A1066 Gr.60/65 Preheat for GMAW — up to 3/4"

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.

On high-strength plate, GMAW wire selection follows the steel's Table 5.6 base-metal group: Table 5.7 marks AWS A5.18 carbon-steel wire N/A for Groups III, IV and V and lists AWS A5.28 low-alloy classifications such as ER80S-Ni1 (Group III), ER90S-D2 (Group IV) and ER100S-1 (Group V). The inherently low hydrogen input of solid wire makes GMAW particularly well-suited for crack-sensitive TMCP grades where minimizing diffusible hydrogen is the primary fabrication objective.

GMAW Tips for High-Strength and TMCP Steels

For A1066 Gr.60/65 HSLA plate (60-65 ksi yield), GMAW with 0.045" wire at 260-280 A handles dual-path preheat: standard Category C or reduced Category E with H8 consumables. H8 path saves significant preheat time on thick plate. Use 75/25 Ar/CO2. Plate supplementary toughness (S-series) must match service temperature.

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

Why GMAW for A1066 Gr.60/65 at up to 3/4"

Why GMAW for A1066 Gr.60/65 at up to 3/4"? GMAW delivers 8-12 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a1066-6065/saw/up-to-3-4-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions (not GMAW-S). Suitability: primarily shop.

A1066 Gr.60/65

ASTM A1066 Grades 60 (60 ksi yield, 75 ksi tensile) and 65 (65 ksi yield, 80 ksi tensile) are higher-strength low-alloy plates used in bridges and structural applications requiring both strength and toughness at sub-zero temperatures. They fall under Category C for standard low-hydrogen processes, reflecting their higher CE-IIW of approximately 0.44-0.50, and qualify for Category E reduced preheat (50°F up to 1”, 120°F above 1”) with H8-certified consumables. The dual-path preheat option (Category C standard vs. Category E with H8) gives fabricators economic flexibility — choosing H8 consumables adds a small material premium but can save significant preheating time and fuel cost on thick-section joints. Both grades are produced in plate thicknesses up to 6" and require ASTM supplementary toughness requirements for bridge or offshore service.

Why This Preheat for A1066 Gr.60/65 with GMAW

Higher-strength 60/65 ksi HSLA plate for bridges with H8 preheat option. 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 50°F minimum with GMAW, the continuous solid wire and gas shielding in GMAW produce inherently low hydrogen levels, typically 2-4 mL/100g, 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 A1066 Gr.60/65

Specified for long-span bridge plate girder flanges, cable-stayed deck plates, offshore wind monopile transition pieces, heavy-wall tubular joints in jacket structures, and demanding structural applications requiring both 60+ ksi yield and sub-zero toughness. The H8 preheat reduction to Category E (50°F up to 1", 120°F above 1") makes these grades economically competitive for heavy plate fabrication where heating thick sections adds hours to the welding cycle. Plate thicknesses in offshore monopile transition pieces can reach 4" or more, with individual circumferential seams requiring sustained preheating over several hours. The combination of high strength, toughness, and H8 preheat eligibility positions A1066 Gr.60/65 as a premium alternative to conventional plate grades in demanding offshore environments. Filler metal selection must achieve tensile matching (80+ ksi) while meeting CVN requirements at the service temperature — typically -4°F to -40°F for North Sea and US Gulf offshore installations.

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.

Category C Preheat for A1066 Gr.60/65

Category C in Table 5.11 applies to higher-strength steels where the combination of hardenability and residual stress requires elevated preheat. For A1066 Gr.60/65 at up to 3/4", the 50°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 GMAW at up to 3/4"

A1066 Gr.60/65 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.

A1066 Gr.60/65 Welding Guides