What is the optimum atmosphere system for furnace brazing stainless steel components?
Traditionally, the atmosphere used in stainless steel brazing has been dissociated ammonia. However, due to cost, safety and environmental concerns with the storage and use of anhydrous ammonia, companies are converting to a nitrogen/hydrogen blended gas mixture. A nitrogen/hydrogen atmosphere can also help you improve flexibility in your operation and minimize the potential for nitriding.
If you need to produce high quality, bright, stainless steel components, an atmosphere composition with a minimum concentration of 25% hydrogen should be adequate. Or, you can achieve higher corrosion resistance and better hermetic sealing for your steel components with an atmosphere containing up to 80% hydrogen.
To produce a well brazed joint, it’s important that your brazing furnace has a metal muffle and that the dew point in the furnace’s hot zone is maintained below –40°F . It is also critical to keep the oxygen content in the cooling zones below 15 ppm (parts per million) to help avoid oxidation and discoloration of the stainless steel.