التسخين المسبق M270M Gr.345W — H8، Low HI، > 60 mm: 375°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 375°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.

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 > 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 عند > 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.

فولاذ جسور أخرى عند H8 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)

M270M Gr.345W / M270 Gr.50W عند H8 1.2–2.0 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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