The welding performance of titanium equipment and titanium alloys has many significant characteristics. These welding characteristics are determined by the physical and chemical properties of titanium and titanium alloys.

1. Influence of gas and impurity pollution on welding performance

At normal temperature, titanium and titanium alloys are relatively stable. However, the test results show that during the welding process, liquid droplets and molten pool metals have a strong absorption of hydrogen, oxygen, and nitrogen, and these gases have interacted with them in the solid state. As the temperature rises, the ability of titanium and titanium alloys to absorb hydrogen, oxygen, and nitrogen also rises significantly. It starts to absorb hydrogen at about 250 ° C, starts to absorb oxygen at 400 ° C, and starts to absorb nitrogen from 600 ° C. These gases After being absorbed, it will directly cause embrittlement of the welded joint, which is a very important factor affecting the welding quality.

Detailed welding problems of titanium alloys-titanium equipment

2. Weld joint crack problem

When titanium and titanium alloys are welded, the possibility of thermal cracks in the welded joint is very small. This is because the content of impurities such as S, P, and C in titanium and titanium alloys is small, and the low melting point eutectic formed by S and P is not easy to appear in Grain boundary, plus effective crystallization temperature interval

Narrow, small shrinkage of titanium and titanium alloys during solidification, and the weld metal will not generate thermal cracks. Cold welding of titanium and titanium alloys can occur in the heat-affected zone on time. It is characterized by the occurrence of cracks several hours or more after welding, so it is also called delayed cracking. Studies have shown that this crack is related to the diffusion of hydrogen during welding. During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower-temperature heat-affected zone. Increasing the hydrogen content increases the amount of TiH2 precipitated in this zone, increasing the brittleness of the heat-affected zone. In addition, due to the volume expansion during the hydride precipitation, larger tissue stress is caused. In addition, the hydrogen atoms diffuse and accumulate in the high stress parts of the region, so that cracks are formed. The way to prevent this delayed crack is to reduce the source of hydrogen in the welded joint.

3.Blowhole problem in weld

Porosity is a common problem when welding titanium and titanium alloys. The root cause of stomata is the result of the effects of hydrogen. The formation of pores in the weld metal mainly affects the fatigue strength of the joint. The main technological measures to prevent pores are:

(1) The protective gas should be pure, and the purity should not be less than 99.99%

(2) Thoroughly remove organic matters such as scale oil on the surface of the welding piece and the surface of the welding wire.

(3) Apply good gas protection to the molten pool, control the flow and velocity of argon gas, prevent turbulence, and affect the protection effect.

(4) Correctly select the welding process parameters and increase the residence time of the molten pool to facilitate the escape of bubbles.