Niobium has excellent thermal strength and high temperature corrosion resistance, and has good stability at 1300℃. Its welded structure with steel is often used in nuclear power plants and atomic reactors. However, niobium can react with superheated steam and metals such as Li, K, Na, etc. Niobium reacts violently with oxygen starting at 500℃. Reaction with hydrogen at 200 ~ 250℃; Nitrides begin to form in nitrogen at 600 ~ 800℃.
The argon arc welding of niobium to stainless steel is as follows: in order to obtain a good joint, before welding, the niobium surface is cleaned with 60%HNO3+40%HF solution to remove oil stains and oxide film. When welding, the arc should be biased to the stainless steel side, and a certain gap from the niobium base material, when the arc is biased to one side, the stainless steel melting and niobium side is heated (1700℃ and insulation 1 ~ 2s), the surface of a little melting. At this time, the stainless steel liquid produces a wetting process on the surface of niobium and forms a brazing metallurgical connection. The post-welding analysis shows that there is no compound phase of metal parts at the interface, and there is no phenomenon of superheated microstructure and grain growth in the heat-affected zone.
Niobium and stainless steel fusion welding - brazing method is like this: it is the use of fusion welding, such as electron beam welding, argon arc welding, so that one side of the metal melt, the other side of the metal does not melt, so as to achieve a metal brazing connection. For example, niobium alloy BH2 with a thickness of 0.3mm and stainless steel 1Cr18Ni9Ti with a thickness of 0.4mm, using electron beam welding or argon arc welding, using fusion-brazing welding process method, the molten stainless steel liquid metal in the welding process has a good wetting effect on solid niobium, forming fusion-brazing connection, weld forming good, It has high strength and good plasticity.
