Weld Electrode Reference -- AWS Classification System and Electrode Properties
This page is a technical reference covering the AWS electrode classification system, electrode mechanical properties, and matching filler metal to base metal for structural steel welding per AWS D1.1. It catalogs electrodes by classification. For practical selection guidance (which electrode to use in which scenario), see the Welding Electrode Selection Guide.
AWS Electrode Classification System (AWS A5.1 / A5.5)
The electrode classification printed on each electrode (e.g., E7018) encodes four pieces of information:
The "E" Prefix
"E" designates an arc welding electrode. All SMAW (shielded metal arc welding, commonly called "stick") electrodes begin with E.
First Two or Three Digits: Tensile Strength
The first digits indicate the minimum tensile strength of the deposited weld metal in ksi:
| Digits | Min Tensile (ksi) | Example Electrodes |
|---|---|---|
| 60 | 60 | E6010, E6011, E6013, E6022 |
| 70 | 70 | E7018, E7016, E7024, E70C-6M |
| 80 | 80 | E8018-B6, E8018-C3 |
| 90 | 90 | E9018-B3, E9018-M |
| 100 | 100 | E10018-D2, E11018-M |
| 110 | 110 | E11018-M |
| 120 | 120 | E12018-M |
For structural steel applications, E60XX and E70XX cover the vast majority of work. E80XX and above are used for matching higher-strength base metals (A572 Gr 50 and A913 Gr 65) or for demand-critical welds where the weld metal must overmatch the base metal (seismic moment frames).
Third Digit: Welding Position
| Digit | Position |
|---|---|
| 1 | All positions (flat, horizontal, vertical, overhead) |
| 2 | Flat and horizontal fillets only |
| 3 | Flat only (for high-deposition electrodes) |
| 4 | Flat, horizontal, overhead, and vertical-down |
E7018 is an all-position electrode. E7024 is flat/horizontal only -- its high iron powder content makes the slag too fluid for out-of-position welding.
Fourth Digit: Coating Type and Current
| Digit | Coating Type | Current | Characteristics |
|---|---|---|---|
| 0 | High cellulose sodium | DCEP | Deep penetration, fast freeze, high spatter (E6010) |
| 1 | High cellulose potassium | AC or DCEP | Similar to 0 but AC-capable (E6011) |
| 2 | Titania sodium | AC or DCEN | Medium penetration, smooth bead (E6012) |
| 3 | Titania potassium | AC or DC either | Soft arc, low penetration, easy slag removal (E6013) |
| 4 | Iron powder titania | AC or DC either | High deposition rate (E6024, E7024) |
| 5 | Low hydrogen sodium | DCEP | Low moisture coating (E7015) |
| 6 | Low hydrogen potassium | AC or DCEP | Low moisture, AC-capable (E7016) |
| 8 | Low hydrogen potassium + iron powder | AC or DCEP | Best combination of strength and usability (E7018) |
Supplementary Suffixes (AWS A5.5 for Low-Alloy Electrodes)
Low-alloy steel electrodes carry additional suffixes designating the alloy composition:
| Suffix | Alloy Type | Typical Application |
|---|---|---|
| -A1 | C-Mo (0.5% Mo) | Elevated temperature service |
| -B1, -B2, -B3 | Cr-Mo (0.5-2.25% Cr, 0.5-1% Mo) | Creep-resistant, petrochemical piping |
| -B6, -B8 | High Cr-Mo (5-9% Cr) | High-temperature refining |
| -C1, -C2, -C3 | Ni steel (1-3.5% Ni) | Low-temperature toughness |
| -D1, -D2 | Mn-Mo (1.5-2% Mn, 0.25-0.45% Mo) | High-strength structural |
| -M | Military grade | Specified impact properties, restricted chemistry |
For structural applications, -C3 and -M suffixes are relevant when Charpy V-notch toughness is specified (seismic moment connections per AISC 341, fracture-critical members per AASHTO).
E7018: The Structural Workhorse
E7018 (AWS A5.1) is the default electrode for structural steel fabrication in the United States. It accounts for over 80% of SMAW electrode consumption in structural shops.
Mechanical properties (as-deposited, per AWS A5.1):
- Tensile strength: 70 ksi minimum (typically 75-82 ksi)
- Yield strength: 58 ksi minimum (typically 60-70 ksi)
- Elongation: 22% in 2 in. minimum
- Charpy V-notch: 20 ft-lb at -20 degrees F (for E7018 with optional H4R designation)
Coating characteristics:
- Low-hydrogen potassium coating with approximately 30% iron powder by weight
- Moisture content must be below 0.6% by weight for the H4 (diffusible hydrogen < 4 mL/100g deposited metal) designation
- Electrodes exposed to atmosphere must be rebaked per AWS D1.1 Table 5.2: 500-800 degrees F for 2 hours for E7018
- After removal from the hermetically sealed container or rod oven, E7018 may be used for 4 hours maximum (D1.1 Clause 5.3.2.2) before requiring rebake
The E7018 H4R designation means: low hydrogen (< 4 mL/100g diffusible hydrogen), moisture-resistant coating. This is the standard for seismic applications where hydrogen-induced cracking must be avoided at all costs.
E70XX Electrodes for FCAW and GMAW
Beyond SMAW, structural fabrication uses FCAW (flux-cored arc welding) and GMAW (gas metal arc welding, "MIG") extensively:
FCAW Electrodes (AWS A5.20)
| Classification | Shielding | Position | Typical Properties |
|---|---|---|---|
| E70T-1 | CO2 | All | 70 ksi tensile, good all-around |
| E70T-1C | CO2 | All | Similar, tighter chemistry |
| E70T-1M | 75Ar/25CO2 | All | Mixed gas, improved toughness |
| E70T-4 | Self-shielded | Flat/H | High deposition, 70 ksi |
| E70T-6 | Self-shielded | All | Seismic prequalified, high toughness |
| E70T-7 | Self-shielded | Flat/H | High deposition, single-pass |
| E71T-8 | Self-shielded | All | Excellent low-temperature toughness |
| E71T-8JD | Self-shielded | All | Seismic demand-critical, 40 ft-lb at -20F |
E70T-6 and E71T-8 are the FCAW electrodes prequalified for seismic moment connections per AISC 358 Annex A. E71T-8 provides the highest level of notch toughness among self-shielded flux-cored wires.
GMAW Electrodes (AWS A5.18)
| Classification | Typical Wire | Shielding | Tensile (ksi) |
|---|---|---|---|
| ER70S-3 | 0.035-0.045 in. solid | CO2 or 75/25 | 70 |
| ER70S-6 | 0.035-0.052 in. solid | 75Ar/25CO2 | 70 |
| ER70S-6 | Higher Si/Mn deoxidizers than S-3. Preferred for mill-scale surfaces. |
Matching Filler Metal to Base Metal (AWS D1.1 Table 3.1)
The filler metal must match or slightly overmatch the base metal tensile strength. Undermatching produces a weld weaker than the base metal; overmatching by more than 20 ksi can reduce ductility.
| Base Metal | Min Fu (ksi) | Matching Electrode | Notes |
|---|---|---|---|
| A36 | 58 | E60XX or E70XX | E70XX preferred for all-position work |
| A572 Gr 42 | 60 | E60XX or E70XX | E6010 for root pass on pipe |
| A572 Gr 50 | 65 | E70XX | E7018 standard for structural |
| A572 Gr 55 | 70 | E70XX | E7018 with CVN optional |
| A572 Gr 60 | 75 | E80XX | E8018-C3 for low-temp toughness |
| A572 Gr 65 | 80 | E80XX | E8018-B2 for Cr-Mo matching |
| A992 | 65 | E70XX | Standard W-shape electrode is E7018 |
| A913 Gr 50 | 65 | E70XX | E7018 -- same as A992 |
| A913 Gr 65 | 80 | E80XX | E8018-C3 |
| A514 Gr 100 | 110-130 | E110XX or E120XX | E11018-M -- demand-critical matching required |
For A36 to A36 connections (the most common case in buildings), E70XX electrodes automatically overmatch the base metal tensile strength (70 ksi weld vs. 58 ksi base metal). The weld is always stronger than the plate, so the base metal controls the connection design.
For A572 Gr 50 to A572 Gr 50, E70XX provides a weld tensile strength of 70 ksi vs. base metal 65 ksi -- a 7.7% overmatch, which is acceptable. E80XX would be an overmatch of 23%, borderline for ductility in demand-critical applications.
Worked Example -- Electrode Specification on a Shop Drawing
Scenario: W24x76 beam (A992, Fu = 65 ksi) to W14x90 column (A992, Fu = 65 ksi) moment connection. CJP groove weld at beam flanges to column flange. Fillet welds at shear tab to column flange.
Electrode specification per AWS D1.1 Table 3.1:
For A992 to A992 matching: E70XX is the matching classification (70 ksi tensile > 65 ksi base metal Fu). The slight overmatch is within the 7.7% range and provides desirable yield overmatch without embrittlement.
CJP groove weld at flanges: Specify E71T-8 (FCAW, self-shielded, 70 ksi tensile, 58 ksi yield, all-position, CVN at -20F: 40 ft-lb minimum). This provides the notch toughness required for the complete-joint-penetration tension flange weld. Alternatively, E70T-6 for seismic prequalified connections per AISC 358.
Fillet weld at shear tab: Specify E70T-1 (FCAW, CO2 shielded, 70 ksi tensile). Notch toughness is not required for the shear tab weld so the more economical E70T-1 is appropriate.
Procedure qualification: AWS D1.1 Clause 4 requires that the WPS (Welding Procedure Specification) be qualified by test (PQR -- Procedure Qualification Record) for the specific electrode classification, base metal group, and welding position. A prequalified WPS per D1.1 Clause 3 may be used for E70XX electrodes on Group I and II base metals (which include A36, A572, and A992) in the as-welded condition, provided all D1.1 Clause 3 essential variables are satisfied.
Preheat and Interpass Temperature Requirements
Preheat prevents hydrogen-induced cracking (cold cracking) by slowing the cooling rate and allowing hydrogen to diffuse out of the weld. AWS D1.1 Table 3.2 specifies minimum preheat temperatures based on the base metal category and thickness.
| Base Metal | Thickness | Min Preheat (F) | Notes |
|---|---|---|---|
| A36 | Up to 3/4" | 50 (none required above 32F) | Category A |
| A36 | 3/4" to 1-1/2" | 50 | Category A |
| A36 | 1-1/2" to 2-1/2" | 150 | Category A |
| A572 Gr 50 | Up to 3/4" | 50 | Category B |
| A572 Gr 50 | 3/4" to 1-1/2" | 50 | Category B |
| A572 Gr 50 | 1-1/2" to 2-1/2" | 225 | Category B |
| A514 | Any | 125-200 | Quenched and tempered -- follow manufacturer |
Higher preheat temperatures are required for higher-strength steels (higher carbon equivalent), thicker sections (faster heat sink), and when the hydrogen level is uncertain (field welding vs. shop welding). Low-hydrogen electrodes (H4, H8) may allow reduced preheat per D1.1 Annex H.
Electrode Storage and Handling
Low-hydrogen electrodes (E7015, E7016, E7018) must be stored in a holding oven at 250-300 degrees F after the hermetically sealed container is opened. Electrodes exposed to the shop atmosphere for more than 4 hours (E7018) or 2 hours (E7015, E7016) must be rebaked before use.
Exposure limits are reduced to 1 hour for E7018 electrodes used in demand-critical welds (per AISC 341 seismic provisions, Section 6.3.4). This is because hydrogen cracking in a CJP moment connection weld is catastrophic and difficult to detect by UT.
Common Questions
Can E6010 and E7018 be used on the same weld? Yes, but not in reverse. The common practice is E6010 for the root pass (deep penetration, fast freeze) and E7018 for fill and cap passes (higher strength, better toughness). Never put E6010 over E7018 -- the higher-hydrogen E6010 would introduce hydrogen into the already-deposited low-hydrogen weld metal.
What does "H4" mean on an E7018 electrode? H4 = diffusible hydrogen less than 4 mL per 100g of deposited weld metal (tested per AWS A4.3). H8 = less than 8 mL. H16 = less than 16 mL. For structural applications, H4 or H8 is standard. For seismic demand-critical, H4 is required.
Why do some shops use E70T-1 rather than E7018? FCAW (E70T-1) has a deposition rate 2-3x higher than SMAW (E7018) and produces a smoother bead with less spatter. The wire is continuously fed, so there is no stub loss. For production shop welding, FCAW is more cost-effective. SMAW (E7018) is used for field welding, small shops, and applications where FCAW equipment is impractical.
Related References
- Welding Electrode Selection Guide
- Steel Connection Design Guide
- End Plate Connection Design
- Steel Grades Reference
- How to Verify Calculations
Disclaimer
This page is for educational and reference use only. It does not constitute professional welding engineering advice. Welding procedure specifications, electrode selection, and quality control must be overseen by a qualified welding engineer or Certified Welding Inspector (CWI) for the specific project conditions. The site operator disclaims liability for any loss arising from the use of this information.