Page 54 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Materials and Their Weldability

and corrosion resistance of steels when
alloyed at levels > 8%. It promotes
austenite formation at temperatures
below the lower critical temperature.
Silicon (Si) Alloyed in small amounts as a deox-
idiser in ferritic steels.
Aluminium (Al) Used as a grain refiner in steels and a
deoxidising agent in triple deoxidised
steels.
Niobium (Nb) and Used to help carbide formation to
Titanium (Ti) stabilise stainless steel.

Titanium
Titanium is becoming more widely used in industry because
of its excellent properties. These are:

. high strength to weight ratio (strong as steel but half the
weight);
. excellent corrosion resistance;
. good mechanical properties at elevated temperatures.
Types of titanium in use are:
. Commercially pure (98–99.5% Ti). May be strengthened
by small additions of O 2, N 2 , C and Fe and is easily
welded.
. Alpha alloys. Mainly single-phase alloys with up to 7% Al
and a small amount of O 2 ,N 2 and C. These can be fusion
welded in the annealed condition.
. Alpha-beta alloys. Two-phase alloys formed by the
addition of up to 6% Al and varying amounts of beta-
forming constituents such as V, Cr and Mo. Can be fusion
welded in the annealed condition.
. Ni–Ti alloys that contain a large beta phase, stabilised by
elements such as Cr, are not easily welded.
Commercially pure grades and variants of the 6% Al and 4%
V alloy are widely used in industry.

39

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200904QG Welding chap4.3d Page 39 of 48