What is the primary purpose of using ER70S-3 electrodes in welding?

The primary purpose of using ER70S-3 electrodes in welding is to provide a filler metal that is well-suited for welding low-carbon steels. ER70S-3 is a common type of solid filler metal that is designed to produce quality welds on low-carbon steel, which is widely used in various fabrication and construction applications. This electrode is favored for its good mechanical properties and deoxidizers that allow for a cleaner weld with lesser inclusions.

In the context of the other options, using ER70S-3 is not suitable for high-temperature applications, as it is specifically designed for low-carbon steels rather than materials requiring high-temperature performance. Additionally, it is not meant for stainless steel welding, as stainless steel electrodes have different chemical compositions and properties tailored for that purpose. Lastly, ER70S-3 is not intended for non-ferrous metals, which typically require specialized electrodes specifically formulated for metals like aluminum or copper. Thus, the application of ER70S-3 is primarily focused on low-carbon steel, making it the correct choice for this question.