Final answer:
The E4918 electrode is best suited for welding high sulphur steels in the flat position due to its low hydrogen coating, which helps to minimize cracking and is suitable for welding in all positions, particularly flat.
Step-by-step explanation:
The best electrode for welding high sulphur steels in the flat position is E4918. This electrode is designed with a low hydrogen coating which helps to minimize cracking and is suitable for such steels. The E4918 electrode provides a smooth arc, good bead appearance and is capable of welding in all positions; however, it is especially effective in the flat position. It's essential to choose the correct electrode for high sulphur steels, as they can be prone to hot cracking, and the low hydrogen characteristic of the E4918 helps prevent this issue.