M270M Gr.345W予熱 — H4、High HI、≤ 20 mm: 100°F

M270M Gr.345W / M270 Gr.50W

AASHTO M270M Gr.345W (M270 Gr.50W) is a weathering bridge steel with 345 MPa (50 ksi) yield that forms a protective oxide patina for unpainted bridge service. The copper-chromium-nickel alloying provides atmospheric corrosion resistance, eliminating lifetime repainting costs estimated at $15–25 per square foot per cycle. Weld filler must match the weathering composition (E8018-W2 or equivalent) for exposed joints. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7 which carry higher preheat than the non-weathering grades.

M270M Gr.345W / M270 Gr.50WのFC予熱を理解する

Weathering 345 MPa (50 ksi) bridge steel for unpainted service. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 100°F minimum preheat at ≤ 20 mm (3/4 in). Lower hydrogen levels (H4 < H8 < H16) allow lower preheat because less hydrogen enters the weld deposit. Similarly, higher heat input reduces preheat requirements because slower cooling rates give hydrogen more time to diffuse out.

M270M Gr.345W / M270 Gr.50Wの使用箇所

Deployed in unpainted bridge plate girders across humid, coastal, and high-maintenance-cost environments. The weathering patina eliminates lifetime repainting cycles estimated at $15–25/sq ft per cycle. Weld filler must match the weathering composition (E8018-W2 or ER80S-G-W) for exposed joints to ensure the weld face develops the same protective oxide as the base metal. Conventional Gr.345W is being replaced by HPS345W in new designs due to superior weldability.

M270M Gr.345W / M270 Gr.50WにおけるH4水素管理

Weathering Gr.345W (50W) with H4 benefits from reduced preheat on field splice joints where maintaining temperature in wind-exposed bridge erection conditions is challenging. The E8018-W2 low-hydrogen electrode commonly used for weathering steel field work typically carries H4 or H8 designation.

≤ 20 mm (3/4 in)で予熱が重要な理由

Material up to 20 mm (3/4 in) covers most cross-frame angles, stiffener clips, lateral bracing members, and light bridge plate. At this thickness, hydrogen diffusion is efficient and preheat requirements are the lowest in Table 6.3 — 10°C (50°F) for both groups. In FC service, this thickness tier also carries the lowest preheat in Tables 12.4–12.7, starting at 40°C (100°F) for H4 consumables.

≤ 20 mm (3/4 in)でのM270M Gr.345W / M270 Gr.50W

Gr.345W (50W) weathering steel at thin plate thickness appears in unpainted bridge bearing stiffeners and web attachment plates exposed to the atmosphere. Filler metal must match the weathering composition — E8018-W2 for SMAW or ER80S-G-W for GMAW. The patina development on thin plate is rapid (6–18 months) but requires proper drainage detailing to prevent pack rust between closely spaced plates.

橋梁FC溶接用H4認定溶接材料

H4補足記号は、溶接材料が溶着金属100gあたり4mL以下の拡散性水素しか溶着しないことを証明します。> 2.8 kJ/mm入熱での≤ 20 mm (3/4 in)板厚における破壊臨界M270M Gr.345W / M270 Gr.50Wにおいて、H4溶接材料はFCテーブルで最低予熱100°F (40°C)を達成します。予熱低減が優先される場合、これが推奨される水素レベルです。

H4 > 2.8 kJ/mm · ≤ 20 mm (3/4 in)における他の橋梁鋼材

H4 > 2.8 kJ/mmでのM270M Gr.345W / M270 Gr.50W

別の組み合わせを試す

D1.5橋梁予熱計算機を使用して、AASHTO M270鋼材の水素レベルと入熱の任意の組み合わせを検索できます。構造用鋼にはD1.1予熱計算機もご覧ください。

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