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Difference between weld and base metal of titanium pressure vessel

Titanium welding seam of titanium pressure vessel and titanium base material exist these differences, in the same case of titanium welding wire impurity content and base metal, the plastic and toughness of titanium welded seam is certainly lower than that of titanium base metal. Compared with titanium base metal, the mechanical properties have the following differences:

(1) for casting titanium weld, than the pressure processing titanium base material is a loose organization, and dendritic structure, porosity, shrinkage, internal stress and other defects (in the allowable range, nondestructive testing) titanium weld plastic toughness than titanium base material is low.

(2) the different solubility of nitrogen, oxygen, carbon and other impurities in titanium liquid, R and Jin Xiangzhong, the phase transition will cause the redistribution of impurities, cooling rate after welding seam is rapid, impurity element diffusion has uniform dendritic segregation of impurity elements in different parts to save less, at the local high impurity content area, cause local lattice distortion. During the cooling process, the phase transition of the P phase to the a phase is changed, and the R phase is changed into. Martensitic phase transformation, resulting in a metastable phase. And the element content distribution of titanium base material is more uniform, which also makes the plastic toughness of titanium welded joint is lower than that of titanium base material.

(3) titanium welding to make full use of inert gas protection, protection of the environment is to make the iron, carbon, nitrogen, oxygen, hydrogen and other impurities to minimize the pollution into titanium weld, well protected, can reduce pollution, reduce the welding process is not the process of weld impurities, but the number of pollution thus, impurities in the weld is always higher than the same as welding wire, welding wire and base metal impurities, impurity components of the weld is always higher than that of the base metal, the weld plastic toughness.

(4) titanium pressure vessels are generally not annealed after welding, the welding seam is the state, and the titanium substrate is annealed, which also makes the plastic toughness of the weld is lower than the base metal.

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