Brazing is a procedure that joins pieces of metal together by using a filler metal. The filler metal is placed between the pieces, and the assembly is heated until the filler metal liquefies. When the filler metal cools and hardens, it binds the pieces together. Heat treating companies perform the same, basic brazing procedure for all types of metal. However, due to its high chromium content (at least 10.5% chromium by mass), brazing stainless steel requires special considerations. Below is the five-part process for brazing the metal.
Clean the metal
Step one is to clean the metal of dirt, grease, and permanent coatings such as paint. If these substances remain on the metal, they will oxidize and tarnish its appearance. Dirt and grease can be removed with a non-residue cleaner / degreaser. The removal of permanent coatings may require grinding or sandblasting, although paint is usually removable with a paint remover.
Establish the proper clearance
Step two is to establish the proper clearance between the work pieces. The ideal clearance is.0015. "A clearance that is greater or less than this dimension may create weak assembly joints by allowing too much filler metal to distribute between the work pieces. as the filler metal; and the filler metal is typically weaker than the base metal.
Place the metal in the furnace
Step three is to position the metal in the furnace while maintaining the proper clearance between the work pieces. Brazing stainless steel is typically performed in an atmosphere-controlled continuous furnace, or a vacuum furnace. The atmosphere-controlled continuous furnace holds a pure atmosphere of nitrogen and / or hydrogen, while the vacuum furnace applications a vacuum to the furnace chamber that removes all of the gases. Heat treating companies braze chromium alloys in an oxygen-free atmosphere because chromium oxidizes when it is heated in an oxygen atmosphere.
Cool the assembly
After the assembly is brazed, it may be quenched, or left to cool in the open air. If the former method is used, the metal may require subsequent tempering to remove stresses that develop from quenching. The service provider will decide what method of cooling the assembly needs based on the composition of its metal, and how the assembly will be used.
Clean the assembly
After the assembly has cooled, traces of oxide and debris should be removed from the surface of the metal with a cleaning rag or a wire brush. Some service providers prefer to clean the metal with an acid-pickle solution, although a non-corrosive, non-residue industrial strength cleaner may work just as well. If the metal is brazed in an oxygen-free atmosphere, it should appear bright and lustrous after it is cleaned.
Conclusion
Brazing stainless steel is similar to brazing other types of metals. However, because the former contains a high degree of chromium, it must be brazed in an oxygen-free atmosphere. This is typically accomplished by treating the metal in an atmosphere-controlled continuous furnace or a vacuum furnace. For more information about brazing chromium alloys, contact heat treating companies that braze stainless steel today.