Precalentamiento M270M Gr.345S — H8, Low HI, ≤ 20 mm: 125°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 H8 hydrogen designation and this heat input band requires 125°F minimum preheat at ≤ 20 mm (3/4 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 H8 para M270M Gr.345S / M270 Gr.50S

For Gr.345S (50S) rolled shapes, H8 is adequate for most connection details where the weld length is short and access allows proper preheat application. Cross-frame gusset connections rarely justify the cost premium of H4 consumables when H8 meets the FC preheat budget.

Por qué el Precalentamiento Importa en ≤ 20 mm (3/4 in)

Material up to 20 mm (3/4 in) covers most cross-frame angles, stiffener clips, lateral bracing members, and light bridge plate. At this thickness, hydrogen diffusion is efficient and preheat requirements are the lowest in Table 6.3 — 10°C (50°F) for both groups. In FC service, this thickness tier also carries the lowest preheat in Tables 12.4–12.7, starting at 40°C (100°F) for H4 consumables.

M270M Gr.345S / M270 Gr.50S en ≤ 20 mm (3/4 in)

Gr.345S (50S) shapes under 20 mm flange thickness include WT sections for K-frame cross-frames and MC channels for diaphragms. The rolled section geometry concentrates stress at the flange-to-web fillet, making proper preheat at gusset connections critical for fatigue performance. SMAW E7018 is the typical process for shape-to-plate connections in bridge subassemblies because of limited access around shape flanges.

Otros Aceros de Puente en H8 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)

M270M Gr.345S / M270 Gr.50S en H8 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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