Pré-aquecimento M270M Gr.345S — H4, High HI, > 60 mm: 250°F

M270M Gr.345S / M270 Gr.50S

AASHTO M270M Gr.345S (M270 Gr.50S) is the structural shape variant of Gr.345, intended for rolled W-shapes and channels used in bridge framing. The "S" suffix indicates the shape-specific chemistry and mechanical property requirements. Used in cross-frame angles, diaphragm members, and built-up sections where rolled shapes are specified rather than plate. Preheat requirements match Gr.345 — Table 6.3 Group 1 for NFC, Tables 12.4/12.5 for FC applications.

Entendendo o Pré-aquecimento FC para M270M Gr.345S / M270 Gr.50S

Shape-grade 345 MPa (50 ksi) steel for rolled bridge members. Under D1.5 fracture-critical requirements (Clause 12), the combination of H4 hydrogen designation and this heat input band requires 250°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.

Onde M270M Gr.345S / M270 Gr.50S é Usado

Used as rolled W-shapes and channels in bridge cross-frames, diaphragm members, and built-up sections. The "S" shape designation indicates procurement under AASHTO M270 with shape-specific chemistry and mandatory CVN testing. Common applications include WT sections for cross-frame members, MC channels for diaphragms, and W-shapes for floor beams on shorter spans. Weld details are primarily fillet welds at gusset connections and clip angles.

Controle de Hidrogênio H4 para M270M Gr.345S / M270 Gr.50S

Shape-grade Gr.345S (50S) benefits from H4 at gusset-to-shape connections where access for torch preheat is limited by flanges and stiffeners. The lower preheat achievable with H4 reduces the thermal management complexity in tight spaces typical of cross-frame subassemblies.

Por que o Pré-aquecimento Importa em > 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.345S / M270 Gr.50S em > 60 mm (> 2½ in)

Gr.345S (50S) above 65 mm flange thickness is limited to the heaviest jumbo W-shapes (W14×730 or similar) used in critical transfer structures. These sections have significant residual stress from the rolling process that compounds with welding stresses. Full 225°F preheat plus controlled cooling is essential — some fabricators specify post-weld hydrogen release holds at 400°F for 2 hours on jumbo section connections.

Consumíveis Certificados H4 para Soldagem FC de Pontes

O designador suplementar H4 certifica que o consumível deposita no máximo 4 mL de hidrogênio difusível por 100g de metal depositado. Para fratura crítica M270M Gr.345S / M270 Gr.50S em espessura > 60 mm (> 2½ in) com aporte de calor > 2.8 kJ/mm, os consumíveis H4 alcançam o menor pré-aquecimento de 250°F (120°C) nas tabelas FC.

Outros Aços de Ponte em H4 > 2.8 kJ/mm · > 60 mm (> 2½ in)

M270M Gr.345S / M270 Gr.50S em H4 > 2.8 kJ/mm

Experimente Diferentes Combinações

Use a Calculadora de Pré-aquecimento D1.5 para Pontes para consultar qualquer aço AASHTO M270, nível de hidrogênio e combinação de aporte de calor. Veja também a Calculadora de Pré-aquecimento D1.1 para aço estrutural.

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