A913 Gr.70 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 A913 Gr.70 TMCP shapes (70 ksi yield), GMAW spray transfer at 210-260 A with 0.035" wire controls heat input for the QST bainitic microstructure. Available primarily as W14 heavy columns with thick flanges often exceeding 3". Pulse mode at 200-240 A preferred for vertical-up on column splice joints. D1.1 Clause 7.7 heat input limits do NOT apply to A913.

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

Why GMAW for A913 Gr.70 at up to 3/4"

Why GMAW for A913 Gr.70 at up to 3/4"? GMAW delivers 8-12 lb/hr deposition — compared to <a href="/welding/preheat-calculator/a913-70/saw/up-to-3-4-inch/">SAW</a> at 15-40 lb/hr. Position capability: all positions (not GMAW-S). Suitability: primarily shop.

A913 Gr.70

ASTM A913 Grade 70 (70 ksi yield, 90 ksi minimum tensile) is a TMCP structural shape used in heavily loaded columns and seismic applications requiring higher strength than Gr.50/60/65. It falls under Category C for standard low-hydrogen processes, with preheat requirements reflecting its higher strength level and CE-IIW of approximately 0.42-0.48. With H8-certified consumables, it qualifies for Category F — 32°F up to 2-1/2”, 150°F above. The TMCP QST microstructure provides inherent resistance to hydrogen cracking through its fine-grained bainitic structure, which is why H8 consumables unlock a reduced-preheat path not available for conventional Q&T steels at similar strength. A913 Gr.70 is primarily available in W14 sections ranging from W14x233 through W14x730, with limited W12 and W36 availability.

Why This Preheat for A913 Gr.70 with GMAW

TMCP 70 ksi shape with Category F reduced preheat using H8 consumables. 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 A913 Gr.70

Used in heavily loaded interior columns of super-tall buildings, transfer truss compression chords, mega-brace members in outrigger systems, stadium roof cantilever supports, and seismic collectors in high-rise cores. A913 Gr.70 TMCP shapes enable smaller column sections, freeing usable floor space on every floor of the building. Column splice butt welds at upper stories and moment connection flange welds carry the highest inspection priority. The 70 ksi yield enables using W14x398 where conventional Gr.50 would require W14x550, saving 38% in material weight and 3-4 inches of floor space per column. Erection splices at every 2-3 stories use CJP groove welds with backing bars removed and back-gouged per seismic detailing requirements. The Category F path with H8 consumables (32°F up to 2-1/2", 150°F above) provides a practical alternative to full Category C preheat on these thick-flange column splices.

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 A913 Gr.70

Category C in Table 5.11 applies to higher-strength steels where the combination of hardenability and residual stress requires elevated preheat. For A913 Gr.70 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"

A913 Gr.70 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.

A913 Gr.70 Welding Guides