What current should be used for TIG welding on steel and stainless steel?

For TIG welding on steel and stainless steel, the correct choice is to use direct current with straight polarity (DCEN). This is because DCEN allows for better control of the arc and provides a more stable and focused heat source, which is essential for producing high-quality welds. When using DCEN, the electrode (tungsten) remains negative, which draws more heat into the workpiece, thus ensuring deeper penetration and cleaner welds. This attribute is particularly beneficial for welding materials such as steel and stainless steel, where penetration and the ability to manipulate the heat are crucial for optimal results.

In contrast, alternating current (AC) is typically used for aluminum welding due to its ability to clean the oxide layer off the surface of the aluminum. DC reverse polarity (DCEP) is more suited for applications like MIG welding and does not provide the correct heat input balance for TIG welding on steel. AC low frequency would not provide the necessary stable arc for effective welding on steel and stainless steel. Therefore, the use of DCEN in TIG welding allows for intensity and control, making it the preferred method for these materials.