Shielding Gas Considerations for Welding Carbon Steels

GMAW (MIG)

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

 

GTAW (TIG)

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.

 

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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.

 

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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