Vacuum Brazing of Dissimilar Joints Mo-SS with Cu-Mn-Ni Brazing Filler Metal

Abstract

The complexity of joining dissimilar materials, such as molybdenum-stainless steel, is due to the difference in thermal coefficients of linear expansion and low oxidation resistance of molybdenum. In this connection, brazing of this pair of materials should be performed in vacuum. The selection of chemical composition of brazing filler metal and its melting temperature range is very important. This work presents the results of metallographic and micro X-Ray spectral analysis investigations of dissimilar brazed joints of molybdenum-stainless steel and shows the features of the formation of brazed seams at application of brazing filler metals of Cu-Mn-Ni(Me) system. It is found that at brazed seam, crystallize reaction layers form the side of molybdenum. One layer is based on molybdenum, enriched in iron and silicon. The second layer is based on iron, enriched in silicon. At brazing temperature of 1100°C, base metal dispersion occurs, which can be avoided at temperature lowering to 1084°C. The structure of solid solution with a small amount of iron-enriched dispersed phase crystallizes in the central zone of brazed seams. The brazed joints produced with application of brazing filler metal based on Cu-Mn-Ni system are characterized by maximum values of shear strength.