Page 55 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A Quick Guide to Welding and Weld Inspection

Welding problems
There are many problems with welding titanium because it
reacts readily with air, moisture, grease, dirt and refractory
to form brittle compounds. It is therefore absolutely essential
that the weld joint surfaces and filler wire are free of any
contamination before and during the entire welding opera-
tion. Titanium cannot be welded to most other metals
because embrittling metallic compounds that lead to weld
cracking are formed.
Above 500 8C, titanium has a very high affinity for
hydrogen, nitrogen and oxygen so an inert atmosphere
protection must be maintained until the weld metal cools
below 426 8C (800 8F). This normally means that a trailing
gas shielding is required, i.e. a process utilising inert gases,
and welding must be slow enough to enable the trailing gas
shielding to be utilised.
. Improper welds might be less corrosion-resistant com-
pared to the base metal.
. Reaction with gases and fluxes makes common welding
processes such as gas welding, MMA, FCAW and SAW
unsuitable.
Typical imperfections
Titanium welding imperfections are:
. Porosity, caused by gas bubbles trapped during solidifica-
tion. The gas is hydrogen from moisture in the arc
environment or from contamination on the filler and/or
parent metal surface.
. Contamination cracking, caused by iron particles present
on the material surface dissolving in the weld metal and
reducing its corrosion resistance. They can also cause
embrittlement at high iron concentrations. Iron particles
present in the HAZ can melt and cause microcracking and
corrosion.
. Embrittlement, caused by weld metal contamination from

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200904QG Welding chap4.3d Page 40 of 48