The influence of alloy elements in titanium plate and tube on welding performance

The welding seam and heat-affected zone have a high temperature after welding, and the cooling rate is very fast under the influence of the surrounding base material. Therefore, after fusion welding of titanium plate and titanium tube, it is easy to produce metastable structures such as martensite a', a", quenched ω phase and metastable β. In alloys with a small content of β stable elements, thick needles Martensitic structure will reduce plasticity. Quenching omega phases in alloys with more β-stabilizing elements will cause weld embrittlement. These meta-stable structures also have an adverse effect on welding performance. Use reasonable welding specifications and welding The post-heat treatment system can reduce or even eliminate this effect.

The composition of the alloy has a great influence on the welding performance. When welding with a welding wire with a high content of β-stabilizing elements, compared with the base metal, the plasticity reduction of the weld is generally more severe than that of the less β-stabilizing element. As their strengthening ability increases, the more serious the reduction in plasticity, the lower the welding performance. Generally speaking, the weldability of a-type titanium plate is better, but the tendency to generate pores and cold cracks is greater; the weldability of a+β-type titanium plate is slightly worse, and it becomes better with the decrease of β-stabilizing element content; The thermally stable β-type titanium tube has better overall performance without heat treatment after welding. Heat-treatable beta alloys tend to have a sharp decline in plasticity after aging of the weld, and it is difficult to obtain good comprehensive properties.

In summary, in order to obtain high-quality welded joints in titanium plates and tubes, the following points must be paid attention to:

(1) Strictly control the harmful impurities in the base metal and welding materials (including filler materials and oxygen-free flux), especially the content of interstitial elements such as hydrogen, oxygen, nitrogen, and carbon. Strictly clean the workpiece, welding materials and equipment before welding;

(2) Use high-purity inert gas, oxygen-free flux or vacuum conditions to protect the weld and heat-affected zone so that it will not be contaminated by gas during welding and cooling;

(3) Use welding specifications with low heat input as much as possible to reduce the tendency of a metal to overheat; for different alloys, choose a suitable post-weld heat treatment system to adjust the structure and mechanical properties of the weld and heat-affected zone.
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