Welding method of stainless steel and molybdenum
Because the physical properties of molybdenum and its alloy are very different from stainless steel, there will be many problems in the welding process. In their welding, when heated to 400 ℃, a slight oxidation occurs, and when above 600 ℃, they rapidly oxidize to MoO3 compounds. The solubility of oxygen in molybdenum is very small. When the oxygen content increases, the oxide precipitates along the grain boundary, and the brittleness of other impurities is also precipitated, which makes the welding difficult. When molybdenum and stainless steel are welded, the high hardness and brittleness zone is easy to appear near the side of molybdenum base metal, the width of which is generally 0.5 ~ 3 mm. The brittleness near the stainless steel side has a small tendency. The high cooling rate after welding results in martensitic structure on the metal side of molybdenum base metal, which leads to the embrittlement of weld heat affected zone and joint area. Under the action of welding stress, the crack tilting of the joint will be seriously increased, so the weldability of stainless steel and molybdenum is poor. The dissimilar weld metal of stainless steel and Mo is composed of three parts, and the weld city distribution is uneven. Near the steel base metal side is a two-phase structure composed of steel and intermetallic compounds, and its hardness increases sharply, and near the molybdenum master metal side is composed of two-phase structure composed of intermetallic compounds, and the hardness also increases sharply. The weld is composed of intermetallic compounds between molybdenum and stainless steel, and the hardness is also high. This is the difficulty of welding Mo and stainless steel. Welding of stainless steel and molybdenum can be achieved by argon arc welding, electron beam welding, gas shielded welding and so on. The essence of this welding process is to melt more metals on the base metal side of the stainless steel, but not to melt or melt at the side of the molybdenum master metal, and to form a brazing weld by infiltrating molybdenum with the liquid metal of the welded stainless steel. This avoids the formation of hard and brittle compounds between carbon and molybdenum in stainless steel and solves the embrittlement problem in the joint region. In order to improve the welding performance of stainless steel and Mo, the method of adding intermediate transition layer can also be adopted. Although the welding process is more complex, but its weldability is very good. The surface treatment of welding parts before welding is very important, and the welding process must be strictly controlled.
