Production method of molybdenum and molybdenum alloy materials
Molybdenum and molybdenum alloy materials can be made by machining, forming, metal processing and welding. The surface of molybdenum and molybdenum alloy is smooth and high precision after machining. However, attention should be paid to the fact that molybdenum has high temperature strength but poor room temperature strength, and its toughness is not as good as that of carbon steel or brass. The higher ductile brittle transition temperature also indicates that molybdenum is prone to internal cracking. In addition, Mo and Mo alloy materials can be processed by grinding, lithography and EDM. Recrystallization layer is often formed on the surface of molybdenum by EDM, which is easy to produce microcracks. It can also be eliminated by mechanical or chemical etching polishing. But if the cooling degree is not enough, the abrasive will overheat and crack the surface.
Forming and metal processing are the common processing methods of bending, punching, drawing and spinning of molybdenum and molybdenum alloy. The machining effect is related to the surface state of the material, the size of the forming section and the deformation rate. In addition, molybdenum and molybdenum alloy have typical plastic anisotropy, that is, when bending molybdenum sheet, the bending axis is perpendicular to the main rolling direction, and the shelling effect will be better. It is easy to produce plane cracks in the formed plate by medium pressure, middle hole and shear, which is the intergranular crack which diffuses along the grain boundary plane during rolling. 0.5 mm thick molybdenum sheet can be sheared at room temperature: the four heat m degree of O.5 ~ 1.2 mm molybdenum sheet 4 is 65 ~ 95 C; the preheating temperature of 1.5 ~ 3.2 mm slab is 350 C; the 6.3 mm thick plate needs to be preheated to 600 ° C.
Molybdenum and molybdenum alloy can be welded, that is, this method is usually used without excessive stress. The ductile brittle transition temperature is much higher than that in the region not affected by welding. It is found that the concentrated deformation of the welding area and the three-dimensional stress due to the limitation of the base metal can lead to brittle fracture. The general welding method of molybdenum and molybdenum alloy, that is to say, when electron beam welding is used to process, the welding seam and heat affected zone are small, so it is not easy to have problems. The results show that oxygen has a negative effect on welding and segregation at grain boundaries, thus reducing plasticity. Therefore, arc melting molybdenum alloy with higher carbon content is easier to weld than powder metallurgy molybdenum alloy. Similarly, carbide strengthened molybdenum alloy is easier to weld than pure molybdenum. Most molybdenum fabricated parts are welded in high purity inert gas to minimize the adverse effect of oxygen. When welding the material containing volatile alloy, the weld will bubble (bubble), so it is not easy to weld the doped molybdenum alloy.
