a lot of problems. Analysis of the problem from the welding concluded

Molybdenum and molybdenum plating alloy welding characteristics (1) Molybdenum and molybdenum alloy welding characteristics of molybdenum and molybdenum alloy steel welded structure, used more often in the actual production, but because of molybdenum and molybdenum alloy and steel physical properties of a larger difference in welding process, a lot of problems. Analysis of the problem from the welding concluded, molybdenum and steel welding performance depends primarily on Molybdenum crucible and molybdenum alloy composition and performance. Iron - molybdenum alloy state diagram in Figure 1. Fe from the state diagram shows the various concentrations of Mo to form α-Fe and α-Mo solid solution. In addition you can also form two intermetallic brittle phase ε-Fe3 No2 and η-FeMo. Fe3 No2 until 1450 ℃ temperature range are relatively stable. State diagram of η-phase, there is a temperature range of its 1180 ~ 1540 ℃, when the cooling time, η-phase decomposition of ε-phase and α-phase solid solution. Molybdenum and steel welding has the following main features. ① molybdenum steels mainly depends on molybdenum and molybdenum alloy composition and performance. Molybdenum and molybdenum alloy and steel welding, when heated to 400 ℃, minor oxidation. Above 600 ℃, the rapidly oxidized to MoO3 compounds. The solubility of oxygen in the molybdenum is small, when the oxygen content increases, the formation of oxides along the grain boundaries, compounds of other impurities are also brittle phase in the grain boundary precipitates, the welding difficult. ② welding molybdenum steel, molybdenum base metal close to the side, prone to high hardness and brittleness zone, the width of up to 0.5 ~ 3μm. Here are the main component of intermetallic compounds Fe3 Mo2 and FeMo. Close to the steel base metal side than on the molybdenum base metal brittleness orientation small, but fast cooling rate after welding, the side of the base metal molybdenum appears martensite, resulting in the weld heat affected zone and the splice area embrittlement in the weld stress under the effect of severely increase the tendency to crack joint. Therefore, molybdenum and steel is a relatively poor weldability. ③ molybdenum and steel welding dissimilar weld metal consists of three parts, components and solder joints uniform. Close to the steel base metal side is made of steel and composed of an intermetallic compound phase organization, its hardness is increased dramatically; near molybdenum base metal side is made of an intermetallic compound consisting way, hardness sharply increased; weld intermediate is made between molybdenum and steel consisting of an intermetallic compound, the hardness is high. Molybdenum steel welded joint tissue components with uneven great influence on hardness, shown in Figure 2. 2, (1) is composed of an intermetallic compound of steel and the duplex structure; (2) between the steel and the intermetallic compound of molybdenum; (3) is a molybdenum compound and a metal phase composed of tissue. (2) molybdenum and steel welding a) molybdenum and steel welding - brazing molybdenum and steel (carbon steel, stainless steel) using welding, electron beam welding and gas welding and other welding methods, welding can be achieved - brazed joints. This welding process is the essence of the steel side of the molten metal more, and molybdenum increase the side just heating without melting or melting little liquid metal is steel formed by infiltration brazed seam. This avoids the formation of iron and molybdenum compounds Fe3 Mo2 and FeMo, the joint area embrittlement problem is solved. Molybdenum steel electron beam butt welding directly, the weld metal composition mainly 20Mo-80Fe in the Mo base material is displayed on the side of the boundary eutectic α + ε, and the formation of large intermetallic Fe3 Mo2 and FeMo. Since the presence of intermetallic compounds, the weld metal brittle and easily cracks increases, reducing the performance of the joint, its poor weldability. Therefore, molybdenum and steel fusion welding, the joint strength is not high, you should avoid direct welding, it is generally used welding - brazing.