The difference between weld and base material of  titanium pressure vessel

There are these differences between the titanium welding seam of the titanium pressure vessel  and the titanium parent material. Under the condition that the content of impurities of the titanium welding wire is the same as that of the base material, the plastic and toughness of the titanium welding seam must be much lower than that of the base material.The mechanical properties of titanium welds are different from that of titanium matrix:

(1) titanium weld for casting organization, osteoporosis than pressure processing of titanium base organization, and hard to avoid has the dendritic structure, porosity, shrinkage, internal stress and other defects (in the range of allowable nondestructive testing), titanium weld plasticity and toughness is lower than titanium material.

(2) the impurities such as nitrogen, oxygen, carbon solubility in the titanium liquid, R and metallographic, phase change will cause the redistribution of impurity elements, after welding seam of the cooling speed faster, impurity elements in each part to evenly spread the dendritic segregation of impurity elements, there are local high content of impurities, cause local lattice distortion. During the cooling process, the phase transition from p phase to a phase occurs partially. The metastasis of martensite phase produces a metastable phase. The distribution of element content of titanium parent material is uniform, which makes the plastic toughness of titanium welding seam lower than that of titanium parent material.

(3) as far as possible when titanium welding with inert gas protection, protection of the purpose is to make the environment of iron, carbon, nitrogen, oxygen, hydrogen and other impurities in weld less pollution as far as possible in titanium, protect good, can only reduce the pollution, not lower impurities in the weld process, welding process and is only the question of how much pollution, and the impurity in the weld is always higher than that of wire, such as the welding wire is the same as the parent metal impurity elements, the weld of impurity composition is always higher than the parent metal, the plastic toughness of weld is lower than the parent metal.

(4) no annealing treatment is carried out for the titanium pressure vessel after general welding, and the welding seam is in the post-welding state, while the titanium base material is in the annealing state, which also makes the plastic toughness of the welding seam lower than that of the base material.

Attn : Jason

Email: jasontitanium@163.com

Skype: txcanberra