Welding Gases 2

[Bucz48]

Gas for GTAW
I am looking for the best gas to use that will give me the lowest hardness in a non-PWHT'd weld and HAZ.
I would like feed back on using 75% Argon and 25% Helium.

 

[metengr]

Bucz48;
Your question is too broad, you need to be more specific regarding base materials and filler metals. The gases used for GTAW are not optimized to increase hardness or affect base metal heat affected zone hardness. This had more to do with weld metal dilution, preheat requirements and filler metal selection.

There are standard gas mixtures to provide suitable weldability, depending on weld joint position and desired toughness (with or without PWHT). Gases will affect depth of penetration and porosity with the GTAW process.

 

[stanweld]

Helium is a great heat conductor. Adding helium to the mix will more than likely increase the hardness of the deposited weld metal and HAZ relative to a pure Argon sheild, assuming all other weld parameters are equal due to the greater quenching effect of He.

While not seeing this in GTAW welds, I have seen increased hardness in carbon and low alloy steels with the GMAW process when similar Ar-He mixes were used versus Argon and Ar-CO2 mixes.

Preheat and interpass temperature controls prove much more effective in controlling hardness, as metengr states.