Precalentamiento M270M Gr.345W — H8, Mid 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.

Entendiendo el Precalentamiento FC para M270M Gr.345W / M270 Gr.50W

Weathering 345 MPa (50 ksi) bridge steel for unpainted service. Under D1.5 fracture-critical requirements (Clause 12), the combination of H8 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.

Dónde se Usa M270M Gr.345W / M270 Gr.50W

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.

Control de Hidrógeno H8 para M270M Gr.345W / M270 Gr.50W

Weathering Gr.345W (50W) with H8 represents the standard practice for most unpainted bridge fabrication. Gas-shielded FCAW wires commonly achieve H8 designation, making this the natural hydrogen level for high-productivity shop welding on weathering grade plate girders.

Por qué el Precalentamiento Importa en ≤ 20 mm (3/4 in)

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.

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

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.

Otros Aceros de Puente en H8 2.0–2.8 kJ/mm · ≤ 20 mm (3/4 in)

M270M Gr.345W / M270 Gr.50W en H8 2.0–2.8 kJ/mm

Prueba Diferentes Combinaciones

Usa la Calculadora de Precalentamiento D1.5 para Puentes para consultar cualquier acero AASHTO M270, nivel de hidrógeno y combinación de aporte térmico. También consulta la Calculadora de Precalentamiento D1.1 para acero estructural.

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