Precalentamiento M270M Gr.345S — H4, Low HI, > 60 mm: 300°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.

Entendiendo el Precalentamiento 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 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.

Dónde se Usa M270M Gr.345S / M270 Gr.50S

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.

Control de Hidrógeno 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 qué el Precalentamiento Importa en > 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 en > 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.

Consumibles Certificados H4 para Soldadura FC de Puentes

El designador suplementario H4 certifica que el consumible deposita no más de 4 mL de hidrógeno difusible por 100g de metal depositado. Para fractura crítica M270M Gr.345S / M270 Gr.50S en espesor > 60 mm (> 2½ in) con aporte térmico 1.2–2.0 kJ/mm, los consumibles H4 logran el menor precalentamiento de 300°F (150°C) en las tablas FC.

Otros Aceros de Puente en H4 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)

M270M Gr.345S / M270 Gr.50S en H4 1.2–2.0 kJ/mm

Prueba Diferentes Combinaciones

Usa la Calculadora de Precalentamiento D1.5 para Puentes para consultar cualquier acero AASHTO M270, nivel de hidrógeno y combinación de aporte térmico. También consulta la Calculadora de Precalentamiento D1.1 para acero estructural.

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