A1066 Gr.70のSMAW (low-hydrogen)用予熱 — up to 3/4"

SMAW (Low-Hydrogen)

Low-hydrogen SMAW (E7018/E7016) uses basic-coated electrodes requiring rod oven storage, assigned to Category B in Table 5.11.

For high-strength shapes and plate, E7018 provides adequate tensile match for steels up to Category C. E8018-C3 or E9018-M may be required for higher-strength steels to meet weld metal strength matching requirements. Bead sequencing on thick TMCP flanges should follow qualified WPS parameters precisely to avoid overheating the refined microstructure.

A1066 Gr.70

ASTM A1066 Grade 70 (70 ksi yield, 85 ksi minimum tensile) is the highest-strength grade in this specification, produced as quenched-and-tempered or TMCP plate for demanding bridge and structural applications. It falls under Category C in Table 5.11 but notably does not qualify for any H8 reduced-preheat category — unlike Grades 50/60/65, Grade 70 must use full Category C preheat regardless of consumable hydrogen designation. This distinction exists because the higher alloying level needed for 70 ksi yield pushes the CE-IIW to approximately 0.48-0.54, a range where even H8 hydrogen control is not sufficient to offset the hardenability-driven cracking risk at reduced preheat. Fabricators working with A1066 Gr.70 should budget for full Category C preheating time on every joint, with no H8 shortcut available.

A1066 Gr.70とSMAW-LHでこの予熱が必要な理由

Highest-strength A1066 at 70 ksi with no H8 preheat reduction available. 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 SMAW-LH, the preheat ensures the cooling rate stays slow enough to prevent hydrogen-induced cracking in this higher-hardenability material. Category C steels demand careful attention to interpass temperature control throughout the weld sequence.

A1066 Gr.70の代表的な適用例

Used in the most demanding bridge and structural applications: main girder flanges on record-span bridges, arch rib plates, suspension bridge stiffening truss chords, and heavy industrial crane runway girders. A1066 Gr.70 does not qualify for any H8 reduced preheat, so full Category C preheat must be applied regardless of consumable certification. This makes preheat management the primary production consideration for heavy-section joints where flange thicknesses of 2-4" are common. Fabrication bid costs for A1066 Gr.70 components must account for the full Category C preheat time in their labor estimates — typically 45-90 minutes per joint on plate over 2". Unlike Grades 50 and 60/65, there is no consumable-based path to reduce preheat duration on Gr.70 joints. Bridge fabrication shops working with this grade maintain dedicated preheat logs and temperature monitoring records for every CJP and PJP weld as part of their quality management system.

up to 3/4"で予熱が重要な理由

Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.

SMAW (low-hydrogen)とup to 3/4"における他の鋼材

A1066 Gr.70とSMAW (low-hydrogen)

別の組み合わせを試す

インタラクティブ予熱計算機を使用して、D1.1:2025 表5.11のあらゆる鋼材・プロセス・板厚の組み合わせを検索できます。

A1066 Gr.70溶接ガイド