Influence of nitrogen in brazing atmospheres on the hardness of the microstructural constituents of brazed stainless steel joints

Abstract

Stainless steel components, such as heat exchangers for energy and air-conditioning technologies are commonly manufactured using nickel-based brazing fillers in continuous furnaces or vacuum furnaces. In the continuous furnace, the brazing process is often supported by a protective gas. As protective gas is commonly used nitrogen or mixtures of nitrogen and hydrogen. In the vacuum furnace, nitrogen is often used as cooling gas. The arising nitrogen enrichment of the braze metal and the base material influences the mechanical properties of the microstructural constituents of the brazed joints, especially the hardness. In this work, the influence of the nitrogen enrichment on the hardness of the microstructural constituents of the joints was investigated with regard to the process conditions. The amount of nitrogen in the braze metal as well as in the base material was determined using a carrier gas hot extraction technique. The hardness of the microstructural constituents of the brazed joints was determined using nanoindentation due to their small size (few microns). The results of samples, brazed with and without the influence of nitrogen, were compared.