17.1 AWS A5 Architecture: SMAW, GMAW/GTAW and FCAW Consumable Classifications

17.1 AWS A5 Consumables: Carbon & Low-Alloy Steels

Quick Answer: The American Welding Society (AWS) A5 series provides the regulatory and metallurgical framework for welding consumables. Carbon steel SMAW electrodes are governed by AWS A5.1 (e.g., E7018 basic low-hydrogen, E6010 cellulosic deep-penetration, E7024 high-deposition rutile/iron powder), while low-alloy electrodes fall under AWS A5.5 with compositional suffixes (-A1 C-Mo, -B2 Cr-Mo, -C3 Ni-alloy, -D2 Mn-Mo, -M military high-toughness). Solid GMAW wires follow AWS A5.18 (ER70S-2 triple-deoxidized, ER70S-6 high Si-Mn) and AWS A5.28 (ER80S-D2, ER90S-B3). Flux-cored wires are classified under AWS A5.20 and AWS A5.29 (including seismic self-shielded E71T-8 and low-temp E81T1-Ni1). Submerged arc systems (AWS A5.17 / A5.23) mandate combined wire-flux callouts (e.g., F7A2-EM12K, F8A4-EA2-A2), where active fluxes must be strictly avoided in multi-pass welding to prevent brittle Mn and Si buildup.

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AWS A5 Specification Architecture & Procurement Framework

The AWS A5 committee establishes standardized chemical composition, mechanical property, usability, and packaging criteria across all commercial arc welding consumables. For a Certified Welding Engineer (CWEng), understanding consumable specifications extends beyond memorizing classification numbers—it requires managing procurement quality control via AWS A5.01M/A5.01 (Procurement Guidelines for Consumables - Welding and Allied Processes - Flux and Gas Shielded Electrical Arc Welding).

+-----------------------------------------------------------------------------------------+
|                        AWS A5 SPECIFICATION MATRIX FOR CARBON & LOW-ALLOY STEELS        |
+------------------------------------+--------------------------+-------------------------+
| Welding Process                    | Carbon Steel Class       | Low-Alloy Steel Class   |
+------------------------------------+--------------------------+-------------------------+
| Shielded Metal Arc Welding (SMAW)  | AWS A5.1 / A5.1M         | AWS A5.5 / A5.5M        |
| Gas Metal / GTAW (Solid Wire/Rod)  | AWS A5.18 / A5.18M       | AWS A5.28 / A5.28M      |
| Flux Cored Arc Welding (FCAW)      | AWS A5.20 / A5.20M       | AWS A5.29 / A5.29M      |
| Submerged Arc Welding (SAW)        | AWS A5.17 / A5.17M       | AWS A5.23 / A5.23M      |
| Metal Cored Arc Welding (GMAW-C)   | AWS A5.18 (or A5.36)     | AWS A5.28 (or A5.36)    |
+------------------------------------+--------------------------+-------------------------+

Quality Verification & Procurement Schedules (AWS A5.01)

When specifying consumables for critical structural (AWS D1.1, AWS D1.8), bridge (AASHTO/AWS D1.5), or pressure containment (ASME Section IX/BPVC Section II Part C) fabrications, the engineer must stipulate testing schedules and lot integrity:

• Lot Classifications:
  • Covered Electrodes (SMAW): Class C1 (manufacturer standard dry blend batch) through Class C5 (strictly controlled chemical and raw material lot).
  • Solid Wire (GMAW/GTAW/SAW): Class S1 (standard heat lot) through Class S4 (controlled heat plus surface conditioning and chemical testing per spool).
  • Flux (SAW): Class T1 (standard blend batch) through Class T4 (homogenized production lot).
• Testing Schedules:
  • Schedule F: Manufacturer typical material test certificate (no specific lot testing).
  • Schedule I: Chemical analysis of the specific lot shipped.
  • Schedule J: Mechanical testing (all-weld-metal tension and Charpy V-Notch impacts) of the specific lot shipped.
  • Schedule K: Full chemical, mechanical, radiography, and diffusible hydrogen testing executed on the actual production lot purchased.

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AWS A5.1 & AWS A5.5: SMAW Consumables & Coating Metallurgy

Shielded Metal Arc Welding consumables rely on extruded mineral, organic, and metallic flux coverings that perform gas shielding, arc stabilization, slag formation, deoxidation, and alloy transfer.

                               AWS A5.1 SMAW CLASSIFICATION SYNTAX

             E             70            1             8         -    H4     R
             |              |            |             |               |     |
         Electrode     Min Tensile    Position     Coating/Current   Diff.   Moisture
                       (ksi x 1000)   1 = All      8 = Low-H Basic   Hydro.  Resistant
                                      2 = Flat/H       Iron Powder   <=4mL
                                      4 = Vert-Dn                    /100g

Core Carbon Steel Electrodes (AWS A5.1)

AWS A5.5 Low-Alloy Suffix System

AWS A5.5 covers low-alloy SMAW electrodes where precise weld deposit chemistry must match base metal hardenability, creep resistance, cryogenic toughness, or weather-resisting characteristics. Suffix designators define nominal chemistry:

• -A1 (Carbon-Molybdenum): 0.5% Mo (nominal). Used for elevated temperature steam piping and boiler tubes (ASTM A204, A335 Gr P1) up to 500°C (930°F).
• -B1, -B2, -B3, -B4, -B5 (Chromium-Molybdenum): Creep-resistant alloys:
  • -B2: 1.25% Cr – 0.5% Mo (e.g., E8018-B2 for ASTM A387 Gr 11).
  • -B3: 2.25% Cr – 1.0% Mo (e.g., E9018-B3 for ASTM A387 Gr 22).
  • Requires preheat (150°C–250°C) and mandatory Postweld Heat Treatment (PWHT) to temper hard martensitic/bainitic microstructures.
• -C1, -C2, -C3 (Nickel Steels): Cryogenic notch toughness:
  • -C1: 2.5% Ni (e.g., E8018-C1, CVN >= 20 ft·lbf at -75°F / -59°C).
  • -C2: 3.5% Ni (e.g., E8018-C2, CVN >= 20 ft·lbf at -100°F / -73°C).
  • -C3: 1.0% Ni, 0.15% Cr, 0.35% Mo (e.g., E8018-C3, CVN >= 20 ft·lbf at -40°F / -40°C), widely used in high-strength structural fabrication.
• -D1, -D2, -D3 (Manganese-Molybdenum): 1.25–2.0% Mn, 0.25–0.45% Mo (e.g., E9018-D2 for ASTM A514/A517 quenched and tempered steels).
• -M (Military / High Toughness): Formulated for high-yield submarine and defense steels (HY-80, HY-100, HSLA-100). Mandates tight chemical windows, ultra-low diffusible hydrogen (H4 max), and high CVN toughness at -60°F (-51°C) (e.g., E10018-M).

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AWS A5.18 & AWS A5.28: GMAW / GTAW Solid Wires & Deoxidation Kinetics

Solid bare wires for Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW) rely entirely on internal chemical alloying elements—predominantly manganese (Mn) and silicon (Si)—to scavenge oxygen from the molten weld puddle, preventing carbon monoxide (CO) gas porosity.

Deoxidation Reactions in Steel Weld Pools

Molten iron dissolves atomic oxygen at temperatures above 1538°C. Upon cooling, dissolved oxygen reacts with dissolved carbon:

$$[C] + [O] \rightleftharpoons CO_{(g)}$$

If CO gas evolves during solidification, severe wormhole and spherical porosity forms. Silicon and manganese deoxidize the weld pool preferentially by forming solid microscopic oxide slags that float to the weld surface:

$$[Si] + 2[O] \rightleftharpoons SiO_{2(s)}$$ $$[Mn] + [O] \rightleftharpoons MnO_{(s)}$$ $$MnO + SiO_2 \rightleftharpoons MnSiO_{3(s)} \quad (\text{Rhodonite Slag Islands})$$

                               AWS A5.18 SOLID WIRE NOMENCLATURE

                ER                 70                 S         -         6
                 |                  |                 |                   |
           Electrode or        Min Tensile          Solid             Chemical
           Welding Rod        (70 ksi / 483 MPa)    Wire             Composition
                                                                    (High Si-Mn)

Comparison of Primary AWS A5.18 Carbon Steel Wires

AWS A5.28 Low-Alloy Solid Wires

• ER80S-D2: Alloyed with 1.60–2.10% Mn and 0.40–0.60% Mo. Provides 80 ksi minimum tensile strength with high yield strength (68 ksi min) in both as-welded and stress-relieved conditions; common in heavy crane construction and cross-country pipeline tie-ins.
• ER90S-B3: 2.25% Cr – 1.0% Mo solid wire for GTAW/GMAW fabrication of boiler headers and refinery hydrocrackers operating at up to 600°C (1112°F).

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AWS A5.20 & AWS A5.29: Flux Cored Arc Welding (FCAW) Consumables

Flux Cored Arc Welding combines continuous wire feeding with internal flux cores that provide gas shielding, arc stabilization, slag formation, and alloy additions.

                                AWS A5.20 FCAW CLASSIFICATION SYNTAX

            E         7         1         T    -    1      C  /  M     -    J    H8
            |         |         |         |         |      |     |          |     |
        Electrode  Tensile  Position   Tubular   Usability Gas Shield       CVN  Diff. H
                   (x10 ksi) 0=Flat/H  (Flux)    & Slag   C = 100% CO2   -40°F  <=8mL/100g
                             1=All-Pos           Type     M = Ar/CO2

Gas-Shielded FCAW-G vs. Self-Shielded FCAW-S

+-----------------------------------------------------------------------------------------+
|                               FCAW PROCESS COMPARISON MATRIX                            |
+------------------------------------+--------------------------+-------------------------+
| Feature                            | Gas-Shielded (FCAW-G)    | Self-Shielded (FCAW-S)  |
+------------------------------------+--------------------------+-------------------------+
| AWS Specification                  | AWS A5.20 / AWS A5.29    | AWS A5.20 / AWS A5.29   |
| Representative Classifications     | E70T-1C, E71T-1M,        | E71T-8, E71T-11,        |
|                                    | E81T1-Ni1M               | E70T-4                  |
| External Gas Supply                | Required (100% CO2 or    | None (flux generates    |
|                                    | 75-80% Ar / balance CO2) | internal vapor shield)  |
| Slag Chemistry Type                | Rutile (TiO2) or Basic   | Fluoride-Aluminate-     |
|                                    | (CaCO3 / CaF2)           | Rutile with BaF2/CaF2   |
| Deoxidation Mechanism              | Mn, Si in core           | Al, Mg in core          |
| Wind Sensitivity Threshold         | > 5 mph (8 km/h) disrupts| Up to 30-35 mph         |
|                                    | gas shield -> porosity   | (48-56 km/h) resistant  |
| Primary Industrial Niche           | Shop fabrication, heavy  | Outdoor civil erection, |
|                                    | manufacturing, vessels   | seismic moment frames   |
+------------------------------------+--------------------------+-------------------------+

Critical Seismic Performance: AWS D1.8 and E71T-8

In earthquake-resistant structural steel moment frames (governed by AWS D1.8/D1.8M Structural Welding Code - Seismic Supplement), Demand Critical Welds require strict notch toughness guarantees:

• Minimum CVN of 20 ft·lbf at -20°F (-29°C).
• Minimum CVN of 40 ft·lbf at 70°F (+21°C).
• Diffusible hydrogen level H8 or H4.
• E71T-8 electrodes (such as Lincoln Innershield NR-232 / NR-233) are specifically qualified for these seismic moment connections. The core contains metallic aluminum which strips oxygen and nitrogen from the arc, forming fine AlN and Al2O3 precipitates that promote a fine acicular ferrite matrix.

CWEng Metallurgical Alert: Intermixing FCAW-S with Other Processes Self-shielded FCAW-S deposits contain high concentrations of residual aluminum (up to 0.5–0.8% Al). If a weld groove is partially filled with FCAW-S and subsequently capped or back-welded with a gas-shielded process (FCAW-G or GMAW) containing titanium or boron, dilution intermixing triggers brittle coarse carbonitrides and free grain boundary nitrogen. Charpy V-notch toughness plummets from 40 ft·lbf to under 5 ft·lbf! AWS D1.8 Clause 6.4 strictly forbids intermixing FCAW-S with other processes without specific PQR CVN verification.

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