What filler metals are commonly used for welding mild steel in Welding 101, and how do they differ?

• A. E6010/E6011 for deep penetration with cellulose coatings; E7018 for strong, low-hydrogen welds.
• B. ER70S-6 for all positions.
• C. 4043 for all steel welds.
• D. E308L for mild steel.

Answer: (A)

Filler metal selection for mild steel hinges on balancing penetration and the strength and toughness of the weld. The cellulose-coated electrodes, like E6010 and E6011, are known for their deep, penetrating arc. That makes them especially useful for the root pass, where you want the weld to bite through any surface contamination and ensure a solid connection even if the joint isn’t perfectly clean. They also work well in less-than-ideal joints because of that penetrating capability, and they can be used with different polarity and current setups to suit the job.

The E7018 electrode, in contrast, provides a strong, low-hydrogen weld. Its flux helps keep hydrogen in the weld metal low, which reduces the risk of cracking and gives you high toughness and good ductility in the finished weld. It does require proper drying and storage to maintain its low-hydrogen properties, and it typically produces a cleaner, more consistent weld once you’re set up correctly.

So, using E6010 or E6011 for a root pass to achieve deep penetration and solid initial fusion, followed by E7018 for the filling and final passes to gain strength and toughness, is a common approach for mild steel in many welding scenarios. The other fillers listed aren’t the standard choices for mild steel in this context: ER70S-6 is a modern MIG filler, 4043 is for aluminum, and E308L is for stainless steel, so they don’t match typical mild-steel SMAW practice.