1018 steel has 0.15-0.20% carbon and 0.60-0.90% manganese. That low carbon content makes it one of the easiest steels to weld. No preheat, no special procedures, no post-weld heat treatment for any normal application. Pick any welding process, use standard 70 ksi filler metal, and you’ll get a sound joint.
The “1018” designation comes from the AISI/SAE numbering system. The “10” means plain carbon steel with no significant alloying elements. The “18” is the nominal carbon content in hundredths of a percent (0.18%). This steel is commonly sold as cold-drawn or cold-rolled bar stock (CRS) in round, square, flat, and hex shapes. It’s the go-to material for shafts, pins, bushings, fixtures, jigs, and machine components where moderate strength and good machinability matter more than high hardness.
1018 Composition and Properties
| Property | Value |
|---|---|
| Carbon | 0.15-0.20% |
| Manganese | 0.60-0.90% |
| Phosphorus (max) | 0.040% |
| Sulfur (max) | 0.050% |
| Yield Strength (cold-drawn) | 54 ksi (370 MPa) |
| Tensile Strength (cold-drawn) | 64 ksi (440 MPa) |
| Yield Strength (hot-rolled) | 32 ksi (220 MPa) |
| Tensile Strength (hot-rolled) | 58 ksi (400 MPa) |
| Elongation | 15-25% |
| Hardness (cold-drawn) | 126 BHN |
| Carbon Equivalent | 0.28-0.33 |
Notice the difference between hot-rolled and cold-drawn properties. Cold drawing work-hardens 1018, raising yield strength from 32 to 54 ksi and tensile from 58 to 64 ksi. Welding destroys those cold-work properties in the HAZ. The heat-affected zone on cold-drawn 1018 reverts to hot-rolled properties because the welding heat recrystallizes the grain structure. This matters for load-bearing designs: the HAZ on cold-drawn 1018 is softer than the parent material.
Why 1018 Welds So Easily
Weldability comes down to two factors: carbon equivalent and hardenability. 1018 scores well on both.
The carbon equivalent (CE = C + Mn/6) for 1018 runs 0.28-0.33. That’s well below the 0.45 threshold where hydrogen cracking becomes a concern. The HAZ on 1018 doesn’t form martensite at normal cooling rates because there simply isn’t enough carbon to support the transformation. You’d need an extreme quench rate on a very thick section to get any measurable hardness increase in the HAZ.
Compared to higher-carbon steels in the 10xx series, 1018 has essentially zero risk of:
- Hydrogen-assisted cracking (cold cracking)
- HAZ hardening above parent metal hardness
- Lamellar tearing (low sulfur content)
- Solidification cracking (low carbon + low impurities)
The only weld defects you’ll see on 1018 come from poor technique: porosity from bad gas coverage, lack of fusion from insufficient heat, or distortion from excessive heat input on thin sections.
Filler Metal Selection for 1018
Standard 70 ksi filler metals overmatch 1018 in both the hot-rolled and cold-drawn conditions. That’s the correct approach: the weld metal should be at least as strong as the weakest part of the joint, which is the HAZ on cold-drawn 1018.
MIG Wire
ER70S-6 handles 1018 in all conditions. It’s the default choice for shop fabrication. Run 75/25 argon/CO2 or straight CO2 depending on whether you prioritize bead appearance (75/25) or penetration and cost savings (CO2). Cold-rolled 1018 bar stock has a clean surface that doesn’t need heavy deoxidizers, so ER70S-3 works equally well if you prefer less silica islands on the bead.
Stick Electrodes
E7018 is the structural choice for 1018. Low hydrogen, excellent mechanical properties, smooth arc. Overkill for most 1018 applications, but there’s never a downside to using it.
E6013 is a reasonable choice for light fabrication, fixtures, and non-structural 1018 work. It’s easier to run, produces a pretty bead, and costs less than 7018. It’s not low-hydrogen, but 1018 doesn’t need low-hydrogen procedures.
E6011 works when the surface is dirty or you need deep penetration on a root pass. It also runs on AC machines.
TIG Rod
ER70S-2 is the standard for TIG welding 1018. Triple deoxidizers produce a clean, fluid puddle with minimal porosity. For clean, prepped cold-rolled stock, ER70S-6 rod works fine and is more readily available.
| Process | Filler | Shielding | Notes |
|---|---|---|---|
| MIG | ER70S-6 (.030" or .035") | 75/25 Ar/CO2 | Default choice for all 1018 work |
| MIG | ER70S-3 (.030" or .035") | 75/25 Ar/CO2 | Cleaner bead on prepped material |
| Stick | E7018 (1/8") | Flux coating | Structural, highest quality |
| Stick | E6013 (1/8") | Flux coating | Non-structural, easy arc |
| TIG | ER70S-2 (1/16" or 3/32") | 100% Argon | Best puddle control and purity |
| Flux-Core | E71T-11 (.030" or .035") | Self-shielded | No gas required, outdoor work |
Welding Procedure for 1018
Joint Preparation
Cold-rolled 1018 has a clean, smooth surface with no mill scale. A quick wipe with acetone to remove machining oil is usually all the prep needed. Don’t skip the degrease step on CRS bar stock because it often has a residual film of drawing lubricant or rust-preventive oil.
Hot-rolled 1018 has mill scale that should be ground off in the weld zone. Light, tight scale can be welded through with ER70S-6 MIG wire, but grinding produces cleaner welds.
Standard joint designs apply. For butt joints on plate, use a 60-degree V-groove on material 1/4 inch and thicker with a 1/16 inch root opening. Fillet welds follow the same sizing rules as any mild steel: weld size equal to the thinner member’s thickness for full-strength joints, or per engineering drawings for specified sizes.
Process-Specific Settings
MIG on 1018 bar stock (typical repair and fabrication):
| Bar Diameter/Thickness | Wire (.030" ER70S-6) | Voltage | WFS (IPM) |
|---|---|---|---|
| 1/4" round or flat | .030" | 17-18 | 280-320 |
| 1/2" round or flat | .030" | 18-20 | 300-360 |
| 3/4" round or flat | .035" | 20-22 | 340-400 |
| 1" and thicker | .035" | 22-24 | 380-440 |
TIG on 1018 runs DCEN with 100% argon at 15-20 CFH. Use a 3/32 inch 2% lanthanated tungsten for most work. Amperage range of 80-180A depending on thickness. 1018’s thermal conductivity is moderate, so heat doesn’t spread as aggressively as with aluminum or copper. Maintain a tight arc length (one tungsten diameter) and feed rod consistently.
Stick on 1018 with 1/8 inch E7018 at 110-140 amps covers 3/16 to 3/8 inch material in all positions. Keep a short arc length (one rod diameter), travel at a pace that maintains a smooth, consistent puddle, and chip slag thoroughly between passes.
Post-Weld Properties and Considerations
HAZ Softening on Cold-Drawn 1018
This is the most important metallurgical effect to understand when welding cold-drawn 1018. Cold drawing increases strength through work hardening. Welding heat eliminates that work hardening in the HAZ. The result is a band of material adjacent to the weld that has reverted to essentially hot-rolled properties.
For a cold-drawn 1018 shaft with 54 ksi yield strength, the HAZ drops back to roughly 32 ksi yield. If the weld is in a critically loaded area, that HAZ is the weakest link. Designing the joint to put the weld in a low-stress zone, or specifying a larger weld to reduce stress concentration, accounts for this effect.
Case Hardening After Welding
1018 is one of the most common case-hardening steels. Carburizing adds carbon to the surface layer (typically 0.060-0.080 inch deep) at 1650-1700F, followed by quenching and tempering. The carbon-enriched case hardens to 58-62 HRC while the core stays soft and tough.
You can carburize welded 1018 assemblies. The weld metal (ER70S-6, for example) will also absorb carbon during carburizing and harden at the surface. The HAZ will carburize normally since it’s still 1018 composition. Keep in mind that welded joints should be designed to avoid carburized surfaces in high-stress areas where a hard, brittle surface layer could initiate fatigue cracks.
Stress Relief
Stress relief on 1018 is rarely needed. When specified, heat to 1100-1200F, hold for 1 hour per inch of thickness, and furnace cool. This relieves residual welding stresses without altering mechanical properties significantly. It’s most commonly done on precision fixtures and jig assemblies where dimensional stability during machining is critical.
1018 vs Other Mild Steels for Welding
| Grade | Carbon % | Typical Form | Welding Difficulty | Notes |
|---|---|---|---|---|
| 1008 | 0.08 | Sheet, strip | Very easy | Even softer than 1018, used for drawn parts |
| 1018 | 0.18 | Bar stock (CRS/HRS) | Very easy | General machining and fabrication |
| 1020 | 0.20 | Plate, bar | Very easy | Nearly identical to 1018 for welding |
| A36 | 0.25 max | Plate, shapes | Easy | Slightly higher carbon possible |
| 1045 | 0.45 | Bar, shaft | Moderate-difficult | Preheat required, hydrogen cracking risk |
For welding purposes, 1018 and 1020 are interchangeable. Same fillers, same procedures, same results. A36 is very similar but can have slightly higher carbon depending on the heat, which occasionally matters on heavy plate. The jump from 1018 to 1045 is where welding gets significantly harder.
Common Problems on 1018
Porosity. Same causes as any mild steel: bad gas coverage, dirty surface, moisture. On cold-rolled stock, the most common contamination is drawing lubricant or rust-preventive oil. Wipe down with acetone before welding.
Distortion on thin sections. 1018 bar stock and thin flat bar warp easily under welding heat. Clamp pieces to a flat surface, use skip welding or backstep sequences, and keep heat input reasonable. On round shafts, rotate and weld opposite sides alternately to balance shrinkage stresses.
Undercut on fillet welds. Too much voltage for the travel speed. Drop voltage 1-2 volts, slow down, and direct the wire into the root of the joint.
Mismatch on dissimilar-thickness joints. When welding thin 1018 bar to thick plate, direct 60-70% of the arc heat onto the thicker piece. On MIG, angle the gun toward the thick member. On stick, use a slight manipulation pattern that spends more time on the plate side.
1018 is about as forgiving as steel gets. If you can weld at all, you can weld 1018. Match the filler to the application, keep the surface clean, control your heat input on thin sections, and the metallurgy takes care of itself.