A36 Preheat for GMAW — up to 3/4"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A36 welded with GMAW at up to 3/4" is 32°F (0°C), Category B. Preheat below this raises hydrogen-cracking risk in the heat-affected zone; the same temperature is the minimum interpass limit maintained through the weld.
Built on AWS D1.1:2025 Table 5.11 — every value traced to the clause.
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GMAW (Gas Metal Arc Welding)
GMAW (MIG) feeds continuous solid wire with shielding gas — an inherently low-hydrogen process assigned to Category B in Table 5.11.
ER70S-6 wire at 0.035" or 0.045" diameter handles most structural work on common grades. Spray transfer at 250-350 amps provides high deposition for shop fillet welds. For thinner material under 1/4", short-circuit transfer at lower parameters reduces heat input. Gas flow rates of 35-45 CFH through a standard nozzle provide adequate shielding in typical shop environments without excessive turbulence.
GMAW Tips for Common Structural Steels
For A36 structural steel (36 ksi yield, 0.26% max carbon), GMAW spray transfer with 0.035" ER70S-6 at a minimum of 210 A or 0.045" at minimum 260 A per D1.1:2025 Table 5.3 provides high deposition for shop fillet welds. Use 75/25 Ar/CO2 shielding at 35–45 CFH. A36 plate at 3/4" and under qualifies for Category A (non-LH) or Category B.
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
Why GMAW for A36 at up to 3/4"
Why GMAW for A36 at up to 3/4"? GMAW delivers 8-12 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a36/saw/up-to-3-4-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions (not GMAW-S). Suitability: primarily shop.
A36
ASTM A36 is the most commonly specified structural steel in North America, with a minimum yield strength of 36 ksi and 58-80 ksi tensile range. It appears in both Category A (non-low-hydrogen SMAW) and Category B (low-hydrogen processes) of Table 5.11. A36 is available as plate (up to 8" thick), W-shapes, channels, angles, and bars from virtually every domestic mill. Its moderate carbon content (0.26% max for shapes, 0.25% max for plate up to 3/4") and typical carbon equivalent of 0.35-0.42 give it good weldability across all prequalified processes. A36 plate thicker than 1-1/2" carries a slightly higher carbon limit of 0.29%, while plate from 3/4" to 1-1/2" stays at 0.25% max.
Why This Preheat for A36 with GMAW
Widely used structural carbon steel with 36 ksi yield and 0.26% max carbon. With low-hydrogen GMAW, this combination falls under Category B rather than Category A — the continuous solid wire and gas shielding in GMAW produce inherently low hydrogen levels, typically 2-4 mL/100g. The 32°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness because GMAW significantly reduces the driving force for hydrogen-induced cracking in the heat-affected zone.
Typical Applications for A36
Common in angle-to-gusset fillet welds, beam web clip angles, stiffener plates, base plate bearing connections, light bracing members, stair stringers, handrail posts, and miscellaneous steel fabrication. A36 plate is the default choice for connection elements such as shear tabs, moment end plates under 36 ksi demand, and simple beam-to-column seated connections. In retrofit and renovation, A36 angles and channels are standard for reinforcement brackets and framing infill. Typical shop drawing callouts include 3/8" and 1/2" A36 plate for gussets, 5/16" fillet welds on clip angles, and partial joint penetration groove welds on base plate stiffeners. A36 is so ubiquitous that most structural steel shops maintain permanent inventory in multiple thicknesses from 1/4" through 2" plate. Fillet weld sizes on A36 connections typically range from 3/16" minimum to 5/8" for heavy gusset-to-column welds, with E70XX electrodes providing significant overmatching strength.
Why Preheat Matters at up to 3/4"
Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.
Other Steels with GMAW at up to 3/4"
| Steel | Category | Preheat |
|---|---|---|
| A53 Gr.B | B | 32°F (0°C) |
| A633 Gr.E | C | 50°F (10°C) |
| A709 HPS70W | C | 50°F (10°C) |
| A710 Gr.A | C | 50°F (10°C) |
A36 with GMAW
Try Different Combinations
Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.
A36 Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A36 plate at or below 3/4 inch with GMAW is the dominant shop-welded combination for general structural fabrication — gusset plates, base plates, anchor-bolt plates, miscellaneous metal — wherever the production environment supports gas-shielded welding with stable shielding-gas coverage.
Pre-weld notes
GMAW on thin A36 has a different defect profile than SMAW: the 32°F floor is rarely the binding constraint, but shielding-gas coverage is. Spatter rate, arc instability, and porosity-cluster patterns at the start of a pass often signal a gas-flow problem (kinked hose, leaking regulator, loose cup) before defect appears in the deposit. Short-circuit transfer at low voltage on thin material can produce lack-of-fusion at the toe of fillets — a CV-machine setup error to confirm before production.
What a CWI verifies
A CWI on a GMAW thin-section joint primarily verifies the shielding-gas mix and flow rate against the WPS, then samples the deposit visually for spatter pattern and contour. Preheat at the 32°F floor is typically self-satisfied by ambient shop temperature, so the inspection focus shifts to gas integrity and operator technique on the start-of-arc.