Reason for various colours in improperly shielded Titanium welds.
1. If the weld shielding inert gas quality is poor, it should be pure 99.998, 99.999%( preferred).
2. If the weld environemnt is having dust/high air flow/high humidity& temperature.
3. If the filler wire is not properly clean, degassed and pickled.
4. If the weld electrode is improperly ground.
5. If the welder, fitter, supervisor, shop engineer is not trained properly.
6. If the weld edges are not cleaned properly, with high pure spirit and lint free cloth.
7. If the used electrode tip is not cleaned 100%.(blackish in colour)
8. If the used filler end is not trimmed after each usage.
1. If the weld shielding inert gas quality is poor, it should be pure 99.998, 99.999%( preferred).
2. If the weld environemnt is having dust/high air flow/high humidity& temperature.
3. If the filler wire is not properly clean, degassed and pickled.
4. If the weld electrode is improperly ground.
5. If the welder, fitter, supervisor, shop engineer is not trained properly.
6. If the weld edges are not cleaned properly, with high pure spirit and lint free cloth.
7. If the used electrode tip is not cleaned 100%.(blackish in colour)
8. If the used filler end is not trimmed after each usage.
Defects in arc welded joints in titanium alloys consist mainly of
1)porosity
2) cold cracks.
Weld penetration can be controlled by adjusting welding conditions.
Titanium Weld Porosity.
Weld porosity is a major problem in arc welding titanium alloys.
Although acceptable limits for porosity in arc welded joints have not been establish, porosity has been observed in tungsten-arc welds in practically all of the alloys which appear suitable for welding operations. It does not extend to the surface of the weld, but has been detected in radiographs.
It usually occurs close to the fusion line of the welds.
Welding torch at 90° can eliminate weld porosity and weld discolouration.
Welding speed generally 1.5 to 2 times the steel is recommended.
Weld porosity may be reduced by a slight agitation of the molten weld puddle and adjusting welding speeds, (slow down).
Also, remelting the weld will eliminate some of the porosity present after the first pass.
However, the latter method of reducing weld porosity tends to increase weld contamination.
Titanium Weld Cracks.
With adequate shielding procedures and suitable alloys, cracks should not be a problem.
However, cracks have been troublesome in welding some alloys.
Weld cracks are attributed to a number of causes.
In commercially pure titanium, weld metal cracks are believed to be caused by excessive oxygen or nitrogen contamination.
These cracks are usually observed in weld craters.
In some of the alpha-beta alloys, transverse cracks in the weld metal and heat affected zones are believed to be due to the low ductility of the weld zones.
However, cracks in these alloys also may be due to contamination.
Cracks also have been observed in alpha-beta welds made under restraint and with high external stresses.
These cracks are sometimes attributed to the hydrogen content of the alloys.
If weld cracking is due to contamination, it may be controlled by improving shielding conditions.
However, repair welding on excessively contaminated welds is not practical in many cases.
Cracks which are caused by the low ductility of welds in alpha-beta alloys can be prevented by heat treating or stress relieving the weldment in a furnace immediately after welding.
Cracks due to hydrogen may be prevented by vacuum annealing treatments prior to welding.
The visual inspection of the color of titanium welds and parts, is a great indication of the resulting weld / part integrity.
A macro examination of that titanium weld will typical reveal weld defects such as porosity, undercut, lack of root or side wall fusion.
What should be the Titanium weld filler strength?
Welding pure titanium, use a pure titanium wire.
If welding a titanium alloy, the next lowest strength alloy should be used as a filler wire.
The weld deposit will pick up through dilution the required strength.
The same considerations are true when MIG welding titanium.
Till what temperature, is the titanium weld and surrounding to be protected?
The primary concern when welding titanium is that both the weld and surrounding metal must be meticulously clean and be totally protected from the reactive gases of the atmosphere.
Typically inert argon, helium or a vacuum unit is used for this protection.
The atmospheric protection must be provided to all sides of the parts that are subject to temperatures above 800°F or 426°C.
Always ensure that the inert atmosphere protection is maintained until the weld metal temperature cools well below 426°C (800°F), keep those 300°C tempsticks handy.
When titanium is subject to heat above 400°C it reacts with the atmosphere oxygen, nitrogen and also will react with carbon and contaminate.
If the contaminants are absorbed into the weld,
the results can be
porosity and low-notch toughness and brittleness.
Properly shielded titanium welds will be bright and silvery in appearence.
Nitrogen contamination may lead to yellow colour.
Oxygen may lead to blue colour.
If the welds are gray,or a white powdery color, these welds should be completely removed,
usually by grinding and cleaned before welding again.
The quality and coverage of the shielding gas 99.998% to 99.999%(ultra high pure)is an extremely important factor for welding titanium.