Cracks and pores in the weld of titanium and titanium tubes
1. Weld cracks of titanium tube and titanium alloy tube
During the welding of titanium alloy, the possibility of hot crack in the welded joint is extremely tiny, because the impurities such as S, P and C in titanium alloy and titanium alloy are tiny, the low melting point eutectic formed by S and P is seldom generated in the grain boundary, and the effective crystallization temperature range is narrow, and the shrinkage of titanium and titanium alloy during solidification is tiny, thus the weld metal will not produce hot crack.
During the welding of titanium and titanium alloy, when the oxygen and nitrogen content of the weld is elevated, the performance of the weld or heat affected zone becomes brittle, and cold cracks will appear under the action of large welding stress. Titanium Tubing is characterized by cracks that occur several hours or more after welding, called delayed cracks. The results show that hydrogen diffusion is the main cause of the crack during welding.
In the process of welding, hydrogen diffused from elevated temperature deep pool to low temperature heat affected zone. The increase of hydrogen content increased the amount of TiH2 precipitated from the zone, which increased the brittleness of the heat affected zone. In addition, the volume expansion of hydride precipitated caused large structural stress, and hydrogen atoms diffused and accumulated to the elevated stress area of the zone, resulting in the formation of cracks. The main way to prevent this delayed crack is to reduce the source of hydrogen in the welded joint.
2. Porosity in the weld of titanium tube and titanium alloy tube
The porosity is a main problem in the welding of titanium pipe. The root cause of the formation of pores is the result of hydrogen influence. The main technological measures to prevent the formation of pores are:
1) Welding should be carried out under the protection of elevated purity argon gas, the purity of which should not be lower than 99.99%
2) Carefully remove the oxide skin oil and additional organic matter on the surface of titanium tube, titanium plate and titanium plate tube eye. It can be cleaned chemically and mechanically.
3) Apply excellent gas protection to the molten pool and control the flow and velocity of argon gas to prevent turbulence and affect the protection effect.
4) Select the appropriate welding process parameters, welding specifications, increase the deep pool residence time to facilitate the use of bubbles escape, can effectively reduce the porosity.
2. Porosity in the weld of titanium tube and titanium alloy tube
The porosity is a main problem in the welding of titanium pipe. The root cause of the formation of pores is the result of hydrogen influence. The main technological measures to prevent the formation of pores are:
1) Welding should be carried out under the protection of elevated purity argon gas, the purity of which should not be lower than 99.99%
2) Carefully remove the oxide skin oil and additional organic matter on the surface of titanium tube, titanium plate and titanium plate tube eye. It can be cleaned chemically and mechanically.
3) Apply excellent gas protection to the molten pool and control the flow and velocity of argon gas to prevent turbulence and affect the protection effect.
4) Select the appropriate welding process parameters, welding specifications, increase the deep pool residence time to facilitate the use of bubbles escape, can effectively reduce the porosity.