Titanium tube weld defects are due to the titanium tube welding, argon arc welding gun formed by the formation of argon gas maintenance layer can only maintain the weld pool from the harmful effects of air, and has been solidified in the vicinity of the high temperature weld and There is no protective effect in the vicinity, but the titanium pipe weld and its vicinity in this state still have strong ability of absorbing nitrogen and oxygen in the air.
Stoma is one of the most frequently encountered problems when welding titanium tubes. The basic reason for the formation of stomata is the result of the hydrogen effect. To prevent the production of stomatal techniques are:
1. Select the appropriate welding process parameters, welding specifications, increase the retention time of the deep pool bubble to facilitate the escape, can effectively reduce the porosity.
2. Welding under high purity argon protection, argon purity should not be less than 99.99%
3. Completely remove the titanium tube, titanium and titanium tube surface of the oxide on the surface of oil and other organic matter. Can be chemically and mechanically cleaned.
4. Apply a good gas protection to the molten pool, control the flow rate and flow rate of argon to prevent turbulence and affect the protection effect.
During the welding of the titanium alloy, the argon gas protective layer formed by the argon arc welding torch can only protect the welding pool from the harmful effects of air, but has no effect on the weld which has been solidified and is in the vicinity of a high-temperature state and its vicinity Protection, and in this state of the titanium pipe weld and its vicinity still have a strong ability to absorb nitrogen and oxygen in the air. With the gradual increase in the degree of oxidation, titanium alloy weld color changes and the plasticity of the weld decline. Silver white (no oxidation), golden yellow (TiO, slightly oxidized), blue (Ti2O3, slightly oxidized), gray (TiO2, heavily oxidized). Titanium alloy welding, welded joints, the possibility of hot cracking is very small, because titanium and titanium alloy S, P, C and other impurities content is very small, formed by the S, P eutectic in the grain boundary few Generated, combined with a narrow range of effective crystallization temperature, titanium and titanium alloy shrinkage is small, the weld metal does not produce hot cracks.
Titanium and titanium alloy pipe welding, when the weld oxygen, nitrogen is high, with the temperature rise, titanium and its alloys absorb hydrogen, oxygen and nitrogen capacity gradually increased. Titanium begins to absorb hydrogen from 250 ° C, oxygen begins at 400 ° C, and nitrogen starts to vaporize from 600 ° C. Due to the high affinity of the titanium alloy with O2, N2, H2, the inclusion of these gases in the joint will make the joint brittle and reduce the impact performance, ductility and toughness of the titanium alloy welded joint. When hydrogen is contained in the titanium alloy, delayed cracking occurs in the heat-affected zone. When the weld contains oxygen and nitrogen, the weld or heat-affected zone will also crack under the action of larger welding stress, and the crack also belongs to the delayed crack. Therefore inert gas (or vacuum chamber) protection is very necessary. Due to the high cost of using a vacuum chamber, inert gas protection is generally used. The main shielding gas helium and argon, the helium price higher than argon, in general, not the special requirements of titanium alloy welded joints and heat-affected zone, the use of high-purity argon to protect the oxidation can be prevented.