GTAW of chrome-moly is performed using which polarity?

• A. DC-
• B. AC
• C. DC+
• D. Alternating polarity

Answer: (A)

Polarity in GTAW determines where the heat goes during the weld. For chrome-moly steel, you want the heat concentrated in the base metal to achieve good penetration and solid fusion while keeping the tungsten from wearing excessively. This is achieved by using direct current with the electrode negative. When the electrode is negative, current flows from the electrode into the workpiece, transferring most of the arc heat to the metal being welded. That gives you better penetration and control on steel. Using alternating polarity would mix cleaning action and heat in ways that aren’t ideal for this material, and direct current with the electrode positive would heat the electrode more and reduce penetration, increasing wear. So the best choice is direct current with the electrode negative.