Vacuum brazing is the most modern brazing process and is at present, far from being completely understood. By brazing under high vacuum, in an atmosphere free of oxidizing gases, a superior product with greater strength, ductility and uniformity may be obtained.
In this thesis, the design of the vacuum brazing equipment and influence of brazing parameters such as base metal characterics, joint clearance and brazing time, on the shear strength of vacuum-brazed joints between carbon steels and 304 stainless steel (SUS304) brazed by copper filler metal were described.
In copper brazing to SUS304 and carbon steels, the columnar Fe-Cr-Ni-Cu-C alloy phase deposits from the carbon steel boundary. At the same time, the surface of carbon steels was decarburized. The driving force for the formation of columnar phase was the difference of carbon content of base metals. As the joint clearance is narrower and brazing time is longer, the formation and growth of columnar phase and decarburization of carbon steels were more noticeable. Because of decarburization of carbon steels, the shear strength of brazed joints were reduced as the formation of columnar phase was increased.
