Préchauffage M270M Gr.345S — H4, Low HI, ≤ 20 mm: 100°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.

Comprendre le Préchauffage FC pour 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 100°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.

Où M270M Gr.345S / M270 Gr.50S est Utilisé

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.

Contrôle d'Hydrogène H4 pour 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.

Pourquoi le Préchauffage est Important à ≤ 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 à ≤ 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.

Consommables Certifiés H4 pour Soudage FC de Ponts

Le désignateur supplémentaire H4 certifie que le consommable dépose au maximum 4 mL d'hydrogène diffusible par 100g de métal déposé. Pour fracture critique M270M Gr.345S / M270 Gr.50S à ≤ 20 mm (3/4 in) d'épaisseur avec apport de chaleur 1.2–2.0 kJ/mm, les consommables H4 atteignent le préchauffage le plus bas de 100°F (40°C) dans les tableaux FC.

Autres Aciers de Pont à H4 1.2–2.0 kJ/mm · ≤ 20 mm (3/4 in)

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

Essayez Différentes Combinaisons

Utilisez le Calculateur de Préchauffage D1.5 pour Ponts pour consulter tout acier AASHTO M270, niveau d'hydrogène et combinaison d'apport de chaleur. Voir aussi le Calculateur de Préchauffage D1.1 pour l'acier de construction.

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