M270M Gr.345W पूर्वतापन — H8, Mid HI, > 60 mm: 350°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 के लिए FC पूर्वतापन को समझना

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 350°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.

M270M Gr.345W / M270 Gr.50W कहाँ उपयोग होता है

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 के लिए H8 हाइड्रोजन नियंत्रण

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.

> 60 mm (> 2½ in) पर पूर्वतापन क्यों महत्वपूर्ण है

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.

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

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.

H8 2.0–2.8 kJ/mm · > 60 mm (> 2½ in) पर अन्य पुल स्टील

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

विभिन्न संयोजन आज़माएँ

किसी भी AASHTO M270 स्टील, हाइड्रोजन स्तर, और ऊष्मा इनपुट संयोजन को देखने के लिए D1.5 ब्रिज पूर्वतापन कैलकुलेटर का उपयोग करें। स्ट्रक्चरल स्टील के लिए D1.1 पूर्वतापन कैलकुलेटर भी देखें।

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