Preheat M270M Gr.345W — H4, High HI, > 60 mm: 300°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.

Memahami Preheat FC untuk 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 H4 hydrogen designation and this heat input band requires 300°F minimum preheat at > 60 mm (> 2½ 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.

Di Mana M270M Gr.345W / M270 Gr.50W Digunakan

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.

Kontrol Hidrogen H4 untuk M270M Gr.345W / M270 Gr.50W

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.

Mengapa Preheat Penting pada > 60 mm (> 2½ in)

Material over 65 mm (2-1/2 in) includes the heaviest bridge girder flanges and box-section walls. Table 6.3 requires 110°C (225°F) for both groups at this thickness. Extended preheat soak time is necessary to achieve uniform through-thickness temperature. FC preheat for the heaviest sections reaches 180–200°C (350–400°F) at the H16 hydrogen level.

M270M Gr.345W / M270 Gr.50W pada > 60 mm (> 2½ in)

Gr.345W (50W) above 65 mm is increasingly rare as HPS345W replaces it in new designs. The conventional weathering composition at this thickness has elevated lamellar tearing risk from sulfide inclusion elongation — the problem that drove development of the HPS grades with calcium-treated, inclusion-shape-controlled steel. Existing bridges with thick 345W flanges require careful Z-direction tension checks during rehabilitation welding.

Bahan Habis Pakai Bersertifikat H4 untuk Pengelasan FC Jembatan

Penunjukan tambahan H4 menyertifikasi bahwa bahan habis pakai mengendapkan tidak lebih dari 4 mL hidrogen difusibel per 100g logam yang diendapkan. Untuk fraktur kritis M270M Gr.345W / M270 Gr.50W pada ketebalan > 60 mm (> 2½ in) dengan masukan panas > 2.8 kJ/mm, bahan habis pakai H4 mencapai preheat terendah 300°F (150°C) di tabel FC.

Baja Jembatan Lain pada H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)

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

Coba Kombinasi Berbeda

Gunakan Kalkulator Preheat Jembatan D1.5 untuk mencari baja AASHTO M270, tingkat hidrogen, dan kombinasi masukan panas. Lihat juga Kalkulator Preheat D1.1 untuk baja struktural.

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