Welding is an important process in the manufacturing process of equipment.
Welding methods are many, according to the design and construction of titanium
equipment or components and specific application conditions to choose the
appropriate welding method.
The principle of choosing welding method is to ensure the quality, high
production efficiency, easy operation and low cost of welding joints. Wherein to
ensure the quality of the weld should be put first.
Only by fully realizing all the factors affecting welding quality can we
achieve the goal of ensuring the quality of welding joints.
Effect of gas impurities on the metal properties of welds
Titanium has a high chemical vibrancy and has a high affinity with oxygen
and nitrogen in the air. At lower temperatures, titanium interacts with oxygen
to create a dense film of oxidation, which thickens as the temperature
increases, and after exceeding 600 degrees Celsius, titanium begins to absorb
oxygen and dissolve it into titanium. When the temperature rises, the activity
of titanium increases dramatically and the oxides of titanium are produced by
reacting violently with oxygen.
Titanium begins to absorb hydrogen above 300 degrees C and nitrogen at more
than 700 degrees C. The result of oxygen and nitrogen contamination of titanium
is increased strength and hardness of titanium and reduced plasticity. Oxygen
has a greater effect than nitrogen.
When the mass fraction of hydrogen in titanium is 0.01% to 0.05%, the
impact toughness of the weld metal decreases sharply, while the plasticity
decreases less. This indicates brittleness (hydrogen brittleness) caused by
hydrogen. Hydrogen is also the cause of the pores that cause welds.
During welding, the melting pool acts like a small metallurgical furnace,
exposing molten metal to the atmosphere.
If the corresponding protective measures are not taken to isolate the
molten metal from the air, then oxygen, nitrogen, hydrogen and other gas
elements will be integrated into titanium, forming brittle oxides or nitride,
resulting in reduced plasticity of the weld metal, stretch strength increased,
in severe cases will be brittle, plasticity equal to 0.
