A710 Gr.A Preheat for FCAW — 3/4" to 1-1/2"

FCAW (Flux Cored Arc Welding)

FCAW uses tubular flux-cored wire, available gas-shielded (E71T-1) or self-shielded (E71T-8) for field work. Category B in Table 5.11.

High-strength FCAW wires such as E81T1-K2 and E91T1-K2 provide tensile matching for Category C steels. The flux system in these wires is formulated for low diffusible hydrogen, often meeting H8 supplementary limits when tested per AWS A4.3. Wire storage requires climate-controlled conditions similar to SMAW electrodes to prevent moisture absorption.

Why FCAW for A710 Gr.A at 3/4" to 1-1/2"

Why FCAW for A710 Gr.A at 3/4" to 1-1/2"? FCAW delivers 8-12 lb/hr deposition — compared to SAW at 15-40 lb/hr. Position capability: all positions. Suitability: field and shop.

Filler Metal for FCAW

Gas-shielded: E71T-1C (AWS A5.20, requires 100% CO2) or E71T-1M (requires 75/25 Ar/CO2 mixed gas) — the C/M suffix designates the required shielding gas. Self-shielded: E71T-8 (no external gas, field-ready). Diameter: 0.045" standard, 1/16" for high-deposition. Stick-out: 3/4" to 1-1/4" (longer than GMAW due to resistive heating of flux core).

Typical values for reference — always verify against your approved WPS and electrode manufacturer data.

A710 Gr.A

ASTM A710 Grade A is a precipitation-hardened low-carbon steel plate achieving high strength through copper precipitation rather than carbon content. Class 2 (65 ksi yield, age-hardened at mill) and Class 3 (75 ksi yield, precipitation-hardened after fabrication) both feature very low carbon (0.07% max) producing a CE-IIW of approximately 0.32-0.38 — among the lowest of any high-strength steel. Table 5.11 assigns Category C for standard low-hydrogen processes and the reduced Category D preheat (32°F all thicknesses) with H8-certified consumables, reflecting the exceptional hydrogen cracking resistance of this ultra-low-carbon metallurgy. The precipitation hardening mechanism means weld thermal cycles can alter the strength in the HAZ depending on peak temperature and cooling rate, requiring attention to heat input control during procedure qualification.

Why This Preheat for A710 Gr.A with FCAW

Precipitation-hardened low-carbon plate with multiple category paths. The higher strength level of this steel places it in Category C of Table 5.11, which carries elevated preheat requirements compared to Category B grades. At 150°F minimum with FCAW, flux-cored wire in FCAW provides a combination of deoxidizers and low-moisture flux formulations that control hydrogen, but the preheat must still ensure the cooling rate stays slow enough to prevent hydrogen-induced cracking in this higher-hardenability material.

Typical Applications for A710 Gr.A

Found in naval hull plates, military vehicle armor brackets, offshore platform node connections, heavy-lift crane boom sections, and mine hoist drum shells. A710 Gr.A precipitation-hardened plate offers a rare combination of high strength and exceptional weldability at low carbon equivalent (CE-IIW approximately 0.32-0.38). The multiple thickness-dependent category paths (B, C, and D with H8) reflect its complex metallurgical response to different section sizes. Class 2 plate is age-hardened at the mill through a controlled thermal cycle, while Class 3 achieves higher strength through precipitation hardening after welding, which makes it particularly suitable for applications where extensive welding occurs before final strengthening. The distinction between Class 2 and Class 3 response to weld thermal cycles requires careful attention during procedure qualification. Plate thicknesses up to 6" are available but procurement requires extended lead times due to limited production volume.

Why Preheat Matters at 3/4" to 1-1/2"

Preheat climbs at this range as thicker material slows heat dissipation, trapping hydrogen at crack-susceptible grain boundaries.

Category C Preheat for A710 Gr.A

Category C in Table 5.11 applies to higher-strength steels where the combination of hardenability and residual stress requires elevated preheat. For A710 Gr.A at 3/4" to 1-1/2", the 150°F minimum preheat slows the weld cooling rate to prevent formation of crack-susceptible martensite in the heat-affected zone. Maintaining interpass temperature at or above this minimum is especially critical for multi-pass welds on restrained joints.

Other Steels with FCAW at 3/4" to 1-1/2"

A710 Gr.A with FCAW

Try Different Combinations

Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.

A710 Gr.A Welding Guides