Gas Tungsten Arc Welding (GTAW) WELD 250 Practice Test 2026 - Free GTAW Practice Questions and Study Guide

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In GTAW of carbon steel, which filler metal is most commonly used and why?

ER70S-2; provides good ductility and good filler/base metal fusion for carbon steel.

For GTAW of carbon steel, you want a filler metal that blends well with the base metal, stays ductile, and provides reliable fusion without introducing excessive hardness or brittleness. ER70S-2 is a general-purpose carbon-steel filler designed for welding low-carbon steels. Its low carbon content keeps the weld metal ductile and tough, and the silicon and manganese deoxidizers help prevent porosity and cracking while promoting good fusion to the base metal. This balance makes it the most versatile and commonly used choice for carbon steel joints in GTAW.

The other options align with different materials or properties: ER70S-6 has more deoxidizers and can produce a somewhat harder, less ductile weld; ER4043 is an aluminum filler, not for steel; ER308L is for stainless steel and offers high corrosion resistance, not suited for carbon steel.

ER70S-6; provides high hardness for wear resistance.

ER4043; reduces cracking in aluminum.

ER308L; high corrosion resistance filler.