The grain size of sintered molybdenum bar blank is fine and equiaxed, and the average grain size is small. However, due to the weak intergrain binding force of molybdenum grains, the grain boundary is fragile and the structure is loose, brittle fracture easily occurs along the grain boundary.

The grain size of sintered molybdenum bar blank is fine and equiaxed, and the average grain size is small. However, due to the weak intergranular bonding force of molybdenum grains, the grain boundary is fragile and the structure is loose, brittle fracture is easy to occur along the grain boundary.

On the one hand, the deformation can not go deep into the interior, resulting in uneven deformation, easy to produce internal stress and uneven organization; on the other hand, in order to avoid the final forging temperature is too low to cause forging in the forging process due to poor plastic cracking defects, need to be tempering heating for many times. Tempering process, the organization will happen recrystallization, grain boundary disappear, mutual integration between adjacent crystal, when the tempering temperature is higher, or for a long time, change form grain to grow up into a bulky shaft such as grain, and harmful impurities gathered at grain boundary, weaken the intensity between the grain boundary, resulting in a decline in performance, as shown in figure 2 a and 2 b. By forging process with large deformation, deformation uniformity, and fewer tempering, the tempering time is short, too late recrystallization or partial recrystallization, grain growth phenomenon, not occurring fibrous tissue is still tiny change form grain or grain mixed with isometric status change form, grain elongated after deformation, grain boundary populations within the same area, the average stress distribution at the grain boundary, greatly reduces the stress concentration, make the material before rupture can withstand larger deformation force.