Which of the following is true about postflow in GTAW?

Postflow in Gas Tungsten Arc Welding (GTAW) is essential for protecting the weld area as it cools after the welding arc has been extinguished. The purpose of postflow is to continue the flow of shielding gas, typically argon, over the weld bead to prevent contamination and oxidation of the molten metal as it solidifies. During the cooling process, if the weld is exposed to air, it can form oxides and affect the integrity of the weld. Continued shielding helps ensure that the mechanical properties and appearance of the weld remain optimal, allowing for better strength and aesthetics.

The other options involve aspects that, while related to the welding process, do not accurately pertain to the primary function of postflow. For instance, preventing overheating of the torch is primarily managed through cooling mechanisms, while further purification of the weld is not a key function of postflow, and it is indeed necessary for ensuring the quality of the weld, making the assertion about it being unnecessary in most applications inaccurate.