Section 2 Welding Processes

**103**

**Chapter 5**

**Abstract**

**1. Introduction**

Vacuum Brazing of Dissimilar

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

Joints Mo-SS with Cu-Mn-Ni

system are characterized by maximum values of shear strength.

stainless steel, micro X-ray spectral analysis, shear strength

**Keywords:** brazing, microstructure, brazing filler metal, molybdenum,

At present materials which are difficult to join by traditional welding methods are widely applied in different industries. These, primarily, are dissimilar materials, for joining which brazing is extensively used. This method of material joining has been known since ancient times, it is developing continuously, and the area of its application becomes wider. Producing permanent joints of a refractory material—molybdenum with stainless steel by brazing is highly important for many industries, related to structure operation at high temperatures. This is due to high melting temperature, high modulus of elasticity, relatively low density, and excellent specific strength of molybdenum at high temperatures. Recrystallization temperature and mechanical properties of molybdenum depend on many factors and, primarily, on the degree of its purity, method of its production, as it is sensitive to interstitial impurities. Recrystallization temperature of unalloyed molybdenum is in the range of 900–1000°C. It depends on metal purity, temperature, degree of deformation, and

Brazing Filler Metal

*Maksymova Svitlana*
