AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is reviewing a Weld Procedure Specification (WPS) for Gas Metal Arc Welding (GMAW) on a critical structural component. The WPS specifies the use of a 100% Argon shielding gas with a solid wire electrode. What is the most likely consequence of using 100% Argon shielding gas for GMAW of carbon steel?
- AImproved wetting of the weld bead and reduced spatter.
- BFaster travel speeds due to increased arc force.
- CA narrow, deep penetrating arc with increased fusion.
- DAn unstable arc, poor bead shape, and excessive undercut.
Show answer & explanationAnswer & explanation
Correct answer: D. An unstable arc, poor bead shape, and excessive undercut.
While 100% Argon works well for aluminum and some stainless steels, it produces an unstable, wandering arc with poor wetting and excessive undercut when used with carbon steel. A small addition of CO2 or oxygen is typically needed to stabilize the arc and improve bead shape on carbon steel.
Why the other options are wrong
- A. 100% Argon typically leads to poor wetting and increased spatter on carbon steel, not improved wetting or reduced spatter.
- B. An unstable arc characteristic of 100% Argon on carbon steel would generally reduce, not increase, practical travel speeds.
- C. While argon can provide a somewhat concentrated arc, without an oxidizing component for carbon steel, the arc becomes unstable and does not provide the desired deep penetration and fusion for carbon steel.
GMAW 100% Argon on Carbon Steel
Using 100% Argon shielding gas for GMAW of carbon steel results in an unstable arc, poor bead shape (ropy/humped), excessive undercut, and poor wetting.
- Argon is an inert gas.
- Suitable for aluminum and some stainless steels.
- On carbon steel, it leads to an unstable arc.
- Causes poor wetting, humped beads, and undercut.
- Requires addition of CO2 or O2 for arc stability and better bead shape on carbon steel.
Memory trick: Carbon steel needs a kick; pure argon leaves it sick.