التسخين المسبق M270M Gr.345W — H8، Mid HI، 40–60 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.

فهم التسخين المسبق FC لـ 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 300°F minimum preheat at 40–60 mm (1½–2½ 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.

أين يُستخدم 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.

التحكم في الهيدروجين H8 لـ 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.

لماذا يهم التسخين المسبق عند 40–60 mm (1½–2½ in)

Material from 40 to 65 mm (1-1/2 to 2-1/2 in) covers heavy girder flanges, thick splice plates, and main member plate. This is the critical thickness range for bridge fabrication — preheat reaches 65°C (150°F) for Group 1 and 80°C (175°F) for Group 2. FC preheat at this thickness can exceed 200°C (400°F) depending on hydrogen level and heat input.

M270M Gr.345W / M270 Gr.50W عند 40–60 mm (1½–2½ in)

Gr.345W (50W) at 40–65 mm covers girder flanges on medium-span unpainted bridges where the lifecycle cost of eliminating repainting outweighs the modest material premium. The higher-alloy chemistry for weathering resistance increases the carbon equivalent compared to plain Gr.345, which is why D1.5 assigns weathering grades to Tables 12.6/12.7 rather than 12.4/12.5 for FC preheat — a separate set of tables with generally higher preheat requirements reflecting the increased cracking susceptibility of the Cu-Cr-Ni alloying elements. Flange splice procedures must account for the weathering composition by matching filler metals to ensure consistent patina development across the weld face.

فولاذ جسور أخرى عند H8 2.0–2.8 kJ/mm · 40–60 mm (1½–2½ in)

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

جرّب تركيبات مختلفة

استخدم حاسبة التسخين المسبق D1.5 للجسور للبحث عن أي فولاذ AASHTO M270 ومستوى هيدروجين وتركيبة مدخل حراري. انظر أيضاً حاسبة التسخين المسبق D1.1 للفولاذ الإنشائي.

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