Mild Steel Alloys Tech Guide

Shielding Gas Considerations for Welding Carbon Steels


Current - DC, Reverse Polarity

Shielding - While CO2 gives deeper penetration at faster welding speeds than Ar - 2% O2, it does produce a more violent arc and more spatter. Adding argon to CO2 will benefit. For example:

25% CO2 - 75% Ar is popularly used for short circuiting transfer in welding mild steels. This mixture is excellent when welding out-of-position on thin gauge steel; and also for high current welding. Spatter is minimized.

50% CO2 - 50% Ar: Frequently used in pipe welding, this mixture gives greater penetration than the above with a quieter arc and more strength than CO2.

Other mixtures of 3% to 10% CO2 with argon can be considered for good penetration with minimal porosity, e.g. 90% Ar - 10% CO2 is excellent for spray transfer, as is 92% Ar - 8% CO2 also, on both mild and low alloy steels.

See Shielding Gas Guide for further details



Current - DC, Straight Polarity (while AC may sometimes be used, DCSP is generally most preferable). Reverse Polarity is never used.

Shielding - Argon. In some instances, the addition of helium might be considered for deeper penetration on large sections, but He-Ar or He are generally restricted to automatic welding.


GMA (MIG) Welding Parameters Mild and Low-Alloy Steel

Short circuit transfer:
Electrode Diameter (inches) Welding Current (amperage) Arc Voltage Wire Feed Speed (IPM)
0.023 30-90 14-19 100-400
0.030 40-145 15-21 160-380
0.035 50-180 16-22 150-340
0.045 75-250 17-22 100-220

Settings based on CO2 shielding gas for mild steel, Ar-CO2 for low-alloy steel.


Spray transfer:
Electrode Diameter (inches) Welding Current (amperage) Arc Voltage Wire Feed Speed (IPM)
0.030 135-230 24-28 390-670
0.035 165-300 24-28 360-520
0.045 200-375 24-30 210-390
1/16 275-500 24-32 150-360
3/32 300-600 24-33 75-125

Settings based on Ar, 5% O2 shielding gas.


File Test to Estimate Hardness of Steel

Approx. Hardness   Surface Reaction to Filing Type of Steel
Brinell Rockwell    
100 60B Metal is readily cut by file Low Carbon
200 15C Metal is readily cut by file under moderate pressure Med. Carbon
300 30C Metal is difficult to file though it can be cut High Alloy
400 40C Metal is cut only with greatest effort High Carbon
500 50C Metal nearly impossible to cut Tool Steel
600 60C Metal cannot be cut with a file Hardened Tool Steel