless steel. At the right temperature, a green tint will be noticed in the flux layer as this is the chromium oxide being fluxed away from the stainless steel surface. You then quickly heat up the joint with the torch with the brazing rod until a molten bead appears and it should stick the stainless at this point. If you do find yourself with a blackish brown mess, you will have to grind it off to shiny stainless before you can retry.
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