Mild Steel — What It Is and Why It Matters
Mild steel (also called low-carbon steel or A36 steel) is the most commonly welded metal in the world. It contains less than 0.30% carbon, making it highly weldable with all major processes — MIG, TIG, stick, and flux-core — without special preheat or post-weld treatment in most thicknesses.
Mild steel is the standard material for structural fabrication, automotive frames, general manufacturing, furniture, gates, trailers, and virtually every hobby and shop welding project. It is affordable, widely available in plate, sheet, tube, angle, and channel forms, and forgiving of technique errors that would cause cracking in higher-carbon or alloy steels.
Standard filler metals for mild steel include ER70S-6 (MIG/TIG), E7018 and E6010 (stick), and E71T-1 (flux-core). The "70" in these designations indicates 70,000 PSI minimum tensile strength, which matches or exceeds the base metal strength of A36 steel (36,000 PSI yield).
Frequently Asked Questions
Is mild steel the same as carbon steel?
Mild steel is a type of carbon steel — specifically low-carbon steel with less than 0.30% carbon content. The broader category of carbon steel also includes medium-carbon (0.30-0.60%) and high-carbon (0.60-1.0%) steels, which are progressively harder to weld due to increased hardenability.
Can you weld mild steel to stainless steel?
Yes, using the correct filler metal. ER309L is the standard choice for joining mild steel to austenitic stainless steel (304, 316). The 309L composition bridges the metallurgical gap between the two base metals, preventing cracking and corrosion at the joint.