Core characteristics of titanium and titanium alloy welding
High sensitivity to active pollution
The welding area will react with gases in the environment when it exceeds 350 ℃:
Hydrogen pollution (>300 ℃): causing hydrogen embrittlement
Oxygen pollution (>600 ℃): Formation of brittle oxides
Nitrogen pollution (>700 ℃): causing nitrogen embrittlement
Color characteristics of oxide film (temperature indication): ∝ 200 ℃: silver white ∝ 400 ℃: golden yellow ∝ 600 ℃: blue purple ∝ 900 ℃: dark gray
When the carbon content is too high, TiC brittle phase is generated
Significant phase transition effects
Critical point of alpha/beta phase transition: 882 ℃
Characteristics of heat affected zone: ✓ Significant coarsening tendency of β - phase grains ✓ High temperature residence time 3-4 times that of ordinary steel
Process control requirements: → Heat input:<1.5kJ/mm → Cooling rate:>30 ℃/s
Strict protection requirements
Protective gas: argon/helium (Ar/He)Protection range: Starting temperature: 200 ℃ Protection area expansion: 20-30% increase compared to stainless steel welding
Difficulty in deformation control: The elastic modulus (110GPa) is only half that of carbon steel, and the deformation amount is twice that of carbon steel, requiring the use of high-strength fixtures (clamping force ≥ 3MPa) and copper pads.
Obvious porosity tendency: Hydrogen pores account for more than 70% of the total defects, and it is necessary to control the environmental humidity (<30%) and clean before welding (acetone degreasing).
Cold crack risk: Hydrogen induced cracking is the main risk, requiring a hydrogen content of less than 50ppm in the welding material and an interlayer temperature of less than 150 ℃.
Limitations of dissimilar metals: Due to the solubility of iron in titanium being only 0.05-0.10%, vanadium/copper intermediate layers need to be added for titanium steel fusion welding.
Note: The actual welding should adopt TB/T4747 standard, and it is recommended to use pulse TIG (frequency 2-5Hz) or electron beam welding process.
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