Advanced Welding Processes: Technologies and Process Control

CVN impact energy (J)
200
150
100
50
0
5.2.4 Shielding gas options
Gases for advanced welding processes 63
A B C
5 8 15 5 8 15 5 8 15
Gas mixtures and consumables
Test temp. –60∞C Test temp. 0∞C
5.4 Toughness of high-strength, low-alloy steel welds made in
various gas mixtures using pulsed GMAW. A, 70S6 wire; B, 70S6
wire; C, K5Ni wire: 5, 8, 15% CO 2 in argon. [60]
The range of viable shielding gas options is limited by the need to satisfy the
criteria listed above. Some of the common gases are listed below.
Argon
Argon is one of the most widely used shielding gases for GTAW welding. It
is totally inert and has a high density relative to air. The low ionization
potential facilitates arc striking and stability.
Helium
Helium is chemically inert, has a lower density than air and requires a higher
arc voltage (at the same current and arc length) than argon. The resultant
increase in power produces increased heat input and fusion area although
lower depth-to-width ratios are normally experienced. The cost of helium is
considerably higher than that of argon, but the welding speeds that are usually
obtained make it a viable option, particularly for high-conductivity materials.
Carbon dioxide
Carbon dioxide is chemically active, but has a higher density than air. It can
dissociate in the arc to release oxygen and carbon monoxide and this can
result in a reduction in the weld metal content of elements such as silicon,